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

Johan Hovold
2023-01-18T10:21:13Z

On Tue, Jan 17, 2023 at 10:34:07PM +0100, Thomas Gleixner wrote:
> 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: ....

Sure. It was originally part of the fix of the race, but I was told to
clean up the code first (and not worry about backporting).

I'll see what I can do about reordering these again with the aim of
making things easier to backport.

> > +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.

Will do.

Johan