linux-kernel - [PATCH tip/core/rcu 48/55] powerpc: strengthen value-returning-atomics memory barriers

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Date:	Tue,  6 Sep 2011 11:00:42 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	patches@...aro.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, anton@...ba.org,
	benh@...nel.crashing.org, paulus@...ba.org
Subject: [PATCH tip/core/rcu 48/55] powerpc: strengthen value-returning-atomics memory barriers

The trailing isync/lwsync in PowerPC value-returning atomics needs
to be a sync in order to provide the required ordering properties.
The leading lwsync/eieio can remain, as the remainder of the required
ordering guarantees are provided by the atomic instructions: Any
reordering will cause the stwcx to fail, which will result in a retry.

This commit provides the needed adjustment.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: anton@...ba.org
Cc: benh@...nel.crashing.org
Cc: paulus@...ba.org
---
 arch/powerpc/include/asm/synch.h |    6 +-----
 1 files changed, 1 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/include/asm/synch.h b/arch/powerpc/include/asm/synch.h
index d7cab44..4d97fbe 100644
--- a/arch/powerpc/include/asm/synch.h
+++ b/arch/powerpc/include/asm/synch.h
@@ -37,11 +37,7 @@ static inline void isync(void)
 #endif
 
 #ifdef CONFIG_SMP
-#define __PPC_ACQUIRE_BARRIER				\
-	START_LWSYNC_SECTION(97);			\
-	isync;						\
-	MAKE_LWSYNC_SECTION_ENTRY(97, __lwsync_fixup);
-#define PPC_ACQUIRE_BARRIER	"\n" stringify_in_c(__PPC_ACQUIRE_BARRIER)
+#define PPC_ACQUIRE_BARRIER	"\n" stringify_in_c(sync;)
 #define PPC_RELEASE_BARRIER	stringify_in_c(LWSYNC) "\n"
 #else
 #define PPC_ACQUIRE_BARRIER
-- 
1.7.3.2

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