From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Subject: Re: [RFC][PATCH] cgroup: fix race between fork and cgroup freezing
Date: Thu, 8 Mar 2012 10:26:22 -0800
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To: Li Zefan <lizf-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
Cc: Frederic Weisbecker <fweisbec-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Mel Gorman <mgorman-l3A5Bk7waGM@public.gmane.org>, David Rientjes <rientjes-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, =?utf-8?B?57yqIOWLsA==?= <miaox-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>

Hello, Li, Frederic.

On Thu, Mar 08, 2012 at 04:45:13PM +0800, Li Zefan wrote:
> +static void freezer_post_fork(struct cgroup_subsys *ss,
> +			      struct task_struct *task)
> +{
> +	struct freezer *freezer;
> +
> +	cgroup_lock();
> +
> +	freezer = task_freezer(task);
> +	if (!freezer->css.cgroup->parent)
> +		goto out;
> +
> +	spin_lock_irq(&freezer->lock);
> +	if (freezer->state != CGROUP_THAWED)
> +		freeze_task(task);
> +	spin_unlock_irq(&freezer->lock);
> +out:
> +	cgroup_unlock();
> +}

Urgh... this is requiring policy implementations to synchronize with
problem caused by cgroup core optimization and it's so very subtle.
IMHO, this definitely should be contained in cgroup core and in a very
confined form even inside cgroup core.

Any other ideas?

Thanks.

-- 
tejun