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BUG: KCSAN: data-race in copy_process / free_pid

write to 0xffffffff8364b458 of 4 bytes by task 7713 on cpu 1:
 free_pid+0x79/0x190 kernel/pid.c:136
 copy_process+0x23ba/0x2f70 kernel/fork.c:2356
 kernel_clone+0x14b/0x680 kernel/fork.c:2509
 __do_sys_clone kernel/fork.c:2626 [inline]
 __se_sys_clone kernel/fork.c:2610 [inline]
 __x64_sys_clone+0xb4/0xe0 kernel/fork.c:2610
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffffffff8364b458 of 4 bytes by task 1840 on cpu 0:
 copy_process+0x1e4a/0x2f70 kernel/fork.c:2269
 kernel_clone+0x14b/0x680 kernel/fork.c:2509
 kernel_thread+0x71/0x90 kernel/fork.c:2561
 call_usermodehelper_exec_work+0x3d/0x150 kernel/umh.c:174
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2276
 worker_thread+0x636/0xae0 kernel/workqueue.c:2422
 kthread+0x262/0x280 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

value changed: 0x800000a0 -> 0x8000009f

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 1840 Comm: kworker/u4:7 Not tainted 5.14.0-rc3-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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