Re: [Bridge] unregister_netdevice: waiting for br0 to become free. Usage count = 1 (2.6.12.3)

[Stephen Hemminger <shemminger@osdl.org>]

On Wed, 31 Aug 2005 19:04:01 -0700
Robert Scott <rbscott@axentra.net> wrote:

> Hello,
> 
> I know that this bug has been discussed before at length on this  
> mailing list, but previous post seemed to indicate that it was fixed  
> before kernel 2.6.12.  I am still seeing this occasionally in kernel  
> 2.6.12.3.  The system is running knoppix, and IPV6 is not compiled  
> into the kernel(other posts mentioned numerous problems with the IPV6  
> code).  But every so often, when bringing down the bridge (it doesn't  
> happen every time), the process hangs, and the following message  
> appears in dmesg repeatedly:
> 
> 'unregister_netdevice: waiting for br0 to become free. Usage count = 1'
> 
> None of the processes involved can be killed, and an attempt to run  
> an ifconfig results in a process that is also waiting forever.  At  
> this point the box must be rebooted forcefully.
> 
> Two questions.
> 1. In a previous post, someone mentioned one solution was to  
> commenting out the check that is hanging in the kernel.   Does this  
> check preventing something terrible from happening(i assumed that it  
> does), or is it safe to remove it

Really bad idea, because if the thing that is holding the reference
like packets stuck in some dead queue, ever get processed the kernel
will die.

> 2. Any ideas of something to try in order to make this repeatable?

Two other recent reports are:
1. Buggy applications that hold packets in their input queue forever,
   and/or netfilters.  The socket buffer's contain a reference for
   packets in flight.

2. The VLAN code had a number of reference bugs, if you look through
   recent netdev mailing list you will see the discussion.