[moderation] [kernel?] upstream test error: KCSAN: data-race in copy_process / free_pid

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 6916d5703ddf Merge tag 'drm-fixes-2026-05-16' of https://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15873fce580000
kernel config: https://syzkaller.appspot.com/x/.config?x=2e40c0f41e01837e
dashboard link: https://syzkaller.appspot.com/bug?extid=ef8218324d06809c7bef
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [linux-...@vger.kernel.org]

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2267ad6832d0/disk-6916d570.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e86f25e25e2c/vmlinux-6916d570.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b7349eb533bc/bzImage-6916d570.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ef8218...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in copy_process / free_pid

read-write to 0xffffffff86c5c3a8 of 4 bytes by task 3302 on cpu 0:
free_pid+0xb3/0x1b0 kernel/pid.c:124
free_pids+0x54/0xb0 kernel/pid.c:156
release_task+0x9a7/0xb60 kernel/exit.c:295
wait_task_zombie kernel/exit.c:1281 [inline]
wait_consider_task+0x1160/0x1670 kernel/exit.c:1508
do_wait_thread kernel/exit.c:1571 [inline]
__do_wait+0xf9/0x510 kernel/exit.c:1689
do_wait+0xb6/0x230 kernel/exit.c:1723
kernel_wait4+0x19f/0x210 kernel/exit.c:1882
__do_sys_wait4 kernel/exit.c:1910 [inline]
__se_sys_wait4 kernel/exit.c:1906 [inline]
__x64_sys_wait4+0x91/0x120 kernel/exit.c:1906
x64_sys_call+0x2aee/0x3020 arch/x86/include/generated/asm/syscalls_64.h:62
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86c5c3a8 of 4 bytes by task 40 on cpu 1:
copy_process+0x1af1/0x2370 kernel/fork.c:2442
kernel_clone+0x1a5/0x5e0 kernel/fork.c:2721
user_mode_thread+0x9c/0xd0 kernel/fork.c:2797
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:3314 [inline]
process_scheduled_works+0x4f0/0x9c0 kernel/workqueue.c:3397
worker_thread+0x58a/0x780 kernel/workqueue.c:3478
kthread+0x22a/0x280 kernel/kthread.c:436
ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x8000009a -> 0x80000099

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 40 Comm: kworker/u8:2 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Workqueue: events_unbound call_usermodehelper_exec_work
==================================================================


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