==================================================================
BUG: KCSAN: data-race in __writeback_single_inode / xas_clear_mark

write to 0xffff888107e6e7ec of 4 bytes by task 1552 on cpu 1:
 xa_mark_clear lib/xarray.c:77 [inline]
 xas_clear_mark+0x16b/0x180 lib/xarray.c:932
 __folio_start_writeback+0x257/0x370 mm/page-writeback.c:3026
 mpage_write_folio fs/mpage.c:620 [inline]
 __mpage_writepages+0xdbd/0x1390 fs/mpage.c:686
 mpage_writepages include/linux/mpage.h:27 [inline]
 fat_writepages+0x26/0x30 fs/fat/inode.c:200
 do_writepages+0x1c6/0x310 mm/page-writeback.c:2571
 filemap_writeback mm/filemap.c:388 [inline]
 filemap_fdatawrite_range mm/filemap.c:413 [inline]
 file_write_and_wait_range+0x178/0x2f0 mm/filemap.c:787
 mmb_fsync_noflush+0x48/0x140 fs/buffer.c:645
 fat_file_fsync+0x98/0x110 fs/fat/file.c:192
 vfs_fsync_range+0xc5/0xe0 fs/sync.c:186
 generic_write_sync include/linux/fs.h:2654 [inline]
 generic_file_write_iter+0x1ba/0x310 mm/filemap.c:4472
 iter_file_splice_write+0x6c4/0xa80 fs/splice.c:736
 do_splice_from fs/splice.c:936 [inline]
 direct_splice_actor+0x156/0x2a0 fs/splice.c:1159
 splice_direct_to_actor+0x311/0x670 fs/splice.c:1103
 do_splice_direct_actor fs/splice.c:1202 [inline]
 do_splice_direct+0x119/0x1a0 fs/splice.c:1228
 do_sendfile+0x382/0x650 fs/read_write.c:1372
 __do_sys_sendfile64 fs/read_write.c:1433 [inline]
 __se_sys_sendfile64 fs/read_write.c:1419 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1419
 x64_sys_call+0x2dc4/0x3020 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888107e6e7ec of 4 bytes by task 1555 on cpu 0:
 xa_marked include/linux/xarray.h:424 [inline]
 mapping_tagged include/linux/fs.h:508 [inline]
 __writeback_single_inode+0x1f1/0x650 fs/fs-writeback.c:1813
 writeback_single_inode+0x16d/0x3f0 fs/fs-writeback.c:1883
 sync_inode_metadata+0x6e/0xa0 fs/fs-writeback.c:2994
 mmb_fsync_noflush+0xfa/0x140 fs/buffer.c:656
 fat_file_fsync+0x98/0x110 fs/fat/file.c:192
 vfs_fsync_range+0xc5/0xe0 fs/sync.c:186
 generic_write_sync include/linux/fs.h:2654 [inline]
 generic_file_write_iter+0x1ba/0x310 mm/filemap.c:4472
 iter_file_splice_write+0x6c4/0xa80 fs/splice.c:736
 do_splice_from fs/splice.c:936 [inline]
 direct_splice_actor+0x156/0x2a0 fs/splice.c:1159
 splice_direct_to_actor+0x311/0x670 fs/splice.c:1103
 do_splice_direct_actor fs/splice.c:1202 [inline]
 do_splice_direct+0x119/0x1a0 fs/splice.c:1228
 do_sendfile+0x382/0x650 fs/read_write.c:1372
 __do_sys_sendfile64 fs/read_write.c:1433 [inline]
 __se_sys_sendfile64 fs/read_write.c:1419 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1419
 x64_sys_call+0x2dc4/0x3020 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0a000021 -> 0x04000021

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 1555 Comm: syz.9.9591 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================