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

[Jiri Kosina]

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.
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