tcp: fix tcp_shifted_skb() adjustment of lost_cnt_hint for FACK

This commit ensures that lost_cnt_hint is correctly updated in
tcp_shifted_skb() for FACK TCP senders. The lost_cnt_hint adjustment
in tcp_sacktag_one() only applies to non-FACK senders, so FACK senders
need their own adjustment.

This applies the spirit of 1e5289e121372a3494402b1b131b41bfe1cf9b7f -
except now that the sequence range passed into tcp_sacktag_one() is
correct we need only have a special case adjustment for FACK.

Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 0 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 8116d06e042c..53c8ce4046b2 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1403,6 +1403,10 @@ static int tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
 
         BUG_ON(!pcount);
 
+        /* Adjust hint for FACK. Non-FACK is handled in tcp_sacktag_one(). */
+        if (tcp_is_fack(tp) && (skb == tp->lost_skb_hint))
+                tp->lost_cnt_hint += pcount;
+
         TCP_SKB_CB(prev)->end_seq += shifted;
         TCP_SKB_CB(skb)->seq += shifted;