tcp: undo spurious timeout after SACK reneging

[ 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: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 1b1f7af17d6a63d429a6bfb3a98c0494c59c6089..3124e17675f95deabe9fffe6ba8db3f590a251bf 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2265,11 +2265,8 @@ void tcp_enter_loss(struct sock *sk, int how)
        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;
        }