Revert "mptcp: Make sure that we don't overfill subflows"

This reverts commit 32c7940.

It has been reported that this commit is causing issues.

Best to revert this if it is causing more issues than what it solves on
these old kernels.

Signed-off-by: Matthieu Baerts <[email protected]>

net/mptcp/mptcp_sched.c

@@ -397,11 +397,10 @@ static struct sk_buff *mptcp_next_segment(struct sock *meta_sk,
 					  unsigned int *limit)
 {
 	struct sk_buff *skb = __mptcp_next_segment(meta_sk, reinject);
-	unsigned int mss_now, in_flight_space;
-	int remaining_in_flight_space;
-	u32 max_len, max_segs, window;
+	unsigned int mss_now;
 	struct tcp_sock *subtp;
 	u16 gso_max_segs;
+	u32 max_len, max_segs, window, needed;
 
 	/* As we set it, we have to reset it as well. */
 	*limit = 0;
@@ -442,6 +441,9 @@ static struct sk_buff *mptcp_next_segment(struct sock *meta_sk,
 	/* The following is similar to tcp_mss_split_point, but
 	 * we do not care about nagle, because we will anyways
 	 * use TCP_NAGLE_PUSH, which overrides this.
+	 *
+	 * So, we first limit according to the cwnd/gso-size and then according
+	 * to the subflow's window.
 	 */
 
 	gso_max_segs = (*subsk)->sk_gso_max_segs;
@@ -451,30 +453,16 @@ static struct sk_buff *mptcp_next_segment(struct sock *meta_sk,
 	if (!max_segs)
 		return NULL;
 
-	/* max_len is what would fit in the cwnd (respecting the 2GSO-limit of
-	 * tcp_cwnd_test), but ignoring whatever was already queued.
-	 */
-	max_len = min(mss_now * max_segs, skb->len);
-
-	in_flight_space = (subtp->snd_cwnd - tcp_packets_in_flight(subtp)) * mss_now;
-	remaining_in_flight_space = (int)in_flight_space - (subtp->write_seq - subtp->snd_nxt);
-
-	if (remaining_in_flight_space <= 0)
-		WARN_ONCE(1, "in_flight %u cwnd %u wseq %u snxt %u mss_now %u cache %u",
-			  tcp_packets_in_flight(subtp), subtp->snd_cwnd,
-			  subtp->write_seq, subtp->snd_nxt, mss_now, subtp->mss_cache);
-	else
-		/* max_len now fits exactly in the write-queue, taking into
-		 * account what was already queued.
-		 */
-		max_len = min_t(u32, max_len, remaining_in_flight_space);
-
+	max_len = mss_now * max_segs;
 	window = tcp_wnd_end(subtp) - subtp->write_seq;
 
-	/* max_len now also respects the announced receive-window */
-	max_len = min(max_len, window);
-
-	*limit = max_len;
+	needed = min(skb->len, window);
+	if (max_len <= skb->len)
+		/* Take max_win, which is actually the cwnd/gso-size */
+		*limit = max_len;
+	else
+		/* Or, take the window */
+		*limit = needed;
 
 	return skb;
 }