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Date: Mon, 28 Sep 2009 12:40:56 -0400 (EDT)
From: Christoph Lameter <cl@linux-foundation.org>
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To: Tejun Heo <tj@kernel.org>
cc: Tony Vroon <tony@linx.net>, Linux Kernel <linux-kernel@vger.kernel.org>,
       Rusty Russell <rusty@rustcorp.com.au>, Ingo Molnar <mingo@elte.hu>,
       "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH] percpu: fix unit_map[] verification in
 pcpu_setup_first_chunk()
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On Tue, 29 Sep 2009, Tejun Heo wrote:

>
> Christoph, can you please elaborate why nr_cpu_ids < NR_CPUS is
> broken?

If its just an internal number that becomes larger than NR_CPUS then
everything is fine.

But if a real cpu id (returned by smp_processor_id()) gets larger than
NR_CPUS then we get into trouble with the parts of the kernel that index
by cpu id.