From 35f079ebbc860dcd1cca70890c9c8d59c1145525 Mon Sep 17 00:00:00 2001 From: Nandita Dukkipati Date: Tue, 21 May 2013 15:12:07 +0000 Subject: [PATCH] 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 Acked-by: Yuchung Cheng Signed-off-by: David S. Miller --- net/ipv4/tcp_input.c | 23 +++++++++++++---------- 1 file changed, 13 insertions(+), 10 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 08bbe6096528..9c6225780bd5 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2743,8 +2743,8 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack) * tcp_xmit_retransmit_queue(). */ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked, - int prior_sacked, bool is_dupack, - int flag) + int prior_sacked, int prior_packets, + bool is_dupack, int flag) { struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); @@ -2804,7 +2804,8 @@ 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; + newly_acked_sacked = prior_packets - tp->packets_out + + tp->sacked_out - prior_sacked; break; case TCP_CA_Loss: tcp_process_loss(sk, flag, is_dupack); @@ -2818,7 +2819,8 @@ 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; + newly_acked_sacked = prior_packets - tp->packets_out + + tp->sacked_out - prior_sacked; if (icsk->icsk_ca_state <= TCP_CA_Disorder) tcp_try_undo_dsack(sk); @@ -3330,9 +3332,10 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) bool is_dupack = false; u32 prior_in_flight; u32 prior_fackets; - int prior_packets; + int prior_packets = tp->packets_out; int prior_sacked = tp->sacked_out; int pkts_acked = 0; + int previous_packets_out = 0; /* If the ack is older than previous acks * then we can probably ignore it. @@ -3403,14 +3406,14 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) sk->sk_err_soft = 0; icsk->icsk_probes_out = 0; tp->rcv_tstamp = tcp_time_stamp; - prior_packets = tp->packets_out; if (!prior_packets) goto no_queue; /* See if we can take anything off of the retransmit queue. */ + previous_packets_out = tp->packets_out; flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una); - pkts_acked = prior_packets - tp->packets_out; + pkts_acked = previous_packets_out - tp->packets_out; if (tcp_ack_is_dubious(sk, flag)) { /* Advance CWND, if state allows this. */ @@ -3418,7 +3421,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int 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, prior_sacked, - is_dupack, flag); + prior_packets, is_dupack, flag); } else { if (flag & FLAG_DATA_ACKED) tcp_cong_avoid(sk, ack, prior_in_flight); @@ -3441,7 +3444,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) /* If data was DSACKed, see if we can undo a cwnd reduction. */ if (flag & FLAG_DSACKING_ACK) tcp_fastretrans_alert(sk, pkts_acked, prior_sacked, - is_dupack, flag); + prior_packets, 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 * it needs to be for normal retransmission. @@ -3464,7 +3467,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) if (TCP_SKB_CB(skb)->sacked) { flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una); tcp_fastretrans_alert(sk, pkts_acked, prior_sacked, - is_dupack, flag); + prior_packets, is_dupack, flag); } SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt); -- GitLab