From 78e4bc34e5d966cfd95f1238565afc399d56225c Mon Sep 17 00:00:00 2001
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date: Tue, 24 Sep 2013 15:04:06 -0700
Subject: [PATCH] rcu: Fix and comment ordering around wait_event()

It is all too easy to forget that wait_event() does not necessarily
imply a full memory barrier.  The case where it does not is where the
condition transitions to true just as wait_event() starts execution.
This is actually a feature: The standard use of wait_event() involves
locking, in which case the locks provide the needed ordering (you hold a
lock across the wake_up() and acquire that same lock after wait_event()
returns).

Given that I did forget that wait_event() does not necessarily imply a
full memory barrier in one case, this commit fixes that case.  This commit
also adds comments calling out the placement of existing memory barriers
relied on by wait_event() calls.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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