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BUG: KCSAN: data-race in do_group_exit / do_group_exit

write to 0xffff88807dbe7774 of 4 bytes by task 14610 on cpu 1:
 do_group_exit+0x137/0x180 kernel/exit.c:897
 __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+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88807dbe7774 of 4 bytes by task 14615 on cpu 0:
 signal_group_exit include/linux/sched/signal.h:268 [inline]
 do_group_exit+0x55/0x180 kernel/exit.c:886
 __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+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 14615 Comm: syz-executor.3 Not tainted 5.9.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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