netdev - Re: VLAN creation may lead to deadlock.

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Message-ID: <CAHA+R7Nk2SeM-Zga4qzrg_4teBUFmVcS=im1JMmF9CjA2nsjMQ@mail.gmail.com>
Date:	Fri, 13 Feb 2015 11:54:25 -0800
From:	Cong Wang <cwang@...pensource.com>
To:	Ignacy Gawedzki <ignacy.gawedzki@...en-communications.fr>,
	netdev <netdev@...r.kernel.org>
Subject: Re: VLAN creation may lead to deadlock.

On Fri, Feb 13, 2015 at 4:02 AM, Ignacy Gawedzki
<ignacy.gawedzki@...en-communications.fr> wrote:
> Hi,
>
> I stumbled upon the following annoying situation: supposing eth0 is some
> interface that is currently DOWN, the following command
>
>   ip link add link eth0 name eth0.1 up type vlan id 1
>
> never returns and the kernel printks the following lines every few seconds
>
>   unregister_netdevice: waiting for eth0.1 to become free. Usage count = 2
>
> I understand that the kernel should prevent me from creating a VLAN interface
> that's initially up when loose-binding is off and the master interface is down
> (and indeed there is absolutely no problem when loose-binding is on), but the
> unregistering of the currently-being-registered device should not block like
> that.  It appears there are too few dev_puts compared to dev_holds in there.

Good catch! It looks like we forgot to call unregister_vlan_dev(),
I am cooking a patch.
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