path: root/net
diff options
authorYuchung Cheng <>2015-05-18 12:31:44 -0700
committerDavid S. Miller <>2015-05-19 16:36:57 -0400
commitda34ac7626b571d262f92b93f11eb32dd58d9c4e (patch)
treee3c4f0b85dd67290c942fafaaed936ef4f73d234 /net
parent33b4b015e1a1ca7a8fdce40af5e71642a8ea355c (diff)
tcp: only undo on partial ACKs in CA_Loss
Undo based on TCP timestamps should only happen on ACKs that advance SND_UNA, according to the Eifel algorithm in RFC 3522: Section 3.2: (4) If the value of the Timestamp Echo Reply field of the acceptable ACK's Timestamps option is smaller than the value of RetransmitTS, then proceed to step (5), Section Terminology: We use the term 'acceptable ACK' as defined in [RFC793]. That is an ACK that acknowledges previously unacknowledged data. This is because upon receiving an out-of-order packet, the receiver returns the last timestamp that advances RCV_NXT, not the current timestamp of the packet in the DUPACK. Without checking the flag, the DUPACK will cause tcp_packet_delayed() to return true and tcp_try_undo_loss() will revert cwnd reduction. Note that we check the condition in CA_Recovery already by only calling tcp_try_undo_partial() if FLAG_SND_UNA_ADVANCED is set or tcp_try_undo_recovery() if snd_una crosses high_seq. Signed-off-by: Yuchung Cheng <> Signed-off-by: Neal Cardwell <> Signed-off-by: David S. Miller <>
Diffstat (limited to 'net')
1 files changed, 6 insertions, 3 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index bc790ea9960f..9faf775a8c4a 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2698,11 +2698,16 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack)
struct tcp_sock *tp = tcp_sk(sk);
bool recovered = !before(tp->snd_una, tp->high_seq);
+ if ((flag & FLAG_SND_UNA_ADVANCED) &&
+ tcp_try_undo_loss(sk, false))
+ return;
if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
/* 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))
+ if ((flag & FLAG_ORIG_SACK_ACKED) &&
+ tcp_try_undo_loss(sk, true))
if (after(tp->snd_nxt, tp->high_seq) &&
@@ -2732,8 +2737,6 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack)
else if (flag & FLAG_SND_UNA_ADVANCED)
- if (tcp_try_undo_loss(sk, false))
- return;