Comment 5 for bug 505112

I am experiencing the bug, too. Installing latest updates on Kubuntu 10.04 prevents the X-server from starting.
System is an Intel Core2Duo P7450; 4 GB RAM; Ati Radeon Mobility 4530 HD.

Part of Xorg.0.log:
[ 0.375361] (II) LoadModule: "exa"
[ 0.375500] (II) Loading /usr/lib/xorg/modules/libexa.so
[ 0.387243] (II) Module exa: vendor="X.Org Foundation"
 compiled for 1.7.3.902, module version = 2.5.0
 ABI class: X.Org Video Driver, version 6.0
[ 0.387268] (II) UnloadModule: "vesa"
[ 0.387274] (II) Unloading /usr/lib/xorg/modules/drivers/vesa_drv.so
[ 0.387281] (II) UnloadModule: "fbdev"
[ 0.387287] (II) Unloading /usr/lib/xorg/modules/drivers/fbdev_drv.so
[ 0.387293] (II) UnloadModule: "fbdevhw"
[ 0.387298] (II) Unloading /usr/lib/xorg/modules/linux/libfbdevhw.so
[ 0.387306] (--) Depth 24 pixmap format is 32 bpp
[ 0.395758] (II) RADEON(0): [DRI2] Setup complete
[ 0.395850] (II) RADEON(0): Front buffer size: 0K
[ 0.395858] (II) RADEON(0): VRAM usage limit set to 228643K
[ 0.410271] (==) RADEON(0): Backing store disabled
[ 0.410281] (II) RADEON(0): Direct rendering enabled
[ 0.425865] (II) RADEON(0): Setting EXA maxPitchBytes
[ 0.425884] (II) EXA(0): Driver allocated offscreen pixmaps
[ 0.425895] (II) EXA(0): Driver registered support for the following operations:
[ 0.425901] (II) Solid
[ 0.425906] (II) Copy
[ 0.425911] (II) Composite (RENDER acceleration)
[ 0.425916] (II) UploadToScreen
[ 0.425921] (II) DownloadFromScreen

Backtrace:
0: /usr/bin/X (xorg_backtrace+0x3b) [0x80e887b]
1: /usr/bin/X (0x8048000+0x61a1d) [0x80a9a1d]
2: (vdso) (__kernel_rt_sigreturn+0x0) [0xb776a410]
3: /usr/lib/xorg/modules/drivers/radeon_drv.so (0xb7255000+0xafd53) [0xb7304d53]
4: /usr/lib/xorg/modules/drivers/radeon_drv.so (0xb7255000+0xb00f8) [0xb73050f8]
5: /usr/lib/xorg/modules/drivers/radeon_drv.so (0xb7255000+0xe63b) [0xb726363b]
6: /usr/lib/xorg/modules/drivers/radeon_drv.so (0xb7255000+0xce4e7) [0xb73234e7]
7: /usr/bin/X (AddScreen+0x198) [0x806ce88]
8: /usr/bin/X (InitOutput+0x820) [0x80b9ce0]
9: /usr/bin/X (0x8048000+0x1eb8b) [0x8066b8b]
10: /lib/tls/i686/cmov/libc.so.6 (__libc_start_main+0xe6) [0xb74aebd6]
11: /usr/bin/X (0x8048000+0x1e931) [0x8066931]
Segmentation fault at address 0x1

Caught signal 11 (Segmentation fault). Server aborting

Please consult the The X.Org Foundation support
  at http://wiki.x.org
 for help.
Please also check the log file at "/var/log/Xorg.0.log" for additional information.

 ddxSigGiveUp: Closing log