linux-kernel - Re: [PATCH 1/4] cgroup: change locking order in attach_task_by

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Message-ID: <20110918185621.GB6159@redhat.com>
Date:	Sun, 18 Sep 2011 20:56:21 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <htejun@...il.com>
Cc:	rjw@...k.pl, paul@...lmenage.org, lizf@...fujitsu.com,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, fweisbec@...il.com,
	matthltc@...ibm.com, akpm@...ux-foundation.org,
	Tejun Heo <tj@...nel.org>, Paul Menage <menage@...gle.com>
Subject: Re: [PATCH 1/4] cgroup: change locking order in
	attach_task_by_pid()

On 09/05, Tejun Heo wrote:
>
> cgroup_mutex is updated to nest inside threadgroup_fork_lock instead
> of the other way around.  threadgroup locking is scheduled to be
> updated to cover all threadgroup altering operations and nesting it
> inside cgroup_mutex complicates locking dependency unnecessarily.

Could you please explain this change?

I can't understand why threadgroup_lock() under cgroup_mutex is bad.
Do you mean we can deadlock otherwise?

And, this means we can't change cpuset_do_move_task() to do
threadgroup_lock().

Oleg.

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