netdev - [PATCH net] fq_codel: fix NET_XMIT

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Message-ID: <1465062227.2968.7.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Sat, 04 Jun 2016 10:43:47 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>,
	Stas Nichiporovich <stasn77@...il.com>,
	WANG Cong <xiyou.wangcong@...il.com>,
	Jamal Hadi Salim <jhs@...atatu.com>
Subject: [PATCH net] fq_codel: fix NET_XMIT_CN behavior

From: Eric Dumazet <edumazet@...gle.com>

My prior attempt to fix the backlogs of parents failed.

If we return NET_XMIT_CN, our parents wont increase their backlog,
so our qdisc_tree_reduce_backlog() should take this into account.

Fixes: 9d18562a2278 ("fq_codel: add batch ability to fq_codel_drop()")
Fixes: 2ccccf5fb43f ("net_sched: update hierarchical backlog too")
Reported-by: Stas Nichiporovich <stasn77@...il.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: WANG Cong <xiyou.wangcong@...il.com>
Cc: Jamal Hadi Salim <jhs@...atatu.com>
---
 net/sched/sch_fq_codel.c |   18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c
index 6883a8971562..c57ec480a2da 100644
--- a/net/sched/sch_fq_codel.c
+++ b/net/sched/sch_fq_codel.c
@@ -240,11 +240,19 @@ static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 	q->drop_overlimit += prev_qlen - sch->q.qlen;
 	if (memory_limited)
 		q->drop_overmemory += prev_qlen - sch->q.qlen;
-	/* As we dropped packet(s), better let upper stack know this */
-	qdisc_tree_reduce_backlog(sch, prev_qlen - sch->q.qlen,
-				  prev_backlog - sch->qstats.backlog);
-
-	return ret == idx ? NET_XMIT_CN : NET_XMIT_SUCCESS;
+	/* As we dropped packet(s), better let upper stack know this.
+	 * If we dropped a packet for this flow, return NET_XMIT_CN,
+	 * but in this case, our parents wont increase their backlogs.
+	 */
+	prev_qlen -= sch->q.qlen;
+	prev_backlog -= sch->qstats.backlog;
+	if (ret == idx) {
+		qdisc_tree_reduce_backlog(sch, prev_qlen - 1,
+					  prev_backlog - qdisc_pkt_len(skb));
+		return NET_XMIT_CN;
+	}
+	qdisc_tree_reduce_backlog(sch, prev_qlen, prev_backlog);
+	return NET_XMIT_SUCCESS;
 }
 
 /* This is the specific function called from codel_dequeue()