[Bug 1761016] Re: cherry-pick https://codereview.qt-project.org/#/c/224684/ to fix image slideshows in KDE Plasma

[Nate Graham]

** Description changed:

- KDE Plasma is affected by a Qt bug that causes image slideshows to leak
- memory, eventually exhausting all available memory and crashing the
- system: https://bugs.kde.org/show_bug.cgi?id=368838
+ [Impact]
  
- This principally affects people who use the popular slideshow wallpaper
- feature. Thankfully, there's a Qt patch to fix it the issue:
- https://codereview.qt-project.org/#/c/224684/
+  * Due to a Qt bug, using an image slideshow for the wallpaper causes a memory leak that eventually causes the system to freeze. The severity of the leak is proportional to the speed with which images are changed in the slideshow.
+  * Given the popularity of the image slideshow wallpaper feature, this is a high-profile, easily reproducible issue.
+  * See https://bugs.kde.org/show_bug.cgi?id=368838 and https://codereview.qt-project.org/#/c/224684/
  
- It's slated to go into Qt 5.11. We should strongly consider cherry-
- picking it into 5.9.x to get this important fix into our users' hands as
- soon as possible.
+  * An attempt was made to backport the fix prior to Bionic's release,
+ but this was overlooked or unsuccessful (see the history here). As a
+ result, it now needs to be done as an SRU.
+ 
+ [Test Case]
+ 
+  * Use KDE Plasma
+  * Right-click on the desktop and choose "Configure Desktop"
+  * Change the wallpaper type to "Slideshow" and choose a folder full of images
+  * Click Apply
+  * Wait a few days; Plasma will eventually totally freeze
+ 
+ [Regression Potential]
+ 
+  * Regressions are unlikely given that the specific backport patch has
+ been well-tested by many in https://bugs.kde.org/show_bug.cgi?id=368838,
+ and the actual code fix in Qt was released to users in Qt 5.11 months
+ ago.

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Title:
  cherry-pick https://codereview.qt-project.org/#/c/224684/ to fix
  image slideshows in KDE Plasma

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