tcp: properly update lost_cnt_hint during shifting

lost_skb_hint is used by tcp_mark_head_lost() to mark the first unhandled skb.
lost_cnt_hint is the number of packets or sacked packets before the lost_skb_hint;
When shifting a skb that is before the lost_skb_hint, if tcp_is_fack() is ture,
the skb has already been counted in the lost_cnt_hint; if tcp_is_fack() is false,
tcp_sacktag_one() will increase the lost_cnt_hint. So tcp_shifted_skb() does not
need to adjust the lost_cnt_hint by itself. When shifting a skb that is equal to
lost_skb_hint, the shifted packets will not be counted by tcp_mark_head_lost().
So tcp_shifted_skb() should adjust the lost_cnt_hint even tcp_is_fack(tp) is true.

Signed-off-by: Zheng Yan <zheng.z.yan@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 3 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 21fab3edb92c..d73aab3fbfc0 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1389,9 +1389,7 @@ static int tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
 
         BUG_ON(!pcount);
 
-        /* Tweak before seqno plays */
-        if (!tcp_is_fack(tp) && tcp_is_sack(tp) && tp->lost_skb_hint &&
-            !before(TCP_SKB_CB(tp->lost_skb_hint)->seq, TCP_SKB_CB(skb)->seq))
+        if (skb == tp->lost_skb_hint)
                 tp->lost_cnt_hint += pcount;
 
         TCP_SKB_CB(prev)->end_seq += shifted;