Xvnc Record extension may cause spurious event flood in KDE Plasma 5/6

[headbank]

Since at least KDE5, running the Plasma desktop session under TigerVNC/Xvnc causes a bug that results in the KDE global keyboard shortcuts daemon (kglobalacceld) going into 100% CPU. It has triggered variously, under different KDE versions, either upon VNC client connection, or upon the first keyboard input received from the client.

At present (under kde-6.2.4), killing and relaunching kglobalacceld allows it to function normally, but the bug can still be re-triggered manually by the use of xdotool and possibly other commands that synthesise X input.

The debugging efforts taken in the KDE bug report have suggested that Xvnc's Record extension may be where the problem originates, causing a flood of SocketNotifier events.

As my system is non-systemd, I have refrained from reporting this here until it could be reproduced by a systemd user, which as you'll see in the KDE bug has now happened. That user will hopefully subscribe here too.

I lack the knowledge to determine whether this ultimately qualifies as KDE's bug or yours, but your input would be appreciated if you can offer any.

Steps to reproduce the behavior:

1. Launch tigervnc service with KDE plasma-x11 session
2. Connect to service using any VNC client
3. [If bug not already triggered] In the client session, press any key
4. [To trigger on-demand] Issue command such as xdotool type foo

Client (please complete the following information):

• OS: Gentoo Linux / Raspberry Pi OS Bookworm / Windows 10
• VNC client: TigerVNC
• VNC client version: 1.14.1 and below
• Client downloaded from: Gentoo portage repo / APT repo / TigerVNC github releases

Server (please complete the following information):

• OS: Gentoo Linux
• VNC server: TigerVNC
• VNC server version: 1.14.1 and below
• Server downloaded from: Gentoo portage repo
• Server was started using: Any of vncserver, systemd unit, Gentoo OpenRC script

[belze-bu]

...
As my system is non-systemd, I have refrained from reporting this here until it could be reproduced by a systemd user, which as you'll see in the KDE bug has now happened. That user will hopefully subscribe here too.
...

Subscribed

[CendioOssman]

Discussion ongoing in the KDE tracker. At this point, I can't reproduce this, and it is unclear if this is an issue in TigerVNC, Xorg, or KDE. More information is needed.