netdev - Re: [patch net-next] net: sched: move block device tracking into tcf_block_get/put

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Message-ID: <CAM0EoMkpzsEWXMw27xgsfzwA2g4CNeDYQ9niTJAkgu3=Kgp81g@mail.gmail.com>
Date: Thu, 11 Jan 2024 10:42:55 -0500
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Ido Schimmel <idosch@...sch.org>
Cc: Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org, kuba@...nel.org, 
	pabeni@...hat.com, davem@...emloft.net, edumazet@...gle.com, 
	xiyou.wangcong@...il.com, victor@...atatu.com, pctammela@...atatu.com, 
	mleitner@...hat.com, vladbu@...dia.com, paulb@...dia.com, 
	Petr Machata <petrm@...dia.com>
Subject: Re: [patch net-next] net: sched: move block device tracking into tcf_block_get/put_ext()

On Thu, Jan 11, 2024 at 10:40 AM Jamal Hadi Salim <jhs@...atatu.com> wrote:
>
> On Wed, Jan 10, 2024 at 7:10 AM Ido Schimmel <idosch@...sch.org> wrote:
> >
> > On Thu, Jan 04, 2024 at 01:58:44PM +0100, Jiri Pirko wrote:
> > > diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
> > > index adf5de1ff773..253b26f2eddd 100644
> > > --- a/net/sched/cls_api.c
> > > +++ b/net/sched/cls_api.c
> > > @@ -1428,6 +1428,7 @@ int tcf_block_get_ext(struct tcf_block **p_block, struct Qdisc *q,
> > >                     struct tcf_block_ext_info *ei,
> > >                     struct netlink_ext_ack *extack)
> > >  {
> > > +     struct net_device *dev = qdisc_dev(q);
> > >       struct net *net = qdisc_net(q);
> > >       struct tcf_block *block = NULL;
> > >       int err;
> > > @@ -1461,9 +1462,18 @@ int tcf_block_get_ext(struct tcf_block **p_block, struct Qdisc *q,
> > >       if (err)
> > >               goto err_block_offload_bind;
> > >
> > > +     if (tcf_block_shared(block)) {
> > > +             err = xa_insert(&block->ports, dev->ifindex, dev, GFP_KERNEL);
> > > +             if (err) {
> > > +                     NL_SET_ERR_MSG(extack, "block dev insert failed");
> > > +                     goto err_dev_insert;
> > > +             }
> > > +     }
> >
> > While this patch fixes the original issue, it creates another one:
> >
> > # ip link add name swp1 type dummy
> > # tc qdisc replace dev swp1 root handle 10: prio bands 8 priomap 7 6 5 4 3 2 1
> > # tc qdisc add dev swp1 parent 10:8 handle 108: red limit 1000000 min 200000 max 200001 probability 1.0 avpkt 8000 burst 38 qevent early_drop block 10
> > RED: set bandwidth to 10Mbit
> > # tc qdisc add dev swp1 parent 10:7 handle 107: red limit 1000000 min 500000 max 500001 probability 1.0 avpkt 8000 burst 63 qevent early_drop block 10
> > RED: set bandwidth to 10Mbit
> > Error: block dev insert failed.
> >
>
>
> +cc Petr
> We'll add a testcase on tdc - it doesnt seem we have any for qevents.
> If you have others that are related let us know.
> But how does this work? I see no mention of block on red code and i
> see no mention of block on the reproducer above.

Context: Yes, i see it on red setup but i dont see any block being setup.
Also: Is it only Red or other qdiscs could behave this way?

cheers,
jamal
> Are the qevents exception packets from the hardware? Is there a good
> description of what qevents do?
>
> cheers,
> jamal
>
>
> > The reproducer does not fail if I revert this patch and apply Victor's
> > [1] instead.
> >
> > [1] https://lore.kernel.org/netdev/20231231172320.245375-1-victor@mojatatu.com/
> >
> > > +
> > >       *p_block = block;
> > >       return 0;
> > >
> > > +err_dev_insert:
> > >  err_block_offload_bind:
> > >       tcf_chain0_head_change_cb_del(block, ei);
> > >  err_chain0_head_change_cb_add: