I've taken a long hard look at this bug and believe I've been able to
nail down the cause. The panic is caused by a NULL pointer being passed
to the 'input_report_switch' function. It occurs if the kernel has
probed the tablet's pen/pad interface and processes a status report from
it before the kernel has a chance to probe the tablet's touchpad
interface. The suggested workaround of loading the module before
connecting the tablet only masks the issue by changing the timing of
events enough so that the kernel is able to finish probing both
interfaces before processing the status report.
This issue was addressed upstream by commit 44b9683 ("HID: wacom - make
sure touch_input is valid before using it") which is part of the 3.19
kernel. Both the Trusty (3.13) and Vivid (3.16) kernels are missing this
patch, however. Commit 44b9683 can be trivially backported; I've
attached such a backport for convenience.
** Patch added: "Upstream 44b9683 modified to apply against Ubuntu's 3.13 and
3.16 kernels"
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1310800/+attachment/4452940/+files/make-sure-touch_input-is-valid-before-using.patch
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https://bugs.launchpad.net/bugs/1310800
Title:
056a:0302 Trusty Tahr, kernel 3.13: automatic load of wacom.ko driver
cause a "hard" kernel panic
Status in linux package in Ubuntu:
Confirmed
Bug description:
I have just upgraded to 14.04 from 13.10.
I have a wacom cth-480 touch+pen tablet, which was not recognized on
13.10 (kernel 3.11). With the stock kernel from 14.04, I have an
immediate kernel panic as soon as I plug in the tablet to the laptop.
The system is a asus 1005PE (32 bit install), Xubuntu, up-to date:
Linux asus-romano 3.13.0-24-generic #46-Ubuntu SMP Thu Apr 10 19:08:14
UTC 2014 i686 i686 i686 GNU/Linux
The really strange thing is that if I manually load the driver with
`sudo modprobe wacom` *before* pluggin the tablet in, then the tablet
is recognized and works ok:
SYS: Apr 21 15:15:47 asus-romano kernel: [ 265.664161] usbcore: registered
new interface driver wacom
SYS: Apr 21 15:15:52 asus-romano kernel: [ 270.088161] usb 2-1: new
full-speed USB device number 2 using uhci_hcd
SYS: Apr 21 15:15:52 asus-romano kernel: [ 270.253626] usb 2-1: New USB
device found, idVendor=056a, idProduct=0302
SYS: Apr 21 15:15:52 asus-romano kernel: [ 270.253641] usb 2-1: New USB
device strings: Mfr=1, Product=2, SerialNumber=0
SYS: Apr 21 15:15:52 asus-romano kernel: [ 270.253651] usb 2-1: Product:
Intuos PTS
SYS: Apr 21 15:15:52 asus-romano kernel: [ 270.253659] usb 2-1:
Manufacturer: Wacom Co.,Ltd.
SYS: Apr 21 15:15:52 asus-romano kernel: [ 270.257027] input: Wacom Intuos
PT S Pen as /devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1:1.0/input/input14
SYS: Apr 21 15:15:52 asus-romano kernel: [ 270.260630] input: Wacom Intuos
PT S Finger as /devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1:1.1/input/input15
SYS: Apr 21 15:15:52 asus-romano mtp-probe: checking bus 2, device 2:
"/sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1"
SYS: Apr 21 15:15:52 asus-romano mtp-probe: bus: 2, device: 2 was not an MTP
device
A screenshot of the kernel panic is added. I can reproduce it at will.
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