[patch 4/5] mutex subsystem: allow architecture defined fast path for mutex_lock_interruptible

[Nicolas Pitre <nico@cam.org>]

This patch adds another architecture helper, 
arch_mutex_fast_lock_retval(), to allows for mutex_lock_interruptible
to have an architecture defined fast path.

Signed-off-by: Nicolas Pitre <nico@cam.org>

---

Index: linux-2.6/include/asm-generic/mutex.h
===================================================================
--- linux-2.6.orig/include/asm-generic/mutex.h
+++ linux-2.6/include/asm-generic/mutex.h
@@ -26,6 +26,24 @@ do {									\
 } while (0)
 
 /**
+ * arch_mutex_fast_lock_retval - lock mutex and call function if already locked
+ * @v: pointer of type atomic_t
+ * @contention_fn: function to call if v was already locked
+ *
+ * Atomically locks @v and calls a function if @v was already locked.
+ * When @v == 1 it is unlocked, <= 0 means locked.
+ *
+ * Returns 0 if no contention, otherwise returns whatever from @contention_fn.
+ */
+#define arch_mutex_fast_lock_retval(v, contention_fn)			\
+({									\
+	int __retval = 0;						\
+	if (unlikely(atomic_xchg(v, 0) != 1))				\
+		__retval = contention_fn(v);				\
+	__retval;							\
+})
+
+/**
  * arch_mutex_fast_unlock - unlock and call function if contended
  * @v: pointer of type atomic_t
  * @contention_fn: function to call if v was contended
Index: linux-2.6/include/asm-i386/mutex.h
===================================================================
--- linux-2.6.orig/include/asm-i386/mutex.h
+++ linux-2.6/include/asm-i386/mutex.h
@@ -14,6 +14,14 @@
 #define arch_mutex_fast_lock(v, contention_fn)				\
 	atomic_dec_call_if_negative(v, contention_fn)
 
+#define arch_mutex_fast_lock_retval(v, contention_fn)			\
+({									\
+	int __retval = 0;						\
+	if (unlikely(atomic_dec_return(v) < 0))				\
+ 		__retval = contention_fnv);				\
+	__retval;							\
+})
+
 #define arch_mutex_fast_unlock(v, contention_fn)			\
 	atomic_inc_call_if_nonpositive(v, contention_fn)
 
Index: linux-2.6/kernel/mutex.c
===================================================================
--- linux-2.6.orig/kernel/mutex.c
+++ linux-2.6/kernel/mutex.c
@@ -336,11 +336,24 @@ static inline void __mutex_lock(struct m
 	__mutex_lock_atomic(lock);
 }
 
+static __sched int FASTCALL(__mutex_lock_interruptible_noinline(atomic_t *lock_count));
+
+static inline int __mutex_lock_interruptible_atomic(struct mutex *lock)
+{
+	return arch_mutex_fast_lock_retval(&lock->count,
+					   __mutex_lock_interruptible_noinline);
+}
+
+static fastcall __sched int __mutex_lock_interruptible_noinline(atomic_t *lock_count)
+{
+	struct mutex *lock = container_of(lock_count, struct mutex, count);
+
+	return __mutex_lock_interruptible_nonatomic(lock);
+}
+
 static inline int __mutex_lock_interruptible(struct mutex *lock)
 {
-	if (unlikely(atomic_dec_return(&lock->count) < 0))
-		return __mutex_lock_interruptible_nonatomic(lock);
-	return 0;
+	return __mutex_lock_interruptible_atomic(lock);
 }
 
 static void __sched FASTCALL(__mutex_unlock_noinline(atomic_t *lock_count));
Index: linux-2.6/include/asm-x86_64/mutex.h
===================================================================
--- linux-2.6.orig/include/asm-x86_64/mutex.h
+++ linux-2.6/include/asm-x86_64/mutex.h
@@ -14,6 +14,14 @@
 #define arch_mutex_fast_lock(v, contention_fn)				\
 	atomic_dec_call_if_negative(v, contention_fn)
 
+#define arch_mutex_fast_lock_retval(v, contention_fn)			\
+({									\
+	int __retval = 0;						\
+	if (unlikely(atomic_dec_return(v) < 0))				\
+ 		__retval = contention_fnv);				\
+	__retval;							\
+})
+
 #define arch_mutex_fast_unlock(v, contention_fn)			\
 	atomic_inc_call_if_nonpositive(v, contention_fn)