kernel: merge a pending fix for HFSC warnings/slowdowns (fixes FS#1136)

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

1 files changed, 86 insertions, 0 deletions

diff --git a/target/linux/generic/pending-4.9/620-net_sched-codel-do-not-defer-queue-length-update.patch b/target/linux/generic/pending-4.9/620-net_sched-codel-do-not-defer-queue-length-update.patch
new file mode 100644
index 0000000..6fe863a
--- /dev/null
+++ b/target/linux/generic/pending-4.9/620-net_sched-codel-do-not-defer-queue-length-update.patch
@@ -0,0 +1,86 @@
+From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
+Date: Mon, 21 Aug 2017 11:14:14 +0300
+Subject: [PATCH] net_sched/codel: do not defer queue length update
+
+When codel wants to drop last packet in ->dequeue() it cannot call
+qdisc_tree_reduce_backlog() right away - it will notify parent qdisc
+about zero qlen and HTB/HFSC will deactivate class. The same class will
+be deactivated second time by caller of ->dequeue(). Currently codel and
+fq_codel defer update. This triggers warning in HFSC when it's qlen != 0
+but there is no active classes.
+
+This patch update parent queue length immediately: just temporary increase
+qlen around qdisc_tree_reduce_backlog() to prevent first class deactivation
+if we have skb to return.
+
+This might open another problem in HFSC - now operation peek could fail and
+deactivate parent class.
+
+Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
+Link: https://bugzilla.kernel.org/show_bug.cgi?id=109581
+---
+
+--- a/net/sched/sch_codel.c
++++ b/net/sched/sch_codel.c
+@@ -95,11 +95,17 @@ static struct sk_buff *codel_qdisc_deque
+ 			    &q->stats, qdisc_pkt_len, codel_get_enqueue_time,
+ 			    drop_func, dequeue_func);
+ 
+-	/* We cant call qdisc_tree_reduce_backlog() if our qlen is 0,
+-	 * or HTB crashes. Defer it for next round.
++	/* If our qlen is 0 qdisc_tree_reduce_backlog() will deactivate
++	 * parent class, dequeue in parent qdisc will do the same if we
++	 * return skb. Temporary increment qlen if we have skb.
+ 	 */
+-	if (q->stats.drop_count && sch->q.qlen) {
+-		qdisc_tree_reduce_backlog(sch, q->stats.drop_count, q->stats.drop_len);
++	if (q->stats.drop_count) {
++		if (skb)
++			sch->q.qlen++;
++		qdisc_tree_reduce_backlog(sch, q->stats.drop_count,
++					  q->stats.drop_len);
++		if (skb)
++			sch->q.qlen--;
+ 		q->stats.drop_count = 0;
+ 		q->stats.drop_len = 0;
+ 	}
+--- a/net/sched/sch_fq_codel.c
++++ b/net/sched/sch_fq_codel.c
+@@ -318,6 +318,21 @@ begin:
+ 	flow->dropped += q->cstats.drop_count - prev_drop_count;
+ 	flow->dropped += q->cstats.ecn_mark - prev_ecn_mark;
+ 
++	/* If our qlen is 0 qdisc_tree_reduce_backlog() will deactivate
++	 * parent class, dequeue in parent qdisc will do the same if we
++	 * return skb. Temporary increment qlen if we have skb.
++	 */
++	if (q->cstats.drop_count) {
++		if (skb)
++			sch->q.qlen++;
++		qdisc_tree_reduce_backlog(sch, q->cstats.drop_count,
++					  q->cstats.drop_len);
++		if (skb)
++			sch->q.qlen--;
++		q->cstats.drop_count = 0;
++		q->cstats.drop_len = 0;
++	}
++
+ 	if (!skb) {
+ 		/* force a pass through old_flows to prevent starvation */
+ 		if ((head == &q->new_flows) && !list_empty(&q->old_flows))
+@@ -328,15 +343,6 @@ begin:
+ 	}
+ 	qdisc_bstats_update(sch, skb);
+ 	flow->deficit -= qdisc_pkt_len(skb);
+-	/* We cant call qdisc_tree_reduce_backlog() if our qlen is 0,
+-	 * or HTB crashes. Defer it for next round.
+-	 */
+-	if (q->cstats.drop_count && sch->q.qlen) {
+-		qdisc_tree_reduce_backlog(sch, q->cstats.drop_count,
+-					  q->cstats.drop_len);
+-		q->cstats.drop_count = 0;
+-		q->cstats.drop_len = 0;
+-	}
+ 	return skb;
+ }
+