rbd: handle locking inside __rbd_client_find()

There is only caller of __rbd_client_find(), and it somewhat
clumsily gets the appropriate lock and gets a reference to the
existing ceph_client structure if it's found.

Instead, have that function handle its own locking, and acquire the
reference if found while it holds the lock.  Drop the underscores
from the name because there's no need to signify anything special
about this function.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Yehuda Sadeh <yehuda@inktank.com>

drivers/block/rbd.c

@@ -322,19 +322,28 @@ static struct rbd_client *rbd_client_create(struct ceph_options *ceph_opts,
 }
 
 /*
- * Find a ceph client with specific addr and configuration.
+ * Find a ceph client with specific addr and configuration.  If
+ * found, bump its reference count.
  */
-static struct rbd_client *__rbd_client_find(struct ceph_options *ceph_opts)
+static struct rbd_client *rbd_client_find(struct ceph_options *ceph_opts)
 {
 	struct rbd_client *client_node;
+	bool found = false;
 
 	if (ceph_opts->flags & CEPH_OPT_NOSHARE)
 		return NULL;
 
-	list_for_each_entry(client_node, &rbd_client_list, node)
-		if (!ceph_compare_options(ceph_opts, client_node->client))
-			return client_node;
-	return NULL;
+	spin_lock(&rbd_client_list_lock);
+	list_for_each_entry(client_node, &rbd_client_list, node) {
+		if (!ceph_compare_options(ceph_opts, client_node->client)) {
+			kref_get(&client_node->kref);
+			found = true;
+			break;
+		}
+	}
+	spin_unlock(&rbd_client_list_lock);
+
+	return found ? client_node : NULL;
 }
 
 /*
@@ -416,22 +425,16 @@ static struct rbd_client *rbd_get_client(const char *mon_addr,
 		return ERR_CAST(ceph_opts);
 	}
 
-	spin_lock(&rbd_client_list_lock);
-	rbdc = __rbd_client_find(ceph_opts);
+	rbdc = rbd_client_find(ceph_opts);
 	if (rbdc) {
 		/* using an existing client */
-		kref_get(&rbdc->kref);
-		spin_unlock(&rbd_client_list_lock);
-
 		ceph_destroy_options(ceph_opts);
 		kfree(rbd_opts);
 
 		return rbdc;
 	}
-	spin_unlock(&rbd_client_list_lock);
 
 	rbdc = rbd_client_create(ceph_opts, rbd_opts);
-
 	if (IS_ERR(rbdc))
 		kfree(rbd_opts);