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

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Message-ID: <20090430180011.GB28139@tsunami.ccur.com>
Date:	Thu, 30 Apr 2009 14:00:12 -0400
From:	Joe Korty <joe.korty@...r.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"venkatesh.pallipadi@...el.com" <venkatesh.pallipadi@...el.com>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clear irq pending when bypassing it

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.

Joe
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