Re: [BUG][PATCH] Fix race condition about network device name allocation

Stephen Hemminger
2007-05-14T15:42:20Z

On Mon, 14 May 2007 10:33:01 +0900
Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com> wrote:

> Hi Stephen,
>
> Thank you for comments. I'll try your patch.
>
> I have one concern about your patch, though I don't know very much
> about netdev codes.
>
> @@ -3411,6 +3410,9 @@ void unregister_netdevice(struct net_dev
> > /* Notifier chain MUST detach us from master device. */
> > BUG_TRAP(!dev->master);
> >
> > + /* Remove entries from sysfs */
> > + netdev_unregister_sysfs(dev);
> > +
> > /* Finish processing unregister after unlock */
> > net_set_todo(dev);
> >
>
> With your patch, the netdev_unregister_sysfs() will be called
> earlier than now. Does it have no side effect? I'm worrying
> about if there are somebody that depend on sysfs entry until
> net_run_todo() is called.

The unregister_sysfs() removes the entry in /sys/class/net and then
decrements the reference count. When ref count goes to zero, the kobject_release
callback gets called and which does kfree().

Changing the shutdown order makes the /sys/class/net entry disappear
sooner. In order to prevent the free from happening until after all the dev_put()
calls have happened, the reference count for the kobject needs to be increased.