problems for making kernel module

I got this message during compiling module.

Building modules, stage 2.

MODPOST

WARNING: "tasklist_lock" [ /Red/src/Red.ko] undefined!

make[1]: Leaving directory `/usr/src/linux-headers-2.6.18-4-686'

Actually, Red.ko had made but can not load the module due to the unknown symbol (tasklist_lock).

What’s the problem?? I can see the symbol is exported in the linux-header-2.6.18-4-686/include/linux/sched.h.

I couldn’t understand why it is shown “undefined”??

Also during searching about this problem, I read this - for linux kernel 2.6.18, the symbol does NOT export any more …. Is this right???

If it is, is there any way to use the symbol ‘tasklist_lock’?

There is my only guess, it is needed the license to use this symbol.

Thanks a lot for any suggestion.