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

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Date:	Sat, 11 Apr 2009 04:01:44 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Yinghai Lu <yhlu.kernel@...il.com>
Cc:	"Pallipadi\, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Shaohua Li <shaohua.li@...el.com>,
	Gary Hade <garyhade@...ibm.com>, mingo@...e.hu,
	mingo@...hat.com, tglx@...utronix.de, hpa@...or.com,
	x86@...nel.org, linux-kernel@...r.kernel.org, lcm@...ibm.com
Subject: Re: [PATCH 2/3] [BUGFIX] x86/x86_64: fix CPU offlining triggered  inactive device IRQ interrruption

Yinghai Lu <yhlu.kernel@...il.com> writes:

> commit 932775a4ab622e3c99bd59f14cc7d96722f79501
> Author: venkatesh.pallipadi@...el.com <venkatesh.pallipadi@...el.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@...el.com>
>     Signed-off-by: Shaohua Li <shaohua.li@...el.com>
>     Signed-off-by: Ingo Molnar <mingo@...e.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.

Eric

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