Bug 502579

Summary: Gamescope crashes when running games with multiple windows, started with KWin 6.3.4
Product: [Plasma] kwin Reporter: Matthew Schwartz <matthew.schwartz>
Component: generic-crashAssignee: KWin default assignee <kwin-bugs-null>
Status: RESOLVED DOWNSTREAM    
Severity: crash CC: kde, putr4.s
Priority: NOR    
Version First Reported In: 6.3.4   
Target Milestone: ---   
Platform: Arch Linux   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:
Attachments: coredump from gamescope w/ backtrace

Description Matthew Schwartz 2025-04-08 20:22:25 UTC 
Created attachment 180101 [details]
coredump from gamescope w/ backtrace

SUMMARY
After the latest version upgrade of KWin (6.3.3.1-2 -> 6.3.4-1) on Arch Linux, Steam games that have multiple game windows, like a launcher that appears and then closes before the game launches, will crash after the first window closes. 


STEPS TO REPRODUCE
1. Download Trackmania (free) from Steam
2. Add `gamescope -- %command%` to the game's launch options
3. Launch the game


OBSERVED RESULT
You should see the UPlay window appear for a few seconds, and then once that window disappears the game crashes instead of opening the main window.

EXPECTED RESULT
Gamescope should not crash under these circumstances, and did not crash until KWin 6.3.4. The crash also does not occur on Gnome.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: CachyOS Linux
KDE Plasma Version: KDE Plasma Version: 6.3.4
KDE Frameworks Version: KDE Frameworks Version: 6.12.0
Qt Version: Qt Version: 6.8.3 (Qt Version 6.9 has the same issue)

ADDITIONAL INFORMATION
Report in gamescope: https://github.com/ValveSoftware/gamescope/issues/1796

I'd recommend using gamescope 3.16.2, as there is a recent regression in 3.16.3 that can present somewhat similarly to this issue.
Comment 1 David Edmundson 2025-04-08 22:36:41 UTC 
If gamescope crashes, this is a gamescope problem
Comment 2 Matthew Schwartz 2025-04-08 23:14:19 UTC 
(In reply to David Edmundson from comment #1)
> If gamescope crashes, this is a gamescope problem

even if I cannot reproduce this issue on mutter, cosmic-comp, or KWin 6.3.3? I'm not discounting that it could be a gamescope bug, but there's only one version of one compositor where I can reproduce this so far, and it's KWin 6.3.4.
Comment 3 Matthew Schwartz 2025-04-09 01:11:37 UTC 
bisected to https://github.com/KDE/kwin/commit/93c9103ed3e1374d34394225ee3aa6cf8c8c955a on the KWin side with gamescope 3.16.2 at least, will flag it for the gamescope developer