ocfs2: fix a panic problem caused by o2cb_ctl

In the process of creating a node, it will cause NULL pointer
dereference in kernel if o2cb_ctl failed in the interval (mkdir,
o2cb_set_node_attribute(node_num)] in function o2cb_add_node.

The node num is initialized to 0 in function o2nm_node_group_make_item,
o2nm_node_group_drop_item will mistake the node number 0 for a valid
node number when we delete the node before the node number is set
correctly.  If the local node number of the current host happens to be
0, cluster->cl_local_node will be set to O2NM_INVALID_NODE_NUM while
o2hb_thread still running.  The panic stack is generated as follows:

  o2hb_thread
      \-o2hb_do_disk_heartbeat
          \-o2hb_check_own_slot
              |-slot = &reg->hr_slots[o2nm_this_node()];
              //o2nm_this_node() return O2NM_INVALID_NODE_NUM

We need to check whether the node number is set when we delete the node.

Link: http://lkml.kernel.org/r/133d8045-72cc-863e-8eae-5013f9f6bc51@huawei.comSigned-off-by: Jia Guo <guojia12@huawei.com>
Reviewed-by: Joseph Qi <jiangqi903@gmail.com>
Acked-by: Jun Piao <piaojun@huawei.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <ge.changwei@h3c.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ocfs2/cluster/nodemanager.c

@@ -621,13 +621,15 @@ static void o2nm_node_group_drop_item(struct config_group *group,
 	struct o2nm_node *node = to_o2nm_node(item);
 	struct o2nm_cluster *cluster = to_o2nm_cluster(group->cg_item.ci_parent);
 
-	o2net_disconnect_node(node);
+	if (cluster->cl_nodes[node->nd_num] == node) {
+		o2net_disconnect_node(node);
 
-	if (cluster->cl_has_local &&
-	    (cluster->cl_local_node == node->nd_num)) {
-		cluster->cl_has_local = 0;
-		cluster->cl_local_node = O2NM_INVALID_NODE_NUM;
-		o2net_stop_listening(node);
+		if (cluster->cl_has_local &&
+		    (cluster->cl_local_node == node->nd_num)) {
+			cluster->cl_has_local = 0;
+			cluster->cl_local_node = O2NM_INVALID_NODE_NUM;
+			o2net_stop_listening(node);
+		}
 	}
 
 	/* XXX call into net to stop this node from trading messages */