Re: [PATCH] mm: migrate: annotate data-race in migrate_folio_unmap()

[David Hildenbrand <david@redhat.com>]

On 24.09.24 15:00, Jeongjun Park wrote:
> 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

Hmm, why stable?

> Fixes: 7e2a5e5ab217 ("mm: migrate: use __folio_test_movable()")
> Signed-off-by: Jeongjun Park <aha310510@gmail.com>
> ---

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb