linux-kernel - Re: [PATCH -mm] slab: update_memcg_params: explicitly check that old array != NULL

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Message-ID: <20150126151359.GD6507@mwanda>
Date:	Mon, 26 Jan 2015 18:13:59 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm] slab: update_memcg_params: explicitly check that old
 array != NULL

On Mon, Jan 26, 2015 at 01:45:34PM +0300, Vladimir Davydov wrote:
> On Mon, Jan 26, 2015 at 01:23:05PM +0300, Dan Carpenter wrote:
> > On Mon, Jan 26, 2015 at 01:01:19PM +0300, Vladimir Davydov wrote:
> > > This warning is false-positive, because @old equals NULL iff
> > > @memcg_nr_cache_ids equals 0.
> > 
> > I don't see how it could be a false positive.  The "old" pointer is
> > dereferenced inside the call to memset() so unless memset is a macro the
> > compiler isn't going to optimize the dereference away.
> 
> old->entries is not dereferenced: memcg_cache_array->entries is not a
> pointer - it is embedded to the memcg_cache_array struct.

Ah.  Ok.  Thanks.

regards,
dan carpenter

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