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> > Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > --- > include/linux/page-flags.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index a558d67ee86f..628ab237665e 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -206,7 +206,7 @@ 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; > } Acked-by: Will Deacon <will@xxxxxxxxxx> Thanks for writing up the patch! Will
