patch-2.4.19 linux-2.4.19/arch/ppc64/kernel/semaphore.c

• Lines: 132
• Date: Fri Aug 2 17:39:43 2002
• Orig file: linux-2.4.18/arch/ppc64/kernel/semaphore.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -urN linux-2.4.18/arch/ppc64/kernel/semaphore.c linux-2.4.19/arch/ppc64/kernel/semaphore.c
@@ -0,0 +1,131 @@
+/*
+ * 
+ *
+ * PowerPC-specific semaphore code.
+ *
+ * Copyright (C) 1999 Cort Dougan <cort@cs.nmt.edu>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ *
+ * April 2001 - Reworked by Paul Mackerras <paulus@samba.org>
+ * to eliminate the SMP races in the old version between the updates
+ * of `count' and `waking'.  Now we use negative `count' values to
+ * indicate that some process(es) are waiting for the semaphore.
+ */
+
+#include <linux/sched.h>
+#include <asm/atomic.h>
+#include <asm/semaphore.h>
+#include <asm/errno.h>
+
+/*
+ * Atomically update sem->count.
+ * This does the equivalent of the following:
+ *
+ *	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"
+"1:	lwarx	%0,0,%3\n"
+"	srawi	%1,%0,31\n"
+"	andc	%1,%0,%1\n"
+"	add	%1,%1,%4\n"
+"	stwcx.	%1,0,%3\n"
+"	bne	1b"
+	: "=&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)
+{
+	/*
+	 * Note that we incremented count in up() before we came here,
+	 * but that was ineffective since the result was <= 0, and
+	 * any negative value of count is equivalent to 0.
+	 * This ends up setting count to 1, unless count is now > 0
+	 * (i.e. because some other cpu has called up() in the meantime),
+	 * in which case we just increment count.
+	 */
+	__sem_update_count(sem, 1);
+	wake_up(&sem->wait);
+}
+
+/*
+ * Note that when we come in to __down or __down_interruptible,
+ * we have already decremented count, but that decrement was
+ * ineffective since the result was < 0, and any negative value
+ * of count is equivalent to 0.
+ * Thus it is only when we decrement count from some value > 0
+ * that we have actually got the semaphore.
+ */
+void __down(struct semaphore *sem)
+{
+	struct task_struct *tsk = current;
+	DECLARE_WAITQUEUE(wait, tsk);
+
+	tsk->state = TASK_UNINTERRUPTIBLE;
+	add_wait_queue_exclusive(&sem->wait, &wait);
+	smp_wmb();
+
+	/*
+	 * Try to get the semaphore.  If the count is > 0, then we've
+	 * got the semaphore; we decrement count and exit the loop.
+	 * If the count is 0 or negative, we set it to -1, indicating
+	 * that we are asleep, and then sleep.
+	 */
+	while (__sem_update_count(sem, -1) <= 0) {
+		schedule();
+		tsk->state = TASK_UNINTERRUPTIBLE;
+	}
+	remove_wait_queue(&sem->wait, &wait);
+	tsk->state = TASK_RUNNING;
+
+	/*
+	 * If there are any more sleepers, wake one of them up so
+	 * that it can either get the semaphore, or set count to -1
+	 * indicating that there are still processes sleeping.
+	 */
+	wake_up(&sem->wait);
+}
+
+int __down_interruptible(struct semaphore * sem)
+{
+	int retval = 0;
+	struct task_struct *tsk = current;
+	DECLARE_WAITQUEUE(wait, tsk);
+
+	tsk->state = TASK_INTERRUPTIBLE;
+	add_wait_queue_exclusive(&sem->wait, &wait);
+	smp_wmb();
+
+	while (__sem_update_count(sem, -1) <= 0) {
+		if (signal_pending(current)) {
+			/*
+			 * A signal is pending - give up trying.
+			 * Set sem->count to 0 if it is negative,
+			 * since we are no longer sleeping.
+			 */
+			__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;
+}