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BUG: KCSAN: data-race in do_exit / exit_signals

write to 0xffff88811e21e0a4 of 4 bytes by task 4823 on cpu 1:
 exit_signals+0x124/0x580 kernel/signal.c:2831
 do_exit+0x19f/0x16e0 kernel/exit.c:761
 do_group_exit+0x17a/0x180 kernel/exit.c:903
 __do_sys_exit_group+0xb/0x10 kernel/exit.c:914
 __se_sys_exit_group+0x5/0x10 kernel/exit.c:912
 __x64_sys_exit_group+0x16/0x20 kernel/exit.c:912
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88811e21e0a4 of 4 bytes by task 4826 on cpu 0:
 find_alive_thread kernel/exit.c:492 [inline]
 find_new_reaper kernel/exit.c:541 [inline]
 forget_original_parent kernel/exit.c:616 [inline]
 exit_notify kernel/exit.c:649 [inline]
 do_exit+0x810/0x16e0 kernel/exit.c:826
 do_group_exit+0xcb/0x180 kernel/exit.c:903
 get_signal+0x106d/0x1650 kernel/signal.c:2743
 do_signal+0x25/0x270 arch/x86/kernel/signal.c:810
 exit_to_usermode_loop arch/x86/entry/common.c:235 [inline]
 __prepare_exit_to_usermode+0x127/0x230 arch/x86/entry/common.c:269
 __syscall_return_slowpath+0x47/0x60 arch/x86/entry/common.c:352
 do_syscall_64+0x5d/0xb0 arch/x86/entry/common.c:393
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 4826 Comm: syz-executor.1 Not tainted 5.8.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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