Re: [PATCH v4 09/19] irqdomain: Fix mapping-creation race

[Thomas Gleixner]

On Mon, Jan 16 2023 at 14:50, Johan Hovold wrote:

> Parallel probing (e.g. due to asynchronous probing) of devices that share
> interrupts can currently result in two mappings for the same hardware
> interrupt to be created.

This lacks an explanation why this can happen.

> @@ -802,6 +811,8 @@ unsigned int irq_create_fwspec_mapping(struct irq_fwspec *fwspec)
>  	if (WARN_ON(type & ~IRQ_TYPE_SENSE_MASK))
>  		type &= IRQ_TYPE_SENSE_MASK;
>  
> +	mutex_lock(&irq_domain_mutex);
> +
>  	/*
>  	 * If we've already configured this interrupt,
>  	 * don't do it again, or hell will break loose.
> @@ -814,7 +825,7 @@ unsigned int irq_create_fwspec_mapping(struct irq_fwspec *fwspec)
>  		 * interrupt number.
>  		 */
>  		if (type == IRQ_TYPE_NONE || type == irq_get_trigger_type(virq))
> -			return virq;
> +			goto out;
>  
>  		/*
>  		 * If the trigger type has not been set yet, then set
> @@ -823,36 +834,43 @@ unsigned int irq_create_fwspec_mapping(struct irq_fwspec *fwspec)
>  		if (irq_get_trigger_type(virq) == IRQ_TYPE_NONE) {
>  			irq_data = irq_get_irq_data(virq);
>  			if (!irq_data)
> -				return 0;
> +				goto err;
>  
>  			irqd_set_trigger_type(irq_data, type);
> -			return virq;
> +			goto out;
>  		}
>  
>  		pr_warn("type mismatch, failed to map hwirq-%lu for %s!\n",
>  			hwirq, of_node_full_name(to_of_node(fwspec->fwnode)));
> -		return 0;
> +		goto err;
>  	}
>  
>  	if (irq_domain_is_hierarchy(domain)) {
> -		virq = irq_domain_alloc_irqs(domain, 1, NUMA_NO_NODE, fwspec);
> +		virq = ___irq_domain_alloc_irqs(domain, -1, 1, NUMA_NO_NODE,
> +						fwspec, false, NULL);
>  		if (virq <= 0)
> -			return 0;
> +			goto err;
>  	} else {
>  		/* Create mapping */
>  		virq = __irq_create_mapping_affinity(domain, hwirq, NULL);
>  		if (!virq)
> -			return virq;
> +			goto err;
>  	}
>  
>  	irq_data = irq_get_irq_data(virq);
>  	if (WARN_ON(!irq_data))
> -		return 0;
> +		goto err;
>  
>  	/* Store trigger type */
>  	irqd_set_trigger_type(irq_data, type);
> +out:
> +	mutex_unlock(&irq_domain_mutex);
>  
>  	return virq;
> +err:
> +	mutex_unlock(&irq_domain_mutex);
> +
> +	return 0;
>  }
>  EXPORT_SYMBOL_GPL(irq_create_fwspec_mapping);

You can spare that goto churn by renaming the existing function to
irq_create_fwspec_mapping_locked() and invoked that guarded by the
mutex, no?

Thanks,

        tglx