kernel: merge pending fq_codel backlog accounting fix

Signed-off-by: Felix Fietkau <nbd@nbd.name>

1 files changed, 70 insertions, 0 deletions

diff --git a/target/linux/generic/patches-4.4/035-fq_codel-fix-NET_XMIT_CN-behavior.patch b/target/linux/generic/patches-4.4/035-fq_codel-fix-NET_XMIT_CN-behavior.patch
new file mode 100644
index 0000000000..a1902fea07
--- /dev/null
+++ b/target/linux/generic/patches-4.4/035-fq_codel-fix-NET_XMIT_CN-behavior.patch
@@ -0,0 +1,70 @@
+From: Eric Dumazet <edumazet@google.com>
+Date: Sat, 4 Jun 2016 12:55:13 -0700
+Subject: [PATCH] fq_codel: fix NET_XMIT_CN behavior
+
+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.
+
+v2: Florian Westphal pointed out that we could drop the packet,
+so we need to save qdisc_pkt_len(skb) in a temp variable before
+calling fq_codel_drop()
+
+Fixes: 9d18562a2278 ("fq_codel: add batch ability to fq_codel_drop()")
+Fixes: 2ccccf5fb43f ("net_sched: update hierarchical backlog too")
+Reported-by: Stas Nichiporovich <stasn77@gmail.com>
+Signed-off-by: Eric Dumazet <edumazet@google.com>
+Cc: WANG Cong <xiyou.wangcong@gmail.com>
+Cc: Jamal Hadi Salim <jhs@mojatatu.com>
+---
+
+--- a/net/sched/sch_fq_codel.c
++++ b/net/sched/sch_fq_codel.c
+@@ -197,6 +197,7 @@ static int fq_codel_enqueue(struct sk_bu
+ 	unsigned int idx, prev_backlog, prev_qlen;
+ 	struct fq_codel_flow *flow;
+ 	int uninitialized_var(ret);
++	unsigned int pkt_len;
+ 	bool memory_limited;
+ 
+ 	idx = fq_codel_classify(skb, sch, &ret);
+@@ -228,6 +229,8 @@ static int fq_codel_enqueue(struct sk_bu
+ 	prev_backlog = sch->qstats.backlog;
+ 	prev_qlen = sch->q.qlen;
+ 
++	/* save this packet length as it might be dropped by fq_codel_drop() */
++	pkt_len = qdisc_pkt_len(skb);
+ 	/* fq_codel_drop() is quite expensive, as it performs a linear search
+ 	 * in q->backlogs[] to find a fat flow.
+ 	 * So instead of dropping a single packet, drop half of its backlog
+@@ -235,14 +238,23 @@ static int fq_codel_enqueue(struct sk_bu
+ 	 */
+ 	ret = fq_codel_drop(sch, q->drop_batch_size);
+ 
+-	q->drop_overlimit += prev_qlen - sch->q.qlen;
++	prev_qlen -= sch->q.qlen;
++	prev_backlog -= sch->qstats.backlog;
++	q->drop_overlimit += prev_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);
++		q->drop_overmemory += prev_qlen;
+ 
+-	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.
++	 */
++	if (ret == idx) {
++		qdisc_tree_reduce_backlog(sch, prev_qlen - 1,
++					  prev_backlog - pkt_len);
++		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()