Bug 461156

Summary:	On X11, kwin locks up with 100% CPU load when external screen gets plugged in
Product:	[Plasma] kwin	Reporter:	Ralf Jung <post>
Component:	general	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED WORKSFORME
Severity:	major	CC:	kde, nate, xaver.hugl
Priority:	NOR	Keywords:	regression
Version First Reported In:	5.26.0
Target Milestone:	---
Platform:	Other
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description Ralf Jung 2022-10-29 13:04:46 UTC

SUMMARY
Each time I plug in my external screen, kwin just freezes up with 100% CPU load. I need to SIGKILL it from a tty (SIGTERM is being ignored), and then somehow get the desktop session to work again.

SOFTWARE/OS VERSIONS
Operating System: Debian GNU/Linux
KDE Plasma Version: 5.26.0
KDE Frameworks Version: 5.98.0
Qt Version: 5.15.6
Kernel Version: 6.0.0-2-amd64 (64-bit)
Graphics Platform: X11
Processors: 8 × Intel® Xeon® CPU E3-1505M v5 @ 2.80GHz
Memory: 31,2 GiB of RAM
Graphics Processor: Mesa Intel® HD Graphics P530
Manufacturer: LENOVO
Product Name: 20ENCTO1WW
System Version: ThinkPad P50

ADDITIONAL INFORMATION
This is just the last in a series of crash/freeze/hang bugs that kwin_x11 is suffering from recently. I am not sure if there is something odd about my system or if nobody is using KDE on X11 any more and hence those codepaths are just bitrotting.

Comment 1 Nate Graham 2022-11-01 13:58:26 UTC

> nobody is using KDE on X11 any more and hence those codepaths are just bitrotting
None of the KWin developers are, at least. So this is a very likely scenario.

Is this a regression in Plasma 5.26?

Comment 2 Ralf Jung 2022-11-01 15:35:16 UTC

Yes this started after upgrading to Plasma 5.26.0 from some 5.25.x.
I am now using the wayland session and experiencing various problems there -- will file / have filed those as separate bugreports.

Comment 3 David Edmundson 2023-01-23 14:00:06 UTC

We haven't had any duplicate reports on X11. Not have we duplicated it in X11 testing.

It could be caused by a rogue kwin script or other third party? Can you check you have none enabled. Please can you confirm if it's still an issue on 5.27?

I'll close this report as there isn't enough information to do anything too useful, but if you can reproduce please run:
 
sudo perf record --call-graph dwarf -p (`pidof kwin_x11`)

and share the log

Comment 4 Ralf Jung 2023-01-25 19:05:33 UTC

I have switched to Wayland to avoid all these X11 issues, and am not able to reproduce this any more.