tcp: bug fix in proportional rate reduction.
This patch is a fix for a bug triggering newly_acked_sacked < 0 in tcp_ack(.). The bug is triggered by sacked_out decreasing relative to prior_sacked, but packets_out remaining the same as pior_packets. This is because the snapshot of prior_packets is taken after tcp_sacktag_write_queue() while prior_sacked is captured before tcp_sacktag_write_queue(). The problem is: tcp_sacktag_write_queue (tcp_match_skb_to_sack() -> tcp_fragment) adjusts the pcount for packets_out and sacked_out (MSS change or other reason). As a result, this delta in pcount is reflected in (prior_sacked - sacked_out) but not in (prior_packets - packets_out). This patch does the following: 1) initializes prior_packets at the start of tcp_ack() so as to capture the delta in packets_out created by tcp_fragment. 2) introduces a new "previous_packets_out" variable that snapshots packets_out right before tcp_clean_rtx_queue, so pkts_acked can be correctly computed as before. 3) Computes pkts_acked using previous_packets_out, and computes newly_acked_sacked using prior_packets. Signed-off-by: Nandita Dukkipati <nanditad@google.com> Acked-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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d02cea0f43
Коммит
35f079ebbc
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@ -2743,8 +2743,8 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack)
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* tcp_xmit_retransmit_queue().
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*/
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static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
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int prior_sacked, bool is_dupack,
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int flag)
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int prior_sacked, int prior_packets,
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bool is_dupack, int flag)
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{
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struct inet_connection_sock *icsk = inet_csk(sk);
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struct tcp_sock *tp = tcp_sk(sk);
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@ -2804,7 +2804,8 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
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tcp_add_reno_sack(sk);
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} else
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do_lost = tcp_try_undo_partial(sk, pkts_acked);
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newly_acked_sacked = pkts_acked + tp->sacked_out - prior_sacked;
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newly_acked_sacked = prior_packets - tp->packets_out +
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tp->sacked_out - prior_sacked;
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break;
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case TCP_CA_Loss:
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tcp_process_loss(sk, flag, is_dupack);
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@ -2818,7 +2819,8 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
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if (is_dupack)
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tcp_add_reno_sack(sk);
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}
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newly_acked_sacked = pkts_acked + tp->sacked_out - prior_sacked;
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newly_acked_sacked = prior_packets - tp->packets_out +
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tp->sacked_out - prior_sacked;
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if (icsk->icsk_ca_state <= TCP_CA_Disorder)
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tcp_try_undo_dsack(sk);
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@ -3330,9 +3332,10 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
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bool is_dupack = false;
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u32 prior_in_flight;
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u32 prior_fackets;
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int prior_packets;
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int prior_packets = tp->packets_out;
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int prior_sacked = tp->sacked_out;
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int pkts_acked = 0;
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int previous_packets_out = 0;
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/* If the ack is older than previous acks
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* then we can probably ignore it.
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@ -3403,14 +3406,14 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
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sk->sk_err_soft = 0;
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icsk->icsk_probes_out = 0;
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tp->rcv_tstamp = tcp_time_stamp;
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prior_packets = tp->packets_out;
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if (!prior_packets)
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goto no_queue;
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/* See if we can take anything off of the retransmit queue. */
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previous_packets_out = tp->packets_out;
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flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una);
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pkts_acked = prior_packets - tp->packets_out;
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pkts_acked = previous_packets_out - tp->packets_out;
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if (tcp_ack_is_dubious(sk, flag)) {
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/* Advance CWND, if state allows this. */
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@ -3418,7 +3421,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
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tcp_cong_avoid(sk, ack, prior_in_flight);
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is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
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tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
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is_dupack, flag);
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prior_packets, is_dupack, flag);
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} else {
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if (flag & FLAG_DATA_ACKED)
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tcp_cong_avoid(sk, ack, prior_in_flight);
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@ -3441,7 +3444,7 @@ no_queue:
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/* If data was DSACKed, see if we can undo a cwnd reduction. */
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if (flag & FLAG_DSACKING_ACK)
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tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
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is_dupack, flag);
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prior_packets, is_dupack, flag);
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/* If this ack opens up a zero window, clear backoff. It was
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* being used to time the probes, and is probably far higher than
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* it needs to be for normal retransmission.
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@ -3464,7 +3467,7 @@ old_ack:
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if (TCP_SKB_CB(skb)->sacked) {
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flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
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tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
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is_dupack, flag);
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prior_packets, is_dupack, flag);
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}
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SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
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