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BUG: KCSAN: data-race in alloc_pid / copy_process

read-write to 0xffffffff86c61f68 of 4 bytes by task 1646 on cpu 0:
 alloc_pid+0x651/0x940 kernel/pid.c:321
 copy_process+0xf37/0x20d0 kernel/fork.c:2239
 kernel_clone+0x16b/0x5d0 kernel/fork.c:2654
 user_mode_thread+0x9c/0xd0 kernel/fork.c:2730
 call_usermodehelper_exec_sync kernel/umh.c:132 [inline]
 call_usermodehelper_exec_work+0x7a/0x160 kernel/umh.c:163
 process_one_work kernel/workqueue.c:3275 [inline]
 process_scheduled_works+0x4de/0x9e0 kernel/workqueue.c:3358
 worker_thread+0x581/0x770 kernel/workqueue.c:3439
 kthread+0x22a/0x280 kernel/kthread.c:467
 ret_from_fork+0x150/0x360 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffffffff86c61f68 of 4 bytes by task 2 on cpu 1:
 copy_process+0x1895/0x20d0 kernel/fork.c:2396
 kernel_clone+0x16b/0x5d0 kernel/fork.c:2654
 kernel_thread+0xe5/0x120 kernel/fork.c:2715
 create_kthread kernel/kthread.c:490 [inline]
 kthreadd+0x25b/0x320 kernel/kthread.c:849
 ret_from_fork+0x150/0x360 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x80000101 -> 0x80000102

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 2 Comm: kthreadd Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
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