Hi Wenchao,

Thanks for your patch.

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On 2021/9/17 17:16, Wenchao Qin wrote:

hulk inclusion category: bugfix bugzilla: N/A CVE: N/A

---

When we are in the arch_get_cpu_freq func for the first time, after arch_probe_cpu_freq is excuted, the return of smp_processor_id() will change due to preemption while cpu_freq get the freq belong to original processor id, so pr_info will print the freq with wrong processor id like below table from dmesg:

[ 1.713211] NMI watchdog: CPU1 freq probed as 2189072384 HZ. [ 1.810819] NMI watchdog: CPU1 freq probed as 2192003108 HZ. [ 1.909910] NMI watchdog: CPU2 freq probed as 2191345967 HZ. [ 2.015327] NMI watchdog: CPU3 freq probed as 2189460398 HZ.

Actually, the first line should print the freq of CPU0, this bu can occur in virtual machine with less then 17 vCPUs.

Changing smp_processor_id() to cpu will fix the bug

Signed-off-by: Wenchao Qin qinwenchao@cmss.chinamobile.com

arch/arm64/kernel/smp.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c index fe56277..d685a27 100644 --- a/arch/arm64/kernel/smp.c +++ b/arch/arm64/kernel/smp.c @@ -1457,7 +1457,7 @@ static u64 arch_get_cpu_freq(void) if (!cpu_freq) { cpu_freq = arch_probe_cpu_freq(); pr_info("NMI watchdog: CPU%u freq probed as %llu HZ.\n",

• 		smp_processor_id(), cpu_freq);
  

• 		cpu, cpu_freq);
  

arch_probe_cpu_freq() 一样也会调用 smp_processor_id()，也可能存在被抢占的情况。 是不是需要关抢占？

if (!cpu_freq)
	cpu_freq = -1;
per_cpu(cpu_freq_probed, cpu) = cpu_freq;