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SubjectRe: [PATCH net RESEND] vlan: don't allow to add VLAN on VLAN device
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On Thu, 2014-02-27 at 19:45 -0800, John Fastabend wrote:
> 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@huawei.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.

I don't think there's any deadlock possible here. We try to acquire the
addr_list_lock for eth2.20, then the addr_list_lock for eth2. We never
try to acquire them in the opposite order. The fix would involve
telling lockdep about lock ordering between stacked net_devices (I have
no idea how that's done).

Ben.

--
Ben Hutchings
For every complex problem
there is a solution that is simple, neat, and wrong.
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