1) the 'head' pointer or an subsequent linked list pointer
is not a valid address of a user space word
2) the calculated location of the 'lock word' (address plus
- 'offset') is not the valud address of a 32 bit user space
+ 'offset') is not the valid address of a 32 bit user space
word
3) if the list contains more than 1 million (subject to
future kernel configuration changes) elements.