linux-kernel - Re: S2R resume crash in 2.6.33-rc7 - NULL pointer dereference in dev_get

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Date:	Sat, 13 Feb 2010 12:46:11 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Bruno Prémont <bonbons@...ux-vserver.org>
cc:	Jiri Kosina <jkosina@...e.cz>, Oliver Neukum <oliver@...kum.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Marcel Holtmann <marcel@...tmann.org>,
	H Hartley Sweeten <hsweeten@...ionengravers.com>,
	<linux-usb@...r.kernel.org>, <linux-input@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: S2R resume crash in 2.6.33-rc7 - NULL pointer dereference in
 dev_get_drvdata() for usbhid

On Sat, 13 Feb 2010, Bruno [UTF-8] PrÃ©mont wrote:

> On Mon, 08 February 2010 Alan Stern <stern@...land.harvard.edu> wrote:
> > Clearly something is setting usbhid->intf to NULL.  But I don't see
> > any code that would do it.  You may have to resort to putting
> > printk() statements at various strategic places to find out where it
> > happens. You could start with the beginnings and ends of hid_suspend,
> > hid_resume, and hid_reset_resume.  Maybe also usbhid_disconnect(),
> > just in case.
> 
> I did add a few printk()s and WARN_ON()s to get a better idea of
> why/when usbhid->intf is NULL and it is already since probe time of the
> second interface anounced by the USB keyboard (hid.debug=1):

...

> This lets me guess that hid_add_device() is doing something wrong
> here when report parsing fails... (as that one is the only one which
> could be doing the initialization of usbhid which does work for the
> first interface announced by my keyboard)

I don't know about doing anything wrong...  However it does appear that
in this case the interface is registered on the HID bus but doesn't get
bound to a driver.  Jiri will know whether or not that's the desired
outcome.

On the other hand, I don't think there would be anything wrong with 
moving the

	usbhid->intf = intf;
	usbhid->ifnum = interface->desc.bInterfaceNumber;

lines from usbhid_start() to usbhid_probe(), just before the call to
hid_add_device().  It should fix the bug, and those lines do belong in
the probe routine.  Jiri, any problems with doing this?

Alan Stern

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