netdev - Re: [PATCH net] net_sched: act_mirred: full rcu conversion

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Message-ID: <CAM_iQpXycdn9_LW_qYzUe5T97ABOj3KrivjCB5ho9wbKeFR0MQ@mail.gmail.com>
Date:   Sun, 11 Sep 2016 23:12:04 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Hadar Hen Zion <hadarh@...lanox.com>,
        Amir Vadai <amirva@...lanox.com>
Subject: Re: [PATCH net] net_sched: act_mirred: full rcu conversion

On Fri, Sep 9, 2016 at 8:52 AM, John Fastabend <john.fastabend@...il.com> wrote:
> On 16-09-08 10:26 PM, Cong Wang wrote:
>> On Thu, Sep 8, 2016 at 8:51 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>>> On Thu, 2016-09-08 at 08:47 -0700, John Fastabend wrote:
>>>
>>>> Works for me. FWIW I find this plenty straightforward and don't really
>>>> see the need to make the hash table itself rcu friendly.
>>>>
>>>> Acked-by: John Fastabend <john.r.fastabend@...el.com>
>>>>
>>>
>>> Yes, it seems this hash table is used in control path, with RTNL held
>>> anyway.
>>
>> Seriously? You never read hashtable in fast path?? I think you need
>> to wake up.
>>
>
> But the actions use refcnt'ing and should never be decremented to zero
> as long as they can still be referenced by an active filter. If each
> action handles its parameters like mirred/gact then I don't see why its
> necessary.

This is correct, by "read" I meant "dereference", the tc actions
are now permanently stored in hashtable directly, so "reading"
a tc action is reading from hashtable.

Sorry if this wasn't clear.