tcp: add LINUX_MIB_TCPRETRANSFAIL counter

It might be useful to get a counter of failed tcp_retransmit_skb()
calls.

Reported-by: Satoru Moriya <satoru.moriya@hds.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 4 insertions, 1 deletions

diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 6afc807ee2ad..02d61079f08b 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -256,6 +256,7 @@ static const struct snmp_mib snmp4_net_list[] = {
         SNMP_MIB_ITEM("TCPTimeWaitOverflow", LINUX_MIB_TCPTIMEWAITOVERFLOW),
         SNMP_MIB_ITEM("TCPReqQFullDoCookies", LINUX_MIB_TCPREQQFULLDOCOOKIES),
         SNMP_MIB_ITEM("TCPReqQFullDrop", LINUX_MIB_TCPREQQFULLDROP),
+        SNMP_MIB_ITEM("TCPRetransFail", LINUX_MIB_TCPRETRANSFAIL),
         SNMP_MIB_SENTINEL
 };
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 8c8de2780c7a..561550ab3c30 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2308,8 +2308,10 @@ begin_fwd:
                 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
                         continue;
 
-                if (tcp_retransmit_skb(sk, skb))
+                if (tcp_retransmit_skb(sk, skb)) {
+                        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
                         return;
+                }
                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
 
                 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Recovery)