syzbot

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BUG: KCSAN: data-race in copy_process / free_pid

read-write to 0xffffffff86860008 of 4 bytes by task 3321 on cpu 0:
 free_pid+0xb9/0x1d0 kernel/pid.c:126
 free_pids+0x54/0xb0 kernel/pid.c:159
 release_task+0x9a7/0xb60 kernel/exit.c:295
 wait_task_zombie kernel/exit.c:1274 [inline]
 wait_consider_task+0x114a/0x1660 kernel/exit.c:1501
 do_wait_thread kernel/exit.c:1564 [inline]
 __do_wait+0xfa/0x510 kernel/exit.c:1682
 do_wait+0xb7/0x250 kernel/exit.c:1716
 kernel_wait4+0x16b/0x1e0 kernel/exit.c:1875
 __do_sys_wait4 kernel/exit.c:1903 [inline]
 __se_sys_wait4 kernel/exit.c:1899 [inline]
 __x64_sys_wait4+0x91/0x120 kernel/exit.c:1899
 x64_sys_call+0x28ec/0x3000 arch/x86/include/generated/asm/syscalls_64.h:62
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xca/0x2b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86860008 of 4 bytes by task 2 on cpu 1:
 copy_process+0x16d4/0x1ef0 kernel/fork.c:2394
 kernel_clone+0x16c/0x5c0 kernel/fork.c:2651
 kernel_thread+0xad/0xe0 kernel/fork.c:2712
 create_kthread kernel/kthread.c:486 [inline]
 kthreadd+0x26c/0x340 kernel/kthread.c:844
 ret_from_fork+0x149/0x290 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

value changed: 0x800000f0 -> 0x800000ef

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 2 Comm: kthreadd Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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