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

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Date: Thu, 11 Jan 2024 10:40:36 -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 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.
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: