linux-kernel - Re: [PATCH] - SN: validate smp_affinity mask on intr redirect

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Message-Id: <200705032119.l43LJTo0037721@fcbayern.americas.sgi.com>
Date:	Thu, 3 May 2007 16:19:28 -0500 (CDT)
From:	John Keller <jpk@....com>
To:	akpm@...ux-foundation.org (Andrew Morton)
Cc:	jpk@....com (John Keller), linux-ia64@...r.kernel.org,
	steiner@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] - SN: validate smp_affinity mask on intr redirect

I'll rework as per your suggestions.

Thanks,
John


> 
> On Thu, 03 May 2007 07:56:02 -0500
> John Keller <jpk@....com> wrote:
> 
> > On SN, only allow one bit to be set in the smp_affinty mask
> > when redirecting an interrupt. Currently setting multiple
> > bits is allowed, but only the first bit is used in
> > determining the CPU to redirect to. This has caused confusion
> > among some customers.
> > 
> > ...
> >
> > +
> > +int is_affinity_mask_valid(cpumask_t cpumask)
> > +{
> > +	if (ia64_platform_is("sn2")) {
> > +		/* Only allow one CPU to be specified in the smp_affinity mask */
> > +		if (cpus_weight(cpumask) != 1)
> > +			return 0;
> > +	}
> > +	return 1;
> > +}
> 
> A bool returning true or false would be appropriate, given this function's
> clearly-boolean name.
> 
> > +#ifndef ARCH_HAS_IRQ_AFFINITY_VALIDATION
> > +#define is_irq_affinity_mask_valid(cpumask)         1
> > +#endif
> 
> The ARCH_HAS_FOO things have never been popular.  There are a couple of
> alternatives going around:
> 
> a) use __attribute__((weak)) and provide a one-line default
>    implementation in kernel/irq/proc.c.  This has a small runtime cost.
> 
> b) In include/asm-ia64/irq.h, do
> 
>    #define is_affinity_mask_valid is_affinity_mask_valid
> 
>    and in kernel/irq/proc.c do
> 
>    #ifndef is_affinity_mask_valid
>    #define is_affinity_mask_valid() 1
>    #endif
> 
>    This has minimal runtime cost, but is a bit tricksy.
> 
>    It has the advantage that it doesn't introduce some new identifier
>    which needs to be maintained.
> 
> >  extern int irq_set_affinity(unsigned int irq, cpumask_t cpumask);
> >  extern int irq_can_set_affinity(unsigned int irq);
> >  
> > Index: linux-2.6/include/asm-ia64/irq.h
> > ===================================================================
> > --- linux-2.6.orig/include/asm-ia64/irq.h	2007-05-01 15:47:01.660643076 -0500
> > +++ linux-2.6/include/asm-ia64/irq.h	2007-05-01 15:48:42.729254805 -0500
> > @@ -11,6 +11,8 @@
> >   * 02/29/00     D.Mosberger	moved most things into hw_irq.h
> >   */
> >  
> > +#include <linux/cpumask.h>
> > +
> 
> This is the sort of inclusion which tends to make things blow up.  I trust
> this was carefully compile-tested.
> 
> With a) above, the is_affinity_mask_valid() declaration would be in a
> different header.  With b), no additional include will be needed.
> 
> >  #define NR_IRQS		256
> >  #define NR_IRQ_VECTORS	NR_IRQS
> >  
> > @@ -30,4 +32,7 @@ extern void disable_irq_nosync (unsigned
> >  extern void enable_irq (unsigned int);
> >  extern void set_irq_affinity_info (unsigned int irq, int dest, int redir);
> >  
> > +#define ARCH_HAS_IRQ_AFFINITY_VALIDATION
> > +extern int is_affinity_mask_valid(cpumask_t cpumask);
> > +
> 
> 

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