Re: [BUG, Regression, bisected] USB mouse causes bug on 1st insert, ignored on 2nd insert, lsusb stuck at usbdev_open

Jiri Kosina
2010-09-21T16:55:42Z

On Tue, 21 Sep 2010, Greg KH wrote:

> > > I have just found out that it's actually CONFIG_USB_DYNAMIC_MINORS which
> > > makes the difference. When unset, the problem doesn't trigger, and
> > > usb_find_interface() always returns the proper interface. When
> > > CONFIG_USB_DYNAMIC_MINORS is being used, the oops happen.
> > >
> > > I'll look into that.
> >
> > Apparently the problem is that intf->minors doesn't get initialized
> > properly. This patch should fix it. Everybody, please try it out.
>
> Wow, what happened to suddenly cause this? Nothing has changed here in
> a long time.
>
> wierd.

It doesn't hit you if you are calling usb_register_dev() for all the
instances you have, as the first device will have minor '0', the second
one '1', etc.

But if you are calling usb_find_interface() for devices that have never
been registered through usb_register_dev(), then you have a problem, as
usb_find_interface() will match those unregistered devices (as minor == 0
in such cases).

This is probably quite rare scenario, and hiddev (which might be the only
in-kernel driver doing this?) has moved to usb_find_interface() only
recently.

--
Jiri Kosina
SUSE Labs, Novell Inc.