linux-kernel - Re: [PATCH 2/8] cgroup: implement cgroup_from

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Message-ID: <20130408154847.GE3021@htj.dyndns.org>
Date:	Mon, 8 Apr 2013 08:48:47 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Li Zefan <lizefan@...wei.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Glauber Costa <glommer@...allels.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH 2/8] cgroup: implement cgroup_from_id()

Oops, one more thing.

On Mon, Apr 08, 2013 at 04:20:59PM +0800, Li Zefan wrote:
> -	cgrp->id = ida_simple_get(&root->cgroup_ida, 1, 0, GFP_KERNEL);
> +	cgrp->id = idr_alloc(&root->cgroup_idr, cgrp, 1, 0, GFP_KERNEL);

This will allow lookups to return half-initialized cgroup, which
shouldn't happen.  Either idr_alloc() should be moved to after
initialization of other fields are finished, or it should be called
with NULL @ptr with idr_replace() added at the end to install @cgrp.

Similarly, the removal path should guarantee that the object is
removed from idr *before* its grace period starts.

Thanks.

-- 
tejun
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