https://bugs.kde.org/show_bug.cgi?id=406180
Bug ID: 406180
Summary: KWin 5.15.4 alt-tab hang regression on nvidia
Product: kwin
Version: 5.15.4
Platform: Archlinux Packages
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: kwin-bugs-n...@kde.org
Reporter: pieterjan.bri...@gmail.com
Target Milestone: ---
SUMMARY
KWin seems to have started to hang for me consistently on nvidia as of 5.15.4
when opening the alt tab menu.
STEPS TO REPRODUCE
1. Hold alt+tab for long enough for the list of programs to open
OBSERVED RESULT
KWin hangs for inconsistent amounts of time between 5 seconds and 30 seconds
(from what I've tried)
Eventually with enough patience, the alt tab window does open and works.
EXPECTED RESULT
KWin to not hang.
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch, everything up to date.
KDE Plasma Version: 5.15.4
KDE Frameworks Version: 5.56.0
Qt Version: 5.12.2
ADDITIONAL INFORMATION
My machine is an Optimus laptop, and the hang only happens when the nvidia card
is selected (not using bumblebee).
There is no hang if you release alt tab quickly enough for the alt tab menu to
not open.
The mouse is still responsive while KWin is hung, and it even changes icon when
going over text boxes.
While KWin is hanging (by holding down alt after hitting down alt tab, which
should normally keep the alt tab menu open),
flicking my mouse to the top or bottom to my screen where I have auto-hiding
panels seems to sometimes instantly unstuck KWin.
Turning off compositing with alt+shift+F12 "avoids" the problem.
The type of task switcher selected seems to have no effect. Both Text Only and
Breeze exhibit the behavior.
While hanging, the kwin_x11 process is taking 100% CPU of a single CPU core.
Sometimes the hang even locks up the mouse but I've yet to have the hang be
permanent requiring a system restart or anything. It always does come back,
eventually.
For some reason, the window of VSCode specifically goes blank after this hang
happens. Just something strange I've noticed.
Also, I think I've always kind of had KWin hang when alt tabbing on nvidia, but
it was very rare. I just chalked it up to nvidia having bad drivers and didn't
mind it too much since it was impossible to reproduce easily. Well not anymore.
This hang seems to be a regression on KWin's part, since rolling back to KWin
5.15.3 fixes the problem (mostly)
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