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Date: Fri, 29 Apr 2016 16:18:10 +0900
From: Joonsoo Kim <iamjoonsoo.kim@....com>
To: Christoph Lameter <cl@...ux.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Thomas Garnier <thgarnie@...gle.com>,
Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>,
Kees Cook <keescook@...omium.org>, gthelen@...gle.com,
labbott@...oraproject.org, kernel-hardening@...ts.openwall.com,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v4] mm: SLAB freelist randomization
On Wed, Apr 27, 2016 at 10:39:29AM -0500, Christoph Lameter wrote:
> On Tue, 26 Apr 2016, Andrew Morton wrote:
>
> > : CONFIG_FREELIST_RANDOM bugs me a bit - "freelist" is so vague.
> > : CONFIG_SLAB_FREELIST_RANDOM would be better. I mean, what Kconfig
> > : identifier could be used for implementing randomisation in
> > : slub/slob/etc once CONFIG_FREELIST_RANDOM is used up?
> >
> > but this pearl appeared to pass unnoticed.
>
> Ok. lets add SLAB here and then use this option for the other allocators
> as well.
>
> > > + /* If it fails, we will just use the global lists */
> > > + cachep->random_seq = kcalloc(count, sizeof(freelist_idx_t), GFP_KERNEL);
> > > + if (!cachep->random_seq)
> > > + return -ENOMEM;
> >
> > OK, no BUG. If this happens, kmem_cache_init_late() will go BUG
> > instead ;)
> >
> > Questions for slab maintainers:
> >
> > What's going on with the gfp_flags in there? kmem_cache_init_late()
> > passes GFP_NOWAIT into enable_cpucache().
> >
> > a) why the heck does it do that? It's __init code!
>
> enable_cpucache() was called when a slab cache was reconfigured by writing to /proc/slabinfo.
> That was changed awhile back when the memcg changes were made ot slab. So
> now its ok to be made init code.
>
> > Finally, all callers of enable_cpucache() (and hence of
> > cache_random_seq_create()) are __init, so we're unnecessarily bloating
> > up vmlinux. Could someone please take a look at this as a separate
> > thing?
>
> Hmmm. Well if that is the case then lots of stuff could be straightened
> out. Joonsoo?
>
As I mentioned in other thread, enable_cpucache() can be called
whenever kmem_cache is created. It should not be __init.
Thanks.
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