Bug 500478

Summary:	Screen locker sometimes only shows black screen after unlocking with password when fingerprint reader is available
Product:	[Plasma] plasmashell	Reporter:	Fabian Blaese <fabian+kdebugs>
Component:	Screen locking	Assignee:	Plasma Bugs List <plasma-bugs-null>
Status:	RESOLVED WORKSFORME
Severity:	grave	CC:	nate, postix
Priority:	VHI	Keywords:	regression
Version First Reported In:	6.3.1
Target Milestone:	1.0
Platform:	Arch Linux
OS:	Linux
See Also:	https://bugs.kde.org/show_bug.cgi?id=483163
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description Fabian Blaese 2025-02-20 17:35:50 UTC

For some time, kscreenlocker sometimes only shows a black screen. The cursor is visible and fingerprint is functional, but all other controls, including password login, don't work. The cursor even changes its appearance if it is hovering above the buttons or text field.

I do not know the exact version since when this issue is present. It might be a dependency, because downgrading only kscreenlocker to a far older version (6.2.3-1) does not fix the issue.

STEPS TO REPRODUCE
1. Lock the screen
2. Sometimes, only a black screen with cursor appears

SOFTWARE/OS VERSIONS
Linux: 6.13.2-arch1-1
KDE Plasma Version: 6.3.1-1
KDE Frameworks Version: 
Qt Version: 6.8.2-2

ADDITIONAL INFORMATION
This issue appears on Wayland. I have not tested X11.
It seems very similar to #483163, but I am already using the Breeze dark theme (proposed workaround).

Comment 1 Fabian Blaese 2025-02-20 17:37:25 UTC

"The cursor even changes its appearance if it is hovering above the buttons or text field."

This is not the case. I have forgotten to remove this statement. I thought this would be the case, but after checking, it does not seem to be.

Comment 2 Fabian Blaese 2025-02-20 18:01:20 UTC

The issue seems to be related to the fingerprint/fprintd integration. I can reproduce this issue by locking the screen once, unlocking it using the password (even though the fingerprint reader is active), and locking it again. If the screen is unlocked using the fingerprint reader, the issue does NOT appear. I assume that the issue is somehow related to leftovers of the previous fingerprint session.

After waiting for the fingerprint session to time out (30s by default), or by stopping fprintd manually, kscreenlocker exits and leaves the session unlocked (!). I have not previously noticed this behavior, because I have significantly increased the fingerprint timeout duration.

I am not sure how kscreenlocker_greet is invoked when locking the session with a Hotkey (Super + L), but to me it looks like kscreenlocker_greet isn't even started when locking for the second time, and the black screen is drawn by a different component.

Comment 3 Nate Graham 2025-05-19 19:52:09 UTC

I recall this very bad issue being fixed early in the Plasma 6.3 cycle. Can you still reproduce the issue with Plasma 6.3.5 or later? Thanks a lot for checking!

Comment 4 Bug Janitor Service 2025-06-03 03:47:53 UTC

🐛🧹 ⚠️ This bug has been in NEEDSINFO status with no change for at least 15 days. Please provide the requested information, then set the bug status to REPORTED. If there is no change for at least 30 days, it will be automatically closed as RESOLVED WORKSFORME.

For more information about our bug triaging procedures, please read https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging.

Thank you for helping us make KDE software even better for everyone!

Comment 5 Bug Janitor Service 2025-06-18 03:47:58 UTC

🐛🧹 This bug has been in NEEDSINFO status with no change for at least 30 days. Closing as RESOLVED WORKSFORME.