Re: [PATCH] drivers/perf: Change WARN_ON() to dev_err() on irq_set_affinity() failure

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Mon, 15 Aug 2022 17:28:15 +0800
Yicong Yang <yangyicong@huawei.com> wrote:

> From: Yicong Yang <yangyicong@hisilicon.com>
> 
> The WARN_ON() on irq_set_affinity() failure is misused according to the [1]
> and may crash people's box unintentionally. This may also be redundant since
> in the failure case we may also trigger the WARN and dump the stack in the
> perf core[2] for a second time.
> 
> So change the WARN_ON() to dev_err() to just print the failure message.
> 
> [1] https://github.com/torvalds/linux/blob/master/include/asm-generic/bug.h#L74
> [2] https://github.com/torvalds/linux/blob/master/kernel/events/core.c#L313
> 
> Suggested-by: Greg KH <gregkh@linuxfoundation.org>
> [https://lore.kernel.org/lkml/YuOi3i0XHV++z1YI@kroah.com/]
> Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>

Looks like progress in a sensible direction to me.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Kind of unrelated question inline.

>


> diff --git a/drivers/perf/arm_smmuv3_pmu.c b/drivers/perf/arm_smmuv3_pmu.c
> index 00d4c45a8017..05e1b3e274d7 100644
> --- a/drivers/perf/arm_smmuv3_pmu.c
> +++ b/drivers/perf/arm_smmuv3_pmu.c
> @@ -646,7 +646,8 @@ static int smmu_pmu_offline_cpu(unsigned int cpu, struct hlist_node *node)
>  
>  	perf_pmu_migrate_context(&smmu_pmu->pmu, cpu, target);
>  	smmu_pmu->on_cpu = target;
> -	WARN_ON(irq_set_affinity(smmu_pmu->irq, cpumask_of(target)));
> +	if (irq_set_affinity(smmu_pmu->irq, cpumask_of(target)))
> +		dev_err(smmu_pmu->dev, "Failed to set interrupt affinity\n");
>  
>  	return 0;
>  }
> @@ -892,7 +893,8 @@ static int smmu_pmu_probe(struct platform_device *pdev)
>  
>  	/* Pick one CPU to be the preferred one to use */
>  	smmu_pmu->on_cpu = raw_smp_processor_id();
> -	WARN_ON(irq_set_affinity(smmu_pmu->irq, cpumask_of(smmu_pmu->on_cpu)));
> +	if (irq_set_affinity(smmu_pmu->irq, cpumask_of(smmu_pmu->on_cpu)))
> +		dev_err(dev, "Failed to set interrupt affinity\n");

In this case we have the option to fail probe.  Failing to set affinity means
we are broken anyway, so perhaps that is cleaner than carrying on.

As a side note, I wonder if other drivers could benefit from what I think
is a micro optimization to short cut calling the hp handlers when the
decision of which CPU is easy...

>  
>  	err = cpuhp_state_add_instance_nocalls(cpuhp_state_num,
>  					       &smmu_pmu->node);