rx: do not rxi_AckAll for one data packet call

rxi_ReceiveDataPacket() calls rxi_AckAll() when the call reaches
the RX_CALL_RECEIVE_DONE state to permit the caller to empty the
transmit queue.  That reduces the memory consumption of the caller
and avoids unnecessary retransmits which the call is in process.

If the call data consists of a single packet it is possible that
Ping ACK packets sent as part of connection establishment could
race with the ACKALL and be delivered out of order.  If the Ping
ACK is delivered second, it will be ignored by the peer forcing
a two second delay in connection establishment.  To avoid the race
do not send an ACKALL for a single packet call.

Change-Id: I69d967b3b2e9ee77636ca12bc7ade4896bb8a071
Reviewed-on: http://gerrit.openafs.org/4799
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>

diff --git a/src/rx/rx.c b/src/rx/rx.c
index 06fdef2..78d8392 100644 (file)
--- a/src/rx/rx.c
+++ b/src/rx/rx.c
@@ -3953,12 +3953,18 @@ rxi_ReceiveDataPacket(struct rx_call *call,
      * received. Always send a soft ack for the last packet in
      * the server's reply.
      *
-     * If we have received all of the packets for the call
-     * immediately send an RX_PACKET_TYPE_ACKALL packet so that
-     * the peer can empty its packet queue and cancel all resend
-     * events.
+     * If there was more than one packet received for the call
+     * and we have received all of them, immediately send an
+     * RX_PACKET_TYPE_ACKALL packet so that the peer can empty
+     * its packet transmit queue and cancel all resend events.
+     *
+     * When there is only one packet in the call there is a
+     * chance that we can race with Ping ACKs sent as part of
+     * connection establishment if the udp packets are delivered
+     * out of order.  When the race occurs, a two second delay
+     * will occur while waiting for a new Ping ACK to be sent.
      */
-    if (call->flags & RX_CALL_RECEIVE_DONE) {
+    if (!isFirst && (call->flags & RX_CALL_RECEIVE_DONE)) {
         rxevent_Cancel(call->delayedAckEvent, call, RX_CALL_REFCOUNT_DELAY);
         rxi_AckAll(NULL, call, 0);
     } else if (ackNeeded) {