Re: [PATCH 0/7] xen/events: bug fixes and some diagnostic aids

[Julien Grall]

Hi Juergen,

On 08/02/2021 10:22, Jürgen Groß wrote:
> On 08.02.21 10:54, Julien Grall wrote:
> > ... I don't really see how the difference matter here. The idea is to 
> > re-use what's already existing rather than trying to re-invent the 
> > wheel with an extra lock (or whatever we can come up).
>
> The difference is that the race is occurring _before_ any IRQ is
> involved. So I don't see how modification of IRQ handling would help.

Roughly our current IRQ handling flow (handle_eoi_irq()) looks like:

if ( irq in progress )
{
  set IRQS_PENDING
  return;
}

do
{
  clear IRQS_PENDING
  handle_irq()
} while (IRQS_PENDING is set)

IRQ handling flow like handle_fasteoi_irq() looks like:

if ( irq in progress )
  return;

handle_irq()

The latter flow would catch "spurious" interrupt and ignore them. So it 
would handle nicely the race when changing the event affinity.

Cheers,

--
Julien Grall