netdev - VLAN creation may lead to deadlock.

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Date:	Fri, 13 Feb 2015 13:02:17 +0100
From:	Ignacy Gawedzki <ignacy.gawedzki@...en-communications.fr>
To:	netdev@...r.kernel.org
Subject: VLAN creation may lead to deadlock.

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.

Regards,

Ignacy

-- 
Ignacy Gawędzki
R&D Engineer
Green Communications
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