linux-kernel - [PATCH 3.2 057/131] s390/locking: Reenable optimistic spinning

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Date:	Thu, 11 Sep 2014 13:32:13 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Heiko Carstens" <heiko.carstens@...ibm.com>,
	"Peter Zijlstra" <peterz@...radead.org>,
	"Christian Borntraeger" <borntraeger@...ibm.com>,
	"Martin Schwidefsky" <schwidefsky@...ibm.com>,
	"Ingo Molnar" <mingo@...nel.org>
Subject: [PATCH 3.2 057/131] s390/locking: Reenable optimistic spinning

3.2.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Christian Borntraeger <borntraeger@...ibm.com>

commit 36e7fdaa1a04fcf65b864232e1af56a51c7814d6 upstream.

commit 4badad352a6bb202ec68afa7a574c0bb961e5ebc (locking/mutex: Disable
optimistic spinning on some architectures) fenced spinning for
architectures without proper cmpxchg.
There is no need to disable mutex spinning on s390, though:
The instructions CS,CSG and friends provide the proper guarantees.
(We dont implement cmpxchg with locks).

Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/s390/Kconfig | 1 +
 1 file changed, 1 insertion(+)

--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -119,6 +119,7 @@ config S390
 	select ARCH_INLINE_WRITE_UNLOCK_BH
 	select ARCH_INLINE_WRITE_UNLOCK_IRQ
 	select ARCH_INLINE_WRITE_UNLOCK_IRQRESTORE
+	select ARCH_SUPPORTS_ATOMIC_RMW
 
 config SCHED_OMIT_FRAME_POINTER
 	def_bool y

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