linux-kernel - Re: [BUGFIX] cgroup: create a workqueue for cgroup

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Message-Id: <20110930153049.6719a14e.akpm00@gmail.com>
Date:	Fri, 30 Sep 2011 15:30:49 -0700
From:	Andrew Morton <akpm00@...il.com>
To:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	container ML <containers@...ts.linux-foundation.org>,
	Paul Menage <paul@...lmenage.org>,
	Li Zefan <lizf@...fujitsu.com>, Ingo Molnar <mingo@...e.hu>,
	Miao Xie <miaox@...fujitsu.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Tejun Heo <htejun@...il.com>
Subject: Re: [BUGFIX] cgroup: create a workqueue for cgroup

On Fri, 30 Sep 2011 16:54:52 +0900
Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:

> In commit:f90d4118, cpuset_wq, a separate workqueue for cpuset, was introduced
> to avoid a dead lock against cgroup_mutex between async_rebuild_sched_domains()
> and cgroup_tasks_write().
> 
> But check_for_release() has a similar problem:
> 
>   check_for_release()
>     schedule_work(release_agent_work)
>       cgroup_release_agent()
>         mutex_lock(&cgroup_mutex)
> 
> And I actually see a lockup which seems to be caused by this problem
> on 2.6.32-131.0.15.el6.x86_64.

Are you sure the bug is still present in current kernels?  Perhaps
Tejun's workqueue changes magically made it go away.

>
> ...
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -27,6 +27,8 @@ struct css_id;
>  
>  extern int cgroup_init_early(void);
>  extern int cgroup_init(void);
> +extern void cgroup_wq_init(void);
> +extern void queue_cgroup_work(struct work_struct *work);
>  extern void cgroup_lock(void);
>  extern int cgroup_lock_is_held(void);
>  extern bool cgroup_lock_live_group(struct cgroup *cgrp);

Can we spot the odd man out?

I shall rename queue_cgroup_work() to cgroup_queue_work().

>
> ...
>
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