It's possible that new SACK blocks that should trigger new LOST markings arrive with new data (which previously made is_dupack false). In addition, I think this fixes a case where we get a cumulative ACK with enough SACK blocks to trigger the fast recovery (is_dupack would be false there too).
I'm not completely pleased with this solution because readability of the code is somewhat questionable as 'is_dupack' in SACK case is no longer about dupacks only but would mean something like 'lost_marker_work_todo' too... But because of Eifel stuff done in CA_Recovery, the FLAG_DATA_SACKED check cannot be placed to the if statement which seems attractive solution. Nevertheless, I didn't like adding another variable just for that either... :-) Signed-off-by: Ilpo Järvinen <[EMAIL PROTECTED]> --- net/ipv4/tcp_input.c | 5 ++++- 1 files changed, 4 insertions(+), 1 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 767f92c..cfe6ac7 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2109,7 +2109,10 @@ tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una, { struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); - int is_dupack = (tp->snd_una == prior_snd_una && !(flag&FLAG_NOT_DUP)); + int is_dupack = (tp->snd_una == prior_snd_una && + (!(flag&FLAG_NOT_DUP) || + ((flag&FLAG_DATA_SACKED) && + (tp->fackets_out > tp->reordering)))); /* Some technical things: * 1. Reno does not count dupacks (sacked_out) automatically. */ -- 1.5.0.6