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

[Jan Kiszka]

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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