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BUG: KCSAN: data-race in wb_wait_for_completion / writeback_sb_inodes

write to 0xffffc9000484fcb8 of 8 bytes by task 7392 on cpu 1:
 wb_wait_for_completion_cb fs/fs-writeback.c:203 [inline]
 wb_wait_for_completion+0x90/0x360 fs/fs-writeback.c:226
 __writeback_inodes_sb_nr fs/fs-writeback.c:2813 [inline]
 writeback_inodes_sb_nr fs/fs-writeback.c:2830 [inline]
 writeback_inodes_sb+0x163/0x1b0 fs/fs-writeback.c:2845
 sync_filesystem+0x69/0x190 fs/sync.c:54
 generic_shutdown_super+0x44/0x210 fs/super.c:622
 kill_block_super+0x2a/0x70 fs/super.c:1722
 ext4_kill_sb+0x42/0x80 fs/ext4/super.c:7444
 deactivate_locked_super+0x75/0x1c0 fs/super.c:474
 deactivate_super+0x97/0xa0 fs/super.c:507
 cleanup_mnt+0x2bb/0x330 fs/namespace.c:1318
 __cleanup_mnt+0x19/0x20 fs/namespace.c:1325
 task_work_run+0x130/0x1a0 kernel/task_work.c:233
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 __exit_to_user_mode_loop kernel/entry/common.c:44 [inline]
 exit_to_user_mode_loop+0x1f7/0x6f0 kernel/entry/common.c:75
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
 do_syscall_64+0x1d3/0x2a0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffc9000484fcb8 of 8 bytes by task 31 on cpu 0:
 writeback_sb_inodes+0x512/0xb70 fs/fs-writeback.c:2033
 wb_writeback+0x24e/0x5b0 fs/fs-writeback.c:2216
 wb_do_writeback fs/fs-writeback.c:2363 [inline]
 wb_workfn+0x194/0x960 fs/fs-writeback.c:2403
 process_one_work kernel/workqueue.c:3257 [inline]
 process_scheduled_works+0x4cd/0x9d0 kernel/workqueue.c:3340
 worker_thread+0x581/0x770 kernel/workqueue.c:3421
 kthread+0x488/0x510 kernel/kthread.c:463
 ret_from_fork+0x148/0x280 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

value changed: 0x0000000000000000 -> 0x00000000fffffd57

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 31 Comm: kworker/u8:1 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: writeback wb_workfn (flush-7:0)
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