Re: [PATCH net] ip[6]: don't register inet[6]dev when dev is down

On Fri, Jul 7, 2017 at 5:39 AM, Nicolas Dichtel
[off-list ref] wrote:

Le 06/07/2017 à 20:16, Cong Wang a écrit :

quoted

On Thu, Jul 6, 2017 at 5:08 AM, Nicolas Dichtel
[off-list ref] wrote:

quoted

Le 06/07/2017 à 00:43, Cong Wang a écrit :

quoted

On Wed, Jul 5, 2017 at 8:57 AM, Nicolas Dichtel
[off-list ref] wrote:

quoted

When a device changes from one netns to another, it's first unregistered,
then the netns reference is updated and the dev is registered in the new
netns. Thus, when a slave moves to another netns, it is first
unregistered. This triggers a NETDEV_UNREGISTER event which is caught by
the bonding driver. The driver calls bond_release(), which calls
dev_set_mtu() and thus triggers NETDEV_CHANGEMTU (the device is still in
the old netns).

I think in this special case it is meaningless to send
NETDEV_CHANGEMTU, because the device is dying within
its old netns, who still cares about its mtu change?

Something like the attached patch...

Yes, your patch seems good and I hesitated with something like this.
But I don't see a valid case where the inet[6]dev must be created on a down
interface. I think the patch is valid, even with your patch.

Your patch is more risky because it affects normal CHANGEMTU path,
I am not sure if it is correct to not to add idev when it is down either.

Why would it be needed to add this idev on a down interface?
If idev wasn't there I don't see why changing the mtu would justify to create
this idev.

There must be a reason to check idev->if_flags & IF_READY instead
of IFF_UP.

quoted

This is a very unusual path, we don't have to take the risk.

I still think that this approach is better for two reasons:
 - we don't know if another path like this exists (need an audit) and it would
be easy to add one again by side effect in the future;

Perhaps we need to add a warning for these events triggered after
UNREGISTER, except UNREGISTER_FINAL, in case of trouble.
But again, the CHANGEMTU case is so special because of the
idev.

 - the patch is easy to backport in older kernel.

Easy to backport doesn't mean easy to verify. ;) As David said, this
code is mess, especially for the keep_addr_on_down logic.