Re: [patch net-next] net: sched: move block device tracking into tcf_block_get/put_ext()

[Jiri Pirko <jiri@resnulli.us>]

Thu, Jan 11, 2024 at 04:42:55PM CET, jhs@mojatatu.com wrote:
>On Thu, Jan 11, 2024 at 10:40 AM Jamal Hadi Salim <jhs@mojatatu.com> wrote:
>>
>> On Wed, Jan 10, 2024 at 7:10 AM Ido Schimmel <idosch@idosch.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?

Just red.

>
>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: