RDMA/cma: Remove dead code for kernel rdmacm multicast

There is no kernel user of RDMA CM multicast so this code managing the
multicast subscription of the kernel-only internal QP is dead. Remove it.

This makes the bug fixes in the next patches much simpler.

Link: https://lore.kernel.org/r/20200902081122.745412-7-leon@kernel.orgSigned-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/core/cma.c

@@ -4337,16 +4337,6 @@ static int cma_ib_mc_handler(int status, struct ib_sa_multicast *multicast)
 	else
 		pr_debug_ratelimited("RDMA CM: MULTICAST_ERROR: failed to join multicast. status %d\n",
 				     status);
-	mutex_lock(&id_priv->qp_mutex);
-	if (!status && id_priv->id.qp) {
-		status = ib_attach_mcast(id_priv->id.qp, &multicast->rec.mgid,
-					 be16_to_cpu(multicast->rec.mlid));
-		if (status)
-			pr_debug_ratelimited("RDMA CM: MULTICAST_ERROR: failed to attach QP. status %d\n",
-					     status);
-	}
-	mutex_unlock(&id_priv->qp_mutex);
-
 	event.status = status;
 	event.param.ud.private_data = mc->context;
 	if (!status) {
@@ -4600,6 +4590,10 @@ int rdma_join_multicast(struct rdma_cm_id *id, struct sockaddr *addr,
 	struct cma_multicast *mc;
 	int ret;
 
+	/* Not supported for kernel QPs */
+	if (WARN_ON(id->qp))
+		return -EINVAL;
+
 	/* ULP is calling this wrong. */
 	if (!id->device || (READ_ONCE(id_priv->state) != RDMA_CM_ADDR_BOUND &&
 			    READ_ONCE(id_priv->state) != RDMA_CM_ADDR_RESOLVED))
@@ -4651,11 +4645,6 @@ void rdma_leave_multicast(struct rdma_cm_id *id, struct sockaddr *addr)
 			list_del(&mc->list);
 			spin_unlock_irq(&id_priv->lock);
 
-			if (id->qp)
-				ib_detach_mcast(id->qp,
-						&mc->multicast.ib->rec.mgid,
-						be16_to_cpu(mc->multicast.ib->rec.mlid));
-
 			BUG_ON(id_priv->cma_dev->device != id->device);
 
 			if (rdma_cap_ib_mcast(id->device, id->port_num)) {