memcg, slab: RCU protect memcg_params for root caches

[platform/adaptation/renesas_rcar/renesas_kernel.git] / mm / slab.h

diff --git a/mm/slab.h b/mm/slab.h
index 72d1f9d..8184a7c 100644 (file)
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -160,14 +160,28 @@ 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;
-       cachep = 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