[PATCH v2 18/18] xprtrdma: Faster server reboot recovery

[Chuck Lever <chuck.lever@oracle.com>]

In a cluster failover scenario, it is desirable for the client to
attempt to reconnect quickly, as an alternate NFS server is already
waiting to take over for the down server. The client can't see that
a server IP address has moved to a new server until the existing
connection is gone.

For fabrics and devices where it is meaningful, set an upper bound
on the amount of time before it is determined that a connection is
no longer valid. This allows the RPC client to detect connection
loss in a timely matter, then perform a fresh resolution of the
server GUID in case it has changed (cluster failover).

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/xprtrdma/verbs.c |   28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index b7a5bc1..5cc57fb 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -211,9 +211,10 @@ rpcrdma_conn_upcall(struct rdma_cm_id *id, struct rdma_cm_event *event)
 	struct rpcrdma_ep *ep = &xprt->rx_ep;
 #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
 	struct sockaddr *sap = (struct sockaddr *)&ep->rep_remote_addr;
-#endif
+	u64 timeout;
 	struct ib_qp_attr *attr = &ia->ri_qp_attr;
 	struct ib_qp_init_attr *iattr = &ia->ri_qp_init_attr;
+#endif
 	int connstate = 0;
 
 	switch (event->event) {
@@ -235,14 +236,23 @@ rpcrdma_conn_upcall(struct rdma_cm_id *id, struct rdma_cm_event *event)
 		complete(&ia->ri_done);
 		break;
 	case RDMA_CM_EVENT_ESTABLISHED:
-		connstate = 1;
+#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
+		memset(attr, 0, sizeof(*attr));
 		ib_query_qp(ia->ri_id->qp, attr,
-			    IB_QP_MAX_QP_RD_ATOMIC | IB_QP_MAX_DEST_RD_ATOMIC,
+			    IB_QP_MAX_QP_RD_ATOMIC |
+			    IB_QP_MAX_DEST_RD_ATOMIC |
+			    IB_QP_TIMEOUT,
 			    iattr);
 		dprintk("RPC:       %s: %d responder resources"
 			" (%d initiator)\n",
 			__func__, attr->max_dest_rd_atomic,
 			attr->max_rd_atomic);
+		timeout = 4096 * (1ULL << attr->timeout);
+		do_div(timeout, NSEC_PER_SEC);
+		dprintk("RPC:       %s: retry timeout: %llu seconds\n",
+			__func__, timeout);
+#endif
+		connstate = 1;
 		goto connected;
 	case RDMA_CM_EVENT_CONNECT_ERROR:
 		connstate = -ENOTCONN;
@@ -554,6 +564,7 @@ rpcrdma_ep_create(struct rpcrdma_ep *ep, struct rpcrdma_ia *ia,
 	ep->rep_attr.recv_cq = recvcq;
 
 	/* Initialize cma parameters */
+	memset(&ep->rep_remote_cma, 0, sizeof(ep->rep_remote_cma));
 
 	/* RPC/RDMA does not use private data */
 	ep->rep_remote_cma.private_data = NULL;
@@ -567,7 +578,16 @@ rpcrdma_ep_create(struct rpcrdma_ep *ep, struct rpcrdma_ia *ia,
 		ep->rep_remote_cma.responder_resources =
 						ia->ri_device->attrs.max_qp_rd_atom;
 
-	ep->rep_remote_cma.retry_count = 7;
+	/* Limit transport retries so client can detect server
+	 * GID changes quickly. RPC layer handles re-establishing
+	 * transport connection and retransmission.
+	 */
+	ep->rep_remote_cma.retry_count = 6;
+
+	/* RPC-over-RDMA handles its own flow control. In addition,
+	 * make all RNR NAKs visible so we know that RPC-over-RDMA
+	 * flow control is working correctly (no NAKs should be seen).
+	 */
 	ep->rep_remote_cma.flow_control = 0;
 	ep->rep_remote_cma.rnr_retry_count = 0;