[TCP]: skb pcount with MTU discovery

The problem is that when doing MTU discovery, the too-large segments in
the write queue will be calculated as having a pcount of >1.  When
tcp_write_xmit() is trying to send, tcp_snd_test() fails the cwnd test
when pcount > cwnd.

The segments are eventually transmitted one at a time by keepalive, but
this can take a long time.

This patch checks if TSO is enabled when setting pcount.

Signed-off-by: John Heffner <jheffner@psc.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 11 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 13c14cb6dee4..a12df6979ffd 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -427,7 +427,7 @@ void tcp_push_one(struct sock *sk, unsigned cur_mss)
         struct tcp_sock *tp = tcp_sk(sk);
         struct sk_buff *skb = sk->sk_send_head;
 
-        if (tcp_snd_test(tp, skb, cur_mss, TCP_NAGLE_PUSH)) {
+        if (tcp_snd_test(sk, skb, cur_mss, TCP_NAGLE_PUSH)) {
                 /* Send it out now. */
                 TCP_SKB_CB(skb)->when = tcp_time_stamp;
                 tcp_tso_set_push(skb);
@@ -440,9 +440,12 @@ void tcp_push_one(struct sock *sk, unsigned cur_mss)
         }
 }
 
-void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_std)
+void tcp_set_skb_tso_segs(struct sock *sk, struct sk_buff *skb)
 {
-        if (skb->len <= mss_std) {
+        struct tcp_sock *tp = tcp_sk(sk);
+
+        if (skb->len <= tp->mss_cache_std ||
+            !(sk->sk_route_caps & NETIF_F_TSO)) {
                 /* Avoid the costly divide in the normal
                  * non-TSO case.
                  */
@@ -451,10 +454,10 @@ void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_std)
         } else {
                 unsigned int factor;
 
-                factor = skb->len + (mss_std - 1);
-                factor /= mss_std;
+                factor = skb->len + (tp->mss_cache_std - 1);
+                factor /= tp->mss_cache_std;
                 skb_shinfo(skb)->tso_segs = factor;
-                skb_shinfo(skb)->tso_size = mss_std;
+                skb_shinfo(skb)->tso_size = tp->mss_cache_std;
         }
 }
 
@@ -525,8 +528,8 @@ static int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len)
         }
 
         /* Fix up tso_factor for both original and new SKB.  */
-        tcp_set_skb_tso_segs(skb, tp->mss_cache_std);
-        tcp_set_skb_tso_segs(buff, tp->mss_cache_std);
+        tcp_set_skb_tso_segs(sk, skb);
+        tcp_set_skb_tso_segs(sk, buff);
 
         if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) {
                 tp->lost_out += tcp_skb_pcount(skb);
@@ -601,7 +604,7 @@ int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
          * factor and mss.
          */
         if (tcp_skb_pcount(skb) > 1)
-                tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb));
+                tcp_set_skb_tso_segs(sk, skb);
 
         return 0;
 }
@@ -752,7 +755,7 @@ int tcp_write_xmit(struct sock *sk, int nonagle)
                 mss_now = tcp_current_mss(sk, 1);
 
                 while ((skb = sk->sk_send_head) &&
-                       tcp_snd_test(tp, skb, mss_now,
+                       tcp_snd_test(sk, skb, mss_now,
                                     tcp_skb_is_last(sk, skb) ? nonagle :
                                                                TCP_NAGLE_PUSH)) {
                         if (skb->len > mss_now) {
@@ -1676,7 +1679,7 @@ int tcp_write_wakeup(struct sock *sk)
                                         tp->mss_cache = tp->mss_cache_std;
                                 }
                         } else if (!tcp_skb_pcount(skb))
-                                tcp_set_skb_tso_segs(skb, tp->mss_cache_std);
+                                tcp_set_skb_tso_segs(sk, skb);
 
                         TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
                         TCP_SKB_CB(skb)->when = tcp_time_stamp;