From: Pei Li peili.dev@gmail.com
mainline inclusion from mainline-v6.11-rc1 commit 7b7aca6d7c0f9b2d9400bfc57cb2b23cfbd5134d category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/IBET92
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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Syzbot reported a possible data race:
BUG: KCSAN: data-race in __swap_writepage / scan_swap_map_slots
read-write to 0xffff888102fca610 of 8 bytes by task 7106 on cpu 1. read to 0xffff888102fca610 of 8 bytes by task 7080 on cpu 0.
While we are in __swap_writepage to read sis->flags, scan_swap_map_slots is trying to update it with SWP_SCANNING.
value changed: 0x0000000000008083 -> 0x0000000000004083.
While this can be updated non-atomicially, this won't affect SWP_SYNCHRONOUS_IO, so we consider this data-race safe.
This is possibly introduced by commit 3222d8c2a7f8 ("block: remove ->rw_page"), where this if branch is introduced.
Link: https://lkml.kernel.org/r/20240711-bug13-v1-1-cea2b8ae8d76@gmail.com Fixes: 3222d8c2a7f8 ("block: remove ->rw_page") Signed-off-by: Pei Li peili.dev@gmail.com Reported-by: syzbot+da25887cc13da6bf3b8c@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=da25887cc13da6bf3b8c Cc: Dan Williams dan.j.williams@intel.com Cc: Shuah Khan skhan@linuxfoundation.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Conflicts: mm/page_io.c [Because HULK-6.6 don't merge mainline patch b99b4e0d9d7f29b428bacd7a61188b2abf340c1e ("mm: pass a folio to __swap_writepage()")] Signed-off-by: Kaixiong Yu yukaixiong@huawei.com --- mm/page_io.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/mm/page_io.c b/mm/page_io.c index f2b3c4eed688..1887cd2093e3 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -381,7 +381,12 @@ void __swap_writepage(struct page *page, struct writeback_control *wbc) */ if (data_race(sis->flags & SWP_FS_OPS)) swap_writepage_fs(page, wbc); - else if (sis->flags & SWP_SYNCHRONOUS_IO) + /* + * ->flags can be updated non-atomicially (scan_swap_map_slots), + * but that will never affect SWP_SYNCHRONOUS_IO, so the data_race + * is safe. + */ + else if (data_race(sis->flags & SWP_SYNCHRONOUS_IO)) swap_writepage_bdev_sync(page, wbc, sis); else swap_writepage_bdev_async(page, wbc, sis);