1 files changed, 9 insertions, 1 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a2364ebf8585..f9e4d7ad68b7 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1240,8 +1240,16 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
                 int fack_count;
                 int dup_sack = (found_dup_sack && (i == first_sack_index));
 
-                if (!tcp_is_sackblock_valid(tp, dup_sack, start_seq, end_seq))
+                if (!tcp_is_sackblock_valid(tp, dup_sack, start_seq, end_seq)) {
+                        if (dup_sack) {
+                                if (!tp->undo_marker)
+                                        NET_INC_STATS_BH(LINUX_MIB_TCPDSACKIGNOREDNOUNDO);
+                                else
+                                        NET_INC_STATS_BH(LINUX_MIB_TCPDSACKIGNOREDOLD);
+                        } else
+                                NET_INC_STATS_BH(LINUX_MIB_TCPSACKDISCARD);
                         continue;
+                }
 
                 skb = cached_skb;
                 fack_count = cached_fack_count;