[PATCH 3.16 193/305] net_sched: fix pfifo_head_drop behavior vs backlog

Ben Hutchings
2016-08-14T18:05:42Z

From: Eric Dumazet <edumazet@google.com>

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>
---
net/sched/sch_fifo.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/net/sched/sch_fifo.c
+++ b/net/sched/sch_fifo.c
@@ -37,14 +37,18 @@ static int pfifo_enqueue(struct sk_buff

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;
}