From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx181.postini.com [74.125.245.181]) by kanga.kvack.org (Postfix) with SMTP id CBBD46B0092 for ; Mon, 8 Apr 2013 02:35:48 -0400 (EDT) Message-ID: <51626516.3000603@huawei.com> Date: Mon, 8 Apr 2013 14:35:02 +0800 From: Li Zefan MIME-Version: 1.0 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 Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Tejun Heo , Glauber Costa , KAMEZAWA Hiroyuki , Johannes Weiner , LKML , Cgroups , linux-mm@kvack.org 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org