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BUG: KCSAN: data-race in copy_process / release_task

write to 0xffffffff89281410 of 4 bytes by task 9557 on cpu 0:
 __unhash_process kernel/exit.c:73 [inline]
 __exit_signal kernel/exit.c:147 [inline]
 release_task+0x6c8/0xb90 kernel/exit.c:198
 exit_notify kernel/exit.c:680 [inline]
 do_exit+0x1140/0x16e0 kernel/exit.c:826
 call_usermodehelper_exec_async+0x2da/0x2e0 kernel/umh.c:125
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

read to 0xffffffff89281410 of 4 bytes by task 3326 on cpu 1:
 copy_process+0xab5/0x32b0 kernel/fork.c:1980
 _do_fork+0xf1/0x660 kernel/fork.c:2443
 kernel_thread+0x85/0xb0 kernel/fork.c:2531
 call_usermodehelper_exec_work+0x4f/0x1b0 kernel/umh.c:195
 process_one_work+0x3cb/0x990 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x210/0x220 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 3326 Comm: kworker/u4:4 Not tainted 5.8.0-rc2-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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