Public bug reported:
On unlock (after locking with Super+L), the external monitor connected via a
USB-C DisplayPort-alt-mode dock does not turn back on. The only workaround is
to unplug and replug the dock, which forces a display reconfiguration.
The internal laptop panel returns normally. Only the docked external monitor
stays black.
Reproducible on every lock/unlock cycle.
Logs show the failure is in mutter, not the kernel. On unlock, gnome-shell
submits an atomic KMS commit that the kernel rejects, then mutter's monitor
manager enters an inconsistent state:
gnome-shell: Page flip failed: drmModeAtomicCommit: Invalid argument
gnome-shell: Failed to post KMS update: drmModeAtomicCommit: Invalid argument
meta_monitor_manager_get_logical_monitor_from_number: assertion
'(unsigned int) number < g_list_length (manager->logical_monitors)' failed
meta_workspace_get_work_area_for_monitor: assertion
'logical_monitor != NULL' failed
No i915/DRM MST errors or USB disconnect events occur during unlock, so the
dock is not dropping the link; mutter is failing to re-light the output.
Replugging the dock generates a hotplug that makes mutter rebuild the monitor
config, which succeeds. This confirms the fault is in the unlock modeset path.
Steps to reproduce:
1. Laptop docked via USB-C, external monitor active.
2. Lock with Super+L (screen blanks).
3. Unlock.
4. External monitor stays black; internal panel returns.
ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: gnome-shell 46.0-0ubuntu6~24.04.14
ProcVersionSignature: Ubuntu 6.17.0-1032.32-oem 6.17.13
Uname: Linux 6.17.0-1032-oem x86_64
ApportVersion: 2.28.3-0ubuntu0.1
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: ubuntu:GNOME
Date: Fri Sep 18 16:49:14 2026
DisplayManager: gdm3
DistributionChannelDescriptor:
# This is the distribution channel descriptor for Ubuntu 24.04 for Dell
# For more information see http://wiki.ubuntu.com/DistributionChannelDescriptor
canonical-oem-somerville-noble-oem-24.04c-20251113-97
InstallationDate: Installed on 2026-03-23 (179 days ago)
InstallationMedia: Ubuntu OEM 24.04.3 LTS "Noble Numbat" - Release amd64
(20251111)
RelatedPackageVersions: mutter-common 46.2-1ubuntu0.24.04.16
SourcePackage: gnome-shell
UpgradeStatus: No upgrade log present (probably fresh install)
** Affects: gnome-shell (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug noble third-party-packages wayland-session
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https://bugs.launchpad.net/bugs/2167728
Title:
External monitor on USB-C dock stays black after unlock; mutter atomic
KMS commit fails with Invalid argument
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