1 files changed, 165 insertions, 0 deletions
diff --git a/arch/ia64/kernel/semaphore.c b/arch/ia64/kernel/semaphore.c
new file mode 100644
index 000000000000..2724ef3fbae2
--- /dev/null
+++ b/arch/ia64/kernel/semaphore.c
@@ -0,0 +1,165 @@
+/*
+ * IA-64 semaphore implementation (derived from x86 version).
+ *
+ * Copyright (C) 1999-2000, 2002 Hewlett-Packard Co
+ *	David Mosberger-Tang <davidm@hpl.hp.com>
+ */
+
+/*
+ * Semaphores are implemented using a two-way counter: The "count"
+ * variable is decremented for each process that tries to acquire the
+ * semaphore, while the "sleepers" variable is a count of such
+ * acquires.
+ *
+ * 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.
+ *
+ * "sleeping" and the contention routine ordering is protected
+ * by the spinlock in the semaphore's waitqueue head.
+ *
+ * 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.
+ */
+#include <linux/sched.h>
+#include <linux/init.h>
+
+#include <asm/errno.h>
+#include <asm/semaphore.h>
+
+/*
+ * Logic:
+ *  - Only on a boundary condition do we need to care. When we go
+ *    from a negative count to a non-negative, we wake people up.
+ *  - When we go from a non-negative count to a negative do we
+ *    (a) synchronize with the "sleepers" count and (b) make sure
+ *    that we're on the wakeup list before we synchronize so that
+ *    we cannot lose wakeup events.
+ */
+
+void
+__up (struct semaphore *sem)
+{
+	wake_up(&sem->wait);
+}
+
+void __sched __down (struct semaphore *sem)
+{
+	struct task_struct *tsk = current;
+	DECLARE_WAITQUEUE(wait, tsk);
+	unsigned long flags;
+
+	tsk->state = TASK_UNINTERRUPTIBLE;
+	spin_lock_irqsave(&sem->wait.lock, flags);
+	add_wait_queue_exclusive_locked(&sem->wait, &wait);
+
+	sem->sleepers++;
+	for (;;) {
+		int sleepers = sem->sleepers;
+
+		/*
+		 * Add "everybody else" into it. They aren't
+		 * playing, because we own the spinlock in
+		 * the wait_queue_head.
+		 */
+		if (!atomic_add_negative(sleepers - 1, &sem->count)) {
+			sem->sleepers = 0;
+			break;
+		}
+		sem->sleepers = 1;	/* us - see -1 above */
+		spin_unlock_irqrestore(&sem->wait.lock, flags);
+
+		schedule();
+
+		spin_lock_irqsave(&sem->wait.lock, flags);
+		tsk->state = TASK_UNINTERRUPTIBLE;
+	}
+	remove_wait_queue_locked(&sem->wait, &wait);
+	wake_up_locked(&sem->wait);
+	spin_unlock_irqrestore(&sem->wait.lock, flags);
+	tsk->state = TASK_RUNNING;
+}
+
+int __sched __down_interruptible (struct semaphore * sem)
+{
+	int retval = 0;
+	struct task_struct *tsk = current;
+	DECLARE_WAITQUEUE(wait, tsk);
+	unsigned long flags;
+
+	tsk->state = TASK_INTERRUPTIBLE;
+	spin_lock_irqsave(&sem->wait.lock, flags);
+	add_wait_queue_exclusive_locked(&sem->wait, &wait);
+
+	sem->sleepers ++;
+	for (;;) {
+		int sleepers = sem->sleepers;
+
+		/*
+		 * With signals pending, this turns into
+		 * the trylock failure case - we won't be
+		 * sleeping, and we* can't get the lock as
+		 * it has contention. Just correct the count
+		 * and exit.
+		 */
+		if (signal_pending(current)) {
+			retval = -EINTR;
+			sem->sleepers = 0;
+			atomic_add(sleepers, &sem->count);
+			break;
+		}
+
+		/*
+		 * Add "everybody else" into it. They aren't
+		 * playing, because we own the spinlock in
+		 * wait_queue_head. The "-1" is because we're
+		 * still hoping to get the semaphore.
+		 */
+		if (!atomic_add_negative(sleepers - 1, &sem->count)) {
+			sem->sleepers = 0;
+			break;
+		}
+		sem->sleepers = 1;	/* us - see -1 above */
+		spin_unlock_irqrestore(&sem->wait.lock, flags);
+
+		schedule();
+
+		spin_lock_irqsave(&sem->wait.lock, flags);
+		tsk->state = TASK_INTERRUPTIBLE;
+	}
+	remove_wait_queue_locked(&sem->wait, &wait);
+	wake_up_locked(&sem->wait);
+	spin_unlock_irqrestore(&sem->wait.lock, flags);
+
+	tsk->state = TASK_RUNNING;
+	return retval;
+}
+
+/*
+ * Trylock failed - make sure we correct for having decremented the
+ * count.
+ */
+int
+__down_trylock (struct semaphore *sem)
+{
+	unsigned long flags;
+	int sleepers;
+
+	spin_lock_irqsave(&sem->wait.lock, flags);
+	sleepers = sem->sleepers + 1;
+	sem->sleepers = 0;
+
+	/*
+	 * Add "everybody else" and us into it. They aren't
+	 * playing, because we own the spinlock in the
+	 * wait_queue_head.
+	 */
+	if (!atomic_add_negative(sleepers, &sem->count)) {
+		wake_up_locked(&sem->wait);
+	}
+
+	spin_unlock_irqrestore(&sem->wait.lock, flags);
+	return 1;
+}