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BUG: KCSAN: data-race in do_notify_parent_cldstop / wait_consider_task

write to 0xffff88812f1674c8 of 4 bytes by task 7984 on cpu 1:
 wait_task_stopped kernel/exit.c:1186 [inline]
 wait_consider_task+0xb84/0x19e0 kernel/exit.c:1372
 ptrace_do_wait kernel/exit.c:1412 [inline]
 do_wait+0x244/0x6b0 kernel/exit.c:1519
 kernel_wait4+0x13c/0x1a0 kernel/exit.c:1678
 __do_sys_wait4 kernel/exit.c:1706 [inline]
 __se_sys_wait4 kernel/exit.c:1702 [inline]
 __x64_sys_wait4+0x7a/0x100 kernel/exit.c:1702
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88812f1674c8 of 4 bytes by task 7980 on cpu 0:
 do_notify_parent_cldstop+0x1a3/0x280 kernel/signal.c:2110
 ptrace_stop+0x2e2/0x670 kernel/signal.c:2254
 ptrace_signal kernel/signal.c:2543 [inline]
 get_signal+0xbf2/0x1610 kernel/signal.c:2723
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7980 Comm: syz-executor.2 Not tainted 5.13.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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