Linux Ethernet Bridging - Apr 2011 - [Bridge] [PATCH] bridge: Module use count must be updated as bridges are created/destroyed

Otherwise 'modprobe -r' on a module having a dependency on bridge will
implicitly unload bridge, bringing down all connectivity that was using
bridges.

Signed-off-by: Jan Beulich <jbeulich at novell.com>
Cc: Jeff Mahoney <jeffm at suse.com>

---
 net/bridge/br_if.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- 2.6.39-rc5/net/bridge/br_if.c
+++ 2.6.39-rc5-bridge-module-get-put/net/bridge/br_if.c
@@ -290,6 +290,11 @@ int br_add_bridge(struct net *net, const
 	if (!dev)
 		return -ENOMEM;
 
+	if (!try_module_get(THIS_MODULE)) {
+		free_netdev(dev);
+		return -ENOENT;
+	}
+
 	rtnl_lock();
 	if (strchr(dev->name, '%')) {
 		ret = dev_alloc_name(dev, dev->name);
@@ -308,6 +313,8 @@ int br_add_bridge(struct net *net, const
 		unregister_netdevice(dev);
  out:
 	rtnl_unlock();
+	if (ret)
+		module_put(THIS_MODULE);
 	return ret;
 
 out_free:
@@ -339,6 +346,8 @@ int br_del_bridge(struct net *net, const
 		del_br(netdev_priv(dev), NULL);
 
 	rtnl_unlock();
+	if (ret == 0)
+		module_put(THIS_MODULE);
 	return ret;
 }

From: "Jan Beulich" <JBeulich at novell.com>
Date: Fri, 29 Apr 2011 08:21:14 +0100
> Otherwise 'modprobe -r' on a module having a dependency on bridge
will
> implicitly unload bridge, bringing down all connectivity that was using
> bridges.
> 
> Signed-off-by: Jan Beulich <jbeulich at novell.com>
> Cc: Jeff Mahoney <jeffm at suse.com>
All network device drivers behave exactly the same way, when you rmmod
the thing we unconfigure all the routes, addresses, etc. going through
that device and let you unload it.

And this behavior is very much intentional.

Don't add an exception here.

>>> On 29.04.11 at 10:10, David Miller <davem at davemloft.net>
wrote:
> From: "Jan Beulich" <JBeulich at novell.com>
> Date: Fri, 29 Apr 2011 08:41:10 +0100
> 
>> You talk of rmmod on the very module, but the issue is about
>> modprobe -r on a dependent module. I cannot believe you consider
>> it correct that *implicit* unloading of bridge.ko should happen when
>> bridges are configured.
> 
> Which module in particular depends upon bridge and causes the
> problem?
The problem was observed (a long time ago) with ebtable_broute,
and I cannot see how this would have changed meanwhile.

Jan