mptcp: correct chronos for meta and subflows

the chronos that track socket states "sendbuf limited" "busy" and
"receive window" limited need to be properly handled by mptcp.

Specifically:
* send buffer is managed only by the meta, so when space is available in
  the meta send buffer, meta and subflow "sendbuf limited" chronos must
  be stopped.
* similarly, the chrono for "send buf limited" is started by the mptcp
  scheduler, both for meta and the available subflow.
* receive window limited chrono added to meta window checks in scheduler
  and mptcp_write_xmit (this was missing).

Fixes: 0bc2117 ("Merge tag 'v4.10' into mptcp_trunk")
Signed-off-by: Tim Froidcoeur <tim.froidcoeur@tessares.net>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>

net/ipv4/tcp_output.c

@@ -1707,8 +1707,11 @@ static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
 		 * 2) not cwnd limited (this else condition)
 		 * 3) no more data to send (tcp_write_queue_empty())
 		 * 4) application is hitting buffer limit (SOCK_NOSPACE)
+		 * 5) For MPTCP subflows, the scheduler determines
+		 *    sndbuf limited.
 		 */
 		if (tcp_write_queue_empty(sk) && sk->sk_socket &&
+		    !(mptcp(tcp_sk(sk)) && !is_meta_sk(sk)) &&
 		    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags) &&
 		    (1 << sk->sk_state) & (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT))
 			tcp_chrono_start(sk, TCP_CHRONO_SNDBUF_LIMITED);

net/mptcp/mptcp_input.c

@@ -1425,6 +1425,19 @@ static void mptcp_snd_una_update(struct tcp_sock *meta_tp, u32 data_ack)
 	meta_tp->snd_una = data_ack;
 }
 
+static void mptcp_stop_subflow_chronos(struct sock *meta_sk,
+				       const enum tcp_chrono type)
+{
+	const struct mptcp_cb *mpcb = tcp_sk(meta_sk)->mpcb;
+	struct mptcp_tcp_sock *mptcp;
+
+	mptcp_for_each_sub(mpcb, mptcp) {
+		struct sock *sk_it = mptcp_to_sock(mptcp);
+
+		tcp_chrono_stop(sk_it, type);
+	}
+}
+
 /* Handle the DATA_ACK */
 static bool mptcp_process_data_ack(struct sock *sk, const struct sk_buff *skb)
 {
@@ -1550,6 +1563,13 @@ static bool mptcp_process_data_ack(struct sock *sk, const struct sk_buff *skb)
 		if (meta_sk->sk_socket &&
 		    test_bit(SOCK_NOSPACE, &meta_sk->sk_socket->flags))
 			meta_sk->sk_write_space(meta_sk);
+
+		if (meta_sk->sk_socket &&
+		    !test_bit(SOCK_NOSPACE, &meta_sk->sk_socket->flags)) {
+			tcp_chrono_stop(meta_sk, TCP_CHRONO_SNDBUF_LIMITED);
+			mptcp_stop_subflow_chronos(meta_sk,
+						   TCP_CHRONO_SNDBUF_LIMITED);
+		}
 	}
 
 	if (meta_sk->sk_state != TCP_ESTABLISHED) {

net/mptcp/mptcp_output.c

@@ -801,6 +801,7 @@ bool mptcp_write_xmit(struct sock *meta_sk, unsigned int mss_now, int nonagle,
 		     int push_one, gfp_t gfp)
 {
 	struct tcp_sock *meta_tp = tcp_sk(meta_sk), *subtp;
+	bool is_rwnd_limited = false;
 	struct mptcp_tcp_sock *mptcp;
 	struct sock *subsk = NULL;
 	struct mptcp_cb *mpcb = meta_tp->mpcb;
@@ -848,8 +849,10 @@ bool mptcp_write_xmit(struct sock *meta_sk, unsigned int mss_now, int nonagle,
 		if (skb_unclone(skb, GFP_ATOMIC))
 			break;
 
-		if (unlikely(!tcp_snd_wnd_test(meta_tp, skb, mss_now)))
+		if (unlikely(!tcp_snd_wnd_test(meta_tp, skb, mss_now))) {
+			is_rwnd_limited = true;
 			break;
+		}
 
 		/* Force tso_segs to 1 by using UINT_MAX.
 		 * We actually don't care about the exact number of segments
@@ -932,6 +935,11 @@ bool mptcp_write_xmit(struct sock *meta_sk, unsigned int mss_now, int nonagle,
 			break;
 	}
 
+	if (is_rwnd_limited)
+		tcp_chrono_start(meta_sk, TCP_CHRONO_RWND_LIMITED);
+	else
+		tcp_chrono_stop(meta_sk, TCP_CHRONO_RWND_LIMITED);
+
 	mptcp_for_each_sub(mpcb, mptcp) {
 		subsk = mptcp_to_sock(mptcp);
 		subtp = tcp_sk(subsk);

net/mptcp/mptcp_sched.c

@@ -372,14 +372,22 @@ static struct sk_buff *__mptcp_next_segment(struct sock *meta_sk, int *reinject)
 		if (!skb && meta_sk->sk_socket &&
 		    test_bit(SOCK_NOSPACE, &meta_sk->sk_socket->flags) &&
 		    sk_stream_wspace(meta_sk) < sk_stream_min_wspace(meta_sk)) {
-			struct sock *subsk = mpcb->sched_ops->get_subflow(meta_sk, NULL,
-									  false);
+			struct sock *subsk;
+
+			/* meta is send buffer limited */
+			tcp_chrono_start(meta_sk, TCP_CHRONO_SNDBUF_LIMITED);
+
+			subsk = mpcb->sched_ops->get_subflow(meta_sk,
+							     NULL, false);
 			if (!subsk)
 				return NULL;
 
 			skb = mptcp_rcv_buf_optimization(subsk, 0);
 			if (skb)
 				*reinject = -1;
+			else
+				tcp_chrono_start(subsk,
+						 TCP_CHRONO_SNDBUF_LIMITED);
 		}
 	}
 	return skb;
@@ -411,13 +419,24 @@ struct sk_buff *mptcp_next_segment(struct sock *meta_sk,
 	mss_now = tcp_current_mss(*subsk);
 
 	if (!*reinject && unlikely(!tcp_snd_wnd_test(tcp_sk(meta_sk), skb, mss_now))) {
+		/* an active flow is selected, but segment will not be sent due
+		 * to no more space in send window
+		 * this means the meta is receive window limited
+		 * the subflow might also be, if we have nothing to reinject
+		 */
+		tcp_chrono_start(meta_sk, TCP_CHRONO_RWND_LIMITED);
 		skb = mptcp_rcv_buf_optimization(*subsk, 1);
 		if (skb)
 			*reinject = -1;
 		else
 			return NULL;
 	}
 
+	if (!*reinject) {
+		/* this will stop any other chronos on the meta */
+		tcp_chrono_start(meta_sk, TCP_CHRONO_BUSY);
+	}
+
 	/* No splitting required, as we will only send one single segment */
 	if (skb->len <= mss_now)
 		return skb;