Re: [PATCH v2 1/3] genirq/affinity: Add irq_update_affinity_desc()

[John Garry]

On 28/10/2020 18:22, Thomas Gleixner wrote:
> On Wed, Oct 28 2020 at 20:33, John Garry wrote:

Hi Thomas,

> >   
> > +int irq_update_affinity_desc(unsigned int irq,
> > +			     struct irq_affinity_desc *affinity)
> > +{
> > +	unsigned long flags;
> > +	struct irq_desc *desc = irq_get_desc_lock(irq, &flags, 0);
> > +
> > +	if (!desc)
> > +		return -EINVAL;
> Just looking at it some more. This needs a check whether the interrupt
> is actually shut down. Otherwise the update will corrupt
> state. Something like this:
>
>          if (irqd_is_started(&desc->irq_data))
>          	return -EBUSY;
>
> But all of this can't work on x86 due to the way how vector allocation
> works. Let me think about that.

Is the problem that we reserve per-cpu managed interrupt space when 
allocated irq vectors on x86, and so later changing managed vs 
non-managed setting for irqs messes up this accounting somehow?

Cheers,
John