syzbot

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BUG: KCSAN: data-race in __change_pid / __task_pid_nr_ns

write to 0xffff8880af792540 of 8 bytes by task 8157 on cpu 1:
 __change_pid+0x10d/0x1e0 kernel/pid.c:299
 detach_pid+0x29/0x40 kernel/pid.c:310
 __unhash_process kernel/exit.c:75 [inline]
 __exit_signal kernel/exit.c:157 [inline]
 release_task+0x760/0xc60 kernel/exit.c:207
 wait_task_zombie kernel/exit.c:1106 [inline]
 wait_consider_task+0x190e/0x1a10 kernel/exit.c:1333
 do_wait_thread kernel/exit.c:1396 [inline]
 do_wait+0x1c9/0x4c0 kernel/exit.c:1467
 kernel_wait4+0x156/0x240 kernel/exit.c:1639
 __do_sys_wait4+0xea/0x100 kernel/exit.c:1651
 __se_sys_wait4 kernel/exit.c:1647 [inline]
 __x64_sys_wait4+0x5e/0x80 kernel/exit.c:1647
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880af792540 of 8 bytes by task 8165 on cpu 0:
 pid_alive include/linux/sched.h:1341 [inline]
 __task_pid_nr_ns+0x57/0x1e0 kernel/pid.c:433
 task_tgid_nr_ns include/linux/sched.h:1367 [inline]
 task_state fs/proc/array.c:215 [inline]
 proc_pid_status+0x5f7/0x1000 fs/proc/array.c:413
 proc_single_show+0x89/0xe0 fs/proc/base.c:756
 seq_read+0x350/0x960 fs/seq_file.c:229
 __vfs_read+0x67/0xc0 fs/read_write.c:425
 vfs_read fs/read_write.c:461 [inline]
 vfs_read+0x143/0x2c0 fs/read_write.c:446
 ksys_read+0xd5/0x1b0 fs/read_write.c:587
 __do_sys_read fs/read_write.c:597 [inline]
 __se_sys_read fs/read_write.c:595 [inline]
 __x64_sys_read+0x4c/0x60 fs/read_write.c:595
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8165 Comm: ps Not tainted 5.4.0-rc6+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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