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BUG: KCSAN: data-race in do_signal_stop / prepare_signal

write to 0xffff888122dbe02c of 4 bytes by task 13690 on cpu 0:
 freezer_count include/linux/freezer.h:121 [inline]
 freezable_schedule include/linux/freezer.h:173 [inline]
 do_signal_stop+0x591/0x710 kernel/signal.c:2432
 get_signal+0xb70/0x1610 kernel/signal.c:2668
 arch_do_signal_or_restart+0x2a/0x220 arch/x86/kernel/signal.c:789
 handle_signal_work kernel/entry/common.c:147 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:171 [inline]
 exit_to_user_mode_prepare+0x109/0x190 kernel/entry/common.c:208
 irqentry_exit_to_user_mode+0x5/0x20 kernel/entry/common.c:314
 irqentry_exit+0xe/0x30 kernel/entry/common.c:405
 asm_sysvec_reschedule_ipi+0x12/0x20 arch/x86/include/asm/idtentry.h:637

read to 0xffff888122dbe02c of 4 bytes by interrupt on cpu 1:
 sig_task_ignored kernel/signal.c:93 [inline]
 sig_ignored kernel/signal.c:118 [inline]
 prepare_signal+0x952/0xeb0 kernel/signal.c:1001
 send_sigqueue+0xea/0x3e0 kernel/signal.c:1897
 posix_timer_event kernel/time/posix-timers.c:354 [inline]
 posix_timer_fn+0xe8/0x210 kernel/time/posix-timers.c:380
 __run_hrtimer+0x160/0x480 kernel/time/hrtimer.c:1537
 __hrtimer_run_queues kernel/time/hrtimer.c:1601 [inline]
 hrtimer_interrupt+0x380/0xaf0 kernel/time/hrtimer.c:1663
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1089 [inline]
 __sysvec_apic_timer_interrupt+0x6f/0x1c0 arch/x86/kernel/apic/apic.c:1106
 sysvec_apic_timer_interrupt+0x64/0x80 arch/x86/kernel/apic/apic.c:1100
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:632
 check_access kernel/kcsan/core.c:634 [inline]
 __tsan_unaligned_write8+0x15f/0x190 kernel/kcsan/core.c:845
 __list_add include/linux/list.h:72 [inline]
 list_add_tail include/linux/list.h:100 [inline]
 plist_add+0x230/0x2c0 lib/plist.c:101
 __queue_me kernel/futex.c:2243 [inline]
 queue_me kernel/futex.c:2262 [inline]
 futex_wait_queue_me+0xe6/0x260 kernel/futex.c:2589
 futex_wait+0x143/0x430 kernel/futex.c:2708
 do_futex+0x9e8/0x1ee0 kernel/futex.c:3733
 __do_sys_futex kernel/futex.c:3796 [inline]
 __se_sys_futex+0x2a8/0x390 kernel/futex.c:3762
 __x64_sys_futex+0x74/0x80 kernel/futex.c:3762
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 13693 Comm: syz-executor.4 Not tainted 5.12.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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