From mboxrd@z Thu Jan  1 00:00:00 1970
From: Frederic Weisbecker <fweisbec-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Subject: Re: Q: cgroup: Questions about possible issues in cgroup locking
Date: Wed, 21 Dec 2011 18:59:45 +0100
Message-ID: <20111221175943.GG17668@somewhere>
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	<20111221130848.GA19679@redhat.com>
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To: Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: Containers <containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>, LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Paul Menage <paul-inf54ven1CmVyaH7bEyXVA@public.gmane.org>, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, "Paul E. McKenney" <paulmck-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>, Mandeep Singh Baines <msb-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
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On Wed, Dec 21, 2011 at 02:08:48PM +0100, Oleg Nesterov wrote:
> On 12/21, Frederic Weisbecker wrote:
> > - By the time we call cgroup_post_fork(), it is ready to be woken up
> > and usable by the scheduler.
> 
> No, the new child can't run until do_fork()->wake_up_new_task().

Out of curiosity, why is it not possible for a task to kill and wake up the child
before that happens?

Understanding that could potentially let us remove the task_lock() in cgroup_post_fork()
(although I need to examine that more deeply).

Thanks!

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Date: Wed, 21 Dec 2011 18:59:45 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>, Tejun Heo <tj@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Mandeep Singh Baines <msb@chromium.org>,
        Containers <containers@lists.linux-foundation.org>,
        Cgroups <cgroups@vger.kernel.org>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Paul Menage <paul@paulmenage.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: Q: cgroup: Questions about possible issues in cgroup locking
Message-ID: <20111221175943.GG17668@somewhere>
References: <20111221034334.GD17668@somewhere>
 <20111221130848.GA19679@redhat.com>
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On Wed, Dec 21, 2011 at 02:08:48PM +0100, Oleg Nesterov wrote:
> On 12/21, Frederic Weisbecker wrote:
> > - By the time we call cgroup_post_fork(), it is ready to be woken up
> > and usable by the scheduler.
> 
> No, the new child can't run until do_fork()->wake_up_new_task().

Out of curiosity, why is it not possible for a task to kill and wake up the child
before that happens?

Understanding that could potentially let us remove the task_lock() in cgroup_post_fork()
(although I need to examine that more deeply).

Thanks!