Re: [PATCH 20/39] irqdomain: Protect the linear revmap with RCU

[Thomas Gleixner]

On Thu, May 20 2021 at 17:37, Marc Zyngier wrote:
>  static void irq_domain_clear_mapping(struct irq_domain *domain,
> @@ -902,12 +901,12 @@ unsigned int irq_find_mapping(struct irq_domain *domain,
>  		return 0;
>  	}
>  
> +	rcu_read_lock();
>  	/* Check if the hwirq is in the linear revmap. */
>  	if (hwirq < domain->revmap_size)
> -		return domain->revmap[hwirq]->irq;
> -
> -	rcu_read_lock();
> -	data = radix_tree_lookup(&domain->revmap_tree, hwirq);
> +		data = rcu_dereference(domain->revmap[hwirq]);
> +	else
> +		data = radix_tree_lookup(&domain->revmap_tree, hwirq);
>  	rcu_read_unlock();
>  	return data ? data->irq : 0;

This is wrong and was wrong before. This wants to be:

     irq = data ? data->irq : 0;
     rcu_read_unlock();
     return irq;

Thanks,

        tglx