linux-kernel - Re: [PATCHv2] mm/slub: fix lockups on PREEMPT && !SMP kernels

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Message-ID: <alpine.DEB.2.11.1503191115030.26866@gentwo.org>
Date:	Thu, 19 Mar 2015 11:16:13 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Joonsoo Kim <js1304@...il.com>
cc:	Mark Rutland <mark.rutland@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	David Rientjes <rientjes@...gle.com>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>,
	Steve Capper <steve.capper@...aro.org>
Subject: Re: [PATCHv2] mm/slub: fix lockups on PREEMPT && !SMP kernels

On Thu, 19 Mar 2015, Joonsoo Kim wrote:

> > I was under the impression that this_cpu operations would always result
> > in an access, much like the *_ONCE accessors, so we should aways redo
> > the access for this_cpu_read(s->cpu_slab->tid). Is that not the case?
>
> I'm not the expert on that operation. Christoph could answer it.

this_cpu_read() always generates a load via an asm instruction.
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