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BUG: KCSAN: data-race in get_cpu_idle_time_us / tick_nohz_idle_exit

read to 0xffff88812bf1dd2c of 1 bytes by task 8155 on cpu 0:
 get_cpu_idle_time_us+0xed/0x180 kernel/time/tick-sched.c:575
 get_idle_time.isra.0+0x6e/0xa0 fs/proc/stat.c:53
 show_stat+0x1be/0x8f0 fs/proc/stat.c:128
 seq_read+0x350/0x960 fs/seq_file.c:229
 proc_reg_read+0xe9/0x140 fs/proc/inode.c:223
 __vfs_read+0x67/0xc0 fs/read_write.c:425
 vfs_read fs/read_write.c:461 [inline]
 vfs_read+0x143/0x2c0 fs/read_write.c:446
 ksys_read+0xd5/0x1b0 fs/read_write.c:587
 __do_sys_read fs/read_write.c:597 [inline]
 __se_sys_read fs/read_write.c:595 [inline]
 __x64_sys_read+0x4c/0x60 fs/read_write.c:595
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff88812bf1dd2c of 1 bytes by task 0 on cpu 1:
 tick_nohz_idle_exit+0xc7/0x1e0 kernel/time/tick-sched.c:1170
 do_idle+0xb1/0x280 kernel/sched/idle.c:276
 cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:355
 start_secondary+0x168/0x1b0 arch/x86/kernel/smpboot.c:264
 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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