linux-kernel - Re: kernel hangs when trying to remove a bridge

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Message-ID: <20060731112220.0c14d1bc@localhost.localdomain>
Date:	Mon, 31 Jul 2006 11:22:20 -0700
From:	Stephen Hemminger <shemminger@...l.org>
To:	Rodrigo Ventura <yoda@....ist.utl.pt>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: kernel hangs when trying to remove a bridge

On Sat, 29 Jul 2006 16:42:04 +0100
Rodrigo Ventura <yoda@....ist.utl.pt> wrote:

> 
> I'm using kernel 2.6.16 (-gentoo-r13 actually). A bridge iface br0 is setup 
> using eth1 and eth0.1 (VLAN) as slaves. To bring br0, what I do is to remove 
> the slaves from the bridge first, "ip link set dev br0 down" next, followed 
> by the brctl command to remove the bridge. What happens is that it seems it 
> tryes to destroy the bridge iface, and then hangs, with dmesg complaining, 
> periodically, about once a second, something like:
> 
> unregister_netdevice: waiting for br0 to become free. Usage count = 1
> unregister_netdevice: waiting for br0 to become free. Usage count = 1
> unregister_netdevice: waiting for br0 to become free. Usage count = 1
> ...
> 
> I say it partially hangs because commands like ifconfig hang (ps state=Disk 
> busy)...
> To reboot the machine, a HARD reset is required, since, the shutdown process 
> hangs... 
> 

Some broken protocol in the kernel, incremented a refcount but forgot
to cleanup when notified on device removal.

There was a bug in the VLAN code that did that, not sure which version
it was fixed in.

Do you have IPV6 installed (as a module)?
In some kernel versions, IPV6 has a problem with device ref counting, and
leaves a dangling reference.


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