rxrpc: Trace discarded ACKs

Add a tracepoint to track received ACKs that are discarded due to being
outside of the Tx window.
Signed-off-by: David Howells <dhowells@redhat.com>

include/trace/events/rxrpc.h

@@ -1541,6 +1541,41 @@ TRACE_EVENT(rxrpc_notify_socket,
 		      __entry->serial)
 	    );
 
+TRACE_EVENT(rxrpc_rx_discard_ack,
+	    TP_PROTO(unsigned int debug_id, rxrpc_serial_t serial,
+		     rxrpc_seq_t first_soft_ack, rxrpc_seq_t call_ackr_first,
+		     rxrpc_seq_t prev_pkt, rxrpc_seq_t call_ackr_prev),
+
+	    TP_ARGS(debug_id, serial, first_soft_ack, call_ackr_first,
+		    prev_pkt, call_ackr_prev),
+
+	    TP_STRUCT__entry(
+		    __field(unsigned int,	debug_id	)
+		    __field(rxrpc_serial_t,	serial		)
+		    __field(rxrpc_seq_t,	first_soft_ack)
+		    __field(rxrpc_seq_t,	call_ackr_first)
+		    __field(rxrpc_seq_t,	prev_pkt)
+		    __field(rxrpc_seq_t,	call_ackr_prev)
+			     ),
+
+	    TP_fast_assign(
+		    __entry->debug_id		= debug_id;
+		    __entry->serial		= serial;
+		    __entry->first_soft_ack	= first_soft_ack;
+		    __entry->call_ackr_first	= call_ackr_first;
+		    __entry->prev_pkt		= prev_pkt;
+		    __entry->call_ackr_prev	= call_ackr_prev;
+			   ),
+
+	    TP_printk("c=%08x r=%08x %08x<%08x %08x<%08x",
+		      __entry->debug_id,
+		      __entry->serial,
+		      __entry->first_soft_ack,
+		      __entry->call_ackr_first,
+		      __entry->prev_pkt,
+		      __entry->call_ackr_prev)
+	    );
+
 #endif /* _TRACE_RXRPC_H */
 
 /* This part must be outside protection */

net/rxrpc/input.c

@@ -866,8 +866,12 @@ static void rxrpc_input_ack(struct rxrpc_call *call, struct sk_buff *skb)
 
 	/* Discard any out-of-order or duplicate ACKs (outside lock). */
 	if (before(first_soft_ack, call->ackr_first_seq) ||
-	    before(prev_pkt, call->ackr_prev_seq))
+	    before(prev_pkt, call->ackr_prev_seq)) {
+		trace_rxrpc_rx_discard_ack(call->debug_id, sp->hdr.serial,
+					   first_soft_ack, call->ackr_first_seq,
+					   prev_pkt, call->ackr_prev_seq);
 		return;
+	}
 
 	buf.info.rxMTU = 0;
 	ioffset = offset + nr_acks + 3;
@@ -879,8 +883,12 @@ static void rxrpc_input_ack(struct rxrpc_call *call, struct sk_buff *skb)
 
 	/* Discard any out-of-order or duplicate ACKs (inside lock). */
 	if (before(first_soft_ack, call->ackr_first_seq) ||
-	    before(prev_pkt, call->ackr_prev_seq))
+	    before(prev_pkt, call->ackr_prev_seq)) {
+		trace_rxrpc_rx_discard_ack(call->debug_id, sp->hdr.serial,
+					   first_soft_ack, call->ackr_first_seq,
+					   prev_pkt, call->ackr_prev_seq);
 		goto out;
+	}
 	call->acks_latest_ts = skb->tstamp;
 
 	call->ackr_first_seq = first_soft_ack;