net/tcp_fastopen: Add snmp counter for blackhole detection

This counter records the number of times the firewall blackhole issue is
detected and active TFO is disabled.

Signed-off-by: Wei Wang <weiwan@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/tcp.h

@@ -1507,7 +1507,7 @@ struct tcp_fastopen_context {
 };
 
 extern unsigned int sysctl_tcp_fastopen_blackhole_timeout;
-void tcp_fastopen_active_disable(void);
+void tcp_fastopen_active_disable(struct sock *sk);
 bool tcp_fastopen_active_should_disable(struct sock *sk);
 void tcp_fastopen_active_disable_ofo_check(struct sock *sk);
 void tcp_fastopen_active_timeout_reset(void);

include/uapi/linux/snmp.h

@@ -259,6 +259,7 @@ enum
 	LINUX_MIB_TCPFASTOPENPASSIVEFAIL,	/* TCPFastOpenPassiveFail */
 	LINUX_MIB_TCPFASTOPENLISTENOVERFLOW,	/* TCPFastOpenListenOverflow */
 	LINUX_MIB_TCPFASTOPENCOOKIEREQD,	/* TCPFastOpenCookieReqd */
+	LINUX_MIB_TCPFASTOPENBLACKHOLE,		/* TCPFastOpenBlackholeDetect */
 	LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES, /* TCPSpuriousRtxHostQueues */
 	LINUX_MIB_BUSYPOLLRXPACKETS,		/* BusyPollRxPackets */
 	LINUX_MIB_TCPAUTOCORKING,		/* TCPAutoCorking */

net/ipv4/proc.c

@@ -281,6 +281,7 @@ static const struct snmp_mib snmp4_net_list[] = {
 	SNMP_MIB_ITEM("TCPFastOpenPassiveFail", LINUX_MIB_TCPFASTOPENPASSIVEFAIL),
 	SNMP_MIB_ITEM("TCPFastOpenListenOverflow", LINUX_MIB_TCPFASTOPENLISTENOVERFLOW),
 	SNMP_MIB_ITEM("TCPFastOpenCookieReqd", LINUX_MIB_TCPFASTOPENCOOKIEREQD),
+	SNMP_MIB_ITEM("TCPFastOpenBlackhole", LINUX_MIB_TCPFASTOPENBLACKHOLE),
 	SNMP_MIB_ITEM("TCPSpuriousRtxHostQueues", LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES),
 	SNMP_MIB_ITEM("BusyPollRxPackets", LINUX_MIB_BUSYPOLLRXPACKETS),
 	SNMP_MIB_ITEM("TCPAutoCorking", LINUX_MIB_TCPAUTOCORKING),

net/ipv4/tcp_fastopen.c

@@ -410,10 +410,11 @@ static unsigned long tfo_active_disable_stamp __read_mostly;
 /* Disable active TFO and record current jiffies and
  * tfo_active_disable_times
  */
-void tcp_fastopen_active_disable(void)
+void tcp_fastopen_active_disable(struct sock *sk)
 {
 	atomic_inc(&tfo_active_disable_times);
 	tfo_active_disable_stamp = jiffies;
+	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENBLACKHOLE);
 }
 
 /* Reset tfo_active_disable_times to 0 */
@@ -469,7 +470,7 @@ void tcp_fastopen_active_disable_ofo_check(struct sock *sk)
 		if (p && !rb_next(p)) {
 			skb = rb_entry(p, struct sk_buff, rbnode);
 			if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) {
-				tcp_fastopen_active_disable();
+				tcp_fastopen_active_disable(sk);
 				return;
 			}
 		}

net/ipv4/tcp_input.c

@@ -5307,7 +5307,7 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
 			 */
 			if (tp->syn_fastopen && !tp->data_segs_in &&
 			    sk->sk_state == TCP_ESTABLISHED)
-				tcp_fastopen_active_disable();
+				tcp_fastopen_active_disable(sk);
 			tcp_send_challenge_ack(sk, skb);
 		}
 		goto discard;
@@ -6061,7 +6061,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 		    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
 			/* Receive out of order FIN after close() */
 			if (tp->syn_fastopen && th->fin)
-				tcp_fastopen_active_disable();
+				tcp_fastopen_active_disable(sk);
 			tcp_done(sk);
 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
 			return 1;