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

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Date:	Thu, 11 Jun 2015 12:26:11 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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, Andrew Morton wrote:

> > > 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.
> >
> > Well that may just indicate that we need to have a look at those
> > callsites and the reason there to use a special cache at all.
>
> This makes no sense.  Go look at the code.
> drivers/staging/lustre/lustre/llite/super25.c, for example.  It's all
> in the basic unwind/recover/exit code.

That is screwed up code. I'd do that without the checks simply with a
series of kmem_cache_destroys().

> > If the cache
> > is just something that kmalloc can provide then why create a special
> > cache. On the other hand if something special needs to be accomplished
> > then it would make sense to have special processing on kmem_cache_destroy.
>
> This has nothing to do with anything.  We're talking about a basic "if
> I created this cache then destroy it" operation.

As you see in this code snipped you cannot continue if a certain operation
during setup fails. At that point it is known which caches exist and
therefore kmem_cache_destroy() can be called without the checks.

> It's a common pattern.  mm/ exists to serve client code and as a lot of
> client code is doing this, we should move it into mm/ so as to serve
> client code better.

Doing this seems to encourage sloppy coding practices.


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