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

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Message-Id: <20150504.145815.2274500932397440771.davem@davemloft.net>
Date:	Mon, 04 May 2015 14:58:15 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	vyasevich@...il.com
Cc:	netdev@...r.kernel.org, jpirko@...hat.com, vfalico@...il.com,
	vyasevic@...hat.com
Subject: Re: [PATCH] core: Correct an over-stringent device loop detection.

From: Vladislav Yasevich <vyasevich@...il.com>
Date: Sat,  2 May 2015 21:33:44 -0400

> 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>

Applied, thanks Vlad.
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