documentation: No acquire/release for RCU readers

Documentation/memory-barriers.txt calls out RCU as one of the sets
of primitives associated with ACQUIRE and RELEASE.  There really
is an association in that rcu_assign_pointer() includes a RELEASE
operation, but a quick read can convince people that rcu_read_lock() and
rcu_read_unlock() have ACQUIRE and RELEASE semantics, which they do not.

This commit therefore removes RCU from this list in order to avoid
this confusion.

Reported-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index 2ba8461b0631de759fefd2a12918a6c4f4ee7562..d336e4d420297eb62c18bc171b98acb36451ac37 100644 (file)
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1789,7 +1789,6 @@ The Linux kernel has a number of locking constructs:
  (*) mutexes
  (*) semaphores
  (*) R/W semaphores
- (*) RCU
 
 In all cases there are variants on "ACQUIRE" operations and "RELEASE" operations
 for each construct.  These operations all imply certain barriers: