[TCP]: fix D-SACK cwnd handling

In the current net-2.6 kernel, handling FLAG_DSACKING_ACK is broken.
The flag is cleared to 1 just after FLAG_DSACKING_ACK is set.

        if (found_dup_sack)
                flag |= FLAG_DSACKING_ACK;
	:
	flag = 1;

To fix it, this patch introduces a part of the tcp_sacktag_state patch:
	http://marc.info/?l=linux-netdev&m=119210560431519&w=2

Signed-off-by: Ryousei Takano <takano-ryousei@aist.go.jp>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 7 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 457697a043d..69d8c38ccd3 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1248,6 +1248,7 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
         int cached_fack_count;
         int i;
         int first_sack_index;
+        int force_one_sack;
 
         if (!tp->sacked_out) {
                 if (WARN_ON(tp->fackets_out))
@@ -1272,18 +1273,18 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
          * if the only SACK change is the increase of the end_seq of
          * the first block then only apply that SACK block
          * and use retrans queue hinting otherwise slowpath */
-        flag = 1;
+        force_one_sack = 1;
         for (i = 0; i < num_sacks; i++) {
                 __be32 start_seq = sp[i].start_seq;
                 __be32 end_seq = sp[i].end_seq;
 
                 if (i == 0) {
                         if (tp->recv_sack_cache[i].start_seq != start_seq)
-                                flag = 0;
+                                force_one_sack = 0;
                 } else {
                         if ((tp->recv_sack_cache[i].start_seq != start_seq) ||
                             (tp->recv_sack_cache[i].end_seq != end_seq))
-                                flag = 0;
+                                force_one_sack = 0;
                 }
                 tp->recv_sack_cache[i].start_seq = start_seq;
                 tp->recv_sack_cache[i].end_seq = end_seq;
@@ -1295,7 +1296,7 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
         }
 
         first_sack_index = 0;
-        if (flag)
+        if (force_one_sack)
                 num_sacks = 1;
         else {
                 int j;
@@ -1321,9 +1322,6 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
                 }
         }
 
-        /* clear flag as used for different purpose in following code */
-        flag = 0;
-
         /* Use SACK fastpath hint if valid */
         cached_skb = tp->fastpath_skb_hint;
         cached_fack_count = tp->fastpath_cnt_hint;