netdev - Re: [Patch net] net_sched: fix a missing rcu barrier in mini_qdisc_pair

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Date:   Fri, 22 Dec 2017 10:38:06 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jiri Pirko <jiri@...lanox.com>,
        John Fastabend <john.fastabend@...il.com>
Subject: Re: [Patch net] net_sched: fix a missing rcu barrier in
 mini_qdisc_pair_swap()

Thu, Dec 21, 2017 at 09:54:06PM CET, xiyou.wangcong@...il.com wrote:
>On Thu, Dec 21, 2017 at 11:01 AM, Cong Wang <xiyou.wangcong@...il.com> wrote:
>> On Thu, Dec 21, 2017 at 1:03 AM, Jiri Pirko <jiri@...nulli.us> wrote:
>>>
>>>
>>> But again, we don't we just free qdisc in call_rcu and avoid the
>>> barrier?
>>
>>
>> Non-sense again. Why qdisc code should be adjusted for your
>> miniq code? It is your own responsibility to take care of this shit.
>> Don't spread it out of minq.
>
>Also, in case you believe call_rcu to free qdisc is queued after
>the call_rcu in miniq, you are wrong again:

I certainly don't :) Not sure why you think I do.

>
>https://www.kernel.org/pub/linux/kernel/people/paulmck/Answers/RCU/RCUCBordering.html
>
>The rcu callbacks don't guarantee FIFO ordering.