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

[Jürgen Groß]

On 08.02.21 11:40, Julien Grall wrote:
> 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.

Sure? Isn't "irq in progress" being reset way before our "lateeoi" is
issued, thus having the same problem again? And I think we want to keep
the lateeoi behavior in order to be able to control event storms.


Juergen

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