/*
 * Copyright (c) 2008 Intel Corporation
 * Author: Matthew Wilcox <willy@linux.intel.com>
 *
 * Distributed under the terms of the GNU GPL, version 2
 *
 * This file implements counting semaphores.
 * A counting semaphore may be acquired 'n' times before sleeping.
 * See mutex.c for single-acquisition sleeping locks which enforce
 * rules which allow code to be debugged more easily.
 */


#include <linux/compiler.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/sched.h>
#include <linux/semaphore.h>
#include <linux/spinlock.h>
#include <linux/ftrace.h>

static noinline void __down(struct semaphore *sem);
static noinline int __down_interruptible(struct semaphore *sem);
static noinline int __down_killable(struct semaphore *sem);
static noinline int __down_timeout(struct semaphore *sem, long jiffies);
static noinline void __up(struct semaphore *sem);

void down(struct semaphore *sem)
{
	unsigned long flags;

	raw_spin_lock_irqsave(&sem->lock, flags);
	if (likely(sem->count > 0))
		sem->count--;
	else
		__down(sem);
	raw_spin_unlock_irqrestore(&sem->lock, flags);
}
EXPORT_SYMBOL(down);

int down_interruptible(struct semaphore *sem)
{
	unsigned long flags;
	int result = 0;

	raw_spin_lock_irqsave(&sem->lock, flags);
	if (likely(sem->count > 0))
		sem->count--;
	else
		result = __down_interruptible(sem);
	raw_spin_unlock_irqrestore(&sem->lock, flags);

	return result;
}
EXPORT_SYMBOL(down_interruptible);

int down_killable(struct semaphore *sem)
{
	unsigned long flags;
	int result = 0;

	raw_spin_lock_irqsave(&sem->lock, flags);
	if (likely(sem->count > 0))
		sem->count--;
	else
		result = __down_killable(sem);
	raw_spin_unlock_irqrestore(&sem->lock, flags);

	return result;
}
EXPORT_SYMBOL(down_killable);

int down_trylock(struct semaphore *sem)
{
	unsigned long flags;
	int count;

	raw_spin_lock_irqsave(&sem->lock, flags);
	count = sem->count - 1;
	if (likely(count >= 0))
		sem->count = count;
	raw_spin_unlock_irqrestore(&sem->lock, flags);

	return (count < 0);
}
EXPORT_SYMBOL(down_trylock);

int down_timeout(struct semaphore *sem, long jiffies)
{
	unsigned long flags;
	int result = 0;

	raw_spin_lock_irqsave(&sem->lock, flags);
	if (likely(sem->count > 0))
		sem->count--;
	else
		result = __down_timeout(sem, jiffies);
	raw_spin_unlock_irqrestore(&sem->lock, flags);

	return result;
}
EXPORT_SYMBOL(down_timeout);

void up(struct semaphore *sem)
{
	unsigned long flags;

	raw_spin_lock_irqsave(&sem->lock, flags);
	if (likely(list_empty(&sem->wait_list)))
		sem->count++;
	else
		__up(sem);
	raw_spin_unlock_irqrestore(&sem->lock, flags);
}
EXPORT_SYMBOL(up);


struct semaphore_waiter {
	struct list_head list;
	struct task_struct *task;
	int up;
};

static inline int __sched __down_common(struct semaphore *sem, long state,
								long timeout)
{
	struct task_struct *task = current;
	struct semaphore_waiter waiter;

	list_add_tail(&waiter.list, &sem->wait_list);
	waiter.task = task;
	waiter.up = 0;

	for (;;) {
		if (signal_pending_state(state, task))
			goto interrupted;
		if (timeout <= 0)
			goto timed_out;
		__set_task_state(task, state);
		raw_spin_unlock_irq(&sem->lock);
		timeout = schedule_timeout(timeout);
		raw_spin_lock_irq(&sem->lock);
		if (waiter.up)
			return 0;
	}

 timed_out:
	list_del(&waiter.list);
	return -ETIME;

 interrupted:
	list_del(&waiter.list);
	return -EINTR;
}

static noinline void __sched __down(struct semaphore *sem)
{
	__down_common(sem, TASK_UNINTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
}

static noinline int __sched __down_interruptible(struct semaphore *sem)
{
	return __down_common(sem, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
}

static noinline int __sched __down_killable(struct semaphore *sem)
{
	return __down_common(sem, TASK_KILLABLE, MAX_SCHEDULE_TIMEOUT);
}

static noinline int __sched __down_timeout(struct semaphore *sem, long jiffies)
{
	return __down_common(sem, TASK_UNINTERRUPTIBLE, jiffies);
}

static noinline void __sched __up(struct semaphore *sem)
{
	struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list,
						struct semaphore_waiter, list);
	list_del(&waiter->list);
	waiter->up = 1;
	wake_up_process(waiter->task);
}