[143/262] tcp: properly update lost_cnt_hint during shifting

[Greg KH]

3.0-stable review patch.  If anyone has any objections, please let me know.

------------------


From: "Yan, Zheng" <zheng.z.yan@xxxxxxxxx>

[ Upstream commit 1e5289e121372a3494402b1b131b41bfe1cf9b7f ]

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@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
---
 net/ipv4/tcp_input.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1380,9 +1380,7 @@ static int tcp_shifted_skb(struct sock *
 
 	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;


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