netdev - Re: [Patch net v2 2/2] net_sched: fix all the madness of tc filter chain

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Date:   Fri, 8 Sep 2017 09:37:55 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jiri Pirko <jiri@...lanox.com>
Subject: Re: [Patch net v2 2/2] net_sched: fix all the madness of tc filter chain

On Thu, Sep 7, 2017 at 1:52 PM, Jiri Pirko <jiri@...nulli.us> wrote:
> Thu, Sep 07, 2017 at 07:45:49PM CEST, xiyou.wangcong@...il.com wrote:
>>Yes it is for chain 0, because block holds a reference to chain 0 during
>>creation. Non-0 chains are created with refcnt==1 too but paired with
>>tcf_chain_put() rather than tcf_block_put(). This is what makes chain 0
>>not special w.r.t. refcnt.
>
> So you need to tcf_chain_put only chain 0 here, right? The rest of the
> chains get destroyed by the previous list_for_each_entry iteration when
> flush happens and actions destroy happens what decrements recnt to 0
> there.


This is correct. And it should be only chain 0 after flush.

>
> What do I miss, who would still hold reference for non-0 chains when all
> tps and all goto_chain actions are gone?

No one. This is totally correct and is exactly what this patch intends to do.

Look, this is why we never need an object with refcnt==0 to exist. ;)