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Date: Wed, 3 Jan 2024 12:08:09 -0500
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Jiri Pirko <jiri@...nulli.us>
Cc: Victor Nogueira <victor@...atatu.com>, davem@...emloft.net, edumazet@...gle.com,
kuba@...nel.org, pabeni@...hat.com, xiyou.wangcong@...il.com,
idosch@...sch.org, mleitner@...hat.com, vladbu@...dia.com, paulb@...dia.com,
pctammela@...atatu.com, netdev@...r.kernel.org, kernel@...atatu.com,
syzbot+84339b9e7330daae4d66@...kaller.appspotmail.com,
syzbot+806b0572c8d06b66b234@...kaller.appspotmail.com,
syzbot+0039110f932d438130f9@...kaller.appspotmail.com
Subject: Re: [PATCH net-next v2 1/1] net/sched: We should only add appropriate
qdiscs blocks to ports' xarray
On Wed, Jan 3, 2024 at 11:09 AM Jiri Pirko <jiri@...nulli.us> wrote:
>
> Wed, Jan 03, 2024 at 03:43:00PM CET, jhs@...atatu.com wrote:
> >On Wed, Jan 3, 2024 at 9:26 AM Jiri Pirko <jiri@...nulli.us> wrote:
> >>
> >> Wed, Jan 03, 2024 at 03:09:14PM CET, jhs@...atatu.com wrote:
> >> >On Wed, Jan 3, 2024 at 7:59 AM Jiri Pirko <jiri@...nulli.us> wrote:
> >> >>
> >> >> Tue, Jan 02, 2024 at 06:06:00PM CET, jhs@...atatu.com wrote:
> >> >> >On Tue, Jan 2, 2024 at 10:54 AM Jiri Pirko <jiri@...nulli.us> wrote:
> >> >> >>
> >> >> >> Tue, Jan 02, 2024 at 03:52:01PM CET, jhs@...atatu.com wrote:
> >> >> >> >On Tue, Jan 2, 2024 at 9:29 AM Jiri Pirko <jiri@...nulli.us> wrote:
> >> >> >> >>
> >> >> >> >> Tue, Jan 02, 2024 at 03:06:28PM CET, jhs@...atatu.com wrote:
> >> >> >> >> >On Tue, Jan 2, 2024 at 4:59 AM Jiri Pirko <jiri@...nulli.us> wrote:
> >> >> >> >> >>
> >> >> >> >> >> The patch subject should briefly describe the nature of the change. Not
> >> >> >> >> >> what "we" should or should not do.
> >> >> >> >> >>
> >> >> >> >> >>
> >> >> >> >> >> Sun, Dec 31, 2023 at 06:23:20PM CET, victor@...atatu.com wrote:
> >> >> >> >> >> >We should only add qdiscs to the blocks ports' xarray in ingress that
> >> >> >> >> >> >support ingress_block_set/get or in egress that support
> >> >> >> >> >> >egress_block_set/get.
> >> >> >> >> >>
> >> >> >> >> >> Tell the codebase what to do, be imperative. Please read again:
> >> >> >> >> >> https://www.kernel.org/doc/html/v6.6/process/submitting-patches.html#describe-your-changes
> >> >> >> >> >>
> >> >> >> >> >
> >> >> >> >> >We need another rule in the doc on nit-picking which states that we
> >> >> >> >> >need to make progress at some point. We made many changes to this
> >> >> >> >> >patchset based on your suggestions for no other reason other that we
> >> >> >> >> >can progress the discussion. This is a patch that fixes a bug of which
> >> >> >> >> >there are multiple syzbot reports and consumers of the API(last one
> >> >> >> >> >just reported from the MTCP people). There's some sense of urgency to
> >> >> >> >> >apply this patch before the original goes into net. More importantly:
> >> >> >> >> >This patch fixes the issue and follows the same common check which was
> >> >> >> >> >already being done in the committed patchset to check if the qdisc
> >> >> >> >> >supports the block set/get operations.
> >> >> >> >> >
> >> >> >> >> >There are about 3 ways to do this check, you objected to the original,
> >> >> >> >> >we picked something that works fine, and now you are picking a
> >> >> >> >> >different way with tcf_block. I dont see how tcf_block check would
> >> >> >> >> >help or solve this problem at all given this is a qdisc issue not a
> >> >> >> >> >class issue. What am I missing?
> >> >> >> >>
> >> >> >> >> Perhaps I got something wrong, but I thought that the issue is
> >> >> >> >> cl_ops->tcf_block being null for some qdiscs, isn't it?
> >> >> >> >>
> >> >> >> >
> >> >> >> >We attach these ports/netdevs only on capable qdiscs i.e ones that
> >> >> >> >have in/egress_block_set/get() - which happen to be ingress and
> >> >> >> >clsact only.
> >> >> >> >The problem was we were blindly assuming that presence of
> >> >> >> >cl->tcf_block() implies presence of in/egress_block_set/get(). The
> >> >> >> >earlier patches surrounded this code with attribute checks and so it
> >> >> >> >worked there.
> >> >> >>
> >> >> >> Syskaller report says:
> >> >> >>
> >> >> >> KASAN: null-ptr-deref in range [0x0000000000000048-0x000000000000004f]
> >> >> >> CPU: 1 PID: 5061 Comm: syz-executor323 Not tainted 6.7.0-rc6-syzkaller-01658-gc2b2ee36250d #0
> >> >> >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
> >> >> >> RIP: 0010:qdisc_block_add_dev net/sched/sch_api.c:1190 [inline]
> >> >> >>
> >> >> >> Line 1190 is:
> >> >> >> block = cl_ops->tcf_block(sch, TC_H_MIN_INGRESS, NULL);
> >> >> >>
> >> >> >> So the cl_ops->tcf_block == NULL
> >> >> >>
> >> >> >> Why can't you just check it? Why do you want to check in/egress_block_set/get()
> >> >> >> instead? I don't follow :/
> >> >> >>
> >> >> >
> >> >> >Does it make sense to add to the port xarray just because we have
> >> >> >cl_ops->tcf_block()? There are many qdiscs which have
> >> >> >cl_ops->tcf_block() (example htb) but cant be used in the block add
> >> >> >syntax (see question further below on tdc test).
> >> >>
> >> >> The whole block usage in qdiscs other than ingress and clsact seems odd
> >> >> to me to be honest. What's the reason for that?.
> >> >
> >> >Well, you added that code so you tell me. Was the original idea to
> >>
> >> Well, I added it only for clsact and ingress. The rest is unrelated to
> >> me.
> >>
> >
> >Well git is blaming you..
>
> Yeah, too long ago to remember I guess. It's no functional change,
> just included new code into existing qdiscs, converting tcf_chain()
> to tcf_block().
>
>
> >
> >> >allow grafting other qdiscs on a hierarchy? This is why i was asking
> >> >for a sample use case to add to tdc.
> >> >This was why our check is for "if (sch_ops->in/egress_block_get)"
> >> >because the check for cl_ops->tcf_block() you suggested is not correct
> >> >(it will match htb just fine for example) whereas this check will only
> >> >catch cls_act and ingress.
> >>
> >> This code went off rails :/
> >> The point is, mixing sch_ops->in/egress_block_get existence and cl_ops->tcf_block
> >> looks awfully odd and inviting another bugs in the future.
> >>
> >
> >What bugs? Be explicit so we can add tdc tests.
> >
> >> >> >--
> >> >> >$sudo tc qdisc add dev lo egress_block 21 handle 1: root htb
> >> >> >Error: Egress block sharing is not supported.
> >> >> >---
> >> >> >
> >> >> >Did you look at the other syzbot reports?
> >> >>
> >> >> Yeah. The block usage in other qdiscs looks very odd.
> >> >>
> >> >
> >> >And we have checks to catch it as you see.
> >> >TBH, the idea of having cls_ops->tcf_block for a qdisc like htb is
> >> >puzzling to me. It seems you are always creating a non-shared block
> >> >for some but not all qdiscs regardless. What is that used for?
> >>
> >> No clue.
> >>
> >
> >Well, if you cant remember a few years later then we'll look at
> >removing it - it will require a lot more testing like i said.
>
> It's actualy part of the conversion to introduce block processing. For
> the existing other qdiscs, not functional change.
>
Ok, does that mean we should look at removing it then or you think
it's functionally needed?
>
> >
> >> >
> >> >>
> >> >> >
> >> >> >> Btw, the checks in __qdisc_destroy() do also look wrong.
> >> >> >
> >> >> >Now I am not following, please explain. The same code structure check
> >> >> >is used in fill_qdisc
> >> >> >(https://elixir.bootlin.com/linux/v6.7-rc8/source/net/sched/sch_api.c#L940)
> >> >> >for example to pull the block info, is that wrong?
> >> >>
> >> >> There, you don't call tcf_block() at all, so how is that relevant?
> >> >>
> >> >
> >> >Why do we need to call it? We just need it to retrieve the block id.
> >>
> >> Uff, that is my point. In the code you are pointing at, you don't use
> >> tcf_block() at all, therefore it is not related to our discussion, is
> >> it?
> >>
> >
> >Huh? We are trying to check if it is legit to add a netdev to the
> >xarray. The only way it is legit is if we have ingress or clsact.
> >Those are the only two qdiscs with the set/get ops for blocks and the
> >only potential ones which we can have valid shared blocks attached. It
> >is related to the discussion.
> >
> >> >
> >> >>
> >> >>
> >> >> >
> >> >> >> >
> >> >> >> >BTW: Do you have an example of a test case where we can test the class
> >> >> >> >grafting (eg using htb with tcf_block)? It doesnt have any impact on
> >> >> >> >this patcheset here but we want to add it as a regression checker on
> >> >> >> >tdc in the future if someone makes a change.
> >> >> >
> >> >> >An answer to this will help.
> >> >>
> >> >> Answer is "no".
> >> >
> >> >Ok, so we cant test this or this is internal use only?
> >> >
> >> >I am going to repeat again here: you are holding back a bug fix (with
> >> >many reports) with this discussion. We can have the discussion
> >> >separately but let's make quick progress. If need be we can send fixes
> >> >after.
> >>
> >> I don't mind. Code is a mess as it is already. One more crap won't
> >> hurt...
> >>
> >
> >Ok, so your code that you added a few years ago is crap then by that
>
> True that.
>
>
> >metric. You can't even remember why you added it.
> >You have provided no legit argument for the approach you are
> >suggesting and i see nothing wrong with what we did. Let's agree to
> >disagree in order to make progress and get the bug resolved.
> >Please ACK the patch and we can discuss if we need to remove the class
> >ops separately.
>
> I looked a bit deeper into the code, looks like the xarray insertion and
> removal is done in inconvenient place, causing this bug. Moving it into
> tcf_block_get/put_ext() seems much more suiting. See following untested
> patch. It should:
> 1) fix the bug
> 2) make things nicer and easier to read
Sigh. Your stubbornness is overwhelming. Sure, let's move forward -
send an official patch but please make sure all tdc tests pass then
we'll do the testing. Please dont see this as a sign that i think your
patch is better - i am agreeing to move forward so we can make
progress.
cheers,
jamal
> 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;
> + }
> + }
> +
> *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:
> @@ -1502,8 +1512,12 @@ EXPORT_SYMBOL(tcf_block_get);
> void tcf_block_put_ext(struct tcf_block *block, struct Qdisc *q,
> struct tcf_block_ext_info *ei)
> {
> + struct net_device *dev = qdisc_dev(q);
> +
> if (!block)
> return;
> + if (tcf_block_shared(block))
> + xa_erase(&block->ports, dev->ifindex);
> tcf_chain0_head_change_cb_del(block, ei);
> tcf_block_owner_del(block, q, ei->binder_type);
>
> diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
> index 299086bb6205..e9eaf637220e 100644
> --- a/net/sched/sch_api.c
> +++ b/net/sched/sch_api.c
> @@ -1180,43 +1180,6 @@ static int qdisc_graft(struct net_device *dev, struct Qdisc *parent,
> return 0;
> }
>
> -static int qdisc_block_add_dev(struct Qdisc *sch, struct net_device *dev,
> - struct netlink_ext_ack *extack)
> -{
> - const struct Qdisc_class_ops *cl_ops = sch->ops->cl_ops;
> - struct tcf_block *block;
> - int err;
> -
> - block = cl_ops->tcf_block(sch, TC_H_MIN_INGRESS, NULL);
> - if (block) {
> - err = xa_insert(&block->ports, dev->ifindex, dev, GFP_KERNEL);
> - if (err) {
> - NL_SET_ERR_MSG(extack,
> - "ingress block dev insert failed");
> - return err;
> - }
> - }
> -
> - block = cl_ops->tcf_block(sch, TC_H_MIN_EGRESS, NULL);
> - if (block) {
> - err = xa_insert(&block->ports, dev->ifindex, dev, GFP_KERNEL);
> - if (err) {
> - NL_SET_ERR_MSG(extack,
> - "Egress block dev insert failed");
> - goto err_out;
> - }
> - }
> -
> - return 0;
> -
> -err_out:
> - block = cl_ops->tcf_block(sch, TC_H_MIN_INGRESS, NULL);
> - if (block)
> - xa_erase(&block->ports, dev->ifindex);
> -
> - return err;
> -}
> -
> static int qdisc_block_indexes_set(struct Qdisc *sch, struct nlattr **tca,
> struct netlink_ext_ack *extack)
> {
> @@ -1387,10 +1350,6 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
> qdisc_hash_add(sch, false);
> trace_qdisc_create(ops, dev, parent);
>
> - err = qdisc_block_add_dev(sch, dev, extack);
> - if (err)
> - goto err_out4;
> -
> return sch;
>
> err_out4:
> diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
> index e33568df97a5..9b3e9262040b 100644
> --- a/net/sched/sch_generic.c
> +++ b/net/sched/sch_generic.c
> @@ -1052,8 +1052,6 @@ static void __qdisc_destroy(struct Qdisc *qdisc)
> {
> const struct Qdisc_ops *ops = qdisc->ops;
> struct net_device *dev = qdisc_dev(qdisc);
> - const struct Qdisc_class_ops *cops;
> - struct tcf_block *block;
>
> #ifdef CONFIG_NET_SCHED
> qdisc_hash_del(qdisc);
> @@ -1064,18 +1062,6 @@ static void __qdisc_destroy(struct Qdisc *qdisc)
>
> qdisc_reset(qdisc);
>
> - cops = ops->cl_ops;
> - if (ops->ingress_block_get) {
> - block = cops->tcf_block(qdisc, TC_H_MIN_INGRESS, NULL);
> - if (block)
> - xa_erase(&block->ports, dev->ifindex);
> - }
> -
> - if (ops->egress_block_get) {
> - block = cops->tcf_block(qdisc, TC_H_MIN_EGRESS, NULL);
> - if (block)
> - xa_erase(&block->ports, dev->ifindex);
> - }
>
> if (ops->destroy)
> ops->destroy(qdisc);
> diff --git a/net/sched/sch_ingress.c b/net/sched/sch_ingress.c
> index 5fa9eaa79bfc..1770083052cd 100644
> --- a/net/sched/sch_ingress.c
> +++ b/net/sched/sch_ingress.c
> @@ -284,7 +284,8 @@ static int clsact_init(struct Qdisc *sch, struct nlattr *opt,
> q->egress_block_info.chain_head_change = clsact_chain_head_change;
> q->egress_block_info.chain_head_change_priv = &q->miniqp_egress;
>
> - return tcf_block_get_ext(&q->egress_block, sch, &q->egress_block_info, extack);
> + return tcf_block_get_ext(&q->egress_block, sch, &q->egress_block_info,
> + extack);
> }
>
> static void clsact_destroy(struct Qdisc *sch)
>
>
> If you don't mind, I would test this and send it instead of your fix. If
> you can test it too, that would be awesome.
>
> Thanks!
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