linux-kernel - Re: [RFC][PATCH 1/2] CGROUP ID and Hierarchy Code

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Date:	Fri, 28 Nov 2008 11:18:32 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Li Zefan <lizf@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"menage@...gle.com" <menage@...gle.com>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	taka@...inux.co.jp
Subject: Re: [RFC][PATCH 1/2] CGROUP ID and Hierarchy Code

On Fri, 28 Nov 2008 10:35:33 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> On Fri, 28 Nov 2008 09:28:33 +0800
> Li Zefan <lizf@...fujitsu.com> wrote:

> > I think the safe way is:
> > 
> > rcu_read_lock();
> > cgrp = cgroup_get_next()
> > if (!inc_not_zero(cgrp) {
> > 	rcu_read_unlock();
> > 	return NULL;
> > }
> > rcu_read_unlock();
> > return cgrp;
> > 
> > But it's also safe to use cgrp = list_entry(&parent->children.next) for the above
> > scenario, seems you don't have to invent this cgroup_get_next().
> > 
> But list-walk can't provide us view of hierarchy. Up-Down list walk is better ?
> please see memcg's code. it met some troubles.
> I'll make kfree(cgrp) to be called by RCU.
> 

Ah please, I have a question.
Following is right ?
	- until mount, cgroup's subsystem root is tied to dummy? root cgroup.
	- cgroup cannot be unmounted while there are any children.
	- cgroup_root is freed/allocated at umount/mount, then I have to handle
	  this event in cgroup-id.
	 (maybe current code has leak? in umount.)
 
Thanks,
-Kame

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