linux-kernel - Re: [PATCH v2 6/8] memcg: fail to create cgroup if the cgroup id is too big

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Date:	Wed, 24 Jul 2013 16:27:51 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Li Zefan <lizefan@...wei.com>
Cc:	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Glauber Costa <glommer@...allels.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH v2 6/8] memcg: fail to create cgroup if the cgroup id is
 too big

On Wed 24-07-13 18:02:19, Li Zefan wrote:
> memcg requires the cgroup id to be smaller than 65536.
> 
> Signed-off-by: Li Zefan <lizefan@...wei.com>

Acked-by: Michal Hocko <mhocko@...e.cz>

One suggestion bellow

> ---
>  mm/memcontrol.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 35d8286..403c8d9 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -512,6 +512,12 @@ static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg)
>  	return (memcg == root_mem_cgroup);
>  }
>  
> +/*
> + * We restrict the id in the range of [1, 65535], so it can fit into
> + * an unsigned short.
> + */
> +#define MEM_CGROUP_ID_MAX	(65535)

USHRT_MAX

> +
>  static inline unsigned short mem_cgroup_id(struct mem_cgroup *memcg)
>  {
>  	/*
> @@ -6243,6 +6249,9 @@ mem_cgroup_css_alloc(struct cgroup *cont)
>  	long error = -ENOMEM;
>  	int node;
>  
> +	if (cont->id > MEM_CGROUP_ID_MAX)
> +		return ERR_PTR(-ENOSPC);
> +
>  	memcg = mem_cgroup_alloc();
>  	if (!memcg)
>  		return ERR_PTR(error);
> -- 
> 1.8.0.2
> 
> --
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-- 
Michal Hocko
SUSE Labs
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