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mm: fix data race in PagePoisoned()
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PagePoisoned() accesses page->flags which can be updated concurrently:

  | BUG: KCSAN: data-race in next_uptodate_page / unlock_page
  |
  | write (marked) to 0xffffea00050f37c0 of 8 bytes by task 1872 on cpu 1:
  |  instrument_atomic_write           include/linux/instrumented.h:87 [inline]
  |  clear_bit_unlock_is_negative_byte include/asm-generic/bitops/instrumented-lock.h:74 [inline]
  |  unlock_page+0x102/0x1b0           mm/filemap.c:1465
  |  filemap_map_pages+0x6c6/0x890     mm/filemap.c:3057
  |  ...
  | read to 0xffffea00050f37c0 of 8 bytes by task 1873 on cpu 0:
  |  PagePoisoned                   include/linux/page-flags.h:204 [inline]
  |  PageReadahead                  include/linux/page-flags.h:382 [inline]
  |  next_uptodate_page+0x456/0x830 mm/filemap.c:2975
  |  ...
  | CPU: 0 PID: 1873 Comm: systemd-udevd Not tainted 5.11.0-rc4-00001-gf9ce0be71d1f #1

To avoid the compiler tearing or otherwise optimizing the access, use
READ_ONCE() to access flags.

Link: https://lore.kernel.org/all/20210826144157.GA26950@xsang-OptiPlex-9020/
Link: https://lkml.kernel.org/r/[email protected]
Reported-by: kernel test robot <[email protected]>
Signed-off-by: Marco Elver <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Acked-by: Will Deacon <[email protected]>
Cc: Marco Elver <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Stephen Rothwell <[email protected]>
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melver authored and sfrothwell committed Oct 31, 2021
1 parent b41d090 commit 85ffadd
Showing 1 changed file with 1 addition and 1 deletion.
2 changes: 1 addition & 1 deletion include/linux/page-flags.h
Original file line number Diff line number Diff line change
Expand Up @@ -215,7 +215,7 @@ static __always_inline int PageCompound(struct page *page)
#define PAGE_POISON_PATTERN -1l
static inline int PagePoisoned(const struct page *page)
{
return page->flags == PAGE_POISON_PATTERN;
return READ_ONCE(page->flags) == PAGE_POISON_PATTERN;
}

#ifdef CONFIG_DEBUG_VM
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