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authorLi Zefan <lizefan@huawei.com>2013-04-08 14:35:02 +0800
committerTejun Heo <tj@kernel.org>2013-04-10 11:07:00 -0700
commit415cf07a1c1c65249773330434878ae7bcd92d0f (patch)
tree2154c7078abde678f7d4fdb9c5f1c10a26ab16df
parent84cfb6ab484b442d5115eb3baf9db7d74a3ea626 (diff)
cgroup: make sure parent won't be destroyed before its children
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 <lizefan@huawei.com> Reviewed-by: Michal Hocko <mhocko@suse.cz> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org>
-rw-r--r--kernel/cgroup.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index fd38e1cfacc..65b72d0367c 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
*/
@@ -4164,6 +4171,9 @@ 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);