[patch 121/262] mm: fix data race in PagePoisoned()

Andrew Morton
2021-11-05T20:41:01Z

From: Marco Elver <elver@google.com>
Subject: mm: fix data race in PagePoisoned()

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/20210913113542.2658064-1-elver@google.com
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Marco Elver <elver@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Will Deacon <will@kernel.org>
Cc: Marco Elver <elver@google.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

include/linux/page-flags.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/linux/page-flags.h~mm-fix-data-race-in-pagepoisoned
+++ a/include/linux/page-flags.h
@@ -215,7 +215,7 @@ static __always_inline int PageCompound(
#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
_