futex: Allow architectures to skip futex_atomic_cmpxchg_inatomic() test

If an architecture has futex_atomic_cmpxchg_inatomic() implemented and there
is no runtime check necessary, allow to skip the test within futex_init().

This allows to get rid of some code which would always give the same result,
and also allows the compiler to optimize a couple of if statements away.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Finn Thain <fthain@telegraphics.com.au>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Link: http://lkml.kernel.org/r/20140302120947.GA3641@osiris
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 7 insertions, 0 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 009a797dd242..d56cb03c1b49 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1387,6 +1387,13 @@ config FUTEX
           support for "fast userspace mutexes".  The resulting kernel may not
           run glibc-based applications correctly.
 
+config HAVE_FUTEX_CMPXCHG
+        bool
+        help
+          Architectures should select this if futex_atomic_cmpxchg_inatomic()
+          is implemented and always working. This removes a couple of runtime
+          checks.
+
 config EPOLL
         bool "Enable eventpoll support" if EXPERT
         default y