[PATCH] mutex subsystem, add asm-generic/mutex-[dec|xchg|null].h implementations

Add three (generic) mutex fastpath implementations.

The mutex-xchg.h implementation is atomic_xchg() based, and should
work fine on every architecture.

The mutex-dec.h implementation is atomic_dec_return() based - this
one too should work on every architecture, but might not perform the
most optimally on architectures that have no atomic-dec/inc instructions.

The mutex-null.h implementation forces all calls into the slowpath. This
is used for mutex debugging, but it can also be used on platforms that do
not want (or need) a fastpath at all.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@infradead.org>

include/asm-generic/mutex-null.h

@@ -0,0 +1,24 @@
+/*
+ * asm-generic/mutex-null.h
+ *
+ * Generic implementation of the mutex fastpath, based on NOP :-)
+ *
+ * This is used by the mutex-debugging infrastructure, but it can also
+ * be used by architectures that (for whatever reason) want to use the
+ * spinlock based slowpath.
+ */
+#ifndef _ASM_GENERIC_MUTEX_NULL_H
+#define _ASM_GENERIC_MUTEX_NULL_H
+
+/* extra parameter only needed for mutex debugging: */
+#ifndef __IP__
+# define __IP__
+#endif
+
+#define __mutex_fastpath_lock(count, fail_fn)	      fail_fn(count __RET_IP__)
+#define __mutex_fastpath_lock_retval(count, fail_fn)  fail_fn(count __RET_IP__)
+#define __mutex_fastpath_unlock(count, fail_fn)       fail_fn(count __RET_IP__)
+#define __mutex_fastpath_trylock(count, fail_fn)      fail_fn(count)
+#define __mutex_slowpath_needs_to_unlock()	      1
+
+#endif