Describe the bug
Full session freeze requiring Magic SysRq (REISUB) to recover. No graceful recovery was possible: keyboard, mouse, and VT switching were all dead. This is a data-loss-risk-class hang for anything with unsaved work.
On GNOME Shell 50.1 (Wayland, Ubuntu 26.04), my entire desktop session hard-froze -- panel gone, no keyboard or mouse response, and VT switching (Ctrl+Alt+F3) was dead. I could only recover with Magic SysRq (REISUB). In the journalctl from the frozen boot, the last activity from my session shell before it went silent was JS errors originating entirely from Coverflow Alt-Tab -- variations of preview is undefined / this._previews[this._currentIndex] is undefined, thrown from switcher.js, coverflowSwitcher.js, and swipeTracker.js during Alt-Tab and gesture handling. I want to be upfront that this is temporal correlation, not proof of causation: the log shows these errors right before the freeze, not that they caused it.
The event that lines up with the freeze is swipeTracker.js's _gestureBegin path: the final shell log lines (13:45:57–13:46:00) are _gestureBegin throwing on an undefined preview, after which my session shell logs nothing further until my SysRq keystrokes appear in the kernel log ~80 seconds later (13:47:21). (Earlier preview is undefined errors on the teardown path -- _buttonReleaseEvent → animateClosed -- occurred ~16 minutes before, at 13:29, and the session kept working afterward, so a thrown teardown exception by itself was not sufficient to freeze it.)
⚠️ One thing that surprised me and may be a clue: this is a desktop with no touchpad and no touchscreen. My pointing devices are Logitech mice plus a keyboard. The last frame before the freeze goes through _beginTouchpadGesture (swipeTracker.js:628, a TOUCHPAD_SWIPE-class event) -- but I have no touchpad to generate one.
Scoped to the freeze window (≈13:45–13:47), my session gnome-shell (PID 7648) did not segfault, dump core, or respawn -- it simply stops logging. That is consistent with a hang rather than a crash. My working hypothesis (unconfirmed -- see Analysis) is that an unhandled exception left a modal/gesture input grab unreleased.
I'm reporting this as a possible regression of, or a distinct path from, the earlier "Alt+tab freezes screen" report (#237). I'm on the current release (v85), so this is not a stale-version issue.
To Reproduce
It just happened the once so far, and I'm sharing the findings in case they help.
Logs
Relevant log excerpt (frozen boot, journalctl -b -1)
All error frames are inside the extension, from my session gnome-shell[7648]. They arrive in three bursts (13:28, 13:29, 13:45–13:46), with normal use in between. The freeze follows the last burst; the SysRq lines at the end are my REISUB recovery ~80 s later.
# 13:28:43 - Alt-Tab / window-destroy path
JS ERROR: TypeError: can't access property "_destoying", preview is undefined
_removeDestroyedWindow@…/CoverflowAltTab@palatis.blogspot.com/switcher.js:1005:13
_windowDestroyed@…/switcher.js:980:14
# 13:28:43 - preview update during show()/_next()
JS ERROR: TypeError: can't access property "make_top_layer", preview is undefined
_updatePreview@…/coverflowSwitcher.js:299:13
_updatePreviews@…/coverflowSwitcher.js:270:37
_previewNext@…/coverflowSwitcher.js:126:18
_next@…/switcher.js:543:22
show@…/switcher.js:240:22
# 13:29:14 - teardown path (session KEPT WORKING for ~16 min after this)
JS ERROR: TypeError: can't access property "removeEffect", preview is undefined
_removeBackgroundEffects@…/switcher.js:362:17
animateClosed@…/switcher.js:1220:18
_activateWithoutSelection@…/switcher.js:1043:14
_buttonReleaseEvent@…/switcher.js:946:22
# 13:45:57 - pan-gesture path (consistent with a mouse click-drag); repeats
JS ERROR: TypeError: can't access property "get_transition", this._previews[this._currentIndex] is undefined
_gestureBegin@…/switcher.js:255:17
_beginGesture@…/swipeTracker.js:616:14
_beginPanGesture@…/swipeTracker.js:622:14
# 13:46:00 - touchpad-swipe path (NOTE: no touchpad on this machine) -- LAST shell activity before the freeze
JS ERROR: TypeError: can't access property "get_transition", this._previews[this._currentIndex] is undefined
_gestureBegin@…/switcher.js:255:17
_beginGesture@…/swipeTracker.js:616:14
_beginTouchpadGesture@…/swipeTracker.js:628:14
_handleEvent@…/swipeTracker.js:384:18
# …no further gnome-shell[7648] output…
# 13:47:21 kernel: sysrq: This sysrq operation is disabled. (my first REISUB keys)
# 13:47:26 kernel: sysrq: Emergency Sync
# 13:47:27 kernel: sysrq: Emergency Remount R/O
Your Environment
- Extension version: 85
- Operating System: Ubuntu 26.04
- GNOME Shell Version: 50.1
- Are you using other GNOME Shell extensions?
- Burn My Windows
- Just Perfection
- Places Status Indicator
- Removable Drive Menu
- Transparent Window Moving
- Vitals
- Plus the default system extensions in Ubuntu 26
Relationship to prior freeze report (#237)
The v76 release notes ("Fix the Freezes") state they fixed the cause of freezes referenced by #237 ("Alt + tab freezes screen"). That issue is, as of now, still open and has no logs, environment, or repro steps, so I can't tell whether what it describes is the same code path I hit. I'm now on v85 under GNOME 50 / Wayland and still seeing a full freeze, so this is either:
- a regression of that fix (or an incomplete fix) on the newer GNOME 50 code path, or
- a distinct freeze path with the same user-visible outcome, but a different trigger (an undefined entry in _previews reached via the swipeTracker _gestureBegin path).
I can't determine which from the log alone -- flagging it as possibly related to #237 so it can be checked, not asserting they're the same bug.
Describe the bug
Full session freeze requiring Magic SysRq (REISUB) to recover. No graceful recovery was possible: keyboard, mouse, and VT switching were all dead. This is a data-loss-risk-class hang for anything with unsaved work.
On GNOME Shell 50.1 (Wayland, Ubuntu 26.04), my entire desktop session hard-froze -- panel gone, no keyboard or mouse response, and VT switching (Ctrl+Alt+F3) was dead. I could only recover with Magic SysRq (REISUB). In the journalctl from the frozen boot, the last activity from my session shell before it went silent was JS errors originating entirely from Coverflow Alt-Tab -- variations of preview is undefined / this._previews[this._currentIndex] is undefined, thrown from switcher.js, coverflowSwitcher.js, and swipeTracker.js during Alt-Tab and gesture handling. I want to be upfront that this is temporal correlation, not proof of causation: the log shows these errors right before the freeze, not that they caused it.
The event that lines up with the freeze is swipeTracker.js's _gestureBegin path: the final shell log lines (13:45:57–13:46:00) are _gestureBegin throwing on an undefined preview, after which my session shell logs nothing further until my SysRq keystrokes appear in the kernel log ~80 seconds later (13:47:21). (Earlier preview is undefined errors on the teardown path -- _buttonReleaseEvent → animateClosed -- occurred ~16 minutes before, at 13:29, and the session kept working afterward, so a thrown teardown exception by itself was not sufficient to freeze it.)
Scoped to the freeze window (≈13:45–13:47), my session gnome-shell (PID 7648) did not segfault, dump core, or respawn -- it simply stops logging. That is consistent with a hang rather than a crash. My working hypothesis (unconfirmed -- see Analysis) is that an unhandled exception left a modal/gesture input grab unreleased.
I'm reporting this as a possible regression of, or a distinct path from, the earlier "Alt+tab freezes screen" report (#237). I'm on the current release (v85), so this is not a stale-version issue.
To Reproduce
It just happened the once so far, and I'm sharing the findings in case they help.
Logs
Relevant log excerpt (frozen boot, journalctl -b -1)
All error frames are inside the extension, from my session gnome-shell[7648]. They arrive in three bursts (13:28, 13:29, 13:45–13:46), with normal use in between. The freeze follows the last burst; the SysRq lines at the end are my REISUB recovery ~80 s later.
Your Environment
Relationship to prior freeze report (#237)
The v76 release notes ("Fix the Freezes") state they fixed the cause of freezes referenced by #237 ("Alt + tab freezes screen"). That issue is, as of now, still open and has no logs, environment, or repro steps, so I can't tell whether what it describes is the same code path I hit. I'm now on v85 under GNOME 50 / Wayland and still seeing a full freeze, so this is either:
I can't determine which from the log alone -- flagging it as possibly related to #237 so it can be checked, not asserting they're the same bug.