netdev - Re: [PATCH net v3] net: sched: fix packet stuck problem for lockless qdisc

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Date:   Tue, 13 Apr 2021 11:34:27 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Hillf Danton <hdanton@...a.com>
CC:     Juergen Gross <jgross@...e.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Jiri Kosina <JKosina@...e.com>
Subject: Re: [PATCH net v3] net: sched: fix packet stuck problem for lockless
 qdisc

On 2021/4/13 11:26, Hillf Danton wrote:
> On Tue, 13 Apr 2021 10:56:42 Yunsheng Lin wrote:
>> On 2021/4/13 10:21, Hillf Danton wrote:
>>> On Mon, 12 Apr 2021 20:00:43  Yunsheng Lin wrote:
>>>>
>>>> Yes, the below patch seems to fix the data race described in
>>>> the commit log.
>>>> Then what is the difference between my patch and your patch below:)
>>>
>>> Hehe, this is one of the tough questions over a bounch of weeks.
>>>
>>> If a seqcount can detect the race between skb enqueue and dequeue then we
>>> cant see any excuse for not rolling back to the point without NOLOCK.
>>
>> I am not sure I understood what you meant above.
>>
>> As my understanding, the below patch is essentially the same as
>> your previous patch, the only difference I see is it uses qdisc->pad
>> instead of __QDISC_STATE_NEED_RESCHEDULE.
>>
>> So instead of proposing another patch, it would be better if you
>> comment on my patch, and make improvement upon that.
>>
> Happy to do that after you show how it helps revert NOLOCK.

Actually I am not going to revert NOLOCK, but add optimization
to it if the patch fixes the packet stuck problem.

Is there any reason why you want to revert it?

> 
> .
>