linux-kernel - Re: [PATCH] clear irq pending when bypassing it

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Message-ID: <m11vrayob8.fsf@fess.ebiederm.org>
Date:	Thu, 30 Apr 2009 11:43:55 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Joe Korty <joe.korty@...r.com>
Cc:	"venkatesh.pallipadi\@intel.com" <venkatesh.pallipadi@...el.com>,
	"mingo\@elte.hu" <mingo@...e.hu>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clear irq pending when bypassing it

Joe Korty <joe.korty@...r.com> writes:

> On Thu, Apr 30, 2009 at 12:49:39PM -0400, Eric W. Biederman wrote:
>> Joe Korty <jak@...hoon.ccur.com> writes:
>> 
>> > IRQ_MOVE_PENDING must be cleared whenever it is bypassed.
>> >
>> > Otherwise, we risk an old, pending affinity change
>> > overtaking and erasing a more recent affinity change that
>> > had been directly applied (eg, IRQ_MOVE_PCNTXT mode).
>> 
>> When can this happen?
>
> Probably doesn't happen.  AFAIK, each IRQ is either fully MSI
> or non-MSI.  The MSI IRQs will always use IRQ_MOVE_PCNTXT and
> the non-MSI's will never use IRQ_MOVE_PCNTXT.  Thus no collision.
>
> It could only happen if it was possible for a MSI and non-MSI
> device to share an IRQ.

Ok.  I thought you might have seen something.

It doesn't happen and it can't happen, making your patch wrong.

Eric





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