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Hugh Dickins 0010275ca2 mm/thp: unmap_mapping_page() to fix THP truncate_cleanup_page() 
[ Upstream commit 22061a1ffa ]

There is a race between THP unmapping and truncation, when truncate sees
pmd_none() and skips the entry, after munmap's zap_huge_pmd() cleared
it, but before its page_remove_rmap() gets to decrement
compound_mapcount: generating false "BUG: Bad page cache" reports that
the page is still mapped when deleted.  This commit fixes that, but not
in the way I hoped.

The first attempt used try_to_unmap(page, TTU_SYNC|TTU_IGNORE_MLOCK)
instead of unmap_mapping_range() in truncate_cleanup_page(): it has
often been an annoyance that we usually call unmap_mapping_range() with
no pages locked, but there apply it to a single locked page.
try_to_unmap() looks more suitable for a single locked page.

However, try_to_unmap_one() contains a VM_BUG_ON_PAGE(!pvmw.pte,page):
it is used to insert THP migration entries, but not used to unmap THPs.
Copy zap_huge_pmd() and add THP handling now? Perhaps, but their TLB
needs are different, I'm too ignorant of the DAX cases, and couldn't
decide how far to go for anon+swap.  Set that aside.

The second attempt took a different tack: make no change in truncate.c,
but modify zap_huge_pmd() to insert an invalidated huge pmd instead of
clearing it initially, then pmd_clear() between page_remove_rmap() and
unlocking at the end.  Nice.  But powerpc blows that approach out of the
water, with its serialize_against_pte_lookup(), and interesting pgtable
usage.  It would need serious help to get working on powerpc (with a
minor optimization issue on s390 too).  Set that aside.

Just add an "if (page_mapped(page)) synchronize_rcu();" or other such
delay, after unmapping in truncate_cleanup_page()? Perhaps, but though
that's likely to reduce or eliminate the number of incidents, it would
give less assurance of whether we had identified the problem correctly.

This successful iteration introduces "unmap_mapping_page(page)" instead
of try_to_unmap(), and goes the usual unmap_mapping_range_tree() route,
with an addition to details.  Then zap_pmd_range() watches for this
case, and does spin_unlock(pmd_lock) if so - just like
page_vma_mapped_walk() now does in the PVMW_SYNC case.  Not pretty, but
safe.

Note that unmap_mapping_page() is doing a VM_BUG_ON(!PageLocked) to
assert its interface; but currently that's only used to make sure that
page->mapping is stable, and zap_pmd_range() doesn't care if the page is
locked or not.  Along these lines, in invalidate_inode_pages2_range()
move the initial unmap_mapping_range() out from under page lock, before
then calling unmap_mapping_page() under page lock if still mapped.

Link: https://lkml.kernel.org/r/a2a4a148-cdd8-942c-4ef8-51b77f643dbe@google.com
Fixes: fc127da085 ("truncate: handle file thp")
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jue Wang <juew@google.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Wang Yugui <wangyugui@e16-tech.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Note on stable backport: fixed up call to truncate_cleanup_page()
in truncate_inode_pages_range().

Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2021-06-30 08:47:27 -04:00
arch x86/fpu: Make init_fpstate correct with optimized XSAVE 2021-06-30 08:47:26 -04:00
block blk-mq: Swap two calls in blk_mq_exit_queue() 2021-05-19 10:13:14 +02:00
certs certs: Fix blacklist flag type confusion 2021-03-04 11:37:59 +01:00
crypto async_xor: check src_offs is not NULL before updating it 2021-06-16 12:01:40 +02:00
Documentation mm/slub: clarify verification reporting 2021-06-23 14:42:53 +02:00
drivers i2c: robotfuzz-osif: fix control-request directions 2021-06-30 08:47:25 -04:00
fs ceph: must hold snap_rwsem when filling inode for async create 2021-06-30 08:47:25 -04:00
include mm/thp: unmap_mapping_page() to fix THP truncate_cleanup_page() 2021-06-30 08:47:27 -04:00
init pid: take a reference when initializing cad_pid 2021-06-10 13:39:26 +02:00
ipc ipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry 2021-05-26 12:06:54 +02:00
kernel kthread: prevent deadlock when kthread_mod_delayed_work() races with kthread_cancel_delayed_work_sync() 2021-06-30 08:47:25 -04:00
lib locking/lockdep: Improve noinstr vs errors 2021-06-30 08:47:18 -04:00
LICENSES LICENSES/deprecated: add Zlib license text 2020-09-16 14:33:49 +02:00
mm mm/thp: unmap_mapping_page() to fix THP truncate_cleanup_page() 2021-06-30 08:47:27 -04:00
net mac80211: handle various extensible elements correctly 2021-06-30 08:47:23 -04:00
samples samples: vfio-mdev: fix error handing in mdpy_fb_probe() 2021-06-10 13:39:15 +02:00
scripts recordmcount: Correct st_shndx handling 2021-06-30 08:47:23 -04:00
security KEYS: trusted: Fix memory leak on object td 2021-05-19 10:12:50 +02:00
sound ASoC: qcom: lpass-cpu: Fix pop noise during audio capture begin 2021-06-23 14:42:49 +02:00
tools KVM: selftests: Fix kvm_check_cap() assertion 2021-06-30 08:47:22 -04:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt KVM: do not allow mapping valid but non-reference-counted pages 2021-06-30 08:47:25 -04:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore kbuild: generate Module.symvers only when vmlinux exists 2021-05-19 10:12:59 +02:00
.mailmap mailmap: add two more addresses of Uwe Kleine-König 2020-12-06 10:19:07 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Jason Cooper to CREDITS 2020-11-30 10:20:34 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS f2fs: move ioctl interface definitions to separated file 2021-05-19 10:13:00 +02:00
Makefile Linux 5.10.46 2021-06-23 14:42:55 +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.