mptcp: do not keep around the first subflow after disconnect

After the previous patch the first subflow is allocated as
needed at bind, connect, listen time. We don't need anymore
to keep alive the first subflow after a disconnect just to
be able to perform such syscall.

Overall, this change makes the passive and active sockets consistent:
even passive sockets will be allowed to complete life cycle after
disconnect.

Closes: #290
Signed-off-by: Paolo Abeni <[email protected]>
Reviewed-by: Matthieu Baerts <[email protected]>

net/mptcp/protocol.c

@@ -2344,11 +2344,9 @@ static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
 			      unsigned int flags)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
-	bool need_push, dispose_it;
+	bool need_push;
 
-	dispose_it = !msk->subflow || ssk != msk->subflow->sk;
-	if (dispose_it)
-		list_del(&subflow->node);
+	list_del(&subflow->node);
 
 	lock_sock_nested(ssk, SINGLE_DEPTH_NESTING);
 
@@ -2362,15 +2360,6 @@ static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
 	}
 
 	need_push = (flags & MPTCP_CF_PUSH) && __mptcp_retransmit_pending_data(sk);
-	if (!dispose_it) {
-		tcp_disconnect(ssk, 0);
-		msk->subflow->state = SS_UNCONNECTED;
-		mptcp_subflow_ctx_reset(subflow);
-		release_sock(ssk);
-
-		goto out;
-	}
-
 	sock_orphan(ssk);
 	subflow->disposable = 1;
 
@@ -2397,10 +2386,11 @@ static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
 
 	sock_put(ssk);
 
-	if (ssk == msk->first)
+	if (ssk == msk->first) {
 		msk->first = NULL;
+		mptcp_dispose_initial_subflow(msk);
+	}
 
-out:
 	if (ssk == msk->last_snd)
 		msk->last_snd = NULL;
 
@@ -3224,10 +3214,6 @@ static void mptcp_destroy(struct sock *sk)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
 
-	/* clears msk->subflow, allowing the following to close
-	 * even the initial subflow
-	 */
-	mptcp_dispose_initial_subflow(msk);
 	mptcp_destroy_common(msk, 0);
 	sk_sockets_allocated_dec(sk);
 }