linux-kernel - Re: [patch] x64: Avoid irq_chip mask/unmask in fixup

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Date:	Thu, 04 Jun 2009 16:13:16 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	suresh.b.siddha@...el.com
Cc:	mingo@...e.hu, hpa@...or.com, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, andi@...ux.intel.com, travis@....com,
	steiner@....com, Gary Hade <garyhade@...ibm.com>
Subject: Re: [patch] x64: Avoid irq_chip mask/unmask in fixup_irqs for interrupt-remapping

Suresh Siddha <suresh.b.siddha@...el.com> writes:

> From: Suresh Siddha <suresh.b.siddha@...el.com>
> Subject: x64: Avoid irq_chip mask/unmask in fixup_irqs for interrupt-remapping
>
> In the presence of interrupt-remapping, irqs will be migrated in the
> process context and we don't do (and there is no need to) irq_chip mask/unmask
> while migrating the interrupt.
>
> Similarly fix the fixup_irqs() that get called during cpu offline and avoid
> calling irq_chip mask/unmask for irqs that are ok to be migrated in the
> process context.
>
> While we didn't observe any race condition with the existing code,
> this change takes complete advantage of interrupt-remapping in
> the newer generation platforms and avoids any potential HW lockup's
> (that often worry Eric :)

You now apparently fail to migrate the irq threads in tandem with
the rest of the irqs.

Eric

> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> Cc: Eric W. Biederman <ebiederm@...ssion.com>
> ---
>
> diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
> index 977d8b4..82265a5 100644
> --- a/arch/x86/kernel/irq_64.c
> +++ b/arch/x86/kernel/irq_64.c
> @@ -95,7 +95,7 @@ void fixup_irqs(void)
>  			affinity = cpu_all_mask;
>  		}
>  
> -		if (desc->chip->mask)
> +		if (!(desc->status & IRQ_MOVE_PCNTXT) && desc->chip->mask)
>  			desc->chip->mask(irq);
>  
>  		if (desc->chip->set_affinity)
> @@ -103,7 +103,7 @@ void fixup_irqs(void)
>  		else if (!(warned++))
>  			set_affinity = 0;
>  
> -		if (desc->chip->unmask)
> +		if (!(desc->status & IRQ_MOVE_PCNTXT) && desc->chip->unmask)
>  			desc->chip->unmask(irq);
>  
>  		spin_unlock(&desc->lock);
--
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