netdev - Re: [PATCH net-next] net: sched: action_ife: take reference to meta module

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Message-ID: <CAM_iQpWr-jXGZ_FEHN7yZ77K0CHWvojDRKzuD9y6h70-Q0BM6g@mail.gmail.com>
Date:   Mon, 3 Sep 2018 10:03:40 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Vlad Buslov <vladbu@...lanox.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH net-next] net: sched: action_ife: take reference to meta module

On Mon, Sep 3, 2018 at 12:10 AM Vlad Buslov <vladbu@...lanox.com> wrote:
>
> Recent refactoring of add_metainfo() caused use_all_metadata() to add
> metainfo to ife action metalist without taking reference to module. This
> causes warning in module_put called from ife action cleanup function.
>
> Implement add_metainfo_and_get_ops() function that returns with reference
> to module taken if metainfo was added successfully, and call it from
> use_all_metadata(), instead of calling __add_metainfo() directly.

Good catch!

I thought every entry in ifeoplist must hold a refcnt to its module, looks
like I was wrong.


>         read_lock(&ife_mod_lock);
>         list_for_each_entry(o, &ifeoplist, list) {
> -               rc = __add_metainfo(o, ife, o->metaid, NULL, 0, true, exists);
> +               rc = add_metainfo_and_get_ops(o, ife, o->metaid, NULL, 0, true,
> +                                             exists);
>                 if (rc == 0)
>                         installed += 1;

I am afraid you have to rollback on failure inside this loop, that is,
releasing all previous module refcnt properly on error.