Frozen (black) screen on resume/unlock in Xorg sessions

[sds]

I have a monitor to which I connect using an HDMI cable.
While connected, I have 2 displays and I can use both fine.
When I disconnect, it is also fine, until I close the laptop or it goes to sleep.
When it wakes up, I get the unlock/login screen, and I can login fine as anyone but myself.
When I login as myself (i.e., unlock the screen rather than login), I get a completely black screen.
I can get the login/unlock screen back using Ctrl-Alt-F1, and repeat an attempt to unlock with the same result - black screen.
My only options appears to be reboot or kill the X server from the console (Ctrl-Alt-F2, login and kill).
This started to happen recently (a month?)

ProblemType: Bug
DistroRelease: Ubuntu 18.10
Package: xorg 1:7.7+19ubuntu8
ProcVersionSignature: Ubuntu 4.18.0-12.13-generic 4.18.17
Uname: Linux 4.18.0-12-generic x86_64
.tmp.unity_support_test.0:

ApportVersion: 2.20.10-0ubuntu13.1
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: None
CurrentDesktop: ubuntu:GNOME
Date: Tue Dec 4 21:18:19 2018
DistUpgraded: 2018-10-28 13:01:03,617 DEBUG Running PostInstallScript: './xorg_fix_proprietary.py'
DistroCodename: cosmic
DistroVariant: ubuntu
DkmsStatus:
 system76, 1.0.0~1540923431~18.10~33e9d57~dev, 4.18.0-11-generic, x86_64: installed
 system76, 1.0.0~1540923431~18.10~33e9d57~dev, 4.18.0-12-generic, x86_64: installed
ExtraDebuggingInterest: Yes, if not too technical
GpuHangFrequency: Several times a week
GpuHangReproducibility: Yes, I can easily reproduce it
GpuHangStarted: Since a couple weeks or more
GraphicsCard:
 Intel Corporation 4th Gen Core Processor Integrated Graphics Controller [8086:0416] (rev 06) (prog-if 00 [VGA controller])
   Subsystem: CLEVO/KAPOK Computer 4th Gen Core Processor Integrated Graphics Controller [1558:6504]
MachineType: System76, Inc. Gazelle Pro
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.18.0-12-generic root=UUID=7d2767f3-1197-464e-97fa-45cecbaa7e66 ro quiet splash vt.handoff=1
SourcePackage: xorg
Symptom: display
Title: Xorg freeze
UpgradeStatus: Upgraded to cosmic on 2018-10-28 (37 days ago)
dmi.bios.date: 06/04/2015
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 1.04SB.01RSY5
dmi.board.asset.tag: Tag 12345
dmi.board.name: Gazelle Pro
dmi.board.vendor: System76, Inc.
dmi.board.version: gazp9c
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 9
dmi.chassis.vendor: Notebook
dmi.chassis.version: N/A
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr1.04SB.01RSY5:bd06/04/2015:svnSystem76,Inc.:pnGazellePro:pvrgazp9c:rvnSystem76,Inc.:rnGazellePro:rvrgazp9c:cvnNotebook:ct9:cvrN/A:
dmi.product.family: Not Applicable
dmi.product.name: Gazelle Pro
dmi.product.sku: Not Applicable
dmi.product.version: gazp9c
dmi.sys.vendor: System76, Inc.
modified.conffile..etc.default.apport: [modified]
mtime.conffile..etc.default.apport: 2015-10-05T22:04:33.987988
version.compiz: compiz 1:0.9.13.1+18.10.20180930-0ubuntu1
version.libdrm2: libdrm2 2.4.95-1
version.libgl1-mesa-dri: libgl1-mesa-dri 18.2.2-0ubuntu1
version.libgl1-mesa-glx: libgl1-mesa-glx 18.2.2-0ubuntu1
version.xserver-xorg-core: xserver-xorg-core 2:1.20.1-3ubuntu2.1
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.10.6-1
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:18.1.0-1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20171229-1ubuntu1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.15-3
xserver.bootTime: Sat Oct 14 23:40:31 2017
xserver.configfile: default
xserver.errors:

xserver.logfile: /var/log/Xorg.0.log
xserver.version: 2:1.19.3-1ubuntu1.1
xserver.video_driver: modeset

[Daniel van Vugt (vanvugt)]

Does the problem only occur in Xorg sessions (the "Ubuntu" login option)? Or does it also occur in "Ubuntu on Wayland" sessions?

[sds (sds-gnu)]

I don't use Wayland.

[Daniel van Vugt (vanvugt)]

Please test "Ubuntu on Wayland" so that we can see if the problem is in code that's common to both.

[sds (sds-gnu)]

When I try `Ubuntu on Wayland`, the behavior is, indeed, different.
After disconnecting HDMI, the system never suspends (so I cannot reproduce the problematic behavior), even when I close the lid.
However, `tmux` hangs and loadavg stays at 1.
After I `kill -9` tmux and force suspend using the power button, I can login fine.

Thus it appears that the problem is not reproducible on Wayland

[Daniel van Vugt (vanvugt)]

Thank you for reporting this bug to Ubuntu.
Ubuntu 18.10 (cosmic) reached end-of-life on July 18, 2019.

See this document for currently supported Ubuntu releases:
https://wiki.ubuntu.com/Releases

We appreciate that this bug may be old and you might not be interested in discussing it any more. But if you are then please upgrade to the latest Ubuntu version and re-test. If you then find the bug is still present in the newer Ubuntu version, please add a comment here telling us which new version it is in and change the bug status to Confirmed.