[PATCH net-next 6/9] net: tcp: store drop reasons in tcp_conn_request()

[menglong8.dong@gmail.com]

From: Menglong Dong <imagedong@tencent.com>

Store the skb drop reasons to tcp_skb_cb for tcp_conn_request(). When
the skb should be freed normally, 'TCP_SKB_CB(skb)->drop_reason' will be
set to SKB_NOT_DROPPED_YET, which means consume_skb() will be called for
the skb.

Now, we can replace the consume_skb() with try_kfree_skb() in
tcp_rcv_state_process() if the skb needs to be dropped.

The new drop reasons 'LISTENOVERFLOWS' and 'TCP_REQQFULLDROP' are added,
which are used for 'accept queue' and 'request queue' full.

Signed-off-by: Menglong Dong <imagedong@tencent.com>
--
---
 include/net/dropreason.h | 12 ++++++++++++
 net/ipv4/tcp_input.c     | 11 +++++++++--
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/include/net/dropreason.h b/include/net/dropreason.h
index cbfd88493ef2..633a05c95026 100644
--- a/include/net/dropreason.h
+++ b/include/net/dropreason.h
@@ -70,6 +70,8 @@
 	FN(PKT_TOO_BIG)			\
 	FN(TCP_PAWSACTIVEREJECTED)	\
 	FN(TIMEWAIT)			\
+	FN(LISTENOVERFLOWS)		\
+	FN(TCP_REQQFULLDROP)		\
 	FNe(MAX)
 
 /**
@@ -312,6 +314,16 @@ enum skb_drop_reason {
 	 * 'SYN' packet
 	 */
 	SKB_DROP_REASON_TIMEWAIT,
+	/**
+	 * @SKB_DROP_REASON_LISTENOVERFLOWS: accept queue of the listen
+	 * socket is full, corresponding to LINUX_MIB_LISTENOVERFLOWS
+	 */
+	SKB_DROP_REASON_LISTENOVERFLOWS,
+	/**
+	 * @SKB_DROP_REASON_TCP_REQQFULLDROP: request queue of the listen
+	 * socket is full, corresponding to LINUX_MIB_TCPREQQFULLDROP
+	 */
+	SKB_DROP_REASON_TCP_REQQFULLDROP,
 	/**
 	 * @SKB_DROP_REASON_MAX: the maximum of drop reason, which shouldn't be
 	 * used as a real 'reason'
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index c0e5c4a29a4e..ad088e228b1e 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6482,7 +6482,9 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 
 			if (!acceptable)
 				return 1;
-			consume_skb(skb);
+
+			reason = TCP_SKB_CB(skb)->drop_reason;
+			try_kfree_skb(skb, reason);
 			return 0;
 		}
 		SKB_DR_SET(reason, TCP_FLAGS);
@@ -6928,12 +6930,15 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 	 */
 	if ((syncookies == 2 || inet_csk_reqsk_queue_is_full(sk)) && !isn) {
 		want_cookie = tcp_syn_flood_action(sk, rsk_ops->slab_name);
-		if (!want_cookie)
+		if (!want_cookie) {
+			TCP_SKB_DR(skb, TCP_REQQFULLDROP);
 			goto drop;
+		}
 	}
 
 	if (sk_acceptq_is_full(sk)) {
 		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
+		TCP_SKB_DR(skb, LISTENOVERFLOWS);
 		goto drop;
 	}
 
@@ -6991,6 +6996,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 			 */
 			pr_drop_req(req, ntohs(tcp_hdr(skb)->source),
 				    rsk_ops->family);
+			TCP_SKB_DR(skb, TCP_REQQFULLDROP);
 			goto drop_and_release;
 		}
 
@@ -7005,6 +7011,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 			inet_rsk(req)->ecn_ok = 0;
 	}
 
+	TCP_SKB_CB(skb)->drop_reason = SKB_NOT_DROPPED_YET;
 	tcp_rsk(req)->snt_isn = isn;
 	tcp_rsk(req)->txhash = net_tx_rndhash();
 	tcp_rsk(req)->syn_tos = TCP_SKB_CB(skb)->ip_dsfield;
-- 
2.37.2