netdev - Re: [Patch net 2/2] net_sched: hold netns refcnt for each action

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Date:   Fri, 3 Nov 2017 18:15:27 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Cc:     Lucas Bates <lucasb@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [Patch net 2/2] net_sched: hold netns refcnt for each action

On Wed, Nov 1, 2017 at 10:23 AM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> TC actions have been destroyed asynchronously for a long time,
> previously in a RCU callback and now in a workqueue. If we
> don't hold a refcnt for its netns, we could use the per netns
> data structure, struct tcf_idrinfo, after it has been freed by
> netns workqueue.
>
> Hold refcnt to ensure netns destroy happens after all actions
> are gone.

This in fact is wrong. If we hold that refcnt, the netns can never
be destroyed until all actions are destroyed by user, this breaks
our netns design.

I am going to send a revert and a right way to fix it. It is more
complicated that I thought due to all of these flying RCU callbacks
and workqueue again, sigh...

Sorry about it.