[PATCH 0/4 V4] Clarify/standardize memory barriers for lock/unlock

[Manfred Spraul]

Hi,

V4: Docu/comment improvements, remove unnecessary barrier for x86.
V3: Bugfix for arm64
V2: Include updated documentation for rcutree patch

As discussed before:
If a high-scalability locking scheme is built with multiple
spinlocks, then often additional memory barriers are required.

The documentation was not as clear as possible, and memory
barriers were missing / superfluous in the implementation.

Patch 1: Documentation, define one standard barrier, update ipc/sem.c
Patch 2: Update rcutree
Patch 3: Update nf_conntrack
Patch 4: Update for qspinlock: smp_mb__after_spin_lock is free.

Patch 3 is larger than required, it rewrites the conntrack logic
with the code from ipc/sem.c. I think the new code is simpler
and more realtime-friendly.

Please review!

@Andrew: The patches are relative to mmots.
Could you include them in your tree, with the target of including in
linux-next?

--
	Manfred