I am experiencing the following with xorg7 with mesalib 6.4.1:

a) glthreads, glxheads freezes server when run (although mouse cursor movable), 

b) glxcontexts segfaults. both problems happen only in direct rendering mode, so i 
suppose it's a dri/drm issue.

I don't get any (EE) or (WW) messages in Xorg.log

Hardware:
x86
SiS 630 (SiS 300 chipset)

Software (all stable releases)
Linux 2.6.12.6
libdrm-2.0.0
Xorg7.0
MesaLib 6.4.1 (I'm using the prebuilt sis_dri.so binary from
http://dri.freedesktop.org/snapshots/sis-20051220-linux.i386.tar.bz2)
gcc 3.4.5
glibc 2.3.6

Configs:
xorg.conf (Device and Screen sections)
Section "Device"
    Identifier  "SiS 630"
    Driver      "sis"
    Option      "FastVram" "yes"
    Option      "DRI" "on"
    Option      "MaxXFBMem" "4096"
    Option      "AGPSize"   "32"
    Option      "UseColorHWCursor" "yes"
    # Insert Clocks lines here if appropriate
EndSection


# **********************************************************************
# Screen sections
# **********************************************************************

# Any number of screen sections may be present.  Each describes
# the configuration of a single screen.  A single specific screen section
# may be specified from the X server command line with the "-screen"
# option.
Section "Screen"
    Identifier  "Screen 1"
    Device      "SiS 630"
    Monitor     "Monitor1"
    DefaultDepth 16

    Subsection "Display"
        Depth       8
        Modes       "1280x1024" "1024x768" "800x600" "640x480"
        ViewPort    0 0
        Virtual     800 600
    EndSubsection

    Subsection "Display"
        Depth       16
        Modes       "800x600" "640x480"
        ViewPort    0 0
        Virtual     800 600
    EndSubsection
    Subsection "Display"
        Depth       24
        Modes       "800x600" "640x480"
        ViewPort    0 0
        Virtual     800 600
    EndSubsection
    Subsection "Display"
        Depth       32
        Modes       "800x600" "640x480"
        ViewPort    0 0
        Virtual     800 600
    EndSubsection