netdev - [PATCH net-2.6.25] [TCP]: Two fixes to new sacktag code

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Date:	Wed, 28 Nov 2007 16:19:36 +0200 (EET)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	Herbert Xu <herbert@...dor.apana.org.au>
cc:	Netdev <netdev@...r.kernel.org>,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	David Miller <davem@...emloft.net>
Subject: [PATCH net-2.6.25] [TCP]: Two fixes to new sacktag code

1) Skip condition used to be wrong way around which made SACK
processing very broken, missed many blocks because of that.

2) Use highest_sack advancement only if some skbs are already
sacked because otherwise tcp_write_queue_next may move things
too far (occurs mainly with GSO). The other similar advancement
is not problem because highest_sack was previosly put to point
a sacked skb.

These problems were located because of problem report from Matt
Mathis <mathis@....edu>.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
---

...I verified result from time-seq graphs now, they are right in my simple 
test case.

In case there's a rebase of net-2.6.25, it might be good to just combine 
173b7ae366ac3f69b3030a6ab308cf3fa3ab751a ([TCP]: Correct DSACK check 
placing) and this one to the a1598ba3339ebeeb0a959141a122cbe69956e713 
([TCP]: Rewrite SACK block processing & sack_recv_cache use), they just 
fix its bugs.

 net/ipv4/tcp_input.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 0cee3dc..cadde8b 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1384,7 +1384,7 @@ static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
 		if (skb == tcp_send_head(sk))
 			break;

-		if (before(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
+		if (!before(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
 			break;
 	}
 	return skb;
@@ -1575,7 +1575,7 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
 			continue;
 		}

-		if (!before(start_seq, tcp_highest_sack_seq(tp))) {
+		if (tp->sacked_out && after(start_seq, tcp_highest_sack_seq(tp))) {
 			skb = tcp_write_queue_next(sk, tp->highest_sack);
 			fack_count = tp->fackets_out;
 		}
-- 
1.5.0.6