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Date: Tue, 5 May 2009 13:41:23 -0700 (PDT)
From: David Rientjes <rientjes@google.com>
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To: Jack Steiner <steiner@sgi.com>
cc: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>, alex.shi@intel.com,
       LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
       Andi Kleen <andi@firstfloor.org>
Subject: Re: [PATCH] Fix early panic issue on machines with memless node
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On Tue, 5 May 2009, Jack Steiner wrote:

> I suspect I mislead you when I mentioned "configurations". I did not mean
> the .config file. I use a more-or-less standard .config file.
> 

Your .config would still let me build a kernel with debugging symbols so 
that your offsets actually made sense to my gdb.

> I do much of my testing on a system simulator. Using a simulator config file,
> I specify the system configuration such as number of nodes, sockets per node,
> cpus per socket, memory per socket, address map, boot options, etc. This
> makes it easy to quickly test a lot of strange (but real) configurations.
> 
> The configuration above that is failing is a 2-socket Nehelem blade that has no
> memory on socket 0. All memory is located on socket 1.  The panic is caused by a
> null dereference of NODE_DATA(0).
> 

A NULL dereference of NODE_DATA(0) should never happen even with 
!CONFIG_NEED_MULTIPLE_NODES.  So when you say the panic is caused by that 
(and I'm speculating since all I've seen is a call trace and not the 
entire panic), I'm assuming it's because NODE_DATA(0)->node_zones + offset 
is NULL because node 0 has no memory?