From: Konstantin Khlebnikov 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 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 @@ -316,6 +316,21 @@ 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)) @@ -326,15 +341,6 @@ 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; }