mptcp: cleanup accept and poll

After the previous patch,  msk->subflow will never be deleted during
the whole msk lifetime. We don't need anymore to acquire references to
it in mptcp_stream_accept() and we can use the listener subflow accept
queue to simplify mptcp_poll() for listener socket.

Overall this removes a lock pair and 4 more atomic operations per
accept().

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mptcp/protocol.c

@@ -3493,17 +3493,9 @@ static int mptcp_stream_accept(struct socket *sock, struct socket *newsock,
 
 	pr_debug("msk=%p", msk);
 
-	lock_sock(sock->sk);
-	if (sock->sk->sk_state != TCP_LISTEN)
-		goto unlock_fail;
-
 	ssock = __mptcp_nmpc_socket(msk);
 	if (!ssock)
-		goto unlock_fail;
-
-	clear_bit(MPTCP_DATA_READY, &msk->flags);
-	sock_hold(ssock->sk);
-	release_sock(sock->sk);
+		return -EINVAL;
 
 	err = ssock->ops->accept(sock, newsock, flags, kern);
 	if (err == 0 && !mptcp_is_tcpsk(newsock->sk)) {
@@ -3543,14 +3535,7 @@ static int mptcp_stream_accept(struct socket *sock, struct socket *newsock,
 		release_sock(newsk);
 	}
 
-	if (inet_csk_listen_poll(ssock->sk))
-		set_bit(MPTCP_DATA_READY, &msk->flags);
-	sock_put(ssock->sk);
 	return err;
-
-unlock_fail:
-	release_sock(sock->sk);
-	return -EINVAL;
 }
 
 static __poll_t mptcp_check_readable(struct mptcp_sock *msk)
@@ -3596,8 +3581,12 @@ static __poll_t mptcp_poll(struct file *file, struct socket *sock,
 
 	state = inet_sk_state_load(sk);
 	pr_debug("msk=%p state=%d flags=%lx", msk, state, msk->flags);
-	if (state == TCP_LISTEN)
-		return test_bit(MPTCP_DATA_READY, &msk->flags) ? EPOLLIN | EPOLLRDNORM : 0;
+	if (state == TCP_LISTEN) {
+		if (WARN_ON_ONCE(!msk->subflow || !msk->subflow->sk))
+			return 0;
+
+		return inet_csk_listen_poll(msk->subflow->sk);
+	}
 
 	if (state != TCP_SYN_SENT && state != TCP_SYN_RECV) {
 		mask |= mptcp_check_readable(msk);

net/mptcp/protocol.h

@@ -111,7 +111,6 @@
 #define MPTCP_RST_TRANSIENT	BIT(0)
 
 /* MPTCP socket flags */
-#define MPTCP_DATA_READY	0
 #define MPTCP_NOSPACE		1
 #define MPTCP_WORK_RTX		2
 #define MPTCP_WORK_EOF		3

net/mptcp/subflow.c

@@ -1293,7 +1293,6 @@ static void subflow_data_ready(struct sock *sk)
 		if (reqsk_queue_empty(&inet_csk(sk)->icsk_accept_queue))
 			return;
 
-		set_bit(MPTCP_DATA_READY, &msk->flags);
 		parent->sk_data_ready(parent);
 		return;
 	}