mutex subsystem, -V8

this is version -V8 of the generic mutex subsystem. It consists of the following 11 patches:

add-atomic-xchg.patch
mutex-generic-asm-implementations.patch
mutex-asm-mutex.h-i386.patch
mutex-asm-mutex.h-x86_64.patch
mutex-asm-mutex.h-arm.patch
mutex-arch-mutex-h.patch
mutex-core.patch
mutex-docs.patch
mutex-debug.patch
mutex-debug-more.patch
xfs-mutex-namespace-collision-fix.patch

the patches are against Linus' latest GIT tree, and they should work fine on every Linux architecture.

i have tested all 5 mutex implementation variants under MUTEX_DEBUG_FULL on x86: native, -dec, -xchg, -null and debug.

Changes since -V7:

 11 files changed, 258 insertions(+), 122 deletions(-)

- added a __mutex_fastpath_trylock(count, fn) method for architectures to define a trylock fastpath.

While trylock has no 'slowpath' in the classic sense, but e.g. the ARMv6 fastpath implementation can 'fail' to take the lock speculatively, and has to call back into the generic code in that case, to guarantee that the trylock is actually attempted. The debug and xchg variant also makes use of the generic code, unconditionally.

The ARMv6 fastpath implementation is from Nicolas Pitre.

this change gets rid of the final #ifdefs from the core kernel/mutex.c code, and makes it squeeky clean ;-)

- inline mutex_is_locked() (Nicolas Pitre)

- more cleanups (of assembly code in particular).

Ingo