linux-kernel - Re: [PATCH 2/3] [BUGFIX] x86/x86_64: fix CPU offlining triggered inactive device IRQ interrruption

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Date:	Mon, 13 Apr 2009 11:50:20 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Pallipadi\, Venkatesh" <venkatesh.pallipadi@...el.com>
Cc:	Yinghai Lu <yhlu.kernel@...il.com>,
	"Li\, Shaohua" <shaohua.li@...el.com>,
	Gary Hade <garyhade@...ibm.com>,
	"mingo\@elte.hu" <mingo@...e.hu>,
	"mingo\@redhat.com" <mingo@...hat.com>,
	"tglx\@linutronix.de" <tglx@...utronix.de>,
	"hpa\@zytor.com" <hpa@...or.com>,
	"x86\@kernel.org" <x86@...nel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"lcm\@us.ibm.com" <lcm@...ibm.com>
Subject: Re: [PATCH 2/3] [BUGFIX] x86/x86_64: fix CPU offlining triggered inactive device IRQ interrruption

"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com> writes:

> On Sat, 2009-04-11 at 04:01 -0700, Eric W. Biederman wrote:
>> Yinghai Lu <yhlu.kernel@...il.com> writes:
>> 
>> > commit 932775a4ab622e3c99bd59f14cc7d96722f79501
>> > Author: venkatesh.pallipadi@...el.com <venkatesh.pallipadi@...el.com>
>> > Date:   Fri Sep 5 18:02:15 2008 -0700
>> >
>> >     x86: HPET_MSI change IRQ affinity in process context when it is disabled
>> >
>> >     Change the IRQ affinity in the process context when the IRQ is disabled.
>> >
>> >     Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
>> >     Signed-off-by: Shaohua Li <shaohua.li@...el.com>
>> >     Signed-off-by: Ingo Molnar <mingo@...e.hu>
>> >
>> > diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
>> > index ddc9568..ad2ce72 100644
>> > --- a/kernel/irq/manage.c
>> > +++ b/kernel/irq/manage.c
>> > @@ -87,10 +87,11 @@ int irq_set_affinity(unsigned int irq, cpumask_t cpumask)
>> >                 return -EINVAL;
>> >
>> >  #ifdef CONFIG_GENERIC_PENDING_IRQ
>> > -       if (desc->status & IRQ_MOVE_PCNTXT) {
>> > +       if (desc->status & IRQ_MOVE_PCNTXT || desc->status & IRQ_DISABLED) {
>> >                 unsigned long flags;
>> >
>> >                 spin_lock_irqsave(&desc->lock, flags);
>> > +               desc->affinity = cpumask;
>> >                 desc->chip->set_affinity(irq, cpumask);
>> >                 spin_unlock_irqrestore(&desc->lock, flags);
>> >         } else
>> 
>> If the goal is moving MSIs, we should modify the msi code to be safe
>> in process context and to set IRQ_MOVE_PCNTXT.
>> 
>> The only reason we migrate MSIs in interrupt context today is that there
>> wasn't infrastructure for support migration both in interrupt context
>> and outside of it.
>> 
>
> Yes. The idea here was to force the MSI migration to happen in process
> context. One of the patches in the series did
>
> 	disable_irq(dev->irq);
> 	irq_set_affinity(dev->irq, cpumask_of(dev->cpu));
> 	enable_irq(dev->irq);
>
> with the above patch adding irq/manage code check for interrupt disabled
> and moving the interrupt in process context.
>
> IIRC, there was no IRQ_MOVE_PCNTXT when we were developing this HPET
> code and we ended up having this ugly hack. IRQ_MOVE_PCNTXT was there
> when we eventually submitted the patch upstream. But, looks like I did a
> blind rebasing instead of using IRQ_MOVE_PCNTXT in hpet MSI code. That
> was my fault. Will send a patch to fix this ugliness.

Thanks.

Eric
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