net_sched: fix pfifo_head_drop behavior vs backlog

commit 6c0d54f1897d229748d4f41ef919078db6db2123 upstream.

When the qdisc is full, we drop a packet at the head of the queue,
queue the current skb and return NET_XMIT_CN

Now we track backlog on upper qdiscs, we need to call
qdisc_tree_reduce_backlog(), even if the qlen did not change.

Fixes: 2ccccf5fb43f ("net_sched: update hierarchical backlog too")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: WANG Cong <xiyou.wangcong@gmail.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/sched/sch_fifo.c b/net/sched/sch_fifo.c
index e15a9eb29087794ccc71408f467e9ae37f9c086b..6475419633e10e69189d7c2dfaa12c695765770e 100644 (file)
--- a/net/sched/sch_fifo.c
+++ b/net/sched/sch_fifo.c
@@ -37,14 +37,18 @@ static int pfifo_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 
 static int pfifo_tail_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 {
+       unsigned int prev_backlog;
+
        if (likely(skb_queue_len(&sch->q) < sch->limit))
                return qdisc_enqueue_tail(skb, sch);
 
+       prev_backlog = sch->qstats.backlog;
        /* queue full, remove one skb to fulfill the limit */
        __qdisc_queue_drop_head(sch, &sch->q);
        sch->qstats.drops++;
        qdisc_enqueue_tail(skb, sch);
 
+       qdisc_tree_reduce_backlog(sch, 0, prev_backlog - sch->qstats.backlog);
        return NET_XMIT_CN;
 }