RPC/RDMA: suppress retransmit on RPC/RDMA clients.

An RPC/RDMA client cannot retransmit on an unbroken connection,
doing so violates its flow control with the server.
Signed-off-by: Tom Talpey <talpey@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/xprtrdma/rpc_rdma.c

@@ -681,6 +681,8 @@ rpcrdma_conn_func(struct rpcrdma_ep *ep)
 	struct rpc_xprt *xprt = ep->rep_xprt;
 
 	spin_lock_bh(&xprt->transport_lock);
+	if (++xprt->connect_cookie == 0)	/* maintain a reserved value */
+		++xprt->connect_cookie;
 	if (ep->rep_connected > 0) {
 		if (!xprt_test_and_set_connected(xprt))
 			xprt_wake_pending_tasks(xprt, 0);

net/sunrpc/xprtrdma/transport.c

@@ -587,6 +587,7 @@ xprt_rdma_allocate(struct rpc_task *task, size_t size)
 	}
 	dprintk("RPC:       %s: size %zd, request 0x%p\n", __func__, size, req);
 out:
+	req->rl_connect_cookie = 0;	/* our reserved value */
 	return req->rl_xdr_buf;
 
 outfail:
@@ -690,13 +691,20 @@ xprt_rdma_send_request(struct rpc_task *task)
 		req->rl_reply->rr_xprt = xprt;
 	}
 
-	if (rpcrdma_ep_post(&r_xprt->rx_ia, &r_xprt->rx_ep, req)) {
-		xprt_disconnect_done(xprt);
-		return -ENOTCONN;	/* implies disconnect */
-	}
+	/* Must suppress retransmit to maintain credits */
+	if (req->rl_connect_cookie == xprt->connect_cookie)
+		goto drop_connection;
+	req->rl_connect_cookie = xprt->connect_cookie;
+
+	if (rpcrdma_ep_post(&r_xprt->rx_ia, &r_xprt->rx_ep, req))
+		goto drop_connection;
 
 	rqst->rq_bytes_sent = 0;
 	return 0;
+
+drop_connection:
+	xprt_disconnect_done(xprt);
+	return -ENOTCONN;	/* implies disconnect */
 }
 
 static void xprt_rdma_print_stats(struct rpc_xprt *xprt, struct seq_file *seq)

net/sunrpc/xprtrdma/xprt_rdma.h

@@ -181,6 +181,7 @@ struct rpcrdma_req {
 	size_t 		rl_size;	/* actual length of buffer */
 	unsigned int	rl_niovs;	/* 0, 2 or 4 */
 	unsigned int	rl_nchunks;	/* non-zero if chunks */
+	unsigned int	rl_connect_cookie;	/* retry detection */
 	struct rpcrdma_buffer *rl_buffer; /* home base for this structure */
 	struct rpcrdma_rep	*rl_reply;/* holder for reply buffer */
 	struct rpcrdma_mr_seg rl_segments[RPCRDMA_MAX_SEGS];/* chunk segments */