Messages in this thread | | | Date | Thu, 12 Oct 2023 21:39:54 +0800 | From | Wei Gong <> | Subject | Re: [PATCH v3] genirq: avoid long loops in handle_edge_irq |
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O Mon, Oct 09, 2023 at 04:32:10PM +0200, Thomas Gleixner wrote: > On Thu, Sep 28 2023 at 18:06, Wei Gong wrote: > > --- a/kernel/irq/chip.c > > +++ b/kernel/irq/chip.c > > @@ -831,7 +831,9 @@ void handle_edge_irq(struct irq_desc *desc) > > handle_irq_event(desc); > > > > } while ((desc->istate & IRQS_PENDING) && > > - !irqd_irq_disabled(&desc->irq_data)); > > + !irqd_irq_disabled(&desc->irq_data) && > > + cpumask_test_cpu(smp_processor_id(), > > + irq_data_get_effective_affinity_mask(&desc->irq_data))); > > Ok. So now that mask part is correct, but what guarantees that this does > not lose interrupts? > > Assume the following scenario: > > CPU 0 CPU 1 > > interrupt > set IN_PROGRESS > do { > change_affinity_to(CPU1); > handle_irq_event() > ack_in_device() > interrupt > set PENDING > } while (COND) > > Now $COND is not true due to the affinity change and the edge handler > returns. As a consequence nothing acks the device and no further > interrupts are sent by the device. > > That might not be true for your case, but that's a generic function and the > zoo of hardware which uses that is massive. > > So no, we are not taking a risk here. > > Thanks, > > tglx > > By maintaining the original loop exit condition, if a mask mismatch is detected within the loop, we will not perform the unmask_irq operation. Instead, we will wait until the loop exits before executing unmask_irq. Could this approach potentially solve the issue of lost interrupts?
Thanks, Wei Gong
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