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BUG: KCSAN: data-race in get_cpu_idle_time_us / tick_irq_enter

write to 0xffff88812c02030c of 1 bytes by task 0 on cpu 0:
 tick_nohz_stop_idle kernel/time/tick-sched.c:557 [inline]
 tick_nohz_irq_enter kernel/time/tick-sched.c:1276 [inline]
 tick_irq_enter+0x17b/0x1b0 kernel/time/tick-sched.c:1295
 irq_enter+0x49/0x50 kernel/softirq.c:354
 entering_irq arch/x86/include/asm/apic.h:527 [inline]
 entering_ack_irq arch/x86/include/asm/apic.h:533 [inline]
 smp_apic_timer_interrupt+0x52/0x270 arch/x86/kernel/apic/apic.c:1136
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
 native_safe_halt+0xe/0x10 arch/x86/include/asm/irqflags.h:60
 arch_safe_halt arch/x86/include/asm/paravirt.h:144 [inline]
 default_idle+0x21/0x170 arch/x86/kernel/process.c:697
 cpuidle_idle_call kernel/sched/idle.c:154 [inline]
 do_idle+0x1b7/0x290 kernel/sched/idle.c:269
 cpu_startup_entry+0x14/0x20 kernel/sched/idle.c:361
 rest_init+0xe4/0xeb init/main.c:667
 arch_call_rest_init+0x13/0x2b
 start_kernel+0x82d/0x852 init/main.c:1005
 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:242

read to 0xffff88812c02030c of 1 bytes by task 18344 on cpu 1:
 get_cpu_idle_time_us+0xe5/0x170 kernel/time/tick-sched.c:596
 get_idle_time.isra.0+0x65/0x90 fs/proc/stat.c:53
 show_stat+0x61d/0xa50 fs/proc/stat.c:172
 seq_read+0x2ef/0x940 fs/seq_file.c:206
 pde_read fs/proc/inode.c:292 [inline]
 proc_reg_read+0xb3/0x1b0 fs/proc/inode.c:302
 do_loop_readv_writev fs/read_write.c:715 [inline]
 do_loop_readv_writev fs/read_write.c:702 [inline]
 do_iter_read+0x33f/0x3a0 fs/read_write.c:936
 vfs_readv+0x9c/0xf0 fs/read_write.c:1054
 do_preadv+0x129/0x1c0 fs/read_write.c:1146
 __do_sys_preadv fs/read_write.c:1196 [inline]
 __se_sys_preadv fs/read_write.c:1191 [inline]
 __x64_sys_preadv+0x5e/0x80 fs/read_write.c:1191
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 18344 Comm: syz-executor.1 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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