linux-kernel - [PATCH tip/core/rcu 15/15] rcu: Add ACCESS_ONCE() for RCU_INIT

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Message-Id: <1409250394-25159-15-git-send-email-paulmck@linux.vnet.ibm.com>
Date:	Thu, 28 Aug 2014 11:26:34 -0700
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, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
	bobby.prani@...il.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 15/15] rcu: Add ACCESS_ONCE() for RCU_INIT_POINTER()

From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>

It is permissible to use RCU_INIT_POINTER() instead of rcu_assign_pointer()
in a couple of cases where readers might be concurrently accessing the
pointer being assigned to: (1) When assigning NULL and (2) When assigning
a pointer that is already visible to readers.  In these two cases, we
should really be using ACCESS_ONCE() to prevent compiler mischief.  This
commit therefore adds the ACCESS_ONCE().

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 321ed0d4e675..7ba3f2470396 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -989,7 +989,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  */
 #define RCU_INIT_POINTER(p, v) \
 	do { \
-		p = RCU_INITIALIZER(v); \
+		ACCESS_ONCE(p) = (v); \
 	} while (0)
 
 /**
-- 
1.8.1.5

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