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BUG: KCSAN: data-race in exit_signals / kthread_unpark

write to 0xffff8880907cc064 of 4 bytes by task 24953 on cpu 0:
 exit_signals+0x13b/0x490 kernel/signal.c:2822
 do_exit+0x188/0x18c0 kernel/exit.c:754
 kthread+0x17f/0x200 drivers/block/aoe/aoecmd.c:1242
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff8880907cc064 of 4 bytes by task 24950 on cpu 1:
 to_kthread kernel/kthread.c:75 [inline]
 kthread_unpark+0x24/0xe0 kernel/kthread.c:474
 kthread_stop+0xe0/0x390 kernel/kthread.c:557
 loop_unprepare_queue drivers/block/loop.c:895 [inline]
 __loop_clr_fd+0x3ad/0x740 drivers/block/loop.c:1157
 loop_clr_fd drivers/block/loop.c:1237 [inline]
 lo_ioctl+0x24c/0xc80 drivers/block/loop.c:1606
 __blkdev_driver_ioctl block/ioctl.c:277 [inline]
 blkdev_ioctl+0xbe5/0x1260 block/ioctl.c:582
 block_ioctl+0x95/0xc0 fs/block_dev.c:1983
 vfs_ioctl fs/ioctl.c:47 [inline]
 file_ioctl fs/ioctl.c:545 [inline]
 do_vfs_ioctl+0x84f/0xcf0 fs/ioctl.c:732
 ksys_ioctl+0xbd/0xe0 fs/ioctl.c:749
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x4c/0x60 fs/ioctl.c:754
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 24950 Comm: syz-executor.3 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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