From: Christian Borntraeger <borntraeger@de.ibm.com>
Date: Tue, 5 Aug 2014 07:57:51 +0000 (+0200)
Subject: s390/locking: Reenable optimistic spinning
X-Git-Tag: v3.2.63~74
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4f365d36bd439a942268dc360a868f75c093670c;p=thirdparty%2Fkernel%2Fstable.git

s390/locking: Reenable optimistic spinning

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@de.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index a3c40e8aa7d6c..aed3d918f959f 100644
--- 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