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BUG: KCSAN: data-race in do_notify_parent_cldstop / prepare_signal

write to 0xffff8881011b25e0 of 4 bytes by interrupt on cpu 0:
 prepare_signal+0xcf6/0xd80 kernel/signal.c:958
 send_sigqueue+0xe7/0x400 kernel/signal.c:1861
 posix_timer_event kernel/time/posix-timers.c:354 [inline]
 posix_timer_fn+0xdd/0x1f0 kernel/time/posix-timers.c:380
 __run_hrtimer+0x133/0x420 kernel/time/hrtimer.c:1519
 __hrtimer_run_queues kernel/time/hrtimer.c:1583 [inline]
 hrtimer_interrupt+0x36e/0xa10 kernel/time/hrtimer.c:1645
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1085 [inline]
 __sysvec_apic_timer_interrupt+0x6f/0x200 arch/x86/kernel/apic/apic.c:1102
 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:1096
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:628
 __ffs arch/x86/include/asm/bitops.h:235 [inline]
 _find_next_bit lib/find_bit.c:68 [inline]
 find_next_bit+0xb2/0xf0 lib/find_bit.c:79
 cpumask_next+0x1e/0x30 lib/cpumask.c:23
 srcu_readers_lock_idx kernel/rcu/srcutree.c:254 [inline]
 srcu_readers_active_idx_check kernel/rcu/srcutree.c:323 [inline]
 try_check_zero+0xfe/0x1f0 kernel/rcu/srcutree.c:703
 srcu_advance_state kernel/rcu/srcutree.c:1147 [inline]
 process_srcu+0x13d/0x770 kernel/rcu/srcutree.c:1242
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2272
 worker_thread+0x635/0xb90 kernel/workqueue.c:2418
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff8881011b25e0 of 4 bytes by task 18081 on cpu 1:
 do_notify_parent_cldstop+0x1a1/0x290 kernel/signal.c:2055
 do_signal_stop+0x502/0x6b0 kernel/signal.c:2390
 get_signal+0xb7c/0x1510 kernel/signal.c:2650
 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+0x109/0x1a0 kernel/entry/common.c:201
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302
 ret_from_fork+0x15/0x30 arch/x86/entry/entry_64.S:289

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 18081 Comm: syz-executor.3 Not tainted 5.10.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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