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BUG: KCSAN: data-race in do_notify_parent_cldstop / do_signal_stop

write to 0xffff888100b1e0e0 of 4 bytes by task 10668 on cpu 1:
 do_signal_stop+0xfb/0x700 kernel/signal.c:2353
 get_signal+0xa29/0x15e0 kernel/signal.c:2748
 arch_do_signal_or_restart+0x2a/0x220 arch/x86/kernel/signal.c:789
 handle_signal_work kernel/entry/common.c:148 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
 exit_to_user_mode_prepare+0x109/0x190 kernel/entry/common.c:209
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302
 do_syscall_64+0x50/0x80 arch/x86/entry/common.c:57
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888100b1e0e0 of 4 bytes by task 10667 on cpu 0:
 do_notify_parent_cldstop+0x192/0x280 kernel/signal.c:2068
 get_signal+0x418/0x15e0 kernel/signal.c:2622
 arch_do_signal_or_restart+0x2a/0x220 arch/x86/kernel/signal.c:789
 handle_signal_work kernel/entry/common.c:148 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
 exit_to_user_mode_prepare+0x109/0x190 kernel/entry/common.c:209
 irqentry_exit_to_user_mode+0x5/0x10 kernel/entry/common.c:315
 irqentry_exit+0xe/0x30 kernel/entry/common.c:406
 sysvec_apic_timer_interrupt+0x3e/0x80 arch/x86/kernel/apic/apic.c:1100
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:638

value changed: 0x00000000 -> 0x00000016

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 10667 Comm: syz-executor.3 Not tainted 5.13.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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