cgroup: remove hierarchy_mutex
It was introduced for memcg to iterate cgroup hierarchy without
holding cgroup_mutex, but soon after that it was replaced with
a lockless way in memcg.
No one used hierarchy_mutex since that, so remove it.
Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index d3f5fba..c90eaa8 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -500,21 +500,8 @@
const char *name;
/*
- * Protects sibling/children links of cgroups in this
- * hierarchy, plus protects which hierarchy (or none) the
- * subsystem is a part of (i.e. root/sibling). To avoid
- * potential deadlocks, the following operations should not be
- * undertaken while holding any hierarchy_mutex:
- *
- * - allocating memory
- * - initiating hotplug events
- */
- struct mutex hierarchy_mutex;
- struct lock_class_key subsys_key;
-
- /*
* Link to parent, and list entry in parent's children.
- * Protected by this->hierarchy_mutex and cgroup_lock()
+ * Protected by cgroup_lock()
*/
struct cgroupfs_root *root;
struct list_head sibling;
@@ -602,7 +589,7 @@
* the lifetime of cgroup_subsys_state is subsys's matter.
*
* Looking up and scanning function should be called under rcu_read_lock().
- * Taking cgroup_mutex()/hierarchy_mutex() is not necessary for following calls.
+ * Taking cgroup_mutex is not necessary for following calls.
* But the css returned by this routine can be "not populated yet" or "being
* destroyed". The caller should check css and cgroup's status.
*/