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Date:	Sun, 3 May 2015 20:07:54 +0200
From:	Veaceslav Falico <>
To:	Vladislav Yasevich <>
	Vladislav Yasevich <>
Subject: Re: [PATCH] core: Correct an over-stringent device loop detection.

On Sat, May 02, 2015 at 09:33:44PM -0400, Vladislav Yasevich 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
>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 <>

Good catch.

Acked-by: Veaceslav Falico <>

> net/core/dev.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>diff --git a/net/core/dev.c b/net/core/dev.c
>index c7ba038..2c1c67f 100644
>--- a/net/core/dev.c
>+++ b/net/core/dev.c
>@@ -5209,7 +5209,7 @@ static int __netdev_upper_dev_link(struct net_device *dev,
> 	if (__netdev_find_adj(upper_dev, dev, &upper_dev->all_adj_list.upper))
> 		return -EBUSY;
>-	if (__netdev_find_adj(dev, upper_dev, &dev->all_adj_list.upper))
>+	if (__netdev_find_adj(dev, upper_dev, &dev->adj_list.upper))
> 		return -EEXIST;
> 	if (master && netdev_master_upper_dev_get(dev))
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