KCSAN: data-race in alloc_pid / copy_process (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 7c3cd68e Merge remote-tracking branch 'linux-rcu/kcsan' in..
git tree: https://github.com/google/ktsan.git kcsan
console output: https://syzkaller.appspot.com/x/log.txt?x=172e5646100000
kernel config: https://syzkaller.appspot.com/x/.config?x=ff291dc25f22cdda
dashboard link: https://syzkaller.appspot.com/bug?extid=0718f65353d72efaac1e
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
CC: [are...@redhat.com ar...@arndb.de chri...@brauner.io ebie...@xmission.com jo...@joelfernandes.org linux-...@vger.kernel.org ol...@redhat.com sar...@sargun.me]

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+0718f6...@syzkaller.appspotmail.com

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

write to 0xffffffff8727e410 of 4 bytes by task 3596 on cpu 1:
alloc_pid+0x63e/0x740 kernel/pid.c:273
copy_process+0x20df/0x3ab0 kernel/fork.c:2102
_do_fork+0xf7/0x790 kernel/fork.c:2430
kernel_thread+0xa9/0xe0 kernel/fork.c:2517
call_usermodehelper_exec_work kernel/umh.c:195 [inline]
call_usermodehelper_exec_work+0x14c/0x190 kernel/umh.c:181
process_one_work+0x424/0x930 kernel/workqueue.c:2268
worker_thread+0x9a/0x7e0 kernel/workqueue.c:2414
kthread+0x203/0x230 kernel/kthread.c:268
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffffffff8727e410 of 4 bytes by task 229 on cpu 0:
copy_process+0x276b/0x3ab0 kernel/fork.c:2230
_do_fork+0xf7/0x790 kernel/fork.c:2430
kernel_thread+0xa9/0xe0 kernel/fork.c:2517
call_usermodehelper_exec_work kernel/umh.c:195 [inline]
call_usermodehelper_exec_work+0x14c/0x190 kernel/umh.c:181
process_one_work+0x424/0x930 kernel/workqueue.c:2268
worker_thread+0x9a/0x7e0 kernel/workqueue.c:2414
kthread+0x203/0x230 kernel/kthread.c:268
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 229 Comm: kworker/u4:3 Not tainted 5.7.0-rc1-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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