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BUG: KCSAN: data-race in do_notify_parent_cldstop / wait_consider_task

write to 0xffff88813afc9508 of 4 bytes by task 2007 on cpu 0:
 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 0xffff88813afc9508 of 4 bytes by task 2005 on cpu 1:
 do_notify_parent_cldstop+0x1a3/0x280 kernel/signal.c:2110
 ptrace_stop+0x2e2/0x670 kernel/signal.c:2254
 ptrace_do_notify kernel/signal.c:2321 [inline]
 ptrace_notify+0x107/0x180 kernel/signal.c:2331
 ptrace_report_syscall include/linux/tracehook.h:66 [inline]
 tracehook_report_syscall_entry include/linux/tracehook.h:105 [inline]
 arch_syscall_enter_tracehook include/linux/entry-common.h:98 [inline]
 syscall_trace_enter+0x87/0x290 kernel/entry/common.c:60
 __syscall_enter_from_user_work kernel/entry/common.c:89 [inline]
 syscall_enter_from_user_mode+0x1c/0x20 kernel/entry/common.c:107
 do_syscall_64+0x27/0x90 arch/x86/entry/common.c:42
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000005 -> 0x00000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 2005 Comm: syz-executor.3 Not tainted 5.13.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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