copy_from_user() function fails inside a kernel thread.

I am working on PowerPC based target board using linux-2.6.24.2-DENX.
I have designed a device driver that calls the function copy_from_user() inside IOCTL , READ & WRITE functions of the driver.
I dont have any problem in this.

My problem :-
If I use the same function inside of a kernel thread started by the driver, then the copy_from_user() always fails.

Has anyone figured out this problem yet? Have you tried using memmove or memcpy?

I have similar problem with my kernel module.

Bif