SUNRPC: Avoid holding locks across the XDR encoding of the RPC message

Currently, we grab the socket bit lock before we allow the message
to be XDR encoded. That significantly slows down the transmission
rate, since we serialise on a potentially blocking operation.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

net/sunrpc/clnt.c

@@ -1949,9 +1949,6 @@ call_transmit(struct rpc_task *task)
 	task->tk_action = call_status;
 	if (task->tk_status < 0)
 		return;
-	if (!xprt_prepare_transmit(task))
-		return;
-	task->tk_action = call_transmit_status;
 	/* Encode here so that rpcsec_gss can use correct sequence number. */
 	if (rpc_task_need_encode(task)) {
 		rpc_xdr_encode(task);
@@ -1965,6 +1962,9 @@ call_transmit(struct rpc_task *task)
 			return;
 		}
 	}
+	if (!xprt_prepare_transmit(task))
+		return;
+	task->tk_action = call_transmit_status;
 	xprt_transmit(task);
 	if (task->tk_status < 0)
 		return;