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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@de.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@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>
---
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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