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

Jan Kiszka
2010-12-15T14:19:06Z

Am 15.12.2010 14:04, Thomas Gleixner wrote:
> On Wed, 15 Dec 2010, Jan Kiszka wrote:
>> 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.
>
> That should read "not set" I guess.

Can't remember who wrote this, but that guy might have been too tired
for clear sentences: Yes, of course, we could run into troubles, if
IRQS_SHARED was _not_ set while the IRQ line is unmasked between hard
and threaded handler.

> Hmm, needs more thoughts :(

Be warned, might be painful.

Jan

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