xprtrdma: "Support" call-only RPCs

RPC-over-RDMA version 1 credit accounting relies on there being a
response message for every RPC Call. This means that RPC procedures
that have no reply will disrupt credit accounting, just in the same
way as a retransmit would (since it is sent because no reply has
arrived). Deal with the "no reply" case the same way.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

include/linux/sunrpc/clnt.h

@@ -217,5 +217,12 @@ void rpc_clnt_xprt_switch_add_xprt(struct rpc_clnt *, struct rpc_xprt *);
 bool rpc_clnt_xprt_switch_has_addr(struct rpc_clnt *clnt,
 			const struct sockaddr *sap);
 void rpc_cleanup_clids(void);
+
+static inline int rpc_reply_expected(struct rpc_task *task)
+{
+	return (task->tk_msg.rpc_proc != NULL) &&
+		(task->tk_msg.rpc_proc->p_decode != NULL);
+}
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_SUNRPC_CLNT_H */

net/sunrpc/sunrpc.h

@@ -37,12 +37,6 @@ struct rpc_buffer {
 	char	data[];
 };
 
-static inline int rpc_reply_expected(struct rpc_task *task)
-{
-	return (task->tk_msg.rpc_proc != NULL) &&
-		(task->tk_msg.rpc_proc->p_decode != NULL);
-}
-
 static inline int sock_is_loopback(struct sock *sk)
 {
 	struct dst_entry *dst;

net/sunrpc/xprtrdma/transport.c

@@ -728,6 +728,12 @@ xprt_rdma_send_request(struct rpc_task *task)
 
 	rqst->rq_xmit_bytes_sent += rqst->rq_snd_buf.len;
 	rqst->rq_bytes_sent = 0;
+
+	/* An RPC with no reply will throw off credit accounting,
+	 * so drop the connection to reset the credit grant.
+	 */
+	if (!rpc_reply_expected(task))
+		goto drop_connection;
 	return 0;
 
 failed_marshal: