Re: [Xen-devel] [PATCH 1/3] x86/HPET: obtain proper lock for changing IRQ affinity

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 16/10/2012 17:11, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

>>>> On 16.10.12 at 17:41, Keir Fraser <keir.xen@xxxxxxxxx> wrote:
>> On 16/10/2012 16:09, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
>> 
>>> The IRQ descriptor lock should be held while adjusting the affinity of
>>> any IRQ; the HPET channel lock isn't sufficient to protect namely
>>> against races with moving the IRQ to a different CPU.
>>> 
>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> 
>> Would be more usual for the underscore-prefixed name to be the one that
>> doesn't take locks?
> 
> Will make the patch bigger, but I can certainly do that. I specifically
> picked only a single underscore to distinguish this a little from the
> "usual" case.

It doesn't make the patch much bigger, and it would be preferable.

> Jan
> 
>>> --- a/xen/arch/x86/hpet.c
>>> +++ b/xen/arch/x86/hpet.c
>>> @@ -436,6 +436,16 @@ static struct hpet_event_channel *hpet_g
>>>      return ch;
>>>  }
>>>  
>>> +static void _hpet_msi_set_affinity(const struct hpet_event_channel *ch)
>>> +{
>>> +    struct irq_desc *desc = irq_to_desc(ch->irq);
>>> +
>>> +    ASSERT(!local_irq_is_enabled());
>>> +    spin_lock(&desc->lock);
>>> +    hpet_msi_set_affinity(desc, cpumask_of(ch->cpu));
>>> +    spin_unlock(&desc->lock);
>>> +}
>>> +
>>>  static void hpet_attach_channel(unsigned int cpu,
>>>                                  struct hpet_event_channel *ch)
>>>  {
>>> @@ -450,7 +460,7 @@ static void hpet_attach_channel(unsigned
>>>      if ( ch->cpu != cpu )
>>>          return;
>>>  
>>> -    hpet_msi_set_affinity(irq_to_desc(ch->irq), cpumask_of(ch->cpu));
>>> +    _hpet_msi_set_affinity(ch);
>>>  }
>>>  
>>>  static void hpet_detach_channel(unsigned int cpu,
>>> @@ -472,7 +482,7 @@ static void hpet_detach_channel(unsigned
>>>      }
>>>  
>>>      ch->cpu = cpumask_first(ch->cpumask);
>>> -    hpet_msi_set_affinity(irq_to_desc(ch->irq), cpumask_of(ch->cpu));
>>> +    _hpet_msi_set_affinity(ch);
>>>  }
>>>  
>>>  #include <asm/mc146818rtc.h>
>>> 
>>> 
>>> 
>>> _______________________________________________
>>> Xen-devel mailing list
>>> Xen-devel@xxxxxxxxxxxxx
>>> http://lists.xen.org/xen-devel
> 
> 
> 



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