# Re: \[PATCH v3 3/4\] powerpc/watchdog: Avoid holding wd\_smp\_lock over printk and smp\_send\_nmi\_ipi

- From: Nicholas Piggin \<npiggin@gmail.com\>
- Date: 2021-11-19 11:06:10 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2021/11/9525154
- Thread: https://ratatoskr.run/linuxppc-dev/2021/11/9525056/t.md

```text
Excerpts from Nicholas Piggin's message of November 10, 2021 12:50 pm:
> @@ -160,11 +187,26 @@ static void watchdog_smp_panic(int cpu, u64 tb)
>  		goto out;
>  	if (cpumask_test_cpu(cpu, &wd_smp_cpus_pending))
>  		goto out;
> -	if (cpumask_weight(&wd_smp_cpus_pending) == 0)
> +	if (!wd_try_report())
>  		goto out;
> +	for_each_online_cpu(c) {
> +		if (!cpumask_test_cpu(c, &wd_smp_cpus_pending))
> +			continue;
> +		if (c == cpu)
> +			continue; // should not happen
> +
> +		__cpumask_set_cpu(c, &wd_smp_cpus_ipi);
> +		if (set_cpu_stuck(c, tb))
> +			break;
> +	}
> +	if (cpumask_empty(&wd_smp_cpus_ipi)) {
> +		wd_end_reporting();
> +		goto out;
> +	}
> +	wd_smp_unlock(&flags);
>  
>  	pr_emerg("CPU %d detected hard LOCKUP on other CPUs %*pbl\n",
> -		 cpu, cpumask_pr_args(&wd_smp_cpus_pending));
> +		 cpu, cpumask_pr_args(&wd_smp_cpus_ipi));
>  	pr_emerg("CPU %d TB:%lld, last SMP heartbeat TB:%lld (%lldms ago)\n",
>  		 cpu, tb, wd_smp_last_reset_tb,
>  		 tb_to_ns(tb - wd_smp_last_reset_tb) / 1000000);

Oops, this has a bug: wd_smp_last_reset_tb gets reset above by
set_cpu_stuck when all the stuck CPUs are taken out of the pending
mask, so this prints nonsense last-reset times.

I might just send out an updated series, because the fix has a slight
clash with the next patch. All I do is take a local copy of
wd_smp_last_reset_tb near the start of the function.

Thanks,
Nick
```