[Xen-devel] Re: [PATCH] irq: Exclude percpu IRQs from being fixed up

[Fengzhe Zhang <fengzhe.zhang@xxxxxxxxx>]

On 2011/2/17 15:52, Jan Beulich wrote:
> > > > On 17.02.11 at 01:15, Fengzhe Zhang<fengzhe.zhang@xxxxxxxxx>  wrote:
> > On 2011/2/16 22:53, Jan Beulich wrote:
> > > > > > On 16.02.11 at 15:26, "Zhang, Fengzhe"<fengzhe.zhang@xxxxxxxxx>   wrote:
> > > > irq: Exclude percpu IRQs from being fixed up
> > > >
> > > > Xen spin unlock uses spurious ipi "lock_kicker_irq" to wake up blocked vCPUs
> > > > waiting on that lock. This irq should always be disabled. However, when Dom0
> > > > is shuting down, function fixup_irqs is called which unmasks all irqs.
> > > > Function unmask_irq effectively re-enables lock_kicker_irq and its irq
> > handler
> > > > is invoked which reports bug and crashes Dom0.
> > > >
> > > > This patch sets IRQ_PER_CPU flag in irq desc and excludes percpu IRQs from
> > > > being fixed up when taking CPUs down.
> > > >
> > > > Signed-off-by: Fengzhe Zhang<fengzhe.zhang@xxxxxxxxx>
> > > >
> > > > diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
> > > > index 977d8b4..f0f9450 100644
> > > > --- a/arch/x86/kernel/irq_64.c
> > > > +++ b/arch/x86/kernel/irq_64.c
> > > > @@ -80,6 +80,9 @@ void fixup_irqs(void)
> > > >                 if (irq == 2)
> > > >                         continue;
> > > >
> > > > +               if (desc->status&   IRQ_PER_CPU)
> > > > +                       continue;
> > > > +
> > > >                 /* interrupt's are disabled at this point */
> > > >                 spin_lock(&desc->lock);
> > > >
> > > > diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> > > > index f34e231..26bc55a 100644
> > > > --- a/kernel/irq/manage.c
> > > > +++ b/kernel/irq/manage.c
> > > > @@ -727,10 +727,9 @@ __setup_irq(unsigned int irq, struct irq_desc *desc,
> > > > struct irqaction *new)
> > > >                                 goto out_thread;
> > > >                 } else
> > > >                         compat_irq_chip_set_default_handler(desc);
> > > > -#if defined(CONFIG_IRQ_PER_CPU)
> > > Why? XEN should select IRQ_PER_CPU instead in its Kconfig.
> > >
> > > Jan
> > IRQ_PER_CPU switch is not found in current Kconfig. I'm not sure if this
> kernel/irq/Kconfig (introduced as a generic option in 2.6.38-rc2). In
> prior kernel you'd have to add a respective Kconfig item in
> drivers/xen/Kconfig.
>
> > feature is going to be brought back in the short term. I remove the
> > ifdef to set IRQ_PER_CPU flag in desc by default but still leave the IRQ
> > handling logic unchanged. This is a temporary solution to fix system
> > crash on poweroff. And this is the fix with minimum impact among the
> > several solutions we tried.
> But it's more a hack than a fix. And making per-CPU IRQs properly
Yes, that's true. Switching on IRQ_PER_CPU can make this patch neat. But 
that isn't my call.
-Fengzhe

> treated as such isn't a bad idea in any case, I would say.
>
> Jan

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