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BUG: KCSAN: data-race in mark_buffer_dirty_inode / sync_mapping_buffers

write to 0xffff88811a6ba190 of 8 bytes by task 13564 on cpu 0:
 __remove_assoc_queue fs/buffer.c:523 [inline]
 fsync_buffers_list fs/buffer.c:796 [inline]
 sync_mapping_buffers+0x163/0x7d0 fs/buffer.c:584
 fat_file_fsync+0xaa/0x100 fs/fat/file.c:195
 vfs_fsync_range+0x10a/0x130 fs/sync.c:187
 generic_write_sync include/linux/fs.h:3042 [inline]
 generic_file_write_iter+0x1b8/0x2f0 mm/filemap.c:4322
 iter_file_splice_write+0x666/0xa60 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+0x312/0x680 fs/splice.c:1105
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0xda/0x150 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+0x2bb0/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811a6ba190 of 8 bytes by task 13569 on cpu 1:
 mark_buffer_dirty_inode+0x95/0x1c0 fs/buffer.c:689
 fat16_ent_put+0x4e/0x60 fs/fat/fatent.c:184
 fat_free_clusters+0x2a9/0x790 fs/fat/fatent.c:597
 fat_free fs/fat/file.c:376 [inline]
 fat_truncate_blocks+0x4c2/0x550 fs/fat/file.c:394
 fat_write_failed fs/fat/inode.c:218 [inline]
 fat_write_end+0xba/0x160 fs/fat/inode.c:246
 generic_perform_write+0x312/0x490 mm/filemap.c:4196
 __generic_file_write_iter+0xec/0x120 mm/filemap.c:4289
 generic_file_write_iter+0x8d/0x2f0 mm/filemap.c:4318
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x527/0x960 fs/read_write.c:686
 ksys_write+0xda/0x1a0 fs/read_write.c:738
 __do_sys_write fs/read_write.c:749 [inline]
 __se_sys_write fs/read_write.c:746 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:746
 x64_sys_call+0x27fe/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff88811a457508 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 13569 Comm: syz.7.2777 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
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