This is a note to let you know that I've just added the patch titled
tcp: do not rearm RTO when future data are sacked
to the 3.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tcp-do-not-rearm-rto-when-future-data-are-sacked.patch
and it can be found in the queue-3.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 22b6cfcd281c80e5bf1d404f67c21303210bd32f Mon Sep 17 00:00:00 2001
From: Yuchung Cheng <ycheng@xxxxxxxxxx>
Date: Thu, 24 Oct 2013 08:59:27 -0700
Subject: tcp: do not rearm RTO when future data are sacked
From: Yuchung Cheng <ycheng@xxxxxxxxxx>
[ Upstream commit 2f715c1dde6e1760f3101358dc26f8c9489be0bf ]
Patch ed08495c3 "tcp: use RTT from SACK for RTO" always re-arms RTO upon
obtaining a RTT sample from newly sacked data.
But technically RTO should only be re-armed when the data sent before
the last (re)transmission of write queue head are (s)acked. Otherwise
the RTO may continue to extend during loss recovery on data sent
in the future.
Note that RTTs from ACK or timestamps do not have this problem, as the RTT
source must be from data sent before.
The new RTO re-arm policy is
1) Always re-arm RTO if SND.UNA is advanced
2) Re-arm RTO if sack RTT is available, provided the sacked data was
sent before the last time write_queue_head was sent.
Signed-off-by: Larry Brakmo <brakmo@xxxxxxxxxx>
Signed-off-by: Yuchung Cheng <ycheng@xxxxxxxxxx>
Acked-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Acked-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/ipv4/tcp_input.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2987,6 +2987,7 @@ static int tcp_clean_rtx_queue(struct so
s32 seq_rtt = -1;
s32 ca_seq_rtt = -1;
ktime_t last_ackt = net_invalid_timestamp();
+ bool rtt_update;
while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
@@ -3063,14 +3064,13 @@ static int tcp_clean_rtx_queue(struct so
if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
flag |= FLAG_SACK_RENEGING;
- if (tcp_ack_update_rtt(sk, flag, seq_rtt, sack_rtt) ||
- (flag & FLAG_ACKED))
- tcp_rearm_rto(sk);
+ rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt, sack_rtt);
if (flag & FLAG_ACKED) {
const struct tcp_congestion_ops *ca_ops
= inet_csk(sk)->icsk_ca_ops;
+ tcp_rearm_rto(sk);
if (unlikely(icsk->icsk_mtup.probe_size &&
!after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
tcp_mtup_probe_success(sk);
@@ -3109,6 +3109,13 @@ static int tcp_clean_rtx_queue(struct so
ca_ops->pkts_acked(sk, pkts_acked, rtt_us);
}
+ } else if (skb && rtt_update && sack_rtt >= 0 &&
+ sack_rtt > (s32)(now - TCP_SKB_CB(skb)->when)) {
+ /* Do not re-arm RTO if the sack RTT is measured from data sent
+ * after when the head was last (re)transmitted. Otherwise the
+ * timeout may continue to extend in loss recovery.
+ */
+ tcp_rearm_rto(sk);
}
#if FASTRETRANS_DEBUG > 0
Patches currently in stable-queue which might be from ycheng@xxxxxxxxxx are
queue-3.12/tcp-only-take-rtt-from-timestamps-if-new-data-is-acked.patch
queue-3.12/tcp-fix-synack-rtt-estimation-in-fast-open.patch
queue-3.12/tcp-do-not-rearm-rto-when-future-data-are-sacked.patch
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