netdev - Re: [PATCH v2 net-next 10/15] net/sched: make stab available before ops->init() call

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Message-ID: <20230210152058.kvn74av2kyzr2sxq@skbuf>
Date:   Fri, 10 Feb 2023 17:20:58 +0200
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Jacob Keller <jacob.e.keller@...el.com>,
        Gerhard Engleder <gerhard@...leder-embedded.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        intel-wired-lan@...ts.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 net-next 10/15] net/sched: make stab available before
 ops->init() call

On Fri, Feb 10, 2023 at 04:07:42PM +0100, Eric Dumazet wrote:
> On Tue, Feb 7, 2023 at 2:55 PM Vladimir Oltean <vladimir.oltean@....com> wrote:
> > Move it earlier, which nicely seems to simplify the error handling path
> > as well.
> 
> Well... if you say so :)

:)

> If TCA_STAB attribute is malformed, we end up calling ->destroy() on a
> not yet initialized qdisc :/

Right. Sorry, I didn't pay enough attention, and the old structure with
"err_out4" having a "goto err_out3" confused me. Because I was trying to
match the old teardown path with the new (linear) one, I was trying to
keep the order between qdisc_put_stab() and ops->destroy(). But I forgot
that I need to *reverse* it, since I reversed their order in the setup
path :-/

> I am going to send the following fix, unless someone disagrees.
> 
> (Moving qdisc_put_stab() _after_ ops->destroy(sch) is not strictly
> needed for a fix,
> but undo should be done in reverse steps for clarity.

Right, and it's a net-next patch, so a larger fix which brings the code
into shape should be fine.

> 
> diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
> index e9780631b5b58202068e20c42ccf1197eac2194c..aba789c30a2eb50d339b8a888495b794825e1775
> 100644
> --- a/net/sched/sch_api.c
> +++ b/net/sched/sch_api.c
> @@ -1286,7 +1286,7 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
>                 stab = qdisc_get_stab(tca[TCA_STAB], extack);
>                 if (IS_ERR(stab)) {
>                         err = PTR_ERR(stab);
> -                       goto err_out4;
> +                       goto err_out3;
>                 }
>                 rcu_assign_pointer(sch->stab, stab);
>         }
> @@ -1294,14 +1294,14 @@ static struct Qdisc *qdisc_create(struct
> net_device *dev,
>         if (ops->init) {
>                 err = ops->init(sch, tca[TCA_OPTIONS], extack);
>                 if (err != 0)
> -                       goto err_out5;
> +                       goto err_out4;
>         }
> 
>         if (tca[TCA_RATE]) {
>                 err = -EOPNOTSUPP;
>                 if (sch->flags & TCQ_F_MQROOT) {
>                         NL_SET_ERR_MSG(extack, "Cannot attach rate
> estimator to a multi-queue root qdisc");
> -                       goto err_out5;
> +                       goto err_out4;
>                 }
> 
>                 err = gen_new_estimator(&sch->bstats,
> @@ -1312,7 +1312,7 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
>                                         tca[TCA_RATE]);
>                 if (err) {
>                         NL_SET_ERR_MSG(extack, "Failed to generate new
> estimator");
> -                       goto err_out5;
> +                       goto err_out4;
>                 }
>         }
> 
> @@ -1321,12 +1321,13 @@ static struct Qdisc *qdisc_create(struct
> net_device *dev,
> 
>         return sch;
> 
> -err_out5:
> -       qdisc_put_stab(rtnl_dereference(sch->stab));
>  err_out4:
> -       /* ops->init() failed, we call ->destroy() like qdisc_create_dflt() */
> +       /* Even if ops->init() failed, we call ops->destroy()
> +        * like qdisc_create_dflt().
> +        */
>         if (ops->destroy)
>                 ops->destroy(sch);
> +       qdisc_put_stab(rtnl_dereference(sch->stab));
>  err_out3:
>         netdev_put(dev, &sch->dev_tracker);
>         qdisc_free(sch);

I applied the changes from this patch manually, and the result looks good.
Thanks (and sorry)!