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SubjectRe: [tip:irq/core] genirq: MSI: Fix freeing of unallocated MSI

* Thomas Gleixner <tglx@linutronix.de> wrote:

> On Thu, 9 Apr 2015, Marc Zyngier wrote:
> > On Thu, 9 Apr 2015 13:00:23 +0100
> > Ingo Molnar <mingo@kernel.org> wrote:
> > >
> > > Hm, so this appears to be the first time that 'irq == 0' assumptions
> > > are getting into the genirq core. Is NO_IRQ dead? I realize that the
> > > MSI code uses '!irq' as a flag, but still, quite a few architectures
> > > define NO_IRQ so it appears to matter to them.
> >
> > NO_IRQ strikes back, everybody takes cover! ;-)
> >
> > More seriously, this seems to be two schools of thoughts on that
> > one. The irqdomain subsystem seems to treat 'irq == 0' as the
> > indication that 'this is not a valid IRQ', and so does MSI (as you
> > noticed). Given that this code deals with MSI in conjunction with
> > irqdomains, it felt natural to adopt the same convention.
> >
> > Also, not all the architecture are defining NO_IRQ, and it only
> > seems to be used in code that is doesn't look portable across
> > architectures. Either these architecture don't care about MSI, or
> > they are happy enough to consider that virtual interrupt 0 is
> > invalid in the MSI case.
> >
> > So I'm a bit lost on that one. I sincerely thought NO_IRQ was
> > being retired (https://lwn.net/Articles/470820/). Should we
> > introduce a NO_MSI_IRQ (set to zero) to take care of this case?
>
> Nah, that'd be overkill. irq 0 is invalid for MSI in any case so we
> really should stick with that convention.

That makes sense - should we more aggressively eliminate NO_IRQ
perhaps?

I'm seeing stuff like:

irq = irq_of_parse_and_map(np, 0);
if (!handle || (irq == NO_IRQ)) {

in fairly recent (2-4 years old) code, and irq_of_parse_and_map() is
used in 300+ places.

Thanks,

Ingo


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