xprtrdma: Trace marshaling failures

Record an event when rpcrdma_marshal_req returns a non-zero return
value to help track down why an xprt close might have occurred.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

include/trace/events/rpcrdma.h

@@ -511,6 +511,33 @@ TRACE_EVENT(xprtrdma_marshal,
 	)
 );
 
+TRACE_EVENT(xprtrdma_marshal_failed,
+	TP_PROTO(const struct rpc_rqst *rqst,
+		 int ret
+	),
+
+	TP_ARGS(rqst, ret),
+
+	TP_STRUCT__entry(
+		__field(unsigned int, task_id)
+		__field(unsigned int, client_id)
+		__field(u32, xid)
+		__field(int, ret)
+	),
+
+	TP_fast_assign(
+		__entry->task_id = rqst->rq_task->tk_pid;
+		__entry->client_id = rqst->rq_task->tk_client->cl_clid;
+		__entry->xid = be32_to_cpu(rqst->rq_xid);
+		__entry->ret = ret;
+	),
+
+	TP_printk("task:%u@%u xid=0x%08x: ret=%d",
+		__entry->task_id, __entry->client_id, __entry->xid,
+		__entry->ret
+	)
+);
+
 TRACE_EVENT(xprtrdma_post_send,
 	TP_PROTO(
 		const struct rpcrdma_req *req,

net/sunrpc/xprtrdma/rpc_rdma.c

@@ -875,6 +875,7 @@ rpcrdma_marshal_req(struct rpcrdma_xprt *r_xprt, struct rpc_rqst *rqst)
 	return 0;
 
 out_err:
+	trace_xprtrdma_marshal_failed(rqst, ret);
 	switch (ret) {
 	case -EAGAIN:
 		xprt_wait_for_buffer_space(rqst->rq_xprt);