locktorture and memory-barriers.txt updates

Hello!

This series contains a few memory-barriers.txt updates and a locktorture cleanup:

1. Add a disclaimer to memory-barrier.txt, courtesy of
Peter Zijlstra.

2. Explicitly state the purpose of memory-barrier.txt, courtesy
of David Howells.

3. Explicitly state that ACQUIRE applies to loads and that
RELEASE applies to stores, courtesy of Will Deacon.

4. Simplify torture_runnable computation in locktorture, replacing
a multiline #ifdef with an IS_ENABLED() that fits into an existing line.

Thanx, Paul

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 Documentation/memory-barriers.txt |   39 +++++++++++++++++++++++++++++++++++++-
 kernel/locking/locktorture.c      |    7 ------
 2 files changed, 39 insertions(+), 7 deletions(-)