https://bugs.kde.org/show_bug.cgi?id=521192
Bug ID: 521192
Summary: plasma-login-greeter crashes with TypeErrors (null
pointer) on placeholder screen when monitor is turned
off manually
Classification: Plasma
Product: plasmashell
Version First master
Reported In:
Platform: Arch Linux
OS: Linux
Status: REPORTED
Severity: crash
Priority: NOR
Component: general
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Target Milestone: 1.0
Created attachment 192980
--> https://bugs.kde.org/attachment.cgi?id=192980&action=edit
journalctl logs showing the QML crashes.
SUMMARY
When using KDE Plasma Wayland session on Arch Linux, turning off the physical
monitor manually causes kwin_wayland to create a placeholder screen. However,
plasma-login-greeter fails to handle this "zero-output" scenario gracefully,
resulting in multiple QML singletons returning null and a cascading series of
TypeErrors, which ultimately crashes the greeter session.
STEPS TO REPRODUCE
1. Start a KDE Plasma Wayland session.
2. Manually turn off the only connected monitor.
3. Wait a moment, then turn the monitor back on (or switch to TTY to check
system logs).
OBSERVED RESULT
The plasma-login-greeter crashes and fails to recover. System logs show that
once the placeholder screen is created, singletons like 'Authenticator' and
'UserModel' return null pointers, causing multiple QML TypeErrors (e.g., Cannot
read property 'needsPassword' of null).
EXPECTED RESULT
The greeter should handle the placeholder screen properly without throwing null
pointer TypeErrors, and gracefully restore the UI when the monitor is turned
back on.
RELATION TO POSSIBLE DUPLICATES
I noticed Bug 519302 in the duplicates list, which also involves
plasma-login-greeter and placeholder screens on Wayland startup. However, Bug
519302 was marked as RESOLVED FIXED and described a SIGSEGV via a dangling
QWindowPrivate pointer.
In my case, the greeter did not immediately trigger a segmentation fault;
instead, it threw multiple explicit QML TypeErrors due to singletons returning
null on the placeholder screen. This seems to be either a regression, an
incomplete fix for Bug 519302, or a distinct edge case caused by manually
power-cycling the monitor.
I have attached my full log.txt for reference.
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