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BUG: KCSAN: data-race in exit_signals / kthread_stop

read-write to 0xffff88812d97202c of 4 bytes by task 15020 on cpu 0:
 exit_signals+0x102/0x530 kernel/signal.c:2865
 do_exit+0x1b4/0x1690 kernel/exit.c:781
 kthread+0x205/0x220 kernel/kthread.c:294
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff88812d97202c of 4 bytes by task 24 on cpu 1:
 to_kthread kernel/kthread.c:83 [inline]
 kthread_stop+0x5f/0x2c0 kernel/kthread.c:617
 vhci_shutdown_connection+0x6e/0x680 drivers/usb/usbip/vhci_hcd.c:1019
 event_handler+0x185/0x320 drivers/usb/usbip/usbip_event.c:78
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x64a/0xaa0 kernel/workqueue.c:2421
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 24 Comm: kworker/u4:1 Not tainted 5.11.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: usbip_event event_handler
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