[PATCH net-next v2 38/39] rxrpc: Fix request for an ACK when cwnd is minimum

[David Howells]

rxrpc_prepare_data_subpacket() sets the REQUEST-ACK flag on the outgoing
DATA packet under a number of circumstances, including, theoretically, when
the cwnd is at minimum (or less).  However, the minimum in this function is
hard-coded as 2, but the actual minimum is RXRPC_MIN_CWND (which is
currently 4) and so this never occurs.

Without this, we will miss the request of some ACKs, potentially leading to
a transmission stall until a timeout occurs on one side or the other that
leads to an ACK being generated.

Fix the function to use RXRPC_MIN_CWND rather than a hard-coded number.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
cc: Eric Dumazet <edumazet@xxxxxxxxxx>
cc: Jakub Kicinski <kuba@xxxxxxxxxx>
cc: Paolo Abeni <pabeni@xxxxxxxxxx>
cc: linux-afs@xxxxxxxxxxxxxxxxxxx
cc: netdev@xxxxxxxxxxxxxxx
---
 net/rxrpc/output.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/rxrpc/output.c b/net/rxrpc/output.c
index ecaf3becee40..f934551a9b1c 100644
--- a/net/rxrpc/output.c
+++ b/net/rxrpc/output.c
@@ -469,7 +469,7 @@ static size_t rxrpc_prepare_data_subpacket(struct rxrpc_call *call,
 		why = rxrpc_reqack_ack_lost;
 	else if (txb->flags & RXRPC_TXBUF_RESENT)
 		why = rxrpc_reqack_retrans;
-	else if (call->cong_ca_state == RXRPC_CA_SLOW_START && call->cong_cwnd <= 2)
+	else if (call->cong_ca_state == RXRPC_CA_SLOW_START && call->cong_cwnd <= RXRPC_MIN_CWND)
 		why = rxrpc_reqack_slow_start;
 	else if (call->tx_winsize <= 2)
 		why = rxrpc_reqack_small_txwin;