linux-kernel - Re: [PATCH 9/9] slab: remove a useless lockdep annotation

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Date:	Tue, 18 Feb 2014 10:21:10 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
cc:	Pekka Enberg <penberg@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 9/9] slab: remove a useless lockdep annotation

On Mon, 17 Feb 2014, Joonsoo Kim wrote:

> > Why change the BAD_ALIEN_MAGIC?
>
> Hello, Christoph.
>
> BAD_ALIEN_MAGIC is only checked by slab_set_lock_classes(). We remove this
> function in this patch, so returning BAD_ALIEN_MAGIC is useless.

Its not useless. The point is if there is a pointer deref then we will see
this as a pointer value and know that it is realted to alien cache
processing.

> And, in fact, BAD_ALIEN_MAGIC is already useless, because alloc_alien_cache()
> can't be called on !CONFIG_NUMA. This function is called if use_alien_caches
> is positive, but on !CONFIG_NUMA, use_alien_caches is always 0. So we don't
> have any chance to meet this BAD_ALIEN_MAGIC in runtime.

Maybe it no longer serves a point. But note that caches may not be
populated because processors/nodes are not up yet.

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