Re: Use of usb_find_interface in open is racy

[Oliver Neukum <oliver@neukum.org>]

Am Mittwoch, 18. November 2009 11:41:25 schrieb Jiri Kosina:
> > User space receives the hotplug event for the class device, makes the
> > device node and notifies another program that opens the device node.
> > The program opens the device node which calls into usb_open and then
> > skel_open. skel_open calls usb_find_interface. usb_find_interfaces
> > searches the klist_devices of skel_driver, finds no device associated
> > with the minor number and returns NULL. skel_open returns -ENODEV.
> > 
> > Control returns to really_probe and really_probe calls driver_bound
> > which adds the device to the list of devices associated with
> > skel_driver (klist_devices).
> > 
> > I'm not sure what the right way to solve this is. A call to
> > wait_for_device_probe() in the skel_open call before calling
> > usb_find_interface fixes the problem, but it is a rather large hammer.
> 

Device core code is hard to follow, but I tried.
How about simply covering all of usb_register_dev() with minor_rwsem?

	Regards
		Oliver