From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760400AbZAWKXy (ORCPT ); Fri, 23 Jan 2009 05:23:54 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753631AbZAWKXq (ORCPT ); Fri, 23 Jan 2009 05:23:46 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:41486 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752897AbZAWKXp (ORCPT ); Fri, 23 Jan 2009 05:23:45 -0500 Date: Fri, 23 Jan 2009 11:22:53 +0100 From: Ingo Molnar To: Paul Menage Cc: akpm@linux-foundation.org, serue@us.ibm.com, linux-kernel@vger.kernel.org, containers@lists.osdl.org, Peter Zijlstra Subject: Re: [PATCH] cgroup: Fix root_count when mount fails due to busy subsystem Message-ID: <20090123102253.GF15188@elte.hu> References: <20090123004703.25103.29754.stgit@menage.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090123004703.25103.29754.stgit@menage.corp.google.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Paul Menage wrote: > cgroup: Fix root_count when mount fails due to busy subsystem > > root_count was being incremented in cgroup_get_sb() after all error > checking was complete, but decremented in cgroup_kill_sb(), which can be > called on a superblock that we gave up on due to an error. This patch > changes cgroup_kill_sb() to only decrement root_count if the root was > previously linked into the list of roots. > > Signed-off-by: Paul Menage > > --- > > I was actually surprised to find that list_del() doesn't crash when > run on an unattached list_head structure. > > kernel/cgroup.c | 6 ++++-- > 1 files changed, 4 insertions(+), 2 deletions(-) > > diff --git a/kernel/cgroup.c b/kernel/cgroup.c > index adcd0bb..9ce27e8 100644 > --- a/kernel/cgroup.c > +++ b/kernel/cgroup.c > @@ -1115,8 +1115,10 @@ static void cgroup_kill_sb(struct super_block *sb) { > } > write_unlock(&css_set_lock); > > - list_del(&root->root_list); > - root_count--; > + if (!list_empty(&root->root_list)) { > + list_del(&root->root_list); > + root_count--; > + } That's ugly. It is _much_ cleaner to always keep the link head consistent - i.e. initialize it with INIT_LIST_HEAD() and then remove from it via list_del_init(). That way the error path will do the right thing automatically, and there's no need for that ugly "if !list_empty" construct either. Ingo