Fix race condition in gdm with simpledrm and real drm drivers

[Mario Limonciello]

[ Impact ]
When the kernel has been compiled with FB_EFI=n, FB_VESA=n, SIMPLEDRM=y a series of events can occur that cause simpledrm to race with GDM. When GDM loses the race then a user is left with a black screen.

This series of events doesn't currently happen in Jammy kernels, but can happen from a mainline kernel or HWE kernel that enables it. To protect users from this circumstance it is better to fix the race condition.

This issue has been readily reproduced in Ubuntu and reported to upstream mutter. It's also already fixed in GNOME 45, included in Mantic and later.
https://gitlab.gnome.org/GNOME/mutter/-/issues/2909

[ Test Plan ]
* Ensure that a kernel with required kernel changes can boot to GDM using DRM driver (amdgpu, i915, or nouveau)

[ Where Problems could occur ]
* GDM can take longer to start up while settling

[ Other Info ]
* Fedora bug: https://bugzilla.redhat.com/show_bug.cgi?id=2022385
* the changes needed to enable this in the kernel are tracked in bug 1965303

[Timo Aaltonen (tjaalton)]

Hello Mario, or anyone else affected,

Accepted gdm3 into jammy-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/gdm3/42.0-1ubuntu7.22.04.4 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-jammy to verification-done-jammy. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-jammy. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

[Mario Limonciello (superm1)]

I've loaded up a system with a hand built kernel that has simpledrm enabled, and then verified the problem occurred. I then updated to proposed and verified it went away.

[Launchpad Janitor (janitor)]

This bug was fixed in the package gdm3 - 42.0-1ubuntu7.22.04.4

---------------
gdm3 (42.0-1ubuntu7.22.04.4) jammy; urgency=medium

  * Add local-display-factory-skip-simpledrm-when-checking-.patch to
    fix a race condition that occurs with simpledrm (LP: #2039757)

 -- Mario Limonciello <email address hidden> Tue, 30 Jan 2024 11:28:18 -0600

[Łukasz Zemczak (sil2100)]

The verification of the Stable Release Update for gdm3 has completed successfully and the package is now being released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.