Re: [PATCH v4 07/19] irqdomain: Look for existing mapping only once

[Thomas Gleixner <tglx@linutronix.de>]

On Mon, Jan 16 2023 at 14:50, Johan Hovold wrote:
> Avoid looking for an existing mapping twice when creating a new mapping
> using irq_create_fwspec_mapping() by factoring out the actual allocation
> which is shared with irq_create_mapping_affinity().

This changelog is incomplete and it took me a while to figure out why
this is before the race fix.

The point is that you need __irq_create_mapping_affinity() later to fix
the shared mapping race. The double check avoidance is just a nice side
effect.

So please spell it out and make it clear that this needs to be
backported too, e.g. by adding:

The split out internal function will be used to fix a shared interrupt
mapping race. This change is therefore tagged with the same fixes tag.

Fixes: ....

>  
> +static unsigned int __irq_create_mapping_affinity(struct irq_domain *domain,
> +						  irq_hw_number_t hwirq,
> +						  const struct irq_affinity_desc *affinity)

Please rename to irq_create_mapping_affinity_locked() so it's clear what
this is about and what the calling convention is. A lockdep assert to
that effect would be nice too.

Thanks,

        tglx