Note upgrading the above listed xorg "bits" to their rawhide version fixes this.

Here is some info for the record from a debugging session with airlied:

<hansg> Program received signal SIGSEGV, Segmentation fault.
<hansg> dixAllocatePrivate (privates=0x290, key=0x7d8d54) at privates.c:117
<hansg> 117     if (!*privates) {
<hansg> (gdb) bt
<hansg> #0  dixAllocatePrivate (privates=0x290, key=0x7d8d54) at privates.c:117
<hansg> #1  0x0000000000445f45 in dixLookupPrivate (privates=<value optimized out>, 
<hansg>     key=<value optimized out>) at privates.c:165
<hansg> #2  0x0000000000481897 in xf86OutputSetEDID (output=0x24c6ae0, 
<hansg>     edid_mon=0x24c81d0) at xf86Crtc.c:2923
<hansg> #3  0x00007f106eb41351 in drmmode_output_get_modes (output=0x24c6ae0)
<hansg>     at drmmode_display.c:600
<hansg> #4  0x0000000000484346 in xf86ProbeOutputModes (scrn=0x24c0130, 
<hansg>     maxX=<value optimized out>, maxY=<value optimized out>) at xf86Crtc.c:1587
<hansg> #5  0x0000000000484d2c in xf86InitialConfiguration (scrn=0x24c0130, 
<hansg>     canGrow=<value optimized out>) at xf86Crtc.c:2373
<hansg> #6  0x00007f106eb41eb1 in drmmode_pre_init (pScrn=<value optimized out>, 
<hansg>     drmmode=<value optimized out>, busId=<value optimized out>, 
<hansg>     driver_name=<value optimized out>, cpp=<value optimized out>, 
<hansg>     zaphod_mask=<value optimized out>) at drmmode_display.c:1225
<hansg> #7  0x00007f106eb3faa7 in RADEONPreInit_KMS (pScrn=0x24c0130, 
<hansg>     flags=<value optimized out>) at radeon_kms.c:445
<hansg> #8  0x000000000046fcb2 in InitOutput (pScreenInfo=<value optimized out>, 
<hansg>     argc=<value optimized out>, argv=<value optimized out>) at xf86Init.c:829
<hansg> #9  0x0000000000421c5a in main (argc=<value optimized out>, 
<airlied> can you list in frame 2
<hansg> (gdb) fr 2
<hansg> #2  0x0000000000481897 in xf86OutputSetEDID (output=0x24c6ae0, 
<hansg>     edid_mon=0x24c81d0) at xf86Crtc.c:2923
<hansg> 2923     rrScrPrivPtr        rrScrPriv = rrGetScrPriv(scrn->pScreen);
<hansg> (gdb) list
<hansg> 2918 xf86OutputSetEDID (xf86OutputPtr output, xf86MonPtr edid_mon)
<hansg> 2919 {
<hansg> 2920     ScrnInfoPtr  scrn = output->scrn;
<hansg> 2921     xf86CrtcConfigPtr config = XF86_CRTC_CONFIG_PTR(scrn);
<hansg> 2922     int   i;
<hansg> 2923     rrScrPrivPtr        rrScrPriv = rrGetScrPriv(scrn->pScreen);
<hansg> 2924 #ifdef RANDR_12_INTERFACE
<hansg> 2925     int   size;
<hansg> 2926 #endif
<hansg> 2927

Seems to be similar to bug #557805. Try use "nomodeset" kernel argument on Grub (or radeon.modeset=0).

I should mention here, that this was worked around by Airlied by reversing ajax'
xserver-1.7.4-randr-unify-primary-compat.patch (in xserver 1.7.4-4

Which later got re-enabled by ajax in 1.7.4-7, I cannot confirm if ajax' fixed
patch is ok, as I'm running rawhide now. I can report that rawhide still does not show this issue.

*** Bug 597063 has been marked as a duplicate of this bug. ***

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This bug has long been fixed, but accidentally left open, closing.