On 11/9/2023 10:39 AM, David Howells wrote:
Fix RTT determination to use a PING ACK that is in marked as being in
response to a DATA packet as the response from which RTT can be calculated
from in lieu of a REQUESTED ACK. The server may send the latter instead of
the former.
Fixes: 4700c4d80b7b ("rxrpc: Fix loss of RTT samples due to interposed ACK")
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
cc: linux-afs@xxxxxxxxxxxxxxxxxxx
---
net/rxrpc/input.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c
index 030d64f282f3..fc0d404f3b91 100644
--- a/net/rxrpc/input.c
+++ b/net/rxrpc/input.c
@@ -806,6 +806,10 @@ static void rxrpc_input_ack(struct rxrpc_call *call, struct sk_buff *skb)
rxrpc_complete_rtt_probe(call, skb->tstamp, acked_serial, ack_serial,
rxrpc_rtt_rx_ping_response);
break;
+ case RXRPC_ACK_PING:
+ if (acked_serial == 0)
+ break;
+ fallthrough;
case RXRPC_ACK_REQUESTED:
rxrpc_complete_rtt_probe(call, skb->tstamp, acked_serial, ack_serial,
rxrpc_rtt_rx_requested_ack);
David,I do not believe the ack_reason matters within rxrpc_input_ack(). As long as the acked_serial is non-zero, rxrpc_complete_rtt_probe() can be called to attempt to compute an RTT. If there is an exact match for the acked_serial then an RTT can be computed and if acked_serial is later than the pending rtt probe, the probe
can be abandoned with the following caveats. 1. Receiving an acked_serial that is later than the serial of the transmitted probe indicates that a packet transmitted after the probe was received first. Or that reordering of the transmitted packets occurred. Or that the probe was never received by the peer; or that the peer's response to the probe was lost in transit. 2. The serial number namespace is unsigned 32-bit shared across all of the call channels of the associated rx connection. As the serial numbers will wrap the use of after() within rxrpc_complete_rtt_probe to compare their values is questionable. If serial numbers will be compared in this manner then they need to be locally tracked and compared as unsigned 64-bit values where only the low 32-bits are transmitted on the wire and any wire serial number equal to zero is ignored. Jeffrey Altman
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