netdev - Re: [PATCH v3 net-next] net: vxlan: when lower dev unregisters remove vxlan dev as well

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Date:	Sat, 11 Jan 2014 11:03:59 -0800
From:	Cong Wang <cwang@...pensource.com>
To:	Daniel Borkmann <dborkman@...hat.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH v3 net-next] net: vxlan: when lower dev unregisters remove
 vxlan dev as well

On Sat, Jan 11, 2014 at 12:46 AM, Daniel Borkmann <dborkman@...hat.com> wrote:
> On 01/11/2014 01:49 AM, Cong Wang wrote:
>>
>> On Fri, Jan 10, 2014 at 2:35 PM, Daniel Borkmann <dborkman@...hat.com>
>> wrote:
>>>
>>> @@ -2673,13 +2712,14 @@ static __net_init int vxlan_init_net(struct net
>>> *net)
>>>   static __net_exit void vxlan_exit_net(struct net *net)
>>>   {
>>>          struct vxlan_net *vn = net_generic(net, vxlan_net_id);
>>> -       struct vxlan_dev *vxlan;
>>> -       LIST_HEAD(list);
>>> +       struct vxlan_dev *vxlan, *next;
>>> +       LIST_HEAD(list_kill);
>>>
>>>          rtnl_lock();
>>> -       list_for_each_entry(vxlan, &vn->vxlan_list, next)
>>> -               unregister_netdevice_queue(vxlan->dev, &list);
>>> -       unregister_netdevice_many(&list);
>>> +       list_for_each_entry_safe(vxlan, next, &vn->vxlan_list, next)
>>> +               vxlan_dellink(vxlan->dev, &list_kill);
>>> +       unregister_netdevice_many(&list_kill);
>>> +       list_del(&list_kill);
>>
>>
>> The last list_del() looks suspicous... Since list_kill is a local list
>> head,
>> why do we need to delete the head at the end??
>
>
> Cong, maybe I'm missing something, but we're doing this rtnl_dellink()
> and elsewehere, e.g. commit 226bd341147 ("net: use batched device unregister
> in veth and macvlan").

list_kill is a list *head* (not a node) on stack. unregister_netdevice_many()
should remove all the nodes in this list after it finishes. So, list_kill is
supposed to be empty after that.

Either unregister_netdevice_many() is mis-designed, i.e. it is not like what I
said above, or list_del() is completely unnecessary.

BTW, there are many places calling unregister_netdevice_many() without
a following list_del(). For example, bond_net_exit().
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