[Bridge] bridge_list orphans in linux-2.4

Stephen Hemminger shemminger at osdl.org
Thu Sep 21 15:56:29 PDT 2006

On Thu, 21 Sep 2006 14:42:22 +0100
Alex Zeffertt <ajz at cambridgebroadband.com> wrote:

> Hi all,
> We use linux-2.4.20 in one of our products and we've found what looks
> to be a problem in the bridge module.  (I know this is old code but we
> don't send our customers kernel upgrades unless we really have to!)
> The problem is that some of our bridges have become orphaned from the
> bridge module.  Specifically
> 	ifconfig ourbridgename
> shows that the device "ourbridgename" is known to the kernel, but
> 	brctl show
> does not list "ourbridgename".

You need to find a sequence of commands that reproduces it.
Unless you run multiple commands in parallel, I don't think
there should be a problem with 2.4.

> I've looked through the bridge module and it seems that the most likely
> explanation is that bridge_list in br_if.c has become corrupted, causing
> the bridge called "ourbridgename" to become orphaned.
> I cannot see how this would happen, however, since bridge_list is only
> ever referenced under the ioctl_mutex.  I should also point out that
> br_del_bridge() is not called by our application.
> I noticed that in later kernels the ioctl_mutex has been replaced by
> the rtnl_lock().  Why was this done?  Could this be related to our
> problem?

In 2.6 it was observed that all changes to bridge list were already
being done under the RT netlink mutex, so no additional locking
was needed.

Stephen Hemminger <shemminger at osdl.org>

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