mptcp: call tcp_cleanup_rbuf on subflows

That is needed to let the subflows announce promptly when new
space is available in the receive buffer.

tcp_cleanup_rbuf() is currently a static function, drop the
scope modifier and add a declaration in the TCP header.
Reviewed-by: NMat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: NPaolo Abeni <pabeni@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/tcp.h

@@ -1414,6 +1414,8 @@ static inline int tcp_full_space(const struct sock *sk)
 	return tcp_win_from_space(sk, READ_ONCE(sk->sk_rcvbuf));
 }
 
+void tcp_cleanup_rbuf(struct sock *sk, int copied);
+
 /* We provision sk_rcvbuf around 200% of sk_rcvlowat.
  * If 87.5 % (7/8) of the space has been consumed, we want to override
  * SO_RCVLOWAT constraint, since we are receiving skbs with too small

net/ipv4/tcp.c

@@ -1527,7 +1527,7 @@ static int tcp_peek_sndq(struct sock *sk, struct msghdr *msg, int len)
  * calculation of whether or not we must ACK for the sake of
  * a window update.
  */
-static void tcp_cleanup_rbuf(struct sock *sk, int copied)
+void tcp_cleanup_rbuf(struct sock *sk, int copied)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	bool time_to_ack = false;

net/mptcp/protocol.c

@@ -515,6 +515,8 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
 	} while (more_data_avail);
 
 	*bytes += moved;
+	if (moved)
+		tcp_cleanup_rbuf(ssk, moved);
 
 	return done;
 }
@@ -1424,10 +1426,14 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied)
 			 */
 			mptcp_for_each_subflow(msk, subflow) {
 				struct sock *ssk;
+				bool slow;
 
 				ssk = mptcp_subflow_tcp_sock(subflow);
+				slow = lock_sock_fast(ssk);
 				WRITE_ONCE(ssk->sk_rcvbuf, rcvbuf);
 				tcp_sk(ssk)->window_clamp = window_clamp;
+				tcp_cleanup_rbuf(ssk, 1);
+				unlock_sock_fast(ssk, slow);
 			}
 		}
 	}

net/mptcp/subflow.c

@@ -823,6 +823,8 @@ static void mptcp_subflow_discard_data(struct sock *ssk, struct sk_buff *skb,
 		sk_eat_skb(ssk, skb);
 	if (mptcp_subflow_get_map_offset(subflow) >= subflow->map_data_len)
 		subflow->map_valid = 0;
+	if (incr)
+		tcp_cleanup_rbuf(ssk, incr);
 }
 
 static bool subflow_check_data_avail(struct sock *ssk)