patch-2.4.5 linux/arch/sparc64/kernel/semaphore.c

• Lines: 195
• Date: Sun May 20 11:32:07 2001
• Orig file: v2.4.4/linux/arch/sparc64/kernel/semaphore.c
• Orig date: Tue Apr 17 17:19:30 2001

diff -u --recursive --new-file v2.4.4/linux/arch/sparc64/kernel/semaphore.c linux/arch/sparc64/kernel/semaphore.c
@@ -1,128 +1,88 @@
-/* $Id: semaphore.c,v 1.6 2001/04/14 01:12:02 davem Exp $
- *  Generic semaphore code. Buyer beware. Do your own
- * specific changes in <asm/semaphore-helper.h>
+/* $Id: semaphore.c,v 1.8 2001/05/18 08:01:35 davem Exp $
+ * semaphore.c: Sparc64 semaphore implementation.
+ *
+ * This is basically the PPC semaphore scheme ported to use
+ * the sparc64 atomic instructions, so see the PPC code for
+ * credits.
  */
 
 #include <linux/sched.h>
-#include <asm/semaphore-helper.h>
 
 /*
- * Semaphores are implemented using a two-way counter:
- * The "count" variable is decremented for each process
- * that tries to sleep, while the "waking" variable is
- * incremented when the "up()" code goes to wake up waiting
- * processes.
- *
- * Notably, the inline "up()" and "down()" functions can
- * efficiently test if they need to do any extra work (up
- * needs to do something only if count was negative before
- * the increment operation.
- *
- * waking_non_zero() (from asm/semaphore.h) must execute
- * atomically.
- *
- * When __up() is called, the count was negative before
- * incrementing it, and we need to wake up somebody.
+ * Atomically update sem->count.
+ * This does the equivalent of the following:
  *
- * This routine adds one to the count of processes that need to
- * wake up and exit.  ALL waiting processes actually wake up but
- * only the one that gets to the "waking" field first will gate
- * through and acquire the semaphore.  The others will go back
- * to sleep.
- *
- * Note that these functions are only called when there is
- * contention on the lock, and as such all this is the
- * "non-critical" part of the whole semaphore business. The
- * critical part is the inline stuff in <asm/semaphore.h>
- * where we want to avoid any extra jumps and calls.
+ *	old_count = sem->count;
+ *	tmp = MAX(old_count, 0) + incr;
+ *	sem->count = tmp;
+ *	return old_count;
  */
+static __inline__ int __sem_update_count(struct semaphore *sem, int incr)
+{
+	int old_count, tmp;
+
+	__asm__ __volatile__("\n"
+"	! __sem_update_count old_count(%0) tmp(%1) incr(%4) &sem->count(%3)\n"
+"1:	ldsw	[%3], %0\n"
+"	mov	%0, %1\n"
+"	cmp	%0, 0\n"
+"	movl	%%icc, 0, %1\n"
+"	add	%1, %4, %1\n"
+"	cas	[%3], %0, %1\n"
+"	cmp	%0, %1\n"
+"	bne,pn	%%icc, 1b\n"
+"	 nop\n"
+	: "=&r" (old_count), "=&r" (tmp), "=m" (sem->count)
+	: "r" (&sem->count), "r" (incr), "m" (sem->count)
+	: "cc");
+
+	return old_count;
+}
+
 void __up(struct semaphore *sem)
 {
-	wake_one_more(sem);
+	__sem_update_count(sem, 1);
 	wake_up(&sem->wait);
 }
 
-/*
- * Perform the "down" function.  Return zero for semaphore acquired,
- * return negative for signalled out of the function.
- *
- * If called from __down, the return is ignored and the wait loop is
- * not interruptible.  This means that a task waiting on a semaphore
- * using "down()" cannot be killed until someone does an "up()" on
- * the semaphore.
- *
- * If called from __down_interruptible, the return value gets checked
- * upon return.  If the return value is negative then the task continues
- * with the negative value in the return register (it can be tested by
- * the caller).
- *
- * Either form may be used in conjunction with "up()".
- *
- */
-
-#define DOWN_VAR				\
-	struct task_struct *tsk = current;	\
+void __down(struct semaphore * sem)
+{
+	struct task_struct *tsk = current;
 	DECLARE_WAITQUEUE(wait, tsk);
 
-#define DOWN_HEAD(task_state)						\
-									\
-									\
-	tsk->state = (task_state);					\
-	add_wait_queue(&sem->wait, &wait);				\
-									\
-	/*								\
-	 * Ok, we're set up.  sem->count is known to be less than zero	\
-	 * so we must wait.						\
-	 *								\
-	 * We can let go the lock for purposes of waiting.		\
-	 * We re-acquire it after awaking so as to protect		\
-	 * all semaphore operations.					\
-	 *								\
-	 * If "up()" is called before we call waking_non_zero() then	\
-	 * we will catch it right away.  If it is called later then	\
-	 * we will have to go through a wakeup cycle to catch it.	\
-	 *								\
-	 * Multiple waiters contend for the semaphore lock to see	\
-	 * who gets to gate through and who has to wait some more.	\
-	 */								\
-	for (;;) {
-
-#define DOWN_TAIL(task_state)			\
-		tsk->state = (task_state);	\
-	}					\
-	tsk->state = TASK_RUNNING;		\
+	tsk->state = TASK_UNINTERRUPTIBLE;
+	add_wait_queue_exclusive(&sem->wait, &wait);
+
+	while (__sem_update_count(sem, -1) <= 0) {
+		schedule();
+		tsk->state = TASK_UNINTERRUPTIBLE;
+	}
 	remove_wait_queue(&sem->wait, &wait);
+	tsk->state = TASK_RUNNING;
 
-void __down(struct semaphore * sem)
-{
-	DOWN_VAR
-	DOWN_HEAD(TASK_UNINTERRUPTIBLE)
-	if (waking_non_zero(sem))
-		break;
-	schedule();
-	DOWN_TAIL(TASK_UNINTERRUPTIBLE)
+	wake_up(&sem->wait);
 }
 
 int __down_interruptible(struct semaphore * sem)
 {
-	int ret = 0;
-	DOWN_VAR
-	DOWN_HEAD(TASK_INTERRUPTIBLE)
-
-	ret = waking_non_zero_interruptible(sem, tsk);
-	if (ret)
-	{
-		if (ret == 1)
-			/* ret != 0 only if we get interrupted -arca */
-			ret = 0;
-		break;
-	}
-	schedule();
-	DOWN_TAIL(TASK_INTERRUPTIBLE)
-	return ret;
-}
+	int retval = 0;
+	struct task_struct *tsk = current;
+	DECLARE_WAITQUEUE(wait, tsk);
 
-int __down_trylock(struct semaphore * sem)
-{
-	return waking_non_zero_trylock(sem);
+	tsk->state = TASK_INTERRUPTIBLE;
+	add_wait_queue_exclusive(&sem->wait, &wait);
+
+	while (__sem_update_count(sem, -1) <= 0) {
+		if (signal_pending(current)) {
+			__sem_update_count(sem, 0);
+			retval = -EINTR;
+			break;
+		}
+		schedule();
+		tsk->state = TASK_INTERRUPTIBLE;
+	}
+	tsk->state = TASK_RUNNING;
+	remove_wait_queue(&sem->wait, &wait);
+	wake_up(&sem->wait);
+	return retval;
 }