rxrpc: Fix RTT determination to use any ACK as a source

Fix RTT determination to be able to use any type of ACK as the response
from which RTT can be calculated provided its ack.serial is non-zero and
matches the serial number of an outgoing DATA or ACK packet. This
shouldn't be limited to REQUESTED-type ACKs as these can have other types
substituted for them for things like duplicate or out-of-order packets.

Fixes: 4700c4d80b7b ("rxrpc: Fix loss of RTT samples due to interposed ACK")
Signed-off-by: David Howells <[e-mail]>
cc: Marc Dionne <[e-mail]>
cc: "David S. Miller" <[e-mail]>
cc: Eric Dumazet <[e-mail]>
cc: Jakub Kicinski <[e-mail]>
cc: Paolo Abeni <[e-mail]>
cc: [e-mail]
cc: [e-mail]
Signed-off-by: David S. Miller <[e-mail]>

include/trace/events/rxrpc.h

···
 	E_(rxrpc_rtt_tx_ping,			"PING")
 
 #define rxrpc_rtt_rx_traces \
-	EM(rxrpc_rtt_rx_cancel,			"CNCL") \
+	EM(rxrpc_rtt_rx_other_ack,		"OACK") \
 	EM(rxrpc_rtt_rx_obsolete,		"OBSL") \
 	EM(rxrpc_rtt_rx_lost,			"LOST") \
 	EM(rxrpc_rtt_rx_ping_response,		"PONG") \

net/rxrpc/input.c

···
 			clear_bit(i + RXRPC_CALL_RTT_PEND_SHIFT, &call->rtt_avail);
 			smp_mb(); /* Read data before setting avail bit */
 			set_bit(i, &call->rtt_avail);
-			if (type != rxrpc_rtt_rx_cancel)
-				rxrpc_peer_add_rtt(call, type, i, acked_serial, ack_serial,
-						   sent_at, resp_time);
-			else
-				trace_rxrpc_rtt_rx(call, rxrpc_rtt_rx_cancel, i,
-						   orig_serial, acked_serial, 0, 0);
+			rxrpc_peer_add_rtt(call, type, i, acked_serial, ack_serial,
+					   sent_at, resp_time);
 			matched = true;
 		}
 
···
 			   summary.ack_reason, nr_acks);
 	rxrpc_inc_stat(call->rxnet, stat_rx_acks[ack.reason]);
 
-	switch (ack.reason) {
-	case RXRPC_ACK_PING_RESPONSE:
-		rxrpc_complete_rtt_probe(call, skb->tstamp, acked_serial, ack_serial,
-					 rxrpc_rtt_rx_ping_response);
-		break;
-	case RXRPC_ACK_REQUESTED:
-		rxrpc_complete_rtt_probe(call, skb->tstamp, acked_serial, ack_serial,
-					 rxrpc_rtt_rx_requested_ack);
-		break;
-	default:
-		if (acked_serial != 0)
+	if (acked_serial != 0) {
+		switch (ack.reason) {
+		case RXRPC_ACK_PING_RESPONSE:
 			rxrpc_complete_rtt_probe(call, skb->tstamp, acked_serial, ack_serial,
-						 rxrpc_rtt_rx_cancel);
-		break;
+						 rxrpc_rtt_rx_ping_response);
+			break;
+		case RXRPC_ACK_REQUESTED:
+			rxrpc_complete_rtt_probe(call, skb->tstamp, acked_serial, ack_serial,
+						 rxrpc_rtt_rx_requested_ack);
+			break;
+		default:
+			rxrpc_complete_rtt_probe(call, skb->tstamp, acked_serial, ack_serial,
+						 rxrpc_rtt_rx_other_ack);
+			break;
+		}
 	}
 
 	if (ack.reason == RXRPC_ACK_PING) {