Documentation updates for 3.21^W4.1

Hello!

This series contains a few documentation updates:

1. Record the fact that the rcutree.kthread_prio kernel boot parameter
also controls the priority of the grace-period kthreads.

2. Update the kernel-per-CPU-kthreads.txt documentation based on
Christoph Lameter's on-demand vmstat workers commit.

3. Update NO_HZ.txt documentation to reflect the fact that POSIX
timers are no longer starved on adaptive-ticks CPUs.

4. Update kernel-per-CPU-kthreads.txt documentation to reflect
workqueue usage and nosoftlockup boot parameter.

5. Clarify memory-barrier semantics of atomic operations.

6. Clarify control-dependency pairing.

Thanx, Paul

------------------------------------------------------------------------

 b/Documentation/atomic_ops.txt              |   45 ++++++++++++++--------------
 b/Documentation/kernel-parameters.txt       |   14 +++++---
 b/Documentation/kernel-per-CPU-kthreads.txt |   34 +++++++++++++--------
 b/Documentation/memory-barriers.txt         |   42 ++++++++++++++++++--------
 b/Documentation/timers/NO_HZ.txt            |   10 +-----
 5 files changed, 85 insertions(+), 60 deletions(-)