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

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Date:	Mon, 28 Sep 2009 12:25:16 -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:

> pcpu_setup_first_chunk() incorrectly used NR_CPUS as the impossible
> unit number while unit number can equal and go over NR_CPUS with
> sparse unit map.  This triggers BUG_ON() spuriously on machines which
> have non-power-of-two number of cpus.  Use UINT_MAX instead.

Uhhh. Funky. The assumption nr_cpu_ids < NR_CPUS has been broken. Wonder
what other effects that will have. In particular since the slab and page
allocators have arrays indexed by the cpu number and those arrays are
dimensioned for NR_CPUS.

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