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BUG: KCSAN: data-race in detach_pid / perf_event_switch_output

write to 0xffff88813988f598 of 8 bytes by task 497 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+0x6e8/0xbf0 kernel/exit.c:199
 wait_task_zombie kernel/exit.c:1107 [inline]
 wait_consider_task+0x10c7/0x19e0 kernel/exit.c:1334
 do_wait_pid kernel/exit.c:1465 [inline]
 do_wait+0x355/0x640 kernel/exit.c:1507
 kernel_wait+0x4e/0xc0 kernel/exit.c:1694
 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+0x262/0x280 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

read to 0xffff88813988f598 of 8 bytes by task 0 on cpu 0:
 pid_alive include/linux/sched.h:1471 [inline]
 perf_event_pid_type kernel/events/core.c:1411 [inline]
 perf_event_tid kernel/events/core.c:1423 [inline]
 perf_event_switch_output+0x1fe/0x330 kernel/events/core.c:8651
 perf_iterate_sb_cpu kernel/events/core.c:7566 [inline]
 perf_iterate_sb+0x37d/0x8f0 kernel/events/core.c:7596
 perf_event_switch kernel/events/core.c:8696 [inline]
 __perf_event_task_sched_in+0x59d/0x850 kernel/events/core.c:3907
 perf_event_task_sched_in include/linux/perf_event.h:1205 [inline]
 finish_task_switch+0x1fd/0x290 kernel/sched/core.c:4552
 context_switch kernel/sched/core.c:4686 [inline]
 __schedule+0x42a/0x670 kernel/sched/core.c:5940
 schedule_idle+0x17/0x30 kernel/sched/core.c:6047
 do_idle+0x215/0x240 kernel/sched/idle.c:334
 cpu_startup_entry+0x15/0x20 kernel/sched/idle.c:403
 rest_init+0xee/0x100 init/main.c:722
 arch_call_rest_init+0xa/0xb
 start_kernel+0x59e/0x623 init/main.c:1084
 secondary_startup_64_no_verify+0xb0/0xbb

value changed: 0xffff888100e87800 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W         5.13.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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