mptcp: introduce MPTCP snd_nxt

Track the next MPTCP sequence number used on xmit,
currently always equal to write_next.
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/mptcp/options.c

@@ -813,7 +813,7 @@ static void update_una(struct mptcp_sock *msk,
 		       struct mptcp_options_received *mp_opt)
 {
 	u64 new_snd_una, snd_una, old_snd_una = atomic64_read(&msk->snd_una);
-	u64 write_seq = READ_ONCE(msk->write_seq);
+	u64 snd_nxt = READ_ONCE(msk->snd_nxt);
 
 	/* avoid ack expansion on update conflict, to reduce the risk of
 	 * wrongly expanding to a future ack sequence number, which is way
@@ -822,7 +822,7 @@ static void update_una(struct mptcp_sock *msk,
 	new_snd_una = expand_ack(old_snd_una, mp_opt->data_ack, mp_opt->ack64);
 
 	/* ACK for data not even sent yet? Ignore. */
-	if (after64(new_snd_una, write_seq))
+	if (after64(new_snd_una, snd_nxt))
 		new_snd_una = old_snd_una;
 
 	while (after64(new_snd_una, old_snd_una)) {

net/mptcp/protocol.c

@@ -834,7 +834,7 @@ static void mptcp_clean_una(struct sock *sk)
 	 * plain TCP
 	 */
 	if (__mptcp_check_fallback(msk))
-		atomic64_set(&msk->snd_una, msk->write_seq);
+		atomic64_set(&msk->snd_una, msk->snd_nxt);
 	snd_una = atomic64_read(&msk->snd_una);
 
 	list_for_each_entry_safe(dfrag, dtmp, &msk->rtx_queue, list) {
@@ -1338,6 +1338,7 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 
 	release_sock(ssk);
 out:
+	msk->snd_nxt = msk->write_seq;
 	ssk_check_wmem(msk);
 	release_sock(sk);
 	return copied ? : ret;
@@ -1629,7 +1630,7 @@ static void mptcp_retransmit_handler(struct sock *sk)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
 
-	if (atomic64_read(&msk->snd_una) == READ_ONCE(msk->write_seq)) {
+	if (atomic64_read(&msk->snd_una) == READ_ONCE(msk->snd_nxt)) {
 		mptcp_stop_timer(sk);
 	} else {
 		set_bit(MPTCP_WORK_RTX, &msk->flags);
@@ -2100,6 +2101,7 @@ struct sock *mptcp_sk_clone(const struct sock *sk,
 	WRITE_ONCE(msk->fully_established, false);
 
 	msk->write_seq = subflow_req->idsn + 1;
+	msk->snd_nxt = msk->write_seq;
 	atomic64_set(&msk->snd_una, msk->write_seq);
 	if (mp_opt->mp_capable) {
 		msk->can_ack = true;
@@ -2409,6 +2411,7 @@ void mptcp_finish_connect(struct sock *ssk)
 	WRITE_ONCE(msk->remote_key, subflow->remote_key);
 	WRITE_ONCE(msk->local_key, subflow->local_key);
 	WRITE_ONCE(msk->write_seq, subflow->idsn + 1);
+	WRITE_ONCE(msk->snd_nxt, msk->write_seq);
 	WRITE_ONCE(msk->ack_seq, ack_seq);
 	WRITE_ONCE(msk->can_ack, 1);
 	atomic64_set(&msk->snd_una, msk->write_seq);

net/mptcp/protocol.h

@@ -92,6 +92,13 @@
 #define MPTCP_FALLBACK_DONE	4
 #define MPTCP_WORK_CLOSE_SUBFLOW 5
 
+static inline bool before64(__u64 seq1, __u64 seq2)
+{
+	return (__s64)(seq1 - seq2) < 0;
+}
+
+#define after64(seq2, seq1)	before64(seq1, seq2)
+
 struct mptcp_options_received {
 	u64	sndr_key;
 	u64	rcvr_key;
@@ -201,6 +208,7 @@ struct mptcp_sock {
 	u64		local_key;
 	u64		remote_key;
 	u64		write_seq;
+	u64		snd_nxt;
 	u64		ack_seq;
 	u64		rcv_data_fin_seq;
 	struct sock	*last_snd;
@@ -276,7 +284,7 @@ static inline struct mptcp_data_frag *mptcp_rtx_tail(const struct sock *sk)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
 
-	if (list_empty(&msk->rtx_queue))
+	if (!before64(msk->snd_nxt, atomic64_read(&msk->snd_una)))
 		return NULL;
 
 	return list_last_entry(&msk->rtx_queue, struct mptcp_data_frag, list);
@@ -528,13 +536,6 @@ static inline struct mptcp_ext *mptcp_get_ext(struct sk_buff *skb)
 	return (struct mptcp_ext *)skb_ext_find(skb, SKB_EXT_MPTCP);
 }
 
-static inline bool before64(__u64 seq1, __u64 seq2)
-{
-	return (__s64)(seq1 - seq2) < 0;
-}
-
-#define after64(seq2, seq1)	before64(seq1, seq2)
-
 void mptcp_diag_subflow_init(struct tcp_ulp_ops *ops);
 
 static inline bool __mptcp_check_fallback(const struct mptcp_sock *msk)