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BUG: KCSAN: data-race in do_signal_stop / prepare_signal

write to 0xffff888037e6402c of 4 bytes by task 20679 on cpu 1:
 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:208
 __syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:301
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888037e6402c of 4 bytes by interrupt on cpu 0:
 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: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/0x200 arch/x86/kernel/apic/apic.c:1106
 sysvec_apic_timer_interrupt+0x69/0x80 arch/x86/kernel/apic/apic.c:1100
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:632
 __sanitizer_cov_trace_pc+0x56/0x60 kernel/kcov.c:204
 xas_load+0x328/0x360 lib/xarray.c:241
 mapping_get_entry+0x83/0x350 mm/filemap.c:1683
 pagecache_get_page+0x34/0xa30 mm/filemap.c:1751
 find_get_page_flags include/linux/pagemap.h:342 [inline]
 __find_get_block_slow+0x61/0x3b0 fs/buffer.c:202
 __find_get_block+0x14d/0x640 fs/buffer.c:1328
 sb_find_get_block include/linux/buffer_head.h:338 [inline]
 recently_deleted fs/ext4/ialloc.c:686 [inline]
 find_inode_bit+0x1b8/0x3a0 fs/ext4/ialloc.c:728
 __ext4_new_inode+0xb6c/0x2fe0 fs/ext4/ialloc.c:1063
 ext4_mkdir+0x28a/0x760 fs/ext4/namei.c:2804
 vfs_mkdir+0x135/0x1f0 fs/namei.c:3817
 do_mkdirat+0x147/0x230 fs/namei.c:3842
 __do_sys_mkdir fs/namei.c:3860 [inline]
 __se_sys_mkdir fs/namei.c:3858 [inline]
 __x64_sys_mkdir+0x32/0x40 fs/namei.c:3858
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 20688 Comm: syz-executor.4 Tainted: G        W         5.12.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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