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BUG: KCSAN: data-race in complete_signal / exit_signals

write to 0xffff888095edc064 of 4 bytes by task 24474 on cpu 0:
 exit_signals+0x124/0x580 kernel/signal.c:2831
 do_exit+0x19f/0x16e0 kernel/exit.c:761
 do_group_exit+0x17a/0x180 kernel/exit.c:903
 __do_sys_exit_group+0xb/0x10 kernel/exit.c:914
 __se_sys_exit_group+0x5/0x10 kernel/exit.c:912
 __x64_sys_exit_group+0x16/0x20 kernel/exit.c:912
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888095edc064 of 4 bytes by interrupt on cpu 1:
 wants_signal kernel/signal.c:977 [inline]
 complete_signal+0x7c/0x600 kernel/signal.c:1000
 send_sigqueue+0x261/0x450 kernel/signal.c:1880
 posix_timer_event kernel/time/posix-timers.c:354 [inline]
 posix_timer_fn+0xe8/0x210 kernel/time/posix-timers.c:380
 __run_hrtimer+0x154/0x4b0 kernel/time/hrtimer.c:1520
 __hrtimer_run_queues kernel/time/hrtimer.c:1584 [inline]
 hrtimer_interrupt+0x37c/0xa40 kernel/time/hrtimer.c:1646
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1080 [inline]
 __sysvec_apic_timer_interrupt+0xa3/0x280 arch/x86/kernel/apic/apic.c:1097
 asm_call_on_stack+0xf/0x20 arch/x86/entry/entry_64.S:711
 __run_on_irqstack arch/x86/include/asm/irq_stack.h:22 [inline]
 run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:48 [inline]
 sysvec_apic_timer_interrupt+0x80/0xd0 arch/x86/kernel/apic/apic.c:1091
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:587
 __sanitizer_cov_trace_pc+0x3f/0x60 kernel/kcov.c:200
 plist_add+0x8a/0x2c0 lib/plist.c:80
 __queue_me kernel/futex.c:2275 [inline]
 queue_me kernel/futex.c:2294 [inline]
 futex_wait_queue_me+0xf4/0x250 kernel/futex.c:2617
 futex_wait+0x145/0x390 kernel/futex.c:2740
 do_futex+0x144a/0x21c0 kernel/futex.c:3811
 __do_sys_futex kernel/futex.c:3872 [inline]
 __se_sys_futex+0x26d/0x330 kernel/futex.c:3840
 __x64_sys_futex+0x74/0x80 kernel/futex.c:3840
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 24475 Comm: syz-executor.5 Not tainted 5.8.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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