3.1rc10 null pointer dereference ideapad_backlight_notify_power

[Sam Tygier <samtygier@yahoo.co.uk>]

In kernels 3.1rc9 and 3.1rc10 (from the ubuntu mainline repo) I get a crash when disabling and then enabling the screen backlight with the alt+f2 key on a lenovo ideapad S12 (intel version). The crash does not occur with 3.0 kernels in ubuntu.  I have not tested earlier 3.1 rcs.

The crash message scrolls to fast to see, it is not writen to a log, and i dont see it on a USB serial console (I may be doing something wrong, but I do see other messages during boot). I managed to get some photos of the message. interesting parts are:

BUG: unable to handle kernel NULL pointer dereference at 00000008
IP: [<f807b29e>]  ideapad_backlight_notify_power+0x2e/0x40 [ideapad_laptop]
*pde = 00000000
Oops: 0002 [#1] SMP

call trace functions:
ideapad_acpi_notify
acpi_device_notify
acpi_ev_notify_dispach
acpi_os_execute_deferred
process_one_work
? acpi_os_wait_events_complete
????????? can't read this one
kthread
kthread_bind
kernel_thread_helper

i put the photos at http://www.hep.manchester.ac.uk/u/sam/pub/ideapad/

if it would be helpfull, i could try a few more times for sharper photos. please let me know if there is any other useful information you need.

thanks,
sam