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BUG: KCSAN: data-race in do_exit / get_signal

write to 0xffff88804f03602c of 4 bytes by task 23836 on cpu 0:
 get_signal+0xeaa/0x1510 kernel/signal.c:2753
 arch_do_signal_or_restart+0x2a/0x270 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+0x11a/0x1b0 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+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88804f03602c of 4 bytes by task 23848 on cpu 1:
 find_alive_thread kernel/exit.c:511 [inline]
 find_new_reaper kernel/exit.c:560 [inline]
 forget_original_parent kernel/exit.c:635 [inline]
 exit_notify kernel/exit.c:668 [inline]
 do_exit+0x570/0x15e0 kernel/exit.c:845
 do_group_exit+0xce/0x180 kernel/exit.c:922
 get_signal+0xf93/0x1510 kernel/signal.c:2781
 arch_do_signal_or_restart+0x2a/0x270 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+0x11a/0x1b0 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+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 23848 Comm: syz-executor.5 Tainted: G        W         5.12.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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