netdev - Re: [RFC PATCH net-next 00/11] netns: don't switch namespace while creating kernel sockets

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Message-ID: <87d22a4t8k.fsf@x220.int.ebiederm.org>
Date:	Fri, 08 May 2015 17:08:59 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Cong Wang <cwang@...pensource.com>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	Ying Xue <ying.xue@...driver.com>,
	netdev <netdev@...r.kernel.org>,
	Pavel Emelyanov <xemul@...nvz.org>,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>, maxk@....qualcomm.com,
	Stephen Hemminger <stephen@...workplumber.org>,
	Thomas Graf <tgraf@...g.ch>,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	Tom Herbert <tom@...bertland.com>,
	James Chapman <jchapman@...alix.com>,
	Erik Hugne <erik.hugne@...csson.com>, jon.maloy@...csson.com,
	Simon Horman <horms@...ge.net.au>
Subject: Re: [RFC PATCH net-next 00/11] netns: don't switch namespace while creating kernel sockets

Cong Wang <cwang@...pensource.com> writes:

> On Fri, May 8, 2015 at 1:27 PM, Cong Wang <cwang@...pensource.com> wrote:
>> On Fri, May 8, 2015 at 10:36 AM, Eric W. Biederman
>> <ebiederm@...ssion.com> wrote:
>>>
>>> It really is invalid for a network namespace init routine to grab the
>>> reference count of it's network namespace (thus making the network
>>> namespace unfreeable).  So I am wondering if perhaps all we need to do
>>> is find a clean refactoring of the socket code so this case does not
>>> come up at all.
>>
>>
>> Good point!
>>
>> I _guess_ the reason is these kernel sockets have to exist longer than
>> netns' life-time, it could be due to on-flying skb's?
>>
>> On the other hand, we do create some fb_tunnel netdevice in netns init
>> too, but we don't take a refcnt there, probably because we wait
>> for netdevice refcnt goes to zero when unregistering.
>
> Answer myself, it looks like we don't need to hold the refcnt at all,
> since we create the socket at init and release it at uninit, so they
> should have the same life-time?
>
> The reason why user-space sockets need this refcnt is they
> could have longer life-time than the netns?

User space sockets by design keep the network namespace alive.

> This seems the right direction to solve this problem for me,
> I am going to try this way to see how far I can go. ;)

I will be interested to see what you come up with.

Eric

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