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
next prev parent 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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