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

Ben Greear greearb at candelatech.com
Wed Aug 31 21:26:27 PDT 2005

Robert Scott 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  
>  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'

I have found an appearant leak of a route object, which holds a reference
to a device.  I reproduced in both 2.6.11 and 2.6.13 using 802.1Q VLANs.
I have a patch that will print out the place of the leaked reference
against 2.6.13.


Enable the feature in the Networking section of Kconfig.

If you can reproduce with this patch in place, you will get a file and line number
for the leak..please CC me.  I'm going to try to debug the leak, but I
could definately use some help...

> 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.

This would be bad...could lead to memory corruption.

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

I have a complex application with a complex script to drive it that reproduces
the problem within an hour...I haven't found a simpler way....


Ben Greear <greearb at candelatech.com>
Candela Technologies Inc  http://www.candelatech.com

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