Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936698Ab3DICXr (ORCPT ); Mon, 8 Apr 2013 22:23:47 -0400 Received: from mail-qe0-f43.google.com ([209.85.128.43]:63648 "EHLO mail-qe0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S936592Ab3DICXo (ORCPT ); Mon, 8 Apr 2013 22:23:44 -0400 From: Tejun Heo To: mingo@redhat.com Cc: a.p.zijlstra@chello.nl, paulus@samba.org, acme@ghostprotocols.net, eranian@google.com, namhyung.kim@lge.com, lizefan@huawei.com, mhocko@suse.cz, kamezawa.hiroyu@jp.fujitsu.com, cgroups@vger.kernel.org, containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Tejun Heo Subject: [PATCH 1/3] cgroup: make sure parent won't be destroyed before its children Date: Mon, 8 Apr 2013 19:23:31 -0700 Message-Id: <1365474213-13354-2-git-send-email-tj@kernel.org> X-Mailer: git-send-email 1.8.1.4 In-Reply-To: <1365474213-13354-1-git-send-email-tj@kernel.org> References: <1365474213-13354-1-git-send-email-tj@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1718 Lines: 53 From: Li Zefan 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 Signed-off-by: Tejun Heo --- kernel/cgroup.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index ba3e24a..d7dfa64 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -876,6 +876,13 @@ 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 */ @@ -4168,6 +4175,9 @@ 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); -- 1.8.1.4 -- 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/