Comment # 6 on bug 86864 from Michel Dänzer

So current Mesa Git master is still affected by this problem, and reverting
commit 7b4276d7acf2e0f77044cb50caa6ad936fa78786 on top of that works around it?

Does setting the environment variable RADEON_THREAD=0 work around the problem?
If not, please attach gdb to the Second Life process to make sure the
environment variable takes effect, i.e. there's no CS helper thread spawned by
the r600g driver.