X-Git-Url: http://pileus.org/git/?a=blobdiff_plain;f=mm%2Fslab.h;h=8184a7cde272b8aa9d6e08e6407482ca5d7bd7df;hb=ca2a650f3dfdc30d71d21bcbb04d2d057779f3f9;hp=0859c4241ba10b2ee602eca48af4e34dd82d6ae3;hpb=db8fbb49df8ae4da155d3b7abf39e79b41f72746;p=~andy%2Flinux

diff --git a/mm/slab.h b/mm/slab.h
index 0859c4241ba..8184a7cde27 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -160,12 +160,36 @@ static inline const char *cache_name(struct kmem_cache *s)
 	return s->name;
 }
 
+/*
+ * Note, we protect with RCU only the memcg_caches array, not per-memcg caches.
+ * That said the caller must assure the memcg's cache won't go away. Since once
+ * created a memcg's cache is destroyed only along with the root cache, it is
+ * true if we are going to allocate from the cache or hold a reference to the
+ * root cache by other means. Otherwise, we should hold either the slab_mutex
+ * or the memcg's slab_caches_mutex while calling this function and accessing
+ * the returned value.
+ */
 static inline struct kmem_cache *
 cache_from_memcg_idx(struct kmem_cache *s, int idx)
 {
+	struct kmem_cache *cachep;
+	struct memcg_cache_params *params;
+
 	if (!s->memcg_params)
 		return NULL;
-	return s->memcg_params->memcg_caches[idx];
+
+	rcu_read_lock();
+	params = rcu_dereference(s->memcg_params);
+	cachep = params->memcg_caches[idx];
+	rcu_read_unlock();
+
+	/*
+	 * Make sure we will access the up-to-date value. The code updating
+	 * memcg_caches issues a write barrier to match this (see
+	 * memcg_register_cache()).
+	 */
+	smp_read_barrier_depends();
+	return cachep;
 }
 
 static inline struct kmem_cache *memcg_root_cache(struct kmem_cache *s)