netdev - Re: sock_create_kern() and network namespace reference counts

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Date:   Tue, 31 Jan 2017 09:37:46 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: sock_create_kern() and network namespace reference counts

On Tue, Jan 31, 2017 at 7:41 AM, David Laight <David.Laight@...lab.com> wrote:
> Commit 26abe1437 changed sock_create_kern() so that it stopped
> holding a reference to the network namespace.
> The rational seemed to be 'to allow to stop it' (presumably 'be deleted').
> Prior to this change some kernel paths used sk_change_net() (etc) to
> change the namespace after the socket was created.
>
> If the socket doesn't hold a reference to the namespace, what actually
> happens when the namespace is deleted?

Kernel socket should have the same lifetime with the net namespace,
that is, created in net_init and released in net_exit. Think about it, if it
really held a refcnt to this netns, how could this netns be teared down?