syzbot

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BUG: KCSAN: data-race in detach_pid / proc_pid_status

write to 0xffff88812d5bd5b8 of 8 bytes by task 4893 on cpu 1:
 __change_pid kernel/pid.c:347 [inline]
 detach_pid+0xd7/0x160 kernel/pid.c:358
 __unhash_process kernel/exit.c:74 [inline]
 __exit_signal kernel/exit.c:147 [inline]
 release_task+0x610/0xd30 kernel/exit.c:198
 wait_task_zombie kernel/exit.c:1105 [inline]
 wait_consider_task+0xf89/0x1820 kernel/exit.c:1332
 do_wait_thread kernel/exit.c:1395 [inline]
 do_wait+0x1b1/0x4e0 kernel/exit.c:1466
 kernel_wait4+0x13c/0x1a0 kernel/exit.c:1628
 __do_sys_wait4 kernel/exit.c:1656 [inline]
 __se_sys_wait4 kernel/exit.c:1652 [inline]
 __x64_sys_wait4+0x7a/0x100 kernel/exit.c:1652
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812d5bd5b8 of 8 bytes by task 4877 on cpu 0:
 pid_alive include/linux/sched.h:1439 [inline]
 task_state fs/proc/array.c:164 [inline]
 proc_pid_status+0xb1/0x13e0 fs/proc/array.c:443
 proc_single_show+0x84/0x100 fs/proc/base.c:775
 seq_read_iter+0x2d8/0x8e0 fs/seq_file.c:227
 seq_read+0x221/0x260 fs/seq_file.c:159
 vfs_read+0x154/0x5c0 fs/read_write.c:494
 ksys_read+0xce/0x180 fs/read_write.c:634
 __do_sys_read fs/read_write.c:644 [inline]
 __se_sys_read fs/read_write.c:642 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:642
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 4877 Comm: systemd-journal Not tainted 5.11.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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