https://bugs.kde.org/show_bug.cgi?id=516601
[email protected] changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |[email protected] --- Comment #1 from [email protected] --- SUMMARY After updating to KDE Plasma 6.6.1, KWin crashes on a multi-GPU desktop setup whenever alt-tabbing, snapping a window to the side, or moving a window between monitors. The desktop compositor restarts immediately after each crash. STEPS TO REPRODUCE 1. Boot system with two monitors — one connected to a discrete Nvidia GPU, the other connected to an AMD iGPU (onboard, via motherboard outputs) 2. Log into KDE Plasma on Wayland via SDDM 3. Alt-tab between windows, snap a window to the side, or drag a window to the second monitor OBSERVED RESULT KWin crashes with SIGSEGV (Signal 11) and the desktop compositor restarts. The crash occurs consistently on any action that triggers window focus changes or window movement across outputs. The crash originates in KWin's scanout candidate assignment during compositing: #0 _ZN4KWin11OutputLayer19setScanoutCandidateEPNS_11SurfaceItemE (libkwin.so.6) #1 (libkwin.so.6) #2 _ZN4KWin10Compositor9compositeEPNS_10RenderLoopE (libkwin.so.6) #3 (libQt6Core.so.6) #4 _ZN4KWin10RenderLoop14frameRequestedEPS0_ (libkwin.so.6) Multiple threads in the coredump show libgallium-26.0.1 activity inside the kwin_wayland process, suggesting KWin is loading both the Nvidia and AMD/Gallium backends simultaneously and hitting a race or null pointer condition in cross-GPU surface assignment. Additionally, kwin_wayland --version and plasmashell --version both emit QThreadStorage destruction warnings, suggesting threading instability: QThreadStorage: entry 7 destroyed before end of thread 0x557b720d0e20 QThreadStorage: entry 2 destroyed before end of thread 0x557b720d0e20 QThreadStorage: entry 1 destroyed before end of thread 0x557b720d0e20 EXPECTED RESULT KDE Plasma runs stably across both monitors without compositor crashes. WORKAROUND Setting KWIN_DRM_DEVICES=/dev/dri/card1 in /etc/environment (forcing KWin to use only the Nvidia GPU) stops the crashes, but disables the AMD-connected monitor. Setting KWIN_DRM_NO_DIRECT_SCANOUT=1 alone does not resolve the issue. SOFTWARE/OS VERSIONS Operating System: Garuda Linux (Arch-based) KDE Plasma Version: 6.6.1 KDE Frameworks Version: 6.6.1 Qt Version: 5.15.18 Kernel Version: 6.18.13-zen1-1 (64-bit) Graphics Platform: Wayland Processor: AMD Ryzen 7 7800X3D 8-Core Processor Memory: 61 GiB RAM Graphics Processor 1: AMD Radeon (onboard iGPU, Gigabyte Aorus x670, card0) Graphics Processor 2: NVIDIA GeForce RTX 4080 (discrete, card1) Nvidia Driver Version: 590.48.01 Mesa Version: 26.0.1 ADDITIONAL INFORMATION This regression appeared after a single garuda-update on 2026-02-26 which upgraded KDE Plasma 6.6.0 → 6.6.1, KWin, and Mesa 25.x → 26.0.1 simultaneously. nvidia_drm modeset is enabled (modeset=Y confirmed). The issue is specific to Wayland — X11 session is unaffected. -- You are receiving this mail because: You are watching all bug changes.
