netdev - Re: [BUG] net/sched : qlen can not really be per cpu ?

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Message-ID: <e3bcab30-a7a4-878b-9d00-d1fa39b1f4e9@gmail.com>
Date:   Wed, 27 Feb 2019 21:15:52 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     John Fastabend <john.fastabend@...il.com>,
        Networking <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [BUG] net/sched : qlen can not really be per cpu ?



On 02/27/2019 06:46 PM, Cong Wang wrote:

> Hmm, looking into this, do we really need to check cl->leaf.q->q.qlen
> in htb_activate() for pfifo_fast? htb_activate() is only called when
> qdisc_enqueue() returns NET_XMIT_SUCCESS, so for pfifo_fast
> that is always qlen!=0, right?
> 
> So something like below? It is ugly but should be sufficient to shut
> up the warning.
> 
> diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
> index 30f9da7e1076..6d0182750f8b 100644
> --- a/net/sched/sch_htb.c
> +++ b/net/sched/sch_htb.c
> @@ -555,7 +555,8 @@ htb_change_class_mode(struct htb_sched *q, struct
> htb_class *cl, s64 *diff)
>   */
>  static inline void htb_activate(struct htb_sched *q, struct htb_class *cl)
>  {
> -       WARN_ON(cl->level || !cl->leaf.q || !cl->leaf.q->q.qlen);
> +       WARN_ON(cl->level || !cl->leaf.q ||
> +               (!(cl->leaf.q->flags & TCQ_F_NOLOCK) && !cl->leaf.q->q.qlen));
> 
>         if (!cl->prio_activity) {
>                 cl->prio_activity = 1 << cl->prio;
> 

Well, this is the tip of the iceberg.

Look at lines 845 & 883

How are we going to fix them ?

(Then there are all the other qdisc I mentioned)