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Date: Thu, 11 Dec 2008 11:05:14 +0800
From: Li Zefan <lizf@cn.fujitsu.com>
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To: menage@google.com
CC: kamezawa.hiroyu@jp.fujitsu.com, balbir@linux.vnet.ibm.com,
       containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
       akpm@linux-foundation.org
Subject: Re: [RFC][PATCH 1/3] CGroups: Add a per-subsystem hierarchy_mutex
References: <20081210233654.563182000@menage.corp.google.com> <20081210234432.065445000@menage.corp.google.com>
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> +static void cgroup_lock_hierarchy(struct cgroupfs_root *root)
> +{
> +	/* We need to take each hierarchy_mutex in a consistent order */

This comment is not so clear. Do you mean for_each_subsys() can't be
used here?

But this function is used in cgroup.c internally, and always called
with cgroup_lock held, so it's OK to use for_each_subsys().

> +	int i;
> +
> +	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
> +		struct cgroup_subsys *ss = subsys[i];
> +		if (ss->root == root)
> +			mutex_lock_nested(&ss->hierarchy_mutex, i);
> +	}
> +}