[ 48/68] tcp: undo spurious timeout after SACK reneging

Greg Kroah-Hartman
2013-04-02T22:22:53Z

From: Yuchung Cheng <ycheng@google.com>

[ Upstream commit 7ebe183c6d444ef5587d803b64a1f4734b18c564 ]

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@google.com>
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 | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)

--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2260,11 +2260,8 @@ void tcp_enter_loss(struct sock *sk, int
if (tcp_is_reno(tp))
tcp_reset_reno_sack(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;
}