Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761675Ab3DCJNq (ORCPT ); Wed, 3 Apr 2013 05:13:46 -0400 Received: from szxga01-in.huawei.com ([119.145.14.64]:46562 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759736Ab3DCJNl (ORCPT ); Wed, 3 Apr 2013 05:13:41 -0400 Message-ID: <515BF2A4.1070703@huawei.com> Date: Wed, 3 Apr 2013 17:13:08 +0800 From: Li Zefan User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130307 Thunderbird/17.0.4 MIME-Version: 1.0 To: CC: LKML , Cgroups , Tejun Heo , Glauber Costa , Michal Hocko , KAMEZAWA Hiroyuki , Johannes Weiner Subject: [RFC][PATCH 5/7] cgroup: make sure parent won't be destroyed before its children References: <515BF233.6070308@huawei.com> In-Reply-To: <515BF233.6070308@huawei.com> Content-Type: text/plain; charset="GB2312" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.135.68.215] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1511 Lines: 47 Suppose we rmdir a cgroup and there're still css refs, this cgroup won't be freed. Then we rmdir the parent cgroup, and the parent is freed due to css ref draining to 0. Now it would be a disaster if the child cgroup tries to access its parent. Make sure this won't happen. Signed-off-by: Li Zefan --- kernel/cgroup.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index fa54b92..78204bc 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -888,6 +888,13 @@ static void cgroup_free_fn(struct work_struct *work) mutex_unlock(&cgroup_mutex); /* + * We get a ref to the parent's dentry, and put the ref when + * this cgroup is being freed, so it's guaranteed that the + * parent won't be destroyed before its children. + */ + dput(cgrp->parent->dentry); + + /* * Drop the active superblock reference that we took when we * created the cgroup */ @@ -4171,6 +4178,9 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry, for_each_subsys(root, ss) dget(dentry); + /* hold a ref to the parent's dentry */ + dget(parent->dentry); + /* creation succeeded, notify subsystems */ for_each_subsys(root, ss) { err = online_css(ss, cgrp); -- 1.8.0.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/