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BUG: KCSAN: data-race in exit_signals / prepare_signal

write to 0xffff8880b23550a4 of 4 bytes by task 13448 on cpu 1:
 exit_signals+0x135/0x4c0 kernel/signal.c:2827
 do_exit+0x17b/0x11e0 kernel/exit.c:744
 do_group_exit+0xae/0x1a0 kernel/exit.c:893
 get_signal+0x2a7/0x1290 kernel/signal.c:2739
 do_signal+0x2b/0x840 arch/x86/kernel/signal.c:784
 exit_to_usermode_loop+0x24a/0x2c0 arch/x86/entry/common.c:161
 prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
 do_syscall_64+0x38b/0x3b0 arch/x86/entry/common.c:305
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880b23550a4 of 4 bytes by task 9084 on cpu 0:
 sig_task_ignored kernel/signal.c:94 [inline]
 sig_ignored kernel/signal.c:119 [inline]
 prepare_signal+0x1f0/0x770 kernel/signal.c:961
 __send_signal+0x95/0x8a0 kernel/signal.c:1081
 send_signal+0x211/0x2a0 kernel/signal.c:1241
 do_send_sig_info+0x59/0xc0 kernel/signal.c:1290
 group_send_sig_info kernel/signal.c:1413 [inline]
 group_send_sig_info+0x8a/0x90 kernel/signal.c:1403
 kill_pid_info+0x4d/0x90 kernel/signal.c:1447
 kill_something_info+0x238/0x290 kernel/signal.c:1562
 __do_sys_kill kernel/signal.c:3645 [inline]
 __se_sys_kill kernel/signal.c:3639 [inline]
 __x64_sys_kill+0xef/0x120 kernel/signal.c:3639
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 9084 Comm: syz-executor.1 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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