Created attachment 117951 [details]
apitrace which shows the problem

In the attached apitrace, *sometimes* (about 50% of the runs) rendering issues
can be observed. They manifest in appearantly missing geometry (compare
attached screenshot; the UI has been disabled for taking the apitrace).

Steps to reproduce:
1. DRI_PRIME=1 apitrace replay r600-renderbug-noui.trace
2. If step 1 did not show the behaviour, retry a few times.

Expected results:
Rendering should work and show a terrain without holes

Actual results:
Holes in the terrain

The results have been observed on mesa-11.0.0-rc1 with and without
http://lists.freedesktop.org/archives/mesa-dev/2015-August/092766.html applied.

The same code has never (in 50+ tests) shown the issue on the Intel integrated
GPU.

The application which produces the given behaviour can be found at 
https://github.com/horazont/scc/tree/f31d90e1579ebda14ce7a0417339b2cd448efde8

The geometry shader is in:
https://github.com/horazont/scc/blob/f31d90e1579ebda14ce7a0417339b2cd448efde8/game/resources/shaders/terrain/main.geom

The usage is in:
https://github.com/horazont/scc/blob/f31d90e1579ebda14ce7a0417339b2cd448efde8/libffengine-render/src/render/fancyterrain.cpp
(search for draw_elements, GL_GEOMETRY_SHADER, GL_LINES_ADJACENCY)


In another commit, the geometry shader has been disabled
(<https://github.com/horazont/scc/commit/4e1e298b02723efcf6555c1c4a7efa31682cf79b>),
which appears to fix the problem or make it very hard to reproduce.


radeon GPU:
Advanced Micro Devices, Inc. [AMD/ATI] Whistler [Radeon HD
6630M/6650M/6750M/7670M/7690M] (rev ff)  {6630M according to notebook specs}
intel GPU:
Intel Corporation 2nd Generation Core Processor Family Integrated Graphics
Controller (rev 09)