target/linux/generic/patches-4.4/620-net_sched-codel-do-not-defer-queue-length-update.patch

   1 From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
   2 Date: Mon, 21 Aug 2017 11:14:14 +0300
   3 Subject: [PATCH] net_sched/codel: do not defer queue length update
   4
   5 When codel wants to drop last packet in ->dequeue() it cannot call
   6 qdisc_tree_reduce_backlog() right away - it will notify parent qdisc
   7 about zero qlen and HTB/HFSC will deactivate class. The same class will
   8 be deactivated second time by caller of ->dequeue(). Currently codel and
   9 fq_codel defer update. This triggers warning in HFSC when it's qlen != 0
  10 but there is no active classes.
  11
  12 This patch update parent queue length immediately: just temporary increase
  13 qlen around qdisc_tree_reduce_backlog() to prevent first class deactivation
  14 if we have skb to return.
  15
  16 This might open another problem in HFSC - now operation peek could fail and
  17 deactivate parent class.
  18
  19 Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
  20 Link: https://bugzilla.kernel.org/show_bug.cgi?id=109581
  21 ---
  22
  23 --- a/net/sched/sch_codel.c
  24 +++ b/net/sched/sch_codel.c
  25 @@ -79,11 +79,17 @@ static struct sk_buff *codel_qdisc_deque
  26
  27         skb = codel_dequeue(sch, &q->params, &q->vars, &q->stats, dequeue);
  28
  29 -       /* We cant call qdisc_tree_reduce_backlog() if our qlen is 0,
  30 -        * or HTB crashes. Defer it for next round.
  31 +       /* If our qlen is 0 qdisc_tree_reduce_backlog() will deactivate
  32 +        * parent class, dequeue in parent qdisc will do the same if we
  33 +        * return skb. Temporary increment qlen if we have skb.
  34          */
  35 -       if (q->stats.drop_count && sch->q.qlen) {
  36 -               qdisc_tree_reduce_backlog(sch, q->stats.drop_count, q->stats.drop_len);
  37 +       if (q->stats.drop_count) {
  38 +               if (skb)
  39 +                       sch->q.qlen++;
  40 +               qdisc_tree_reduce_backlog(sch, q->stats.drop_count,
  41 +                                         q->stats.drop_len);
  42 +               if (skb)
  43 +                       sch->q.qlen--;
  44                 q->stats.drop_count = 0;
  45                 q->stats.drop_len = 0;
  46         }
  47 --- a/net/sched/sch_fq_codel.c
  48 +++ b/net/sched/sch_fq_codel.c
  49 @@ -311,6 +311,21 @@ begin:
  50         flow->dropped += q->cstats.drop_count - prev_drop_count;
  51         flow->dropped += q->cstats.ecn_mark - prev_ecn_mark;
  52
  53 +       /* If our qlen is 0 qdisc_tree_reduce_backlog() will deactivate
  54 +        * parent class, dequeue in parent qdisc will do the same if we
  55 +        * return skb. Temporary increment qlen if we have skb.
  56 +        */
  57 +       if (q->cstats.drop_count) {
  58 +               if (skb)
  59 +                       sch->q.qlen++;
  60 +               qdisc_tree_reduce_backlog(sch, q->cstats.drop_count,
  61 +                                         q->cstats.drop_len);
  62 +               if (skb)
  63 +                       sch->q.qlen--;
  64 +               q->cstats.drop_count = 0;
  65 +               q->cstats.drop_len = 0;
  66 +       }
  67 +
  68         if (!skb) {
  69                 /* force a pass through old_flows to prevent starvation */
  70                 if ((head == &q->new_flows) && !list_empty(&q->old_flows))
  71 @@ -321,15 +336,6 @@ begin:
  72         }
  73         qdisc_bstats_update(sch, skb);
  74         flow->deficit -= qdisc_pkt_len(skb);
  75 -       /* We cant call qdisc_tree_reduce_backlog() if our qlen is 0,
  76 -        * or HTB crashes. Defer it for next round.
  77 -        */
  78 -       if (q->cstats.drop_count && sch->q.qlen) {
  79 -               qdisc_tree_reduce_backlog(sch, q->cstats.drop_count,
  80 -                                         q->cstats.drop_len);
  81 -               q->cstats.drop_count = 0;
  82 -               q->cstats.drop_len = 0;
  83 -       }
  84         return skb;
  85  }
  86