kernel: cgroup: push rcu read locking from css_is_ancestor() to callsite
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 may
already hold the rcu read-side lock.
Change-Id: I0ec7ec0059ed588d8f85bc9be8fdc42ce0ca7f5d
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Git-commit: 91c63734f6908425903aed69c04035592f18d398
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 2f0d7542..01f68c4 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4902,7 +4902,7 @@
* @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.
@@ -4914,18 +4914,18 @@
{
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 af09b14..02bded4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1147,12 +1147,16 @@
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)