netdev - Re: [Patch net-next] audit: remove useless synchronize

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Message-ID: <CAM_iQpW1Dt-HKW6fyx_k8E_K8BfAjCqDnw5ud7qVtAWmQ+GviA@mail.gmail.com>
Date:   Wed, 30 Nov 2016 09:20:04 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Richard Guy Briggs <rgb@...hat.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        linux-audit@...hat.com, Paul Moore <pmoore@...hat.com>
Subject: Re: [Patch net-next] audit: remove useless synchronize_net()

On Wed, Nov 30, 2016 at 1:16 AM, Richard Guy Briggs <rgb@...hat.com> wrote:
> On 2016-11-29 09:14, Cong Wang wrote:
>> netlink kernel socket is protected by refcount, not RCU.
>> Its rcv path is neither protected by RCU. So the synchronize_net()
>> is just pointless.
>
> If I understand correctly, xfrm_user_net_exit() usage of
> RCU_INIT_POINTER() and synchronize_net() is similarly pointless?  Also
> net/phonet/socket.c?  I probably modelled things based on the former...

Possibly, but xfrm case is slightly different, it has two copies of the pointer
to the netlink socket, also it uses exit_batch(). I need to double check.

Take a look at better examples, fib_front, genetlink, rtnetlink.