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Date:   Mon, 18 Feb 2019 11:08:15 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Vlad Buslov <vladbu@...lanox.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH net-next 01/12] net: sched: flower: don't check for rtnl
 on head dereference

On Wed, Feb 13, 2019 at 11:47 PM Vlad Buslov <vladbu@...lanox.com> wrote:
>
> Flower classifier only changes root pointer during init and destroy. Cls
> API implements reference counting for tcf_proto, so there is no danger of
> concurrent access to tp when it is being destroyed, even without protection
> provided by rtnl lock.

How about atomicity? Refcnt doesn't guarantee atomicity, how do
you make sure two concurrent modifications are atomic?


>
> Implement new function fl_head_dereference() to dereference tp->root
> without checking for rtnl lock. Use it in all flower function that obtain
> head pointer instead of rtnl_dereference().
>

So what lock protects RCU writers after this patch?

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