documentation: Remove obsolete reference to RCU-protected indexes
Commit #1ebee8017d84 (rcu: Eliminate array-index-based RCU primitives)
eliminated the primitives supporting RCU-protected array indexes, but
failed to update Documentation/memory-barriers.txt accordingly. This
commit therefore removes the discussion of RCU-protected array indexes.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index c90922b..6bee0a2 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -565,21 +565,6 @@
but the old value of the variable B (2).
-Another example of where data dependency barriers might be required is where a
-number is read from memory and then used to calculate the index for an array
-access:
-
- CPU 1 CPU 2
- =============== ===============
- { M[0] == 1, M[1] == 2, M[3] = 3, P == 0, Q == 3 }
- M[1] = 4;
- <write barrier>
- WRITE_ONCE(P, 1);
- Q = READ_ONCE(P);
- <data dependency barrier>
- D = M[Q];
-
-
The data dependency barrier is very important to the RCU system,
for example. See rcu_assign_pointer() and rcu_dereference() in
include/linux/rcupdate.h. This permits the current target of an RCU'd