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BUG: KCSAN: data-race in __ptrace_unlink / ptrace_stop

write to 0xffff88812972706c of 4 bytes by task 11315 on cpu 1:
 freezer_count include/linux/freezer.h:121 [inline]
 freezable_schedule include/linux/freezer.h:173 [inline]
 ptrace_stop+0x3a5/0x670 kernel/signal.c:2268
 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

read to 0xffff88812972706c of 4 bytes by task 11319 on cpu 0:
 __ptrace_unlink+0x187/0x320 kernel/ptrace.c:145
 __ptrace_detach+0x1b/0x1d0 kernel/ptrace.c:539
 exit_ptrace+0x93/0x160 kernel/ptrace.c:599
 forget_original_parent kernel/exit.c:629 [inline]
 exit_notify kernel/exit.c:669 [inline]
 do_exit+0x126d/0x1560 kernel/exit.c:846
 do_group_exit+0xa4/0x1a0 kernel/exit.c:923
 __do_sys_exit_group+0xb/0x10 kernel/exit.c:934
 __se_sys_exit_group+0x5/0x10 kernel/exit.c:932
 __x64_sys_exit_group+0x16/0x20 kernel/exit.c:932
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x40404140 -> 0x00404140

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 11319 Comm: syz-executor.5 Not tainted 5.13.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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