mptcp: add rmem queue accounting

If userspace never drains the receive buffers we must stop draining
the subflow socket(s) at some point.

This adds the needed rmem accouting for this.
If the threshold is reached, we stop draining the subflows.
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mptcp/protocol.c

@@ -124,7 +124,7 @@ static void __mptcp_move_skb(struct mptcp_sock *msk, struct sock *ssk,
 	struct sock *sk = (struct sock *)msk;
 
 	__skb_unlink(skb, &ssk->sk_receive_queue);
-	skb_orphan(skb);
+	skb_set_owner_r(skb, sk);
 	__skb_queue_tail(&sk->sk_receive_queue, skb);
 
 	msk->ack_seq += copy_len;
@@ -136,10 +136,16 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
 					   unsigned int *bytes)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+	struct sock *sk = (struct sock *)msk;
 	unsigned int moved = 0;
 	bool more_data_avail;
 	struct tcp_sock *tp;
 	bool done = false;
+	int rcvbuf;
+
+	rcvbuf = max(ssk->sk_rcvbuf, sk->sk_rcvbuf);
+	if (rcvbuf > sk->sk_rcvbuf)
+		sk->sk_rcvbuf = rcvbuf;
 
 	tp = tcp_sk(ssk);
 	do {
@@ -183,6 +189,11 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
 
 		WRITE_ONCE(tp->copied_seq, seq);
 		more_data_avail = mptcp_subflow_data_available(ssk);
+
+		if (atomic_read(&sk->sk_rmem_alloc) > READ_ONCE(sk->sk_rcvbuf)) {
+			done = true;
+			break;
+		}
 	} while (more_data_avail);
 
 	*bytes = moved;
@@ -196,9 +207,14 @@ void mptcp_data_ready(struct sock *sk)
 
 	set_bit(MPTCP_DATA_READY, &msk->flags);
 
+	/* don't schedule if mptcp sk is (still) over limit */
+	if (atomic_read(&sk->sk_rmem_alloc) > READ_ONCE(sk->sk_rcvbuf))
+		goto wake;
+
 	if (schedule_work(&msk->work))
 		sock_hold((struct sock *)msk);
 
+wake:
 	sk->sk_data_ready(sk);
 }