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BUG: KCSAN: data-race in do_signal_stop / prepare_signal

write to 0xffff88810a9d402c of 4 bytes by task 20838 on cpu 0:
 freezer_count include/linux/freezer.h:121 [inline]
 freezable_schedule include/linux/freezer.h:173 [inline]
 do_signal_stop+0x562/0x6d0 kernel/signal.c:2396
 get_signal+0x9ed/0x1510 kernel/signal.c:2733
 arch_do_signal_or_restart+0x2a/0x270 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+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 0xffff88810a9d402c 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+0x891/0xdb0 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+0x59/0x60 kernel/kcov.c:205
 copy_pte_range+0x82b/0x1ba0 mm/memory.c:992
 copy_pmd_range mm/memory.c:1064 [inline]
 copy_pud_range mm/memory.c:1101 [inline]
 copy_p4d_range mm/memory.c:1125 [inline]
 copy_page_range+0x85e/0xb70 mm/memory.c:1198
 dup_mmap+0x77b/0xaa0 kernel/fork.c:594
 dup_mm+0x7c/0x210 kernel/fork.c:1368
 copy_mm kernel/fork.c:1424 [inline]
 copy_process+0x12da/0x2e60 kernel/fork.c:2113
 kernel_clone+0x14b/0x690 kernel/fork.c:2500
 __do_sys_clone kernel/fork.c:2617 [inline]
 __se_sys_clone kernel/fork.c:2601 [inline]
 __x64_sys_clone+0xb4/0xe0 kernel/fork.c:2601
 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: 1 PID: 16452 Comm: syz-executor.0 Tainted: G        W         5.12.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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