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

[Jiri Kosina]

On Mon, 20 Sep 2010, Alan Stern wrote:

> > Thanks Matt and Phill for confirming the line that triggers the oops. As I 
> > am not able to reproduce it myself, it's a bit tricky to track down what 
> > went wrong.
> > 
> > Could you please apply the patch below? It's printing the hid <-> hiddev 
> > <-> usb_interface connections at various stages of probing and open. 
> > Hopefully it'll reveal a little bit what goes wrong and where.
> 
> Jiri:
> 
> There's something very fishy going on here.  Even more so than these 
> bug reports suggest.
> 
> The whole business about hiddev_driver in hiddev.c looks bogus.  It
> doesn't get used for anything and it never binds to an interface.  
> Which means that the usb_find_interface call in hiddev_open should
> never succeed.  At the very least it would need to specify hid_driver
> instead of hiddev_driver.

Yeah. That has been introduced by Arnd while removing BKL, and was bogus. 
It has been fixed by 8fe294caf8c868edd9046251824a0af91991bf43 ("HID: fix 
hiddev's use of usb_find_interface"), which makes it use hid_driver 
(hopefully) correctly.

But since that commit, we are getting NULL pointer dereferences on 
intfdata->hiddev in hiddev_open(). Very likely, it's not fault of that 
commit -- after Arnd's bd25f4dd6972755579d0ea50d1a5ace2e9b00d1a and before 
Guillaume's 8fe294caf8c868edd9046251824a0af91991bf43 we were not hitting 
that codepath at all in fact.

> I have no idea what's really happening.  Can you figure it out?

I am trying, but on my testing systems everything is behaving correctly, 
so it's a bit more difficult. Ideas welcome.

Thanks,

-- 
Jiri Kosina
SUSE Labs, Novell Inc.
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