linux-kernel - Re: [PATCH 3/8] cgroup: use cgroup_lock_live_group(parent) in cgroup

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Message-ID: <20121031170431.GF2945@htj.dyndns.org>
Date:	Wed, 31 Oct 2012 10:04:31 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	lizefan@...wei.com, hannes@...xchg.org, bsingharora@...il.com,
	kamezawa.hiroyu@...fujitsu.com,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/8] cgroup: use cgroup_lock_live_group(parent) in
 cgroup_create()

Hey, Michal.

On Wed, Oct 31, 2012 at 04:55:14PM +0100, Michal Hocko wrote:
> > +	/*
> > +	 * Only live parents can have children.  Note that the liveliness
> > +	 * check isn't strictly necessary because cgroup_mkdir() and
> > +	 * cgroup_rmdir() are fully synchronized by i_mutex; however, do it
> > +	 * anyway so that locking is contained inside cgroup proper and we
> > +	 * don't get nasty surprises if we ever grow another caller.
> > +	 */
> > +	if (!cgroup_lock_live_group(parent)) {
> > +		err = -ENODEV;
> > +		goto err_free;
> > +	}
> > +
> 
> I think this should be moved up before we try to allocate any memory.
> Or is your motivation to keep cgroup_lock held for shorter time?
> I could agree with that but a small comment would be helpful.

Then I have to change the error out path more and I'm not sure I wanna
call deactivate_super() under cgroup_mutex.  It's just simpler this
way.

Thanks.

-- 
tejun
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