Actually it dumps core in macro DRI_VALIDATE_DRAWABLE_INFO(sPriv, dPriv) at line
167 in radeonGetLock(). dPriv = radeon->dri.drawable is NULL here.

Well, this seams to be the underlying reason, why running any OpenGL app with
Xgl causes a crash. I just invoked "glxinfo" 

(gdb) bt
#0  radeonGetLock (radeon=0x1b00d10, flags=0) at radeon_lock.c:167
#1  0x00002b0ba1c70027 in r300FlushCmdBuf (r300=0x1b00d10, 
    caller=0x2b0ba1dda8f0 "r300DestroyContext") at r300_cmdbuf.c:117
#2  0x00002b0ba1c6dab6 in r300DestroyContext (driContextPriv=0x1)
    at r300_context.c:464
#3  0x00002b0ba1c6120a in driDestroyContext (dpy=0x67d190, scrn=0, 
    contextPrivate=0x13f55b0) at dri_util.c:719
#4  0x00002b0ba0e58b6d in DestroyContext (dpy=0x67d190, gc=0x1b00b00)
    at glxcmds.c:472
#5  0x00002b0ba0d355c5 in glitz_glx_fini () from /usr/lib/libglitz-glx.so.1
#6  0x00002b0ba0be37ce in xglxInitXorg ()
   from /usr/lib64/xorg/modules/xgl/libxglx.so
#7  0x00002b0ba085c29a in DoMakeCurrent ()
   from /usr/lib64/xorg/modules/xgl/libglxext.so
#8  0x00002b0ba086113f in __glXsetEnterLeaveServerFuncs ()
   from /usr/lib64/xorg/modules/xgl/libglxext.so
#9  0x0000000000449c6e in Dispatch ()
#10 0x00000000004599b5 in main ()

 (gdb) p radeon->dri
$13 = {context = 0x13f55b0, screen = 0x697be0, drawable = 0x0, hwContext = 5, 
  hwLock = 0x2b0baa0af000, fd = 1, drmMinor = 25}