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BUG: KCSAN: data-race in do_exit / zap_pid_ns_processes

write to 0xffff88812379948c of 4 bytes by task 30473 on cpu 1:
 reparent_leader kernel/exit.c:601 [inline]
 forget_original_parent kernel/exit.c:653 [inline]
 exit_notify kernel/exit.c:669 [inline]
 do_exit+0x981/0x1560 kernel/exit.c:846
 do_group_exit+0xce/0x1a0 kernel/exit.c:923
 get_signal+0xfc3/0x1610 kernel/signal.c:2818
 arch_do_signal_or_restart+0x2a/0x220 arch/x86/kernel/signal.c:789
 handle_signal_work kernel/entry/common.c:147 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:171 [inline]
 exit_to_user_mode_prepare+0x109/0x190 kernel/entry/common.c:208
 __syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:301
 do_syscall_64+0x56/0x90 arch/x86/entry/common.c:57
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88812379948c of 4 bytes by task 30480 on cpu 0:
 thread_group_leader include/linux/sched/signal.h:667 [inline]
 zap_pid_ns_processes+0x39/0x370 kernel/pid_namespace.c:170
 find_child_reaper kernel/exit.c:543 [inline]
 forget_original_parent kernel/exit.c:632 [inline]
 exit_notify kernel/exit.c:669 [inline]
 do_exit+0x13f0/0x1560 kernel/exit.c:846
 do_group_exit+0xce/0x1a0 kernel/exit.c:923
 get_signal+0xfc3/0x1610 kernel/signal.c:2818
 arch_do_signal_or_restart+0x2a/0x220 arch/x86/kernel/signal.c:789
 handle_signal_work kernel/entry/common.c:147 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:171 [inline]
 exit_to_user_mode_prepare+0x109/0x190 kernel/entry/common.c:208
 irqentry_exit_to_user_mode+0x5/0x20 kernel/entry/common.c:314
 irqentry_exit+0xe/0x30 kernel/entry/common.c:405
 exc_general_protection+0x202/0x340 arch/x86/kernel/traps.c:531
 asm_exc_general_protection+0x1e/0x30 arch/x86/include/asm/idtentry.h:571

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 30480 Comm: syz-executor.1 Tainted: G        W         5.12.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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