From: Eric Dumazet 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 Signed-off-by: Eric Dumazet Cc: WANG Cong Cc: Jamal Hadi Salim --- --- 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()