SIGSEGV in meta_window_unmaximize when restarting Cinnamon on X11

Environment

• Linux Mint 22.3 Zena
• Cinnamon 6.6.9+zena
• Muffin 6.6.3+zena
• X11 session
• Kernel 7.0.0-31-generic
• NVIDIA GeForce RTX 2060 SUPER (kernel reports the nvidia driver in use)

Problem

Selecting Panel → Troubleshoot → Restart Cinnamon can freeze the desktop, requiring a manual reboot.

A recorded Cinnamon crash from the restart/replace path shows:

Signal: 11 (SEGV)
Command Line: cinnamon --replace
#0  meta_window_unmaximize (libmuffin.so.0)
#1  meta_window_x11_client_message (libmuffin.so.0)
#2  meta_x11_display_handle_xevent (libmuffin.so.0)

The crash record is from 2026-09-11. No later Cinnamon/Muffin core dumps were recorded because the subsequent desktop freezes were recovered by manually rebooting.

Related observation

A custom third-width tiling helper had explicitly sent an X11/EWMH unmaximize request before applying a resize. That explicit request has been removed as a local workaround because it appears to exercise the same meta_window_unmaximize path. This is a correlation, not a reliable reproduction or proof of causation.

No Cinnamon JavaScript exceptions implicated an applet. The issue is intermittent and is not yet reliably reproducible.

Expected behavior

Restarting Cinnamon should return to a responsive desktop, and an X11 unmaximize request should not crash the compositor.

Actual behavior

Cinnamon/Muffin can freeze or crash; the available crash record shows SIGSEGV in meta_window_unmaximize.

Start by tracing the reported X11 path from meta_x11_display_handle_xevent through meta_window_x11_client_message to meta_window_unmaximize in libmuffin.so.0. Try the Panel → Troubleshoot → Restart Cinnamon flow and the described X11/EWMH unmaximize request, while accounting for the issue's intermittent, unreliably reproducible behavior. Done means identifying and fixing the SIGSEGV so restart and unmaximize requests no longer crash or freeze the desktop.