linux-kernel - Re: [PATCH v10 06/17] mm: slub: introduce metadata_access_enable()/metadata_access

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Date:	Fri, 30 Jan 2015 13:42:17 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andrey Ryabinin <a.ryabinin@...sung.com>
Cc:	linux-kernel@...r.kernel.org, Dmitry Vyukov <dvyukov@...gle.com>,
	Konstantin Serebryany <kcc@...gle.com>,
	Dmitry Chernenkov <dmitryc@...gle.com>,
	Andrey Konovalov <adech.fo@...il.com>,
	Yuri Gribov <tetra2005@...il.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Christoph Lameter <cl@...ux.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Dave Hansen <dave.hansen@...el.com>,
	Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
	linux-mm@...ck.org, Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v10 06/17] mm: slub: introduce
 metadata_access_enable()/metadata_access_disable()

On Fri, 30 Jan 2015 20:05:13 +0300 Andrey Ryabinin <a.ryabinin@...sung.com> wrote:

> >> --- a/mm/slub.c
> >> +++ b/mm/slub.c
> >> @@ -467,13 +467,23 @@ static int slub_debug;
> >>  static char *slub_debug_slabs;
> >>  static int disable_higher_order_debug;
> >>  
> >> +static inline void metadata_access_enable(void)
> >> +{
> >> +}
> >> +
> >> +static inline void metadata_access_disable(void)
> >> +{
> >> +}
> > 
> > Some code comments here would be useful.  What they do, why they exist,
> > etc.  The next patch fills them in with
> > kasan_disable_local/kasan_enable_local but that doesn't help the reader
> > to understand what's going on.  The fact that
> > kasan_disable_local/kasan_enable_local are also undocumented doesn't
> > help.
> > 
> 
> Ok, How about this?
> 
> /*
>  * This hooks separate payload access from metadata access.
>  * Useful for memory checkers that have to know when slub
>  * accesses metadata.
>  */

"These hooks".

I still don't understand :( Maybe I'm having a more-stupid-than-usual
day.  How can a function "separate access"?  What does this mean?  More
details, please.  I think I've only once seen a comment which had too
much info!


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