On 2014/3/5 8:10, Ben Hutchings wrote:

On Thu, 2014-02-27 at 19:45 -0800, John Fastabend wrote:

quoted

On 2/27/2014 6:43 PM, Ding Tianhong wrote:

quoted

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:

[...]

quoted

========================================================================

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 <redacted>
---

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.

Yep, it is a warning when the lockdep is open, I review the code again, and the deadlock would not happen,
just the same class of locks twice, so I think it is not a bugfix, just like a optimization.

Regards
Ding