Created attachment 131130 [details]
/sys/class/drm/card0/error

I don't exactly know what happened but I found this in my logs:

Apr 28 09:29:45 simon-laptop kernel: [140726.749554] [drm] stuck on render ring
Apr 28 09:29:45 simon-laptop kernel: [140726.749859] [drm] GPU HANG: ecode 9:0:0x87d6fffe, in Xorg [25978], reason: Engine(s) hung, action: reset
Apr 28 09:29:45 simon-laptop kernel: [140726.749861] [drm] GPU hangs can indicate a bug anywhere in the entire gfx stack, including userspace.
Apr 28 09:29:45 simon-laptop kernel: [140726.749862] [drm] Please file a _new_ bug report on bugs.freedesktop.org against DRI -> DRM/Intel
Apr 28 09:29:45 simon-laptop kernel: [140726.749863] [drm] drm/i915 developers can then reassign to the right component if it's not a kernel issue.
Apr 28 09:29:45 simon-laptop kernel: [140726.749864] [drm] The gpu crash dump is required to analyze gpu hangs, so please always attach it.
Apr 28 09:29:45 simon-laptop kernel: [140726.749866] [drm] GPU crash dump saved to /sys/class/drm/card0/error
Apr 28 09:29:45 simon-laptop kernel: [140726.751659] drm/i915: Resetting chip after gpu hang
Apr 28 09:29:47 simon-laptop kernel: [140728.749834] [drm] RC6 on

I searched my logs for previous GPU hangs and found another case on April 1st with the same "signature":

Apr  1 21:07:25 simon-laptop kernel: [ 3281.489363] [drm] GPU HANG: ecode 9:0:0x87d6fffe, in Xorg [4906], reason: Engine(s) hung, action: reset

So not a frequent issue but I thought I should still report it.

Machine informations:

$ cat /etc/os-release 
NAME="Ubuntu"
VERSION="16.04.2 LTS (Xenial Xerus)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 16.04.2 LTS"
VERSION_ID="16.04"
HOME_URL="http://www.ubuntu.com/"
SUPPORT_URL="http://help.ubuntu.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"
VERSION_CODENAME=xenial
UBUNTU_CODENAME=xenial
$ uname -a
Linux simon-laptop 4.4.0-75-generic #96-Ubuntu SMP Thu Apr 20 09:56:33 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

My external display is connected through VGA.