linux-kernel - Re: [RFC][PATCH 0/5] do not dereference NULL pools in pools' destroy() functions

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Message-Id: <20150609185150.8c9fed8d.akpm@linux-foundation.org>
Date:	Tue, 9 Jun 2015 18:51:50 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Minchan Kim <minchan@...nel.org>,
	Pekka Enberg <penberg@...nel.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Michal Hocko <mhocko@...e.cz>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, sergey.senozhatsky.work@...il.com,
	Joe Perches <joe@...ches.com>
Subject: Re: [RFC][PATCH 0/5] do not dereference NULL pools in pools'
 destroy() functions

On Tue, 9 Jun 2015 20:11:25 -0500 (CDT) Christoph Lameter <cl@...ux.com> wrote:

> On Tue, 9 Jun 2015, Andrew Morton wrote:
> 
> > Well I like it, even though it's going to cause a zillion little cleanup
> > patches.
> >
> > checkpatch already has a "kfree(NULL) is safe and this check is
> > probably not required" test so I guess Joe will need to get busy ;)
> >
> > I'll park these patches until after 4.1 is released - it's getting to
> > that time...
> 
> Why do this at all?

For the third time: because there are approx 200 callsites which are
already doing it.

> I understand that kfree/kmem_cache_free can take a
> null pointer but this is the destruction of a cache and it usually
> requires multiple actions to clean things up and these actions have to be
> properly sequenced. All other processors have to stop referencing this
> cache before it can be destroyed. I think failing if someone does
> something strange like doing cache destruction with a NULL pointer is
> valuable.

More than half of the kmem_cache_destroy() callsites are declining that
value by open-coding the NULL test.  That's reality and we should recognize
it.

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