From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keir Fraser <keir.xen@gmail.com>
Subject: Re: [PATCH 1/3] x86/HPET: obtain proper lock for
 changing IRQ affinity
Date: Tue, 16 Oct 2012 16:41:43 +0100
Message-ID: <CCA33EC7.41CC9%keir.xen@gmail.com>
References: <507D94BD02000078000A1BBD@nat28.tlf.novell.com>
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To: Jan Beulich <JBeulich@suse.com>, xen-devel <xen-devel@lists.xen.org>
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On 16/10/2012 16:09, "Jan Beulich" <JBeulich@suse.com> 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@suse.com>

Would be more usual for the underscore-prefixed name to be the one that
doesn't take locks?

 -- Keir

> --- 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>
> 
> 
> 
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