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BUG: KCSAN: data-race in detach_pid / perf_event_switch_output

write to 0xffff888108e925d8 of 8 bytes by task 16981 on cpu 1:
 __change_pid kernel/pid.c:347 [inline]
 detach_pid+0xd7/0x160 kernel/pid.c:358
 __unhash_process kernel/exit.c:75 [inline]
 __exit_signal kernel/exit.c:148 [inline]
 release_task+0x6d8/0xbe0 kernel/exit.c:200
 wait_task_zombie kernel/exit.c:1108 [inline]
 wait_consider_task+0x10ce/0x19e0 kernel/exit.c:1335
 do_wait_pid kernel/exit.c:1466 [inline]
 do_wait+0x3a6/0x6b0 kernel/exit.c:1508
 kernel_wait+0x4e/0xc0 kernel/exit.c:1695
 call_usermodehelper_exec_sync kernel/umh.c:139 [inline]
 call_usermodehelper_exec_work+0x98/0x150 kernel/umh.c:166
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2276
 worker_thread+0x636/0xae0 kernel/workqueue.c:2422
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff888108e925d8 of 8 bytes by task 1770 on cpu 0:
 pid_alive include/linux/sched.h:1454 [inline]
 perf_event_pid_type kernel/events/core.c:1410 [inline]
 perf_event_tid kernel/events/core.c:1422 [inline]
 perf_event_switch_output+0x1fe/0x330 kernel/events/core.c:8643
 perf_iterate_sb_cpu kernel/events/core.c:7556 [inline]
 perf_iterate_sb+0x37d/0x8f0 kernel/events/core.c:7586
 perf_event_switch kernel/events/core.c:8687 [inline]
 __perf_event_task_sched_in+0x3b9/0x4c0 kernel/events/core.c:3899
 perf_event_task_sched_in include/linux/perf_event.h:1205 [inline]
 finish_task_switch+0x1fd/0x290 kernel/sched/core.c:4208
 context_switch kernel/sched/core.c:4342 [inline]
 __schedule+0x427/0x5b0 kernel/sched/core.c:5147
 schedule+0x67/0x90 kernel/sched/core.c:5226
 freezable_schedule include/linux/freezer.h:172 [inline]
 do_nanosleep+0x107/0x3d0 kernel/time/hrtimer.c:1896
 hrtimer_nanosleep+0xfa/0x1f0 kernel/time/hrtimer.c:1949
 common_nsleep+0x69/0x80 kernel/time/posix-timers.c:1227
 __do_sys_clock_nanosleep kernel/time/posix-timers.c:1267 [inline]
 __se_sys_clock_nanosleep kernel/time/posix-timers.c:1245 [inline]
 __x64_sys_clock_nanosleep+0x1ee/0x220 kernel/time/posix-timers.c:1245
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0xffff888100afa300 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 1770 Comm: syz-executor.1 Not tainted 5.13.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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