[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <ZSf3KrAk8fpyNEZr@MacBook-Pro-3.local>
Date: Thu, 12 Oct 2023 21:39:54 +0800
From: Wei Gong <gongwei833x@...il.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] genirq: avoid long loops in handle_edge_irq
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
Powered by blists - more mailing lists