The greeter freezes for multi-display setups

[nicolasdumitru]

I am testing COSMIC on my laptop and I have issues logging into the desktop environment when my external is plugged in. Mainly, the login screen is frozen from the very beginning and I cannot type in my password if I have my external monitor plugged in. When no external monitors are plugged in, the greeter more or less works.

In my attempts to fix this, I have tried deleting ~/.local/state/cosmic-comp/outputs.ron to no avail. I have also tried to disable variable refresh rates on both of my displays; this enabled me to log in... twice. I decided, however, to save the "working" outputs.ron file, switch vrr back on to test it. It has not worked since; I attempted to reproduce the desired behavior by applying the "fix" two more times and it failed.
This is my outputs.ron.
The exact version of COSMIC that I tested can be pinpointed by examining my NixOS config at this particular commit, and, in particular, the flake.lock file. I have an Intel CPU and a dedicated Nvidia GPU (this may or may not be relevant). Disabling the Nvidia driver in my config and rebuilding the system does not seem to fix the issue.

[AlternateIf]

don't think this is cpu or gpu related. have the same issue on my dual screen desktop. when i start it with only the main one being turned on it works. (after login enabling second monitor works too)

but when i have both monitors enabled from the beginning the login is frozen

[nicolasdumitru]

@AlternateIf I don't think it's necessarily hardware related either. In fact, I probably should have been clearer about this, but still, I thought that it might be worth mentioning, just in case.

[GeorgEchterling]

This may be the same issue: pop-os/cosmic-greeter#93

The issue seems to depend on the monitor and/or GPU. I have two systems running the Pop!_OS alpha:

• One desktop with an RX 7900 XTX with 2 MSI MAG274QRF-QD connected via DP. This system has the issue on (almost?) every startup if both monitors are turned on. There's no issue if I turn off one monitor before booting.
• One Framework 16 (with the AMD GPU) with a CF791 connected via a DP module and some Acer monitor connected via a USB C to HDMI cable. This system does not have the freeze issue.

[nicolasdumitru]

Indeed, it seems like it is, in fact, the same issue. I'd be willing to close it as a duplicate, but I'd like a confirmation before taking action. Can you check to see if you can reproduce it on your Nvidia desktop with the version indicated in my issue description? This would be a strong indicator that it's an Nvidia problem. Another reason to believe this is that I first started to experience the issue when the Nvidia driver was updated in nixpkgs. Also, what Nvidia driver version have you managed to reproduce this bug with?

[GeorgEchterling]

My Desktop has an AMD GPU, so it's not an Nvidia problem.

[nicolasdumitru]

I misread that, my bad

[GeorgEchterling]

I've now had a Greeter freeze once on my (until now unaffected) Framework system. It happened when I changed the display input on the CF791 from HDMI to the DisplayPort connected to the system.

The problem may be related to display (dis)connection event timing. Some monitors may be less/more affected depending on how fast they initialize on startup. (But this is just a wild guess.)

[nicolasdumitru]

I've resorted to using SDDM for the moment. The desktop environment itself is working fine and the greeter is the only broken critical component for me. I'd like to also keep testing the greeter, but I will be unable to do so until this issue and pop-os/cosmic-greeter#93 are properly addressed.

[GeorgEchterling]

I've swapped the DisplayPort connectors on my monitors, such that my left display is now initialized first (both for the LUKS password screen and for the Greeter) and is shown as display 0 in the settings app. I've rebooted 4 times since then, and the issue only occurred once. The one time it occurred, the LUKS password screen was using a 4:3 resolution, instead of the usual 16:9. Maybe this issue occurs when the leftmost screen's resolution is changed while the Greeter is running/starting?