IB/mad: Fix error path if response alloc fails in ib_mad_recv_done_handler()

If ib_mad_recv_done_handler() fails to allocate response, then it just
printed a warning and continued, which leads to an oops if the MAD is
being handled for a switch device, because the switch code uses
response without checking for NULL.  Fix this by bailing out of the
function if the allocation fails.
Signed-off-by: Suresh Shelvapille <suri@baymicrosystems.com>
Signed-off-by: Hal Rosenstock <hal.rosenstock@gmail.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/core/mad.c

@@ -1842,16 +1842,11 @@ static void ib_mad_recv_done_handler(struct ib_mad_port_private *port_priv,
 {
 	struct ib_mad_qp_info *qp_info;
 	struct ib_mad_private_header *mad_priv_hdr;
-	struct ib_mad_private *recv, *response;
+	struct ib_mad_private *recv, *response = NULL;
 	struct ib_mad_list_head *mad_list;
 	struct ib_mad_agent_private *mad_agent;
 	int port_num;
 
-	response = kmem_cache_alloc(ib_mad_cache, GFP_KERNEL);
-	if (!response)
-		printk(KERN_ERR PFX "ib_mad_recv_done_handler no memory "
-		       "for response buffer\n");
-
 	mad_list = (struct ib_mad_list_head *)(unsigned long)wc->wr_id;
 	qp_info = mad_list->mad_queue->qp_info;
 	dequeue_mad(mad_list);
@@ -1879,6 +1874,13 @@ static void ib_mad_recv_done_handler(struct ib_mad_port_private *port_priv,
 	if (!validate_mad(&recv->mad.mad, qp_info->qp->qp_num))
 		goto out;
 
+	response = kmem_cache_alloc(ib_mad_cache, GFP_KERNEL);
+	if (!response) {
+		printk(KERN_ERR PFX "ib_mad_recv_done_handler no memory "
+		       "for response buffer\n");
+		goto out;
+	}
+
 	if (port_priv->device->node_type == RDMA_NODE_IB_SWITCH)
 		port_num = wc->port_num;
 	else