Firefox seems to be most severely affected, to the point of making it hard to finish this message, perhaps because of its more complex UI composition pipeline. This looks like a bug in graphics primitives (EGL?). Apps render correctly into surfaces, but then the surfaces are incorrectly composited.

Relevant recent package upgrades:

firefox.x86_64 84.0.2-1.fc32
kernel*.x86_64 5.10.11-100.fc32
firefox.x86_64 85.0-2.fc32
gnome-desktop3.x86_64 3.36.8-1.fc32
kernel*.x86_64 5.10.12-100.fc32
gtk3.x86_64 3.24.23-1.fc32

Might be a Firefox-specific issue after all. Firefox restart resolves the flickering for some time. I will try to test with disabled WebRender. How Firefox managed to cause the flickering in another app during system lockup is a mystery to me.

I think the correct component is mutter. But I suggest to update to Fedora 33 first.

After disabling WebRender in Firefox, I haven't seen any more visual instability in Firefox.

I have however observed flickering of title bars in a flatpak app (custom-built Eclipse flatpak) and the lockup I mentioned before happened when another flatpak app (Zim) was flickering. Since these two issues (Firefox WebRender issue and title bar flickering) occurred at about the same time, I assumed they are related, but perhaps they are not.

I wouldn't be able to upgrade to F33 for several weeks. This issue nevertheless became a low priority after disabling WebRender.

Robert, please attach your about:support page.
Thanks.

Created attachment 1755690 [details]
Firefox support:about page

This is with software WebRender. I can also post the same page with hardware WebRender enabled if needed.

Interestingly, while saving the page, I notices visual artefacts even in software rendering mode. Parts of the main menu appear and disappear as I move mouse cursor over it.

Thanks.
Software WebRender is not finished yet, you should use Basic compositor.

This is definitely not just Firefox issue. I have now seen odd highlight gradient when hovering mouse over Gnome system menu in the top right corner of the screen. And I have observed flickering in desktop area not covered by any window. Bits of some app were flickering in that area several times per second as I moved mouse over it. This happened shortly after I have observed flickering of window title in one app (switching between old and new title text rapidly).

All of this behavior is new in the last 1-2 weeks. The desktop was visually stable before. Judging by package updates, it's either gtk3, gnome-desktop, or kernel.

Try downgrading the kernel and/or mesa. Random glitches suddenly appearing tends to be OpenGL driver issues.

After some tinkering with downgrades of packages, I have narrowed it down to kernel 5.10.x. When I boot with 5.10.x kernel, I get severe flickering within one hour in all apps, rendering the computer unusable. When I reboot with kernel 5.9.13, I can use the computer all day long with next to no flickering. The only artifact that remains after downgrade to 5.9.13 is that one of my monitors occasionally goes black for a few seconds once in a few hours and there are also rare glitches (image skewed for a split-second) on that monitor. This was not happening a month or two ago, so I guess there is something else besides the kernel that contains less severe version of the bug. Nevertheless, upgrade to kernel 5.10.x explains 99% of the artifacts.

Chances are that this is the same issue with the new i915 CVE mitigations which landed in 5.10.9 as which others are seeing, see  bug 1931065 comment 1. for a number of workarounds / things you can do to help debug this.

Passing boot param "i915.mitigations=off" to 5.10.x kernel removes the visual glitches. This is indeed the same issue as 1931065.

(In reply to Robert Vazan from comment #13)
> Passing boot param "i915.mitigations=off" to 5.10.x kernel removes the
> visual glitches. This is indeed the same issue as 1931065.

Ok, so this is the same issue which we've been working on fixing / trying to pin down in bug 1925346 (bug 1931065 is a dup of bug 1925346). There are 3 fixes upstream for this which help fix this for almost all users (there is 1 report/case of the fixes not fully fixing things).

It would be great if you (and other people seeing this) can try a kernel which I build with the 3 fixes added:

https://koji.fedoraproject.org/koji/taskinfo?taskID=61751956

Here are some generic instructions on directly installing a kernel from koji (the Fedora buildsystem):
https://fedorapeople.org/~jwrdegoede/kernel-test-instructions.txt

Note this kernel is a test-build and as such is not signed, so to run this one you do need to disable secure-boot.

*** This bug has been marked as a duplicate of bug 1925346 ***