tcp: add two drop reasons for tcp_ack()

Add TCP_TOO_OLD_ACK and TCP_ACK_UNSENT_DATA drop
reasons so that tcp_rcv_established() can report
them.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -390,6 +390,8 @@ enum skb_drop_reason {
 	SKB_DROP_REASON_TCP_CLOSE,	/* TCP socket in CLOSE state */
 	SKB_DROP_REASON_TCP_FASTOPEN,	/* dropped by FASTOPEN request socket */
 	SKB_DROP_REASON_TCP_OLD_ACK,	/* TCP ACK is old, but in window */
+	SKB_DROP_REASON_TCP_TOO_OLD_ACK, /* TCP ACK is too old */
+	SKB_DROP_REASON_TCP_ACK_UNSENT_DATA, /* TCP ACK for data we haven't sent yet */
 	SKB_DROP_REASON_IP_OUTNOROUTES,	/* route lookup failed */
 	SKB_DROP_REASON_BPF_CGROUP_EGRESS,	/* dropped by
 						 * BPF_PROG_TYPE_CGROUP_SKB

include/trace/events/skb.h

@@ -45,6 +45,9 @@
 	EM(SKB_DROP_REASON_TCP_CLOSE, TCP_CLOSE)		\
 	EM(SKB_DROP_REASON_TCP_FASTOPEN, TCP_FASTOPEN)		\
 	EM(SKB_DROP_REASON_TCP_OLD_ACK, TCP_OLD_ACK)		\
+	EM(SKB_DROP_REASON_TCP_TOO_OLD_ACK, TCP_TOO_OLD_ACK)	\
+	EM(SKB_DROP_REASON_TCP_ACK_UNSENT_DATA,			\
+	   TCP_ACK_UNSENT_DATA)					\
 	EM(SKB_DROP_REASON_IP_OUTNOROUTES, IP_OUTNOROUTES)	\
 	EM(SKB_DROP_REASON_BPF_CGROUP_EGRESS,			\
 	   BPF_CGROUP_EGRESS)					\

net/ipv4/tcp_input.c

@@ -3766,7 +3766,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 		if (before(ack, prior_snd_una - tp->max_window)) {
 			if (!(flag & FLAG_NO_CHALLENGE_ACK))
 				tcp_send_challenge_ack(sk);
-			return -1;
+			return -SKB_DROP_REASON_TCP_TOO_OLD_ACK;
 		}
 		goto old_ack;
 	}
@@ -3775,7 +3775,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 	 * this segment (RFC793 Section 3.9).
 	 */
 	if (after(ack, tp->snd_nxt))
-		return -1;
+		return -SKB_DROP_REASON_TCP_ACK_UNSENT_DATA;
 
 	if (after(ack, prior_snd_una)) {
 		flag |= FLAG_SND_UNA_ADVANCED;
@@ -5962,7 +5962,8 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb)
 		return;
 
 step5:
-	if (tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0)
+	reason = tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT);
+	if (reason < 0)
 		goto discard;
 
 	tcp_rcv_rtt_measure_ts(sk, skb);