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BUG: KCSAN: data-race in alloc_pid / copy_process

write to 0xffffffff8727e410 of 4 bytes by task 10600 on cpu 0:
 alloc_pid+0x63e/0x740 kernel/pid.c:273
 copy_process+0x20df/0x3ab0 kernel/fork.c:2102
 _do_fork+0xf7/0x790 kernel/fork.c:2430
 kernel_thread+0xa9/0xe0 kernel/fork.c:2517
 call_usermodehelper_exec_work kernel/umh.c:195 [inline]
 call_usermodehelper_exec_work+0x14c/0x190 kernel/umh.c:181
 process_one_work+0x424/0x930 kernel/workqueue.c:2268
 worker_thread+0x9a/0x7e0 kernel/workqueue.c:2414
 kthread+0x203/0x230 kernel/kthread.c:268
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffffffff8727e410 of 4 bytes by task 21 on cpu 1:
 copy_process+0x276b/0x3ab0 kernel/fork.c:2230
 _do_fork+0xf7/0x790 kernel/fork.c:2430
 kernel_thread+0xa9/0xe0 kernel/fork.c:2517
 call_usermodehelper_exec_work kernel/umh.c:195 [inline]
 call_usermodehelper_exec_work+0x14c/0x190 kernel/umh.c:181
 process_one_work+0x424/0x930 kernel/workqueue.c:2268
 worker_thread+0x9a/0x7e0 kernel/workqueue.c:2414
 kthread+0x203/0x230 kernel/kthread.c:268
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 21 Comm: kworker/u4:1 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_unbound call_usermodehelper_exec_work
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