915G random lockup on xscreensaver GL programs

Hello,

I use an intel 915G chip onboard. My dystro is a slackware v11.
The Xserver version is 6.9.0 with a 2.6.18.1 linux kernel.
All works fine, except I encounter Xserver random crash or lockup when 
the xscreensaver is running mesa3d programs. Sometimes, the video is 
completely trashed and I must reboot the system. The xorg.log says :

Error in I830WaitLpRing(), now is 82092561, start is 77694512
pgetbl_ctl: 0x3ffc0001 pgetbl_err: 0x0
ipeir: 0 iphdr: 2000011
LP ring tail: 15d48 head: 15d44 len: 1f001 start 0
eir: 0 esr: 1 emr: ffff
instdone: fa41 instpm: 0
memmode: 108 instps: 800f00c4
hwstam: fffe ier: 2 imr: 8 iir: a0
space: 131060 wanted 131064
(II) I810(0): [drm] removed 1 reserved context for kernel
(II) I810(0): [drm] unmapping 8192 bytes of SAREA 0xb8473000 at 0x6ffc4000

Fatal server error:
lockup


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.

(WW) I810(0): Successfully set original devices
(WW) I810(0): Setting the original video mode instead of restoring
        the saved state
(II) I810(0): BIOS call 0x5f05 not supported, setting refresh with VBE 3 
method.
(II) I810(0): xf86UnbindGARTMemory: unbind key 7
(II) I810(0): xf86UnbindGARTMemory: unbind key 0
(II) I810(0): xf86UnbindGARTMemory: unbind key 1
(II) I810(0): xf86UnbindGARTMemory: unbind key 3
(II) I810(0): xf86UnbindGARTMemory: unbind key 2
(II) I810(0): xf86UnbindGARTMemory: unbind key 4
(II) I810(0): xf86UnbindGARTMemory: unbind key 5
(II) I810(0): xf86UnbindGARTMemory: unbind key 6
(WW) I810(0): Successfully set original devices (2)

and sometimes, not at each crash, there is this message from kernel :
[drm:i915_wait_irq] *ERROR* i915_wait_irq: EBUSY -- rec: 2016347 
emitted: 2016350

I have found this pointer, but I don't know if it is the same bug 
referenced in v7.0.0 :
https://bugs.freedesktop.org/show_bug.cgi?id=5774

Any help would be greatly appreciated!

Thank you


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