[BUG] genirq: Race condition in ONESHOT IRQ handler disabling IRQ forever

Lothar Waßmann
2012-02-07T12:52:16Z

Hi,

Yong Zhang writes:
> On Tue, Feb 07, 2012 at 11:01:06AM +0100, Lothar Wa?mann wrote:
> > Hi,
> >
> > > On Mon, Feb 06, 2012 at 09:14:47AM +0100, Lothar Wa?mann wrote:
> > > > Hi,
> > > >
> > > > I already sent this to <linux-kernel@vger.kernel.org> on Feb. 1, 2012
> > > > but did not get any response there. So resending to a wider audience
> > > > with improved subject line:
> > > >
> > > > there is a race condition in the threaded IRQ handler code for oneshot
> > > > interrupts that may lead to disabling an IRQ indefinitely. IRQs are
> > > > masked before calling the hard-irq handler and are unmasked only after
> > > > the soft-irq handler has been run. Thus if the hard-irq handler
> > > > returns IRQ_HANDLED instead of IRQ_WAKE_THREAD, meaning the soft-irq
> > > > will not be called, the interrupt will remain masked forever.
> > > >
> > > > This can happen due to a short pulse on the interrupt line, that
> > > > triggers the interrupt logic, but goes undetected by the hard-irq
> > > > handler. The problem can be reproduced with the TSC2007 touch
> > > > controller driver that uses ONESHOT interrupts.
> > >
> > > Isn't it the responsibility of the driver (say TSC2007)?
> > >
> > > In this case, TSC2007 should return IRQ_WAKE_THREAD IMHO.
> > >
> > That would mean it had to return IRQ_WAKE_THREAD unconditionally
> > making the return code useless.
> > And it would cause an extra useless loop through the softirq
> > handler.
>
> Yeah, it's the default behavior when we introduce 'theadirqs',
> and it's safe.
>
So, the correct solution would be to remove the check for
IRQ_WAKE_THREAD in handle_irq_event_percpu() and always invoke the
softirq handler?
Note that this problem is not specific to the TSC2007 driver, but may
occur with any hardware.

Or maybe do the unmasking in handle_irq_event() as proposed by
Lars-Peter Clausen in <4F2FAE93.5020205@metafoo.de>?
Like that:
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index f7c543a..fbf68c7 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -343,6 +343,8 @@ EXPORT_SYMBOL_GPL(handle_simple_irq);
void
handle_level_irq(unsigned int irq, struct irq_desc *desc)
{
+ int ret;
+
raw_spin_lock(&desc->lock);
mask_ack_irq(desc);

@@ -360,10 +362,12 @@ handle_level_irq(unsigned int irq, struct irq_desc *desc)
if (unlikely(!desc->action || irqd_irq_disabled(&desc->irq_data)))
goto out_unlock;

- handle_irq_event(desc);
+ ret = handle_irq_event(desc);

- if (!irqd_irq_disabled(&desc->irq_data) && !(desc->istate & IRQS_ONESHOT))
+ if (!irqd_irq_disabled(&desc->irq_data) &&
+ (!(desc->istate & IRQS_ONESHOT) || ret != IRQ_WAKE_THREAD))
unmask_irq(desc);
+
out_unlock:
raw_spin_unlock(&desc->lock);
}

Lothar Wa?mann
--
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