lightdm crashes during normal operation with no obvious cause

[James Tait]

This has happened several times in the last few weeks, including twice yesterday. There is no obvious user action that triggers the crash: the first crash yesterday, I was composing an e-mail in the GMail pop-out editor; the second I was editing a config file on a remote server via SSH; previously, the crash has happened while I've been just reading something on the screen, not interacting with the computer at all.

The symptoms are a non-responsive display, with the exception of the mouse pointer. I'm not even able to switch to a different vt - just get a black screen. However, I *am* able to SSH into the machine, and when I did so yesterday I tried:

 * killing compiz
 * restarting the unity7 upstart job (my windows flashed briefly on the screen, then I got the login background)
 * restarting lightdm

The latter action got me to a login prompt, where I was able to login and start a standard desktop session and, thankfully, resume my screen and tmux sessions and not lose any work.

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: lightdm 1.12.3-0ubuntu1
ProcVersionSignature: Ubuntu 3.16.0-30.40-generic 3.16.7-ckt3
Uname: Linux 3.16.0-30-generic x86_64
ApportVersion: 2.14.7-0ubuntu8.2
Architecture: amd64
CurrentDesktop: Unity
Date: Wed Apr 8 14:55:47 2015
EcryptfsInUse: Yes
InstallationDate: Installed on 2014-07-04 (277 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
SourcePackage: lightdm
UpgradeStatus: Upgraded to utopic on 2015-01-31 (66 days ago)

[James Tait (jamestait)]

Since it doesn't look like the bug report includes it, my display information is:

jtait@gazpacho:~$ sudo lshw -numeric -C display
  *-display
       description: VGA compatible controller
       product: 4th Gen Core Processor Integrated Graphics Controller [8086:416]
       vendor: Intel Corporation [8086]
       physical id: 2
       bus info: pci@0000:00:02.0
       version: 06
       width: 64 bits
       clock: 33MHz
       capabilities: msi pm vga_controller bus_master cap_list rom
       configuration: driver=i915 latency=0
       resources: irq:45 memory:f7800000-f7bfffff memory:e0000000-efffffff ioport:f000(size=64)