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BUG: KCSAN: data-race in get_cpu_idle_time_us / tick_nohz_idle_enter

read-write to 0xffff88812c11f17c of 1 bytes by task 0 on cpu 1:
 tick_nohz_idle_enter+0x8c/0x110 kernel/time/tick-sched.c:1032
 do_idle+0x36/0x2c0 kernel/sched/idle.c:248
 cpu_startup_entry+0x15/0x20 kernel/sched/idle.c:369
 secondary_startup_64_no_verify+0xa6/0xab

read to 0xffff88812c11f17c of 1 bytes by task 20799 on cpu 0:
 get_cpu_idle_time_us+0x6b/0x1f0 kernel/time/tick-sched.c:599
 get_idle_time fs/proc/stat.c:53 [inline]
 show_stat+0x26f/0xdc0 fs/proc/stat.c:131
 seq_read+0x2de/0x890 fs/seq_file.c:208
 pde_read fs/proc/inode.c:306 [inline]
 proc_reg_read+0xe1/0x1b0 fs/proc/inode.c:316
 do_loop_readv_writev fs/read_write.c:742 [inline]
 do_iter_read+0x3b1/0x4b0 fs/read_write.c:784
 vfs_readv fs/read_write.c:902 [inline]
 do_preadv+0x139/0x210 fs/read_write.c:994
 __do_sys_preadv fs/read_write.c:1044 [inline]
 __se_sys_preadv fs/read_write.c:1039 [inline]
 __x64_sys_preadv+0x54/0x60 fs/read_write.c:1039
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 20799 Comm: syz-executor.3 Not tainted 5.9.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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