[PATCH v2] tcp: properly update lost_cnt_hint during shifting

["Yan, Zheng" <zheng.z.yan@intel.com>]

lost_skb_hint is used by tcp_mark_head_lost() to mark the first unhandled skb.
lost_cnt_hint is the number of sacked packets before the lost_skb_hint. When
shifting a skb that is before the lost_skb_hint, tcp_shifted_skb() doesn't need
to adjust lost_cnt_hint by itself because it calls tcp_sacktag_one() which will
do the job right.

Signed-off-by: Zheng Yan <zheng.z.yan@intel.com>
Acked-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
---
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 21fab3e..ae5a934 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 (!tcp_is_fack(tp) && tcp_is_sack(tp) && tp->lost_skb_hint == skb)
 		tp->lost_cnt_hint += pcount;
 
 	TCP_SKB_CB(prev)->end_seq += shifted;