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BUG: KCSAN: data-race in exit_signals / kthread_unpark

write to 0xffff88812702906c of 4 bytes by task 8594 on cpu 0:
 exit_signals+0xe1/0x4a0 kernel/signal.c:2927
 do_exit+0x194/0x1560 kernel/exit.c:782
 kthread+0x1d8/0x1f0 kernel/kthread.c:315
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff88812702906c of 4 bytes by task 1767 on cpu 1:
 to_kthread kernel/kthread.c:83 [inline]
 kthread_unpark+0x1f/0x150 kernel/kthread.c:557
 kthread_stop+0xa6/0x250 kernel/kthread.c:640
 loop_unprepare_queue drivers/block/loop.c:927 [inline]
 __loop_clr_fd+0x4cb/0x640 drivers/block/loop.c:1258
 lo_release+0xfc/0x120 drivers/block/loop.c:1924
 __blkdev_put+0x408/0x460 fs/block_dev.c:1583
 blkdev_put+0x23e/0x2c0 fs/block_dev.c:1636
 kill_block_super+0x7b/0x90 fs/super.c:1398
 deactivate_locked_super+0x65/0xd0 fs/super.c:335
 deactivate_super+0x85/0x90 fs/super.c:366
 cleanup_mnt+0x267/0x2d0 fs/namespace.c:1136
 __cleanup_mnt+0x15/0x20 fs/namespace.c:1143
 task_work_run+0xae/0x130 kernel/task_work.c:164
 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+0x156/0x190 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+0x56/0x90 arch/x86/entry/common.c:57
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00388040 -> 0x00388044

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1767 Comm: syz-executor.5 Not tainted 5.13.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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