On 03/27/2013 07:50 AM, Jan Kiszka wrote:
> On 2013-03-27 00:05, Gilles Chanteperdrix wrote:
>>
>> Hi Jan,
>>
>> I seem to recall you sent patches to fix threaded irqs some time ago. I
>
> In fact, that was Wolfgang with commits fdda86bca9 and 54d161b85b for
> 2.6.38 back then.
>
>> am having a problem here without SMP, whereas the system works with
>> SMP. A fasteoi irq handler triggers repeatedly while its threaded
>> counterpart never gets triggered. I believe this is because
>> handle_fasteoi_irq unconditionally releases the irq line.
>
> You mean it doesn't respect the conditions in cond_unmask_irq?
>
>> The following
>> patch seems to fix the issue though I would prefer a cleaner solution.
>>
>> diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
>> index 11e75d1..2ff8d3a 100644
>> --- a/kernel/irq/chip.c
>> +++ b/kernel/irq/chip.c
>> @@ -463,8 +463,11 @@ handle_fasteoi_irq(unsigned int irq, struct irq_desc
>> *desc)
>>
>> #ifdef CONFIG_IPIPE
>> /* XXX: IRQCHIP_EOI_IF_HANDLED is ignored. */
>> - if (desc->irq_data.chip->irq_release)
>> - desc->irq_data.chip->irq_release(&desc->irq_data);
>> + if (desc->irq_data.chip->irq_release) {
>> + if ((!(desc->istate & IRQS_ONESHOT) ||
>> + !desc->threads_oneshot))
>> + desc->irq_data.chip->irq_release(&desc->irq_data);
>> + }
>> out_eoi:
>> #else /* !CONFIG_IPIPE */
>> if (desc->istate & IRQS_ONESHOT)
>> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
>> index e49a288..485c2c4 100644
>> --- a/kernel/irq/manage.c
>> +++ b/kernel/irq/manage.c
>> @@ -715,9 +715,15 @@ again:
>>
>> desc->threads_oneshot &= ~action->thread_mask;
>>
>> - if (!desc->threads_oneshot && !irqd_irq_disabled(&desc->irq_data) &&
>> - irqd_irq_masked(&desc->irq_data))
>> - unmask_irq(desc);
>> + if (!desc->threads_oneshot && !irqd_irq_disabled(&desc->irq_data)) {
>> +#ifdef CONFIG_IPIPE
>> + if (desc->irq_data.chip->irq_release)
>> + desc->irq_data.chip->irq_release(&desc->irq_data);
>> + else
>> +#endif
>> + if (irqd_irq_masked(&desc->irq_data))
>> + unmask_irq(desc);
>> + }
>>
>> out_unlock:
>> raw_spin_unlock_irq(&desc->lock);
>>
>>
>
> So this basically extends I-pipe's held phase of the IRQ to the threaded
> handler if we are working in oneshot mode, right?
>
> I will have to dig into this again, but without remembering all details,
> there are some things that do not look OK:
> - Shouldn't we just replace unmask_irq with irq_release for the I-pipe
> case? IOW: There is too much code under #ifdef CONFIG_IPIPE.
No, unmask_irq still has to use ->irq_unmask, while the masking done by
the I-pipe has to use ->irq_release.
> - It seems we do not respect masking done by Linux, rather
> unconditionally release (AKA unmask) the line.
You mean masking which could be done by the interrupt handler?
>
> The latter was right in 2.6.38 but apparently got broken during to port
> from 3.2 to 3.4.
fasteoi irqs were reworked with the introduction of ->irq_hold and
->irq_release, because the 2.6.38 was found not to work either...
--
Gilles.
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