Input devices stop responding and high X.org and kglobalaccel5 CPU usage when connecting a USB device

I have been having this issue for a while now, but have no idea on how to debug it, so I’ll report the details here:

Whenever I connect a USB Webcam, a Wacom graphic tablet or my Bluetooth headphones, the main xorg process starts using around 50% CPU usage and at the same time input devices start behaving strangely. The keyboard stops working completely, the mouse still works, but I can’t click anywhere (either it doesn’t react or it tries to move the window even when I click inside). Some random things like use the mousewheel over the workspace indicator to switch still works.

After rebooting or disconnecting the device and waiting a while everything returns to normal.

I am using Debian Testing with KDE and SDDM.

The .xsession-errors shows nothing related to this. The /var/log/Xorg.0.log is a bit odd as it mentions detecting a Keyboard (but I think this is unrelated, as the log for the wacom tablet looks normal):

[   652.297] (II) config/udev: Adding input device HD Pro Webcam C920 (/dev/input/event16)
[   652.297] (**) HD Pro Webcam C920: Applying InputClass "libinput keyboard catchall"
[   652.297] (II) Using input driver 'libinput' for 'HD Pro Webcam C920'
[   652.297] (**) HD Pro Webcam C920: always reports core events
[   652.297] (**) Option "Device" "/dev/input/event16"
[   652.297] (**) Option "_source" "server/udev"
[   652.298] (II) event16 - HD Pro Webcam C920: is tagged by udev as: Keyboard
[   652.298] (II) event16 - HD Pro Webcam C920: device is a keyboard
[   652.298] (II) event16 - HD Pro Webcam C920: device removed
[   652.360] (**) Option "config_info" "udev:/sys/devices/pci0000:00/0000:00:01.3/0000:03:00.0/usb1/1-4/1-4:1.0/input/input25/event16"
[   652.360] (II) XINPUT: Adding extended input device "HD Pro Webcam C920" (type: KEYBOARD, id 12)
[   652.360] (**) Option "xkb_model" "pc105"
[   652.360] (**) Option "xkb_layout" "de"
[   652.360] (WW) Option "xkb_variant" requires a string value
[   652.360] (WW) Option "xkb_options" requires a string value
[   652.361] (II) event16 - HD Pro Webcam C920: is tagged by udev as: Keyboard
[   652.361] (II) event16 - HD Pro Webcam C920: device is a keyboard
[   721.766] (II) config/udev: removing device HD Pro Webcam C920
[   721.766] (II) event16 - HD Pro Webcam C920: device removed

More things I noticed during debugging:

  • stace isn’t helpful as finding anything “wrong” in thousands of lines per seconds is like a needle in a haystack
  • it is probably unrelated to this bug as I use a far newer kernel (5.2.0) and there is a normal amount of devices in /dev/input
  • when I switch to tty1 quickly before everything hangs, I can use it fine while the issue is occuring.
  • this way I noticed something new (as before htop froze before it occured): /usr/bin/kglobalaccel5 also has a really high CPU usage at the same time
Asked By: lw1.at

||

The mystery is solved!

kglobalaccel5 made it far easier to research for this bug and indeed it has been reported on https://bugs.kde.org/show_bug.cgi?id=306352.

I looked in my home directory and indeed there was a .Xmodmap (last modified 4 years ago) lying around. I deleted it and after a reboot all devices are working fine again.

Answered By: lw1.at
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