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BUG: KCSAN: data-race in get_cpu_idle_time_us / tick_irq_enter

write to 0xffff888237c1dd28 of 8 bytes by interrupt on cpu 0:
 update_ts_time_stats kernel/time/tick-sched.c:598 [inline]
 tick_nohz_stop_idle kernel/time/tick-sched.c:612 [inline]
 tick_nohz_irq_enter kernel/time/tick-sched.c:1329 [inline]
 tick_irq_enter+0x102/0x1e0 kernel/time/tick-sched.c:1348
 sysvec_apic_timer_interrupt+0x5c/0x80 arch/x86/kernel/apic/apic.c:1100
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:647
 native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
 arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
 acpi_safe_halt drivers/acpi/processor_idle.c:108 [inline]
 acpi_idle_do_entry drivers/acpi/processor_idle.c:513 [inline]
 acpi_idle_enter+0x25b/0x2e0 drivers/acpi/processor_idle.c:648
 cpuidle_enter_state+0x2b6/0x750 drivers/cpuidle/cpuidle.c:237
 cpuidle_enter+0x3c/0x60 drivers/cpuidle/cpuidle.c:351
 call_cpuidle kernel/sched/idle.c:158 [inline]
 cpuidle_idle_call kernel/sched/idle.c:239 [inline]
 do_idle+0x1a3/0x240 kernel/sched/idle.c:306
 cpu_startup_entry+0x15/0x20 kernel/sched/idle.c:403
 rest_init+0xc9/0xd0 init/main.c:721
 arch_call_rest_init+0xa/0xb
 start_kernel+0x59e/0x623 init/main.c:1087
 secondary_startup_64_no_verify+0xb0/0xbb

read to 0xffff888237c1dd28 of 8 bytes by task 4660 on cpu 1:
 get_cpu_idle_time_us+0x1e1/0x1f0 kernel/time/tick-sched.c:655
 get_idle_time fs/proc/stat.c:54 [inline]
 show_stat+0x2cf/0xdb0 fs/proc/stat.c:134
 seq_read_iter+0x2ef/0x910 fs/seq_file.c:227
 proc_reg_read_iter+0xd6/0x170 fs/proc/inode.c:296
 call_read_iter include/linux/fs.h:2108 [inline]
 generic_file_splice_read+0x22a/0x310 fs/splice.c:311
 do_splice_to fs/splice.c:796 [inline]
 splice_direct_to_actor+0x2aa/0x650 fs/splice.c:870
 do_splice_direct+0xf5/0x170 fs/splice.c:979
 do_sendfile+0x773/0xda0 fs/read_write.c:1260
 __do_sys_sendfile64 fs/read_write.c:1325 [inline]
 __se_sys_sendfile64 fs/read_write.c:1311 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1311
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 4660 Comm: syz-executor.2 Not tainted 5.13.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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