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BUG: KCSAN: data-race in exit_signals / kthread_unpark

write to 0xffff88810e7ac024 of 4 bytes by task 10910 on cpu 1:
 exit_signals+0x135/0x4c0 kernel/signal.c:2827
 do_exit+0x17b/0x11e0 kernel/exit.c:744
 kthread+0x1aa/0x230 kernel/kthread.c:270
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff88810e7ac024 of 4 bytes by task 9114 on cpu 0:
 to_kthread kernel/kthread.c:75 [inline]
 kthread_unpark+0x1f/0xd0 kernel/kthread.c:487
 kthread_stop+0xd5/0x370 kernel/kthread.c:570
 loop_unprepare_queue drivers/block/loop.c:917 [inline]
 __loop_clr_fd+0x39f/0x710 drivers/block/loop.c:1179
 lo_release+0x140/0x150 drivers/block/loop.c:1852
 __blkdev_put+0x29c/0x3e0 fs/block_dev.c:1909
 blkdev_put+0x84/0x2b0 fs/block_dev.c:1971
 kill_block_super+0x85/0xa0 fs/super.c:1447
 deactivate_locked_super+0x5d/0xb0 fs/super.c:335
 deactivate_super fs/super.c:366 [inline]
 deactivate_super+0xca/0xe0 fs/super.c:362
 cleanup_mnt+0x27a/0x330 fs/namespace.c:1102
 __cleanup_mnt+0x1c/0x30 fs/namespace.c:1109
 task_work_run+0xba/0x120 kernel/task_work.c:123
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x2ae/0x2c0 arch/x86/entry/common.c:165
 prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
 do_syscall_64+0x38b/0x3b0 arch/x86/entry/common.c:305
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 9114 Comm: syz-executor.2 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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