Subject: Re: [net-next,1/3] bonding: fix vlan 0 addition and removal

From: Veaceslav Falico <[email-masked]>
Date: Tue, 6 Aug 2013 10:59:41 +0200

On Tue, Aug 06, 2013 at 10:39:22AM +0200, Nikolay Aleksandrov wrote:
>> From 1c89abefebe90568ed52d2df59fcfdd650bc4696 Mon Sep 17 00:00:00 2001
>> From: Veaceslav Falico <[email-masked]>
>> Date: Mon, 5 Aug 2013 23:29:12 +0200
>> Subject: [PATCH] bonding: add vlan_uses_dev_rcu() and make bond_vlan_used()
>> use it
>>
>> Currently, bond_vlan_used() looks for any vlan, including the pseudo-vlan
>> id 0, and always returns true if 8021q is loaded. This creates several bad
>> situations - some warnings in __bond_release_one() because it thinks that
>> we still have vlans while removing, sending LB packets with vlan id 0 and,
>> possibly, other caused by vlan id 0.
>>
>> Fix it by adding a new call, vlan_uses_dev_rcu(), which is the same as
>> vlan_uses_dev(), but uses rcu_dereference() instead of rtnl, and thus we
>> can use it in bond_vlan_used() wrapped in rcu_read_lock().
>>
>> Also, use the pure vlan_uses_dev() in __bond_release_one() cause the rtnl
>> lock is held there.
>>
>Just 1 more note, you can't trust nr_vlan_devs under RCU.

Yes, you're right, however we actually don't care anyway if we race with
(un)register_vlan_dev() - we'll end up either in using the (un)registered
vlan or not, and in both cases it's ok. So I don't see a real problem here,
tbh, though I'll look into this also.