linux-kernel - Re: [PATCH] percpu: fix unit_map[] verification in pcpu_setup_first

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Date:	Mon, 28 Sep 2009 12:40:56 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Tejun Heo <tj@...nel.org>
cc:	Tony Vroon <tony@...x.net>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] percpu: fix unit_map[] verification in
 pcpu_setup_first_chunk()

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.

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