linux-kernel - Re: [PATCH 14/14] genirq: Mask irqs when migrating them.

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Message-Id: <20070227122657.a8c9d2c0.akpm@linux-foundation.org>
Date:	Tue, 27 Feb 2007 12:26:57 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
Cc:	ebiederm@...ssion.com, linux-kernel@...r.kernel.org,
	zwane@...radead.org, ashok.raj@...el.com, mingo@...e.hu,
	yinghai.lu@....com, protasnb@...il.com, ak@...e.de,
	suresh.b.siddha@...el.com, torvalds@...ux-foundation.org
Subject: Re: [PATCH 14/14] genirq: Mask irqs when migrating them.

> On Fri, 23 Feb 2007 18:06:55 -0800 "Siddha, Suresh B" <suresh.b.siddha@...el.com> wrote:
> > 
> > move_native_irqs tries to do the right thing when migrating irqs
> > by disabling them.  However disabling them is a software logical
> > thing, not a hardware thing.  This has always been a little flaky
> > and after Ingo's latest round of changes it is guaranteed to not
> > mask the apic.
> > 
> > So this patch fixes move_native_irq to directly call the mask and
> > unmask chip methods to guarantee that we mask the irq when we
> > are migrating it.  We must do this as it is required by
> > all code that call into the path.
> > 
> > Since we don't know the masked status when IRQ_DISABLED is
> > set so we will not be able to restore it.   The patch makes the code
> > just give up and trying again the next time this routing is called.
> > 
> > Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
> > ---
> >  kernel/irq/migration.c |    9 ++++-----
> >  1 files changed, 4 insertions(+), 5 deletions(-)
> > 
> > diff --git a/kernel/irq/migration.c b/kernel/irq/migration.c
> > index 4baa3bb..77b7acc 100644
> > --- a/kernel/irq/migration.c
> > +++ b/kernel/irq/migration.c
> > @@ -65,12 +65,11 @@ void move_native_irq(int irq)
> >  	if (likely(!(desc->status & IRQ_MOVE_PENDING)))
> >  		return;
> >  
> > -	if (likely(!(desc->status & IRQ_DISABLED)))
> > -		desc->chip->disable(irq);
> > +	if (unlikely(desc->status & IRQ_DISABLED))
> > +		return;
> >  
> > +	desc->chip->mask(irq);
> >  	move_masked_irq(irq);
> > -
> > -	if (likely(!(desc->status & IRQ_DISABLED)))
> > -		desc->chip->enable(irq);
> > +	desc->chip->unmask(irq);
> >  }
>

arghg.  Please don't top-post.  Ever.  At all.  Don't even think about 
thinking about it.

<edit, edit>

> Andrew, This is a bug fix and must go in before 2.6.21.
> 
> Acked-by: Suresh Siddha <suresh.b.siddha@...el.com>

OK.  But the rest of the patch series was a bit of a trainwreck against
Andi's pending tree so I ducked it all.

If it's really needed for 2.6.21 then we have some work to do.  Presumably
carefully reviewing and testing this new work then repairing Andi's tree. 
 
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