linux-kernel - Re: [PATCH] cgroup: use read lock to guard find_existing_css

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Message-ID: <480EDBD2.2060709@linux.vnet.ibm.com>
Date:	Wed, 23 Apr 2008 12:18:50 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Li Zefan <lizf@...fujitsu.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	Paul Menage <menage@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cgroup: use read lock to guard find_existing_css_set()

Li Zefan wrote:
> The function does not modify anything (except the temporary
> css template), so it's sufficient to hold read lock.
> 
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> ---
>  kernel/cgroup.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 2727f92..e9eb5da 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -406,11 +406,11 @@ static struct css_set *find_css_set(
> 
>  	/* First see if we already have a cgroup group that matches
>  	 * the desired set */
> -	write_lock(&css_set_lock);
> +	read_lock(&css_set_lock);
>  	res = find_existing_css_set(oldcg, cgrp, template);
>  	if (res)
>  		get_css_set(res);
> -	write_unlock(&css_set_lock);
> +	read_unlock(&css_set_lock);
> 
>  	if (res)
>  		return res;

Looks good to me. Did you run lockdep?



-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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