tree e430291c48ec41b22e31865bf5aa13c4db87a3cb
parent 6193c76aba8ec3cc5f083c35efbab9ed924125f6
author Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1380060246 -0700
committer Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1386094218 -0800

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>