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BUG: KCSAN: data-race in free_pid / zap_pid_ns_processes

read-write to 0xffff88811257b5c8 of 4 bytes by task 10493 on cpu 1:
 free_pid+0x80/0x170 kernel/pid.c:143
 __change_pid+0x19a/0x1c0 kernel/pid.c:367
 detach_pid+0x1c/0x30 kernel/pid.c:372
 __unhash_process kernel/exit.c:133 [inline]
 __exit_signal kernel/exit.c:202 [inline]
 release_task+0x6e7/0xc30 kernel/exit.c:259
 exit_notify kernel/exit.c:774 [inline]
 do_exit+0xf7d/0x1740 kernel/exit.c:898
 do_group_exit+0x102/0x150 kernel/exit.c:1027
 get_signal+0xf2f/0x1080 kernel/signal.c:2911
 arch_do_signal_or_restart+0x95/0x4b0 arch/x86/kernel/signal.c:310
 exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
 syscall_exit_to_user_mode+0x59/0x130 kernel/entry/common.c:218
 do_syscall_64+0xe2/0x1d0 arch/x86/entry/common.c:89
 entry_SYSCALL_64_after_hwframe+0x72/0x7a

read to 0xffff88811257b5c8 of 4 bytes by task 10223 on cpu 0:
 zap_pid_ns_processes+0x1ec/0x2c0 kernel/pid_namespace.c:249
 find_child_reaper kernel/exit.c:610 [inline]
 forget_original_parent kernel/exit.c:699 [inline]
 exit_notify kernel/exit.c:736 [inline]
 do_exit+0x14b4/0x1740 kernel/exit.c:898
 do_group_exit+0x102/0x150 kernel/exit.c:1027
 get_signal+0xf2f/0x1080 kernel/signal.c:2911
 arch_do_signal_or_restart+0x95/0x4b0 arch/x86/kernel/signal.c:310
 exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
 syscall_exit_to_user_mode+0x59/0x130 kernel/entry/common.c:218
 do_syscall_64+0xe2/0x1d0 arch/x86/entry/common.c:89
 entry_SYSCALL_64_after_hwframe+0x72/0x7a

value changed: 0x00000002 -> 0x00000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 10223 Comm: syz-executor.4 Tainted: G        W          6.9.0-rc3-syzkaller-00011-g20cb38a7af88 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
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