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BUG: KCSAN: data-race in do_signal_stop / prepare_signal

write to 0xffff88801551402c of 4 bytes by task 13505 on cpu 0:
 freezer_count include/linux/freezer.h:121 [inline]
 freezable_schedule include/linux/freezer.h:173 [inline]
 do_signal_stop+0x56f/0x6e0 kernel/signal.c:2396
 get_signal+0x65d/0x14e0 kernel/signal.c:2733
 arch_do_signal_or_restart+0x2a/0x270 arch/x86/kernel/signal.c:811
 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+0x11a/0x1b0 kernel/entry/common.c:201
 __syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:294
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88801551402c of 4 bytes by interrupt on cpu 1:
 sig_task_ignored kernel/signal.c:94 [inline]
 sig_ignored kernel/signal.c:119 [inline]
 prepare_signal+0x872/0xd80 kernel/signal.c:962
 send_sigqueue+0xea/0x430 kernel/signal.c:1861
 posix_timer_event kernel/time/posix-timers.c:354 [inline]
 posix_timer_fn+0xe8/0x210 kernel/time/posix-timers.c:380
 __run_hrtimer+0x163/0x460 kernel/time/hrtimer.c:1519
 __hrtimer_run_queues kernel/time/hrtimer.c:1583 [inline]
 hrtimer_interrupt+0x36e/0xa30 kernel/time/hrtimer.c:1645
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1089 [inline]
 __sysvec_apic_timer_interrupt+0x6f/0x200 arch/x86/kernel/apic/apic.c:1106
 asm_call_irq_on_stack+0xf/0x20
 __run_sysvec_on_irqstack arch/x86/include/asm/irq_stack.h:37 [inline]
 run_sysvec_on_irqstack_cond arch/x86/include/asm/irq_stack.h:89 [inline]
 sysvec_apic_timer_interrupt+0x52/0x90 arch/x86/kernel/apic/apic.c:1100
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:629
 __tsan_read8+0xa/0x180 kernel/kcsan/core.c:842
 jbd2_handle_buffer_credits include/linux/jbd2.h:1775 [inline]
 jbd2_journal_dirty_metadata+0x27c/0x670 fs/jbd2/transaction.c:1512
 __ext4_handle_dirty_metadata+0xc1/0x5a0 fs/ext4/ext4_jbd2.c:331
 ext4_do_update_inode fs/ext4/inode.c:5144 [inline]
 ext4_mark_iloc_dirty+0x12f2/0x16f0 fs/ext4/inode.c:5725
 __ext4_mark_inode_dirty+0x4d6/0x5e0 fs/ext4/inode.c:5919
 ext4_evict_inode+0x99c/0xef0 fs/ext4/inode.c:280
 evict+0x1aa/0x410 fs/inode.c:577
 iput_final fs/inode.c:1653 [inline]
 iput+0x3fd/0x520 fs/inode.c:1679
 do_unlinkat+0x2c9/0x4d0 fs/namei.c:3905
 __do_sys_unlink fs/namei.c:3945 [inline]
 __se_sys_unlink fs/namei.c:3943 [inline]
 __x64_sys_unlink+0x2c/0x30 fs/namei.c:3943
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8404 Comm: syz-executor.0 Not tainted 5.11.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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