Patch "net_sched: fix pfifo_head_drop behavior vs backlog" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

    net_sched: fix pfifo_head_drop behavior vs backlog

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     net_sched-fix-pfifo_head_drop-behavior-vs-backlog.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let [off-list ref] know about it.

From foo@baz Wed Jul  6 16:50:47 PDT 2016

From: Eric Dumazet <redacted>
Date: Sun, 12 Jun 2016 20:01:25 -0700
Subject: net_sched: fix pfifo_head_drop behavior vs backlog

From: Eric Dumazet <redacted>

[ Upstream commit 6c0d54f1897d229748d4f41ef919078db6db2123 ]

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 <redacted>
Cc: WANG Cong <redacted>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Acked-by: Cong Wang <redacted>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 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);
 	qdisc_qstats_drop(sch);
 	qdisc_enqueue_tail(skb, sch);
 
+	qdisc_tree_reduce_backlog(sch, 0, prev_backlog - sch->qstats.backlog);
 	return NET_XMIT_CN;
 }
 

Patches currently in stable-queue which might be from edumazet@google.com are

queue-4.4/net-alx-work-around-the-dma-rx-overflow-issue.patch
queue-4.4/netem-fix-a-use-after-free.patch
queue-4.4/net_sched-fix-pfifo_head_drop-behavior-vs-backlog.patch