diff --git a/fs/ocfs2/cluster/nodemanager.c b/fs/ocfs2/cluster/nodemanager.c
index a51200e..da64c3a2 100644
--- a/fs/ocfs2/cluster/nodemanager.c
+++ b/fs/ocfs2/cluster/nodemanager.c
@@ -40,6 +40,9 @@ char *o2nm_fence_method_desc[O2NM_FENCE_METHODS] = {
 		"panic",	/* O2NM_FENCE_PANIC */
 };
 
+static inline void o2nm_lock_subsystem(void);
+static inline void o2nm_unlock_subsystem(void);
+
 struct o2nm_node *o2nm_get_node_by_num(u8 node_num)
 {
 	struct o2nm_node *node = NULL;
@@ -181,7 +184,10 @@ static struct o2nm_cluster *to_o2nm_cluster_from_node(struct o2nm_node *node)
 {
 	/* through the first node_set .parent
 	 * mycluster/nodes/mynode == o2nm_cluster->o2nm_node_group->o2nm_node */
-	return to_o2nm_cluster(node->nd_item.ci_parent->ci_parent);
+	if (node->nd_item.ci_parent)
+		return to_o2nm_cluster(node->nd_item.ci_parent->ci_parent);
+	else
+		return NULL;
 }
 
 enum {
@@ -194,7 +200,7 @@ static ssize_t o2nm_node_num_store(struct config_item *item, const char *page,
 				   size_t count)
 {
 	struct o2nm_node *node = to_o2nm_node(item);
-	struct o2nm_cluster *cluster = to_o2nm_cluster_from_node(node);
+	struct o2nm_cluster *cluster;
 	unsigned long tmp;
 	char *p = (char *)page;
 	int ret = 0;
@@ -214,6 +220,13 @@ static ssize_t o2nm_node_num_store(struct config_item *item, const char *page,
 	    !test_bit(O2NM_NODE_ATTR_PORT, &node->nd_set_attributes))
 		return -EINVAL; /* XXX */
 
+	o2nm_lock_subsystem();
+	cluster = to_o2nm_cluster_from_node(node);
+	if (!cluster) {
+		o2nm_unlock_subsystem();
+		return -EINVAL;
+	}
+
 	write_lock(&cluster->cl_nodes_lock);
 	if (cluster->cl_nodes[tmp])
 		ret = -EEXIST;
@@ -226,6 +239,8 @@ static ssize_t o2nm_node_num_store(struct config_item *item, const char *page,
 		set_bit(tmp, cluster->cl_nodes_bitmap);
 	}
 	write_unlock(&cluster->cl_nodes_lock);
+	o2nm_unlock_subsystem();
+
 	if (ret)
 		return ret;
 
@@ -269,7 +284,7 @@ static ssize_t o2nm_node_ipv4_address_store(struct config_item *item,
 					    size_t count)
 {
 	struct o2nm_node *node = to_o2nm_node(item);
-	struct o2nm_cluster *cluster = to_o2nm_cluster_from_node(node);
+	struct o2nm_cluster *cluster;
 	int ret, i;
 	struct rb_node **p, *parent;
 	unsigned int octets[4];
@@ -286,6 +301,13 @@ static ssize_t o2nm_node_ipv4_address_store(struct config_item *item,
 		be32_add_cpu(&ipv4_addr, octets[i] << (i * 8));
 	}
 
+	o2nm_lock_subsystem();
+	cluster = to_o2nm_cluster_from_node(node);
+	if (!cluster) {
+		o2nm_unlock_subsystem();
+		return -EINVAL;
+	}
+
 	ret = 0;
 	write_lock(&cluster->cl_nodes_lock);
 	if (o2nm_node_ip_tree_lookup(cluster, ipv4_addr, &p, &parent))
@@ -298,6 +320,8 @@ static ssize_t o2nm_node_ipv4_address_store(struct config_item *item,
 		rb_insert_color(&node->nd_ip_node, &cluster->cl_node_ip_tree);
 	}
 	write_unlock(&cluster->cl_nodes_lock);
+	o2nm_unlock_subsystem();
+
 	if (ret)
 		return ret;
 
@@ -315,7 +339,7 @@ static ssize_t o2nm_node_local_store(struct config_item *item, const char *page,
 				     size_t count)
 {
 	struct o2nm_node *node = to_o2nm_node(item);
-	struct o2nm_cluster *cluster = to_o2nm_cluster_from_node(node);
+	struct o2nm_cluster *cluster;
 	unsigned long tmp;
 	char *p = (char *)page;
 	ssize_t ret;
@@ -333,17 +357,26 @@ static ssize_t o2nm_node_local_store(struct config_item *item, const char *page,
 	    !test_bit(O2NM_NODE_ATTR_PORT, &node->nd_set_attributes))
 		return -EINVAL; /* XXX */
 
+	o2nm_lock_subsystem();
+	cluster = to_o2nm_cluster_from_node(node);
+	if (!cluster) {
+		ret = -EINVAL;
+		goto out;
+	}
+
 	/* the only failure case is trying to set a new local node
 	 * when a different one is already set */
 	if (tmp && tmp == cluster->cl_has_local &&
-	    cluster->cl_local_node != node->nd_num)
-		return -EBUSY;
+	    cluster->cl_local_node != node->nd_num) {
+		ret = -EBUSY;
+		goto out;
+	}
 
 	/* bring up the rx thread if we're setting the new local node. */
 	if (tmp && !cluster->cl_has_local) {
 		ret = o2net_start_listening(node);
 		if (ret)
-			return ret;
+			goto out;
 	}
 
 	if (!tmp && cluster->cl_has_local &&
@@ -358,7 +391,11 @@ static ssize_t o2nm_node_local_store(struct config_item *item, const char *page,
 		cluster->cl_local_node = node->nd_num;
 	}
 
-	return count;
+	ret = count;
+
+out:
+	o2nm_unlock_subsystem();
+	return ret;
 }
 
 CONFIGFS_ATTR(o2nm_node_, num);
@@ -738,6 +775,16 @@ static struct o2nm_cluster_group o2nm_cluster_group = {
 	},
 };
 
+static inline void o2nm_lock_subsystem(void)
+{
+	mutex_lock(&o2nm_cluster_group.cs_subsys.su_mutex);
+}
+
+static inline void o2nm_unlock_subsystem(void)
+{
+	mutex_unlock(&o2nm_cluster_group.cs_subsys.su_mutex);
+}
+
 int o2nm_depend_item(struct config_item *item)
 {
 	return configfs_depend_item(&o2nm_cluster_group.cs_subsys, item);