patch-2.4.5 linux/include/asm-ppc/semaphore.h

• Lines: 141
• Date: Mon May 21 15:02:06 2001
• Orig file: v2.4.4/linux/include/asm-ppc/semaphore.h
• Orig date: Tue Apr 17 17:19:31 2001

diff -u --recursive --new-file v2.4.4/linux/include/asm-ppc/semaphore.h linux/include/asm-ppc/semaphore.h
@@ -1,3 +1,6 @@
+/*
+ * BK Id: SCCS/s.semaphore.h 1.15 05/17/01 18:14:25 cort
+ */
 #ifndef _PPC_SEMAPHORE_H
 #define _PPC_SEMAPHORE_H
 
@@ -7,6 +10,11 @@
  *
  * Stole some rw spinlock-based semaphore stuff from asm-alpha/semaphore.h
  * -- Ani Joshi (ajoshi@unixbox.com)
+ *
+ * Remove spinlock-based RW semaphores; RW semaphore definitions are
+ * now in rwsem.h and we use the the generic lib/rwsem.c implementation.
+ * Rework semaphores to use atomic_dec_if_positive.
+ * -- Paul Mackerras (paulus@samba.org)
  */
 
 #ifdef __KERNEL__
@@ -17,8 +25,12 @@
 #include <linux/rwsem.h>
 
 struct semaphore {
+	/*
+	 * Note that any negative value of count is equivalent to 0,
+	 * but additionally indicates that some process(es) might be
+	 * sleeping on `wait'.
+	 */
 	atomic_t count;
-	atomic_t waking;
 	wait_queue_head_t wait;
 #if WAITQUEUE_DEBUG
 	long __magic;
@@ -32,23 +44,23 @@
 # define __SEM_DEBUG_INIT(name)
 #endif
 
-#define __SEMAPHORE_INITIALIZER(name,count) \
-{ ATOMIC_INIT(count), ATOMIC_INIT(0), __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
-	__SEM_DEBUG_INIT(name) }
+#define __SEMAPHORE_INITIALIZER(name, count) \
+	{ ATOMIC_INIT(count), \
+	  __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
+	  __SEM_DEBUG_INIT(name) }
 
 #define __MUTEX_INITIALIZER(name) \
-	__SEMAPHORE_INITIALIZER(name,1)
+	__SEMAPHORE_INITIALIZER(name, 1)
 
-#define __DECLARE_SEMAPHORE_GENERIC(name,count) \
+#define __DECLARE_SEMAPHORE_GENERIC(name, count) \
 	struct semaphore name = __SEMAPHORE_INITIALIZER(name,count)
 
-#define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name,1)
-#define DECLARE_MUTEX_LOCKED(name) __DECLARE_SEMAPHORE_GENERIC(name,0)
+#define DECLARE_MUTEX(name)		__DECLARE_SEMAPHORE_GENERIC(name, 1)
+#define DECLARE_MUTEX_LOCKED(name)	__DECLARE_SEMAPHORE_GENERIC(name, 0)
 
-extern inline void sema_init (struct semaphore *sem, int val)
+static inline void sema_init (struct semaphore *sem, int val)
 {
 	atomic_set(&sem->count, val);
-	atomic_set(&sem->waking, 0);
 	init_waitqueue_head(&sem->wait);
 #if WAITQUEUE_DEBUG
 	sem->__magic = (long)&sem->__magic;
@@ -67,46 +79,59 @@
 
 extern void __down(struct semaphore * sem);
 extern int  __down_interruptible(struct semaphore * sem);
-extern int  __down_trylock(struct semaphore * sem);
 extern void __up(struct semaphore * sem);
 
 extern inline void down(struct semaphore * sem)
 {
-	if (atomic_dec_return(&sem->count) >= 0)
-		wmb();
-	else
+#if WAITQUEUE_DEBUG
+	CHECK_MAGIC(sem->__magic);
+#endif
+
+	/*
+	 * Try to get the semaphore, take the slow path if we fail.
+	 */
+	if (atomic_dec_return(&sem->count) < 0)
 		__down(sem);
+	smp_wmb();
 }
 
 extern inline int down_interruptible(struct semaphore * sem)
 {
 	int ret = 0;
 
-	if (atomic_dec_return(&sem->count) >= 0)
-		wmb();
-	else
+#if WAITQUEUE_DEBUG
+	CHECK_MAGIC(sem->__magic);
+#endif
+
+	if (atomic_dec_return(&sem->count) < 0)
 		ret = __down_interruptible(sem);
+	smp_wmb();
 	return ret;
 }
 
 extern inline int down_trylock(struct semaphore * sem)
 {
-	int ret = 0;
+	int ret;
 
-	if (atomic_dec_return(&sem->count) >= 0)
-		wmb();
-	else
-		ret = __down_trylock(sem);
+#if WAITQUEUE_DEBUG
+	CHECK_MAGIC(sem->__magic);
+#endif
+
+	ret = atomic_dec_if_positive(&sem->count) < 0;
+	smp_wmb();
 	return ret;
 }
 
 extern inline void up(struct semaphore * sem)
 {
-	mb();
+#if WAITQUEUE_DEBUG
+	CHECK_MAGIC(sem->__magic);
+#endif
+
+	smp_wmb();
 	if (atomic_inc_return(&sem->count) <= 0)
 		__up(sem);
-}	
-
+}
 
 #endif /* __KERNEL__ */