[IB] mthca: Don't enter QP into MCG more than once.

Avoid entering a QP as member of a multicast group multiple times.
Signed-off-by: Jack Morgenstein <jackm@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/mthca/mthca_mcg.c

@@ -185,7 +185,12 @@ int mthca_multicast_attach(struct ib_qp *ibqp, union ib_gid *gid, u16 lid)
 	}
 
 	for (i = 0; i < MTHCA_QP_PER_MGM; ++i)
-		if (!(mgm->qp[i] & cpu_to_be32(1 << 31))) {
+		if (mgm->qp[i] == cpu_to_be32(ibqp->qp_num | (1 << 31))) {
+			mthca_dbg(dev, "QP %06x already a member of MGM\n", 
+				  ibqp->qp_num);
+			err = 0;
+			goto out;
+		} else if (!(mgm->qp[i] & cpu_to_be32(1 << 31))) {
 			mgm->qp[i] = cpu_to_be32(ibqp->qp_num | (1 << 31));
 			break;
 		}