[PATCH] RCU documentation 1Q09 update

[Paul E. McKenney]

Update the RCU documentation to call out the need for callers of
primitives like call_rcu() and synchronize_rcu() to prevent subsequent
RCU readers from hazard.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---

 checklist.txt |   12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index 6e25340..accfe2f 100644
--- a/Documentation/RCU/checklist.txt
+++ b/Documentation/RCU/checklist.txt
@@ -298,3 +298,15 @@ over a rather long period of time, but improvements are always welcome!
 
 	Note that, rcu_assign_pointer() and rcu_dereference() relate to
 	SRCU just as they do to other forms of RCU.
+
+15.	The whole point of call_rcu(), synchronize_rcu(), and friends
+	is to wait until all pre-existing readers have finished before
+	carrying out some otherwise-destructive operation.  It is
+	therefore critically important to -first- remove any path
+	that readers can follow that could be affected by the
+	destructive operation, and -only- -then- invoke call_rcu(),
+	synchronize_rcu(), or friends.
+
+	Because these primitives only wait for pre-existing readers,
+	it is the caller's responsibility to guarantee safety to
+	any subsequent readers.
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