https://bugs.freedesktop.org/show_bug.cgi?id=79756
--- Comment #5 from Michel Dänzer michel@daenzer.net --- I can't reproduce this with glamor from xserver Git, can you try that?
If not, or if it still happens with that, please get a backtrace with gdb, and make sure /usr/lib/xorg/modules/dri/radeonsi_dri.so and /usr/lib/xorg/modules/extensions/libglx.so have debugging symbols.