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BUG: KCSAN: data-race in nilfs_detach_log_writer / nilfs_segctor_thread

write to 0xffff88802bb5b7e8 of 8 bytes by task 16426 on cpu 0:
 nilfs_segctor_thread+0x6b1/0x710 fs/nilfs2/segment.c:2606
 kthread+0x20b/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff88802bb5b7e8 of 8 bytes by task 8414 on cpu 1:
 nilfs_segctor_kill_thread fs/nilfs2/segment.c:2636 [inline]
 nilfs_segctor_destroy fs/nilfs2/segment.c:2718 [inline]
 nilfs_detach_log_writer+0x169/0x5a0 fs/nilfs2/segment.c:2807
 nilfs_put_super+0x2f/0xf0 fs/nilfs2/super.c:467
 generic_shutdown_super+0xde/0x210 fs/super.c:464
 kill_block_super+0x4a/0x90 fs/super.c:1394
 deactivate_locked_super+0x6a/0xb0 fs/super.c:335
 deactivate_super+0x85/0x90 fs/super.c:366
 cleanup_mnt+0x277/0x2e0 fs/namespace.c:1136
 __cleanup_mnt+0x15/0x20 fs/namespace.c:1143
 task_work_run+0x8e/0x110 kernel/task_work.c:140
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
 exit_to_user_mode_prepare+0x17c/0x1b0 kernel/entry/common.c:208
 __syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:301
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8414 Comm: syz-executor.3 Not tainted 5.12.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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