On Tue, Feb 18, 2014 at 10:21:10AM -0600, Christoph Lameter wrote:

On Mon, 17 Feb 2014, Joonsoo Kim wrote:

quoted

quoted

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.

quoted

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.

Hello,

Let me clarify about alloc_alien_cache().

alloc_alien_cache() has two definitions, one for !CONFIG_NUMA, and the other for
CONFIG_NUMA. BAD_ALIEN_MAGIC is only assigned on !CONFIG_NUMA definition. On
CONFIG_NUMA, alloc_alien_cache() doesn't use BAD_ALIEN_MAGIC. So it is sufficient
to consider just !CONFIG_NUMA case.

As I mentioned before, this function isn't called if use_alien_caches is zero
and use_alien_caches is always zero on !CONFIG_NUMA. Therefore we cannot see
BAD_ALIEN_MAGIC on any configuration. I don't know why BAD_ALIEN_MAGIC is
introduced, however, it no longer serves a point, so it is better to remove it.

There are lots of code to check whether processor/nodes are up or not and these
doesn't use BAD_ALIEN_MAGIC. Instead, it checks NULL on alien_cache of specific node.
So removing BAD_ALIEN_MAGIC doesn't harm anything here.

Thanks.

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