[TCP]: Fix packet counting during retransmission.

We run into a potential problem if we are doing
TSO and we reduce the congestion window.  We might
create a case where the TSO packet is what we need
to resend but the congestion window is not large
enough to allow it through.

The fix is very simple, since tcp_retransmit_skb()
is going to chop the size of the packet down to size
of the normal non-TSO MSS, we can pretend at the top
level that each SKB is composed of only one real MSS
worth of data.

Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index a77c17ba48df72337da10b42973b85b5a496c52a..535e438a32762520292b01777a8aaa477f9d654f 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1065,12 +1065,15 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
        if (packet_cnt) {
                sk_stream_for_retrans_queue(skb, sk) {
                        __u8 sacked = TCP_SKB_CB(skb)->sacked;
-                       int pkts = TCP_SKB_CB(skb)->tso_factor;
 
-                       BUG_ON(!pkts);
-
-                       if ((tcp_packets_in_flight(tp) + (pkts-1)) >=
-                           tp->snd_cwnd)
+                       /* Assume this retransmit will generate
+                        * only one packet for congestion window
+                        * calculation purposes.  This works because
+                        * tcp_retransmit_skb() will chop up the
+                        * packet to be MSS sized and all the
+                        * packet counting works out.
+                        */
+                       if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
                                return;
 
                        if (sacked&TCPCB_LOST) {
@@ -1117,15 +1120,16 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
        packet_cnt = 0;
 
        sk_stream_for_retrans_queue(skb, sk) {
-               int pkts = TCP_SKB_CB(skb)->tso_factor;
-
-               BUG_ON(!pkts);
-
-               packet_cnt += pkts;
-               if (packet_cnt > tcp_get_pcount(&tp->fackets_out))
+               /* Similar to the retransmit loop above we
+                * can pretend that the retransmitted SKB
+                * we send out here will be composed of one
+                * real MSS sized packet because tcp_retransmit_skb()
+                * will fragment it if necessary.
+                */
+               if (++packet_cnt > tcp_get_pcount(&tp->fackets_out))
                        break;
 
-               if ((tcp_packets_in_flight(tp) + (pkts-1)) >= tp->snd_cwnd)
+               if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
                        break;
 
                if (TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS)