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BUG: KCSAN: data-race in detach_pid / perf_event_switch_output

write to 0xffff88813b0715e0 of 8 bytes by task 8341 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+0x402/0x910 kernel/workqueue.c:2297
 worker_thread+0x636/0xae0 kernel/workqueue.c:2444
 kthread+0x262/0x280 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

read to 0xffff88813b0715e0 of 8 bytes by task 24430 on cpu 0:
 pid_alive include/linux/sched.h:1558 [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:8662
 perf_iterate_sb_cpu kernel/events/core.c:7579 [inline]
 perf_iterate_sb+0x37d/0x8f0 kernel/events/core.c:7609
 perf_event_switch kernel/events/core.c:8709 [inline]
 __perf_event_task_sched_in+0x59d/0x850 kernel/events/core.c:3907
 perf_event_task_sched_in include/linux/perf_event.h:1206 [inline]
 finish_task_switch+0x1fd/0x290 kernel/sched/core.c:4809
 context_switch kernel/sched/core.c:4943 [inline]
 __schedule+0x42c/0x670 kernel/sched/core.c:6287
 schedule+0x67/0x90 kernel/sched/core.c:6366
 exit_to_user_mode_loop kernel/entry/common.c:163 [inline]
 exit_to_user_mode_prepare+0xbb/0x190 kernel/entry/common.c:209
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302
 do_syscall_64+0x49/0x90 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0xffff888101002080 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 24430 Comm: syz-executor.4 Not tainted 5.14.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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