netdev - Re: Question: Patch:("net: sched: cbq: dont intepret cls results when asked to drop") may be not bug for branch LTS 5.10

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Date:   Tue, 17 Jan 2023 09:03:29 +0800
From:   shaozhengchao <shaozhengchao@...wei.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     <zengyhkyle@...il.com>, David Miller <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        netdev <netdev@...r.kernel.org>,
        YueHaibing <yuehaibing@...wei.com>
Subject: Re: Question: Patch:("net: sched: cbq: dont intepret cls results when
 asked to drop") may be not bug for branch LTS 5.10

+cc netdev@...r.kernel.org yuehaibing

On 2023/1/16 16:27, shaozhengchao wrote:
> When I analyzed the following LTS 5.10 patch, I had a small question:
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.10.y&id=b2c917e510e5ddbc7896329c87d20036c8b82952
> 
> As described in this patch, res is obtained through the tcf_classify()
> interface. If result is TC_ACT_SHOT, res may be an abnormal value.
> Accessing class in res will cause abnormal access.
> 
> For LTS version 5.10, if tcf_classify() is to return a positive value,
> the classify hook function to the filter must be called, and the hook 
> function returns a positive number. Observe the classify function of 
> each filter. Generally, res is initialized in four scenarios.
> 1. res is assigned a value by res in the private member of each filter.
> Generally, kzalloc is used to assign initial values to res of various
> filters. Therefore, class in res is initialized to 0. Then use the
> tcf_bind_filter() interface to assign values to members in res.
> Therefore, value of class is assigned. For example, cls_basic.
> 2. The classify function of the filter directly assigns a value to the
> class of res, for example, cls_cgroup.
> 3. The filter classify function references tp and assigns a value to
> res, for example, cls_u32.
> 4. The change function of the filter references fh and assigns a value
> to class in res, for example, cls_rsvp.
> 
> This Mainline problem is caused by commit:3aa260559455 (" net/sched:
> store the last executed chain also for clsact egress") and
> commit:9410c9409d3e ("net: sched: Introduce ingress classification
> function"). I don't know if my analysis is correct, please help correct, 
> thank you very much.
> 
> Zhengchao Shao