Re: [Xen-devel] [PATCH v2 3/3] xen/arm: don't try to re-register vcpu_info on cpu_hotplug.

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 16 Oct 2015, Julien Grall wrote:
> Hi Stefano,
> 
> On 16/10/15 17:35, Stefano Stabellini wrote:
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > ---
> >  arch/arm/xen/enlighten.c |   10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> > index 6c09cc4..b193811 100644
> > --- a/arch/arm/xen/enlighten.c
> > +++ b/arch/arm/xen/enlighten.c
> > @@ -93,6 +93,16 @@ static void xen_percpu_init(void)
> >     int err;
> >     int cpu = get_cpu();
> >  
> > +   /* 
> > +    * VCPUOP_register_vcpu_info cannot be called twice for the same
> > +    * vcpu, so if vcpu_info is already registered, just get out. This
> > +    * can happen with cpu-hotplug.
> > +    */
> > +   if (per_cpu(xen_vcpu, cpu) != NULL) {
> > +           put_cpu();
> > +           return;
> > +   }
> 
> 
> Not really related to this patch. By side effect this patch is also not
> calling irq_percpu_enable.
> 
> Looking around, all the caller of irq_percpu_enable will call
> irq_percpu_disable when the CPU is dying. Is there any side effect to
> not doing this?

Given that Xen won't inject any event irqs when a cpu is offline, I
don't think there are any side effects.


> > +
> >     pr_info("Xen: initializing cpu%d\n", cpu);
> >     vcpup = per_cpu_ptr(xen_vcpu_info, cpu);
> >  
> > 
> 
> 
> -- 
> Julien Grall
> 

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