Re: [Xen-devel] [PATCH v3a 14/39] ARM: new VGIC: Add GICv2 world switch backend

[Andre Przywara <andre.przywara@xxxxxxxxxx>]

Hi,

On 22/03/18 14:06, Julien Grall wrote:
> Hi Andre,
> 
> On 03/22/2018 11:56 AM, Andre Przywara wrote:
>> +        /* The locking order forces us to drop and re-take the locks
>> here. */
>> +        if ( irq->hw )
>> +        {
>> +            spin_unlock(&irq->irq_lock);
>> +
>> +            desc = irq_to_desc(irq->hwintid);
>> +            spin_lock(&desc->lock);
>> +            spin_lock(&irq->irq_lock);
>> +
>> +            /* This h/w IRQ should still be assigned to the virtual
>> IRQ. */
>> +            ASSERT(irq->hw && desc->irq == irq->hwintid);
>> +
>> +            have_desc_lock = true;
>> +        }
> 
> I am a bit concerned of this dance in fold_lr_state(). This looks
> awfully complex but I don't have better solution here.

I agree.

> I will have a think during the night.
> 
> However, this is not going to solve the race condition I mentioned
> between clearing _IRQ_INPROGRESS here and setting _IRQ_INPROGRESS in
> do_IRQ. This is because you don't know the order they are going to be
> executed.
> 
> I wanted to make sure you didn't intend to solve that one. Am I correct?

This is right, this is orthogonal and not addressed by this patch. I
have a hunch we need to solve this in irq.c instead.

Cheers,
Andre.

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