Cinnamon 6.6.7 freezes after screensaver/unlock with X11 fractional scaling, NVIDIA, dual monitor; muffin BadMatch at 6000x1440 #13820

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1. thinkingocto

   added

   BUG

   on Jun 18, 2026
2. mc-123 commented on Jun 19, 2026

   

   mc-123

   on Jun 19, 2026

   Last edited by mc-123

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   I am also experiencing the same bug in cinnamon 6.67 with a different hardware/display set up which also occurs when locking the screen. This occurs despite fractional scaling being disabled.

   Distribution
   Linux Mint 22.3 Cinnamon

   Package version
   Cinnamon 6.6.7

   Graphics hardware in use
   NVIDIA GeForce RTX 5090, NVIDIA driver 580.159.03. Dual-monitor setup: Samsung Odyssey G5 34” Curved Gaming Monitor each running at 3440x1440 @ 99.98 Hz and both connected via DisplayPort. Session type: X11. Fractional scaling disabled.

   Frequency
   Almost always (although time until an unrecoverable display crash varies)

   Bug description
   The system/session freezes sometime after the lock screen has been activated and both monitors turned off with cinnamon typically crashing several hours after lock screen and monitors are off. I can recover to a tty terminal session (Ctrl+Alt+F1) and restart the GUI session with "sudo systemctl restart lightdm" but cinnamon cannot be restored otherwise.

   journal_ctl_log.txt

   crash_report.txt
3. lupin-de-mid commented on Aug 22, 2026

   

   lupin-de-mid

   on Aug 22, 2026

   Last edited by lupin-de-mid

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   I encountered what appears to be the same bug, with additional evidence that the lock-screen process retained the X11 input grab after monitor geometry changed during authentication.

   Environment

   • Ubuntu 26.04-based system

   • Cinnamon 6.4.13 (6.4.13-2)

   • cinnamon-screensaver 6.4.1 (6.4.1-1)

   • X11 / Xorg 1.21.1.22 under LightDM

   • NVIDIA GeForce RTX 3090, proprietary driver 595.84

   • Two DisplayPort monitors: 3840x2160 and 1920x1200

   • Experimental Muffin features enabled: scale-monitor-framebuffer, x11-randr-fractional-scaling

   • Session uptime before failure: approximately 5 days 16 hours

   Symptoms

   After entering the password to unlock, the desktop became visible but the mouse pointer was invisible and Alt+Tab had no effect. Xorg and Cinnamon remained alive. There was no NVIDIA Xid, GPU reset, OOM, Xorg crash, Cinnamon crash, or coredump.

   The screensaver had started at 12:15. At 14:39:57 PAM reported an authentication failure. Two seconds later cinnamon-screensaver reported that its screen and monitor rectangles did not add up. The topology then changed through two monitors, one 960x600 monitor, and back to the two-monitor fractional layout. PAM subsequently reported conversation failed.

   After the failure:

   • cinnamon-screensaver-command --query did not respond within a three-second timeout.
   • cinnamon-screensaver, cs-backup-locker, and a stale PAM helper remained alive.
   • cs-backup-locker appeared to retain the input grab, explaining the missing pointer and blocked Cinnamon keybindings.
   • Killing only those three screensaver processes from an authenticated TTY immediately restored the pointer and Alt+Tab without restarting Cinnamon, Xorg, or applications.

   The correlated journal excerpt and a sanitized diagnostic summary are attached. The geometry/PAM sequence makes X11 fractional-scaling monitor reconfiguration during unlock the most likely trigger in this occurrence.

   incident-journal-sanitized.txt

   system-and-config-sanitized.txt
4. good-vi commented on Oct 8, 2026

   

   good-vi

   on Oct 8, 2026

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   The same
5. Devepoper commented on Oct 8, 2026

   

   Devepoper

   on Oct 8, 2026

   Last edited by Devepoper

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   I hit what looks like the same crash on Cinnamon 6.6.9 / muffin 6.6.3 / cjs 115.1 (Mint 22.3, AMD, X11 fractional scaling, 3 monitors) and got two coredumps for it. Both crash while the panel re-lays out after a monitor change, right after the Impossible to resize screen at size ... BadMatch warnings:

   #1  js::ToNumberSlow
   #2  js::ToInt32Slow
   #7  gjs_value_to_g_argument (arg_type=GJS_ARGUMENT_FIELD, arg_name="x")
   #8  BoxedInstance::field_setter_impl      <- Meta.Rectangle.x
   #9  BoxedBase::field_setter
   

   JS site: js/ui/panel.js _shouldClipPanel(), test_rect.x = this.actor.x. In both dumps the value read from the actor's x property has raw bits 0xffff300000000000: a NaN with a payload. cjs 115 stores floats from C with setNumber() without JS::CanonicalizeNaN(), so SpiderMonkey misreads the NaN as a tagged pointer and the next use of it segfaults. GJS fixed this in 1.80 (commit 4aef713129, GNOME/gjs#591); Mint's 128/140 cjs branches have it, 115 does not.

   Backport PR for cjs 115: linuxmint/cjs#138. With it, the actor's NaN position becomes a plain JS NaN and ToInt32 yields 0 instead of a crash. Why the panel actor's position goes NaN during the layout change (fractional scaling + a monitor briefly disappearing on DPMS off/on in my case) is still open, but it stops being fatal.

   Standalone reproducer without Cinnamon, crashes on cjs 115.1:

   const GLib = imports.gi.GLib;
   let [v] = GLib.ascii_strtod("-nan(0xf300000000000)");
   print(typeof v);