linux-kernel - Re: [PATCH] memcg: fix memcg_cache_name() to use cgroup

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Message-ID: <515153C0.5070908@huawei.com>
Date:	Tue, 26 Mar 2013 15:52:32 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	Michal Hocko <mhocko@...e.cz>
CC:	Glauber Costa <glommer@...allels.com>, Tejun Heo <tj@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>, <linux-mm@...ck.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH] memcg: fix memcg_cache_name() to use cgroup_name()

>>> >From 7ed7f53bb597e8cb40d9ac91ce16142fb60f1e93 Mon Sep 17 00:00:00 2001
>>> From: Michal Hocko <mhocko@...e.cz>
>>> Date: Fri, 22 Mar 2013 10:22:54 +0100
>>> Subject: [PATCH] memcg: fix memcg_cache_name() to use cgroup_name()
>>>
>>> As cgroup supports rename, it's unsafe to dereference dentry->d_name
>>> without proper vfs locks. Fix this by using cgroup_name() rather than
>>> dentry directly.
>>>
>>> Also open code memcg_cache_name because it is called only from
>>> kmem_cache_dup which frees the returned name right after
>>> kmem_cache_create_memcg makes a copy of it. Such a short-lived
>>> allocation doesn't make too much sense. So replace it by a static
>>> buffer as kmem_cache_dup is called with memcg_cache_mutex.
>>>
>>
>> I doubt it's a win to add 4K to kernel text size instead of adding
>> a few extra lines of code... but it's up to you.
> 
> I will leave the decision to Glauber. The updated version which uses
> kmalloc for the static buffer is bellow.
> 

I don't have strong preference. Glauber, what's your opinion?

...
>  static struct kmem_cache *kmem_cache_dup(struct mem_cgroup *memcg,
>  					 struct kmem_cache *s)
>  {
> -	char *name;
>  	struct kmem_cache *new;
> +	static char *tmp_name = NULL;

(minor nitpick) why not preserve the name "name"

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