linux-kernel - Re: [PATCH 07/16] cgroup: fix warning when building without any subsys

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Message-ID: <20121005155006.GB5124@ghc17.ghc.andrew.cmu.edu>
Date:	Fri, 5 Oct 2012 11:50:06 -0400
From:	Ben Blum <bblum@...rew.cmu.edu>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	arm@...nel.org, Tejun Heo <tj@...nel.org>,
	Li Zefan <lizefan@...wei.com>, Ben Blum <bblum@...rew.cmu.edu>
Subject: Re: [PATCH 07/16] cgroup: fix warning when building without any
 subsys

On Fri, Oct 05, 2012 at 04:55:21PM +0200, Arnd Bergmann wrote:
> In a configuration where the base cgroup support is enabled but
> every single cgroup subsys is turned off, CGROUP_BUILTIN_SUBSYS_COUNT
> is zero, which causes the sanity check code in cgroup_load_subsys
> to trigger:
> 
>        BUG_ON(ss->subsys_id >= CGROUP_BUILTIN_SUBSYS_COUNT);
>        BUG_ON(subsys[ss->subsys_id] != ss);
> 
> Gcc first confirms that subsys_id cannot be 0 or larger and consequently
> warns in the second line.
> 
> kernel/cgroup.c: In function 'cgroup_load_subsys':
> kernel/cgroup.c:4326:38: warning: array subscript is below array bounds [-Warray-bounds]
> 
> Since the subsys_id can never be less than zero, we can just change the
> type to an unsigned int, which makes the warning go away.
> 
> Found by building ARM cns3420vb_defconfig.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Li Zefan <lizefan@...wei.com>
> Cc: Ben Blum <bblum@...rew.cmu.edu>
> ---
>  include/linux/cgroup.h |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index c90eaa8..26b99df 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -475,7 +475,7 @@ struct cgroup_subsys {
>  	void (*post_clone)(struct cgroup *cgrp);
>  	void (*bind)(struct cgroup *root);
>  
> -	int subsys_id;
> +	unsigned int subsys_id;
>  	int active;
>  	int disabled;
>  	int early_init;
> -- 
> 1.7.10
> 
> 

Oops. Thank you!

Acked-by: Ben Blum <bblum@...rew.cmu.edu>
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