From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1423205Ab2KNTEN (ORCPT ); Wed, 14 Nov 2012 14:04:13 -0500 Received: from mail-pa0-f46.google.com ([209.85.220.46]:64845 "EHLO mail-pa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1423130Ab2KNTEM (ORCPT ); Wed, 14 Nov 2012 14:04:12 -0500 Date: Wed, 14 Nov 2012 11:04:07 -0800 From: Tejun Heo To: Li Zefan Cc: containers@lists.linux-foundation.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, mhocko@suse.cz, glommer@parallels.com Subject: Re: [PATCH 04/17] cgroup: create directory before linking while creating a new cgroup Message-ID: <20121114190407.GI21185@mtj.dyndns.org> References: <1352775704-9023-1-git-send-email-tj@kernel.org> <1352775704-9023-5-git-send-email-tj@kernel.org> <50A30E0F.7000408@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50A30E0F.7000408@huawei.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Li. On Wed, Nov 14, 2012 at 11:20:47AM +0800, Li Zefan wrote: > > It also removes the need to check whether cgroup->dentry is %NULL in > > cgroup_path. If a cgroup is visible, its dentry is guaranteed to be > > visible too. > > I'm afraid this isn't safe. > > The cgroup is visible to a controller soon after ss->create(), and then > the controller might call cgroup_path() while cgrp->dentry is still NULL. Hmmm... I can't find any case where ss->create() is calling cgroup_path(). Do you remember which one that was? > This can happen for cpu cgroup I think, and in fact the NULL check was > added for this reason IIRC. Then, I think we better move the dentry assignment further up. It's really silly to be unable to answer "what's this new cgroup's name?" for any callback really. Will update accordingly. Thanks. -- tejun