Alt-Tab switcher regularly goes into "flicker loop of death" or just hangs

[Nathaniel W. Turner]

Recently when doing Alt-Tab (and Alt-`) to switch between windows, the rectangle display showing the icons for all the applications and windows will suddenly start flickering rapidly and the whole X sessions will become unresponsive to keypresses and mouse actions. Sometimes instead of flickering, the Alt-Tab display will simply fail to appear and the same unresponsive X session results.

This seems to happen very frequently during the course of a day. When it happens, my only recourse is to press Ctrl-Alt-F2 to get a text console, log in, and run "killall compiz" and then "DISPLAY=:0 metacity" to kill the hung window manager and start a new one. (I tried running "DISPLAY=:0 compiz" from VT2, but that doesn't seem to start compiz in a fully functional manner.)

I'm reporting this from a system with an NVidia card, but I experience the same thing on another system using an ATI "Radeon HD 7970/R9 280X" card, so I don't think it's video-driver specific.

Needless to say, this makes Unity pretty hard to use effectively.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: unity 7.1.2+14.04.20140217-0ubuntu1
ProcVersionSignature: Ubuntu 3.13.0-8.28-generic 3.13.2
Uname: Linux 3.13.0-8-generic x86_64
NonfreeKernelModules: nvidia
.proc.driver.nvidia.gpus.0: Error: [Errno 21] Is a directory: '/proc/driver/nvidia/gpus/0'
.proc.driver.nvidia.registry: Binary: ""
.proc.driver.nvidia.version:
 NVRM version: NVIDIA UNIX x86_64 Kernel Module 304.117 Tue Nov 26 21:25:36 PST 2013
 GCC version: gcc version 4.8.2 (Ubuntu/Linaro 4.8.2-14ubuntu4)
.tmp.unity.support.test.0:

ApportVersion: 2.13.2-0ubuntu4
Architecture: amd64
CompizPlugins: [core,composite,opengl,decor,mousepoll,grid,vpswitch,compiztoolbox,imgpng,gnomecompat,regex,move,place,resize,snap,unitymtgrabhandles,wall,animation,session,expo,workarounds,fade,ezoom,scale,unityshell]
CompositorRunning: compiz
CompositorUnredirectDriverBlacklist: '(nouveau|Intel).*Mesa 8.0'
CompositorUnredirectFSW: true
CurrentDesktop: Unity
Date: Tue Feb 18 15:24:16 2014
DistUpgraded: 2014-01-22 19:30:50,196 DEBUG enabling apt cron job
DistroCodename: trusty
DistroVariant: ubuntu
DkmsStatus:
 nvidia-304-updates, 304.117, 3.11.0-15-generic, x86_64: installed
 nvidia-304-updates, 304.117, 3.13.0-7-generic, x86_64: installed
 nvidia-304-updates, 304.117, 3.13.0-8-generic, x86_64: installed
EcryptfsInUse: Yes
GraphicsCard:
 NVIDIA Corporation G73 [GeForce 7600 GT] [10de:0391] (rev a1) (prog-if 00 [VGA controller])
   Subsystem: BFG Tech Device [19f1:201f]
JockeyStatus:
 kmod:nvidia_173 - NVIDIA legacy binary driver - version 173.14.39 (Proprietary, Disabled, Not in use)
 kmod:nvidia_304_updates - nvidia_304_updates (Proprietary, Enabled, Not in use)
 kmod:nvidia_304 - NVIDIA legacy binary driver - version 304.117 (Proprietary, Disabled, Not in use)
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.13.0-8-generic root=UUID=cd444f9d-672e-4d7b-aea8-657fff0ea1f4 ro quiet splash crashkernel=384M-:128M crashkernel=384M-:128M crashkernel=384M-:128M crashkernel=384M-:128M
SourcePackage: unity
UpgradeStatus: Upgraded to trusty on 2014-01-23 (26 days ago)
dmi.bios.date: 06/26/2012
dmi.bios.vendor: Intel Corp.
dmi.bios.version: WBIBX10J.86A.0336.2012.0626.0141
dmi.board.asset.tag: Base Board Asset Tag
dmi.board.name: DP55WB
dmi.board.vendor: Intel Corporation
dmi.board.version: AAE64798-207
dmi.chassis.type: 2
dmi.modalias: dmi:bvnIntelCorp.:bvrWBIBX10J.86A.0336.2012.0626.0141:bd06/26/2012:svn:pn:pvr:rvnIntelCorporation:rnDP55WB:rvrAAE64798-207:cvn:ct2:cvr:
drirc:
 <driconf>
 </driconf>
version.compiz: compiz 1:0.9.11+14.04.20140217-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.52-1
version.libgl1-mesa-dri: libgl1-mesa-dri 10.0.1-1ubuntu2
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 10.0.1-1ubuntu2
version.nvidia-graphics-drivers: nvidia-graphics-drivers N/A
version.xserver-xorg-core: xserver-xorg-core 2:1.15.0-1ubuntu6
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.8.2-1ubuntu2
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.3.0-1ubuntu2
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.910-0ubuntu1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.10-1ubuntu2
xserver.bootTime: Tue Feb 18 10:57:01 2014
xserver.configfile: /etc/X11/xorg.conf
xserver.devices:
 input Power Button KEYBOARD, id 6
 input Sleep Button KEYBOARD, id 7
 input Logitech Optical USB Mouse MOUSE, id 8
 input BTC USB Multimedia Keyboard KEYBOARD, id 9
 input BTC USB Multimedia Keyboard KEYBOARD, id 10
xserver.errors:
 open /dev/dri/card0: No such file or directory
 open /dev/fb0: No such file or directory
xserver.logfile: /var/log/Xorg.0.log
xserver.outputs:

xserver.version: 2:1.15.0-1ubuntu6

[Nathaniel W. Turner (nturner)]

I just observed this "flicker loop of death" while closing a Thunderbird message window. I chose Send, and after the dialog with the progress bar got to 100%, both the dialog and the message window started flickering madly and the whole session became unusable.

I suspect this is related to the Alt-Tab switcher, as the symptoms are visually similar, and in both cases it appears to occur when a window *should* be disappearing.

[Nathaniel W. Turner (nturner)]

This is still happening several times per day, even with the latest updates.

What can I do to help identify the root cause?

[Nathaniel W. Turner (nturner)]

This also seems to happen (almost) every time I click on the Dash button.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Marco Trevisan (Treviño) (3v1n0)]

Could you try to install the unity and compiz debug symbols (https://wiki.ubuntu.com/DebuggingProgramCrash#Debug_Symbol_Packages), and attach to compiz process from tty1 when you get the hang?

Go Ctrl+Alt+F1, then do something like:
  sudo gdb -p `pidof compiz`

Then inside the gdb session:
  bt full

[Nathaniel W. Turner (nturner)]

Marco, sorry for not following up. I reluctantly stopped using Unity awhile back because it was too buggy (and I couldn't get any work done). Hopefully you've been able to reproduce this.

[Nathaniel W. Turner (nturner)]

FWIW, I've been using Unity again on Xenial and this has not been an issue.

However, I'm no longer using nvidia hardware, and I've disabled framebuffer objects to work around another bug per https://bugs.launchpad.net/ubuntu/+source/unity/+bug/1467695/comments/6