subflow: place further subflows on new 'join_list'

When the pm workqueue establishes a new subflow, we never place this
socket on any list, ie. if such a request would time out/never
complete we can't clean it up later on -- it never made it to the
conn_list of established subflows.

Place them on a new join_list. When the connection completes, the
subflow is moved to the conn_list.

If it never completes, the socket gets closed at mptcp_shutdown time.

Not done yet:
1. extend mptcp worker to collect timed-out entries
2. prevent arbitrary growth of pending ssks.

Signed-off-by: Florian Westphal <fw@strlen.de>

net/mptcp/protocol.c

@@ -137,6 +137,16 @@ static struct socket *__mptcp_socket_create(struct mptcp_sock *msk, int state)
 	return ssock;
 }
 
+static void __mptcp_flush_join_list(struct mptcp_sock *msk)
+{
+	if (likely(list_empty(&msk->join_list)))
+		return;
+
+	spin_lock_bh(&msk->join_list_lock);
+	list_splice_tail(&msk->join_list, &msk->conn_list);
+	spin_unlock_bh(&msk->join_list_lock);
+}
+
 static void mptcp_set_timeout(const struct sock *sk, const struct sock *ssk)
 {
 	long tout = ssk && inet_csk(ssk)->icsk_pending ?
@@ -556,6 +566,7 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 
 	mptcp_clean_una(sk);
 
+	__mptcp_flush_join_list(msk);
 	ssk = mptcp_subflow_get_send(msk);
 	while (!sk_stream_memory_free(sk) || !ssk) {
 		ret = sk_stream_wait_memory(sk, &timeo);
@@ -694,6 +705,7 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 
 	len = min_t(size_t, len, INT_MAX);
 	target = sock_rcvlowat(sk, flags & MSG_WAITALL, len);
+	__mptcp_flush_join_list(msk);
 
 	while (!done) {
 		u32 map_remaining;
@@ -945,6 +957,7 @@ static void mptcp_worker(struct work_struct *work)
 	if (!dfrag)
 		goto unlock;
 
+	__mptcp_flush_join_list(msk);
 	ssk = mptcp_subflow_get_retrans(msk);
 	if (!ssk)
 		goto reset_unlock;
@@ -990,7 +1003,10 @@ static int __mptcp_init_sock(struct sock *sk)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
 
+	spin_lock_init(&msk->join_list_lock);
+
 	INIT_LIST_HEAD(&msk->conn_list);
+	INIT_LIST_HEAD(&msk->join_list);
 	INIT_LIST_HEAD(&msk->rtx_queue);
 
 	__set_bit(MPTCP_SEND_SPACE, &msk->flags);
@@ -1076,6 +1092,8 @@ static void __mptcp_close(struct sock *sk, long timeout)
 	mptcp_token_destroy(msk->token);
 	inet_sk_state_store(sk, TCP_CLOSE);
 
+	__mptcp_flush_join_list(msk);
+
 	list_for_each_entry_safe(subflow, tmp, &msk->conn_list, node) {
 		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
 
@@ -1388,6 +1406,13 @@ bool mptcp_finish_join(struct sock *sk)
 	if (parent_sock) {
 		if (!sk->sk_socket)
 			mptcp_sock_graft(sk, parent_sock);
+
+		/* active connections are already on conn_list */
+		if (list_empty(&subflow->node)) {
+			spin_lock(&msk->join_list_lock);
+			list_add_tail(&subflow->node, &msk->join_list);
+			spin_unlock(&msk->join_list_lock);
+		}
 	}
 	return true;
 }

net/mptcp/protocol.h

@@ -139,9 +139,11 @@ struct mptcp_sock {
 	u32		token;
 	unsigned long	flags;
 	bool		can_ack;
+	spinlock_t	join_list_lock;
 	struct work_struct rtx_work;
 	struct list_head conn_list;
 	struct list_head rtx_queue;
+	struct list_head join_list;
 	struct skb_ext	*cached_ext;	/* for the next sendmsg */
 	struct socket	*subflow; /* outgoing connect/listener/!mp_capable */
 	struct sock	*first;