Hi Tomek, Sorry for the very long delay. Could you still reproduce this on a supported release? Bullseye, where you saw it, reaches the end of its LTS support on 2026-08-31; trixie ships cinnamon 6.4.10 and unstable 6.6.9.
For the record, the crash is not in glib: XShmGetImage() fails with an X error and GDK turns X errors into fatal ones, so glib just aborts. That code path is the "texture from pixmap" fallback used when GLX_EXT_texture_from_pixmap is unavailable, which is your VirtualGL case — muffin logs "NOTE: Not using GLX TFP!" when it happens — and the X calls there are not wrapped in an error trap, so a pixmap invalidated by the resize is enough to kill the session. The code is unchanged in current versions, so the problem may well still be there; it lives in cogl, which since Cinnamon 5.x is bundled inside muffin, and the bug would then be reassigned there. If you can still reproduce it, please say which release and versions, and whether the "NOTE: Not using GLX TFP!" warning appears in the log.
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