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BUG: KCSAN: data-race in do_notify_parent_cldstop / wait_consider_task

write to 0xffff88804245f4f0 of 4 bytes by task 18425 on cpu 1:
 wait_task_stopped kernel/exit.c:1185 [inline]
 wait_consider_task+0xb62/0x18e0 kernel/exit.c:1371
 ptrace_do_wait kernel/exit.c:1411 [inline]
 do_wait+0x224/0x4e0 kernel/exit.c:1472
 kernel_wait4+0x13c/0x1a0 kernel/exit.c:1630
 __do_sys_wait4 kernel/exit.c:1658 [inline]
 __se_sys_wait4 kernel/exit.c:1654 [inline]
 __x64_sys_wait4+0x7a/0x100 kernel/exit.c:1654
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88804245f4f0 of 4 bytes by task 18423 on cpu 0:
 do_notify_parent_cldstop+0x1b7/0x290 kernel/signal.c:2058
 ptrace_stop+0x2be/0x650 kernel/signal.c:2202
 ptrace_signal kernel/signal.c:2491 [inline]
 get_signal+0x80a/0x14e0 kernel/signal.c:2669
 arch_do_signal_or_restart+0x2a/0x270 arch/x86/kernel/signal.c:811
 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+0x11a/0x1b0 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+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 18423 Comm: syz-executor.1 Not tainted 5.12.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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