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

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Message-ID: <20150503174632.GA2438@nanopsycho>
Date:	Sun, 3 May 2015 19:46:32 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	Vladislav Yasevich <vyasevich@...il.com>
Cc:	netdev@...r.kernel.org, jpirko@...hat.com, vfalico@...il.com,
	Vladislav Yasevich <vyasevic@...hat.com>
Subject: Re: [PATCH] core: Correct an over-stringent device loop detection.

Sun, May 03, 2015 at 03:33:44AM CEST, vyasevich@...il.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@...hat.com>

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