Re: [PATCH rc v6 3/7] iommu/arm-smmu-v3: Do not enable EVTQ/PRIQ interrupts in kdump kernel

[Nicolin Chen <nicolinc@nvidia.com>]

On Mon, Jun 29, 2026 at 08:48:11AM +0000, Pranjal Shrivastava wrote:
> On Wed, May 20, 2026 at 10:03:20AM -0700, Nicolin Chen wrote:
> > @@ -5020,19 +5029,30 @@ static int arm_smmu_setup_irqs(struct arm_smmu_device *smmu)
> >  		/*
> >  		 * Cavium ThunderX2 implementation doesn't support unique irq
> >  		 * lines. Use a single irq line for all the SMMUv3 interrupts.
> > +		 *
> > +		 * In kdump, EVTQ/PRIQ are disabled, so no threaded handling.
> >  		 */
> > -		ret = devm_request_threaded_irq(smmu->dev, irq,
> > -					arm_smmu_combined_irq_handler,
> > -					arm_smmu_combined_irq_thread,
> > -					IRQF_ONESHOT,
> > -					"arm-smmu-v3-combined-irq", smmu);
> > +		if (is_kdump_kernel())
> > +			ret = devm_request_irq(smmu->dev, irq,
> > +					       arm_smmu_combined_irq_handler, 0,
> > +					       "arm-smmu-v3-combined-irq",
> > +					       smmu);
> 
> This `if` isn't needed, we can continue using devm_request_threaded_irq,
> if you look at the doc for devm_request_threaded_irq [1] it says:
[...]
> So, we can pass handler() here while leaving the thread_fn == NULL:
> 
> ret = devm_request_threaded_irq(smmu->dev, irq,
>          arm_smmu_combined_irq_handler,
>          is_kdump_kernel() ? NULL : arm_smmu_combined_irq_thread,
>          IRQF_ONESHOT,
>          "arm-smmu-v3-combined-irq", smmu);

Are you sure?

__setup_irq():
1497-   /*
1498:    * IRQF_ONESHOT means the interrupt source in the IRQ chip will be
1499-    * masked until the threaded handled is done. If there is no thread
1500:    * handler then it makes no sense to have IRQF_ONESHOT.
1501-    */
1502:   WARN_ON_ONCE(new->flags & IRQF_ONESHOT && !new->thread_fn);

> Additionally, the arm_smmu_combined_irq_handler() returns 
> IRQ_WAKE_THREAD unconditionally, which causes us to hit the warn_on[3] in
> __handle_irq_event_percpu.

arm_smmu_combined_irq_handler() does not return IRQ_WAKE_THREAD
unconditionally.

This is the first part of PATCH-3 in v6:

@@ -2464,7 +2464,11 @@ static irqreturn_t arm_smmu_combined_irq_thread(int irq, void *dev)
 
 static irqreturn_t arm_smmu_combined_irq_handler(int irq, void *dev)
 {
-	arm_smmu_gerror_handler(irq, dev);
+	irqreturn_t ret = arm_smmu_gerror_handler(irq, dev);
+
+	/* In kdump, EVTQ/PRIQ are disabled and there is no thread to wake */
+	if (is_kdump_kernel())
+		return ret;
 	return IRQ_WAKE_THREAD;
 }
 
Nicolin