kernel/linux
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ synced 2026-10-16 22:39:48 +00:00
Code Issues Releases Packages Activity
No description
1,201,766 commits 116 branches 5,798 tags 5.6 GiB
  • C 96.9%
  • Assembly 0.9%
  • Rust 0.6%
  • Shell 0.6%
  • Python 0.5%
  • Other 0.3%
Find a file
Linus Torvalds 4542057e18 mm: avoid 'might_sleep()' in get_mmap_lock_carefully() 
This might_sleep() goes back a long time: it was originally introduced
way back when by commit 010060741a ("x86: add might_sleep() to
do_page_fault()"), and made it into the generic VM code when the x86
fault path got re-organized and generalized in commit c2508ec5a5 ("mm:
introduce new 'lock_mm_and_find_vma()' page fault helper").

However, it turns out that the placement of that might_sleep() has
always been rather questionable simply because it's not only a debug
statement to warn about sleeping in contexts that shouldn't sleep (which
was the original reason for adding it), but it also implies a voluntary
scheduling point.

That, in turn, is less than desirable for two reasons:

 (a) it ends up being done after we successfully got the mmap_lock, so
     just as we got the lock we will now eagerly schedule away and
     increase lock contention

and

 (b) this is all very possibly part of the "oops, things went horribly
     wrong" path and we just haven't figured that out yet

After all, the whole _reason_ for having that get_mmap_lock_carefully()
rather than just doing the obvious mmap_read_lock() is because this code
wants to deal somewhat gracefully with potential kernel wild pointer
bugs.

So then a voluntary scheduling point here is simply not a good idea.

We could certainly turn the 'might_sleep()' into a '__might_sleep()' and
make it be just the debug check that it was originally intended to be.

But even that seems questionable in the wild kernel pointer case - which
again is part of the whole point of this code.  The problem wouldn't be
about the _sleeping_ part of the page fault, but about a bad kernel
access.  The fact that that bad kernel access might happen in a section
that you shouldn't sleep in is secondary.

So it really ends up being the case that this is simply entirely the
wrong place to do this debug check and related scheduling point at all.

So let's just remove the check entirely.  It's been around for over a
decade, it has served its purpose.

The re-schedule will happen at return to user space anyway for the
normal case, and the warning - if we even need it - might be better off
done as a special case for "page fault from kernel mode" once we've
dealt with any potential kernel oopses where the oops is the relevant
thing, not some artificial "scheduling while atomic" test.

Reported-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://lore.kernel.org/lkml/20230820104303.2083444-1-mjguzik@gmail.com/
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
History 2023-08-21 06:11:33 +02:00
arch - Use LEA ...%rsp instead of ADD %rsp in the Zen1/2 SRSO return sequence 2023-08-19 10:46:02 +02:00
block block-6.5-2023-08-19 2023-08-19 17:31:46 +02:00
certs KEYS: Add missing function documentation 2023-04-24 16:15:52 +03:00
crypto crypto: algif_hash - Fix race between MORE and non-MORE sends 2023-07-08 22:48:42 +10:00
Documentation Usual set of driver fixes. A bit more than usual because I was 2023-08-19 19:22:41 +02:00
drivers TTY/Serial fixes for 6.5-rc7 2023-08-20 08:26:51 +02:00
fs for-6.5-rc6-tag 2023-08-19 17:57:07 +02:00
include TTY/Serial fixes for 6.5-rc7 2023-08-20 08:26:51 +02:00
init Kbuild updates for v6.5 2023-07-01 09:24:31 -07:00
io_uring io_uring/parisc: Adjust pgoff in io_uring mmap() for parisc 2023-08-08 12:37:01 -06:00
ipc Merge branch 'work.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2023-02-24 19:20:07 -08:00
kernel Power management fixes for 6.5-rc6 2023-08-11 12:24:22 -07:00
lib 14 hotfixes. 11 of these are cc:stable and the remainder address post-6.4 2023-08-11 14:19:20 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm: avoid 'might_sleep()' in get_mmap_lock_carefully() 2023-08-21 06:11:33 +02:00
net Including fixes from ipsec and netfilter. 2023-08-18 06:52:23 +02:00
rust rust: macros: vtable: fix HAS_* redefinition (gen_const_name) 2023-08-09 21:15:07 +02:00
samples arm64: ftrace: Add direct call trampoline samples support 2023-07-10 17:51:54 -04:00
scripts Kbuild fixes for v6.5 (2nd) 2023-08-13 08:56:24 -07:00
security sysctl: set variable key_sysctls storage-class-specifier to static 2023-08-07 17:55:54 +00:00
sound ALSA: hda/realtek - Remodified 3k pull low procedure 2023-08-16 14:20:27 +02:00
tools - Use LEA ...%rsp instead of ADD %rsp in the Zen1/2 SRSO return sequence 2023-08-19 10:46:02 +02:00
usr initramfs: Encode dependency on KBUILD_BUILD_TIMESTAMP 2023-06-06 17:54:49 +09:00
virt KVM: Grab a reference to KVM for VM and vCPU stats file descriptors 2023-07-29 11:05:28 -04:00
.clang-format iommu: Add for_each_group_device() 2023-05-23 08:15:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Revert ".gitignore: ignore *.cover and *.mbx" 2023-07-04 15:05:12 -07:00
.mailmap mailmap: add entries for Simon Horman 2023-08-16 09:53:10 +01:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS - Address -Wmissing-prototype warnings 2023-06-26 16:43:54 -07:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS TTY/Serial fixes for 6.5-rc7 2023-08-20 08:26:51 +02:00
Makefile Linux 6.5-rc7 2023-08-20 15:02:52 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.