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

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Message-ID: <Y8e7OGlPXolkC1+R@hovoldconsulting.com>
Date:   Wed, 18 Jan 2023 10:26:16 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Marc Zyngier <maz@...nel.org>, x86@...nel.org,
        platform-driver-x86@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org, Hsin-Yi Wang <hsinyi@...omium.org>,
        Mark-PK Tsai <mark-pk.tsai@...iatek.com>
Subject: Re: [PATCH v4 07/19] irqdomain: Look for existing mapping only once

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