syzbot

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BUG: KCSAN: data-race in copy_process / free_pid

read-write to 0xffffffff86a88588 of 4 bytes by task 16731 on cpu 1:
 free_pid+0x71/0x180 kernel/pid.c:136
 copy_process+0x20d2/0x2da0 kernel/fork.c:2333
 kernel_clone+0x14b/0x680 kernel/fork.c:2464
 __do_sys_clone kernel/fork.c:2581 [inline]
 __se_sys_clone kernel/fork.c:2565 [inline]
 __x64_sys_clone+0xc8/0xf0 kernel/fork.c:2565
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffffff86a88588 of 4 bytes by task 16503 on cpu 0:
 copy_process+0x1bd1/0x2da0 kernel/fork.c:2247
 kernel_clone+0x14b/0x680 kernel/fork.c:2464
 kernel_thread+0x85/0xb0 kernel/fork.c:2516
 call_usermodehelper_exec_work+0x3d/0x150 kernel/umh.c:172
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x635/0xb90 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: 0 PID: 16503 Comm: kworker/u4:8 Not tainted 5.11.0-rc4-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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