It think one of the reasons the kernel can't kill a process is because one of the process's threads is blocked inside a kernel call (not completely sure about this). Hes using ps's 'wchan' option to get the address of the kernel function that the process is currently blocked or sleeping on. After he gets the wchan address, he uses gdb to map the address to function name.

Taken from: http://unixhelp.ed.ac.uk/CGI/man-cgi?ps

nwchan WCHAN address of the kernel function where the process is sleeping (use wchan if you want the kernel function name). Running tasks will display a dash ('-') in this column.