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BUG: KCSAN: data-race in detach_pid / perf_event_switch_output

write to 0xffff888150552558 of 8 bytes by task 29 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_thread kernel/exit.c:1398 [inline]
 do_wait+0x1b1/0x4a0 kernel/exit.c:1469
 kernel_wait+0x4e/0xc0 kernel/exit.c:1648
 call_usermodehelper_exec_sync kernel/umh.c:137 [inline]
 call_usermodehelper_exec_work+0x98/0x150 kernel/umh.c:164
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2275
 worker_thread+0x636/0xae0 kernel/workqueue.c:2421
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff888150552558 of 8 bytes by task 0 on cpu 0:
 pid_alive include/linux/sched.h:1454 [inline]
 perf_event_pid_type kernel/events/core.c:1410 [inline]
 perf_event_pid kernel/events/core.c:1417 [inline]
 perf_event_switch_output+0x174/0x330 kernel/events/core.c:8648
 perf_iterate_sb_cpu kernel/events/core.c:7563 [inline]
 perf_iterate_sb+0x37d/0x8f0 kernel/events/core.c:7593
 perf_event_switch kernel/events/core.c:8694 [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_idle+0x27/0x40 kernel/sched/core.c:5254
 do_idle+0x215/0x240 kernel/sched/idle.c:334
 cpu_startup_entry+0x15/0x20 kernel/sched/idle.c:403
 rest_init+0xc9/0xd0 init/main.c:721
 arch_call_rest_init+0xa/0xb
 start_kernel+0x59e/0x623 init/main.c:1087
 secondary_startup_64_no_verify+0xb0/0xbb

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.12.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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