I found a report from syzbot [1]

This report shows that the value can be changed, but in reality, the value of __folio_set_movable() cannot be changed because it holds the folio refcount.

Therefore, it is appropriate to add an annotate to make KCSAN ignore that data-race.

[1]

================================================================== BUG: KCSAN: data-race in __filemap_remove_folio / migrate_pages_batch

write to 0xffffea0004b81dd8 of 8 bytes by task 6348 on cpu 0: page_cache_delete mm/filemap.c:153 [inline] __filemap_remove_folio+0x1ac/0x2c0 mm/filemap.c:233 filemap_remove_folio+0x6b/0x1f0 mm/filemap.c:265 truncate_inode_folio+0x42/0x50 mm/truncate.c:178 shmem_undo_range+0x25b/0xa70 mm/shmem.c:1028 shmem_truncate_range mm/shmem.c:1144 [inline] shmem_evict_inode+0x14d/0x530 mm/shmem.c:1272 evict+0x2f0/0x580 fs/inode.c:731 iput_final fs/inode.c:1883 [inline] iput+0x42a/0x5b0 fs/inode.c:1909 dentry_unlink_inode+0x24f/0x260 fs/dcache.c:412 __dentry_kill+0x18b/0x4c0 fs/dcache.c:615 dput+0x5c/0xd0 fs/dcache.c:857 __fput+0x3fb/0x6d0 fs/file_table.c:439 ____fput+0x1c/0x30 fs/file_table.c:459 task_work_run+0x13a/0x1a0 kernel/task_work.c:228 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline] exit_to_user_mode_loop kernel/entry/common.c:114 [inline] exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline] __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline] syscall_exit_to_user_mode+0xbe/0x130 kernel/entry/common.c:218 do_syscall_64+0xd6/0x1c0 arch/x86/entry/common.c:89 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffea0004b81dd8 of 8 bytes by task 6342 on cpu 1: __folio_test_movable include/linux/page-flags.h:699 [inline] migrate_folio_unmap mm/migrate.c:1199 [inline] migrate_pages_batch+0x24c/0x1940 mm/migrate.c:1797 migrate_pages_sync mm/migrate.c:1963 [inline] migrate_pages+0xff1/0x1820 mm/migrate.c:2072 do_mbind mm/mempolicy.c:1390 [inline] kernel_mbind mm/mempolicy.c:1533 [inline] __do_sys_mbind mm/mempolicy.c:1607 [inline] __se_sys_mbind+0xf76/0x1160 mm/mempolicy.c:1603 __x64_sys_mbind+0x78/0x90 mm/mempolicy.c:1603 x64_sys_call+0x2b4d/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:238 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff888127601078 -> 0x0000000000000000

Reported-by: syzbot syzkaller@googlegroups.com Cc: stable@vger.kernel.org Fixes: 7e2a5e5ab217 ("mm: migrate: use __folio_test_movable()") Signed-off-by: Jeongjun Park aha310510@gmail.com --- mm/migrate.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c index 923ea80ba744..368ab3878fa6 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1118,7 +1118,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio, int rc = -EAGAIN; int old_page_state = 0; struct anon_vma *anon_vma = NULL; - bool is_lru = !__folio_test_movable(src); + bool is_lru = data_race(!__folio_test_movable(src)); bool locked = false; bool dst_locked = false;

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