Bug 505232

SUMMARY
The KWin compositor freezes for 1-3 seconds when a GUI application forwarded from a Docker container over X11 is closed. The freeze is visible during the closing animation. The system recovers on its own. The issue does not happen under GNOME with Mutter, confirming it is a KWin-specific bug.

This happens in both wayland and xorg.

STEPS TO REPRODUCE
1. Run Fedora 42 on a system with Intel Lunar Lake graphics (xe driver).
2. Start a Docker container that has a GUI application (e.g., Exegol with burpsuite or firefox).
3. Launch the GUI application from the container's terminal (burpsuite &) so its window appears on the host KDE desktop via X11 forwarding.
4. Move mouse around and click around GUI elements or close the application window by clicking the 'X' button.

OBSERVED RESULT
The whole window and entire desktop (including mouse cursor) freezes for 1-3 seconds. The window begins its closing animation, then the entire desktop (including the mouse cursor) freezes for several seconds. The system then unfreezes.

EXPECTED RESULT
GUI works without freezing or The window closes smoothly with a normal animation.

SOFTWARE/OS VERSIONS
Operating System: Fedora Linux 42
KDE Plasma Version: 6.3.5
KDE Frameworks Version: 6.14.0
Qt Version: 6.9.0
Kernel Version: 6.14.9-300.fc42.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 8 × Intel® Core™ Ultra 7 258V
Memory: 30.8 GiB of RAM
Graphics Processor: Intel® Graphics

ADDITIONAL INFORMATION
journalctl -f output

Jun 05 20:10:59 fedora ghostty[10763]: warning(gtk): unimplemented action=apprt.action.Action.Key.cell_size
Jun 05 20:10:59 fedora ghostty[10763]: info(io_exec): started subcommand path=/bin/bash pid=12747
Jun 05 20:10:59 fedora ghostty[10763]: info(io_exec): subcommand cgroup=/user.slice/user-1000.slice/user@1000.service/app.slice/app-ghostty-transient-10763.scope/surfaces/2CF67510.scope
Jun 05 20:10:59 fedora ghostty[10763]: info(grid): reallocating GPU buffer old=0 new=16
Jun 05 20:10:59 fedora ghostty[10763]: info(grid): reallocating GPU buffer old=16 new=27
Jun 05 20:11:01 fedora ghostty[10763]: info(grid): reallocating GPU buffer old=27 new=43
Jun 05 20:11:02 fedora ghostty[10763]: info(grid): reallocating GPU buffer old=43 new=238
Jun 05 20:11:02 fedora ghostty[10763]: info(grid): reallocating GPU buffer old=238 new=360
Jun 05 20:11:02 fedora ghostty[10763]: info(grid): reallocating GPU buffer old=360 new=543
Jun 05 20:11:03 fedora ghostty[10763]: info(stream): OSC 1 (change icon) received and ignored icon=/workspace
Jun 05 20:11:03 fedora ghostty[10763]: warning(stream): unimplemented OSC command: change_window_icon
Jun 05 20:11:03 fedora ghostty[10763]: warning(io_handler): OSC 7 host must be local
Jun 05 20:11:05 fedora ghostty[10763]: info(stream): OSC 1 (change icon) received and ignored icon=burpsuite
Jun 05 20:11:05 fedora ghostty[10763]: warning(stream): unimplemented OSC command: change_window_icon
Jun 05 20:11:05 fedora ghostty[10763]: info(stream): OSC 1 (change icon) received and ignored icon=/workspace
Jun 05 20:11:05 fedora ghostty[10763]: warning(stream): unimplemented OSC command: change_window_icon
Jun 05 20:11:05 fedora ghostty[10763]: warning(io_handler): OSC 7 host must be local
Jun 05 20:11:05 fedora ghostty[10763]: info(grid): reallocating GPU buffer old=543 new=817
Jun 05 20:11:05 fedora kwin_wayland[8839]: kf.windowsystem: static bool KX11Extras::mapViewport() may only be used on X11
Jun 05 20:11:07 fedora kwin_wayland[8839]: kf.windowsystem: static bool KX11Extras::mapViewport() may only be used on X11
Jun 05 20:11:10 fedora kwin_wayland[8839]: kf.windowsystem: static bool KX11Extras::mapViewport() may only be used on X11
Jun 05 20:11:13 fedora kwin_wayland[8839]: kwin_wayland_drm: The main thread was hanging temporarily!
Jun 05 20:11:20 fedora kwin_wayland[8839]: kf.windowsystem: static bool KX11Extras::mapViewport() may only be used on X11
Jun 05 20:11:24 fedora kwin_wayland[8839]: kwin_wayland_drm: The main thread was hanging temporarily!
Jun 05 20:11:28 fedora kwin_wayland[8839]: kwin_wayland_drm: The main thread was hanging temporarily!
Jun 05 20:11:32 fedora kwin_wayland[8839]: kwin_wayland_drm: The main thread was hanging temporarily!
Jun 05 20:11:37 fedora kwin_wayland[8839]: kwin_wayland_drm: The main thread was hanging temporarily!
Jun 05 20:11:42 fedora kwin_wayland[8839]: kwin_wayland_drm: The main thread was hanging temporarily!


Graphics:
  Device-1: Intel Lunar Lake [Intel Arc Graphics 130V / 140V] driver: xe
    v: kernel
  Device-2: Chicony Integrated Camera driver: uvcvideo type: USB
  Display: wayland server: X.org v: 1.21.1.16 with: Xwayland v: 24.1.6
    compositor: kwin_wayland driver: X: loaded: modesetting dri: iris gpu: xe
    resolution: 2880x1800~120Hz
  API: EGL v: 1.5 drivers: iris,swrast
    platforms: gbm,wayland,x11,surfaceless,device
  API: OpenGL v: 4.6 compat-v: 4.5 vendor: intel mesa v: 25.0.6
    renderer: Mesa Intel Graphics (LNL)
  API: Vulkan v: 1.4.313 drivers: intel,llvmpipe surfaces: N/A
  Info: Tools: api: clinfo, eglinfo, glxinfo, vulkaninfo
    de: kscreen-console,kscreen-doctor wl: wayland-info x11: xdriinfo,
    xdpyinfo, xprop, xrandr