1899455 - Parts of pages disappeared and reappeared when scrolling

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, defect)

Description

[Matt Fagnani]

Steps to reproduce:

I ran Firefox 128.0a1 20240528214532 on Wayland with WebRender compositing in Plasma 6.0.5 in a Fedora 40 KDE Plasma installation. I selected More Troubleshooting information from the Help menu or about:support and pages like https://bodhi.fedoraproject.org/updates/?releases=F40 I scrolled down and up the pages many times.

Actual results:

Parts of the about:support page disappeared when I scrolled down them such the boxes with information below the headers Application Basics, Crash Reports in the last 3 days, Nightly Features, ... but not those headers themselves. Scrolling up sometimes made parts of those areas appear again. I first noticed this problem on https://bodhi.fedoraproject.org/updates/?releases=F40 where the images with pending -> testing and the search box and the top right disappeared when scrolling and the Login button went from blue to white at the same times. On bugs on bugzilla.mozilla.org some parts like the users' icons to the left of the commenters' names and the Open status at the top left were missing and reappeared.

The problem didn't happen with 128.0a1 20240528001238. I bisected the problem to a patch for Bug 1898625 - Pt 1 - Snap clip display items prior to applying external scroll offset

8:25.39 INFO: Narrowed integration regression window from [a0891af7, a8c42063] (3 builds) to [6a6614ed, a8c42063] (2 builds) (~1 steps left)
8:25.39 INFO: No more integration revisions, bisection finished.
8:25.39 INFO: Last good revision: 6a6614edc627b811946a1628bcb249bc08408076
8:25.39 INFO: First bad revision: a8c42063aedd5fe4f5c5ca10cd297b3b200f43f1
8:25.39 INFO: Pushlog:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=6a6614edc627b811946a1628bcb249bc08408076&tochange=a8c42063aedd5fe4f5c5ca10cd297b3b200f43f1

I'm assigning the problem to Core: Graphics: WebRender since that is the component for Bug 1898625

Expected results:

The pages should have been shown normally when scrolling.

Comment 1

[Glenn Watson [:gw]]

I've asked for this patch to be backed out for now - I think I can see the problem in the patch, but we'll back it out for now anyway.

Comment 2

[Matt Fagnani]

Thanks. This problem didn't happen with 128.0a1 20240529013712 which appeared to have that patch backed out https://hg.mozilla.org/mozilla-central/rev/198b8c4a9b506b8bb15c4bc93dba876c4bdb1289