3.10-stable review patch. If anyone has any objections, please let me know.
------------------ From: Yuchung Cheng <ych...@google.com> [ Upstream commit 0cfa5c07d6d1d7f8e710fc671c5ba1ce85e09fa4 ] 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 <ych...@google.com> Signed-off-by: Neal Cardwell <ncardw...@google.com> Signed-off-by: David S. Miller <da...@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> --- net/ipv4/tcp_input.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2720,13 +2720,12 @@ static void tcp_process_loss(struct sock 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 */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
