https://bugs.kde.org/show_bug.cgi?id=505926
Bug ID: 505926
Summary: kscreenlocker_greet segfaults when the wallpaper is
set to certain SVGs (e.g. most Debian default
Wallpapers)
Classification: Plasma
Product: plasmashell
Version First 6.3.5
Reported In:
Platform: Debian testing
OS: Linux
Status: REPORTED
Severity: crash
Priority: NOR
Component: Screen locking
Assignee: plasma-b...@kde.org
Reporter: doms...@proton.me
Target Milestone: 1.0
Created attachment 182489
--> https://bugs.kde.org/attachment.cgi?id=182489&action=edit
Backtrace fetched via "gdb --args
/usr/lib/x86_64-linux-gnu/libexec/kscreenlocker_greet --testing"
SUMMARY
After installing the latest updates on a debian trixie/testing system, the
screen locker stopped working. When locking the screen the fallback message,
that the screen locker has failed and loginctl should be used to unlock, is
shown. Further investigation with gdb shows, that kscreenlocker_greet segfault
in libQt6Svg QSvgRenderer::load(QByteArray const&). Backtrace is attached.
Clearing qt caches, setting qt to software rendering
(QMLSCENE_DEVICE=softwarecontext) or reinstalling qt and plasma packages does
not change the outcome.
The issue can be mitigated by setting the lock screen background/wallpaper to
an non-SVG image or the debian "Homeworld" SVG also works, other SVGs like
"Ceratopsian", "Emerald" or any other debian provided SVG background I have
tried causes the segfault.
STEPS TO REPRODUCE
1. install latest packages on a debian trixie system
2. set lock screen background/wallpaper to debian's default ceratopsian
3. launch kscreenlocker_greet manually or just lock the screen
OBSERVED RESULT
Fallback message, that screen locker has failed is shown, session needs to be
unlocked via other vt/loginctl
EXPECTED RESULT
Lock screen is shown
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Debian 13/Trixie/testing + Side loaded nvidia drivers (see
additional information)
KDE Plasma Version: 6.3.5
KDE Frameworks Version: 6.13.0
Qt Version: 6.8.2
ADDITIONAL INFORMATION
The issue can NOT be observed on a second debian trixie system after installing
the same updates. One difference, which might be important, is, that the
affected system uses an nvidia GPU, the second one an Intel GPU. The nvidia
driver is the current production branch 570 version from nvidia directly. I
know this is discouraged but I just cannot reliably run a wayland session with
the outdated drivers from the debian repos at all.
I tried to rule out the nvidia drivers, though I'm not sure if there might
still be a connection:
- software rendering does not mitigate the issue
- anything else regarding rendering, open gl etc. works fine on the nvidia GPU
- a minimal qt example to load an SVG file on the affected system also works
just fine
- updated and rolled back the previous nvidia driver version
- rebuilt nvidia kernel modules
Maybe also interesting, this issue has actually happened for the first time a
couple of months ago, after some qt packages where updated in debian trixie.
Also a segfault in the SVG lib from qt. Back then the issue could be resolved
permanently by clearing the qt caches or temporarily by setting qt to software
rendering.
The qt packages where not touched since then, the latest updates only included
an update of libkscreenlocker to 6.3.5-1, from 6.3.4-1 among other supposedly
unrelated packages.
I tried to revert the libkscreenlocker package to 6.3.4-1, that did not fix the
issue, though I am not sure how sound that configuration with just that
packages reverted even is.
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