Re: [Xen-devel] [PATCH] xen: do not unmask disabled IRQ on eoi.

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 15.10.10 at 19:03, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> 
>>> wrote:
> @@ -1074,9 +1081,6 @@ static void __xen_evtchn_do_upcall(struct pt_regs 
> *regs)
>                               int irq = evtchn_to_irq[port];
>                               struct irq_desc *desc;
>  
> -                             mask_evtchn(port);
> -                             clear_evtchn(port);
> -
>                               if (irq != -1) {
>                                       desc = irq_to_desc(irq);
>                                       if (desc)
> @@ -1202,7 +1206,7 @@ static void ack_dynirq(unsigned int irq)
>       move_masked_irq(irq);
>  
>       if (VALID_EVTCHN(evtchn))
> -             unmask_evtchn(evtchn);
> +             clear_evtchn(evtchn);
>  }
>  
>  static int retrigger_irq(unsigned int irq)

These two hunks together don't look right, for two reasons: First,
ack_dynirq() is used as both .eoi and .ack, but those certainly
have different requirements (and this might have been a problem
already before, though I didn't spend much thought on what may
go wrong). Second, clearing the event channel in the .eoi handler
after it wasn't masked while being handled has the potential of
losing an event (if it got raised between the IRQ handler checking
relevant state and the execution of clear_evtchn()).

Jan


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