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BUG: KCSAN: data-race in do_nanosleep / prepare_signal

write to 0xffff8881278cc06c of 4 bytes by task 11443 on cpu 1:
 freezer_count include/linux/freezer.h:121 [inline]
 freezable_schedule include/linux/freezer.h:173 [inline]
 do_nanosleep+0x121/0x3d0 kernel/time/hrtimer.c:1896
 hrtimer_nanosleep_restart+0x57/0x80 kernel/time/hrtimer.c:1930
 __do_sys_restart_syscall+0x2d/0x40 kernel/signal.c:2958
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8881278cc06c of 4 bytes by interrupt on cpu 0:
 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:647
 __sanitizer_cov_trace_pc+0x56/0x60 kernel/kcov.c:204
 futex_wait_setup+0x31a/0x390 kernel/futex.c:2675
 futex_wait+0x11d/0x430 kernel/futex.c:2703
 do_futex+0x9d8/0x1ee0 kernel/futex.c:3732
 __do_sys_futex kernel/futex.c:3805 [inline]
 __se_sys_futex+0x21c/0x380 kernel/futex.c:3786
 __x64_sys_futex+0x74/0x80 kernel/futex.c:3786
 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: 0 PID: 11458 Comm: syz-executor.3 Not tainted 5.13.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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