lightdm spawning X servers at high rate on secondary seat in multiseat setup

[Schlomo Schapiro]

OS:
XUbuntu 14.10 amd64 with all updates installed.

Scenario:
Using a multiseat setup with 2 graphics cards.

Problem:
User on non-primary seat (seat-1) uses xscreensaver to lock screen (light-locker not working correctly). When the screen is in power saving mode lightdm tries to spawn an extra X server at a rate of about 20 per second, apparently to show the greeter which would be used to unlock the session.

From the lightdm.log file:
[+38145.59s] DEBUG: Seat seat-1: Stopping display server, no sessions require it
[+38145.59s] DEBUG: Seat seat-1: Active display server stopped, starting greeter
[+38145.59s] DEBUG: Seat seat-1: Creating greeter session
[+38145.59s] DEBUG: Seat seat-1: Creating display server of type x
[+38145.59s] DEBUG: Seat seat-1: Starting local X display
[+38145.59s] DEBUG: DisplayServer x-2: Logging to /var/log/lightdm/x-2.log
[+38145.59s] DEBUG: DisplayServer x-2: Writing X server authority to /var/run/lightdm/root/:2
[+38145.59s] DEBUG: DisplayServer x-2: Launching X Server
[+38145.60s] DEBUG: Launching process 22681: /usr/bin/X -core :2 -seat seat-1 -sharevts -auth /var/run/lightdm/root/:2 -nolisten tcp
[+38145.60s] DEBUG: DisplayServer x-2: Waiting for ready signal from X server :2
[+38145.69s] DEBUG: Process 22681 terminated with signal 6
[+38145.69s] DEBUG: DisplayServer x-2: X server stopped
[+38145.69s] DEBUG: DisplayServer x-2: Removing X server authority /var/run/lightdm/root/:2
[+38145.69s] DEBUG: Seat seat-1: Display server stopped
[+38145.69s] DEBUG: Seat seat-1: Stopping session
[+38145.69s] DEBUG: Seat seat-1: Session stopped
[+38145.69s] DEBUG: Seat seat-1: Stopping display server, no sessions require it
[+38145.69s] DEBUG: Seat seat-1: Active display server stopped, starting greeter
[+38145.69s] DEBUG: Seat seat-1: Creating greeter session
[+38145.69s] DEBUG: Seat seat-1: Creating display server of type x
[+38145.69s] DEBUG: Seat seat-1: Starting local X display

and so on, filling up the disk with junk logs.

From the corresponding X server log:
X.Org X Server 1.16.0
Release Date: 2014-07-16
X Protocol Version 11, Revision 0
Build Operating System: Linux 3.2.0-54-generic x86_64 Ubuntu
Current Operating System: Linux brho 3.16.0-28-generic #38-Ubuntu SMP Fri Dec 12 17:37:40 UTC 2014 x86_64
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.16.0-28-generic root=UUID=e080193a-c36a-47f5-8f9b-cb8b5528fdd4 ro quiet splash vt.handoff=7
Build Date: 09 December 2014 11:01:03PM
xorg-server 2:1.16.0-1ubuntu1.2 (For technical support please see http://www.ubuntu.com/support)
Current version of pixman: 0.32.4
 Before reporting problems, check http://wiki.x.org
 to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
 (++) from command line, (!!) notice, (II) informational,
 (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/var/log/Xorg.2.log", Time: Thu Jan 1 01:58:41 2015
(==) Using system config directory "/usr/share/X11/xorg.conf.d"
(II) [KMS] Kernel modesetting enabled.
(EE)
Fatal server error:
(EE) no screens found(EE)
(EE)
Please consult the The X.Org Foundation support
  at http://wiki.x.org
 for help.
(EE) Please also check the log file at "/var/log/Xorg.2.log" for additional information.
(EE)
(EE) Server terminated with error (1). Closing log file.

and from /var/log/Xorg.2.log:
[ 38270.601] (II) modesetting: Driver for Modesetting Kernel Drivers: kms
[ 38270.601] (II) FBDEV: driver for framebuffer: fbdev
[ 38270.601] (II) VESA: driver for VESA chipsets: vesa
[ 38270.601] (II) [KMS] Kernel modesetting enabled.
[ 38270.601] (WW) Falling back to old probe method for modesetting
[ 38270.601] (WW) Falling back to old probe method for fbdev
[ 38270.601] (II) Loading sub module "fbdevhw"
[ 38270.601] (II) LoadModule: "fbdevhw"
[ 38270.601] (II) Loading /usr/lib/xorg/modules/libfbdevhw.so
[ 38270.601] (II) Module fbdevhw: vendor="X.Org Foundation"
[ 38270.601] compiled for 1.16.0, module version = 0.0.2
[ 38270.601] ABI class: X.Org Video Driver, version 18.0
[ 38270.601] (WW) Falling back to old probe method for vesa
[ 38270.601] (II) RADEON(0): Creating default Display subsection in Screen section
 "Default Screen Section" for depth/fbbpp 24/32
[ 38270.601] (==) RADEON(0): Depth 24, (--) framebuffer bpp 32
[ 38270.601] (II) RADEON(0): Pixel depth = 24 bits stored in 4 bytes (32 bpp pixmaps)
[ 38270.601] (==) RADEON(0): Default visual is TrueColor
[ 38270.601] (==) RADEON(0): RGB weight 888
[ 38270.601] (II) RADEON(0): Using 8 bits per RGB (8 bit DAC)
[ 38270.601] (--) RADEON(0): Chipset: "ATI Radeon HD 3450" (ChipID = 0x95c5)
[ 38270.601] (EE) RADEON(0): [drm] failed to set drm interface version.
[ 38270.601] (EE) RADEON(0): Kernel modesetting setup failed
[ 38270.601] (II) UnloadModule: "radeon"
[ 38270.601] (EE) Screen(s) found, but none have a usable configuration.
[ 38270.601] (EE)
Fatal server error:
[ 38270.601] (EE) no screens found(EE)
[ 38270.601] (EE)

kernel log shows nothing at the times indicated.

Expected behaviour:
Should be able to start X server that shows a greeter. According to https://lists.launchpad.net/ubuntu-multiseat/msg00505.html this should work in utopic.

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: lightdm 1.12.1-0ubuntu1
ProcVersionSignature: Ubuntu 3.16.0-28.38-generic 3.16.7-ckt1
Uname: Linux 3.16.0-28-generic x86_64
ApportVersion: 2.14.7-0ubuntu8
Architecture: amd64
Date: Thu Jan 1 01:50:25 2015
InstallationDate: Installed on 2014-12-26 (5 days ago)
InstallationMedia: Xubuntu 14.10 "Utopic Unicorn" - Release amd64 (20141022.1)
SourcePackage: lightdm
UpgradeStatus: No upgrade log present (probably fresh install)

[penalvch (penalvch)]

Schlomo Schapiro, thank you for reporting this bug to Ubuntu. Utopic reached EOL on July 23, 2015.
See this document for currently supported Ubuntu releases: https://wiki.ubuntu.com/Releases

If this is reproducible in a supported release, please file a new report.