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Date: Mon, 21 Jan 2013 01:40:41 +0000
From: Christoph Lameter <cl@linux.com>
Subject: Re: [RFC][PATCH v3] slub: Keep page and object in sync in
 slab_alloc_node()
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To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>, LKML <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>, Andrew Morton <akpm@linux-foundation.org>, Pekka Enberg <penberg@kernel.org>, Matt Mackall <mpm@selenic.com>, Thomas Gleixner <tglx@linutronix.de>, RT <linux-rt-users@vger.kernel.org>, Clark Williams <clark@redhat.com>, John Kacur <jkacur@gmail.com>, "Luis Claudio R. Goncalves" <lgoncalv@redhat.com>

On Fri, 18 Jan 2013, Eric Dumazet wrote:

> On Fri, 2013-01-18 at 18:40 +0000, Christoph Lameter wrote:
>
> > The fetching of the tid is the only critical thing here. If the tid is
> > retrieved from the right cpu then the cmpxchg will fail if any changes
> > occured to freelist or the page variable.
> >
> > The tid can be retrieved without disabling preemption through
> > this_cpu_read().
>
> Strictly speaking, this_cpu_read() _does_ disable preemption.

Yes on x86 the relocation and the fetch is just a single instruction and
therefore no preemption can occur.

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