Comment 16 for bug 491852

Older, but may be usefull, errors from /var/log/Xorg.log:

X.Org X Server 1.7.3.902 (1.7.4 RC 2)
Release Date: 2009-12-26
X Protocol Version 11, Revision 0
Build Operating System: Linux 2.6.24-23-server x86_64 Ubuntu
Current Operating System: Linux sweetie 2.6.32-11-generic #15-Ubuntu SMP Tue Jan 19 20:38:41 UTC 2010 x86_64
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-2.6.32-11-generic root=UUID=26a40a7b-95dd-4565-8f86-c2cd3f3359a9 ro quiet
Build Date: 19 January 2010 07:28:22AM
xorg-server 2:1.7.3.902-1ubuntu9 (buildd@)
...
(II) LoadModule: "radeon"
(II) Loading /usr/lib/xorg/modules/drivers/radeon_drv.so
(II) Module radeon: vendor="X.Org Foundation"
        compiled for 1.7.3.902, module version = 6.12.99
...
[mi] EQ overflowing. The server is probably stuck in an infinite loop.

Backtrace:
0: /usr/bin/X (xorg_backtrace+0x28) [0x4a22b8]
1: /usr/bin/X (mieqEnqueue+0x1f4) [0x4a1b64]
2: /usr/bin/X (xf86PostMotionEventP+0xce) [0x47c66e]
3: /usr/lib/xorg/modules/input/evdev_drv.so (0x7fae5ada2000+0x53df) [0x7fae5ada73df]
4: /usr/bin/X (0x400000+0x6f527) [0x46f527]
5: /usr/bin/X (0x400000+0x11bcb3) [0x51bcb3]
6: /lib/libpthread.so.0 (0x7fae5d7bf000+0xf780) [0x7fae5d7ce780]
7: /lib/libc.so.6 (ioctl+0x7) [0x7fae5c578da7]
8: /usr/lib/libdrm.so.2 (drmIoctl+0x23) [0x7fae5b1b45b3]
9: /usr/lib/libdrm.so.2 (drmCommandWriteRead+0x1c) [0x7fae5b1b47fc]
10: /usr/lib/libdrm_radeon.so.1 (0x7fae5a00a000+0x1599) [0x7fae5a00b599]
11: /usr/lib/libdrm_radeon.so.1 (0x7fae5a00a000+0x15e4) [0x7fae5a00b5e4]
12: /usr/lib/xorg/modules/drivers/radeon_drv.so (0x7fae5a20f000+0xb9d70) [0x7fae5a2c8d70]
13: /usr/lib/xorg/modules/libexa.so (0x7fae59bd4000+0x828a) [0x7fae59bdc28a]
14: /usr/bin/X (0x400000+0x158154) [0x558154]
15: /usr/lib/xorg/modules/libexa.so (exaGetPixmapFirstPixel+0xa9) [0x7fae59be3109]
16: /usr/lib/xorg/modules/libexa.so (0x7fae59bd4000+0xe375) [0x7fae59be2375]
17: /usr/bin/X (0x400000+0xd6cf0) [0x4d6cf0]
18: /usr/bin/X (0x400000+0xd085e) [0x4d085e]
19: /usr/bin/X (0x400000+0x30a4c) [0x430a4c]
20: /usr/bin/X (0x400000+0x260aa) [0x4260aa]
21: /lib/libc.so.6 (__libc_start_main+0xfd) [0x7fae5c4bbc4d]
22: /usr/bin/X (0x400000+0x25c59) [0x425c59]

X.Org X Server 1.7.3.902 (1.7.4 RC 2)
Release Date: 2009-12-26
X Protocol Version 11, Revision 0
Build Operating System: Linux 2.6.24-23-server x86_64 Ubuntu
Current Operating System: Linux sweetie 2.6.32-11-generic #15-Ubuntu SMP Tue Jan 19 20:38:41 UTC 2010 x86_64
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-2.6.32-11-generic root=UUID=26a40a7b-95dd-4565-8f86-c2cd3f3359a9 ro quiet
Build Date: 19 January 2010 07:28:22AM
xorg-server 2:1.7.3.902-1ubuntu9 (buildd@)
...
Backtrace:
0: /usr/bin/X (xorg_backtrace+0x28) [0x4a22b8]
1: /usr/bin/X (0x400000+0x65059) [0x465059]
2: /lib/libpthread.so.0 (0x7fd54c048000+0xf780) [0x7fd54c057780]
3: /usr/bin/X (DamageUnregister+0x53) [0x4d5e93]
4: /usr/lib/xorg/modules/libshadow.so (shadowRemove+0x33) [0x7fd54897d3c3]
5: /usr/lib/xorg/modules/libshadow.so (0x7fd54897c000+0x1884) [0x7fd54897d884]
6: /usr/bin/X (0x400000+0xa6859) [0x4a6859]
7: /usr/bin/X (0x400000+0x165e3c) [0x565e3c]
8: /usr/bin/X (0x400000+0x2614c) [0x42614c]
9: /lib/libc.so.6 (__libc_start_main+0xfd) [0x7fd54ad44c4d]
10: /usr/bin/X (0x400000+0x25c59) [0x425c59]
Segmentation fault at address 0x40

Fatal server error:
Caught signal 11 (Segmentation fault). Server aborting