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Message-Id: <1369185127-27255-1-git-send-email-nanditad@google.com>
Date: Tue, 21 May 2013 18:12:07 -0700
From: Nandita Dukkipati <nanditad@...gle.com>
To: "David S. Miller" <davem@...emloft.net>
Cc: netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
Neal Cardwell <ncardwell@...gle.com>,
Yuchung Cheng <ycheng@...gle.com>,
Nandita Dukkipati <nanditad@...gle.com>
Subject: [PATCH v2] 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@...gle.com>
---
Changelog since v1:
- Compute newly_acked_sacked using prior_packets.
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 d7d3694..8230cd6 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2679,8 +2679,8 @@ 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);
@@ -2740,7 +2740,8 @@ 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);
@@ -2754,7 +2755,8 @@ 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);
@@ -3265,9 +3267,10 @@ 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.
@@ -3338,14 +3341,14 @@ 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. */
@@ -3353,7 +3356,7 @@ 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);
@@ -3376,7 +3379,7 @@ 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, 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.
@@ -3399,7 +3402,7 @@ old_ack:
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);
--
1.8.2.1
--
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