diff options
Diffstat (limited to 'kernel/cgroup.c')
| -rw-r--r-- | kernel/cgroup.c | 31 |
1 files changed, 26 insertions, 5 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 6db8b7f297a1..6d870f2d1228 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4464,15 +4464,36 @@ unsigned short css_depth(struct cgroup_subsys_state *css) } EXPORT_SYMBOL_GPL(css_depth); +/** + * css_is_ancestor - test "root" css is an ancestor of "child" + * @child: the css to be tested. + * @root: the css supporsed to be an ancestor of the child. + * + * Returns true if "root" is an ancestor of "child" in its hierarchy. Because + * this function reads css->id, this use rcu_dereference() and rcu_read_lock(). + * But, considering usual usage, the csses should be valid objects after test. + * Assuming that the caller will do some action to the child if this returns + * returns true, the caller must take "child";s reference count. + * If "child" is valid object and this returns true, "root" is valid, too. + */ + bool css_is_ancestor(struct cgroup_subsys_state *child, const struct cgroup_subsys_state *root) { - struct css_id *child_id = rcu_dereference(child->id); - struct css_id *root_id = rcu_dereference(root->id); + struct css_id *child_id; + struct css_id *root_id; + bool ret = true; - if (!child_id || !root_id || (child_id->depth < root_id->depth)) - return false; - return child_id->stack[root_id->depth] == root_id->id; + rcu_read_lock(); + child_id = rcu_dereference(child->id); + root_id = rcu_dereference(root->id); + if (!child_id + || !root_id + || (child_id->depth < root_id->depth) + || (child_id->stack[root_id->depth] != root_id->id)) + ret = false; + rcu_read_unlock(); + return ret; } static void __free_css_id_cb(struct rcu_head *head) |