SIGSEGV with KMS

[tsuraan]

(this is a re-post of a problem I was having yesterday, but today it's
more accurate and has better details, and a worthwhile subject).

I'm trying to get KMS working on my centrino laptop.  The problem that
I'm having is that a moment after X starts (I get the mouse cursor for
a bit under a second), X crashes with this backtrace:

Backtrace:
0: X(xorg_backtrace+0x26) [0x4e0f16]
1: X(xf86SigHandler+0x39) [0x48c539]
2: /lib/libc.so.6 [0x7f1b759861d0]
3: /usr/lib/libdrm_intel.so.1 [0x7f1b747fe2c4]
4: /usr/lib/libdrm_intel.so.1 [0x7f1b747fe1e4]
5: /usr/lib/libdrm_intel.so.1 [0x7f1b747fe68c]
6: /usr/lib64/xorg/modules/drivers//intel_drv.so(intel_batch_flush+0xa2)
[0x7f1b74a21bf2]
7: /usr/lib64/xorg/modules/drivers//intel_drv.so [0x7f1b74a4912b]
8: /usr/lib64/xorg/modules/drivers//intel_drv.so [0x7f1b74a5dcaf]
9: /usr/lib64/xorg/modules/drivers//intel_drv.so [0x7f1b74a5e0b2]
10: X [0x520eaf]
11: X [0x4f99e7]
12: X [0x4fa875]
13: X(Dispatch+0x334) [0x448ab4]
14: X(main+0x415) [0x430735]
15: /lib/libc.so.6(__libc_start_main+0xf4) [0x7f1b759734a4]
16: X [0x42fb39]

Fatal server error:
Caught signal 11.  Server aborting

I've tried with kernels 2.6.29 and 2.6.30rc6, tiling enabled and
disabled.  My software versions are:

x11-base/xorg-server-1.5.3-r6
x11-drivers/xf86-video-intel-2.7.1
libdrm developement, but also tried 2.4.11.

lspci reports the video card as "Intel Corporation Mobile 4 Series
Chipset Integrated Graphics Controller"; the laptop is a Sony Vaio
Z590, if that helps any.  I also notice that when I startx, the screen
goes blank for a moment before it brings up the graphical mode; I
thought that KMS was supposed to eliminate that flicker, so maybe I'm
doing something wrong?  My xorg.conf, config.gz, and Xorg.0.log are
all attached.
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