linux-kernel - Re: [tip:irq/core] genirq: MSI: Fix freeing of unallocated MSI

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Message-ID: <alpine.DEB.2.11.1504091450570.3845@nanos>
Date:	Thu, 9 Apr 2015 14:52:00 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Marc Zyngier <marc.zyngier@....com>
cc:	Ingo Molnar <mingo@...nel.org>,
	"jiang.liu@...ux.intel.com" <jiang.liu@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hpa@...or.com" <hpa@...or.com>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:irq/core] genirq: MSI: Fix freeing of unallocated MSI

On Thu, 9 Apr 2015, Marc Zyngier wrote:
> On Thu, 9 Apr 2015 13:00:23 +0100
> Ingo Molnar <mingo@...nel.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.

Thanks,

	tglx
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