tools/memory-model: docs/README: Update introduction of locking.txt

Commit 9bc931e9e1 ("tools/memory-model: Add locking.txt and
glossary.txt to README") failed to mention the relation of the "Locking"
section in recipes.txt and locking.txt.

The latter is a detailed version of the former intended to be read on
its own.

Reword the description in README and add notes in locking.txt and
recipes.txt to clarify their relationship.

[ paulmck: Wordsmithing. ]

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Andrea Parri <parri.andrea@gmail.com>

tools/memory-model/Documentation/README

@@ -23,8 +23,11 @@ o	You are familiar with the Linux-kernel concurrency primitives
 	that you need, and just want to get started with LKMM litmus
 	tests:  litmus-tests.txt
 
-o	You would like to access lock-protected shared variables without
-	having their corresponding locks held:  locking.txt
+o	You need to locklessly access shared variables that are otherwise
+	protected by a lock: locking.txt
+
+	This locking.txt file expands on the "Locking" section in
+	recipes.txt, but is self-contained.
 
 o	You are familiar with Linux-kernel concurrency, and would
 	like a detailed intuitive understanding of LKMM, including

tools/memory-model/Documentation/locking.txt

@@ -1,3 +1,8 @@
+[!] Note:
+	This file expands on the "Locking" section of recipes.txt,
+	focusing on locklessly accessing shared variables that are
+	otherwise protected by a lock.
+
 Locking
 =======
 

tools/memory-model/Documentation/recipes.txt

@@ -61,6 +61,10 @@ usual) some things to be careful of:
 Locking
 -------
 
+[!] Note:
+	locking.txt expands on this section, providing more detail on
+	locklessly accessing lock-protected shared variables.
+
 Locking is well-known and straightforward, at least if you don't think
 about it too hard.  And the basic rule is indeed quite simple: Any CPU that
 has acquired a given lock sees any changes previously seen or made by any