sch_cake: Correctly update parent qlen when splitting GSO packets

To ensure parent qdiscs have the same notion of the number of enqueued
packets even after splitting a GSO packet, update the qdisc tree with the
number of packets that was added due to the split.
Reported-by: NPete Heist <pete@heistp.net>
Tested-by: NPete Heist <pete@heistp.net>
Signed-off-by: NToke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/sch_cake.c

@@ -1667,7 +1667,7 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 	if (skb_is_gso(skb) && q->rate_flags & CAKE_FLAG_SPLIT_GSO) {
 		struct sk_buff *segs, *nskb;
 		netdev_features_t features = netif_skb_features(skb);
-		unsigned int slen = 0;
+		unsigned int slen = 0, numsegs = 0;
 
 		segs = skb_gso_segment(skb, features & ~NETIF_F_GSO_MASK);
 		if (IS_ERR_OR_NULL(segs))
@@ -1683,6 +1683,7 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 			flow_queue_add(flow, segs);
 
 			sch->q.qlen++;
+			numsegs++;
 			slen += segs->len;
 			q->buffer_used += segs->truesize;
 			b->packets++;
@@ -1696,7 +1697,7 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		sch->qstats.backlog += slen;
 		q->avg_window_bytes += slen;
 
-		qdisc_tree_reduce_backlog(sch, 1, len);
+		qdisc_tree_reduce_backlog(sch, 1-numsegs, len-slen);
 		consume_skb(skb);
 	} else {
 		/* not splitting */