linux-kernel - Re: MSI problem since 2.6.21 for devices not providing a mask in their MSI capability

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Date:	Thu, 04 Oct 2007 11:03:38 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Loic Prylli <loic@...i.com>
Cc:	linux-pci@...ey.karlin.mff.cuni.cz,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: MSI problem since 2.6.21 for devices not providing a mask in their MSI capability

Loic Prylli <loic@...i.com> writes:

I still looking through my copy of the pci specs and so will reply to
that part in a bit.

> To detect a crazy device generating storms of edge interrupts, I guess
> note_interrupt() could be called during this "reentrant detection" if
> masking was made conditional.

Hmm. Something like this?

Only mask it if the irq is disabled, and only disable it if
the user requests it or if note_interrupt decides we are screaming?

void handle_edge_irq(unsigned int irq, struct irq_desc *desc)
{
	const unsigned int cpu = smp_processor_id();

	spin_lock(&desc->lock);

	desc->status &= ~(IRQ_REPLAY | IRQ_WAITING);

	/*
	 * If we're currently running this IRQ, or its disabled,
	 * we shouldn't process the IRQ. Mark it pending, handle
	 * the necessary masking and go out
	 */
	if (unlikely((desc->status & IRQ_DISABLED) || !desc->action)){
        	desc->status |= (IRQ_PENDING | IRQ_MASKED);
                mask_ack_irq(desc, irq);
                goto out_unlock;
	}    
	if (unlikely(desc->status & IRQ_INPROGRESS)) {
		desc->status |= IRQ_PENDING;
		desc->chip->ack(desc, irq);
                note_interrupt(irq, desc, IRQ_NONE /* IRQ_DUP? */);
		goto out_unlock;
	}

	kstat_cpu(cpu).irqs[irq]++;

	/* Start handling the irq */
	desc->chip->ack(irq);

	/* Mark the IRQ currently in progress.*/
	desc->status |= IRQ_INPROGRESS;

	do {
		struct irqaction *action = desc->action;
		irqreturn_t action_ret;

		if (unlikely(!action)) {
			desc->chip->mask(irq);
			goto out_unlock;
		}

		desc->status &= ~IRQ_PENDING;
		spin_unlock(&desc->lock);
		action_ret = handle_IRQ_event(irq, action);
		if (!noirqdebug)
			note_interrupt(irq, desc, action_ret);
		spin_lock(&desc->lock);

	} while ((desc->status & (IRQ_PENDING | IRQ_DISABLED)) == IRQ_PENDING);

	desc->status &= ~IRQ_INPROGRESS;
out_unlock:
	spin_unlock(&desc->lock);
}

Eric
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