Comment 23 for bug 1310800

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.