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Message-ID: <20090308001138.GA15335@linux.vnet.ibm.com>
Date: Sat, 7 Mar 2009 16:11:38 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...e.hu, akpm@...ux-foundation.org, dipankar@...ibm.com,
niv@...ibm.com, dvhltc@...ibm.com
Subject: [PATCH] RCU documentation 1Q09 update
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@...ux.vnet.ibm.com>
---
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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