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BUG: KCSAN: data-race in do_exit / get_signal

write to 0xffff88810c587024 of 4 bytes by task 12157 on cpu 1:
 get_signal+0xf5a/0x1650 kernel/signal.c:2723
 arch_do_signal+0x25/0x270 arch/x86/kernel/signal.c:811
 exit_to_user_mode_loop kernel/entry/common.c:135 [inline]
 exit_to_user_mode_prepare+0x12d/0x220 kernel/entry/common.c:166
 syscall_exit_to_user_mode+0x16/0x30 kernel/entry/common.c:241
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88810c587024 of 4 bytes by task 12149 on cpu 0:
 find_alive_thread kernel/exit.c:493 [inline]
 find_new_reaper kernel/exit.c:542 [inline]
 forget_original_parent kernel/exit.c:617 [inline]
 exit_notify kernel/exit.c:650 [inline]
 do_exit+0x7e0/0x16a0 kernel/exit.c:826
 do_group_exit+0xcb/0x180 kernel/exit.c:903
 get_signal+0x106d/0x1650 kernel/signal.c:2743
 arch_do_signal+0x25/0x270 arch/x86/kernel/signal.c:811
 exit_to_user_mode_loop kernel/entry/common.c:135 [inline]
 exit_to_user_mode_prepare+0x12d/0x220 kernel/entry/common.c:166
 irqentry_exit_to_user_mode+0x5/0x20 kernel/entry/common.c:254
 irqentry_exit+0xe/0x40 kernel/entry/common.c:342
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:538

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 12149 Comm: syz-executor.5 Not tainted 5.8.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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