SUNRPC: Add a tracepoint for server socket out-of-space conditions

Add a tracepoint to track when the processing of incoming RPC data gets
deferred due to out-of-space issues on the outgoing transport.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

include/trace/events/sunrpc.h

@@ -553,7 +553,7 @@ TRACE_EVENT(svc_xprt_do_enqueue,
 		__entry->pid, show_svc_xprt_flags(__entry->flags))
 );
 
-TRACE_EVENT(svc_xprt_dequeue,
+DECLARE_EVENT_CLASS(svc_xprt_event,
 	TP_PROTO(struct svc_xprt *xprt),
 
 	TP_ARGS(xprt),
@@ -582,6 +582,14 @@ TRACE_EVENT(svc_xprt_dequeue,
 		show_svc_xprt_flags(__entry->flags))
 );
 
+DEFINE_EVENT(svc_xprt_event, svc_xprt_dequeue,
+	TP_PROTO(struct svc_xprt *xprt),
+	TP_ARGS(xprt));
+
+DEFINE_EVENT(svc_xprt_event, svc_xprt_no_write_space,
+	TP_PROTO(struct svc_xprt *xprt),
+	TP_ARGS(xprt));
+
 TRACE_EVENT(svc_wake_up,
 	TP_PROTO(int pid),
 

net/sunrpc/svc_xprt.c

@@ -333,8 +333,12 @@ static bool svc_xprt_has_something_to_do(struct svc_xprt *xprt)
 {
 	if (xprt->xpt_flags & ((1<<XPT_CONN)|(1<<XPT_CLOSE)))
 		return true;
-	if (xprt->xpt_flags & ((1<<XPT_DATA)|(1<<XPT_DEFERRED)))
-		return xprt->xpt_ops->xpo_has_wspace(xprt);
+	if (xprt->xpt_flags & ((1<<XPT_DATA)|(1<<XPT_DEFERRED))) {
+		if (xprt->xpt_ops->xpo_has_wspace(xprt))
+			return true;
+		trace_svc_xprt_no_write_space(xprt);
+		return false;
+	}
 	return false;
 }