netdev - Re: [PATCH net RESEND] vlan: don't allow to add VLAN on VLAN device

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Date:	Thu, 27 Feb 2014 19:45:59 -0800
From:	John Fastabend <john.r.fastabend@...el.com>
To:	Ding Tianhong <dingtianhong@...wei.com>
CC:	Patrick McHardy <kaber@...sh.net>,
	"David S. Miller" <davem@...emloft.net>,
	Netdev <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net RESEND] vlan: don't allow to add VLAN on VLAN device

On 2/27/2014 6:43 PM, Ding Tianhong wrote:
> I run these steps:
>
> modprobe 8021q
> vconfig add eth2 20
> vconfig add eth2.20 20
> ifconfig eth2 xx.xx.xx.xx
>
> then the Call Trace happened:
>

[...]

> ========================================================================
>
> The reason is that if add vlan on vlan dev, the vlan dev will create vlan_info,
> then the notification will let the real dev to run dev_set_rx_mode() and hold
> netif_addr_lock, and then the real dev will call ndo_set_rx_mode(), if the real
> dev is vlan dev, the ndo_set_rx_mode() will hold netif_addr_lock again, so deadlock
> happened.
>
> Don't allow to add vlan on vlan dev to fix this problem.
>
> Signed-off-by: Ding Tianhong <dingtianhong@...wei.com>
> ---

I'm not sure we can just disable stacked vlans. There might be something
using them today and they have worked in the past. Lets try to find a
better fix.

.John
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