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BUG: KCSAN: data-race in detach_pid / perf_event_switch_output

write to 0xffff88816066a558 of 8 bytes by task 8121 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:199
 wait_task_zombie kernel/exit.c:1107 [inline]
 wait_consider_task+0x10ce/0x19e0 kernel/exit.c:1334
 do_wait_thread kernel/exit.c:1397 [inline]
 do_wait+0x1b1/0x4a0 kernel/exit.c:1468
 kernel_wait+0x4e/0xc0 kernel/exit.c:1647
 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:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff88816066a558 of 8 bytes by task 11475 on cpu 0:
 pid_alive include/linux/sched.h:1442 [inline]
 perf_event_pid_type kernel/events/core.c:1414 [inline]
 perf_event_tid kernel/events/core.c:1426 [inline]
 perf_event_switch_output+0x1fe/0x330 kernel/events/core.c:8530
 perf_iterate_sb_cpu kernel/events/core.c:7443 [inline]
 perf_iterate_sb+0x37d/0x8f0 kernel/events/core.c:7473
 perf_event_switch kernel/events/core.c:8574 [inline]
 __perf_event_task_sched_in+0x3b9/0x4c0 kernel/events/core.c:3864
 perf_event_task_sched_in include/linux/perf_event.h:1210 [inline]
 finish_task_switch+0x1fd/0x290 kernel/sched/core.c:4189
 context_switch kernel/sched/core.c:4325 [inline]
 __schedule+0x427/0x5b0 kernel/sched/core.c:5073
 schedule+0x67/0x90 kernel/sched/core.c:5152
 freezable_schedule include/linux/freezer.h:172 [inline]
 futex_wait_queue_me+0x1a1/0x260 kernel/futex.c:2606
 futex_wait+0x143/0x430 kernel/futex.c:2708
 do_futex+0x9e8/0x1e10 kernel/futex.c:3734
 __do_sys_futex kernel/futex.c:3797 [inline]
 __se_sys_futex+0x2a8/0x390 kernel/futex.c:3763
 __x64_sys_futex+0x74/0x80 kernel/futex.c:3763
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 11475 Comm: syz-executor.4 Not tainted 5.12.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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