Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935084Ab3DHGfd (ORCPT ); Mon, 8 Apr 2013 02:35:33 -0400 Received: from szxga01-in.huawei.com ([119.145.14.64]:4829 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934754Ab3DHGfa (ORCPT ); Mon, 8 Apr 2013 02:35:30 -0400 Message-ID: <51626516.3000603@huawei.com> Date: Mon, 8 Apr 2013 14:35:02 +0800 From: Li Zefan User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130328 Thunderbird/17.0.5 MIME-Version: 1.0 To: Andrew Morton CC: Tejun Heo , Glauber Costa , KAMEZAWA Hiroyuki , Johannes Weiner , LKML , Cgroups , Subject: [PATCH 09/12] cgroup: make sure parent won't be destroyed before its children References: <5162648B.9070802@huawei.com> In-Reply-To: <5162648B.9070802@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: 1639 Lines: 49 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 immediately due to css ref draining to 0. Now it would be a disaster if the still-alive child cgroup tries to access its parent. Make sure this won't happen. Signed-off-by: Li Zefan Reviewed-by: Michal Hocko Acked-by: KAMEZAWA Hiroyuki --- kernel/cgroup.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 06aeb42..7ee3bdf 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 */ @@ -4170,6 +4177,9 @@ 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/