3.3-stable review patch.  If anyone has any objections, please let me know.

------------------


From: Yuchung Cheng <redacted>

[ Upstream commit 1cebce36d660c83bd1353e41f3e66abd4686f215 ]

When the cwnd reduction is done, ssthresh may be infinite
if TCP enters CWR via ECN or F-RTO. If cwnd is not undone, i.e.,
undo_marker is set, tcp_complete_cwr() falsely set cwnd to the
infinite ssthresh value. The correct operation is to keep cwnd
intact because it has been updated in ECN or F-RTO.

Signed-off-by: Yuchung Cheng <redacted>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv4/tcp_input.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c

@@ -2866,11 +2866,14 @@ static inline void tcp_complete_cwr(stru
 
 	/* Do not moderate cwnd if it's already undone in cwr or recovery. */
 	if (tp->undo_marker) {
-		if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR)
+		if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR) {
 			tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
-		else /* PRR */
+			tp->snd_cwnd_stamp = tcp_time_stamp;
+		} else if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH) {
+			/* PRR algorithm. */
 			tp->snd_cwnd = tp->snd_ssthresh;
-		tp->snd_cwnd_stamp = tcp_time_stamp;
+			tp->snd_cwnd_stamp = tcp_time_stamp;
+		}
 	}
 	tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
 }