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BUG: KCSAN: data-race in detach_pid / perf_event_switch_output

write to 0xffff888167de7598 of 8 bytes by task 1031 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+0x1d1/0x6b0 kernel/exit.c:1515
 kernel_wait4+0x13c/0x1a0 kernel/exit.c:1678
 __do_sys_wait4 kernel/exit.c:1706 [inline]
 __se_sys_wait4 kernel/exit.c:1702 [inline]
 __x64_sys_wait4+0x7a/0x100 kernel/exit.c:1702
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888167de7598 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_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_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 5.13.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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