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BUG: KCSAN: data-race in detach_pid / perf_event_switch_output

write to 0xffff888167b7c598 of 8 bytes by task 1767 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_thread kernel/exit.c:1397 [inline]
 do_wait+0x182/0x640 kernel/exit.c:1514
 kernel_wait4+0x13c/0x1a0 kernel/exit.c:1677
 __do_sys_wait4 kernel/exit.c:1705 [inline]
 __se_sys_wait4 kernel/exit.c:1701 [inline]
 __x64_sys_wait4+0x7a/0x100 kernel/exit.c:1701
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888167b7c598 of 8 bytes by task 4728 on cpu 0:
 pid_alive include/linux/sched.h:1471 [inline]
 perf_event_pid_type kernel/events/core.c:1411 [inline]
 perf_event_pid kernel/events/core.c:1418 [inline]
 perf_event_switch_output+0x174/0x330 kernel/events/core.c:8649
 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:4550
 schedule_tail+0x6/0x40 kernel/sched/core.c:4617
 ret_from_fork+0x8/0x30 arch/x86/entry/entry_64.S:280

value changed: 0xffff888167298700 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 4728 Comm: syz-executor.2 Not tainted 5.14.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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