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BUG: KCSAN: data-race in exit_signals / prepare_signal

read to 0xffff8880a6dab024 of 4 bytes by task 7663 on cpu 1:
 sig_task_ignored kernel/signal.c:94 [inline]
 sig_ignored kernel/signal.c:119 [inline]
 prepare_signal+0x1f5/0x7a0 kernel/signal.c:956
 __send_signal+0x96/0x870 kernel/signal.c:1076
 send_signal+0x224/0x2b0 kernel/signal.c:1236
 do_send_sig_info+0x5f/0xc0 kernel/signal.c:1285
 group_send_sig_info kernel/signal.c:1408 [inline]
 group_send_sig_info+0x91/0xa0 kernel/signal.c:1398
 kill_pid_info+0x51/0xa0 kernel/signal.c:1442
 kill_something_info+0x242/0x2a0 kernel/signal.c:1557
 __do_sys_kill kernel/signal.c:3640 [inline]
 __se_sys_kill kernel/signal.c:3634 [inline]
 __x64_sys_kill+0xf1/0x120 kernel/signal.c:3634
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff8880a6dab024 of 4 bytes by task 24780 on cpu 0:
 exit_signals+0x13b/0x490 kernel/signal.c:2822
 do_exit+0x18b/0x18f0 kernel/exit.c:763
 do_group_exit+0xb4/0x1c0 kernel/exit.c:921
 get_signal+0x2a2/0x1320 kernel/signal.c:2734
 do_signal+0x2f/0x6c0 arch/x86/kernel/signal.c:815
 exit_to_usermode_loop+0x250/0x2c0 arch/x86/entry/common.c:159
 prepare_exit_to_usermode+0x180/0x1a0 arch/x86/entry/common.c:194
 swapgs_restore_regs_and_return_to_usermode+0x0/0x40

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 24780 Comm: syz-executor.2 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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