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BUG: KCSAN: data-race in exit_signals / prepare_signal

write to 0xffff88808e8c10e4 of 4 bytes by task 16502 on cpu 0:
 exit_signals+0x130/0x460 kernel/signal.c:2822
 do_exit+0x17b/0x1880 kernel/exit.c:750
 do_group_exit+0xae/0x1a0 kernel/exit.c:899
 get_signal+0x2a7/0x1290 kernel/signal.c:2734
 do_signal+0x2b/0x670 arch/x86/kernel/signal.c:813
 exit_to_usermode_loop+0x24a/0x2c0 arch/x86/entry/common.c:160
 prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
 do_syscall_64+0x36e/0x390 arch/x86/entry/common.c:304
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88808e8c10e4 of 4 bytes by task 7765 on cpu 1:
 sig_task_ignored kernel/signal.c:94 [inline]
 sig_ignored kernel/signal.c:119 [inline]
 prepare_signal+0x1f0/0x770 kernel/signal.c:956
 __send_signal+0x95/0x8a0 kernel/signal.c:1076
 send_signal+0x211/0x2a0 kernel/signal.c:1236
 do_send_sig_info+0x59/0xc0 kernel/signal.c:1285
 group_send_sig_info kernel/signal.c:1408 [inline]
 group_send_sig_info+0x8a/0x90 kernel/signal.c:1398
 kill_pid_info+0x4d/0x90 kernel/signal.c:1442
 kill_something_info+0x238/0x290 kernel/signal.c:1557
 __do_sys_kill kernel/signal.c:3640 [inline]
 __se_sys_kill kernel/signal.c:3634 [inline]
 __x64_sys_kill+0xef/0x120 kernel/signal.c:3634
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 7765 Comm: syz-executor.1 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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