[PATCH 061/102] tcp: undo spurious timeout after SACK reneging

From: Luis Henriques
Date: Mon Apr 08 2013 - 06:08:30 EST -stable review patch. If anyone has any objections, please let me know.


From: Yuchung Cheng <ycheng@xxxxxxxxxx>

commit 7ebe183c6d444ef5587d803b64a1f4734b18c564 upstream.

On SACK reneging the sender immediately retransmits and forces a
timeout but disables Eifel (undo). If the (buggy) receiver does not
drop any packet this can trigger a false slow-start retransmit storm
driven by the ACKs of the original packets. This can be detected with
undo and TCP timestamps.

Signed-off-by: Yuchung Cheng <ycheng@xxxxxxxxxx>
Acked-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
net/ipv4/tcp_input.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 410b7c4..e75e4fb 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2267,11 +2267,8 @@ void tcp_enter_loss(struct sock *sk, int how)
if (tcp_is_reno(tp))

- if (!how) {
- /* Push undo marker, if it was plain RTO and nothing
- * was retransmitted. */
- tp->undo_marker = tp->snd_una;
- } else {
+ tp->undo_marker = tp->snd_una;
+ if (how) {
tp->sacked_out = 0;
tp->fackets_out = 0;

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