Kernel NULL pointer dereference when using Wacom pen

[Arvid Norlander]

When using the Wacom pen that was included for the touch screen on my Lenovo Thinkpad P15 Gen1 laptop, the kernel hangs. This worked a few weeks ago. Looking at journalctl after rebooting shows the following two lines:

mar 22 13:26:33 minerva kernel: wacom 0003:056A:51E9.0001: wacom_wac_queue_insert: kfifo has filled, starting to drop events
mar 22 13:26:33 minerva kernel: BUG: kernel NULL pointer dereference, address: 0000000000000000

This appears to be the following bug, which has already been solved upstream and presumably needs to be backported to Ubuntu 20.04: https://github.com/linuxwacom/input-wacom/issues/230

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: linux-image-5.8.0-45-generic 5.8.0-45.51~20.04.1+1
ProcVersionSignature: Ubuntu 5.8.0-45.51~20.04.1-generic 5.8.18
Uname: Linux 5.8.0-45-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu27.16
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Mon Mar 22 14:56:52 2021
InstallationDate: Installed on 2021-01-18 (62 days ago)
InstallationMedia: Ubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
SourcePackage: linux-signed-hwe-5.8
UpgradeStatus: No upgrade log present (probably fresh install)

[Arvid Norlander (vorpalblade)]

Since the hardware device in question is attached via USB I'm adding lsusb output here.

The device in question is "Bus 001 Device 007: ID 056a:51e9 Wacom Co., Ltd Pen and multitouch sensor"

[AaronMa (mapengyu)]

It should be caused by a stable kernel backport:
Author: Ping Cheng <email address hidden>
Date: Wed Dec 9 20:52:30 2020 -0800

    HID: wacom: Fix memory leakage caused by kfifo_alloc

    BugLink: https://bugs.launchpad.net/bugs/1915473

    commit 37309f47e2f5674f3e86cb765312ace42cfcedf5 upstream.

It should be fixed by:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=179e8e47c02a1950f1c556f2b854bdb2259078fb

groovy Ubuntu-5.8.0-46.52 already got this fix, could you try it?
I am not sure when will it be landed in focal/hwe-5.8 kernel.

[Arvid Norlander (vorpalblade)]

If there is an easy way to install the newer kernel on Focal I'll happily try it (I don't particularly want to build a kernel by hand again, I left Gentoo many years ago for a reason). I presume I could download a couple of deb from somewhere and install them by hand, then run some dkms commands for the nvidia drivers and then update-initramfs & update-grub? If you can point me to where I can get those debs I'll try it.

I did however try the backport module mentioned in https://github.com/linuxwacom/input-wacom/issues/230 and it solves the issue. This would indicate that upstream kernel update should also likely fix the problem.

Also, it seems strange to delay a crash fix from the hwe kernel. Isn't the hwe kernel literally just the standard kernel from a newer ubuntu version recompiled with an older toolchain?

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.