Re: [PATCH] mm: fix data race in PagePoisoned()

[Kirill A. Shutemov]

On Mon, Sep 13, 2021 at 01:35:43PM +0200, Marco Elver wrote:
> 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/
> Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>

Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

-- 
 Kirill A. Shutemov