linux-kernel - Re: [PATCH net 6/6] net/sched: qdisc_destroy() old ingress and clsact Qdiscs before grafting

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Date:   Tue, 16 May 2023 14:50:10 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vlad Buslov <vladbu@...dia.com>
Cc:     Peilin Ye <yepeilin.cs@...il.com>, Jiri Pirko <jiri@...nulli.us>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        "Jamal Hadi Salim" <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        "Peilin Ye" <peilin.ye@...edance.com>,
        John Fastabend <john.fastabend@...il.com>,
        Pedro Tammela <pctammela@...atatu.com>,
        Hillf Danton <hdanton@...a.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Cong Wang <cong.wang@...edance.com>
Subject: Re: [PATCH net 6/6] net/sched: qdisc_destroy() old ingress and
 clsact Qdiscs before grafting

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?