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BUG: KCSAN: data-race in copy_process / free_pid

write to 0xffffffff85a542d8 of 4 bytes by task 15480 on cpu 0:
 free_pid+0x79/0x190 kernel/pid.c:136
 copy_process+0x2443/0x2fd0 kernel/fork.c:2429
 kernel_clone+0x15c/0x6a0 kernel/fork.c:2582
 __do_sys_clone kernel/fork.c:2699 [inline]
 __se_sys_clone kernel/fork.c:2683 [inline]
 __x64_sys_clone+0xc6/0xf0 kernel/fork.c:2683
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffffffff85a542d8 of 4 bytes by task 2 on cpu 1:
 copy_process+0x1f1f/0x2fd0 kernel/fork.c:2342
 kernel_clone+0x15c/0x6a0 kernel/fork.c:2582
 kernel_thread+0x85/0xb0 kernel/fork.c:2634
 create_kthread kernel/kthread.c:350 [inline]
 kthreadd+0x2b6/0x360 kernel/kthread.c:685
 ret_from_fork+0x1f/0x30

value changed: 0x800001c6 -> 0x800001c5

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 2 Comm: kthreadd Not tainted 5.16.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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