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From: Tejun Heo <tj@kernel.org>
To: Christoph Lameter <cl@linux-foundation.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()
Date: Tue, 29 Sep 2009 01:53:06 +0900	[thread overview]
Message-ID: <4AC0E9F2.1020408@kernel.org> (raw)
In-Reply-To: <alpine.DEB.1.10.0909281239100.16040@gentwo.org>

Christoph Lameter wrote:
> 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.

It's a unit number.  Each cpu has exactly one unit number assigned to
it but there can be holes, so unit number can legally go over both
nr_cpu_ids and NR_CPUS, so yeap, it's just an internal number used
inside percpu allocator.

Tony, the original patch should be correct.  Please verify.

Thanks.

-- 
tejun

  reply	other threads:[~2009-09-28 16:53 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-09-24  0:53 [PATCH] percpu: make pcpu_setup_first_chunk() failures more verbose Tejun Heo
2009-09-24 12:49 ` [PATCH] percpu: make allocation " Tejun Heo
2009-09-27 12:49 ` 2.6.31-09194-g0d9df25 Early boot exception Tony Vroon
2009-09-28 16:19   ` [PATCH] percpu: fix unit_map[] verification in pcpu_setup_first_chunk() Tejun Heo
2009-09-28 16:25     ` Christoph Lameter
2009-09-28 16:35       ` Tejun Heo
2009-09-28 16:38         ` Tejun Heo
2009-09-28 16:40           ` Christoph Lameter
2009-09-28 16:53             ` Tejun Heo [this message]
2009-09-28 22:07     ` Tony Vroon
2009-09-29  0:15       ` Tejun Heo

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