[PATCH] tcp: fix TSO cwnd caching bug

tcp_write_xmit caches the cwnd value indirectly in cwnd_quota.  When
tcp_transmit_skb reduces the cwnd because of tcp_enter_cwr, the cached
value becomes invalid.

This patch ensures that the cwnd value is always reread after each
tcp_transmit_skb call.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index e118b4b5b32690f1341ead275edc6aca8562301d..7d076f0db1003b7ba43250c6f80da756d5d84f80 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -972,19 +972,18 @@ static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle)
        if (unlikely(sk->sk_state == TCP_CLOSE))
                return 0;
 
-       skb = sk->sk_send_head;
-       if (unlikely(!skb))
-               return 0;
-
-       tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
-       cwnd_quota = tcp_cwnd_test(tp, skb);
-       if (unlikely(!cwnd_quota))
-               goto out;
-
        sent_pkts = 0;
-       while (likely(tcp_snd_wnd_test(tp, skb, mss_now))) {
+       while ((skb = sk->sk_send_head)) {
+               tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
                BUG_ON(!tso_segs);
 
+               cwnd_quota = tcp_cwnd_test(tp, skb);
+               if (!cwnd_quota)
+                       break;
+
+               if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
+                       break;
+
                if (tso_segs == 1) {
                        if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
                                                     (tcp_skb_is_last(sk, skb) ?
@@ -1026,27 +1025,12 @@ static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle)
 
                tcp_minshall_update(tp, mss_now, skb);
                sent_pkts++;
-
-               /* Do not optimize this to use tso_segs. If we chopped up
-                * the packet above, tso_segs will no longer be valid.
-                */
-               cwnd_quota -= tcp_skb_pcount(skb);
-
-               BUG_ON(cwnd_quota < 0);
-               if (!cwnd_quota)
-                       break;
-
-               skb = sk->sk_send_head;
-               if (!skb)
-                       break;
-               tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
        }
 
        if (likely(sent_pkts)) {
                tcp_cwnd_validate(sk, tp);
                return 0;
        }
-out:
        return !tp->packets_out && sk->sk_send_head;
 }