linux-kernel - Re: [RFC][PATCH 7/9 v2] cgroup: avoid attaching task to a cgroup under rmdir()

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Message-ID: <20120427103927.GA3514@somewhere.redhat.com>
Date:	Fri, 27 Apr 2012 12:39:29 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Glauber Costa <glommer@...allels.com>,
	Tejun Heo <tj@...nel.org>, Han Ying <yinghan@...gle.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	kamezawa.hiroyuki@...il.com
Subject: Re: [RFC][PATCH 7/9 v2] cgroup: avoid attaching task to a cgroup
 under rmdir()

On Fri, Apr 27, 2012 at 03:02:22PM +0900, KAMEZAWA Hiroyuki wrote:
> attach_task() is done under cgroup_mutex() but ->pre_destroy() callback
> in rmdir() isn't called under cgroup_mutex().
> 
> It's better to avoid attaching a task to a cgroup which
> is under pre_destroy(). Considering memcg, the attached task may
> increase resource usage after memcg's pre_destroy() confirms that
> memcg is empty. This is not good.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
>  kernel/cgroup.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index ad8eae5..7a3076b 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -1953,6 +1953,9 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
>  	if (cgrp == oldcgrp)
>  		return 0;
>  
> +	if (test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags))
> +		return -EBUSY;
> +

You probably need to update cgroup_attach_proc() as well?

>  	tset.single.task = tsk;
>  	tset.single.cgrp = oldcgrp;
>  
> @@ -4181,7 +4184,6 @@ again:
>  		mutex_unlock(&cgroup_mutex);
>  		return -EBUSY;
>  	}
> -	mutex_unlock(&cgroup_mutex);
>  
>  	/*
>  	 * In general, subsystem has no css->refcnt after pre_destroy(). But
> @@ -4193,6 +4195,7 @@ again:
>  	 * and css_tryget() and cgroup_wakeup_rmdir_waiter() implementation.
>  	 */
>  	set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
> +	mutex_unlock(&cgroup_mutex);
>  
>  	/*
>  	 * Call pre_destroy handlers of subsys. Notify subsystems
> -- 
> 1.7.4.1
> 
> 
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