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BUG: KCSAN: data-race in exit_signals / kthread_unpark

write to 0xffff8880a1f52064 of 4 bytes by task 29168 on cpu 0:
 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 0xffff8880a1f52064 of 4 bytes by task 29162 on cpu 1:
 to_kthread kernel/kthread.c:75 [inline]
 kthread_unpark+0x1f/0xd0 kernel/kthread.c:487
 kthread_stop+0xd5/0x370 kernel/kthread.c:570
 destroy_workqueue+0xd6/0x4c0 kernel/workqueue.c:4368
 ucma_close+0x190/0x1b0 drivers/infiniband/core/ucma.c:1816
 __fput+0x1e9/0x500 fs/file_table.c:280
 ____fput+0x1b/0x30 fs/file_table.c:313
 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: 1 PID: 29162 Comm: syz-executor.5 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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