netdev - Re: [PATCH net] Panic when tc_lookup_action_n finds a partially initialized action.

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Date:   Tue, 11 Oct 2016 10:36:21 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Krister Johansen <kjlx@...pleofstupid.com>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net] Panic when tc_lookup_action_n finds a partially
 initialized action.

On Sat, Oct 8, 2016 at 11:13 PM, Krister Johansen
<kjlx@...pleofstupid.com> wrote:
> Hi Cong,
> Thanks for the follow-up.
>
> On Thu, Oct 06, 2016 at 12:01:15PM -0700, Cong Wang wrote:
>> On Wed, Oct 5, 2016 at 11:11 PM, Krister Johansen
>> > pernet_operations pointer.  The code in register_pernet_subsys() makes
>> > no attempt to check for duplicates.  If we add a pointer that's already
>> > in the list, and subsequently call unregister, the results seem
>> > undefined.  It looks like we'll remove the pernet_operations for the
>> > existing action, assuming we don't corrupt the list in the process.
>> >
>> > Is this actually safe?  If so, what corner case is the act->type /
>> > act->kind protecting us from?
>>
>> ops->type and ops->kind should be unique too, user-space already
>> relies on this (tc action ls action xxx). The code exists probably just
>> for sanity check.
>
> With that in mind, would it make sense to change the check to a WARN/BUG
> or some kind of assertion?  I mistakenly inferred that it was possible to
> legtimately end up in this scenario.


Yes, it makes sense to me.


>> > Part of the desire to inhibit extra modprobe calls is that if hundreds
>> > of these all start at once on boot, it's really unnecessary to have all
>> > of the rest of them wait while lots of extra modprobe calls are forked
>> > by the kernel.
>>
>> You can tell systemd to load these modules before starting these
>> containers to avoid blocking, no?
>
> That was exactly what I did to work around the panic until I was able to
> get a patch together.  The preload of the modules is still occurring,
> but I was hoping to excise that workaround entirely.

Or you can compile these modules into kernel, but I am not sure about
the dependencies. :-D

Thanks.