linux-kernel - Re: [patch 6/6] x86: cpumask_of_node() should handle -1 as a node

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Message-ID: <alpine.DEB.2.00.1001061454580.11653@chino.kir.corp.google.com>
Date:	Wed, 6 Jan 2010 15:00:45 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
cc:	Anton Blanchard <anton@...ba.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 6/6] x86: cpumask_of_node() should handle -1 as a node

On Wed, 6 Jan 2010, Rusty Russell wrote:

> > pcibus_to_node can return -1 if we cannot determine which node a pci bus
> > is on. If passed -1, cpumask_of_node will negatively index the lookup array
> > and pull in random data:
> 
> If you grep for the callers, you'll see those which do this (now-obsolete)
> check.  One more patch :)
> 

Do we really want to do this?  A nid of -1 is undefined, so the result of 
cpumask_of_node(-1) should be undefined; there's no formal definition that 
a nid of -1 follows the semantics that we use for x86 pci buses, for 
example, where it implies no NUMA locality in all cases.

I think a better fix would be to define -1 where appropriate to either be 
an invalid node, cpu_all_mask, or whatever in the caller:

	mask = (nid != -1) ? cpumask_of_node(nid) : cpu_all_mask;
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