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BUG: KCSAN: data-race in do_exit / exit_signals

write to 0xffff88814ac2806c of 4 bytes by task 16410 on cpu 0:
 exit_signals+0xe1/0x4a0 kernel/signal.c:2910
 do_exit+0x194/0x1560 kernel/exit.c:782
 do_group_exit+0xce/0x1a0 kernel/exit.c:923
 get_signal+0xfc3/0x1610 kernel/signal.c:2818
 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 0xffff88814ac2806c of 4 bytes by task 16413 on cpu 1:
 find_alive_thread kernel/exit.c:512 [inline]
 find_new_reaper kernel/exit.c:561 [inline]
 forget_original_parent kernel/exit.c:636 [inline]
 exit_notify kernel/exit.c:669 [inline]
 do_exit+0x56c/0x1560 kernel/exit.c:846
 do_group_exit+0x19b/0x1a0 kernel/exit.c:923
 get_signal+0xfc3/0x1610 kernel/signal.c:2818
 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
 irqentry_exit_to_user_mode+0x5/0x20 kernel/entry/common.c:314
 irqentry_exit+0xe/0x30 kernel/entry/common.c:405
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:577

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 16413 Comm: syz-executor.2 Not tainted 5.13.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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