DRM IOCTL fail

[cckuo]

Dear all:
Recently I met some problem while enable drm function.
Each time when I call drmAgpBind, defined in Xf86drm.c, OS will either hang
or reboot so fast that it doesn't leave any log, including XFree86.0.log or
/var/log/messages. By the way, I have elevated the kernel message-level to
KERN_ALERT.

Below I list some test I have done:
1. if I mark drmAgpBind, I can see all messages I add in XFree86 and kernel
drm functions.
2. if I call the drmAgpBind before drmAgpAlloc, I can see the unbind message
reported by kernel. (I change the order purposely to make sure whether the
function works, and it seems work.)

The kernel version I have tried is 2.4.19, 2.4.30,