Re: [PATCH net 2/3] net: sched: multiq: don't call qdisc_put() while holding tree lock

[Cong Wang]

On Wed, Sep 18, 2019 at 12:32 AM Vlad Buslov <vla...@mellanox.com> wrote:
> diff --git a/net/sched/sch_multiq.c b/net/sched/sch_multiq.c
> index e1087746f6a2..4cfa9a7bd29e 100644
> --- a/net/sched/sch_multiq.c
> +++ b/net/sched/sch_multiq.c
> @@ -187,18 +187,21 @@ static int multiq_tune(struct Qdisc *sch, struct nlattr 
> *opt,
>
>         sch_tree_lock(sch);
>         q->bands = qopt->bands;
> +       sch_tree_unlock(sch);
> +
>         for (i = q->bands; i < q->max_bands; i++) {
>                 if (q->queues[i] != &noop_qdisc) {
>                         struct Qdisc *child = q->queues[i];
>
> +                       sch_tree_lock(sch);
>                         q->queues[i] = &noop_qdisc;
>                         qdisc_tree_flush_backlog(child);
> +                       sch_tree_unlock(sch);
> +
>                         qdisc_put(child);
>                 }
>         }

Repeatedly acquiring and releasing a spinlock in a loop
does not seem to be a good idea. Is it possible to save
those qdisc pointers to an array or something similar?

Thanks.