Commit 7c4a56fe authored by Yuchung Cheng's avatar Yuchung Cheng Committed by David S. Miller
Browse files

tcp: fix cwnd reduction for non-sack recovery 



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: default avatarYuchung Cheng <ycheng@google.com>
Acked-by: default avatarNandita Dukkipati <nanditad@google.com>
Acked-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 20e1db19

net/ipv4/tcp_input.c

+7 −8
Original line number Diff line number Diff line
@@ -2926,13 +2926,14 @@ static void tcp_enter_recovery(struct sock *sk, bool ece_ack) 
 * 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;



	if (WARN_ON(!tp->packets_out && tp->sacked_out))
@@ -2992,6 +2993,7 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked, 
				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)
@@ -3013,6 +3015,7 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked, 
			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);
@@ -3590,7 +3593,6 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) 
	int prior_packets;

	int prior_sacked = tp->sacked_out;

	int pkts_acked = 0;

	int newly_acked_sacked = 0;

	bool frto_cwnd = false;



	/* If the ack is older than previous acks
@@ -3666,8 +3668,6 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) 
	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);
@@ -3681,7 +3681,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) 
		    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)
@@ -3698,7 +3698,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) 
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
@@ -3718,8 +3718,7 @@ 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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