syzbot

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BUG: KCSAN: data-race in xas_find_marked / xas_set_mark

write to 0xffff88811a854e14 of 4 bytes by task 609 on cpu 1:
 xa_mark_set lib/xarray.c:71 [inline]
 xas_set_mark+0x12b/0x140 lib/xarray.c:900
 tag_pages_for_writeback+0xe3/0x2e0 mm/page-writeback.c:2392
 writeback_iter+0x340/0x810 mm/page-writeback.c:2529
 mpage_writepages+0x87/0x1310 fs/mpage.c:669
 fat_writepages+0x24/0x30 fs/fat/inode.c:200
 do_writepages+0x1c6/0x310 mm/page-writeback.c:2598
 filemap_writeback mm/filemap.c:387 [inline]
 filemap_fdatawrite_range mm/filemap.c:412 [inline]
 file_write_and_wait_range+0x178/0x2f0 mm/filemap.c:786
 __generic_file_fsync+0x46/0x160 fs/libfs.c:1558
 fat_file_fsync+0x49/0x100 fs/fat/file.c:191
 vfs_fsync_range+0x10d/0x130 fs/sync.c:188
 generic_write_sync include/linux/fs.h:2616 [inline]
 generic_file_write_iter+0x1ba/0x310 mm/filemap.c:4461
 iter_file_splice_write+0x6bc/0xa80 fs/splice.c:738
 do_splice_from fs/splice.c:938 [inline]
 direct_splice_actor+0x156/0x2a0 fs/splice.c:1161
 splice_direct_to_actor+0x311/0x670 fs/splice.c:1105
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0x119/0x1a0 fs/splice.c:1230
 do_sendfile+0x380/0x650 fs/read_write.c:1370
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64 fs/read_write.c:1417 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
 x64_sys_call+0x2db1/0x3000 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811a854e14 of 4 bytes by task 604 on cpu 0:
 xa_marked include/linux/xarray.h:424 [inline]
 xas_find_marked+0x5d7/0x620 lib/xarray.c:1483
 find_get_entry+0x5d/0x380 mm/filemap.c:2064
 filemap_get_folios_tag+0xb6/0x230 mm/filemap.c:2332
 __filemap_fdatawait_range mm/filemap.c:523 [inline]
 filemap_fdatawait_range+0x88/0x1e0 mm/filemap.c:558
 filemap_fdatawait include/linux/pagemap.h:51 [inline]
 __writeback_single_inode+0xdb/0x7b0 fs/fs-writeback.c:1747
 writeback_single_inode+0x16d/0x3f0 fs/fs-writeback.c:1858
 sync_inode_metadata+0x6e/0xa0 fs/fs-writeback.c:2949
 __generic_file_fsync+0x109/0x160 fs/libfs.c:1569
 fat_file_fsync+0x49/0x100 fs/fat/file.c:191
 vfs_fsync_range+0x10d/0x130 fs/sync.c:188
 generic_write_sync include/linux/fs.h:2616 [inline]
 generic_file_write_iter+0x1ba/0x310 mm/filemap.c:4461
 iter_file_splice_write+0x6bc/0xa80 fs/splice.c:738
 do_splice_from fs/splice.c:938 [inline]
 direct_splice_actor+0x156/0x2a0 fs/splice.c:1161
 splice_direct_to_actor+0x311/0x670 fs/splice.c:1105
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0x119/0x1a0 fs/splice.c:1230
 do_sendfile+0x380/0x650 fs/read_write.c:1370
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64 fs/read_write.c:1417 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
 x64_sys_call+0x2db1/0x3000 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x02000021 -> 0x04000021

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 604 Comm: syz.8.7972 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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