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BUG: KCSAN: data-race in exit_signals / kthread_unpark

read-write to 0xffff88812afe1024 of 4 bytes by task 32419 on cpu 1:
 exit_signals+0x102/0x530 kernel/signal.c:2846
 do_exit+0x15d/0x1630 kernel/exit.c:765
 kthread+0x205/0x220 kernel/kthread.c:294
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff88812afe1024 of 4 bytes by task 10127 on cpu 0:
 to_kthread kernel/kthread.c:83 [inline]
 kthread_unpark+0x1f/0x140 kernel/kthread.c:511
 kthread_stop+0xa6/0x2c0 kernel/kthread.c:594
 loop_unprepare_queue drivers/block/loop.c:932 [inline]
 __loop_clr_fd+0x424/0x5a0 drivers/block/loop.c:1266
 lo_release+0x101/0x130 drivers/block/loop.c:1927
 __blkdev_put+0x370/0x4a0 fs/block_dev.c:1782
 blkdev_put+0x1d9/0x200 fs/block_dev.c:1844
 blkdev_close+0x47/0x50 fs/block_dev.c:1851
 __fput+0x243/0x4d0 fs/file_table.c:281
 ____fput+0x11/0x20 fs/file_table.c:314
 task_work_run+0x8e/0x110 kernel/task_work.c:151
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:164 [inline]
 exit_to_user_mode_prepare+0x13c/0x170 kernel/entry/common.c:191
 syscall_exit_to_user_mode+0x16/0x30 kernel/entry/common.c:266
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 10127 Comm: systemd-udevd Not tainted 5.10.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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