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Subject[ 025/218] tcp: fix cwnd reduction for non-sack recovery
Date
3.4-stable review patch.  If anyone has any objections, please let me know.

------------------


From: Yuchung Cheng <ycheng@google.com>

[ Upstream commit 7c4a56fec379ac0d7754e0d4da6a7361f1a4fe64 ]

The cwnd reduction in fast recovery is based on the number of packets
newly delivered per ACK. For non-sack connections every DUPACK
signifies a packet has been delivered, but the sender mistakenly
skips counting them for cwnd reduction.

The fix is to compute newly_acked_sacked after DUPACKs are accounted
in sacked_out for non-sack connections.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Nandita Dukkipati <nanditad@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
net/ipv4/tcp_input.c | 15 +++++++--------
1 file changed, 7 insertions(+), 8 deletions(-)

--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3037,13 +3037,14 @@ static void tcp_update_cwnd_in_recovery(
* tcp_xmit_retransmit_queue().
*/
static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
- int newly_acked_sacked, bool is_dupack,
+ int prior_sacked, bool is_dupack,
int flag)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
int do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
(tcp_fackets_out(tp) > tp->reordering));
+ int newly_acked_sacked = 0;
int fast_rexmit = 0, mib_idx;

if (WARN_ON(!tp->packets_out && tp->sacked_out))
@@ -3103,6 +3104,7 @@ static void tcp_fastretrans_alert(struct
tcp_add_reno_sack(sk);
} else
do_lost = tcp_try_undo_partial(sk, pkts_acked);
+ newly_acked_sacked = pkts_acked + tp->sacked_out - prior_sacked;
break;
case TCP_CA_Loss:
if (flag & FLAG_DATA_ACKED)
@@ -3124,6 +3126,7 @@ static void tcp_fastretrans_alert(struct
if (is_dupack)
tcp_add_reno_sack(sk);
}
+ newly_acked_sacked = pkts_acked + tp->sacked_out - prior_sacked;

if (icsk->icsk_ca_state <= TCP_CA_Disorder)
tcp_try_undo_dsack(sk);
@@ -3695,7 +3698,6 @@ static int tcp_ack(struct sock *sk, cons
int prior_packets;
int prior_sacked = tp->sacked_out;
int pkts_acked = 0;
- int newly_acked_sacked = 0;
int frto_cwnd = 0;

/* If the ack is older than previous acks
@@ -3768,8 +3770,6 @@ static int tcp_ack(struct sock *sk, cons
flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una);

pkts_acked = prior_packets - tp->packets_out;
- newly_acked_sacked = (prior_packets - prior_sacked) -
- (tp->packets_out - tp->sacked_out);

if (tp->frto_counter)
frto_cwnd = tcp_process_frto(sk, flag);
@@ -3783,7 +3783,7 @@ static int tcp_ack(struct sock *sk, cons
tcp_may_raise_cwnd(sk, flag))
tcp_cong_avoid(sk, ack, prior_in_flight);
is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
- tcp_fastretrans_alert(sk, pkts_acked, newly_acked_sacked,
+ tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
is_dupack, flag);
} else {
if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
@@ -3798,7 +3798,7 @@ static int tcp_ack(struct sock *sk, cons
no_queue:
/* If data was DSACKed, see if we can undo a cwnd reduction. */
if (flag & FLAG_DSACKING_ACK)
- tcp_fastretrans_alert(sk, pkts_acked, newly_acked_sacked,
+ tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
is_dupack, flag);
/* If this ack opens up a zero window, clear backoff. It was
* being used to time the probes, and is probably far higher than
@@ -3818,8 +3818,7 @@ old_ack:
*/
if (TCP_SKB_CB(skb)->sacked) {
flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
- newly_acked_sacked = tp->sacked_out - prior_sacked;
- tcp_fastretrans_alert(sk, pkts_acked, newly_acked_sacked,
+ tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
is_dupack, flag);
}




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