linux-kernel - [PATCH v2 tip/core/rcu 3/4] rcu: Make rcu_assign_pointer's assignment volatile and type-safe

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Date:	Wed, 11 Dec 2013 15:08:47 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com,
	edumazet@...gle.com, darren@...art.com, fweisbec@...il.com,
	oleg@...hat.com, sbw@....edu,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH v2 tip/core/rcu 3/4] rcu: Make rcu_assign_pointer's assignment volatile and type-safe

From: Josh Triplett <josh@...htriplett.org>

The rcu_assign_pointer() primitive needs to use ACCESS_ONCE to make
the assignment to the destination pointer volatile, to protect against
compilers too clever for their own good.

Signed-off-by: Josh Triplett <josh@...htriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 include/linux/rcupdate.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 00ad28168ef0..97853cd2d7b4 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -551,7 +551,7 @@ static inline void rcu_preempt_sleep_check(void)
 #define __rcu_assign_pointer(p, v, space) \
 	do { \
 		smp_wmb(); \
-		(p) = (typeof(*v) __force space *)(v); \
+		ACCESS_ONCE(p) = (typeof(*(v)) __force space *)(v); \
 	} while (0)
 
 
-- 
1.8.1.5

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