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BUG: KCSAN: data-race in do_exit / ptrace_stop

read-write to 0xffff888028adb024 of 4 bytes by task 12454 on cpu 0:
 freezer_count include/linux/freezer.h:121 [inline]
 freezable_schedule include/linux/freezer.h:173 [inline]
 ptrace_stop+0x36e/0x620 kernel/signal.c:2216
 ptrace_signal kernel/signal.c:2491 [inline]
 get_signal+0xbed/0x1510 kernel/signal.c:2654
 arch_do_signal+0x25/0x260 arch/x86/kernel/signal.c:811
 exit_to_user_mode_loop kernel/entry/common.c:161 [inline]
 exit_to_user_mode_prepare+0xde/0x170 kernel/entry/common.c:191
 irqentry_exit_to_user_mode+0x5/0x20 kernel/entry/common.c:279
 irqentry_exit+0xe/0x40 kernel/entry/common.c:367
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:583

read to 0xffff888028adb024 of 4 bytes by task 12461 on cpu 1:
 find_alive_thread kernel/exit.c:496 [inline]
 find_new_reaper kernel/exit.c:545 [inline]
 forget_original_parent kernel/exit.c:620 [inline]
 exit_notify kernel/exit.c:653 [inline]
 do_exit+0x53c/0x1630 kernel/exit.c:829
 do_group_exit+0xc8/0x170 kernel/exit.c:906
 get_signal+0xf9b/0x1510 kernel/signal.c:2758
 arch_do_signal+0x25/0x260 arch/x86/kernel/signal.c:811
 exit_to_user_mode_loop kernel/entry/common.c:161 [inline]
 exit_to_user_mode_prepare+0xde/0x170 kernel/entry/common.c:191
 syscall_exit_to_user_mode+0x16/0x30 kernel/entry/common.c:266
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 12461 Comm: syz-executor.5 Not tainted 5.10.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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