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From:   Vlad Buslov <vladbu@nvidia.com>
To:     Jakub Kicinski <kuba@kernel.org>
CC:     Peilin Ye <yepeilin.cs@gmail.com>, Jiri Pirko <jiri@resnulli.us>,
        "Daniel Borkmann" <daniel@iogearbox.net>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Paolo Abeni <pabeni@redhat.com>,
        "Jamal Hadi Salim" <jhs@mojatatu.com>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        "Peilin Ye" <peilin.ye@bytedance.com>,
        John Fastabend <john.fastabend@gmail.com>,
        Pedro Tammela <pctammela@mojatatu.com>,
        Hillf Danton <hdanton@sina.com>, <netdev@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, Cong Wang <cong.wang@bytedance.com>
Subject: Re: [PATCH net 6/6] net/sched: qdisc_destroy() old ingress and
 clsact Qdiscs before grafting
Date:   Wed, 17 May 2023 11:49:10 +0300
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On Tue 16 May 2023 at 17:39, Jakub Kicinski <kuba@kernel.org> wrote:
> On Tue, 16 May 2023 15:58:46 -0700 Peilin Ye wrote:
>> > Given Peilin's investigation I think fix without changing core may
>> > indeed be hard. I'm not sure if returning -EBUSY when qdisc refcnt
>> > is elevated will be appreciated by the users, do we already have
>> > similar behavior in other parts of TC?  
>> 
>> Seems like trying to delete an "in-use" cls_u32 filter returns -EBUSY
>
> I meant -EBUSY due to a race (another operation being in flight).
> I think that's different.

I wonder if somehow leveraging existing tc_modify_qdisc() 'replay'
functionality instead of returning error to the user would be a better
approach? Currently the function is replayed when qdisc_create() returns
EAGAIN. It should be trivial to do the same for qdisc_graft() result.