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SubjectRe: [RFC][PATCH] IRQ: Fix oneshot irq race between irq_finalize_oneshot and handle_level_irq
On Wed, 10 Mar 2010, Yong Zhang wrote:

> On Wed, Mar 10, 2010 at 12:22:12AM +0100, Thomas Gleixner wrote:
> > B1;2005;0cOn Tue, 9 Mar 2010, Lars-Peter Clausen wrote:
> > >
> > > - desc->status |= IRQ_INPROGRESS;
> > > + desc->status |= IRQ_INPROGRESS | IRQ_ONESHOT_INPROGRESS;
> > > raw_spin_unlock(&desc->lock);
> >
> > That keeps the IRQ_ONESHOT_INPROGRESS dangling for non ONESHOT
> > interrupts. Not a big deal, but not pretty either.
> >
> > The race between the thread and the irq handler exists indeed on SMP,
> > but I think there are more fundamental issues about the state which
> > need to be addressed.
> >
> > The first thing is that we do not mark the status MASKED when we
> > actually mask the interrupt in mask_ack_irq().
> >
> > That conditional MASKED after running the primary handler is really
> > horrible - I already ranted in private at the moron who committed that
> > crime :)
> >
> > So the following patch fixes that and the SMP race scenario:
>
> Hi Thomas,
>
> How about the following patch(maybe a little ugly). I think it will
> resolve your concerns.

No it does not, but you are right that it's ugly. And it is patently
wrong as well.

> diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
> index d70394f..23b79c6 100644
> --- a/kernel/irq/chip.c
> +++ b/kernel/irq/chip.c
> @@ -461,9 +461,24 @@ handle_level_irq(unsigned int irq, struct irq_desc *desc)
> raw_spin_lock(&desc->lock);
> mask_ack_irq(desc, irq);
>
> - if (unlikely(desc->status & IRQ_INPROGRESS))
> - goto out_unlock;
> + /*
> + * if we are in oneshot mode and the irq thread is running on
> + * another cpu, just return because the irq thread will unmask
> + * the irq
> + */
> + if (unlikely(desc->status & IRQ_ONESHOT)) {
> + if (unlikely(desc->status & (IRQ_INPROGRESS | IRQ_MASKED)
> + == IRQ_INPROGRESS | IRQ_MASKED))
> + goto out_unlock;
> + }
> + else {
> + if (unlikely(desc->status & IRQ_INPROGRESS))
> + goto out_unlock;
> + }

In case of IRQ_SHOT and IRQ_INPROGRESS and the other CPU having
unmasked the interrupt already you are reentering the handler which
is a nono.

Thanks,

tglx


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