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Date: Fri, 21 Feb 2014 14:42:03 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>
Subject: Re: [PATCH 1/3] mm: return NUMA_NO_NODE in local_memory_node if
 zonelists are not setup
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Cc: Michal Hocko <mhocko@suse.cz>, linux-mm@kvack.org,
 Mel Gorman <mgorman@suse.de>, David Rientjes <rientjes@google.com>,
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On Thu, 20 Feb 2014 10:28:47 -0800 Nishanth Aravamudan <nacc@linux.vnet.ibm.com> wrote:

> On 20.02.2014 [10:05:39 -0600], Christoph Lameter wrote:
> > On Wed, 19 Feb 2014, Nishanth Aravamudan wrote:
> > 
> > > We can call local_memory_node() before the zonelists are setup. In that
> > > case, first_zones_zonelist() will not set zone and the reference to
> > > zone->node will Oops. Catch this case, and, since we presumably running
> > > very early, just return that any node will do.
> > 
> > Really? Isnt there some way to avoid this call if zonelists are not setup
> > yet?
> 
> How do I best determine if zonelists aren't setup yet?
> 
> The call-path in question (after my series is applied) is:
> 
> arch/powerpc/kernel/setup_64.c::setup_arch ->
> 	arch/powerpc/mm/numa.c::do_init_bootmem() ->
> 		cpu_numa_callback() ->
> 			numa_setup_cpu() ->
> 				map_cpu_to_node() ->
> 					update_numa_cpu_node() ->
> 						set_cpu_numa_mem()
> 
> and setup_arch() is called before build_all_zonelists(NULL, NULL) in
> start_kernel(). This seemed like the most reasonable path, as it's used
> on hotplug as well.
> 

But the call to local_memory_node() you added was in start_secondary(),
which isn't in that trace.

I do agree that calling local_memory_node() too early then trying to
fudge around the consequences seems rather wrong.