---

yaml
---
r: 190787
b: refs/heads/master
c: 7f0f154
h: refs/heads/master
i:
  190785: 21a6afe
  190783: 6abd9c2
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 11cad320a4f4bc53d3585c85600c782faa12b99e
+refs/heads/master: 7f0f15464185a92f9d8791ad231bcd7bf6df54e4

trunk/kernel/cgroup.c

@@ -4435,7 +4435,15 @@ __setup("cgroup_disable=", cgroup_disable);
  */
 unsigned short css_id(struct cgroup_subsys_state *css)
 {
-	struct css_id *cssid = rcu_dereference(css->id);
+	struct css_id *cssid;
+
+	/*
+	 * This css_id() can return correct value when somone has refcnt
+	 * on this or this is under rcu_read_lock(). Once css->id is allocated,
+	 * it's unchanged until freed.
+	 */
+	cssid = rcu_dereference_check(css->id,
+			rcu_read_lock_held() || atomic_read(&css->refcnt));
 
 	if (cssid)
 		return cssid->id;
@@ -4445,7 +4453,10 @@ EXPORT_SYMBOL_GPL(css_id);
 
 unsigned short css_depth(struct cgroup_subsys_state *css)
 {
-	struct css_id *cssid = rcu_dereference(css->id);
+	struct css_id *cssid;
+
+	cssid = rcu_dereference_check(css->id,
+			rcu_read_lock_held() || atomic_read(&css->refcnt));
 
 	if (cssid)
 		return cssid->depth;

trunk/mm/memcontrol.c

@@ -2314,9 +2314,7 @@ mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)
 
 	/* record memcg information */
 	if (do_swap_account && swapout && memcg) {
-		rcu_read_lock();
 		swap_cgroup_record(ent, css_id(&memcg->css));
-		rcu_read_unlock();
 		mem_cgroup_get(memcg);
 	}
 	if (swapout && memcg)
@@ -2373,10 +2371,8 @@ static int mem_cgroup_move_swap_account(swp_entry_t entry,
 {
 	unsigned short old_id, new_id;
 
-	rcu_read_lock();
 	old_id = css_id(&from->css);
 	new_id = css_id(&to->css);
-	rcu_read_unlock();
 
 	if (swap_cgroup_cmpxchg(entry, old_id, new_id) == old_id) {
 		mem_cgroup_swap_statistics(from, false);
@@ -4044,16 +4040,11 @@ static int is_target_pte_for_mc(struct vm_area_struct *vma,
 			put_page(page);
 	}
 	/* throught */
-	if (ent.val && do_swap_account && !ret) {
-		unsigned short id;
-		rcu_read_lock();
-		id = css_id(&mc.from->css);
-		rcu_read_unlock();
-		if (id == lookup_swap_cgroup(ent)) {
-			ret = MC_TARGET_SWAP;
-			if (target)
-				target->ent = ent;
-		}
+	if (ent.val && do_swap_account && !ret &&
+			css_id(&mc.from->css) == lookup_swap_cgroup(ent)) {
+		ret = MC_TARGET_SWAP;
+		if (target)
+			target->ent = ent;
 	}
 	return ret;
 }