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

Lars-Peter Clausen lars at metafoo.de
Mon Feb 6 05:42:27 EST 2012

On 02/06/2012 09:14 AM, =?utf-8?Q?Lothar_Wa=C3=9Fmann?= wrote:
> Hi,
> I already sent this to <linux-kernel at 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.

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