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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;
}
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