netdev - Re: [PATCH net] net: rtnl_register in net_ns_init need rtnl

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Message-ID: <CAM_iQpUsYLWxWvcuVzHt=Q9hRjZ1vKJHWjS6ZKWc0rjdtdOo8w@mail.gmail.com>
Date:   Thu, 22 Sep 2016 10:20:19 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net] net: rtnl_register in net_ns_init need rtnl_lock

On Thu, Sep 22, 2016 at 6:41 AM, Hannes Frederic Sowa
<hannes@...essinduktion.org> wrote:
> On 22.09.2016 15:03, Eric Dumazet wrote:
>> On Thu, 2016-09-22 at 13:03 +0200, Hannes Frederic Sowa wrote:
>>> Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
>>> ---
>>>  net/core/net_namespace.c | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
>>> index 2c2eb1b629b11d..a2ace299f28355 100644
>>> --- a/net/core/net_namespace.c
>>> +++ b/net/core/net_namespace.c
>>> @@ -758,9 +758,11 @@ static int __init net_ns_init(void)
>>>
>>>      register_pernet_subsys(&net_ns_ops);
>>>
>>> +    rtnl_lock();
>>>      rtnl_register(PF_UNSPEC, RTM_NEWNSID, rtnl_net_newid, NULL, NULL);
>>>      rtnl_register(PF_UNSPEC, RTM_GETNSID, rtnl_net_getid, rtnl_net_dumpid,
>>>                    NULL);
>>> +    rtnl_unlock();
>>>
>>>      return 0;
>>>  }
>>
>> Hi Hannes
>>
>> Why is this needed here, and not in other places ?
>
> I found this during working on the file and actually saw no live issues
> (belonged to another series which I just split up).
>
> I don't think it is a big issue but wanted the writes to the
> rtnl_msg_handlers array to be strictly serialized. I was working on
> adding this to other places, too. Maybe better for net-next even?

But they are called during boot, why is it possible to have a parallel
reader/writer at that time?