s390/locking: Reenable optimistic spinning

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>
Cc: <stable@vger.kernel.org>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index bb63499fc5d3c50ec35108d66271d7b801bd4767..9f00f93016137b14142103dc87766dbb589cf1e3 100644 (file)
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -92,6 +92,7 @@ config S390
        select ARCH_INLINE_WRITE_UNLOCK_IRQ
        select ARCH_INLINE_WRITE_UNLOCK_IRQRESTORE
        select ARCH_SAVE_PAGE_KEYS if HIBERNATION
+       select ARCH_SUPPORTS_ATOMIC_RMW
        select ARCH_USE_CMPXCHG_LOCKREF
        select ARCH_WANT_IPC_PARSE_VERSION
        select BUILDTIME_EXTABLE_SORT