From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ross Zwisler <ross.zwisler-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
Subject: Re: [PATCH] cgroup: Fix uninitialized variable warning
Date: Wed, 23 Dec 2015 14:38:13 -0700
Message-ID: <20151223213813.GA21287@linux.intel.com>
References: <1450906240-21821-1-git-send-email-ross.zwisler@linux.intel.com>
 <20151223213519.GM5003@mtj.duckdns.org>
Mime-Version: 1.0
Return-path: <cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Content-Disposition: inline
In-Reply-To: <20151223213519.GM5003-qYNAdHglDFBN0TnZuCh8vA@public.gmane.org>
Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
List-ID: <cgroups.vger.kernel.org>
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
To: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: Ross Zwisler <ross.zwisler-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>, Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>, Daniel Wagner <daniel.wagner-98C5kh4wR6ohFhg+JK9F0w@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Dave Jones <davej-rdkfGonbjUTCLXcRTR1eJlpr/1R2p/CL@public.gmane.org>, kernel-team-b10kYP2dOMg@public.gmane.org, Aleksa Sarai <cyphar-gVpy/LI/lHzQT0dZR+AlfA@public.gmane.org>, Michal Hocko <mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, Neil Horman <nhorman-2XuSBdqkA4R54TAoqtyWWQ@public.gmane.org>

On Wed, Dec 23, 2015 at 04:35:19PM -0500, Tejun Heo wrote:
> Hello, Ross.
> 
> On Wed, Dec 23, 2015 at 02:30:40PM -0700, Ross Zwisler wrote:
> >  static int mem_cgroup_can_attach(struct cgroup_taskset *tset)
> >  {
> >  	struct cgroup_subsys_state *css;
> > -	struct mem_cgroup *memcg;
> > +	struct mem_cgroup *memcg = NULL;
> 
> It's one thing to add spurious init to shut up gcc
> 
> > @@ -4805,7 +4805,7 @@ static int mem_cgroup_can_attach(struct cgroup_taskset *tset)
> >  		p = leader;
> >  		memcg = mem_cgroup_from_css(css);
> >  	}
> > -	if (!p)
> > +	if (!p || !memcg)
> 
> and to another to add an additional processing on it.

Do you believe that the additional processing is incorrect?  If somehow we
*do* get through the above loop without setting memcg, the next deref will
OOPs the kernel...