Re: [PATCH] memcg: don't do cleanup manually if mem_cgroup_css_online() fails

[Michal Hocko <mhocko@suse.cz>]

On Tue 02-04-13 18:20:56, Glauber Costa wrote:
> On 04/02/2013 06:16 PM, Michal Hocko wrote:
> >  mem_cgroup_css_online
> >       memcg_init_kmem
> >         mem_cgroup_get		# refcnt = 2
> >           memcg_update_all_caches
> >             memcg_update_cache_size	# fails with ENOMEM
> 
> Here is the thing: this one in kmem only happens for kmem enabled
> memcgs. For those, we tend to do a get once, and put only when the last
> kmem reference is gone.
> 
> For non-kmem memcgs, refcnt will be 1 here, and will be balanced out by
> the mem_cgroup_put() in css_free.

So we need this, right?
---
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f608546..2ef875d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5306,6 +5306,8 @@ static int memcg_propagate_kmem(struct mem_cgroup *memcg)
 	ret = memcg_update_cache_sizes(memcg);
 	mutex_unlock(&set_limit_mutex);
 out:
+	if (ret)
+		mem_cgroup_put(memcg);
 	return ret;
 }
 #endif /* CONFIG_MEMCG_KMEM */
@@ -6417,16 +6419,6 @@ mem_cgroup_css_online(struct cgroup *cont)
 
 	error = memcg_init_kmem(memcg, &mem_cgroup_subsys);
 	mutex_unlock(&memcg_create_mutex);
-	if (error) {
-		/*
-		 * We call put now because our (and parent's) refcnts
-		 * are already in place. mem_cgroup_put() will internally
-		 * call __mem_cgroup_free, so return directly
-		 */
-		mem_cgroup_put(memcg);
-		if (parent->use_hierarchy)
-			mem_cgroup_put(parent);
-	}
 	return error;
 }
 
-- 
Michal Hocko
SUSE Labs

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