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

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Date:   Fri, 11 Aug 2017 23:36:45 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     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 11.08.2017 23:18, Cong Wang 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.
> 

For example in hfsc_destroy_qdisc() since a4aebb83cf0da0363684f1c339f7e6149a3e74c1
second time in hfsc_destroy_class() called from it.

Actually, I see the same pattern in all classy qdiscs.