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Date: Wed, 2 Sep 2020 16:14:48 +0800 From: Yunsheng Lin <linyunsheng@...wei.com> To: Eric Dumazet <eric.dumazet@...il.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 2020/9/2 15:32, Eric Dumazet wrote: > > > 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() That is a good point. Do we allow skb left in qdisc when the qdisc is deactivated state? And qdisc_destroy() is not always called after qdisc_deactivate() is called. If we allow skb left in qdisc when the qdisc is deactivated state, then it is huge change of semantics for qdisc_deactivate(), and I am not sure how many cases will affected by this change. > > >
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