I did. I still maintain that the reason why the exploit doesn't work is this:

include/asm-generic/atomic-long.h:

  #if BITS_PER_LONG == 64
  typedef atomic64_t atomic_long_t;
  ...
  #else
  typedef atomic_t atomic_long_t;

Just checking it with a 32-bit VM with the latest upstream kernel.

EDIT: No, I was wrong. atomic_t is 32 bits also with 64 bit architecture. Must be something else then, let's see.