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BUG: KCSAN: data-race in get_cpu_idle_time_us / tick_nohz_idle_enter

write to 0xffff88812c12024c of 1 bytes by task 0 on cpu 1:
 tick_nohz_idle_enter+0x8f/0x100 kernel/time/tick-sched.c:1018
 do_idle+0x38/0x290 kernel/sched/idle.c:244
 cpu_startup_entry+0x14/0x20 kernel/sched/idle.c:361
 start_secondary+0x164/0x1b0 arch/x86/kernel/smpboot.c:264
 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:242

read to 0xffff88812c12024c of 1 bytes by task 19406 on cpu 0:
 get_cpu_idle_time_us+0xe5/0x170 kernel/time/tick-sched.c:590
 get_idle_time.isra.0+0x65/0x90 fs/proc/stat.c:53
 show_stat+0x61d/0xa50 fs/proc/stat.c:172
 seq_read+0x346/0x9d0 fs/seq_file.c:229
 proc_reg_read+0xe8/0x140 fs/proc/inode.c:223
 do_loop_readv_writev fs/read_write.c:714 [inline]
 do_loop_readv_writev fs/read_write.c:701 [inline]
 do_iter_read+0x33d/0x3a0 fs/read_write.c:935
 vfs_readv+0x9c/0xf0 fs/read_write.c:1053
 do_preadv+0x129/0x1c0 fs/read_write.c:1145
 __do_sys_preadv fs/read_write.c:1195 [inline]
 __se_sys_preadv fs/read_write.c:1190 [inline]
 __x64_sys_preadv+0x5e/0x80 fs/read_write.c:1190
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 19406 Comm: syz-executor.5 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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