[PATCH v2] bug: further enhance use of CHECK_DATA_CORRUPTION

[Kees Cook]

This continues in applying the CHECK_DATA_CORRUPTION tests where
appropriate, and pulling similar CONFIGs under the same check. Most
notably, this adds the checks to refcount_t so that system builders can
Oops their kernels when encountering a potential refcounter attack. (And
so now the LKDTM tests for refcount issues pass correctly.)

The series depends on the changes in -next made to lib/refcount.c,
so it might be easiest if this goes through the locking tree...

v2 is a rebase to -next and adjusts to using WARN_ONCE() instead of WARN().

-Kees

v1 was here: https://lkml.org/lkml/2017/3/6/720