From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932141AbZAWSL5 (ORCPT ); Fri, 23 Jan 2009 13:11:57 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754309AbZAWSLr (ORCPT ); Fri, 23 Jan 2009 13:11:47 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:33097 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753279AbZAWSLq (ORCPT ); Fri, 23 Jan 2009 13:11:46 -0500 Date: Fri, 23 Jan 2009 19:10:56 +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 Subject: Re: [PATCH] cgroup: Fix root_count when mount fails due to busy subsystem Message-ID: <20090123181056.GA31142@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. i'm wondering, what happens in the buggy case: does cgroup_kill_sb() get called twice (if yes, why?), or do we call cgroup_kill_sb() on a not yet added sb and hence root_count has not been elevated yet? (if yes, which codepath does this?) The error handling in cgroup_get_sb() definitely seems a bit twisted - find below a few error path and other cleanups. Thanks, Ingo diff --git a/kernel/cgroup.c b/kernel/cgroup.c index c298310..28d1b67 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -1025,18 +1026,12 @@ static int cgroup_get_sb(struct file_system_type *fs_type, * have some link structures left over */ ret = allocate_cg_links(css_set_count, &tmp_cg_links); - if (ret) { - mutex_unlock(&cgroup_mutex); - mutex_unlock(&inode->i_mutex); - goto drop_new_super; - } + if (ret) + goto drop_new_super_unlock; ret = rebind_subsystems(root, root->subsys_bits); - if (ret == -EBUSY) { - mutex_unlock(&cgroup_mutex); - mutex_unlock(&inode->i_mutex); + if (ret == -EBUSY) goto free_cg_links; - } /* EBUSY should be the only error here */ BUG_ON(ret); @@ -1075,18 +1070,24 @@ static int cgroup_get_sb(struct file_system_type *fs_type, free_cg_links: free_cg_links(&tmp_cg_links); + + drop_new_super_unlock: + mutex_unlock(&cgroup_mutex); + mutex_unlock(&inode->i_mutex); drop_new_super: up_write(&sb->s_umount); deactivate_super(sb); + return ret; } -static void cgroup_kill_sb(struct super_block *sb) { +static void cgroup_kill_sb(struct super_block *sb) +{ struct cgroupfs_root *root = sb->s_fs_info; struct cgroup *cgrp = &root->top_cgroup; - int ret; - struct cg_cgroup_link *link; struct cg_cgroup_link *saved_link; + struct cg_cgroup_link *link; + int ret; BUG_ON(!root);