3.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Nandita Dukkipati <nanditad@xxxxxxxxxx>
[ Upstream commit 35f079ebbc860dcd1cca70890c9c8d59c1145525 ]
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@xxxxxxxxxx>
Acked-by: Yuchung Cheng <ycheng@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/ipv4/tcp_input.c | 23 +++++++++++++----------
1 file changed, 13 insertions(+), 10 deletions(-)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2885,8 +2885,8 @@ static void tcp_enter_recovery(struct so
* 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);
@@ -2952,7 +2952,8 @@ 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;
+ newly_acked_sacked = prior_packets - tp->packets_out +
+ tp->sacked_out - prior_sacked;
break;
case TCP_CA_Loss:
if (flag & FLAG_DATA_ACKED)
@@ -2974,7 +2975,8 @@ static void tcp_fastretrans_alert(struct
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);
@@ -3597,9 +3599,10 @@ static int tcp_ack(struct sock *sk, cons
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;
bool frto_cwnd = false;
/* If the ack is older than previous acks
@@ -3670,14 +3673,14 @@ static int tcp_ack(struct sock *sk, cons
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 (tp->frto_counter)
frto_cwnd = tcp_process_frto(sk, flag);
@@ -3692,7 +3695,7 @@ static int tcp_ack(struct sock *sk, cons
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) && !frto_cwnd)
tcp_cong_avoid(sk, ack, prior_in_flight);
@@ -3709,7 +3712,7 @@ 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.
@@ -3729,7 +3732,7 @@ 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);
--
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