2019-05-19 13:08:55 +01:00
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2006-03-30 15:15:30 +02:00
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2006-04-11 13:56:34 +02:00
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2006-03-30 15:15:30 +02:00
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2006-09-04 15:41:16 +02:00
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2006-04-11 13:56:34 +02:00
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2006-03-30 15:15:30 +02:00
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2016-11-01 07:40:16 -06:00
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2006-03-30 15:15:30 +02:00
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2007-06-04 09:59:47 +02:00
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memcg: synchronized LRU
A big patch for changing memcg's LRU semantics.
Now,
- page_cgroup is linked to mem_cgroup's its own LRU (per zone).
- LRU of page_cgroup is not synchronous with global LRU.
- page and page_cgroup is one-to-one and statically allocated.
- To find page_cgroup is on what LRU, you have to check pc->mem_cgroup as
- lru = page_cgroup_zoneinfo(pc, nid_of_pc, zid_of_pc);
- SwapCache is handled.
And, when we handle LRU list of page_cgroup, we do following.
pc = lookup_page_cgroup(page);
lock_page_cgroup(pc); .....................(1)
mz = page_cgroup_zoneinfo(pc);
spin_lock(&mz->lru_lock);
.....add to LRU
spin_unlock(&mz->lru_lock);
unlock_page_cgroup(pc);
But (1) is spin_lock and we have to be afraid of dead-lock with zone->lru_lock.
So, trylock() is used at (1), now. Without (1), we can't trust "mz" is correct.
This is a trial to remove this dirty nesting of locks.
This patch changes mz->lru_lock to be zone->lru_lock.
Then, above sequence will be written as
spin_lock(&zone->lru_lock); # in vmscan.c or swap.c via global LRU
mem_cgroup_add/remove/etc_lru() {
pc = lookup_page_cgroup(page);
mz = page_cgroup_zoneinfo(pc);
if (PageCgroupUsed(pc)) {
....add to LRU
}
spin_lock(&zone->lru_lock); # in vmscan.c or swap.c via global LRU
This is much simpler.
(*) We're safe even if we don't take lock_page_cgroup(pc). Because..
1. When pc->mem_cgroup can be modified.
- at charge.
- at account_move().
2. at charge
the PCG_USED bit is not set before pc->mem_cgroup is fixed.
3. at account_move()
the page is isolated and not on LRU.
Pros.
- easy for maintenance.
- memcg can make use of laziness of pagevec.
- we don't have to duplicated LRU/Active/Unevictable bit in page_cgroup.
- LRU status of memcg will be synchronized with global LRU's one.
- # of locks are reduced.
- account_move() is simplified very much.
Cons.
- may increase cost of LRU rotation.
(no impact if memcg is not configured.)
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-01-07 18:08:01 -08:00
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2006-03-30 15:15:30 +02:00
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2006-03-30 15:16:46 +02:00
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2006-04-02 23:04:46 +02:00
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2011-11-16 23:57:37 -05:00
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2006-04-02 23:04:46 +02:00
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2006-04-26 10:59:21 +02:00
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2023-03-22 14:25:19 +08:00
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2007-07-13 11:44:32 +02:00
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include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h
percpu.h is included by sched.h and module.h and thus ends up being
included when building most .c files. percpu.h includes slab.h which
in turn includes gfp.h making everything defined by the two files
universally available and complicating inclusion dependencies.
percpu.h -> slab.h dependency is about to be removed. Prepare for
this change by updating users of gfp and slab facilities include those
headers directly instead of assuming availability. As this conversion
needs to touch large number of source files, the following script is
used as the basis of conversion.
http://userweb.kernel.org/~tj/misc/slabh-sweep.py
The script does the followings.
* Scan files for gfp and slab usages and update includes such that
only the necessary includes are there. ie. if only gfp is used,
gfp.h, if slab is used, slab.h.
* When the script inserts a new include, it looks at the include
blocks and try to put the new include such that its order conforms
to its surrounding. It's put in the include block which contains
core kernel includes, in the same order that the rest are ordered -
alphabetical, Christmas tree, rev-Xmas-tree or at the end if there
doesn't seem to be any matching order.
* If the script can't find a place to put a new include (mostly
because the file doesn't have fitting include block), it prints out
an error message indicating which .h file needs to be added to the
file.
The conversion was done in the following steps.
1. The initial automatic conversion of all .c files updated slightly
over 4000 files, deleting around 700 includes and adding ~480 gfp.h
and ~3000 slab.h inclusions. The script emitted errors for ~400
files.
2. Each error was manually checked. Some didn't need the inclusion,
some needed manual addition while adding it to implementation .h or
embedding .c file was more appropriate for others. This step added
inclusions to around 150 files.
3. The script was run again and the output was compared to the edits
from #2 to make sure no file was left behind.
4. Several build tests were done and a couple of problems were fixed.
e.g. lib/decompress_*.c used malloc/free() wrappers around slab
APIs requiring slab.h to be added manually.
5. The script was run on all .h files but without automatically
editing them as sprinkling gfp.h and slab.h inclusions around .h
files could easily lead to inclusion dependency hell. Most gfp.h
inclusion directives were ignored as stuff from gfp.h was usually
wildly available and often used in preprocessor macros. Each
slab.h inclusion directive was examined and added manually as
necessary.
6. percpu.h was updated not to include slab.h.
7. Build test were done on the following configurations and failures
were fixed. CONFIG_GCOV_KERNEL was turned off for all tests (as my
distributed build env didn't work with gcov compiles) and a few
more options had to be turned off depending on archs to make things
build (like ipr on powerpc/64 which failed due to missing writeq).
* x86 and x86_64 UP and SMP allmodconfig and a custom test config.
* powerpc and powerpc64 SMP allmodconfig
* sparc and sparc64 SMP allmodconfig
* ia64 SMP allmodconfig
* s390 SMP allmodconfig
* alpha SMP allmodconfig
* um on x86_64 SMP allmodconfig
8. percpu.h modifications were reverted so that it could be applied as
a separate patch and serve as bisection point.
Given the fact that I had only a couple of failures from tests on step
6, I'm fairly confident about the coverage of this conversion patch.
If there is a breakage, it's likely to be something in one of the arch
headers which should be easily discoverable easily on most builds of
the specific arch.
Signed-off-by: Tejun Heo <tj@kernel.org>
Guess-its-ok-by: Christoph Lameter <cl@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
2010-03-24 17:04:11 +09:00
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2023-06-07 19:19:09 +01:00
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2012-04-05 03:05:35 +00:00
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2017-02-02 19:15:33 +01:00
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2013-03-20 13:19:30 -04:00
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2006-03-30 15:15:30 +02:00
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2023-04-24 16:32:55 -06:00
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2025-04-23 18:00:23 +00:00
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2023-04-24 16:32:55 -06:00
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2006-04-02 23:05:09 +02:00
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2020-05-20 17:58:16 +02:00
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2006-03-30 15:16:46 +02:00
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2022-02-12 22:48:55 -05:00
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2006-06-20 15:01:12 +02:00
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2006-03-30 15:16:46 +02:00
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2022-02-11 23:39:03 -05:00
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2006-04-19 15:57:31 +02:00
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2022-02-11 23:39:03 -05:00
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2006-06-20 15:01:12 +02:00
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2022-02-11 23:39:03 -05:00
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2006-03-30 15:16:46 +02:00
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2006-06-20 15:01:12 +02:00
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2022-02-11 23:39:03 -05:00
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2006-06-20 15:01:12 +02:00
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2022-02-11 23:39:03 -05:00
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2006-06-20 15:01:12 +02:00
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2022-02-11 23:39:03 -05:00
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2006-04-02 23:10:32 +02:00
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mm: merge folio_has_private()/filemap_release_folio() call pairs
Patch series "mm, netfs, fscache: Stop read optimisation when folio
removed from pagecache", v7.
This fixes an optimisation in fscache whereby we don't read from the cache
for a particular file until we know that there's data there that we don't
have in the pagecache. The problem is that I'm no longer using PG_fscache
(aka PG_private_2) to indicate that the page is cached and so I don't get
a notification when a cached page is dropped from the pagecache.
The first patch merges some folio_has_private() and
filemap_release_folio() pairs and introduces a helper,
folio_needs_release(), to indicate if a release is required.
The second patch is the actual fix. Following Willy's suggestions[1], it
adds an AS_RELEASE_ALWAYS flag to an address_space that will make
filemap_release_folio() always call ->release_folio(), even if
PG_private/PG_private_2 aren't set. folio_needs_release() is altered to
add a check for this.
This patch (of 2):
Make filemap_release_folio() check folio_has_private(). Then, in most
cases, where a call to folio_has_private() is immediately followed by a
call to filemap_release_folio(), we can get rid of the test in the pair.
There are a couple of sites in mm/vscan.c that this can't so easily be
done. In shrink_folio_list(), there are actually three cases (something
different is done for incompletely invalidated buffers), but
filemap_release_folio() elides two of them.
In shrink_active_list(), we don't have have the folio lock yet, so the
check allows us to avoid locking the page unnecessarily.
A wrapper function to check if a folio needs release is provided for those
places that still need to do it in the mm/ directory. This will acquire
additional parts to the condition in a future patch.
After this, the only remaining caller of folio_has_private() outside of
mm/ is a check in fuse.
Link: https://lkml.kernel.org/r/20230628104852.3391651-1-dhowells@redhat.com
Link: https://lkml.kernel.org/r/20230628104852.3391651-2-dhowells@redhat.com
Reported-by: Rohith Surabattula <rohiths.msft@gmail.com>
Suggested-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Steve French <sfrench@samba.org>
Cc: Shyam Prasad N <nspmangalore@gmail.com>
Cc: Rohith Surabattula <rohiths.msft@gmail.com>
Cc: Dave Wysochanski <dwysocha@redhat.com>
Cc: Dominique Martinet <asmadeus@codewreck.org>
Cc: Ilya Dryomov <idryomov@gmail.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Xiubo Li <xiubli@redhat.com>
Cc: Jingbo Xu <jefflexu@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-06-28 11:48:51 +01:00
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2008-05-20 21:27:41 +02:00
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2006-04-02 23:04:46 +02:00
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2006-06-20 15:01:12 +02:00
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2022-02-12 22:48:55 -05:00
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2006-06-20 15:01:12 +02:00
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2020-05-20 17:58:16 +02:00
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2006-06-20 15:01:12 +02:00
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2006-04-19 15:57:31 +02:00
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2006-03-30 15:16:46 +02:00
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2006-06-20 15:01:12 +02:00
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2022-02-11 23:39:03 -05:00
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2006-06-20 15:01:12 +02:00
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2008-05-20 21:27:41 +02:00
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2022-02-11 23:39:03 -05:00
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2020-05-20 17:58:16 +02:00
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2006-03-30 15:16:46 +02:00
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2006-05-03 10:41:33 +02:00
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2006-03-30 15:15:30 +02:00
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mm, fs: get rid of PAGE_CACHE_* and page_cache_{get,release} macros
PAGE_CACHE_{SIZE,SHIFT,MASK,ALIGN} macros were introduced *long* time
ago with promise that one day it will be possible to implement page
cache with bigger chunks than PAGE_SIZE.
This promise never materialized. And unlikely will.
We have many places where PAGE_CACHE_SIZE assumed to be equal to
PAGE_SIZE. And it's constant source of confusion on whether
PAGE_CACHE_* or PAGE_* constant should be used in a particular case,
especially on the border between fs and mm.
Global switching to PAGE_CACHE_SIZE != PAGE_SIZE would cause to much
breakage to be doable.
Let's stop pretending that pages in page cache are special. They are
not.
The changes are pretty straight-forward:
- <foo> << (PAGE_CACHE_SHIFT - PAGE_SHIFT) -> <foo>;
- <foo> >> (PAGE_CACHE_SHIFT - PAGE_SHIFT) -> <foo>;
- PAGE_CACHE_{SIZE,SHIFT,MASK,ALIGN} -> PAGE_{SIZE,SHIFT,MASK,ALIGN};
- page_cache_get() -> get_page();
- page_cache_release() -> put_page();
This patch contains automated changes generated with coccinelle using
script below. For some reason, coccinelle doesn't patch header files.
I've called spatch for them manually.
The only adjustment after coccinelle is revert of changes to
PAGE_CAHCE_ALIGN definition: we are going to drop it later.
There are few places in the code where coccinelle didn't reach. I'll
fix them manually in a separate patch. Comments and documentation also
will be addressed with the separate patch.
virtual patch
@@
expression E;
@@
- E << (PAGE_CACHE_SHIFT - PAGE_SHIFT)
+ E
@@
expression E;
@@
- E >> (PAGE_CACHE_SHIFT - PAGE_SHIFT)
+ E
@@
@@
- PAGE_CACHE_SHIFT
+ PAGE_SHIFT
@@
@@
- PAGE_CACHE_SIZE
+ PAGE_SIZE
@@
@@
- PAGE_CACHE_MASK
+ PAGE_MASK
@@
expression E;
@@
- PAGE_CACHE_ALIGN(E)
+ PAGE_ALIGN(E)
@@
expression E;
@@
- page_cache_get(E)
+ get_page(E)
@@
expression E;
@@
- page_cache_release(E)
+ put_page(E)
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-04-01 15:29:47 +03:00
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2006-05-03 10:35:26 +02:00
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2006-03-30 15:15:30 +02:00
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2007-06-12 20:51:32 +02:00
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2007-06-14 13:10:48 +02:00
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2006-03-30 15:15:30 +02:00
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2023-08-21 15:15:41 +01:00
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2006-04-10 09:04:41 +02:00
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2006-03-30 15:15:30 +02:00
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2023-08-21 15:15:41 +01:00
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2006-04-10 09:04:41 +02:00
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2023-08-21 15:15:41 +01:00
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2006-04-11 13:57:21 +02:00
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2006-04-10 09:04:41 +02:00
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2023-08-21 15:15:41 +01:00
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2006-04-10 09:04:41 +02:00
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2006-04-11 13:57:21 +02:00
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2006-04-10 09:04:41 +02:00
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2023-08-21 15:15:41 +01:00
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2006-04-10 09:04:41 +02:00
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2023-08-21 15:15:41 +01:00
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2006-03-30 15:15:30 +02:00
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2006-05-01 19:59:03 +02:00
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2006-04-10 09:04:41 +02:00
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2023-08-21 15:15:41 +01:00
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2006-05-01 19:59:03 +02:00
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2006-04-11 15:51:17 +02:00
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2011-07-25 17:12:32 -07:00
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2020-05-20 17:58:16 +02:00
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2006-03-30 15:15:30 +02:00
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2020-05-20 17:58:16 +02:00
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2006-04-26 10:59:21 +02:00
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2006-05-01 20:02:33 +02:00
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2020-05-20 17:58:16 +02:00
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2006-05-01 20:02:33 +02:00
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2006-05-03 10:35:26 +02:00
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2020-05-20 17:58:16 +02:00
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2006-04-26 10:59:21 +02:00
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2006-12-13 00:34:04 -08:00
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2020-05-20 17:58:16 +02:00
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2006-04-26 10:59:21 +02:00
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2011-05-23 19:58:53 +02:00
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pipe: use exclusive waits when reading or writing
This makes the pipe code use separate wait-queues and exclusive waiting
for readers and writers, avoiding a nasty thundering herd problem when
there are lots of readers waiting for data on a pipe (or, less commonly,
lots of writers waiting for a pipe to have space).
While this isn't a common occurrence in the traditional "use a pipe as a
data transport" case, where you typically only have a single reader and
a single writer process, there is one common special case: using a pipe
as a source of "locking tokens" rather than for data communication.
In particular, the GNU make jobserver code ends up using a pipe as a way
to limit parallelism, where each job consumes a token by reading a byte
from the jobserver pipe, and releases the token by writing a byte back
to the pipe.
This pattern is fairly traditional on Unix, and works very well, but
will waste a lot of time waking up a lot of processes when only a single
reader needs to be woken up when a writer releases a new token.
A simplified test-case of just this pipe interaction is to create 64
processes, and then pass a single token around between them (this
test-case also intentionally passes another token that gets ignored to
test the "wake up next" logic too, in case anybody wonders about it):
#include <unistd.h>
int main(int argc, char **argv)
{
int fd[2], counters[2];
pipe(fd);
counters[0] = 0;
counters[1] = -1;
write(fd[1], counters, sizeof(counters));
/* 64 processes */
fork(); fork(); fork(); fork(); fork(); fork();
do {
int i;
read(fd[0], &i, sizeof(i));
if (i < 0)
continue;
counters[0] = i+1;
write(fd[1], counters, (1+(i & 1)) *sizeof(int));
} while (counters[0] < 1000000);
return 0;
}
and in a perfect world, passing that token around should only cause one
context switch per transfer, when the writer of a token causes a
directed wakeup of just a single reader.
But with the "writer wakes all readers" model we traditionally had, on
my test box the above case causes more than an order of magnitude more
scheduling: instead of the expected ~1M context switches, "perf stat"
shows
231,852.37 msec task-clock # 15.857 CPUs utilized
11,250,961 context-switches # 0.049 M/sec
616,304 cpu-migrations # 0.003 M/sec
1,648 page-faults # 0.007 K/sec
1,097,903,998,514 cycles # 4.735 GHz
120,781,778,352 instructions # 0.11 insn per cycle
27,997,056,043 branches # 120.754 M/sec
283,581,233 branch-misses # 1.01% of all branches
14.621273891 seconds time elapsed
0.018243000 seconds user
3.611468000 seconds sys
before this commit.
After this commit, I get
5,229.55 msec task-clock # 3.072 CPUs utilized
1,212,233 context-switches # 0.232 M/sec
103,951 cpu-migrations # 0.020 M/sec
1,328 page-faults # 0.254 K/sec
21,307,456,166 cycles # 4.074 GHz
12,947,819,999 instructions # 0.61 insn per cycle
2,881,985,678 branches # 551.096 M/sec
64,267,015 branch-misses # 2.23% of all branches
1.702148350 seconds time elapsed
0.004868000 seconds user
0.110786000 seconds sys
instead. Much better.
[ Note! This kernel improvement seems to be very good at triggering a
race condition in the make jobserver (in GNU make 4.2.1) for me. It's
a long known bug that was fixed back in June 2017 by GNU make commit
b552b0525198 ("[SV 51159] Use a non-blocking read with pselect to
avoid hangs.").
But there wasn't a new release of GNU make until 4.3 on Jan 19 2020,
so a number of distributions may still have the buggy version. Some
have backported the fix to their 4.2.1 release, though, and even
without the fix it's quite timing-dependent whether the bug actually
is hit. ]
Josh Triplett says:
"I've been hammering on your pipe fix patch (switching to exclusive
wait queues) for a month or so, on several different systems, and I've
run into no issues with it. The patch *substantially* improves
parallel build times on large (~100 CPU) systems, both with parallel
make and with other things that use make's pipe-based jobserver.
All current distributions (including stable and long-term stable
distributions) have versions of GNU make that no longer have the
jobserver bug"
Tested-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-12-09 09:48:27 -08:00
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2011-05-23 19:58:53 +02:00
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2007-06-21 13:10:21 +02:00
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2007-07-27 08:08:51 +02:00
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2007-06-21 13:10:21 +02:00
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2006-04-02 23:05:09 +02:00
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2007-06-04 09:59:47 +02:00
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2006-03-30 15:15:30 +02:00
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2007-06-15 13:14:22 +02:00
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2019-11-15 13:30:32 +00:00
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2023-12-12 11:44:36 +02:00
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2006-03-30 15:15:30 +02:00
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2016-03-10 21:19:06 +01:00
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2016-09-17 20:44:45 -04:00
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2006-03-30 15:15:30 +02:00
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2019-10-16 16:47:32 +01:00
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2025-03-07 05:29:19 +00:00
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2006-03-30 15:15:30 +02:00
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2016-09-17 20:44:45 -04:00
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2017-02-16 17:49:02 +01:00
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2006-03-30 15:15:30 +02:00
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2019-11-15 13:30:32 +00:00
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2016-09-17 20:44:45 -04:00
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2007-06-15 13:14:22 +02:00
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2007-11-06 23:29:47 -08:00
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2006-03-30 15:15:30 +02:00
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2015-05-21 17:00:01 +02:00
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2006-03-30 15:15:30 +02:00
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2016-09-17 22:38:20 -04:00
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2019-11-15 13:30:32 +00:00
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2016-09-17 22:38:20 -04:00
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2019-10-16 16:47:32 +01:00
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2016-09-17 22:38:20 -04:00
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2025-03-07 05:29:19 +00:00
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2019-11-15 13:30:32 +00:00
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2016-09-17 22:38:20 -04:00
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2016-09-27 10:45:12 +02:00
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2016-09-17 22:38:20 -04:00
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2010-05-20 10:43:18 +02:00
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2012-06-12 15:24:40 +02:00
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2010-05-20 10:43:18 +02:00
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2019-10-16 16:47:32 +01:00
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2012-06-12 15:24:40 +02:00
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2019-11-15 13:30:32 +00:00
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2010-05-20 10:43:18 +02:00
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2026-02-21 16:37:42 -08:00
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2010-05-20 10:43:18 +02:00
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2012-06-12 15:24:40 +02:00
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2010-05-20 10:43:18 +02:00
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2012-06-12 15:24:40 +02:00
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2010-05-20 10:43:18 +02:00
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2023-05-22 14:50:18 +01:00
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splice: Add a func to do a splice from an O_DIRECT file without ITER_PIPE
Implement a function, direct_file_splice(), that deals with this by using
an ITER_BVEC iterator instead of an ITER_PIPE iterator as the former won't
free its buffers when reverted. The function bulk allocates all the
buffers it thinks it is going to use in advance, does the read
synchronously and only then trims the buffer down. The pages we did use
get pushed into the pipe.
This fixes a problem with the upcoming iov_iter_extract_pages() function,
whereby pages extracted from a non-user-backed iterator such as ITER_PIPE
aren't pinned. __iomap_dio_rw(), however, calls iov_iter_revert() to
shorten the iterator to just the bufferage it is going to use - which has
the side-effect of freeing the excess pipe buffers, even though they're
attached to a bio and may get written to by DMA (thanks to Hillf Danton for
spotting this[1]).
This then causes memory corruption that is particularly noticeable when the
syzbot test[2] is run. The test boils down to:
out = creat(argv[1], 0666);
ftruncate(out, 0x800);
lseek(out, 0x200, SEEK_SET);
in = open(argv[1], O_RDONLY | O_DIRECT | O_NOFOLLOW);
sendfile(out, in, NULL, 0x1dd00);
run repeatedly in parallel. What I think is happening is that ftruncate()
occasionally shortens the DIO read that's about to be made by sendfile's
splice core by reducing i_size.
This should be more efficient for DIO read by virtue of doing a bulk page
allocation, but slightly less efficient by ignoring any partial page in the
pipe.
Reported-by: syzbot+a440341a59e3b7142895@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: David Hildenbrand <david@redhat.com>
cc: John Hubbard <jhubbard@nvidia.com>
cc: linux-mm@kvack.org
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20230207094731.1390-1-hdanton@sina.com/ [1]
Link: https://lore.kernel.org/r/000000000000b0b3c005f3a09383@google.com/ [2]
Signed-off-by: Steve French <stfrench@microsoft.com>
2023-02-07 10:45:40 +00:00
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2023-05-22 14:49:50 +01:00
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splice: Add a func to do a splice from an O_DIRECT file without ITER_PIPE
Implement a function, direct_file_splice(), that deals with this by using
an ITER_BVEC iterator instead of an ITER_PIPE iterator as the former won't
free its buffers when reverted. The function bulk allocates all the
buffers it thinks it is going to use in advance, does the read
synchronously and only then trims the buffer down. The pages we did use
get pushed into the pipe.
This fixes a problem with the upcoming iov_iter_extract_pages() function,
whereby pages extracted from a non-user-backed iterator such as ITER_PIPE
aren't pinned. __iomap_dio_rw(), however, calls iov_iter_revert() to
shorten the iterator to just the bufferage it is going to use - which has
the side-effect of freeing the excess pipe buffers, even though they're
attached to a bio and may get written to by DMA (thanks to Hillf Danton for
spotting this[1]).
This then causes memory corruption that is particularly noticeable when the
syzbot test[2] is run. The test boils down to:
out = creat(argv[1], 0666);
ftruncate(out, 0x800);
lseek(out, 0x200, SEEK_SET);
in = open(argv[1], O_RDONLY | O_DIRECT | O_NOFOLLOW);
sendfile(out, in, NULL, 0x1dd00);
run repeatedly in parallel. What I think is happening is that ftruncate()
occasionally shortens the DIO read that's about to be made by sendfile's
splice core by reducing i_size.
This should be more efficient for DIO read by virtue of doing a bulk page
allocation, but slightly less efficient by ignoring any partial page in the
pipe.
Reported-by: syzbot+a440341a59e3b7142895@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: David Hildenbrand <david@redhat.com>
cc: John Hubbard <jhubbard@nvidia.com>
cc: linux-mm@kvack.org
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20230207094731.1390-1-hdanton@sina.com/ [1]
Link: https://lore.kernel.org/r/000000000000b0b3c005f3a09383@google.com/ [2]
Signed-off-by: Steve French <stfrench@microsoft.com>
2023-02-07 10:45:40 +00:00
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2023-05-22 14:49:51 +01:00
|
|
|
|
splice: Add a func to do a splice from an O_DIRECT file without ITER_PIPE
Implement a function, direct_file_splice(), that deals with this by using
an ITER_BVEC iterator instead of an ITER_PIPE iterator as the former won't
free its buffers when reverted. The function bulk allocates all the
buffers it thinks it is going to use in advance, does the read
synchronously and only then trims the buffer down. The pages we did use
get pushed into the pipe.
This fixes a problem with the upcoming iov_iter_extract_pages() function,
whereby pages extracted from a non-user-backed iterator such as ITER_PIPE
aren't pinned. __iomap_dio_rw(), however, calls iov_iter_revert() to
shorten the iterator to just the bufferage it is going to use - which has
the side-effect of freeing the excess pipe buffers, even though they're
attached to a bio and may get written to by DMA (thanks to Hillf Danton for
spotting this[1]).
This then causes memory corruption that is particularly noticeable when the
syzbot test[2] is run. The test boils down to:
out = creat(argv[1], 0666);
ftruncate(out, 0x800);
lseek(out, 0x200, SEEK_SET);
in = open(argv[1], O_RDONLY | O_DIRECT | O_NOFOLLOW);
sendfile(out, in, NULL, 0x1dd00);
run repeatedly in parallel. What I think is happening is that ftruncate()
occasionally shortens the DIO read that's about to be made by sendfile's
splice core by reducing i_size.
This should be more efficient for DIO read by virtue of doing a bulk page
allocation, but slightly less efficient by ignoring any partial page in the
pipe.
Reported-by: syzbot+a440341a59e3b7142895@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: David Hildenbrand <david@redhat.com>
cc: John Hubbard <jhubbard@nvidia.com>
cc: linux-mm@kvack.org
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20230207094731.1390-1-hdanton@sina.com/ [1]
Link: https://lore.kernel.org/r/000000000000b0b3c005f3a09383@google.com/ [2]
Signed-off-by: Steve French <stfrench@microsoft.com>
2023-02-07 10:45:40 +00:00
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fs/pipe: add simpler helpers for common cases
The fix to atomically read the pipe head and tail state when not holding
the pipe mutex has caused a number of headaches due to the size change
of the involved types.
It turns out that we don't have _that_ many places that access these
fields directly and were affected, but we have more than we strictly
should have, because our low-level helper functions have been designed
to have intimate knowledge of how the pipes work.
And as a result, that random noise of direct 'pipe->head' and
'pipe->tail' accesses makes it harder to pinpoint any actual potential
problem spots remaining.
For example, we didn't have a "is the pipe full" helper function, but
instead had a "given these pipe buffer indexes and this pipe size, is
the pipe full". That's because some low-level pipe code does actually
want that much more complicated interface.
But most other places literally just want a "is the pipe full" helper,
and not having it meant that those places ended up being unnecessarily
much too aware of this all.
It would have been much better if only the very core pipe code that
cared had been the one aware of this all.
So let's fix it - better late than never. This just introduces the
trivial wrappers for "is this pipe full or empty" and to get how many
pipe buffers are used, so that instead of writing
if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
the places that literally just want to know if a pipe is full can just
say
if (pipe_is_full(pipe))
instead. The existing trivial cases were converted with a 'sed' script.
This cuts down on the places that access pipe->head and pipe->tail
directly outside of the pipe code (and core splice code) quite a lot.
The splice code in particular still revels in doing the direct low-level
accesses, and the fuse fuse_dev_splice_write() code also seems a bit
unnecessarily eager to go very low-level, but it's at least a bit better
than it used to be.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2025-03-06 18:25:35 -10:00
|
|
|
|
splice: Add a func to do a splice from an O_DIRECT file without ITER_PIPE
Implement a function, direct_file_splice(), that deals with this by using
an ITER_BVEC iterator instead of an ITER_PIPE iterator as the former won't
free its buffers when reverted. The function bulk allocates all the
buffers it thinks it is going to use in advance, does the read
synchronously and only then trims the buffer down. The pages we did use
get pushed into the pipe.
This fixes a problem with the upcoming iov_iter_extract_pages() function,
whereby pages extracted from a non-user-backed iterator such as ITER_PIPE
aren't pinned. __iomap_dio_rw(), however, calls iov_iter_revert() to
shorten the iterator to just the bufferage it is going to use - which has
the side-effect of freeing the excess pipe buffers, even though they're
attached to a bio and may get written to by DMA (thanks to Hillf Danton for
spotting this[1]).
This then causes memory corruption that is particularly noticeable when the
syzbot test[2] is run. The test boils down to:
out = creat(argv[1], 0666);
ftruncate(out, 0x800);
lseek(out, 0x200, SEEK_SET);
in = open(argv[1], O_RDONLY | O_DIRECT | O_NOFOLLOW);
sendfile(out, in, NULL, 0x1dd00);
run repeatedly in parallel. What I think is happening is that ftruncate()
occasionally shortens the DIO read that's about to be made by sendfile's
splice core by reducing i_size.
This should be more efficient for DIO read by virtue of doing a bulk page
allocation, but slightly less efficient by ignoring any partial page in the
pipe.
Reported-by: syzbot+a440341a59e3b7142895@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: David Hildenbrand <david@redhat.com>
cc: John Hubbard <jhubbard@nvidia.com>
cc: linux-mm@kvack.org
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20230207094731.1390-1-hdanton@sina.com/ [1]
Link: https://lore.kernel.org/r/000000000000b0b3c005f3a09383@google.com/ [2]
Signed-off-by: Steve French <stfrench@microsoft.com>
2023-02-07 10:45:40 +00:00
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2023-05-22 14:49:51 +01:00
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2024-12-23 17:00:38 -05:00
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|
splice: Add a func to do a splice from an O_DIRECT file without ITER_PIPE
Implement a function, direct_file_splice(), that deals with this by using
an ITER_BVEC iterator instead of an ITER_PIPE iterator as the former won't
free its buffers when reverted. The function bulk allocates all the
buffers it thinks it is going to use in advance, does the read
synchronously and only then trims the buffer down. The pages we did use
get pushed into the pipe.
This fixes a problem with the upcoming iov_iter_extract_pages() function,
whereby pages extracted from a non-user-backed iterator such as ITER_PIPE
aren't pinned. __iomap_dio_rw(), however, calls iov_iter_revert() to
shorten the iterator to just the bufferage it is going to use - which has
the side-effect of freeing the excess pipe buffers, even though they're
attached to a bio and may get written to by DMA (thanks to Hillf Danton for
spotting this[1]).
This then causes memory corruption that is particularly noticeable when the
syzbot test[2] is run. The test boils down to:
out = creat(argv[1], 0666);
ftruncate(out, 0x800);
lseek(out, 0x200, SEEK_SET);
in = open(argv[1], O_RDONLY | O_DIRECT | O_NOFOLLOW);
sendfile(out, in, NULL, 0x1dd00);
run repeatedly in parallel. What I think is happening is that ftruncate()
occasionally shortens the DIO read that's about to be made by sendfile's
splice core by reducing i_size.
This should be more efficient for DIO read by virtue of doing a bulk page
allocation, but slightly less efficient by ignoring any partial page in the
pipe.
Reported-by: syzbot+a440341a59e3b7142895@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: David Hildenbrand <david@redhat.com>
cc: John Hubbard <jhubbard@nvidia.com>
cc: linux-mm@kvack.org
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20230207094731.1390-1-hdanton@sina.com/ [1]
Link: https://lore.kernel.org/r/000000000000b0b3c005f3a09383@google.com/ [2]
Signed-off-by: Steve French <stfrench@microsoft.com>
2023-02-07 10:45:40 +00:00
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2023-08-28 17:13:18 +02:00
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splice: Add a func to do a splice from an O_DIRECT file without ITER_PIPE
Implement a function, direct_file_splice(), that deals with this by using
an ITER_BVEC iterator instead of an ITER_PIPE iterator as the former won't
free its buffers when reverted. The function bulk allocates all the
buffers it thinks it is going to use in advance, does the read
synchronously and only then trims the buffer down. The pages we did use
get pushed into the pipe.
This fixes a problem with the upcoming iov_iter_extract_pages() function,
whereby pages extracted from a non-user-backed iterator such as ITER_PIPE
aren't pinned. __iomap_dio_rw(), however, calls iov_iter_revert() to
shorten the iterator to just the bufferage it is going to use - which has
the side-effect of freeing the excess pipe buffers, even though they're
attached to a bio and may get written to by DMA (thanks to Hillf Danton for
spotting this[1]).
This then causes memory corruption that is particularly noticeable when the
syzbot test[2] is run. The test boils down to:
out = creat(argv[1], 0666);
ftruncate(out, 0x800);
lseek(out, 0x200, SEEK_SET);
in = open(argv[1], O_RDONLY | O_DIRECT | O_NOFOLLOW);
sendfile(out, in, NULL, 0x1dd00);
run repeatedly in parallel. What I think is happening is that ftruncate()
occasionally shortens the DIO read that's about to be made by sendfile's
splice core by reducing i_size.
This should be more efficient for DIO read by virtue of doing a bulk page
allocation, but slightly less efficient by ignoring any partial page in the
pipe.
Reported-by: syzbot+a440341a59e3b7142895@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: David Hildenbrand <david@redhat.com>
cc: John Hubbard <jhubbard@nvidia.com>
cc: linux-mm@kvack.org
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20230207094731.1390-1-hdanton@sina.com/ [1]
Link: https://lore.kernel.org/r/000000000000b0b3c005f3a09383@google.com/ [2]
Signed-off-by: Steve French <stfrench@microsoft.com>
2023-02-07 10:45:40 +00:00
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2023-05-22 14:49:51 +01:00
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splice: Add a func to do a splice from an O_DIRECT file without ITER_PIPE
Implement a function, direct_file_splice(), that deals with this by using
an ITER_BVEC iterator instead of an ITER_PIPE iterator as the former won't
free its buffers when reverted. The function bulk allocates all the
buffers it thinks it is going to use in advance, does the read
synchronously and only then trims the buffer down. The pages we did use
get pushed into the pipe.
This fixes a problem with the upcoming iov_iter_extract_pages() function,
whereby pages extracted from a non-user-backed iterator such as ITER_PIPE
aren't pinned. __iomap_dio_rw(), however, calls iov_iter_revert() to
shorten the iterator to just the bufferage it is going to use - which has
the side-effect of freeing the excess pipe buffers, even though they're
attached to a bio and may get written to by DMA (thanks to Hillf Danton for
spotting this[1]).
This then causes memory corruption that is particularly noticeable when the
syzbot test[2] is run. The test boils down to:
out = creat(argv[1], 0666);
ftruncate(out, 0x800);
lseek(out, 0x200, SEEK_SET);
in = open(argv[1], O_RDONLY | O_DIRECT | O_NOFOLLOW);
sendfile(out, in, NULL, 0x1dd00);
run repeatedly in parallel. What I think is happening is that ftruncate()
occasionally shortens the DIO read that's about to be made by sendfile's
splice core by reducing i_size.
This should be more efficient for DIO read by virtue of doing a bulk page
allocation, but slightly less efficient by ignoring any partial page in the
pipe.
Reported-by: syzbot+a440341a59e3b7142895@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: David Hildenbrand <david@redhat.com>
cc: John Hubbard <jhubbard@nvidia.com>
cc: linux-mm@kvack.org
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20230207094731.1390-1-hdanton@sina.com/ [1]
Link: https://lore.kernel.org/r/000000000000b0b3c005f3a09383@google.com/ [2]
Signed-off-by: Steve French <stfrench@microsoft.com>
2023-02-07 10:45:40 +00:00
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2023-06-14 16:03:39 +02:00
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splice: Add a func to do a splice from an O_DIRECT file without ITER_PIPE
Implement a function, direct_file_splice(), that deals with this by using
an ITER_BVEC iterator instead of an ITER_PIPE iterator as the former won't
free its buffers when reverted. The function bulk allocates all the
buffers it thinks it is going to use in advance, does the read
synchronously and only then trims the buffer down. The pages we did use
get pushed into the pipe.
This fixes a problem with the upcoming iov_iter_extract_pages() function,
whereby pages extracted from a non-user-backed iterator such as ITER_PIPE
aren't pinned. __iomap_dio_rw(), however, calls iov_iter_revert() to
shorten the iterator to just the bufferage it is going to use - which has
the side-effect of freeing the excess pipe buffers, even though they're
attached to a bio and may get written to by DMA (thanks to Hillf Danton for
spotting this[1]).
This then causes memory corruption that is particularly noticeable when the
syzbot test[2] is run. The test boils down to:
out = creat(argv[1], 0666);
ftruncate(out, 0x800);
lseek(out, 0x200, SEEK_SET);
in = open(argv[1], O_RDONLY | O_DIRECT | O_NOFOLLOW);
sendfile(out, in, NULL, 0x1dd00);
run repeatedly in parallel. What I think is happening is that ftruncate()
occasionally shortens the DIO read that's about to be made by sendfile's
splice core by reducing i_size.
This should be more efficient for DIO read by virtue of doing a bulk page
allocation, but slightly less efficient by ignoring any partial page in the
pipe.
Reported-by: syzbot+a440341a59e3b7142895@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: David Hildenbrand <david@redhat.com>
cc: John Hubbard <jhubbard@nvidia.com>
cc: linux-mm@kvack.org
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20230207094731.1390-1-hdanton@sina.com/ [1]
Link: https://lore.kernel.org/r/000000000000b0b3c005f3a09383@google.com/ [2]
Signed-off-by: Steve French <stfrench@microsoft.com>
2023-02-07 10:45:40 +00:00
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2023-05-22 14:49:51 +01:00
|
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|
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|
splice: Add a func to do a splice from an O_DIRECT file without ITER_PIPE
Implement a function, direct_file_splice(), that deals with this by using
an ITER_BVEC iterator instead of an ITER_PIPE iterator as the former won't
free its buffers when reverted. The function bulk allocates all the
buffers it thinks it is going to use in advance, does the read
synchronously and only then trims the buffer down. The pages we did use
get pushed into the pipe.
This fixes a problem with the upcoming iov_iter_extract_pages() function,
whereby pages extracted from a non-user-backed iterator such as ITER_PIPE
aren't pinned. __iomap_dio_rw(), however, calls iov_iter_revert() to
shorten the iterator to just the bufferage it is going to use - which has
the side-effect of freeing the excess pipe buffers, even though they're
attached to a bio and may get written to by DMA (thanks to Hillf Danton for
spotting this[1]).
This then causes memory corruption that is particularly noticeable when the
syzbot test[2] is run. The test boils down to:
out = creat(argv[1], 0666);
ftruncate(out, 0x800);
lseek(out, 0x200, SEEK_SET);
in = open(argv[1], O_RDONLY | O_DIRECT | O_NOFOLLOW);
sendfile(out, in, NULL, 0x1dd00);
run repeatedly in parallel. What I think is happening is that ftruncate()
occasionally shortens the DIO read that's about to be made by sendfile's
splice core by reducing i_size.
This should be more efficient for DIO read by virtue of doing a bulk page
allocation, but slightly less efficient by ignoring any partial page in the
pipe.
Reported-by: syzbot+a440341a59e3b7142895@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: David Hildenbrand <david@redhat.com>
cc: John Hubbard <jhubbard@nvidia.com>
cc: linux-mm@kvack.org
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20230207094731.1390-1-hdanton@sina.com/ [1]
Link: https://lore.kernel.org/r/000000000000b0b3c005f3a09383@google.com/ [2]
Signed-off-by: Steve French <stfrench@microsoft.com>
2023-02-07 10:45:40 +00:00
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2023-05-22 14:49:51 +01:00
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|
splice: Add a func to do a splice from an O_DIRECT file without ITER_PIPE
Implement a function, direct_file_splice(), that deals with this by using
an ITER_BVEC iterator instead of an ITER_PIPE iterator as the former won't
free its buffers when reverted. The function bulk allocates all the
buffers it thinks it is going to use in advance, does the read
synchronously and only then trims the buffer down. The pages we did use
get pushed into the pipe.
This fixes a problem with the upcoming iov_iter_extract_pages() function,
whereby pages extracted from a non-user-backed iterator such as ITER_PIPE
aren't pinned. __iomap_dio_rw(), however, calls iov_iter_revert() to
shorten the iterator to just the bufferage it is going to use - which has
the side-effect of freeing the excess pipe buffers, even though they're
attached to a bio and may get written to by DMA (thanks to Hillf Danton for
spotting this[1]).
This then causes memory corruption that is particularly noticeable when the
syzbot test[2] is run. The test boils down to:
out = creat(argv[1], 0666);
ftruncate(out, 0x800);
lseek(out, 0x200, SEEK_SET);
in = open(argv[1], O_RDONLY | O_DIRECT | O_NOFOLLOW);
sendfile(out, in, NULL, 0x1dd00);
run repeatedly in parallel. What I think is happening is that ftruncate()
occasionally shortens the DIO read that's about to be made by sendfile's
splice core by reducing i_size.
This should be more efficient for DIO read by virtue of doing a bulk page
allocation, but slightly less efficient by ignoring any partial page in the
pipe.
Reported-by: syzbot+a440341a59e3b7142895@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: David Hildenbrand <david@redhat.com>
cc: John Hubbard <jhubbard@nvidia.com>
cc: linux-mm@kvack.org
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20230207094731.1390-1-hdanton@sina.com/ [1]
Link: https://lore.kernel.org/r/000000000000b0b3c005f3a09383@google.com/ [2]
Signed-off-by: Steve French <stfrench@microsoft.com>
2023-02-07 10:45:40 +00:00
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2023-05-22 14:49:50 +01:00
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splice: Add a func to do a splice from an O_DIRECT file without ITER_PIPE
Implement a function, direct_file_splice(), that deals with this by using
an ITER_BVEC iterator instead of an ITER_PIPE iterator as the former won't
free its buffers when reverted. The function bulk allocates all the
buffers it thinks it is going to use in advance, does the read
synchronously and only then trims the buffer down. The pages we did use
get pushed into the pipe.
This fixes a problem with the upcoming iov_iter_extract_pages() function,
whereby pages extracted from a non-user-backed iterator such as ITER_PIPE
aren't pinned. __iomap_dio_rw(), however, calls iov_iter_revert() to
shorten the iterator to just the bufferage it is going to use - which has
the side-effect of freeing the excess pipe buffers, even though they're
attached to a bio and may get written to by DMA (thanks to Hillf Danton for
spotting this[1]).
This then causes memory corruption that is particularly noticeable when the
syzbot test[2] is run. The test boils down to:
out = creat(argv[1], 0666);
ftruncate(out, 0x800);
lseek(out, 0x200, SEEK_SET);
in = open(argv[1], O_RDONLY | O_DIRECT | O_NOFOLLOW);
sendfile(out, in, NULL, 0x1dd00);
run repeatedly in parallel. What I think is happening is that ftruncate()
occasionally shortens the DIO read that's about to be made by sendfile's
splice core by reducing i_size.
This should be more efficient for DIO read by virtue of doing a bulk page
allocation, but slightly less efficient by ignoring any partial page in the
pipe.
Reported-by: syzbot+a440341a59e3b7142895@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: David Hildenbrand <david@redhat.com>
cc: John Hubbard <jhubbard@nvidia.com>
cc: linux-mm@kvack.org
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20230207094731.1390-1-hdanton@sina.com/ [1]
Link: https://lore.kernel.org/r/000000000000b0b3c005f3a09383@google.com/ [2]
Signed-off-by: Steve French <stfrench@microsoft.com>
2023-02-07 10:45:40 +00:00
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2016-09-22 16:33:12 -04:00
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2020-05-20 17:58:16 +02:00
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2009-05-07 15:37:36 +02:00
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2014-01-22 19:36:57 +01:00
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2020-05-20 17:58:16 +02:00
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2014-01-22 19:36:57 +01:00
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2009-04-14 19:48:36 +02:00
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pipe: use exclusive waits when reading or writing
This makes the pipe code use separate wait-queues and exclusive waiting
for readers and writers, avoiding a nasty thundering herd problem when
there are lots of readers waiting for data on a pipe (or, less commonly,
lots of writers waiting for a pipe to have space).
While this isn't a common occurrence in the traditional "use a pipe as a
data transport" case, where you typically only have a single reader and
a single writer process, there is one common special case: using a pipe
as a source of "locking tokens" rather than for data communication.
In particular, the GNU make jobserver code ends up using a pipe as a way
to limit parallelism, where each job consumes a token by reading a byte
from the jobserver pipe, and releases the token by writing a byte back
to the pipe.
This pattern is fairly traditional on Unix, and works very well, but
will waste a lot of time waking up a lot of processes when only a single
reader needs to be woken up when a writer releases a new token.
A simplified test-case of just this pipe interaction is to create 64
processes, and then pass a single token around between them (this
test-case also intentionally passes another token that gets ignored to
test the "wake up next" logic too, in case anybody wonders about it):
#include <unistd.h>
int main(int argc, char **argv)
{
int fd[2], counters[2];
pipe(fd);
counters[0] = 0;
counters[1] = -1;
write(fd[1], counters, sizeof(counters));
/* 64 processes */
fork(); fork(); fork(); fork(); fork(); fork();
do {
int i;
read(fd[0], &i, sizeof(i));
if (i < 0)
continue;
counters[0] = i+1;
write(fd[1], counters, (1+(i & 1)) *sizeof(int));
} while (counters[0] < 1000000);
return 0;
}
and in a perfect world, passing that token around should only cause one
context switch per transfer, when the writer of a token causes a
directed wakeup of just a single reader.
But with the "writer wakes all readers" model we traditionally had, on
my test box the above case causes more than an order of magnitude more
scheduling: instead of the expected ~1M context switches, "perf stat"
shows
231,852.37 msec task-clock # 15.857 CPUs utilized
11,250,961 context-switches # 0.049 M/sec
616,304 cpu-migrations # 0.003 M/sec
1,648 page-faults # 0.007 K/sec
1,097,903,998,514 cycles # 4.735 GHz
120,781,778,352 instructions # 0.11 insn per cycle
27,997,056,043 branches # 120.754 M/sec
283,581,233 branch-misses # 1.01% of all branches
14.621273891 seconds time elapsed
0.018243000 seconds user
3.611468000 seconds sys
before this commit.
After this commit, I get
5,229.55 msec task-clock # 3.072 CPUs utilized
1,212,233 context-switches # 0.232 M/sec
103,951 cpu-migrations # 0.020 M/sec
1,328 page-faults # 0.254 K/sec
21,307,456,166 cycles # 4.074 GHz
12,947,819,999 instructions # 0.61 insn per cycle
2,881,985,678 branches # 551.096 M/sec
64,267,015 branch-misses # 2.23% of all branches
1.702148350 seconds time elapsed
0.004868000 seconds user
0.110786000 seconds sys
instead. Much better.
[ Note! This kernel improvement seems to be very good at triggering a
race condition in the make jobserver (in GNU make 4.2.1) for me. It's
a long known bug that was fixed back in June 2017 by GNU make commit
b552b0525198 ("[SV 51159] Use a non-blocking read with pselect to
avoid hangs.").
But there wasn't a new release of GNU make until 4.3 on Jan 19 2020,
so a number of distributions may still have the buggy version. Some
have backported the fix to their 4.2.1 release, though, and even
without the fix it's quite timing-dependent whether the bug actually
is hit. ]
Josh Triplett says:
"I've been hammering on your pipe fix patch (switching to exclusive
wait queues) for a month or so, on several different systems, and I've
run into no issues with it. The patch *substantially* improves
parallel build times on large (~100 CPU) systems, both with parallel
make and with other things that use make's pipe-based jobserver.
All current distributions (including stable and long-term stable
distributions) have versions of GNU make that no longer have the
jobserver bug"
Tested-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-12-09 09:48:27 -08:00
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2009-04-14 19:48:36 +02:00
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2014-04-05 04:35:49 -04:00
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2009-04-14 19:48:36 +02:00
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2019-11-15 13:30:32 +00:00
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2009-04-14 19:48:36 +02:00
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2019-12-06 12:40:35 -08:00
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2025-03-07 05:29:19 +00:00
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2009-04-14 19:48:36 +02:00
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2016-09-27 10:45:12 +02:00
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2010-12-17 08:56:44 +01:00
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2009-04-14 19:48:36 +02:00
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2010-12-17 08:56:44 +01:00
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2009-04-14 19:48:36 +02:00
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2016-09-27 10:45:12 +02:00
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2019-11-15 13:30:32 +00:00
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2013-03-21 11:01:38 -04:00
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2009-04-14 19:48:36 +02:00
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splice: teach splice pipe reading about empty pipe buffers
Tetsuo Handa reports that splice() can return 0 before the real EOF, if
the data in the splice source pipe is an empty pipe buffer. That empty
pipe buffer case doesn't happen in any normal situation, but you can
trigger it by doing a write to a pipe that fails due to a page fault.
Tetsuo has a test-case to show the behavior:
#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
const int fd = open("/tmp/testfile", O_WRONLY | O_CREAT, 0600);
int pipe_fd[2] = { -1, -1 };
pipe(pipe_fd);
write(pipe_fd[1], NULL, 4096);
/* This splice() should wait unless interrupted. */
return !splice(pipe_fd[0], NULL, fd, NULL, 65536, 0);
}
which results in
write(5, NULL, 4096) = -1 EFAULT (Bad address)
splice(4, NULL, 3, NULL, 65536, 0) = 0
and this can confuse splice() users into believing they have hit EOF
prematurely.
The issue was introduced when the pipe write code started pre-allocating
the pipe buffers before copying data from user space.
This is modified verion of Tetsuo's original patch.
Fixes: a194dfe6e6f6 ("pipe: Rearrange sequence in pipe_write() to preallocate slot")
Link:https://lore.kernel.org/linux-fsdevel/20201005121339.4063-1-penguin-kernel@I-love.SAKURA.ne.jp/
Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Acked-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-05 11:26:27 -07:00
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2025-03-07 05:29:19 +00:00
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splice: teach splice pipe reading about empty pipe buffers
Tetsuo Handa reports that splice() can return 0 before the real EOF, if
the data in the splice source pipe is an empty pipe buffer. That empty
pipe buffer case doesn't happen in any normal situation, but you can
trigger it by doing a write to a pipe that fails due to a page fault.
Tetsuo has a test-case to show the behavior:
#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
const int fd = open("/tmp/testfile", O_WRONLY | O_CREAT, 0600);
int pipe_fd[2] = { -1, -1 };
pipe(pipe_fd);
write(pipe_fd[1], NULL, 4096);
/* This splice() should wait unless interrupted. */
return !splice(pipe_fd[0], NULL, fd, NULL, 65536, 0);
}
which results in
write(5, NULL, 4096) = -1 EFAULT (Bad address)
splice(4, NULL, 3, NULL, 65536, 0) = 0
and this can confuse splice() users into believing they have hit EOF
prematurely.
The issue was introduced when the pipe write code started pre-allocating
the pipe buffers before copying data from user space.
This is modified verion of Tetsuo's original patch.
Fixes: a194dfe6e6f6 ("pipe: Rearrange sequence in pipe_write() to preallocate slot")
Link:https://lore.kernel.org/linux-fsdevel/20201005121339.4063-1-penguin-kernel@I-love.SAKURA.ne.jp/
Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Acked-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-05 11:26:27 -07:00
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2009-04-14 19:48:36 +02:00
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2014-04-05 04:35:49 -04:00
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2009-04-14 19:48:36 +02:00
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2015-11-23 13:09:50 +01:00
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splice: teach splice pipe reading about empty pipe buffers
Tetsuo Handa reports that splice() can return 0 before the real EOF, if
the data in the splice source pipe is an empty pipe buffer. That empty
pipe buffer case doesn't happen in any normal situation, but you can
trigger it by doing a write to a pipe that fails due to a page fault.
Tetsuo has a test-case to show the behavior:
#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
const int fd = open("/tmp/testfile", O_WRONLY | O_CREAT, 0600);
int pipe_fd[2] = { -1, -1 };
pipe(pipe_fd);
write(pipe_fd[1], NULL, 4096);
/* This splice() should wait unless interrupted. */
return !splice(pipe_fd[0], NULL, fd, NULL, 65536, 0);
}
which results in
write(5, NULL, 4096) = -1 EFAULT (Bad address)
splice(4, NULL, 3, NULL, 65536, 0) = 0
and this can confuse splice() users into believing they have hit EOF
prematurely.
The issue was introduced when the pipe write code started pre-allocating
the pipe buffers before copying data from user space.
This is modified verion of Tetsuo's original patch.
Fixes: a194dfe6e6f6 ("pipe: Rearrange sequence in pipe_write() to preallocate slot")
Link:https://lore.kernel.org/linux-fsdevel/20201005121339.4063-1-penguin-kernel@I-love.SAKURA.ne.jp/
Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Acked-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-05 11:26:27 -07:00
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fs/pipe: add simpler helpers for common cases
The fix to atomically read the pipe head and tail state when not holding
the pipe mutex has caused a number of headaches due to the size change
of the involved types.
It turns out that we don't have _that_ many places that access these
fields directly and were affected, but we have more than we strictly
should have, because our low-level helper functions have been designed
to have intimate knowledge of how the pipes work.
And as a result, that random noise of direct 'pipe->head' and
'pipe->tail' accesses makes it harder to pinpoint any actual potential
problem spots remaining.
For example, we didn't have a "is the pipe full" helper function, but
instead had a "given these pipe buffer indexes and this pipe size, is
the pipe full". That's because some low-level pipe code does actually
want that much more complicated interface.
But most other places literally just want a "is the pipe full" helper,
and not having it meant that those places ended up being unnecessarily
much too aware of this all.
It would have been much better if only the very core pipe code that
cared had been the one aware of this all.
So let's fix it - better late than never. This just introduces the
trivial wrappers for "is this pipe full or empty" and to get how many
pipe buffers are used, so that instead of writing
if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
the places that literally just want to know if a pipe is full can just
say
if (pipe_is_full(pipe))
instead. The existing trivial cases were converted with a 'sed' script.
This cuts down on the places that access pipe->head and pipe->tail
directly outside of the pipe code (and core splice code) quite a lot.
The splice code in particular still revels in doing the direct low-level
accesses, and the fuse fuse_dev_splice_write() code also seems a bit
unnecessarily eager to go very low-level, but it's at least a bit better
than it used to be.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2025-03-06 18:25:35 -10:00
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2009-04-14 19:48:36 +02:00
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pipe: remove 'waiting_writers' merging logic
This code is ancient, and goes back to when we only had a single page
for the pipe buffers. The exact history is hidden in the mists of time
(ie "before git", and in fact predates the BK repository too).
At that long-ago point in time, it actually helped to try to merge big
back-and-forth pipe reads and writes, and not limit pipe reads to the
single pipe buffer in length just because that was all we had at a time.
However, since then we've expanded the pipe buffers to multiple pages,
and this logic really doesn't seem to make sense. And a lot of it is
somewhat questionable (ie "hmm, the user asked for a non-blocking read,
but we see that there's a writer pending, so let's wait anyway to get
the extra data that the writer will have").
But more importantly, it makes the "go to sleep" logic much less
obvious, and considering the wakeup issues we've had, I want to make for
less of those kinds of things.
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-12-07 13:21:01 -08:00
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2009-04-14 19:48:36 +02:00
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pipe: remove pipe_wait() and fix wakeup race with splice
The pipe splice code still used the old model of waiting for pipe IO by
using a non-specific "pipe_wait()" that waited for any pipe event to
happen, which depended on all pipe IO being entirely serialized by the
pipe lock. So by checking the state you were waiting for, and then
adding yourself to the wait queue before dropping the lock, you were
guaranteed to see all the wakeups.
Strictly speaking, the actual wakeups were not done under the lock, but
the pipe_wait() model still worked, because since the waiter held the
lock when checking whether it should sleep, it would always see the
current state, and the wakeup was always done after updating the state.
However, commit 0ddad21d3e99 ("pipe: use exclusive waits when reading or
writing") split the single wait-queue into two, and in the process also
made the "wait for event" code wait for _two_ wait queues, and that then
showed a race with the wakers that were not serialized by the pipe lock.
It's only splice that used that "pipe_wait()" model, so the problem
wasn't obvious, but Josef Bacik reports:
"I hit a hang with fstest btrfs/187, which does a btrfs send into
/dev/null. This works by creating a pipe, the write side is given to
the kernel to write into, and the read side is handed to a thread that
splices into a file, in this case /dev/null.
The box that was hung had the write side stuck here [pipe_write] and
the read side stuck here [splice_from_pipe_next -> pipe_wait].
[ more details about pipe_wait() scenario ]
The problem is we're doing the prepare_to_wait, which sets our state
each time, however we can be woken up either with reads or writes. In
the case above we race with the WRITER waking us up, and re-set our
state to INTERRUPTIBLE, and thus never break out of schedule"
Josef had a patch that avoided the issue in pipe_wait() by just making
it set the state only once, but the deeper problem is that pipe_wait()
depends on a level of synchonization by the pipe mutex that it really
shouldn't. And the whole "wait for any pipe state change" model really
isn't very good to begin with.
So rather than trying to work around things in pipe_wait(), remove that
legacy model of "wait for arbitrary pipe event" entirely, and actually
create functions that wait for the pipe actually being readable or
writable, and can do so without depending on the pipe lock serializing
everything.
Fixes: 0ddad21d3e99 ("pipe: use exclusive waits when reading or writing")
Link: https://lore.kernel.org/linux-fsdevel/bfa88b5ad6f069b2b679316b9e495a970130416c.1601567868.git.josef@toxicpanda.com/
Reported-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-and-tested-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-01 19:14:36 -07:00
|
|
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|
2009-04-14 19:48:36 +02:00
|
|
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|
|
splice: teach splice pipe reading about empty pipe buffers
Tetsuo Handa reports that splice() can return 0 before the real EOF, if
the data in the splice source pipe is an empty pipe buffer. That empty
pipe buffer case doesn't happen in any normal situation, but you can
trigger it by doing a write to a pipe that fails due to a page fault.
Tetsuo has a test-case to show the behavior:
#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
const int fd = open("/tmp/testfile", O_WRONLY | O_CREAT, 0600);
int pipe_fd[2] = { -1, -1 };
pipe(pipe_fd);
write(pipe_fd[1], NULL, 4096);
/* This splice() should wait unless interrupted. */
return !splice(pipe_fd[0], NULL, fd, NULL, 65536, 0);
}
which results in
write(5, NULL, 4096) = -1 EFAULT (Bad address)
splice(4, NULL, 3, NULL, 65536, 0) = 0
and this can confuse splice() users into believing they have hit EOF
prematurely.
The issue was introduced when the pipe write code started pre-allocating
the pipe buffers before copying data from user space.
This is modified verion of Tetsuo's original patch.
Fixes: a194dfe6e6f6 ("pipe: Rearrange sequence in pipe_write() to preallocate slot")
Link:https://lore.kernel.org/linux-fsdevel/20201005121339.4063-1-penguin-kernel@I-love.SAKURA.ne.jp/
Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Acked-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-05 11:26:27 -07:00
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2009-04-14 19:48:36 +02:00
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2009-04-16 19:09:55 -07:00
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2009-04-14 19:48:36 +02:00
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2014-04-05 04:35:49 -04:00
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2009-04-14 19:48:36 +02:00
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2014-04-05 04:35:49 -04:00
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2009-04-14 19:48:36 +02:00
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2007-06-21 13:10:21 +02:00
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2023-06-07 19:19:09 +01:00
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2007-06-21 13:10:21 +02:00
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2006-04-02 23:05:09 +02:00
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2007-06-12 21:17:17 +02:00
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2006-03-30 15:15:30 +02:00
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2009-04-14 19:48:36 +02:00
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2006-03-30 15:15:30 +02:00
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2009-04-14 19:48:36 +02:00
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2015-11-23 13:09:51 +01:00
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2009-04-14 19:48:36 +02:00
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2006-03-30 15:15:30 +02:00
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2009-04-14 19:48:36 +02:00
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2006-03-30 15:15:30 +02:00
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2007-03-21 13:11:02 +01:00
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2006-03-30 15:15:30 +02:00
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2007-06-21 13:10:21 +02:00
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2009-04-14 19:48:37 +02:00
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2007-06-21 13:10:21 +02:00
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2006-10-17 18:43:07 +02:00
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2007-06-12 21:17:17 +02:00
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2007-06-14 13:08:55 +02:00
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2007-06-12 21:17:17 +02:00
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2006-10-17 18:43:07 +02:00
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2009-04-14 19:48:41 +02:00
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2007-06-12 21:17:17 +02:00
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2009-04-14 19:48:41 +02:00
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2006-10-17 18:43:07 +02:00
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2014-04-05 04:27:08 -04:00
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2019-10-16 16:47:32 +01:00
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2023-11-23 18:51:44 +01:00
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2014-04-05 04:27:08 -04:00
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2023-11-23 18:51:44 +01:00
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2026-02-21 16:37:42 -08:00
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2014-04-05 04:27:08 -04:00
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2023-11-23 18:51:44 +01:00
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2014-04-05 04:27:08 -04:00
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2025-03-07 05:29:19 +00:00
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2014-04-05 04:27:08 -04:00
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2019-11-15 13:30:32 +00:00
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2014-04-05 04:27:08 -04:00
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2019-10-16 16:47:32 +01:00
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2014-04-05 04:27:08 -04:00
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2019-10-16 16:47:32 +01:00
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2026-02-21 16:37:42 -08:00
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2014-04-05 04:27:08 -04:00
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2019-12-06 12:40:35 -08:00
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2014-04-05 04:27:08 -04:00
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2021-01-09 16:02:57 +00:00
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2025-03-07 05:29:19 +00:00
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2014-04-05 04:27:08 -04:00
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2021-01-09 16:02:57 +00:00
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2014-04-05 04:27:08 -04:00
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2016-09-27 10:45:12 +02:00
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2014-04-05 04:27:08 -04:00
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2023-02-03 16:06:28 +01:00
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2014-04-05 04:27:08 -04:00
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2021-01-09 16:02:57 +00:00
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2014-04-05 04:27:08 -04:00
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2022-09-15 20:25:47 -04:00
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2023-11-23 18:51:44 +01:00
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2023-08-28 17:13:18 +02:00
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2023-11-23 18:51:44 +01:00
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2014-04-05 04:27:08 -04:00
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netfs: Fix unbuffered write error handling
If all the subrequests in an unbuffered write stream fail, the subrequest
collector doesn't update the stream->transferred value and it retains its
initial LONG_MAX value. Unfortunately, if all active streams fail, then we
take the smallest value of { LONG_MAX, LONG_MAX, ... } as the value to set
in wreq->transferred - which is then returned from ->write_iter().
LONG_MAX was chosen as the initial value so that all the streams can be
quickly assessed by taking the smallest value of all stream->transferred -
but this only works if we've set any of them.
Fix this by adding a flag to indicate whether the value in
stream->transferred is valid and checking that when we integrate the
values. stream->transferred can then be initialised to zero.
This was found by running the generic/750 xfstest against cifs with
cache=none. It splices data to the target file. Once (if) it has used up
all the available scratch space, the writes start failing with ENOSPC.
This causes ->write_iter() to fail. However, it was returning
wreq->transferred, i.e. LONG_MAX, rather than an error (because it thought
the amount transferred was non-zero) and iter_file_splice_write() would
then try to clean up that amount of pipe bufferage - leading to an oops
when it overran. The kernel log showed:
CIFS: VFS: Send error in write = -28
followed by:
BUG: kernel NULL pointer dereference, address: 0000000000000008
with:
RIP: 0010:iter_file_splice_write+0x3a4/0x520
do_splice+0x197/0x4e0
or:
RIP: 0010:pipe_buf_release (include/linux/pipe_fs_i.h:282)
iter_file_splice_write (fs/splice.c:755)
Also put a warning check into splice to announce if ->write_iter() returned
that it had written more than it was asked to.
Fixes: 288ace2f57c9 ("netfs: New writeback implementation")
Reported-by: Xiaoli Feng <fengxiaoli0714@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220445
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/915443.1755207950@warthog.procyon.org.uk
cc: Paulo Alcantara <pc@manguebit.org>
cc: Steve French <sfrench@samba.org>
cc: Shyam Prasad N <sprasad@microsoft.com>
cc: netfs@lists.linux.dev
cc: linux-cifs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: stable@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
2025-08-14 22:45:50 +01:00
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2014-04-05 04:27:08 -04:00
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2015-01-25 21:11:59 +01:00
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2014-04-05 04:27:08 -04:00
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2019-11-15 13:30:32 +00:00
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2014-04-05 04:27:08 -04:00
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2025-03-07 05:29:19 +00:00
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2014-04-05 04:27:08 -04:00
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2016-09-27 10:45:12 +02:00
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2019-11-15 13:30:32 +00:00
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2014-04-05 04:27:08 -04:00
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2023-06-07 19:19:09 +01:00
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2006-04-02 23:05:09 +02:00
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2023-06-07 19:19:09 +01:00
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2007-06-21 13:10:21 +02:00
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2006-04-02 23:05:09 +02:00
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2007-06-21 13:10:21 +02:00
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2006-04-02 23:05:09 +02:00
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2007-06-21 13:10:21 +02:00
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2006-04-02 23:05:09 +02:00
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2023-06-07 19:19:09 +01:00
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2006-03-30 15:15:30 +02:00
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2023-06-07 19:19:09 +01:00
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2006-03-30 15:15:30 +02:00
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2023-06-07 19:19:09 +01:00
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2025-03-07 05:29:19 +00:00
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2023-06-07 19:19:09 +01:00
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|
fs/pipe: add simpler helpers for common cases
The fix to atomically read the pipe head and tail state when not holding
the pipe mutex has caused a number of headaches due to the size change
of the involved types.
It turns out that we don't have _that_ many places that access these
fields directly and were affected, but we have more than we strictly
should have, because our low-level helper functions have been designed
to have intimate knowledge of how the pipes work.
And as a result, that random noise of direct 'pipe->head' and
'pipe->tail' accesses makes it harder to pinpoint any actual potential
problem spots remaining.
For example, we didn't have a "is the pipe full" helper function, but
instead had a "given these pipe buffer indexes and this pipe size, is
the pipe full". That's because some low-level pipe code does actually
want that much more complicated interface.
But most other places literally just want a "is the pipe full" helper,
and not having it meant that those places ended up being unnecessarily
much too aware of this all.
It would have been much better if only the very core pipe code that
cared had been the one aware of this all.
So let's fix it - better late than never. This just introduces the
trivial wrappers for "is this pipe full or empty" and to get how many
pipe buffers are used, so that instead of writing
if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
the places that literally just want to know if a pipe is full can just
say
if (pipe_is_full(pipe))
instead. The existing trivial cases were converted with a 'sed' script.
This cuts down on the places that access pipe->head and pipe->tail
directly outside of the pipe code (and core splice code) quite a lot.
The splice code in particular still revels in doing the direct low-level
accesses, and the fuse fuse_dev_splice_write() code also seems a bit
unnecessarily eager to go very low-level, but it's at least a bit better
than it used to be.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2025-03-06 18:25:35 -10:00
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2023-06-07 19:19:09 +01:00
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2025-03-07 05:29:19 +00:00
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2023-06-07 19:19:09 +01:00
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2023-06-14 11:09:48 +01:00
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2023-06-07 19:19:09 +01:00
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2023-06-14 11:09:48 +01:00
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2023-06-07 19:19:09 +01:00
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2023-07-24 19:39:04 +02:00
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2023-06-07 19:19:09 +01:00
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2025-03-07 05:29:19 +00:00
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2023-06-07 19:19:09 +01:00
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2006-03-30 23:06:13 -05:00
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2020-09-03 16:22:34 +02:00
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2006-04-02 23:05:09 +02:00
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2023-12-12 11:44:36 +02:00
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2006-03-30 15:15:30 +02:00
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2020-09-03 16:22:34 +02:00
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2006-03-30 15:15:30 +02:00
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2023-06-07 19:19:10 +01:00
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2023-11-22 14:27:02 +02:00
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2023-12-12 11:44:36 +02:00
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2023-11-22 14:27:02 +02:00
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|
fs/pipe: add simpler helpers for common cases
The fix to atomically read the pipe head and tail state when not holding
the pipe mutex has caused a number of headaches due to the size change
of the involved types.
It turns out that we don't have _that_ many places that access these
fields directly and were affected, but we have more than we strictly
should have, because our low-level helper functions have been designed
to have intimate knowledge of how the pipes work.
And as a result, that random noise of direct 'pipe->head' and
'pipe->tail' accesses makes it harder to pinpoint any actual potential
problem spots remaining.
For example, we didn't have a "is the pipe full" helper function, but
instead had a "given these pipe buffer indexes and this pipe size, is
the pipe full". That's because some low-level pipe code does actually
want that much more complicated interface.
But most other places literally just want a "is the pipe full" helper,
and not having it meant that those places ended up being unnecessarily
much too aware of this all.
It would have been much better if only the very core pipe code that
cared had been the one aware of this all.
So let's fix it - better late than never. This just introduces the
trivial wrappers for "is this pipe full or empty" and to get how many
pipe buffers are used, so that instead of writing
if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
the places that literally just want to know if a pipe is full can just
say
if (pipe_is_full(pipe))
instead. The existing trivial cases were converted with a 'sed' script.
This cuts down on the places that access pipe->head and pipe->tail
directly outside of the pipe code (and core splice code) quite a lot.
The splice code in particular still revels in doing the direct low-level
accesses, and the fuse fuse_dev_splice_write() code also seems a bit
unnecessarily eager to go very low-level, but it's at least a bit better
than it used to be.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2025-03-06 18:25:35 -10:00
|
|
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|
2023-11-22 14:27:02 +02:00
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2023-05-22 14:49:52 +01:00
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2006-04-02 23:05:09 +02:00
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2023-12-12 11:44:36 +02:00
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2006-03-30 15:15:30 +02:00
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2023-12-12 11:44:36 +02:00
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2006-03-30 15:15:30 +02:00
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2006-04-11 14:57:50 +02:00
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2006-03-30 15:15:30 +02:00
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2023-11-22 14:27:02 +02:00
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2006-03-30 15:15:30 +02:00
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2023-05-22 14:49:52 +01:00
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2006-03-30 15:15:30 +02:00
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2007-06-21 13:10:21 +02:00
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2007-07-27 08:08:51 +02:00
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2007-06-21 13:10:21 +02:00
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2007-06-12 21:17:17 +02:00
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2006-04-11 13:52:07 +02:00
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2023-12-12 11:44:36 +02:00
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2007-06-12 21:17:17 +02:00
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splice: sendfile() at once fails for big files
Using sendfile with below small program to get MD5 sums of some files,
it appear that big files (over 64kbytes with 4k pages system) get a
wrong MD5 sum while small files get the correct sum.
This program uses sendfile() to send a file to an AF_ALG socket
for hashing.
/* md5sum2.c */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <linux/if_alg.h>
int main(int argc, char **argv)
{
int sk = socket(AF_ALG, SOCK_SEQPACKET, 0);
struct stat st;
struct sockaddr_alg sa = {
.salg_family = AF_ALG,
.salg_type = "hash",
.salg_name = "md5",
};
int n;
bind(sk, (struct sockaddr*)&sa, sizeof(sa));
for (n = 1; n < argc; n++) {
int size;
int offset = 0;
char buf[4096];
int fd;
int sko;
int i;
fd = open(argv[n], O_RDONLY);
sko = accept(sk, NULL, 0);
fstat(fd, &st);
size = st.st_size;
sendfile(sko, fd, &offset, size);
size = read(sko, buf, sizeof(buf));
for (i = 0; i < size; i++)
printf("%2.2x", buf[i]);
printf(" %s\n", argv[n]);
close(fd);
close(sko);
}
exit(0);
}
Test below is done using official linux patch files. First result is
with a software based md5sum. Second result is with the program above.
root@vgoip:~# ls -l patch-3.6.*
-rw-r--r-- 1 root root 64011 Aug 24 12:01 patch-3.6.2.gz
-rw-r--r-- 1 root root 94131 Aug 24 12:01 patch-3.6.3.gz
root@vgoip:~# md5sum patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
root@vgoip:~# ./md5sum2 patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
5fd77b24e68bb24dcc72d6e57c64790e patch-3.6.3.gz
After investivation, it appears that sendfile() sends the files by blocks
of 64kbytes (16 times PAGE_SIZE). The problem is that at the end of each
block, the SPLICE_F_MORE flag is missing, therefore the hashing operation
is reset as if it was the end of the file.
This patch adds SPLICE_F_MORE to the flags when more data is pending.
With the patch applied, we get the correct sums:
root@vgoip:~# md5sum patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
root@vgoip:~# ./md5sum2 patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Jens Axboe <axboe@fb.com>
2015-05-06 17:26:47 +02:00
|
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2006-04-11 13:52:07 +02:00
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2022-06-29 15:06:58 +02:00
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2006-04-11 13:52:07 +02:00
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2022-06-29 15:06:58 +02:00
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2006-04-11 13:52:07 +02:00
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2006-04-11 13:56:09 +02:00
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2013-03-21 11:04:15 -04:00
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2006-04-11 13:52:07 +02:00
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2006-04-26 14:39:29 +02:00
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2006-04-11 13:52:07 +02:00
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2006-04-11 13:57:21 +02:00
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2006-04-11 13:52:07 +02:00
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2007-06-12 21:17:17 +02:00
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splice, net: Fix SPLICE_F_MORE signalling in splice_direct_to_actor()
splice_direct_to_actor() doesn't manage SPLICE_F_MORE correctly[1] - and,
as a result, it incorrectly signals/fails to signal MSG_MORE when splicing
to a socket. The problem I'm seeing happens when a short splice occurs
because we got a short read due to hitting the EOF on a file: as the length
read (read_len) is less than the remaining size to be spliced (len),
SPLICE_F_MORE (and thus MSG_MORE) is set.
The issue is that, for the moment, we have no way to know *why* the short
read occurred and so can't make a good decision on whether we *should* keep
MSG_MORE set.
MSG_SENDPAGE_NOTLAST was added to work around this, but that is also set
incorrectly under some circumstances - for example if a short read fills a
single pipe_buffer, but the next read would return more (seqfile can do
this).
This was observed with the multi_chunk_sendfile tests in the tls kselftest
program. Some of those tests would hang and time out when the last chunk
of file was less than the sendfile request size:
build/kselftest/net/tls -r tls.12_aes_gcm.multi_chunk_sendfile
This has been observed before[2] and worked around in AF_TLS[3].
Fix this by making splice_direct_to_actor() always signal SPLICE_F_MORE if
we haven't yet hit the requested operation size. SPLICE_F_MORE remains
signalled if the user passed it in to splice() but otherwise gets cleared
when we've read sufficient data to fulfill the request.
If, however, we get a premature EOF from ->splice_read(), have sent at
least one byte and SPLICE_F_MORE was not set by the caller, ->splice_eof()
will be invoked.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Matthew Wilcox <willy@infradead.org>
cc: Jan Kara <jack@suse.cz>
cc: Jeff Layton <jlayton@kernel.org>
cc: David Hildenbrand <david@redhat.com>
cc: Christian Brauner <brauner@kernel.org>
cc: Chuck Lever <chuck.lever@oracle.com>
cc: Boris Pismenny <borisp@nvidia.com>
cc: John Fastabend <john.fastabend@gmail.com>
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/499791.1685485603@warthog.procyon.org.uk/ [1]
Link: https://lore.kernel.org/r/1591392508-14592-1-git-send-email-pooja.trivedi@stackpath.com/ [2]
Link: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=d452d48b9f8b1a7f8152d33ef52cfd7fe1735b0a [3]
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2023-06-07 19:19:16 +01:00
|
|
|
|
|
|
|
|
|
2007-06-12 21:17:17 +02:00
|
|
|
|
splice, net: Fix SPLICE_F_MORE signalling in splice_direct_to_actor()
splice_direct_to_actor() doesn't manage SPLICE_F_MORE correctly[1] - and,
as a result, it incorrectly signals/fails to signal MSG_MORE when splicing
to a socket. The problem I'm seeing happens when a short splice occurs
because we got a short read due to hitting the EOF on a file: as the length
read (read_len) is less than the remaining size to be spliced (len),
SPLICE_F_MORE (and thus MSG_MORE) is set.
The issue is that, for the moment, we have no way to know *why* the short
read occurred and so can't make a good decision on whether we *should* keep
MSG_MORE set.
MSG_SENDPAGE_NOTLAST was added to work around this, but that is also set
incorrectly under some circumstances - for example if a short read fills a
single pipe_buffer, but the next read would return more (seqfile can do
this).
This was observed with the multi_chunk_sendfile tests in the tls kselftest
program. Some of those tests would hang and time out when the last chunk
of file was less than the sendfile request size:
build/kselftest/net/tls -r tls.12_aes_gcm.multi_chunk_sendfile
This has been observed before[2] and worked around in AF_TLS[3].
Fix this by making splice_direct_to_actor() always signal SPLICE_F_MORE if
we haven't yet hit the requested operation size. SPLICE_F_MORE remains
signalled if the user passed it in to splice() but otherwise gets cleared
when we've read sufficient data to fulfill the request.
If, however, we get a premature EOF from ->splice_read(), have sent at
least one byte and SPLICE_F_MORE was not set by the caller, ->splice_eof()
will be invoked.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Matthew Wilcox <willy@infradead.org>
cc: Jan Kara <jack@suse.cz>
cc: Jeff Layton <jlayton@kernel.org>
cc: David Hildenbrand <david@redhat.com>
cc: Christian Brauner <brauner@kernel.org>
cc: Chuck Lever <chuck.lever@oracle.com>
cc: Boris Pismenny <borisp@nvidia.com>
cc: John Fastabend <john.fastabend@gmail.com>
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/499791.1685485603@warthog.procyon.org.uk/ [1]
Link: https://lore.kernel.org/r/1591392508-14592-1-git-send-email-pooja.trivedi@stackpath.com/ [2]
Link: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=d452d48b9f8b1a7f8152d33ef52cfd7fe1735b0a [3]
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2023-06-07 19:19:16 +01:00
|
|
|
|
2007-06-12 21:17:17 +02:00
|
|
|
|
|
|
|
|
|
splice, net: Fix SPLICE_F_MORE signalling in splice_direct_to_actor()
splice_direct_to_actor() doesn't manage SPLICE_F_MORE correctly[1] - and,
as a result, it incorrectly signals/fails to signal MSG_MORE when splicing
to a socket. The problem I'm seeing happens when a short splice occurs
because we got a short read due to hitting the EOF on a file: as the length
read (read_len) is less than the remaining size to be spliced (len),
SPLICE_F_MORE (and thus MSG_MORE) is set.
The issue is that, for the moment, we have no way to know *why* the short
read occurred and so can't make a good decision on whether we *should* keep
MSG_MORE set.
MSG_SENDPAGE_NOTLAST was added to work around this, but that is also set
incorrectly under some circumstances - for example if a short read fills a
single pipe_buffer, but the next read would return more (seqfile can do
this).
This was observed with the multi_chunk_sendfile tests in the tls kselftest
program. Some of those tests would hang and time out when the last chunk
of file was less than the sendfile request size:
build/kselftest/net/tls -r tls.12_aes_gcm.multi_chunk_sendfile
This has been observed before[2] and worked around in AF_TLS[3].
Fix this by making splice_direct_to_actor() always signal SPLICE_F_MORE if
we haven't yet hit the requested operation size. SPLICE_F_MORE remains
signalled if the user passed it in to splice() but otherwise gets cleared
when we've read sufficient data to fulfill the request.
If, however, we get a premature EOF from ->splice_read(), have sent at
least one byte and SPLICE_F_MORE was not set by the caller, ->splice_eof()
will be invoked.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Matthew Wilcox <willy@infradead.org>
cc: Jan Kara <jack@suse.cz>
cc: Jeff Layton <jlayton@kernel.org>
cc: David Hildenbrand <david@redhat.com>
cc: Christian Brauner <brauner@kernel.org>
cc: Chuck Lever <chuck.lever@oracle.com>
cc: Boris Pismenny <borisp@nvidia.com>
cc: John Fastabend <john.fastabend@gmail.com>
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/499791.1685485603@warthog.procyon.org.uk/ [1]
Link: https://lore.kernel.org/r/1591392508-14592-1-git-send-email-pooja.trivedi@stackpath.com/ [2]
Link: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=d452d48b9f8b1a7f8152d33ef52cfd7fe1735b0a [3]
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2023-06-07 19:19:16 +01:00
|
|
|
|
|
|
|
|
|
2007-06-12 21:17:17 +02:00
|
|
|
|
splice: sendfile() at once fails for big files
Using sendfile with below small program to get MD5 sums of some files,
it appear that big files (over 64kbytes with 4k pages system) get a
wrong MD5 sum while small files get the correct sum.
This program uses sendfile() to send a file to an AF_ALG socket
for hashing.
/* md5sum2.c */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <linux/if_alg.h>
int main(int argc, char **argv)
{
int sk = socket(AF_ALG, SOCK_SEQPACKET, 0);
struct stat st;
struct sockaddr_alg sa = {
.salg_family = AF_ALG,
.salg_type = "hash",
.salg_name = "md5",
};
int n;
bind(sk, (struct sockaddr*)&sa, sizeof(sa));
for (n = 1; n < argc; n++) {
int size;
int offset = 0;
char buf[4096];
int fd;
int sko;
int i;
fd = open(argv[n], O_RDONLY);
sko = accept(sk, NULL, 0);
fstat(fd, &st);
size = st.st_size;
sendfile(sko, fd, &offset, size);
size = read(sko, buf, sizeof(buf));
for (i = 0; i < size; i++)
printf("%2.2x", buf[i]);
printf(" %s\n", argv[n]);
close(fd);
close(sko);
}
exit(0);
}
Test below is done using official linux patch files. First result is
with a software based md5sum. Second result is with the program above.
root@vgoip:~# ls -l patch-3.6.*
-rw-r--r-- 1 root root 64011 Aug 24 12:01 patch-3.6.2.gz
-rw-r--r-- 1 root root 94131 Aug 24 12:01 patch-3.6.3.gz
root@vgoip:~# md5sum patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
root@vgoip:~# ./md5sum2 patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
5fd77b24e68bb24dcc72d6e57c64790e patch-3.6.3.gz
After investivation, it appears that sendfile() sends the files by blocks
of 64kbytes (16 times PAGE_SIZE). The problem is that at the end of each
block, the SPLICE_F_MORE flag is missing, therefore the hashing operation
is reset as if it was the end of the file.
This patch adds SPLICE_F_MORE to the flags when more data is pending.
With the patch applied, we get the correct sums:
root@vgoip:~# md5sum patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
root@vgoip:~# ./md5sum2 patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Jens Axboe <axboe@fb.com>
2015-05-06 17:26:47 +02:00
|
|
|
|
splice, net: Fix SPLICE_F_MORE signalling in splice_direct_to_actor()
splice_direct_to_actor() doesn't manage SPLICE_F_MORE correctly[1] - and,
as a result, it incorrectly signals/fails to signal MSG_MORE when splicing
to a socket. The problem I'm seeing happens when a short splice occurs
because we got a short read due to hitting the EOF on a file: as the length
read (read_len) is less than the remaining size to be spliced (len),
SPLICE_F_MORE (and thus MSG_MORE) is set.
The issue is that, for the moment, we have no way to know *why* the short
read occurred and so can't make a good decision on whether we *should* keep
MSG_MORE set.
MSG_SENDPAGE_NOTLAST was added to work around this, but that is also set
incorrectly under some circumstances - for example if a short read fills a
single pipe_buffer, but the next read would return more (seqfile can do
this).
This was observed with the multi_chunk_sendfile tests in the tls kselftest
program. Some of those tests would hang and time out when the last chunk
of file was less than the sendfile request size:
build/kselftest/net/tls -r tls.12_aes_gcm.multi_chunk_sendfile
This has been observed before[2] and worked around in AF_TLS[3].
Fix this by making splice_direct_to_actor() always signal SPLICE_F_MORE if
we haven't yet hit the requested operation size. SPLICE_F_MORE remains
signalled if the user passed it in to splice() but otherwise gets cleared
when we've read sufficient data to fulfill the request.
If, however, we get a premature EOF from ->splice_read(), have sent at
least one byte and SPLICE_F_MORE was not set by the caller, ->splice_eof()
will be invoked.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Matthew Wilcox <willy@infradead.org>
cc: Jan Kara <jack@suse.cz>
cc: Jeff Layton <jlayton@kernel.org>
cc: David Hildenbrand <david@redhat.com>
cc: Christian Brauner <brauner@kernel.org>
cc: Chuck Lever <chuck.lever@oracle.com>
cc: Boris Pismenny <borisp@nvidia.com>
cc: John Fastabend <john.fastabend@gmail.com>
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/499791.1685485603@warthog.procyon.org.uk/ [1]
Link: https://lore.kernel.org/r/1591392508-14592-1-git-send-email-pooja.trivedi@stackpath.com/ [2]
Link: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=d452d48b9f8b1a7f8152d33ef52cfd7fe1735b0a [3]
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2023-06-07 19:19:16 +01:00
|
|
|
|
2006-04-11 13:52:07 +02:00
|
|
|
|
fs/pipe: add simpler helpers for common cases
The fix to atomically read the pipe head and tail state when not holding
the pipe mutex has caused a number of headaches due to the size change
of the involved types.
It turns out that we don't have _that_ many places that access these
fields directly and were affected, but we have more than we strictly
should have, because our low-level helper functions have been designed
to have intimate knowledge of how the pipes work.
And as a result, that random noise of direct 'pipe->head' and
'pipe->tail' accesses makes it harder to pinpoint any actual potential
problem spots remaining.
For example, we didn't have a "is the pipe full" helper function, but
instead had a "given these pipe buffer indexes and this pipe size, is
the pipe full". That's because some low-level pipe code does actually
want that much more complicated interface.
But most other places literally just want a "is the pipe full" helper,
and not having it meant that those places ended up being unnecessarily
much too aware of this all.
It would have been much better if only the very core pipe code that
cared had been the one aware of this all.
So let's fix it - better late than never. This just introduces the
trivial wrappers for "is this pipe full or empty" and to get how many
pipe buffers are used, so that instead of writing
if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
the places that literally just want to know if a pipe is full can just
say
if (pipe_is_full(pipe))
instead. The existing trivial cases were converted with a 'sed' script.
This cuts down on the places that access pipe->head and pipe->tail
directly outside of the pipe code (and core splice code) quite a lot.
The splice code in particular still revels in doing the direct low-level
accesses, and the fuse fuse_dev_splice_write() code also seems a bit
unnecessarily eager to go very low-level, but it's at least a bit better
than it used to be.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2025-03-06 18:25:35 -10:00
|
|
|
|
2018-11-30 10:37:49 -08:00
|
|
|
|
2006-04-11 13:52:07 +02:00
|
|
|
|
2007-07-13 14:11:43 +02:00
|
|
|
|
2008-05-09 13:28:36 +02:00
|
|
|
|
2006-04-11 13:52:07 +02:00
|
|
|
|
2023-11-22 14:27:02 +02:00
|
|
|
|
2007-07-13 14:11:43 +02:00
|
|
|
|
2023-06-07 19:19:10 +01:00
|
|
|
|
2006-04-11 13:52:07 +02:00
|
|
|
|
|
|
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|
|
2007-06-12 21:17:17 +02:00
|
|
|
|
2006-04-11 13:52:07 +02:00
|
|
|
|
splice: sendfile() at once fails for big files
Using sendfile with below small program to get MD5 sums of some files,
it appear that big files (over 64kbytes with 4k pages system) get a
wrong MD5 sum while small files get the correct sum.
This program uses sendfile() to send a file to an AF_ALG socket
for hashing.
/* md5sum2.c */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <linux/if_alg.h>
int main(int argc, char **argv)
{
int sk = socket(AF_ALG, SOCK_SEQPACKET, 0);
struct stat st;
struct sockaddr_alg sa = {
.salg_family = AF_ALG,
.salg_type = "hash",
.salg_name = "md5",
};
int n;
bind(sk, (struct sockaddr*)&sa, sizeof(sa));
for (n = 1; n < argc; n++) {
int size;
int offset = 0;
char buf[4096];
int fd;
int sko;
int i;
fd = open(argv[n], O_RDONLY);
sko = accept(sk, NULL, 0);
fstat(fd, &st);
size = st.st_size;
sendfile(sko, fd, &offset, size);
size = read(sko, buf, sizeof(buf));
for (i = 0; i < size; i++)
printf("%2.2x", buf[i]);
printf(" %s\n", argv[n]);
close(fd);
close(sko);
}
exit(0);
}
Test below is done using official linux patch files. First result is
with a software based md5sum. Second result is with the program above.
root@vgoip:~# ls -l patch-3.6.*
-rw-r--r-- 1 root root 64011 Aug 24 12:01 patch-3.6.2.gz
-rw-r--r-- 1 root root 94131 Aug 24 12:01 patch-3.6.3.gz
root@vgoip:~# md5sum patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
root@vgoip:~# ./md5sum2 patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
5fd77b24e68bb24dcc72d6e57c64790e patch-3.6.3.gz
After investivation, it appears that sendfile() sends the files by blocks
of 64kbytes (16 times PAGE_SIZE). The problem is that at the end of each
block, the SPLICE_F_MORE flag is missing, therefore the hashing operation
is reset as if it was the end of the file.
This patch adds SPLICE_F_MORE to the flags when more data is pending.
With the patch applied, we get the correct sums:
root@vgoip:~# md5sum patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
root@vgoip:~# ./md5sum2 patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Jens Axboe <axboe@fb.com>
2015-05-06 17:26:47 +02:00
|
|
|
|
splice, net: Fix SPLICE_F_MORE signalling in splice_direct_to_actor()
splice_direct_to_actor() doesn't manage SPLICE_F_MORE correctly[1] - and,
as a result, it incorrectly signals/fails to signal MSG_MORE when splicing
to a socket. The problem I'm seeing happens when a short splice occurs
because we got a short read due to hitting the EOF on a file: as the length
read (read_len) is less than the remaining size to be spliced (len),
SPLICE_F_MORE (and thus MSG_MORE) is set.
The issue is that, for the moment, we have no way to know *why* the short
read occurred and so can't make a good decision on whether we *should* keep
MSG_MORE set.
MSG_SENDPAGE_NOTLAST was added to work around this, but that is also set
incorrectly under some circumstances - for example if a short read fills a
single pipe_buffer, but the next read would return more (seqfile can do
this).
This was observed with the multi_chunk_sendfile tests in the tls kselftest
program. Some of those tests would hang and time out when the last chunk
of file was less than the sendfile request size:
build/kselftest/net/tls -r tls.12_aes_gcm.multi_chunk_sendfile
This has been observed before[2] and worked around in AF_TLS[3].
Fix this by making splice_direct_to_actor() always signal SPLICE_F_MORE if
we haven't yet hit the requested operation size. SPLICE_F_MORE remains
signalled if the user passed it in to splice() but otherwise gets cleared
when we've read sufficient data to fulfill the request.
If, however, we get a premature EOF from ->splice_read(), have sent at
least one byte and SPLICE_F_MORE was not set by the caller, ->splice_eof()
will be invoked.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Matthew Wilcox <willy@infradead.org>
cc: Jan Kara <jack@suse.cz>
cc: Jeff Layton <jlayton@kernel.org>
cc: David Hildenbrand <david@redhat.com>
cc: Christian Brauner <brauner@kernel.org>
cc: Chuck Lever <chuck.lever@oracle.com>
cc: Boris Pismenny <borisp@nvidia.com>
cc: John Fastabend <john.fastabend@gmail.com>
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/499791.1685485603@warthog.procyon.org.uk/ [1]
Link: https://lore.kernel.org/r/1591392508-14592-1-git-send-email-pooja.trivedi@stackpath.com/ [2]
Link: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=d452d48b9f8b1a7f8152d33ef52cfd7fe1735b0a [3]
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2023-06-07 19:19:16 +01:00
|
|
|
|
|
|
|
|
|
splice: sendfile() at once fails for big files
Using sendfile with below small program to get MD5 sums of some files,
it appear that big files (over 64kbytes with 4k pages system) get a
wrong MD5 sum while small files get the correct sum.
This program uses sendfile() to send a file to an AF_ALG socket
for hashing.
/* md5sum2.c */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <linux/if_alg.h>
int main(int argc, char **argv)
{
int sk = socket(AF_ALG, SOCK_SEQPACKET, 0);
struct stat st;
struct sockaddr_alg sa = {
.salg_family = AF_ALG,
.salg_type = "hash",
.salg_name = "md5",
};
int n;
bind(sk, (struct sockaddr*)&sa, sizeof(sa));
for (n = 1; n < argc; n++) {
int size;
int offset = 0;
char buf[4096];
int fd;
int sko;
int i;
fd = open(argv[n], O_RDONLY);
sko = accept(sk, NULL, 0);
fstat(fd, &st);
size = st.st_size;
sendfile(sko, fd, &offset, size);
size = read(sko, buf, sizeof(buf));
for (i = 0; i < size; i++)
printf("%2.2x", buf[i]);
printf(" %s\n", argv[n]);
close(fd);
close(sko);
}
exit(0);
}
Test below is done using official linux patch files. First result is
with a software based md5sum. Second result is with the program above.
root@vgoip:~# ls -l patch-3.6.*
-rw-r--r-- 1 root root 64011 Aug 24 12:01 patch-3.6.2.gz
-rw-r--r-- 1 root root 94131 Aug 24 12:01 patch-3.6.3.gz
root@vgoip:~# md5sum patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
root@vgoip:~# ./md5sum2 patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
5fd77b24e68bb24dcc72d6e57c64790e patch-3.6.3.gz
After investivation, it appears that sendfile() sends the files by blocks
of 64kbytes (16 times PAGE_SIZE). The problem is that at the end of each
block, the SPLICE_F_MORE flag is missing, therefore the hashing operation
is reset as if it was the end of the file.
This patch adds SPLICE_F_MORE to the flags when more data is pending.
With the patch applied, we get the correct sums:
root@vgoip:~# md5sum patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
root@vgoip:~# ./md5sum2 patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Jens Axboe <axboe@fb.com>
2015-05-06 17:26:47 +02:00
|
|
|
|
splice, net: Fix SPLICE_F_MORE signalling in splice_direct_to_actor()
splice_direct_to_actor() doesn't manage SPLICE_F_MORE correctly[1] - and,
as a result, it incorrectly signals/fails to signal MSG_MORE when splicing
to a socket. The problem I'm seeing happens when a short splice occurs
because we got a short read due to hitting the EOF on a file: as the length
read (read_len) is less than the remaining size to be spliced (len),
SPLICE_F_MORE (and thus MSG_MORE) is set.
The issue is that, for the moment, we have no way to know *why* the short
read occurred and so can't make a good decision on whether we *should* keep
MSG_MORE set.
MSG_SENDPAGE_NOTLAST was added to work around this, but that is also set
incorrectly under some circumstances - for example if a short read fills a
single pipe_buffer, but the next read would return more (seqfile can do
this).
This was observed with the multi_chunk_sendfile tests in the tls kselftest
program. Some of those tests would hang and time out when the last chunk
of file was less than the sendfile request size:
build/kselftest/net/tls -r tls.12_aes_gcm.multi_chunk_sendfile
This has been observed before[2] and worked around in AF_TLS[3].
Fix this by making splice_direct_to_actor() always signal SPLICE_F_MORE if
we haven't yet hit the requested operation size. SPLICE_F_MORE remains
signalled if the user passed it in to splice() but otherwise gets cleared
when we've read sufficient data to fulfill the request.
If, however, we get a premature EOF from ->splice_read(), have sent at
least one byte and SPLICE_F_MORE was not set by the caller, ->splice_eof()
will be invoked.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Matthew Wilcox <willy@infradead.org>
cc: Jan Kara <jack@suse.cz>
cc: Jeff Layton <jlayton@kernel.org>
cc: David Hildenbrand <david@redhat.com>
cc: Christian Brauner <brauner@kernel.org>
cc: Chuck Lever <chuck.lever@oracle.com>
cc: Boris Pismenny <borisp@nvidia.com>
cc: John Fastabend <john.fastabend@gmail.com>
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/499791.1685485603@warthog.procyon.org.uk/ [1]
Link: https://lore.kernel.org/r/1591392508-14592-1-git-send-email-pooja.trivedi@stackpath.com/ [2]
Link: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=d452d48b9f8b1a7f8152d33ef52cfd7fe1735b0a [3]
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2023-06-07 19:19:16 +01:00
|
|
|
|
splice: sendfile() at once fails for big files
Using sendfile with below small program to get MD5 sums of some files,
it appear that big files (over 64kbytes with 4k pages system) get a
wrong MD5 sum while small files get the correct sum.
This program uses sendfile() to send a file to an AF_ALG socket
for hashing.
/* md5sum2.c */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <linux/if_alg.h>
int main(int argc, char **argv)
{
int sk = socket(AF_ALG, SOCK_SEQPACKET, 0);
struct stat st;
struct sockaddr_alg sa = {
.salg_family = AF_ALG,
.salg_type = "hash",
.salg_name = "md5",
};
int n;
bind(sk, (struct sockaddr*)&sa, sizeof(sa));
for (n = 1; n < argc; n++) {
int size;
int offset = 0;
char buf[4096];
int fd;
int sko;
int i;
fd = open(argv[n], O_RDONLY);
sko = accept(sk, NULL, 0);
fstat(fd, &st);
size = st.st_size;
sendfile(sko, fd, &offset, size);
size = read(sko, buf, sizeof(buf));
for (i = 0; i < size; i++)
printf("%2.2x", buf[i]);
printf(" %s\n", argv[n]);
close(fd);
close(sko);
}
exit(0);
}
Test below is done using official linux patch files. First result is
with a software based md5sum. Second result is with the program above.
root@vgoip:~# ls -l patch-3.6.*
-rw-r--r-- 1 root root 64011 Aug 24 12:01 patch-3.6.2.gz
-rw-r--r-- 1 root root 94131 Aug 24 12:01 patch-3.6.3.gz
root@vgoip:~# md5sum patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
root@vgoip:~# ./md5sum2 patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
5fd77b24e68bb24dcc72d6e57c64790e patch-3.6.3.gz
After investivation, it appears that sendfile() sends the files by blocks
of 64kbytes (16 times PAGE_SIZE). The problem is that at the end of each
block, the SPLICE_F_MORE flag is missing, therefore the hashing operation
is reset as if it was the end of the file.
This patch adds SPLICE_F_MORE to the flags when more data is pending.
With the patch applied, we get the correct sums:
root@vgoip:~# md5sum patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
root@vgoip:~# ./md5sum2 patch-3.6.*
b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Jens Axboe <axboe@fb.com>
2015-05-06 17:26:47 +02:00
|
|
|
|
splice, net: Fix SPLICE_F_MORE signalling in splice_direct_to_actor()
splice_direct_to_actor() doesn't manage SPLICE_F_MORE correctly[1] - and,
as a result, it incorrectly signals/fails to signal MSG_MORE when splicing
to a socket. The problem I'm seeing happens when a short splice occurs
because we got a short read due to hitting the EOF on a file: as the length
read (read_len) is less than the remaining size to be spliced (len),
SPLICE_F_MORE (and thus MSG_MORE) is set.
The issue is that, for the moment, we have no way to know *why* the short
read occurred and so can't make a good decision on whether we *should* keep
MSG_MORE set.
MSG_SENDPAGE_NOTLAST was added to work around this, but that is also set
incorrectly under some circumstances - for example if a short read fills a
single pipe_buffer, but the next read would return more (seqfile can do
this).
This was observed with the multi_chunk_sendfile tests in the tls kselftest
program. Some of those tests would hang and time out when the last chunk
of file was less than the sendfile request size:
build/kselftest/net/tls -r tls.12_aes_gcm.multi_chunk_sendfile
This has been observed before[2] and worked around in AF_TLS[3].
Fix this by making splice_direct_to_actor() always signal SPLICE_F_MORE if
we haven't yet hit the requested operation size. SPLICE_F_MORE remains
signalled if the user passed it in to splice() but otherwise gets cleared
when we've read sufficient data to fulfill the request.
If, however, we get a premature EOF from ->splice_read(), have sent at
least one byte and SPLICE_F_MORE was not set by the caller, ->splice_eof()
will be invoked.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Matthew Wilcox <willy@infradead.org>
cc: Jan Kara <jack@suse.cz>
cc: Jeff Layton <jlayton@kernel.org>
cc: David Hildenbrand <david@redhat.com>
cc: Christian Brauner <brauner@kernel.org>
cc: Chuck Lever <chuck.lever@oracle.com>
cc: Boris Pismenny <borisp@nvidia.com>
cc: John Fastabend <john.fastabend@gmail.com>
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/499791.1685485603@warthog.procyon.org.uk/ [1]
Link: https://lore.kernel.org/r/1591392508-14592-1-git-send-email-pooja.trivedi@stackpath.com/ [2]
Link: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=d452d48b9f8b1a7f8152d33ef52cfd7fe1735b0a [3]
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2023-06-07 19:19:16 +01:00
|
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2006-04-11 13:52:07 +02:00
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2007-06-12 21:17:17 +02:00
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2008-05-09 13:28:36 +02:00
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2006-04-11 13:52:07 +02:00
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2008-05-09 13:28:36 +02:00
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2006-04-11 13:52:07 +02:00
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2007-07-16 14:41:49 +02:00
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2006-04-11 13:52:07 +02:00
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2008-05-09 13:28:36 +02:00
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2007-07-13 14:11:43 +02:00
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2008-05-09 13:28:36 +02:00
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2006-04-11 13:52:07 +02:00
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2008-01-29 21:05:57 +01:00
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2019-11-15 13:30:32 +00:00
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2008-01-30 12:24:48 +01:00
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2006-04-11 13:52:07 +02:00
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2023-06-07 19:19:10 +01:00
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2006-04-11 13:52:07 +02:00
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2019-11-15 13:30:32 +00:00
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2006-04-11 13:52:07 +02:00
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2016-09-27 10:45:12 +02:00
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2006-04-11 13:52:07 +02:00
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2008-01-29 21:05:57 +01:00
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2007-06-12 21:17:17 +02:00
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2008-01-29 21:05:57 +01:00
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2007-06-12 21:17:17 +02:00
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2007-06-14 13:08:55 +02:00
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2023-11-30 16:16:23 +02:00
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2007-06-12 21:17:17 +02:00
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2023-11-30 16:16:23 +02:00
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2007-06-12 21:17:17 +02:00
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2023-06-07 19:19:10 +01:00
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2023-12-12 11:44:36 +02:00
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2023-11-30 16:16:22 +02:00
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2023-12-12 11:44:36 +02:00
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2023-11-30 16:16:22 +02:00
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2007-06-21 13:10:21 +02:00
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2013-06-22 19:44:08 -07:00
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2007-06-21 13:10:21 +02:00
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2023-11-22 14:27:01 +02:00
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2007-06-21 13:10:21 +02:00
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2023-12-12 11:44:36 +02:00
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2007-06-12 21:17:17 +02:00
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2023-11-30 16:16:22 +02:00
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2006-04-11 13:52:07 +02:00
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2014-10-24 00:14:35 +02:00
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2006-04-11 13:52:07 +02:00
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2023-11-30 16:16:22 +02:00
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2023-12-12 11:44:37 +02:00
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2023-11-30 16:16:23 +02:00
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2023-11-30 16:16:22 +02:00
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2023-12-12 11:44:36 +02:00
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2023-11-30 16:16:22 +02:00
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2023-12-12 11:44:37 +02:00
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2023-11-30 16:16:22 +02:00
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2016-09-17 20:44:45 -04:00
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2016-12-21 10:59:34 -08:00
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fs/pipe: add simpler helpers for common cases
The fix to atomically read the pipe head and tail state when not holding
the pipe mutex has caused a number of headaches due to the size change
of the involved types.
It turns out that we don't have _that_ many places that access these
fields directly and were affected, but we have more than we strictly
should have, because our low-level helper functions have been designed
to have intimate knowledge of how the pipes work.
And as a result, that random noise of direct 'pipe->head' and
'pipe->tail' accesses makes it harder to pinpoint any actual potential
problem spots remaining.
For example, we didn't have a "is the pipe full" helper function, but
instead had a "given these pipe buffer indexes and this pipe size, is
the pipe full". That's because some low-level pipe code does actually
want that much more complicated interface.
But most other places literally just want a "is the pipe full" helper,
and not having it meant that those places ended up being unnecessarily
much too aware of this all.
It would have been much better if only the very core pipe code that
cared had been the one aware of this all.
So let's fix it - better late than never. This just introduces the
trivial wrappers for "is this pipe full or empty" and to get how many
pipe buffers are used, so that instead of writing
if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
the places that literally just want to know if a pipe is full can just
say
if (pipe_is_full(pipe))
instead. The existing trivial cases were converted with a 'sed' script.
This cuts down on the places that access pipe->head and pipe->tail
directly outside of the pipe code (and core splice code) quite a lot.
The splice code in particular still revels in doing the direct low-level
accesses, and the fuse fuse_dev_splice_write() code also seems a bit
unnecessarily eager to go very low-level, but it's at least a bit better
than it used to be.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2025-03-06 18:25:35 -10:00
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2016-12-21 10:59:34 -08:00
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2016-09-17 20:44:45 -04:00
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pipe: remove pipe_wait() and fix wakeup race with splice
The pipe splice code still used the old model of waiting for pipe IO by
using a non-specific "pipe_wait()" that waited for any pipe event to
happen, which depended on all pipe IO being entirely serialized by the
pipe lock. So by checking the state you were waiting for, and then
adding yourself to the wait queue before dropping the lock, you were
guaranteed to see all the wakeups.
Strictly speaking, the actual wakeups were not done under the lock, but
the pipe_wait() model still worked, because since the waiter held the
lock when checking whether it should sleep, it would always see the
current state, and the wakeup was always done after updating the state.
However, commit 0ddad21d3e99 ("pipe: use exclusive waits when reading or
writing") split the single wait-queue into two, and in the process also
made the "wait for event" code wait for _two_ wait queues, and that then
showed a race with the wakers that were not serialized by the pipe lock.
It's only splice that used that "pipe_wait()" model, so the problem
wasn't obvious, but Josef Bacik reports:
"I hit a hang with fstest btrfs/187, which does a btrfs send into
/dev/null. This works by creating a pipe, the write side is given to
the kernel to write into, and the read side is handed to a thread that
splices into a file, in this case /dev/null.
The box that was hung had the write side stuck here [pipe_write] and
the read side stuck here [splice_from_pipe_next -> pipe_wait].
[ more details about pipe_wait() scenario ]
The problem is we're doing the prepare_to_wait, which sets our state
each time, however we can be woken up either with reads or writes. In
the case above we race with the WRITER waking us up, and re-set our
state to INTERRUPTIBLE, and thus never break out of schedule"
Josef had a patch that avoided the issue in pipe_wait() by just making
it set the state only once, but the deeper problem is that pipe_wait()
depends on a level of synchonization by the pipe mutex that it really
shouldn't. And the whole "wait for any pipe state change" model really
isn't very good to begin with.
So rather than trying to work around things in pipe_wait(), remove that
legacy model of "wait for arbitrary pipe event" entirely, and actually
create functions that wait for the pipe actually being readable or
writable, and can do so without depending on the pipe lock serializing
everything.
Fixes: 0ddad21d3e99 ("pipe: use exclusive waits when reading or writing")
Link: https://lore.kernel.org/linux-fsdevel/bfa88b5ad6f069b2b679316b9e495a970130416c.1601567868.git.josef@toxicpanda.com/
Reported-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-and-tested-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-01 19:14:36 -07:00
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2016-09-17 20:44:45 -04:00
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splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
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2006-11-04 12:49:32 +01:00
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2023-12-12 11:44:36 +02:00
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2021-01-25 22:23:03 -05:00
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2023-12-12 11:44:36 +02:00
|
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2021-01-25 22:23:03 -05:00
|
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|
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2023-11-22 14:27:03 +02:00
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2021-01-25 22:23:03 -05:00
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2006-04-02 23:05:09 +02:00
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|
2023-12-12 11:44:36 +02:00
|
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|
|
2006-03-30 15:15:30 +02:00
|
|
|
|
splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
|
|
|
|
|
|
|
|
|
2013-06-20 18:58:36 +04:00
|
|
|
|
2023-12-12 11:44:36 +02:00
|
|
|
|
2006-03-30 15:15:30 +02:00
|
|
|
|
2020-05-04 22:39:35 +03:00
|
|
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|
|
pipe: Add general notification queue support
Make it possible to have a general notification queue built on top of a
standard pipe. Notifications are 'spliced' into the pipe and then read
out. splice(), vmsplice() and sendfile() are forbidden on pipes used for
notifications as post_one_notification() cannot take pipe->mutex. This
means that notifications could be posted in between individual pipe
buffers, making iov_iter_revert() difficult to effect.
The way the notification queue is used is:
(1) An application opens a pipe with a special flag and indicates the
number of messages it wishes to be able to queue at once (this can
only be set once):
pipe2(fds, O_NOTIFICATION_PIPE);
ioctl(fds[0], IOC_WATCH_QUEUE_SET_SIZE, queue_depth);
(2) The application then uses poll() and read() as normal to extract data
from the pipe. read() will return multiple notifications if the
buffer is big enough, but it will not split a notification across
buffers - rather it will return a short read or EMSGSIZE.
Notification messages include a length in the header so that the
caller can split them up.
Each message has a header that describes it:
struct watch_notification {
__u32 type:24;
__u32 subtype:8;
__u32 info;
};
The type indicates the source (eg. mount tree changes, superblock events,
keyring changes, block layer events) and the subtype indicates the event
type (eg. mount, unmount; EIO, EDQUOT; link, unlink). The info field
indicates a number of things, including the entry length, an ID assigned to
a watchpoint contributing to this buffer and type-specific flags.
Supplementary data, such as the key ID that generated an event, can be
attached in additional slots. The maximum message size is 127 bytes.
Messages may not be padded or aligned, so there is no guarantee, for
example, that the notification type will be on a 4-byte bounary.
Signed-off-by: David Howells <dhowells@redhat.com>
2020-01-14 17:07:11 +00:00
|
|
|
|
|
|
|
|
|
splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
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|
2019-02-07 17:45:19 +02:00
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2023-07-03 16:42:13 +02:00
|
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2006-04-10 15:18:58 +02:00
|
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|
2006-04-11 13:52:07 +02:00
|
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|
|
2010-06-29 13:10:36 +02:00
|
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|
|
2006-04-11 13:52:07 +02:00
|
|
|
|
2020-10-22 14:15:51 -06:00
|
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|
|
2013-06-20 18:58:36 +04:00
|
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2006-04-10 15:18:58 +02:00
|
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2013-06-19 15:41:54 +04:00
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2019-02-07 17:45:19 +02:00
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|
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2013-05-23 20:07:11 -04:00
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|
2013-06-20 18:58:36 +04:00
|
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|
2013-05-23 20:07:11 -04:00
|
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|
2006-04-19 15:57:05 +02:00
|
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|
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2013-06-20 18:58:36 +04:00
|
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|
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2020-10-22 14:15:51 -06:00
|
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|
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|
2023-07-03 16:42:13 +02:00
|
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2006-04-10 15:18:58 +02:00
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|
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2006-04-11 13:52:07 +02:00
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2010-06-29 13:10:36 +02:00
|
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2006-04-11 13:52:07 +02:00
|
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2020-10-22 14:15:51 -06:00
|
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2013-06-20 18:58:36 +04:00
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2006-04-10 15:18:58 +02:00
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2023-11-22 14:27:03 +02:00
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2019-02-07 17:45:19 +02:00
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|
|
2021-01-25 22:23:03 -05:00
|
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|
2023-03-22 14:25:19 +08:00
|
|
|
|
2013-06-20 18:58:36 +04:00
|
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|
2020-10-22 14:15:51 -06:00
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2023-07-03 16:42:13 +02:00
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2006-04-10 15:18:58 +02:00
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2006-03-30 15:15:30 +02:00
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2023-07-03 16:42:13 +02:00
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2006-03-30 15:15:30 +02:00
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2023-12-12 11:44:36 +02:00
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2020-10-22 14:15:51 -06:00
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2023-12-12 11:44:36 +02:00
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2020-10-22 14:15:51 -06:00
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2023-04-24 16:32:55 -06:00
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2020-10-22 14:15:51 -06:00
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2023-12-12 11:44:36 +02:00
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2006-04-26 10:59:21 +02:00
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2016-09-17 22:38:20 -04:00
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2023-12-12 11:44:36 +02:00
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2016-09-17 22:38:20 -04:00
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2022-06-09 11:07:52 -04:00
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2016-09-17 22:38:20 -04:00
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2022-06-09 11:07:52 -04:00
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2016-09-17 20:25:06 -04:00
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2022-06-09 11:07:52 -04:00
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2006-04-26 10:59:21 +02:00
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2022-06-09 11:07:52 -04:00
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2016-09-17 22:38:20 -04:00
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2006-04-26 10:59:21 +02:00
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2022-06-09 11:07:52 -04:00
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2025-11-19 22:41:26 +00:00
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2022-06-09 11:07:52 -04:00
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2016-09-17 22:38:20 -04:00
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2022-06-09 11:07:52 -04:00
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2006-04-26 10:59:21 +02:00
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2022-06-09 11:07:52 -04:00
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2016-09-17 22:38:20 -04:00
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2006-04-26 10:59:21 +02:00
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2007-06-14 13:08:55 +02:00
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2014-02-03 18:19:51 -05:00
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2007-06-14 13:08:55 +02:00
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2025-11-20 21:13:16 +00:00
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2007-06-14 13:08:55 +02:00
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2023-12-12 11:44:36 +02:00
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2007-06-14 13:08:55 +02:00
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|
pipe: Add general notification queue support
Make it possible to have a general notification queue built on top of a
standard pipe. Notifications are 'spliced' into the pipe and then read
out. splice(), vmsplice() and sendfile() are forbidden on pipes used for
notifications as post_one_notification() cannot take pipe->mutex. This
means that notifications could be posted in between individual pipe
buffers, making iov_iter_revert() difficult to effect.
The way the notification queue is used is:
(1) An application opens a pipe with a special flag and indicates the
number of messages it wishes to be able to queue at once (this can
only be set once):
pipe2(fds, O_NOTIFICATION_PIPE);
ioctl(fds[0], IOC_WATCH_QUEUE_SET_SIZE, queue_depth);
(2) The application then uses poll() and read() as normal to extract data
from the pipe. read() will return multiple notifications if the
buffer is big enough, but it will not split a notification across
buffers - rather it will return a short read or EMSGSIZE.
Notification messages include a length in the header so that the
caller can split them up.
Each message has a header that describes it:
struct watch_notification {
__u32 type:24;
__u32 subtype:8;
__u32 info;
};
The type indicates the source (eg. mount tree changes, superblock events,
keyring changes, block layer events) and the subtype indicates the event
type (eg. mount, unmount; EIO, EDQUOT; link, unlink). The info field
indicates a number of things, including the entry length, an ID assigned to
a watchpoint contributing to this buffer and type-specific flags.
Supplementary data, such as the key ID that generated an event, can be
attached in additional slots. The maximum message size is 127 bytes.
Messages may not be padded or aligned, so there is no guarantee, for
example, that the notification type will be on a 4-byte bounary.
Signed-off-by: David Howells <dhowells@redhat.com>
2020-01-14 17:07:11 +00:00
|
|
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|
2018-05-26 21:39:52 -04:00
|
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2023-12-12 11:44:36 +02:00
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2007-06-14 13:08:55 +02:00
|
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2023-04-24 16:32:55 -06:00
|
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2015-03-21 19:17:55 -04:00
|
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2007-06-14 13:08:55 +02:00
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2023-07-03 16:42:17 +02:00
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2007-06-14 13:08:55 +02:00
|
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2006-04-26 10:59:21 +02:00
|
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2023-12-12 11:44:36 +02:00
|
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2006-04-26 10:59:21 +02:00
|
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2006-11-04 12:49:32 +01:00
|
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2023-12-12 11:44:36 +02:00
|
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2016-09-17 22:38:20 -04:00
|
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|
|
2006-04-26 10:59:21 +02:00
|
|
|
|
pipe: Add general notification queue support
Make it possible to have a general notification queue built on top of a
standard pipe. Notifications are 'spliced' into the pipe and then read
out. splice(), vmsplice() and sendfile() are forbidden on pipes used for
notifications as post_one_notification() cannot take pipe->mutex. This
means that notifications could be posted in between individual pipe
buffers, making iov_iter_revert() difficult to effect.
The way the notification queue is used is:
(1) An application opens a pipe with a special flag and indicates the
number of messages it wishes to be able to queue at once (this can
only be set once):
pipe2(fds, O_NOTIFICATION_PIPE);
ioctl(fds[0], IOC_WATCH_QUEUE_SET_SIZE, queue_depth);
(2) The application then uses poll() and read() as normal to extract data
from the pipe. read() will return multiple notifications if the
buffer is big enough, but it will not split a notification across
buffers - rather it will return a short read or EMSGSIZE.
Notification messages include a length in the header so that the
caller can split them up.
Each message has a header that describes it:
struct watch_notification {
__u32 type:24;
__u32 subtype:8;
__u32 info;
};
The type indicates the source (eg. mount tree changes, superblock events,
keyring changes, block layer events) and the subtype indicates the event
type (eg. mount, unmount; EIO, EDQUOT; link, unlink). The info field
indicates a number of things, including the entry length, an ID assigned to
a watchpoint contributing to this buffer and type-specific flags.
Supplementary data, such as the key ID that generated an event, can be
attached in additional slots. The maximum message size is 127 bytes.
Messages may not be padded or aligned, so there is no guarantee, for
example, that the notification type will be on a 4-byte bounary.
Signed-off-by: David Howells <dhowells@redhat.com>
2020-01-14 17:07:11 +00:00
|
|
|
|
2006-11-04 12:49:32 +01:00
|
|
|
|
2006-04-26 10:59:21 +02:00
|
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|
2023-04-24 16:32:55 -06:00
|
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2016-09-17 20:44:45 -04:00
|
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2016-09-17 22:38:20 -04:00
|
|
|
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2018-05-26 21:39:52 -04:00
|
|
|
|
2016-09-17 20:44:45 -04:00
|
|
|
|
2023-07-03 16:42:17 +02:00
|
|
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|
2016-09-17 20:44:45 -04:00
|
|
|
|
2023-07-03 16:42:17 +02:00
|
|
|
|
|
|
|
|
|
2010-05-20 10:43:18 +02:00
|
|
|
|
2006-04-26 10:59:21 +02:00
|
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2007-06-14 13:08:55 +02:00
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2018-05-26 21:39:52 -04:00
|
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2018-03-17 15:00:24 +01:00
|
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|
2018-05-26 21:39:52 -04:00
|
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|
|
|
2019-05-14 16:02:22 -06:00
|
|
|
|
2018-05-26 21:39:52 -04:00
|
|
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|
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|
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2020-09-25 06:51:44 +02:00
|
|
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2024-06-06 15:50:15 -04:00
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2018-05-26 21:39:52 -04:00
|
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2020-09-25 06:51:44 +02:00
|
|
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2024-06-06 15:50:15 -04:00
|
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|
2020-09-25 06:51:44 +02:00
|
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2022-09-15 20:25:47 -04:00
|
|
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2024-05-31 14:12:01 -04:00
|
|
|
|
2020-09-25 06:51:44 +02:00
|
|
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|
2024-05-31 14:12:01 -04:00
|
|
|
|
2020-09-25 06:51:44 +02:00
|
|
|
|
|
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|
2018-05-26 21:39:52 -04:00
|
|
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|
2018-03-17 15:00:24 +01:00
|
|
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|
|
2009-01-14 14:14:33 +01:00
|
|
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2006-03-30 15:15:30 +02:00
|
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2016-12-10 13:17:32 -05:00
|
|
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2024-07-19 21:19:02 -04:00
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2023-12-12 11:44:36 +02:00
|
|
|
|
2006-03-30 15:15:30 +02:00
|
|
|
|
2006-04-11 15:51:17 +02:00
|
|
|
|
2006-07-10 11:00:01 +02:00
|
|
|
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|
|
splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
|
|
|
|
2006-07-10 11:00:01 +02:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2019-11-15 13:30:32 +00:00
|
|
|
|
2006-07-10 11:00:01 +02:00
|
|
|
|
|
|
|
|
|
fs/pipe: add simpler helpers for common cases
The fix to atomically read the pipe head and tail state when not holding
the pipe mutex has caused a number of headaches due to the size change
of the involved types.
It turns out that we don't have _that_ many places that access these
fields directly and were affected, but we have more than we strictly
should have, because our low-level helper functions have been designed
to have intimate knowledge of how the pipes work.
And as a result, that random noise of direct 'pipe->head' and
'pipe->tail' accesses makes it harder to pinpoint any actual potential
problem spots remaining.
For example, we didn't have a "is the pipe full" helper function, but
instead had a "given these pipe buffer indexes and this pipe size, is
the pipe full". That's because some low-level pipe code does actually
want that much more complicated interface.
But most other places literally just want a "is the pipe full" helper,
and not having it meant that those places ended up being unnecessarily
much too aware of this all.
It would have been much better if only the very core pipe code that
cared had been the one aware of this all.
So let's fix it - better late than never. This just introduces the
trivial wrappers for "is this pipe full or empty" and to get how many
pipe buffers are used, so that instead of writing
if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
the places that literally just want to know if a pipe is full can just
say
if (pipe_is_full(pipe))
instead. The existing trivial cases were converted with a 'sed' script.
This cuts down on the places that access pipe->head and pipe->tail
directly outside of the pipe code (and core splice code) quite a lot.
The splice code in particular still revels in doing the direct low-level
accesses, and the fuse fuse_dev_splice_write() code also seems a bit
unnecessarily eager to go very low-level, but it's at least a bit better
than it used to be.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2025-03-06 18:25:35 -10:00
|
|
|
|
2006-07-10 11:00:01 +02:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2009-04-14 19:48:41 +02:00
|
|
|
|
2006-07-10 11:00:01 +02:00
|
|
|
|
fs/pipe: add simpler helpers for common cases
The fix to atomically read the pipe head and tail state when not holding
the pipe mutex has caused a number of headaches due to the size change
of the involved types.
It turns out that we don't have _that_ many places that access these
fields directly and were affected, but we have more than we strictly
should have, because our low-level helper functions have been designed
to have intimate knowledge of how the pipes work.
And as a result, that random noise of direct 'pipe->head' and
'pipe->tail' accesses makes it harder to pinpoint any actual potential
problem spots remaining.
For example, we didn't have a "is the pipe full" helper function, but
instead had a "given these pipe buffer indexes and this pipe size, is
the pipe full". That's because some low-level pipe code does actually
want that much more complicated interface.
But most other places literally just want a "is the pipe full" helper,
and not having it meant that those places ended up being unnecessarily
much too aware of this all.
It would have been much better if only the very core pipe code that
cared had been the one aware of this all.
So let's fix it - better late than never. This just introduces the
trivial wrappers for "is this pipe full or empty" and to get how many
pipe buffers are used, so that instead of writing
if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
the places that literally just want to know if a pipe is full can just
say
if (pipe_is_full(pipe))
instead. The existing trivial cases were converted with a 'sed' script.
This cuts down on the places that access pipe->head and pipe->tail
directly outside of the pipe code (and core splice code) quite a lot.
The splice code in particular still revels in doing the direct low-level
accesses, and the fuse fuse_dev_splice_write() code also seems a bit
unnecessarily eager to go very low-level, but it's at least a bit better
than it used to be.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2025-03-06 18:25:35 -10:00
|
|
|
|
2006-07-10 11:00:01 +02:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
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|
|
|
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|
|
|
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|
|
|
pipe: remove 'waiting_writers' merging logic
This code is ancient, and goes back to when we only had a single page
for the pipe buffers. The exact history is hidden in the mists of time
(ie "before git", and in fact predates the BK repository too).
At that long-ago point in time, it actually helped to try to merge big
back-and-forth pipe reads and writes, and not limit pipe reads to the
single pipe buffer in length just because that was all we had at a time.
However, since then we've expanded the pipe buffers to multiple pages,
and this logic really doesn't seem to make sense. And a lot of it is
somewhat questionable (ie "hmm, the user asked for a non-blocking read,
but we see that there's a writer pending, so let's wait anyway to get
the extra data that the writer will have").
But more importantly, it makes the "go to sleep" logic much less
obvious, and considering the wakeup issues we've had, I want to make for
less of those kinds of things.
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-12-07 13:21:01 -08:00
|
|
|
|
|
|
|
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|
|
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|
|
|
2006-07-10 11:00:01 +02:00
|
|
|
|
pipe: remove pipe_wait() and fix wakeup race with splice
The pipe splice code still used the old model of waiting for pipe IO by
using a non-specific "pipe_wait()" that waited for any pipe event to
happen, which depended on all pipe IO being entirely serialized by the
pipe lock. So by checking the state you were waiting for, and then
adding yourself to the wait queue before dropping the lock, you were
guaranteed to see all the wakeups.
Strictly speaking, the actual wakeups were not done under the lock, but
the pipe_wait() model still worked, because since the waiter held the
lock when checking whether it should sleep, it would always see the
current state, and the wakeup was always done after updating the state.
However, commit 0ddad21d3e99 ("pipe: use exclusive waits when reading or
writing") split the single wait-queue into two, and in the process also
made the "wait for event" code wait for _two_ wait queues, and that then
showed a race with the wakers that were not serialized by the pipe lock.
It's only splice that used that "pipe_wait()" model, so the problem
wasn't obvious, but Josef Bacik reports:
"I hit a hang with fstest btrfs/187, which does a btrfs send into
/dev/null. This works by creating a pipe, the write side is given to
the kernel to write into, and the read side is handed to a thread that
splices into a file, in this case /dev/null.
The box that was hung had the write side stuck here [pipe_write] and
the read side stuck here [splice_from_pipe_next -> pipe_wait].
[ more details about pipe_wait() scenario ]
The problem is we're doing the prepare_to_wait, which sets our state
each time, however we can be woken up either with reads or writes. In
the case above we race with the WRITER waking us up, and re-set our
state to INTERRUPTIBLE, and thus never break out of schedule"
Josef had a patch that avoided the issue in pipe_wait() by just making
it set the state only once, but the deeper problem is that pipe_wait()
depends on a level of synchonization by the pipe mutex that it really
shouldn't. And the whole "wait for any pipe state change" model really
isn't very good to begin with.
So rather than trying to work around things in pipe_wait(), remove that
legacy model of "wait for arbitrary pipe event" entirely, and actually
create functions that wait for the pipe actually being readable or
writable, and can do so without depending on the pipe lock serializing
everything.
Fixes: 0ddad21d3e99 ("pipe: use exclusive waits when reading or writing")
Link: https://lore.kernel.org/linux-fsdevel/bfa88b5ad6f069b2b679316b9e495a970130416c.1601567868.git.josef@toxicpanda.com/
Reported-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-and-tested-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-01 19:14:36 -07:00
|
|
|
|
2006-07-10 11:00:01 +02:00
|
|
|
|
|
|
|
|
|
2009-04-14 19:48:41 +02:00
|
|
|
|
2006-07-10 11:00:01 +02:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
|
|
|
|
2006-07-10 11:00:01 +02:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2019-11-15 13:30:32 +00:00
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2006-07-10 11:00:01 +02:00
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fs/pipe: add simpler helpers for common cases
The fix to atomically read the pipe head and tail state when not holding
the pipe mutex has caused a number of headaches due to the size change
of the involved types.
It turns out that we don't have _that_ many places that access these
fields directly and were affected, but we have more than we strictly
should have, because our low-level helper functions have been designed
to have intimate knowledge of how the pipes work.
And as a result, that random noise of direct 'pipe->head' and
'pipe->tail' accesses makes it harder to pinpoint any actual potential
problem spots remaining.
For example, we didn't have a "is the pipe full" helper function, but
instead had a "given these pipe buffer indexes and this pipe size, is
the pipe full". That's because some low-level pipe code does actually
want that much more complicated interface.
But most other places literally just want a "is the pipe full" helper,
and not having it meant that those places ended up being unnecessarily
much too aware of this all.
It would have been much better if only the very core pipe code that
cared had been the one aware of this all.
So let's fix it - better late than never. This just introduces the
trivial wrappers for "is this pipe full or empty" and to get how many
pipe buffers are used, so that instead of writing
if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
the places that literally just want to know if a pipe is full can just
say
if (pipe_is_full(pipe))
instead. The existing trivial cases were converted with a 'sed' script.
This cuts down on the places that access pipe->head and pipe->tail
directly outside of the pipe code (and core splice code) quite a lot.
The splice code in particular still revels in doing the direct low-level
accesses, and the fuse fuse_dev_splice_write() code also seems a bit
unnecessarily eager to go very low-level, but it's at least a bit better
than it used to be.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2025-03-06 18:25:35 -10:00
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2006-07-10 11:00:01 +02:00
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2009-04-14 19:48:41 +02:00
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2006-07-10 11:00:01 +02:00
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fs/pipe: add simpler helpers for common cases
The fix to atomically read the pipe head and tail state when not holding
the pipe mutex has caused a number of headaches due to the size change
of the involved types.
It turns out that we don't have _that_ many places that access these
fields directly and were affected, but we have more than we strictly
should have, because our low-level helper functions have been designed
to have intimate knowledge of how the pipes work.
And as a result, that random noise of direct 'pipe->head' and
'pipe->tail' accesses makes it harder to pinpoint any actual potential
problem spots remaining.
For example, we didn't have a "is the pipe full" helper function, but
instead had a "given these pipe buffer indexes and this pipe size, is
the pipe full". That's because some low-level pipe code does actually
want that much more complicated interface.
But most other places literally just want a "is the pipe full" helper,
and not having it meant that those places ended up being unnecessarily
much too aware of this all.
It would have been much better if only the very core pipe code that
cared had been the one aware of this all.
So let's fix it - better late than never. This just introduces the
trivial wrappers for "is this pipe full or empty" and to get how many
pipe buffers are used, so that instead of writing
if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
the places that literally just want to know if a pipe is full can just
say
if (pipe_is_full(pipe))
instead. The existing trivial cases were converted with a 'sed' script.
This cuts down on the places that access pipe->head and pipe->tail
directly outside of the pipe code (and core splice code) quite a lot.
The splice code in particular still revels in doing the direct low-level
accesses, and the fuse fuse_dev_splice_write() code also seems a bit
unnecessarily eager to go very low-level, but it's at least a bit better
than it used to be.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2025-03-06 18:25:35 -10:00
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2006-07-10 11:00:01 +02:00
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pipe: remove pipe_wait() and fix wakeup race with splice
The pipe splice code still used the old model of waiting for pipe IO by
using a non-specific "pipe_wait()" that waited for any pipe event to
happen, which depended on all pipe IO being entirely serialized by the
pipe lock. So by checking the state you were waiting for, and then
adding yourself to the wait queue before dropping the lock, you were
guaranteed to see all the wakeups.
Strictly speaking, the actual wakeups were not done under the lock, but
the pipe_wait() model still worked, because since the waiter held the
lock when checking whether it should sleep, it would always see the
current state, and the wakeup was always done after updating the state.
However, commit 0ddad21d3e99 ("pipe: use exclusive waits when reading or
writing") split the single wait-queue into two, and in the process also
made the "wait for event" code wait for _two_ wait queues, and that then
showed a race with the wakers that were not serialized by the pipe lock.
It's only splice that used that "pipe_wait()" model, so the problem
wasn't obvious, but Josef Bacik reports:
"I hit a hang with fstest btrfs/187, which does a btrfs send into
/dev/null. This works by creating a pipe, the write side is given to
the kernel to write into, and the read side is handed to a thread that
splices into a file, in this case /dev/null.
The box that was hung had the write side stuck here [pipe_write] and
the read side stuck here [splice_from_pipe_next -> pipe_wait].
[ more details about pipe_wait() scenario ]
The problem is we're doing the prepare_to_wait, which sets our state
each time, however we can be woken up either with reads or writes. In
the case above we race with the WRITER waking us up, and re-set our
state to INTERRUPTIBLE, and thus never break out of schedule"
Josef had a patch that avoided the issue in pipe_wait() by just making
it set the state only once, but the deeper problem is that pipe_wait()
depends on a level of synchonization by the pipe mutex that it really
shouldn't. And the whole "wait for any pipe state change" model really
isn't very good to begin with.
So rather than trying to work around things in pipe_wait(), remove that
legacy model of "wait for arbitrary pipe event" entirely, and actually
create functions that wait for the pipe actually being readable or
writable, and can do so without depending on the pipe lock serializing
everything.
Fixes: 0ddad21d3e99 ("pipe: use exclusive waits when reading or writing")
Link: https://lore.kernel.org/linux-fsdevel/bfa88b5ad6f069b2b679316b9e495a970130416c.1601567868.git.josef@toxicpanda.com/
Reported-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-and-tested-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-01 19:14:36 -07:00
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2006-07-10 11:00:01 +02:00
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2009-04-14 19:48:41 +02:00
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2006-07-10 11:00:01 +02:00
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splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
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2019-11-15 13:30:32 +00:00
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splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
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2019-11-15 13:30:32 +00:00
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splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
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2019-11-15 13:30:32 +00:00
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splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
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2019-11-15 13:30:32 +00:00
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splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
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2019-11-15 13:30:32 +00:00
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2019-10-16 16:47:32 +01:00
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splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
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2025-03-07 05:29:19 +00:00
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splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
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2019-11-15 13:30:32 +00:00
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splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
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2019-11-15 13:30:32 +00:00
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splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
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2019-04-05 14:02:10 -07:00
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splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
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2020-05-20 17:58:12 +02:00
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splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
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2020-05-20 17:58:12 +02:00
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splice: don't merge into linked buffers
Before this patch, it was possible for two pipes to affect each other after
data had been transferred between them with tee():
============
$ cat tee_test.c
int main(void) {
int pipe_a[2];
if (pipe(pipe_a)) err(1, "pipe");
int pipe_b[2];
if (pipe(pipe_b)) err(1, "pipe");
if (write(pipe_a[1], "abcd", 4) != 4) err(1, "write");
if (tee(pipe_a[0], pipe_b[1], 2, 0) != 2) err(1, "tee");
if (write(pipe_b[1], "xx", 2) != 2) err(1, "write");
char buf[5];
if (read(pipe_a[0], buf, 4) != 4) err(1, "read");
buf[4] = 0;
printf("got back: '%s'\n", buf);
}
$ gcc -o tee_test tee_test.c
$ ./tee_test
got back: 'abxx'
$
============
As suggested by Al Viro, fix it by creating a separate type for
non-mergeable pipe buffers, then changing the types of buffers in
splice_pipe_to_pipe() and link_pipe().
Cc: <stable@vger.kernel.org>
Fixes: 7c77f0b3f920 ("splice: implement pipe to pipe splicing")
Fixes: 70524490ee2e ("[PATCH] splice: add support for sys_tee()")
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-01-23 15:19:17 +01:00
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splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
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2019-11-15 13:30:32 +00:00
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splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
|
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2019-11-15 13:30:32 +00:00
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|
splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
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2011-05-23 19:58:53 +02:00
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splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
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2006-04-11 15:51:17 +02:00
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2023-12-12 11:44:36 +02:00
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2006-04-11 15:51:17 +02:00
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2019-11-15 13:30:32 +00:00
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2023-12-12 11:44:36 +02:00
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2006-04-11 15:51:17 +02:00
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2009-04-14 19:48:41 +02:00
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2006-04-11 15:51:17 +02:00
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2009-04-14 19:48:41 +02:00
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2006-04-11 15:51:17 +02:00
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2019-11-15 13:30:32 +00:00
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2006-07-10 11:00:01 +02:00
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2006-04-11 15:51:17 +02:00
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2019-11-15 13:30:32 +00:00
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2006-04-11 15:51:17 +02:00
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2019-11-15 13:30:32 +00:00
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2006-07-10 11:00:01 +02:00
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2006-04-11 15:51:17 +02:00
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2019-11-15 13:30:32 +00:00
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2019-10-16 16:47:32 +01:00
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2006-04-11 15:51:17 +02:00
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2006-07-10 11:00:01 +02:00
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2025-03-07 05:29:19 +00:00
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2006-07-10 11:00:01 +02:00
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2006-04-19 15:56:40 +02:00
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2006-07-10 11:00:01 +02:00
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2006-04-19 15:56:40 +02:00
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2019-04-05 14:02:10 -07:00
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2006-04-11 15:51:17 +02:00
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2006-07-10 11:00:01 +02:00
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2006-04-11 15:51:17 +02:00
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2006-07-10 11:00:01 +02:00
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2020-05-20 17:58:12 +02:00
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2006-07-10 11:00:01 +02:00
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2020-05-20 17:58:12 +02:00
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|
splice: don't merge into linked buffers
Before this patch, it was possible for two pipes to affect each other after
data had been transferred between them with tee():
============
$ cat tee_test.c
int main(void) {
int pipe_a[2];
if (pipe(pipe_a)) err(1, "pipe");
int pipe_b[2];
if (pipe(pipe_b)) err(1, "pipe");
if (write(pipe_a[1], "abcd", 4) != 4) err(1, "write");
if (tee(pipe_a[0], pipe_b[1], 2, 0) != 2) err(1, "tee");
if (write(pipe_b[1], "xx", 2) != 2) err(1, "write");
char buf[5];
if (read(pipe_a[0], buf, 4) != 4) err(1, "read");
buf[4] = 0;
printf("got back: '%s'\n", buf);
}
$ gcc -o tee_test tee_test.c
$ ./tee_test
got back: 'abxx'
$
============
As suggested by Al Viro, fix it by creating a separate type for
non-mergeable pipe buffers, then changing the types of buffers in
splice_pipe_to_pipe() and link_pipe().
Cc: <stable@vger.kernel.org>
Fixes: 7c77f0b3f920 ("splice: implement pipe to pipe splicing")
Fixes: 70524490ee2e ("[PATCH] splice: add support for sys_tee()")
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-01-23 15:19:17 +01:00
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2006-07-10 11:00:01 +02:00
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2019-11-15 13:30:32 +00:00
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2006-07-10 11:00:01 +02:00
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2006-04-11 15:51:17 +02:00
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2009-04-14 19:48:41 +02:00
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2006-04-11 15:51:17 +02:00
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2006-07-10 11:00:01 +02:00
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2011-05-23 19:58:53 +02:00
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2006-04-11 15:51:17 +02:00
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2023-12-12 11:44:36 +02:00
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2006-04-11 15:51:17 +02:00
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pipe: Add general notification queue support
Make it possible to have a general notification queue built on top of a
standard pipe. Notifications are 'spliced' into the pipe and then read
out. splice(), vmsplice() and sendfile() are forbidden on pipes used for
notifications as post_one_notification() cannot take pipe->mutex. This
means that notifications could be posted in between individual pipe
buffers, making iov_iter_revert() difficult to effect.
The way the notification queue is used is:
(1) An application opens a pipe with a special flag and indicates the
number of messages it wishes to be able to queue at once (this can
only be set once):
pipe2(fds, O_NOTIFICATION_PIPE);
ioctl(fds[0], IOC_WATCH_QUEUE_SET_SIZE, queue_depth);
(2) The application then uses poll() and read() as normal to extract data
from the pipe. read() will return multiple notifications if the
buffer is big enough, but it will not split a notification across
buffers - rather it will return a short read or EMSGSIZE.
Notification messages include a length in the header so that the
caller can split them up.
Each message has a header that describes it:
struct watch_notification {
__u32 type:24;
__u32 subtype:8;
__u32 info;
};
The type indicates the source (eg. mount tree changes, superblock events,
keyring changes, block layer events) and the subtype indicates the event
type (eg. mount, unmount; EIO, EDQUOT; link, unlink). The info field
indicates a number of things, including the entry length, an ID assigned to
a watchpoint contributing to this buffer and type-specific flags.
Supplementary data, such as the key ID that generated an event, can be
attached in additional slots. The maximum message size is 127 bytes.
Messages may not be padded or aligned, so there is no guarantee, for
example, that the notification type will be on a 4-byte bounary.
Signed-off-by: David Howells <dhowells@redhat.com>
2020-01-14 17:07:11 +00:00
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2023-12-12 11:44:36 +02:00
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2006-04-11 15:51:17 +02:00
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2020-05-04 22:39:35 +03:00
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2006-04-11 15:51:17 +02:00
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2006-07-10 11:00:01 +02:00
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2006-04-11 15:51:17 +02:00
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2006-07-10 11:00:01 +02:00
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2019-02-07 17:45:19 +02:00
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2006-07-10 11:00:01 +02:00
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splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
|
|
|
|
2006-07-10 11:00:01 +02:00
|
|
|
|
splice: implement pipe to pipe splicing
Allow splice(2) to work when both the input and the output is a pipe.
Based on the impementation of the tee(2) syscall, but instead of
duplicating the buffer references move the buffers from the input pipe
to the output pipe.
Moving the whole buffer only succeeds if the full length of the buffer
is spliced. Otherwise duplicate the buffer, just like tee(2), set the
length of the output buffer and advance the offset on the input
buffer.
Since splice is operating on two pipes, special care needs to be taken
with locking to prevent AN ABBA deadlock. Again this is done
similarly to the tee(2) syscall, first preparing the input and output
pipes so there's data to consume and space for that data, and then
doing the move operation while holding both locks.
If other processes are doing I/O on the same pipes parallel to the
splice, then by the time both inodes are locked there might be no
buffers left to move, or no space to move them to. In this case retry
the whole operation, including the preparation phase. This could lead
to starvation, but I'm not sure if that's serious enough to worry
about.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-05-07 15:37:35 +02:00
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2008-02-20 10:34:51 +01:00
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2006-07-10 11:00:01 +02:00
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2006-04-11 15:51:17 +02:00
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2023-07-03 16:42:21 +02:00
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2006-07-10 11:00:01 +02:00
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2006-04-11 15:51:17 +02:00
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2009-01-14 14:14:33 +01:00
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2006-04-11 15:51:17 +02:00
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2016-12-10 13:17:32 -05:00
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2006-04-11 15:51:17 +02:00
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2024-07-19 21:19:02 -04:00
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2006-04-11 15:51:17 +02:00
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2024-07-19 21:19:02 -04:00
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2006-04-11 15:51:17 +02:00
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