Messages in this thread Patch in this message | | | From | Luis Henriques <> | Subject | [PATCH 3.11 142/198] tcp: fix cwnd undo on DSACK in F-RTO | Date | Thu, 3 Jul 2014 10:19:45 +0100 |
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3.11.10.13 -stable review patch. If anyone has any objections, please let me know.
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From: Yuchung Cheng <ycheng@google.com>
commit 0cfa5c07d6d1d7f8e710fc671c5ba1ce85e09fa4 upstream.
This bug is discovered by an recent F-RTO issue on tcpm list https://www.ietf.org/mail-archive/web/tcpm/current/msg08794.html
The bug is that currently F-RTO does not use DSACK to undo cwnd in certain cases: upon receiving an ACK after the RTO retransmission in F-RTO, and the ACK has DSACK indicating the retransmission is spurious, the sender only calls tcp_try_undo_loss() if some never retransmisted data is sacked (FLAG_ORIG_DATA_SACKED).
The correct behavior is to unconditionally call tcp_try_undo_loss so the DSACK information is used properly to undo the cwnd reduction.
Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- net/ipv4/tcp_input.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 723951aec07e..d8e4c81bc114 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2622,13 +2622,12 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack) bool recovered = !before(tp->snd_una, tp->high_seq); if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */ - if (flag & FLAG_ORIG_SACK_ACKED) { - /* Step 3.b. A timeout is spurious if not all data are - * lost, i.e., never-retransmitted data are (s)acked. - */ - tcp_try_undo_loss(sk, true); + /* Step 3.b. A timeout is spurious if not all data are + * lost, i.e., never-retransmitted data are (s)acked. + */ + if (tcp_try_undo_loss(sk, flag & FLAG_ORIG_SACK_ACKED)) return; - } + if (after(tp->snd_nxt, tp->high_seq) && (flag & FLAG_DATA_SACKED || is_dupack)) { tp->frto = 0; /* Loss was real: 2nd part of step 3.a */ -- 1.9.1
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