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Date:   Tue, 16 May 2023 14:50:10 -0700
From:   Jakub Kicinski <kuba@kernel.org>
To:     Vlad Buslov <vladbu@nvidia.com>
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
Message-ID: <20230516145010.67a7fa67@kernel.org>
In-Reply-To: <87y1lojbus.fsf@nvidia.com>
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        <87y1lojbus.fsf@nvidia.com>
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On Tue, 16 May 2023 22:35:51 +0300 Vlad Buslov wrote:
> > Vlad, could you please clarify how you expect the unlocked filter
> > operations to work when the qdisc has global state?  
> 
> Jakub, I didn't account for per-net_device pointer usage by miniqp code
> hence this bug. I didn't comment on the fix because I was away from my
> PC last week but Peilin's approach seems reasonable to me. When Peilin
> brought up the issue initially I also tried to come up with some trick
> to contain the changes to miniqp code instead of changing core but
> couldn't think of anything workable due to the limitations already
> discussed in this thread. I'm open to explore alternative approaches to
> solving this issue, if that is what you suggest.

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?