Date: Thu, 3 Nov 2016 15:33:27 -0500 (CDT)
From: Christoph Lameter <cl@linux.com>
To: David Rientjes <rientjes@google.com>
cc: Thomas Garnier <thgarnie@google.com>,
        Pekka Enberg <penberg@kernel.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
        Greg Thelen <gthelen@google.com>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH v2] memcg: Prevent memcg caches to be both OFF_SLAB &
 OBJFREELIST_SLAB
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On Wed, 2 Nov 2016, David Rientjes wrote:

> > Christoph on the first version advised removing invalid flags on the
> > caller and checking they are correct in kmem_cache_create. The memcg
> > path putting the wrong flags is through create_cache but I still used
> > this approach.
> >
>
> I think this is a rather trivial point since it doesn't matter if we clear
> invalid flags on the caller or in the callee and obviously
> kmem_cache_create() does it in the callee.

In order to be correct we need to do the following:

kmem_cache_create should check for invalid flags (and that includes
internal alloocator flgs) being set and refuse to create the slab cache.

memcg needs to call kmem_cache_create without any internal flags.

I also want to make sure that there are no other callers that specify
extraneou flags while we are at it.