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

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Message-ID: <20170811203246.GA32076@breakpoint.cc>
Date:   Fri, 11 Aug 2017 22:32:46 +0200
From:   Florian Westphal <fw@...len.de>
To:     Cong Wang <xiyou.wangcong@...il.com>
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()

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).