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