linux-kernel - [PATCH] rcu: small rcu

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Date:	Fri, 17 Apr 2015 12:33:36 +0200
From:	Milos Vyletel <milos@...hat.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Jonathan Corbet <corbet@....net>,
	linux-kernel@...r.kernel.org (open list:READ-COPY UPDATE...),
	linux-doc@...r.kernel.org (open list:DOCUMENTATION)
Cc:	jeff.haran@...rix.com, Milos Vyletel <milos@...hat.com>
Subject: [PATCH] rcu: small rcu_dereference doc update

Make a note stating that repeated calls of rcu_dereference() may not
return the same pointer if update happens while in critical section.

Reported-by: Jeff Haran <jeff.haran@...rix.com>
Signed-off-by: Milos Vyletel <milos@...hat.com>
---
 Documentation/RCU/whatisRCU.txt | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index 88dfce1..82b1b2c 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -256,7 +256,9 @@ rcu_dereference()
 	If you are going to be fetching multiple fields from the
 	RCU-protected structure, using the local variable is of
 	course preferred.  Repeated rcu_dereference() calls look
-	ugly and incur unnecessary overhead on Alpha CPUs.
+	ugly, do not guarantee that same pointer will be returned
+	if update happened while in critical section and incur
+	unnecessary overhead on Alpha CPUs.
 
 	Note that the value returned by rcu_dereference() is valid
 	only within the enclosing RCU read-side critical section.
-- 
2.1.0

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