Re: [PATCH v3 2/4] genirq: Inform handler about line sharing state

Jan Kiszka
2010-12-14T23:00:45Z

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Am 14.12.2010 21:54, Thomas Gleixner wrote:
> On Mon, 13 Dec 2010, Jan Kiszka wrote:
>> @@ -943,6 +950,9 @@ static struct irqaction *__free_irq(unsigned int irq, void *dev_id)
>> /* Make sure it's not being used on another CPU: */
>> synchronize_irq(irq);
>>
>> + if (single_handler)
>> + desc->irq_data.drv_status &= ~IRQS_SHARED;
>> +
>
> What's the reason to clear this flag outside of the desc->lock held
> region.

We need to synchronize the irq first before clearing the flag.

The problematic scenario behind this: An IRQ started in shared mode,
this the line was unmasked after the hardirq. Now we clear IRQS_SHARED
before calling into the threaded handler. And that handler may now think
that the line is still masked as IRQS_SHARED is set.

> I need this status for other purposes as well, where I
> definitely need serialization.

Well, two options: wrap all bit manipulations with desc->lock
acquisition/release or turn drv_status into an atomic. I don't know what
your plans with drv_status are, so...

>
>> + mutex_lock(&register_lock);
>> +
>> + old_action = desc->action;
>> + if (old_action && (old_action->flags & IRQF_ADAPTIVE) &&
>> + !(desc->irq_data.drv_status & IRQS_SHARED)) {
>> + /*
>> + * Signal the old handler that is has to switch to shareable
>> + * handling mode. Disable the line to avoid any conflict with
>> + * a real IRQ.
>> + */
>> + disable_irq(irq);
>> + local_irq_disable();
>> +
>> + desc->irq_data.drv_status |= IRQS_SHARED | IRQS_MAKE_SHAREABLE;
>
> Unserialized access as well. Will think about it.
>
>> + old_action->handler(irq, old_action->dev_id);
>> + desc->irq_data.drv_status &= ~IRQS_MAKE_SHAREABLE;
>
> Thanks,
>
> tglx

Jan

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