[regression] gdm 3.27 shows blank login screen on primary monitor when two monitors are connected on a hybrid intel/nvidia system

[Rocko]

I normally have a second monitor plugged into my laptop. Recently in Ubuntu 18.04 (this is a regression that has happened in the last week or so), when I boot the laptop I get presented with a blank login screen - there is a mouse pointer, but the screen is just black instead of displaying the user names and top status bar. (The external monitor just shows the background screen, so it looks as if gdm3 has hung or crashed.)

If I unplug the external monitor, gdm draws the login screen correctly and I can log in.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: gdm3 3.27.90-0ubuntu1
ProcVersionSignature: Ubuntu 4.15.0-10.11-generic 4.15.3
Uname: Linux 4.15.0-10-generic x86_64
ApportVersion: 2.20.8-0ubuntu10
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Thu Mar 8 10:59:11 2018
InstallationDate: Installed on 2017-08-16 (203 days ago)
InstallationMedia: Ubuntu 17.04 "Zesty Zapus" - Release amd64 (20170412)
SourcePackage: gdm3
UpgradeStatus: Upgraded to bionic on 2017-11-17 (110 days ago)

[Daniel van Vugt (vanvugt)]

Rocko,

Please report the issue to the gdm developers here:

  https://bugzilla.gnome.org/enter_bug.cgi?product=gdm

and then let us know the new bug ID.

[Rocko (rockorequin)]

I have reported it at https://bugzilla.gnome.org/show_bug.cgi?id=794167.

[Rocko (rockorequin)]

It's not necessarily related to nvidia-graphics-drivers-390: I now have nvidia-387 installed and still experience the problem.

Also, the problem persists if I completely remove all nvidia drivers.

[Jean-Louis Dupond (dupondje)]

having the same issue here with intel/nvidia system but on Nouveau!

[Daniel van Vugt (vanvugt)]

Rocko: nvidia-387 doesn't seem to be an official Ubuntu package so we can't add a task for it.

Are you sure that's not a typo? Maybe nvidia-384?

[Rocko (rockorequin)]

nvidia-387 is from the http://ppa.launchpad.net/graphics-drivers/ppa/ubuntu ppa.

But I'd say that this bug is not at all related to the nvidia module, because the problem persists when I completely remove all nvidia packages from the system.

At all times I'm using the i915 module, so it is more likely to be related to that or the modeset(?) driver than to nvidia.

[Rocko (rockorequin)]

I'll try and describe the gdm login screen behaviour in more detail:

1. With no external monitor, the gdm login screen is shown as expected. This is true whether I unplug the external monitor after gdm is running or boot up without it plugged in at all. If I unplug the monitor, it takes a bit longer than I would expect before I see gdm's login screen, but it does eventually appear.

2. With an external monitor plugged in, the external monitor works correctly (it shows the gdm background) but the laptop monitor shows only a mouse cursor (or text cursor when entering a password). The background that it shows is whatever the last tty console was showing, so eg if I switch to tty3 and log in, then switch back to tty1, I see the mouse cursor and all the text left on the screen from tty3. This behaviour occurs on boot and also when I switch users or log out, ie whenever gdm's login screen should be visible.

[Rocko (rockorequin)]

There hasn't been any feedback from the developers at the upstream bug. Is there any other information I could provide to help debug this?

Also, I see on my bionic installation that mutter is at 3.28.0-2 but gdm3 is still at 3.27.92-0ubuntu1. Is there a 3.28 version of gdm that's coming out soon?

[Daniel van Vugt (vanvugt)]

I would go further and probably blame gdm3 or mutter. However we assign the bug to all related packages in the meantime, just so other people can find it.

[Rocko (rockorequin)]

And finally: I didn't install nvidia-384 because it actually installs nvidia-graphics-drivers-390 and that was a complete disaster for me because it didn't work at all with bumblebee.

[Rocko (rockorequin)]

Ok, I've finally got nvidia-driver-390 installed. I still get the black screen in gdm problem in intel and gdm crashes with a divide-by-zero error when I tried to boot using nvidia.

But I still don't think this is at all related to the nvidia driver, because if I purge all the nvidia drivers gdm still gives me a black screen. Is it possible it's checking the hardware and doing something weird? Doesn't gnome 3.28 do that so that it can support multiple graphics cards - I think I read that somewhere?

[Rocko (rockorequin)]

And I just rebooted and saw the login screen working again on the primary monitor. Since the previous reboot it looks like mutter upgraded to 3.28.0-2, so could the fix be in there?

[Daniel van Vugt (vanvugt)]

If you really have encountered a fix then I doubt it happened in:

  https://launchpad.net/ubuntu/+source/mutter/3.28.0-2

More likely it happened in:

  https://launchpad.net/ubuntu/+source/mutter/3.28.0-1

Regardless, a fix is great. If the problem reoccurs then please change the status back to New.

[Rocko (rockorequin)]

It definitely still happened with 3.28.0-1 (I reported that at the upstream bug, so I'm sure about that). Another change I made was to boot the kernel with nvidia-drm.modeset=0, but I'm not sure how that would affect things.

[Rocko (rockorequin)]

It wasn't due to nvidia-drm.modeset=0. gdm still works with that absent from the boot parameters.

It could be a fix in gdm3, which is now at 3.27.92-0ubuntu1. But https://launchpad.net/ubuntu/+source/gdm3/ suggests that was released over a week ago, and this problem was definitely still present yesterday.

It could also have been a fix in mesa, which I see has gone from 18.0.0~rc4 to 18.0.0~rc5.

[Daniel van Vugt (vanvugt)]

Yes it might have been Mesa.

Fortunately we won't need to figure out what fixed it, if the problem stays fixed.