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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 <>
Signed-off-by: David S. Miller <>
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1 parent 260fcbe commit 1e5289e121372a3494402b1b131b41bfe1cf9b7f Yan, Zheng committed with Oct 2, 2011
Showing with 1 addition and 3 deletions.
  1. +1 −3 net/ipv4/tcp_input.c
@@ -1389,9 +1389,7 @@ static int tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
- /* 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;

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