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-rw-r--r--mm/slab.h26
1 files changed, 25 insertions, 1 deletions
diff --git a/mm/slab.h b/mm/slab.h
index 0859c4241ba1..8184a7cde272 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)