netdev - Re: [PATCH] net/sched: reset block pointer in tcf_block

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Message-ID: <CAM_iQpUoa5vWfQGpqCJ7dXx542uC-5JyNpRK-zukVbq=EfAAEA@mail.gmail.com>
Date:   Fri, 11 Aug 2017 14:06:31 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Florian Westphal <fw@...len.de>
Cc:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jiri Pirko <jiri@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jamal Hadi Salim <jhs@...atatu.com>
Subject: Re: [PATCH] net/sched: reset block pointer in tcf_block_put()

On Fri, Aug 11, 2017 at 1:32 PM, Florian Westphal <fw@...len.de> wrote:
> Cong Wang <xiyou.wangcong@...il.com> wrote:
>> On Thu, Aug 10, 2017 at 2:31 AM, Konstantin Khlebnikov
>> <khlebnikov@...dex-team.ru> wrote:
>> > In previous API tcf_destroy_chain() could be called several times and
>> > some schedulers like hfsc and atm use that. In new API tcf_block_put()
>> > frees block but leaves stale pointer, second call will free it once again.
>>
>> Which call path do we call tcf_block_put() for multiple times on
>> the same block? Please be specific, it is not obvious.
>
> you can use tools/testing/selftests/net/rtnetlink.sh to reproduce this
> (kernel panics on delete of root qdisc).

I am sure this is not how changelog works. We have enough space
in changelog to describe a bug, don't have to leave details in a
following-up email which will almost surely be lost in history.