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BUG: KCSAN: data-race in get_signal / prepare_signal

read to 0xffff88812115b064 of 4 bytes by task 27515 on cpu 0:
 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
 __group_send_sig_info kernel/signal.c:1275 [inline]
 do_notify_parent_cldstop+0x363/0x370 kernel/signal.c:2062
 ptrace_stop+0x1ba/0x520 kernel/signal.c:2196
 ptrace_do_notify+0xed/0x120 kernel/signal.c:2263
 ptrace_notify+0x93/0xd0 kernel/signal.c:2273
 ptrace_report_syscall include/linux/tracehook.h:66 [inline]
 tracehook_report_syscall_exit include/linux/tracehook.h:129 [inline]
 syscall_slow_exit_work+0x144/0x320 arch/x86/entry/common.c:250
 syscall_return_slowpath arch/x86/entry/common.c:275 [inline]
 do_syscall_64+0x359/0x3a0 arch/x86/entry/common.c:304
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff88812115b064 of 4 bytes by task 27517 on cpu 1:
 get_signal+0x7c7/0x1320 kernel/signal.c:2714
 do_signal+0x2f/0x6c0 arch/x86/kernel/signal.c:815
 exit_to_usermode_loop+0x250/0x2c0 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+0x384/0x3a0 arch/x86/entry/common.c:304
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 27517 Comm: syz-executor.2 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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