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BUG: KCSAN: data-race in do_signal_stop / prepare_signal

write to 0xffff888100cba0ac of 4 bytes by task 4668 on cpu 1:
 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+0xa16/0x1610 kernel/signal.c:2770
 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
 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:647

read to 0xffff888100cba0ac 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
 _raw_spin_unlock_irqrestore+0x34/0x40 kernel/locking/spinlock.c:192
 spin_unlock_irqrestore include/linux/spinlock.h:409 [inline]
 delete_from_page_cache_batch+0x56b/0x690 mm/filemap.c:350
 truncate_inode_pages_range+0x1a5/0xa80 mm/truncate.c:329
 truncate_inode_pages mm/truncate.c:427 [inline]
 truncate_inode_pages_final+0x6a/0x80 mm/truncate.c:466
 ext4_evict_inode+0x2b7/0xdb0 fs/ext4/inode.c:223
 evict+0x1c8/0x3c0 fs/inode.c:584
 iput_final fs/inode.c:1660 [inline]
 iput+0x433/0x590 fs/inode.c:1686
 do_unlinkat+0x293/0x4f0 fs/namei.c:4099
 __do_sys_unlink fs/namei.c:4139 [inline]
 __se_sys_unlink fs/namei.c:4137 [inline]
 __x64_sys_unlink+0x2c/0x30 fs/namei.c:4137
 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: 1745 Comm: syz-executor.0 Not tainted 5.13.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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hrtimer: interrupt took 15482 ns