tcp_htcp: last_cong bug fix

This patch fixes a minor bug in tcp_htcp.c which has been
highlighted by Lachlan Andrew and Lawrence Stewart.  Currently, the
time since the last congestion event, which is stored in variable
last_cong, is reset whenever there is a state change into
TCP_CA_Open.  This includes transitions of the type
TCP_CA_Open->TCP_CA_Disorder->TCP_CA_Open which are not associated
with backoff of cwnd.  The patch changes last_cong to be updated
only on transitions into TCP_CA_Open that occur after experiencing
the congestion-related states TCP_CA_Loss, TCP_CA_Recovery,
TCP_CA_CWR.

Signed-off-by: Doug Leith <doug.leith@nuim.ie>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 4 deletions

diff --git a/net/ipv4/tcp_htcp.c b/net/ipv4/tcp_htcp.c
index af99776146ff..937549b8a921 100644
--- a/net/ipv4/tcp_htcp.c
+++ b/net/ipv4/tcp_htcp.c
@@ -69,9 +69,12 @@ static u32 htcp_cwnd_undo(struct sock *sk)
         const struct tcp_sock *tp = tcp_sk(sk);
         struct htcp *ca = inet_csk_ca(sk);
 
-        ca->last_cong = ca->undo_last_cong;
-        ca->maxRTT = ca->undo_maxRTT;
-        ca->old_maxB = ca->undo_old_maxB;
+        if (ca->undo_last_cong) {
+                ca->last_cong = ca->undo_last_cong;
+                ca->maxRTT = ca->undo_maxRTT;
+                ca->old_maxB = ca->undo_old_maxB;
+                ca->undo_last_cong = 0;
+        }
 
         return max(tp->snd_cwnd, (tp->snd_ssthresh << 7) / ca->beta);
 }
@@ -268,7 +271,10 @@ static void htcp_state(struct sock *sk, u8 new_state)
         case TCP_CA_Open:
                 {
                         struct htcp *ca = inet_csk_ca(sk);
-                        ca->last_cong = jiffies;
+                        if (ca->undo_last_cong) {
+                                ca->last_cong = jiffies;
+                                ca->undo_last_cong = 0;
+                        }
                 }
                 break;
         case TCP_CA_CWR: