netdev - Re: [PATCH net-next] net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc

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Date:   Wed, 2 Sep 2020 09:32:48 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Yunsheng Lin <linyunsheng@...wei.com>,
        Cong Wang <xiyou.wangcong@...il.com>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>, Jiri Pirko <jiri@...nulli.us>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, linuxarm@...wei.com
Subject: Re: [PATCH net-next] net: sch_generic: aviod concurrent reset and
 enqueue op for lockless qdisc



On 9/1/20 11:34 PM, Yunsheng Lin wrote:

> 
> I am not familiar with TCQ_F_CAN_BYPASS.
> From my understanding, the problem is that there is no order between
> qdisc enqueuing and qdisc reset.

Thw qdisc_reset() should be done after rcu grace period, when there is guarantee no enqueue is in progress.

qdisc_destroy() already has a qdisc_reset() call, I am not sure why qdisc_deactivate() is also calling qdisc_reset()