Bug 286023

Summary:	KWin freezes when presenting desktop grid
Product:	[Plasma] kwin	Reporter:	Allan Sandfeld <kde>
Component:	effects-window-management	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED DUPLICATE
Severity:	normal
Priority:	NOR
Version:	CVS
Target Milestone:	---
Platform:	Unlisted Binaries
OS:	Linux
Latest Commit:		Version Fixed In:
Sentry Crash Report:
Attachments:	Proposed patch

Description Allan Sandfeld 2011-11-07 17:45:11 UTC

Version:           CVS (using Devel) 
OS:                Linux

When activating the present desktop grid effect, the +- button is drawn but otherwise the screen remains unchanged, and kwin hangs until forcibly restarted.

The problem is reproducible with both XRender and OpenGL effects. It should maybe be noted I have a 2x3 layout of desktops. The effect works without fault in KDE 4.7, but is broken in TRUNK (to be 4.8 beta)

Reproducible: Didn't try

Steps to Reproduce:
Activate present desktop grid (ctrl+f8)

Actual Results:  
KWin freezes

Expected Results:  
Desktop grid presented

Comment 1 Thomas Lübking 2011-11-07 19:01:34 UTC

This is most likely bug #282461 - did you try the _very_ latest git version?

Comment 2 Allan Sandfeld 2011-11-07 21:47:53 UTC

This is from a completely clean build of git trunk checked out earlier today.

Comment 3 Allan Sandfeld 2011-11-07 21:57:10 UTC

It seems to be the same as bug #282461 description though, except here is is 100% reproducible. 

Backtrace shows three threads, all in what appears to be their central loops. 

The first in QEventLoop::exec()
The second in QTWFT::TCMalloc_PageHeap::scanvengerThread() 
The last in QProcessManager::run()

Comment 4 Allan Sandfeld 2011-11-08 12:32:48 UTC

Key observation for reproducing: The issue only happens when the "present windows" option is disabled. I think this options is enabled by default, but I have disabled it to present the desktops as they actually look.

Comment 5 Allan Sandfeld 2011-11-08 12:46:53 UTC

Created attachment 65383 [details]
Proposed patch

Only one changed seems to have been made since 4.7, so by looking at that I have a suggestion on how to fix the bug. The patch seems to work, but I don't know the code well enough to know if this is the correct solution. Please review.

Comment 6 Martin Flöser 2011-11-12 15:17:12 UTC

next time please do a review request - I just did the same patch myself :-(

*** This bug has been marked as a duplicate of bug 282461 ***

Comment 7 Allan Sandfeld 2011-11-15 16:48:28 UTC

Sorry. I had no real way of knowing if what I did made any sense, it was only a guess. It was only based on reviewing changes, and changing one check to another similar check used elsewhere in the code.

Btw. That a random guess is correct, is a sign of great software clarity :)