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SubjectRe: [PATCH] uio: uio_pdrv_genirq V2
On Thu, 10 Jul 2008 12:30:36 +0200
Uwe Kleine-König <Uwe.Kleine-Koenig@digi.com> wrote:

> Alan Cox wrote:
> >
> > > > + else if (!irq_on && !priv->irq_disabled)
> > > > + disable_irq(dev_info->irq);
> > > I'm not sure if this is a problem on SMP. Should you use
> > > disable_irq_nosync here, too? Probably it's OK.
> >
> > That one will also deadlock.
> Can you explain why? I think irqcontrol is only called in task context.
> I only see one possible deadlock and that's disable_irq being called
> while the irq is IRQ_INPROGRESS on the same cpu. I'm always willing to
> learn.

CPU0 (UIO IRQ) CPU1 (irqcontrol)
take IRQ
take spin lock
spin on spinlock
disable_irq (blocks)

> I think I didn't understand you right here, with the lock this can
> happen, too, doesn't it?

Actually yes - so it would simplify it without changing behaviour.

Alan
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