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BUG: KCSAN: data-race in do_notify_parent_cldstop / wait_consider_task

write to 0xffff888133085488 of 4 bytes by task 936 on cpu 1:
 wait_task_stopped kernel/exit.c:1185 [inline]
 wait_consider_task+0xb7d/0x19e0 kernel/exit.c:1371
 do_wait_pid kernel/exit.c:1465 [inline]
 do_wait+0x355/0x640 kernel/exit.c:1507
 kernel_wait4+0x13c/0x1a0 kernel/exit.c:1677
 __do_sys_wait4 kernel/exit.c:1705 [inline]
 __se_sys_wait4 kernel/exit.c:1701 [inline]
 __x64_sys_wait4+0x7a/0x100 kernel/exit.c:1701
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888133085488 of 4 bytes by task 937 on cpu 0:
 do_notify_parent_cldstop+0x1a3/0x280 kernel/signal.c:2083
 ptrace_stop+0x2e2/0x670 kernel/signal.c:2227
 ptrace_signal kernel/signal.c:2516 [inline]
 get_signal+0xbcc/0x15e0 kernel/signal.c:2696
 arch_do_signal_or_restart+0x2a/0x220 arch/x86/kernel/signal.c:865
 handle_signal_work kernel/entry/common.c:148 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
 exit_to_user_mode_prepare+0x109/0x190 kernel/entry/common.c:209
 irqentry_exit_to_user_mode+0x5/0x10 kernel/entry/common.c:315
 irqentry_exit+0xe/0x30 kernel/entry/common.c:406
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:568

value changed: 0x00000013 -> 0x00000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 937 Comm: syz-executor.4 Not tainted 5.14.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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