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: 4700c4d8 ("rxrpc: Fix loss of RTT samples due to interposed ACK")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: linux-afs@lists.infradead.org
cc: netdev@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>

include/trace/events/rxrpc.h

@@ -328,7 +328,7 @@
 	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

@@ -643,12 +643,8 @@ static void rxrpc_complete_rtt_probe(struct rxrpc_call *call,
 			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);
 			matched = true;
 		}
 
@@ -801,6 +797,7 @@ static void rxrpc_input_ack(struct rxrpc_call *call, struct sk_buff *skb)
 			   summary.ack_reason, nr_acks);
 	rxrpc_inc_stat(call->rxnet, stat_rx_acks[ack.reason]);
 
+	if (acked_serial != 0) {
 		switch (ack.reason) {
 		case RXRPC_ACK_PING_RESPONSE:
 			rxrpc_complete_rtt_probe(call, skb->tstamp, acked_serial, ack_serial,
@@ -811,11 +808,11 @@ static void rxrpc_input_ack(struct rxrpc_call *call, struct sk_buff *skb)
 						 rxrpc_rtt_rx_requested_ack);
 			break;
 		default:
-		if (acked_serial != 0)
 			rxrpc_complete_rtt_probe(call, skb->tstamp, acked_serial, ack_serial,
-						 rxrpc_rtt_rx_cancel);
+						 rxrpc_rtt_rx_other_ack);
 			break;
 		}
+	}
 
 	if (ack.reason == RXRPC_ACK_PING) {
 		rxrpc_send_ACK(call, RXRPC_ACK_PING_RESPONSE, ack_serial,