Bug 471866

Summary:	Krita crash with QT_QPA_PLATFORMTHEME=kde
Product:	[Applications] krita	Reporter:	Oleg Nikitin <asrifox>
Component:	* Unknown	Assignee:	Krita Bugs <krita-bugs-null>
Status:	RESOLVED DOWNSTREAM
Severity:	crash	CC:	asrifox, dimula73, halla, kde
Priority:	NOR
Version First Reported In:	5.1.5
Target Milestone:	---
Platform:	Arch Linux
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description Oleg Nikitin 2023-07-02 10:40:57 UTC

SUMMARY
Krita crashes immediately upon launching with environment variable `QT_QPA_PLATFORMTHEME=kde`. When set to other values (tried empty and `qt5ct`) it works as intended. 

STEPS TO REPRODUCE
1. Set `QT_QPA_PLATFORMTHEME` environment variable to `kde`.
2. Launch Krita. 

OBSERVED RESULT
Immediate crash.

EXPECTED RESULT
Krita should launch.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 
KDE Plasma Version: 5.27.6
KDE Frameworks Version: 5.107.0
Qt Version: 5.15.10

ADDITIONAL INFORMATION
Application: krita (krita), signal: Segmentation fault

[KCrash Handler]
#4  0x00007f51cb78b09c in QOpenGLContext::create() () at /usr/lib/libQt5Gui.so.5
#5  0x00007f51c4288d51 in  () at /usr/lib/qt/plugins/platformthemes/KDEPlasmaPlatformTheme.so
#6  0x00007f51cb29b087 in QCoreApplicationPrivate::init() () at /usr/lib/libQt5Core.so.5
#7  0x00007f51cb29ec92 in QCoreApplication::QCoreApplication(int&, char**, int) () at /usr/lib/libQt5Core.so.5
#8  0x000055dbe50f4f49 in  ()
#9  0x00007f51caa39850 in  () at /usr/lib/libc.so.6
#10 0x00007f51caa3990a in __libc_start_main () at /usr/lib/libc.so.6
#11 0x000055dbe50f8795 in  ()
[Inferior 1 (process 440809) detached]

Comment 1 Halla Rempt 2023-07-02 10:42:21 UTC

Please report this to Arch. It's not something we can fix in Krita.

Comment 2 pdf 2023-10-01 01:17:59 UTC

FWIW, this happens on Fedora too, so is this a problem for all downstreams? And if it is, what path should they take to resolve it? It seems rather bizarre to me that a KDE-affiliated application crashes on start with `QT_QPA_PLATFORMTHEME=kde` to me, but maybe I don't understand the implications.

Comment 3 Halla Rempt 2023-10-01 09:36:13 UTC

The crash obviously happens in KDEPlasmaPlatformTheme.so, somewhere in Qt's opengl code. So, how is this a bug in krita?

Comment 4 pdf 2023-10-01 10:49:57 UTC

If the bug is in QT, then why was the advice to punt the report down to Arch, instead of up to QT?

Also, the fact that it's *only* Krita that segfaults in this fashion suggests that this is unlikely to be a general, common QT problem, and is likely somehow related to how Krita is instantiating the QCoreApplication. In addition, the fact that Krita stops crashing if QT_QPA_PLATFORMTHEME is set to something other than `kde` suggests that the problem is related to the combination of Krita+KDEPlasmaPlatformTheme+QT.

Since this is 100% reproducable, I'm happy to assist in providing information, if anyone cand provide some indication on what info would be useful.

Comment 5 Dmitry Kazakov 2023-10-02 07:42:53 UTC

Hi, pdf!

During startup phase, Krita creates a dozen of QApplication objects to probe all supported openGL modes and then discards them. That is usually not favored by the themes code, because they expect QApplication to be created only once (they tend to use static data that they don't dispose on destruction). That is the problem we had to patch/workaround in our version of Qt/KF5. Most probably, this crash has the same nature.