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

From: ebiederm@xmission.com (Eric W. Biederman)
To: "Pallipadi\, Venkatesh" <venkatesh.pallipadi@intel.com>
Cc: Yinghai Lu <yhlu.kernel@gmail.com>, "Li\,
	Shaohua" <shaohua.li@intel.com>, Gary Hade <garyhade@us.ibm.com>,
	"mingo\@elte.hu" <mingo@elte.hu>,
	"mingo\@redhat.com" <mingo@redhat.com>,
	"tglx\@linutronix.de" <tglx@linutronix.de>,
	"hpa\@zytor.com" <hpa@zytor.com>,
	"x86\@kernel.org" <x86@kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"lcm\@us.ibm.com" <lcm@us.ibm.com>
Subject: Re: [PATCH 2/3] [BUGFIX] x86/x86_64: fix CPU offlining triggered inactive device IRQ interrruption
Date: Mon, 13 Apr 2009 11:50:20 -0700	[thread overview]
Message-ID: <m1ab6kfkwj.fsf@fess.ebiederm.org> (raw)
In-Reply-To: <1239644495.4529.8580.camel@localhost.localdomain> (Venkatesh Pallipadi's message of "Mon\, 13 Apr 2009 10\:41\:35 -0700")

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

> On Sat, 2009-04-11 at 04:01 -0700, Eric W. Biederman wrote:
>> Yinghai Lu <yhlu.kernel@gmail.com> writes:
>> 
>> > commit 932775a4ab622e3c99bd59f14cc7d96722f79501
>> > Author: venkatesh.pallipadi@intel.com <venkatesh.pallipadi@intel.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@intel.com>
>> >     Signed-off-by: Shaohua Li <shaohua.li@intel.com>
>> >     Signed-off-by: Ingo Molnar <mingo@elte.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