Re: [PATCH nf-next] netns: add and use net_ns_barrier

[Cong Wang <xiyou.wangcong@gmail.com>]

On Mon, Jun 12, 2017 at 11:16 PM, Florian Westphal <fw@strlen.de> wrote:
> Cong Wang <xiyou.wangcong@gmail.com> wrote:
>> On Thu, Jun 1, 2017 at 1:52 AM, Florian Westphal <fw@strlen.de> wrote:
>> > Joe described it nicely, problem is that after unload we may have
>> > conntracks that still have a nf_conn_help extension attached that
>> > has a pointer to a structure that resided in the (unloaded) module.
>>
>> Why not hold a refcnt for its module?
>
> That would work as well.
>
> I'm not sure its nice to disallow rmmod of helper modules if they are
> used by a connection however.

I am _not_ suggesting to disallow rmmod.

>
> Right now you can "rmmod nf_conntrack_foo" at any time and this should
> work just fine without first having to flush affected conntracks
> manually.

My point is that since netns wq could invoke code of that module,
why it doesn't hold a refcnt of that module?

I am not familiar with netfilter code base so not sure if that is
hard to do or not, but it looks more elegant than this barrier.