Re: [PATCH] core: Correct an over-stringent device loop detection.

[Jiri Pirko <jiri@resnulli.us>]

Sun, May 03, 2015 at 03:33:44AM CEST, vyasevich@gmail.com wrote:
>The code in __netdev_upper_dev_link() has an over-stringent
>loop detection logic that actually prevents valid configurations
>from working correctly.
>
>In particular, the logic returns an error if an upper device
>is already in the list of all upper devices for a given dev.
>This particular check seems to be a overzealous as it disallows
>perfectly valid configurations.  For example:
>  # ip l a link eth0 name eth0.10 type vlan id 10
>  # ip l a dev br0 typ bridge
>  # ip l s eth0.10 master br0
>  # ip l s eth0 master br0  <--- Will fail
>
>If you switch the last two commands (add eth0 first), then both
>will succeed.  If after that, you remove eth0 and try to re-add
>it, it will fail!
>
>It appears to be enough to simply check adj_list to keeps things
>safe.
>
>I've tried stacking multiple devices multiple times in all different
>combinations, and either rx_handler registration prevented the stacking
>of the device linking cought the error.
>
>Signed-off-by: Vladislav Yasevich <vyasevic@redhat.com>

Acked-by: Jiri Pirko <jiri@resnulli.us>