OSDev.org

Code: Select all

static inline void down(struct semaphore * sem)
{
	__asm__ __volatile__(
		"# atomic down operation\n\t"
		LOCK "decl %0\n\t"     /* --sem->count */
		"js 2f\n"
		"1:\n"
		".section .text.lock,\"ax\"\n"
		"2:\tcall __down_failed\n\t"
		"jmp 1b\n"
		".previous"
		:"=m" (sem->count)
		:"c" (sem)
		:"memory");
}

static inline void up(struct semaphore * sem)
{
	__asm__ __volatile__(
		"# atomic up operation\n\t"
		LOCK "incl %0\n\t"     /* ++sem->count */
		"jle 2f\n"
		"1:\n"
		".section .text.lock,\"ax\"\n"
		"2:\tcall __up_wakeup\n\t"
		"jmp 1b\n"
		".previous"
		:"=m" (sem->count)
		:"c" (sem)
		:"memory");
}

Code: Select all

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

	spin_lock_irqsave(&sem->lock, flags);
	if (likely(sem->count > 0))
		sem->count--;
	else
		__down(sem);
	spin_unlock_irqrestore(&sem->lock, flags);
}

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

	spin_lock_irqsave(&sem->lock, flags);
	if (likely(list_empty(&sem->wait_list)))
		sem->count++;
	else
		__up(sem);
	spin_unlock_irqrestore(&sem->lock, flags);
}