linux-kernel - Re: [PATCH v2] cgroup: avoid false positive gcc-6 warning

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Message-ID: <20160316203309.GF21104@mtj.duckdns.org>
Date:	Wed, 16 Mar 2016 13:33:09 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Li Zefan <lizefan@...wei.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Aditya Kali <adityakali@...gle.com>,
	Aleksa Sarai <cyphar@...har.com>, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] cgroup: avoid false positive gcc-6 warning

On Tue, Mar 15, 2016 at 12:21:06AM +0100, Arnd Bergmann wrote:
> When all subsystems are disabled, gcc notices that cgroup_subsys_enabled_key
> is a zero-length array and that any access to it must be out of bounds:
> 
> In file included from ../include/linux/cgroup.h:19:0,
>                  from ../kernel/cgroup.c:31:
> ../kernel/cgroup.c: In function 'cgroup_add_cftypes':
> ../kernel/cgroup.c:261:53: error: array subscript is above array bounds [-Werror=array-bounds]
>   return static_key_enabled(cgroup_subsys_enabled_key[ssid]);
>                             ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~
> ../include/linux/jump_label.h:271:40: note: in definition of macro 'static_key_enabled'
>   static_key_count((struct static_key *)x) > 0;    \
>                                         ^
> 
> We should never call the function in this particular case, so this is
> not a bug. In order to silence the warning, this adds an explicit check
> for the CGROUP_SUBSYS_COUNT==0 case.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Applied to cgroup/for-4.6.

Thanks.

-- 
tejun