Serious bug in the Intel graphics stack

Martin Sandsmark martin.sandsmark at kde.org
Wed Aug 5 09:53:04 UTC 2015


Hi, wonderful people!

This mail is primarily aimed at package maintainers in various distributions,
but I've CCed kde-devel at kde.org as well to raise more awareness of this in
general.


TL;DR
=====
I'd like to draw your attention to a pretty serious bug that is leading to
massive amount of crashes for users of Plasma (and other applications using
OpenGL), provide a workaround and ask kindly for you to help counteract some
of the misdirected bad reputation.


OVERVIEW
========
It seems to have been semi-recently introduced, so it doesn't seem to affect
distributions without some older versions of the Intel graphics driver stack.
I haven't been able to track down exactly which version introduced it, so it
would be appreciated if some of you could chime in with the version of the
Intel graphics stack you have and whether you are affected by this bug.

Since the backtrace ends in mesa, the bug is currently tracked in the mesa
bug tracker here: https://bugs.freedesktop.org/show_bug.cgi?id=86281

This bug is for the crashes in the Plasma shell, it is now resolved as
'upstream': https://bugs.kde.org/show_bug.cgi?id=349519

It also affects many other applications using OpenGL, like Kodi, mpv and even
Gwenview: https://bugs.kde.org/show_bug.cgi?id=350340


RESULTS
=======
This is starting to put Plasma 5 in an unjustified and really bad light, even
I myself thought Plasma 5 was just buggy and "not ready", before I actually
dug into the issue. If you follow various social media you will find a ton of
people talking about how buggy and unstable Plasma 5 is, and every time I
have engaged them to figure out what is happening with them it is that Intel
bug.

As I mentioned above it seems to have been introduced pretty recently, which
is also a problem because distributions who ship Plasma 5 usually also ship
newer versions of other things like the Intel driver. And because it affects
pretty much every application using OpenGL, which more and more Qt5 based
applications use because of QtQuick, many other KDE applications ported to
Qt5 now also get a reputation of being unstable and unfinished.


WORKAROUND
==========
A workaround is simply to switch back to the older UXA acceleration method
from the current default SNA method in the intel DDX. One way to do this is
to put the following in e. g. /etc/X11/xorg.conf.d/20-intel.conf:

    Section "Device"
        Identifier  "Intel Graphics"
        Driver      "intel"
        Option      "AccelMethod"  "uxa"
    EndSection


I found this workaround in a forum post on the Manjaro forum by Philip
Müller, the Manjaro manager and leader who also used to work with me
ChakraOS. An awesome guy, and all thanks for this workaround should be
directed at him.

My recommendation is that distributions apply this workaround, or downgrade
or hold back upgrading the Intel graphics driver stack (IMHO the first
solution is the best). I have reached out to the Intel developers, and was
able to both make them aware of the seriousness and allowed to raise the
importance of the bug. Until the bug is resolved and a patch is available
and/or there has been a new release of the Intel graphics stack the
workaround should be added as soon as possible.


COMMUNICATION
=============
Lastly I would greatly appreciate it if distributions could inform their
users about how this bug affects Plasma 5. The early KDE 4 releases got a lot
of bad press because of regressions and being a bit unstable in general, and
while people might argue whether it was justified, people are now comparing
the Plasma 5 release to that. I'm not a Plasma developer myself, but
considering how much time and effort they have spent to make Plasma 5 stable
to avoid getting similar bad press as KDE 4, this is in my opinion extremely
unfortunate.

Please excuse my lack of brevity.

-- 
Martin Sandsmark


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