Re: CPU hotplug and chained interrupts on x86

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Thu, Oct 01, 2015 at 11:45:23PM +0200, Thomas Gleixner wrote:
> On Thu, 1 Oct 2015, Thomas Gleixner wrote:
> > On Thu, 1 Oct 2015, Mika Westerberg wrote:
> > > Now if I plug/unplug the card I may get few interrupts to CPU0 but rest
> > > of the interrupts never happen. Probably because IO-APIC forwards them
> > > to the lowest priority CPU which is offline at this point.
> > > 
> > > There is following check in fixup_irqs():
> > > 
> > > 	if (!irq_has_action(irq) || irqd_is_per_cpu(data) ||
> > > 	    cpumask_subset(affinity, cpu_online_mask)) {
> > > 		raw_spin_unlock(&desc->lock);
> > > 		continue;
> > > 	}   
> > > 
> > > If an interrupt is requested by a driver it will force new affinity and
> > > everything works fine. However if the interrupt is chained (it does not
> > > have ->action) this is skipped and the current affinity remains.
> > > 
> > > We could detect here if the interrupt is chained but there seems to be
> > > no easy way to determine it currently so we would need to add a new flag
> > > to desc->status_use_accessors that gets set in __irq_do_set_handler()
> > > when is_chained is 1.
> > 
> > Either there or in irq_data. Need to look at it in detail.
> 
> desc->status_use_accessors is the place where this wants to go.

Thank you.

I'll prepare a patch fixing this shortly.