[Bug 71983] libdrm 2.4.49 makes gpu crash (HD7770)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=71983

--- Comment #5 from Dave Witbrodt <dawitbro at sbcglobal.net> ---
Same problem here on HD 7850 (PITCAIRN 0x1002:0x6819 0x1787:0x2320).

Yesterday I was upgrading my X server to test 1.15 RC2, which requires some
libraries not available on Debian yet.  All was well when I began:

    libdrm     :  2.4.48
    mesa       :  10.1.0-devel (commit 53f89a43 of Nov. 17)
    xorg-server:  1.14.99.3
    radeon DDX :  7.2.99 (commit d571d6af of Nov. 13)
    glamor     :  0.5.1 (commit 890a7738 of Nov. 6)
    linux      :  3.12.1 (+ some DRM from 3.13rc1)

I had some build failures last time I tried to update the X server, and I saw
bigger than usual changes coming for 1.15, so I thought I should invest some
time into trying to get things working.  After getting the dependencies
satisfied and having succesfully built 1.14.99.902 (with the drivers rebuilt
against it) everything was fine.  In fact, I saw a very noticeable performance
boost.  On a roll, I decided to update Mesa and libdrm, ending up with this set
of packages:

    libdrm     :  2.4.49
    mesa       :  10.1.0-devel (commit f56f875b of Nov. 21)
    xorg-server:  1.14.99.902
    radeon DDX :  7.2.99 (commit d571d6af of Nov. 13)
    glamor     :  0.5.1 (commit 71e7168d of Nov. 13)
    linux      :  3.12.1 (+ some DRM from 3.13rc1)

That's when it all stopped working.  Even downgrading the X stack and Mesa (in
any combination) to the previous working versions still causes failures.  The
symptoms are that everything seems to be fine (kernel boots, X starts, you can
use the desktop, etc.) until you touch OpenGL.  Any attempt to try a game like
'torcs' (or even 'prboom-plus', which is much less GL intensive) causes X to
freeze.  It is sometimes possible to switch to a VT, but the screen goes black
in a few moments so there is nothing to see; if the system does not reboot on
its own, it is possible to use sysrq keys to shut it down somewhat sanely.

When changing everything back (except libdrm) to previous working versions
_also_ was not working, I began to suspect libdrm.  After downgrading to libdrm
2.4.48, everything was working again flawlessly; even upgrading Mesa and the X
stack continued to work perfectly, so I can once again enjoy the 1.15
performance improvements!

It took so many hours to identify libdrm 2.4.49 as the culprit -- I was
assuming that xorg-server, mesa, or glamor were at fault -- that I ran out of
time last night.  I only have to work 2 days this week, so I should be able to
bisect it in 2 days (if no developer can reproduce it by then).

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