Library functions should not grab locks when the callsites can do it,
even if the lock nests like the rcu read-side lock does.
Push the rcu_read_lock() from css_is_ancestor() to its single user,
mem_cgroup_same_or_subtree(), in preparation for another user that
already holds the rcu read-side lock.
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Acked-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
---
kernel/cgroup.c | 20 ++++++++++----------
mm/memcontrol.c | 14 +++++++++-----
2 files changed, 19 insertions(+), 15 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index ad8eae5..240b02f 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -5132,7 +5132,7 @@ EXPORT_SYMBOL_GPL(css_depth);
* @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().
+ * this function reads css->id, the caller must hold 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.
@@ -5144,18 +5144,18 @@ bool css_is_ancestor(struct cgroup_subsys_state *child,
{
struct css_id *child_id;
struct css_id *root_id;
- bool ret = true;
- rcu_read_lock();
child_id = rcu_dereference(child->id);
+ if (!child_id)
+ return false;
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;
+ if (!root_id)
+ return false;
+ if (child_id->depth < root_id->depth)
+ return false;
+ if (child_id->stack[root_id->depth] != root_id->id)
+ return false;
+ return true;
}
void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1a28dd8..a1fea51 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1146,12 +1146,16 @@ struct lruvec *mem_cgroup_lru_move_lists(struct zone *zone,
static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
struct mem_cgroup *memcg)
{
- if (root_memcg != memcg) {
- return (root_memcg->use_hierarchy &&
- css_is_ancestor(&memcg->css, &root_memcg->css));
- }
+ bool ret;
- return true;
+ if (root_memcg == memcg)
+ return true;
+ if (!root_memcg->use_hierarchy)
+ return false;
+ rcu_read_lock();
+ ret = css_is_ancestor(&memcg->css, &root_memcg->css);
+ rcu_read_unlock();
+ return ret;
}
int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *memcg)
--
1.7.7.6
--
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