linux-kernel - [RFC v2 7/7] powerpc: atomic: Make atomic{,64}

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Date:	Wed, 16 Sep 2015 23:49:35 +0800
From:	Boqun Feng <boqun.feng@...il.com>
To:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <will.deacon@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Waiman Long <waiman.long@...com>,
	Boqun Feng <boqun.feng@...il.com>
Subject: [RFC v2 7/7] powerpc: atomic: Make atomic{,64}_cmpxchg and cmpxchg a full barrier

According to memory-barriers.txt, cmpxchg and its atomic{,64}_ versions
need to imply a full barrier, however they are now just RELEASE+ACQUIRE,
which is not a full barrier.

So replace PPC_RELEASE_BARRIER and PPC_ACQUIRE_BARRIER with
PPC_ATOMIC_ENTRY_BARRIER and PPC_ATOMIC_EXIT_BARRIER in
__cmpxchg_{u32,u64} respectively to guarantee full-barrier semantics
of atomic{,64}_cmpxchg() and cmpxchg().

Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---
 arch/powerpc/include/asm/cmpxchg.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/include/asm/cmpxchg.h b/arch/powerpc/include/asm/cmpxchg.h
index 9f0379a..5c58743 100644
--- a/arch/powerpc/include/asm/cmpxchg.h
+++ b/arch/powerpc/include/asm/cmpxchg.h
@@ -151,14 +151,14 @@ __cmpxchg_u32(volatile unsigned int *p, unsigned long old, unsigned long new)
 	unsigned int prev;
 
 	__asm__ __volatile__ (
-	PPC_RELEASE_BARRIER
+	PPC_ATOMIC_ENTRY_BARRIER
 "1:	lwarx	%0,0,%2		# __cmpxchg_u32\n\
 	cmpw	0,%0,%3\n\
 	bne-	2f\n"
 	PPC405_ERR77(0,%2)
 "	stwcx.	%4,0,%2\n\
 	bne-	1b"
-	PPC_ACQUIRE_BARRIER
+	PPC_ATOMIC_EXIT_BARRIER
 	"\n\
 2:"
 	: "=&r" (prev), "+m" (*p)
@@ -239,13 +239,13 @@ __cmpxchg_u64(volatile unsigned long *p, unsigned long old, unsigned long new)
 	unsigned long prev;
 
 	__asm__ __volatile__ (
-	PPC_RELEASE_BARRIER
+	PPC_ATOMIC_ENTRY_BARRIER
 "1:	ldarx	%0,0,%2		# __cmpxchg_u64\n\
 	cmpd	0,%0,%3\n\
 	bne-	2f\n\
 	stdcx.	%4,0,%2\n\
 	bne-	1b"
-	PPC_ACQUIRE_BARRIER
+	PPC_ATOMIC_EXIT_BARRIER
 	"\n\
 2:"
 	: "=&r" (prev), "+m" (*p)
-- 
2.5.1

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