Nvidia Prime graphics: unity8/unity8-dash crashed with SIGSEGV in glGetString()

[János Milus]

https://errors.ubuntu.com/problem/b0dbc65a7887deabcd906b0a95bd8d5ace8919df
https://errors.ubuntu.com/problem/f9fe7febed582c1e8f7bf8421f8d73a51de2ab37

Lenovo Y50 notebook with NVidia Prime profile. Login with unity8 shows black screen. Login with ubuntu works fine.

ProblemType: Crash
DistroRelease: Ubuntu 16.04
Package: unity8 8.11+16.04.20160216.1-0ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-8.23-generic 4.4.2
Uname: Linux 4.4.0-8-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia
ApportVersion: 2.20-0ubuntu3
Architecture: amd64
Date: Sun Feb 28 19:27:08 2016
ExecutablePath: /usr/bin/unity8-dash
InstallationDate: Installed on 2014-10-02 (514 days ago)
InstallationMedia: Ubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2)
ProcCmdline: unity8-dash --desktop_file_hint=/usr/share/applications/unity8-dash.desktop
ProcEnviron:
 LANGUAGE=hu
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=hu_HU.UTF-8
 SHELL=/bin/bash
Signal: 11
SourcePackage: unity8
StacktraceTop:
 glGetString () from /usr/lib/nvidia-340-updates/libGL.so.1
 QOpenGLContext::makeCurrent(QSurface*) () from /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
 ?? () from /usr/lib/x86_64-linux-gnu/libQt5Quick.so.5
 ?? () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
 start_thread (arg=0x7f1e26dc9700) at pthread_create.c:333
Title: unity8-dash crashed with SIGSEGV in glGetString()
UpgradeStatus: Upgraded to xenial on 2016-02-21 (7 days ago)
UserGroups: adm cdrom dip docker lpadmin plugdev sambashare sudo

[Apport retracing service (apport)]

StacktraceTop:
 glGetString () from /tmp/apport_sandbox_laPLHZ/usr/lib/nvidia-340-updates/libGL.so.1
 QOpenGLContext::makeCurrent(QSurface*) () from /tmp/apport_sandbox_laPLHZ/usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
 QSGRenderThread::run() () from /tmp/apport_sandbox_laPLHZ/usr/lib/x86_64-linux-gnu/libQt5Quick.so.5
 QThreadPrivate::start(void*) () from /tmp/apport_sandbox_laPLHZ/usr/lib/x86_64-linux-gnu/libQt5Core.so.5
 start_thread (arg=0x7f1e26dc9700) at pthread_create.c:333

[Albert Astals Cid (aacid)]

Don't think this is a bug in unity8 itself seems more either Qt, mir or the nvidia drivers.

[Daniel van Vugt (vanvugt)]

Nvidia Prime is a bit deceiving here. Prime typically works by wiring the Intel GPU to the display and just using the Nvidia chip for indirect rendering (if desired).

And that's what's going on here too. Mir does not support the Nvidia driver, but it started successfully because Mir is actually just using the Intel graphics driver:

[2016-02-28 19:27:03.147913] mirplatform: Found graphics driver: mir:mesa-kms (version 0.20.0)
[2016-02-28 19:27:03.147975] mirplatform: Found graphics driver: mir:mesa-x11 (version 0.20.0)
qtmir.mir: MirServer created
[2016-02-28 19:27:03.148721] mirserver: Starting
[2016-02-28 19:27:03.298794] mirserver: Using nested cursor
[2016-02-28 19:27:03.445320] mirserver: Initial display configuration:
[2016-02-28 19:27:03.445621] mirserver: 0.34: eDP 15,3" 340x190mm
[2016-02-28 19:27:03.445633] mirserver: Current mode 3840x2160 47,99Hz
[2016-02-28 19:27:03.445648] mirserver: Preferred mode 3840x2160 47,99Hz
[2016-02-28 19:27:03.445653] mirserver: Logical position +0+0
[2016-02-28 19:27:03.445661] mirserver: 0.31: unused VGA
[2016-02-28 19:27:03.445667] mirserver: 0.42: unused HDMI-A

7f1e67234000-7f1e6780b000 r-xp 00000000 00:15 4064527 /usr/lib/x86_64-linux-gnu/dri/i965_dri.so
7f1e6780b000-7f1e67a0b000 ---p 005d7000 00:15 4064527 /usr/lib/x86_64-linux-gnu/dri/i965_dri.so
7f1e67a0b000-7f1e67a3c000 r--p 005d7000 00:15 4064527 /usr/lib/x86_64-linux-gnu/dri/i965_dri.so
7f1e67a3c000-7f1e67a43000 rw-p 00608000 00:15 4064527 /usr/lib/x86_64-linux-gnu/dri/i965_dri.so

The crash is occurring still, unfortunately because of Nvidia prime. You have Unity8 starting, but trying to use the wrong libGL (the Nvidia one which we don't support). The reason why USC will work here, but Unity8 won't is possibly because USC is native GLESv2, but Unity8/QtMir on desktop uses full GL. So you may not encounter a crash till Unity8 starts.

Still, we have started up OK apparently using Intel graphics. I wonder if we can make Unity8 find the correct libGL...

[Daniel van Vugt (vanvugt)]

Several reports from more users too:
https://errors.ubuntu.com/problem/f9fe7febed582c1e8f7bf8421f8d73a51de2ab37

[Michał Sawicz (saviq)]

Syncing task from Mir.