| Message ID | 20271.35831.227679.177366@ipc1.ka-ro |
|---|---|
| State | New |
| Headers | show |
On 02/06/2012 09:14 AM, =?utf-8?Q?Lothar_Wa=C3=9Fmann?= 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. > > The problem arises also with interrupt controllers that latch a level > triggered IRQ until it is acknowledged (like the i.MX28 does). > In this case the IRQ status bit will remain asserted after the > soft-irq finishes and retrigger the interrupt while the interrupt line > is already deasserted. > > The following patch would solve the problem, but I'm not sure whether > it's the Right Thing(TM) to do. Especially wrt. shared interrupts. > > diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c > index 470d08c..93beadb 100644 > --- a/kernel/irq/handle.c > +++ b/kernel/irq/handle.c > @@ -146,6 +146,11 @@ handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action) > /* Fall through to add to randomness */ > case IRQ_HANDLED: > random |= action->flags; > + /* unmask the IRQ that has been left masked > + * due to race condition > + */ > + if (res == IRQ_HANDLED && (action->flags & IRQF_ONESHOT)) > + unmask_irq(desc); > break; > > default: I think a better fix is to check the return value of handle_irq_event in handle_level_irq and if the IRQ_WAKE_THREADED bit is not set unmask the irq. The same should probably also be done for handle_fasteoi_irq.
On Mon, Feb 06, 2012 at 09:14:47AM +0100, =?utf-8?Q?Lothar_Wa=C3=9Fmann?= 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. Thanks, Yong > > The problem arises also with interrupt controllers that latch a level > triggered IRQ until it is acknowledged (like the i.MX28 does). > In this case the IRQ status bit will remain asserted after the > soft-irq finishes and retrigger the interrupt while the interrupt line > is already deasserted. > > The following patch would solve the problem, but I'm not sure whether > it's the Right Thing(TM) to do. Especially wrt. shared interrupts. > > diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c > index 470d08c..93beadb 100644 > --- a/kernel/irq/handle.c > +++ b/kernel/irq/handle.c > @@ -146,6 +146,11 @@ handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action) > /* Fall through to add to randomness */ > case IRQ_HANDLED: > random |= action->flags; > + /* unmask the IRQ that has been left masked > + * due to race condition > + */ > + if (res == IRQ_HANDLED && (action->flags & IRQF_ONESHOT)) > + unmask_irq(desc); > break; > > default: > > Best regards, > > Lothar Wassmann > -- > ___________________________________________________________ > > Ka-Ro electronics GmbH | Pascalstraße 22 | D - 52076 Aachen > Phone: +49 2408 1402-0 | Fax: +49 2408 1402-10 > Geschäftsführer: Matthias Kaussen > Handelsregistereintrag: Amtsgericht Aachen, HRB 4996 > > www.karo-electronics.de | info@karo-electronics.de > ___________________________________________________________ > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
Hi, > On Mon, Feb 06, 2012 at 09:14:47AM +0100, Lothar Waßmann 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. Lothar Waßmann
On Tue, Feb 07, 2012 at 11:01:06AM +0100, Lothar Waßmann wrote: > Hi, > > > On Mon, Feb 06, 2012 at 09:14:47AM +0100, Lothar Waßmann 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. You know in your patch unmask_irq() is called locklessly and it will introduce other race. Thanks, Yong
diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c index 470d08c..93beadb 100644 --- a/kernel/irq/handle.c +++ b/kernel/irq/handle.c @@ -146,6 +146,11 @@ handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action) /* Fall through to add to randomness */ case IRQ_HANDLED: random |= action->flags; + /* unmask the IRQ that has been left masked + * due to race condition + */ + if (res == IRQ_HANDLED && (action->flags & IRQF_ONESHOT)) + unmask_irq(desc); break; default: