![Linus Torvalds](/assets/img/avatar_default.png)
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
156 lines
3.9 KiB
C
156 lines
3.9 KiB
C
/* $Id: semaphore.c,v 1.7 2001/04/18 21:06:05 davem Exp $ */
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/* sparc32 semaphore implementation, based on i386 version */
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#include <linux/sched.h>
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#include <linux/errno.h>
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#include <linux/init.h>
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#include <asm/semaphore.h>
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/*
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* Semaphores are implemented using a two-way counter:
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* The "count" variable is decremented for each process
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* that tries to acquire the semaphore, while the "sleeping"
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* variable is a count of such acquires.
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*
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* Notably, the inline "up()" and "down()" functions can
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* efficiently test if they need to do any extra work (up
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* needs to do something only if count was negative before
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* the increment operation.
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*
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* "sleeping" and the contention routine ordering is
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* protected by the semaphore spinlock.
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*
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* Note that these functions are only called when there is
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* contention on the lock, and as such all this is the
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* "non-critical" part of the whole semaphore business. The
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* critical part is the inline stuff in <asm/semaphore.h>
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* where we want to avoid any extra jumps and calls.
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*/
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/*
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* Logic:
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* - only on a boundary condition do we need to care. When we go
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* from a negative count to a non-negative, we wake people up.
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* - when we go from a non-negative count to a negative do we
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* (a) synchronize with the "sleeper" count and (b) make sure
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* that we're on the wakeup list before we synchronize so that
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* we cannot lose wakeup events.
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*/
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void __up(struct semaphore *sem)
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{
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wake_up(&sem->wait);
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}
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static DEFINE_SPINLOCK(semaphore_lock);
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void __sched __down(struct semaphore * sem)
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{
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struct task_struct *tsk = current;
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DECLARE_WAITQUEUE(wait, tsk);
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tsk->state = TASK_UNINTERRUPTIBLE;
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add_wait_queue_exclusive(&sem->wait, &wait);
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spin_lock_irq(&semaphore_lock);
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sem->sleepers++;
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for (;;) {
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int sleepers = sem->sleepers;
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/*
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* Add "everybody else" into it. They aren't
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* playing, because we own the spinlock.
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*/
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if (!atomic24_add_negative(sleepers - 1, &sem->count)) {
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sem->sleepers = 0;
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break;
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}
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sem->sleepers = 1; /* us - see -1 above */
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spin_unlock_irq(&semaphore_lock);
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schedule();
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tsk->state = TASK_UNINTERRUPTIBLE;
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spin_lock_irq(&semaphore_lock);
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}
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spin_unlock_irq(&semaphore_lock);
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remove_wait_queue(&sem->wait, &wait);
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tsk->state = TASK_RUNNING;
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wake_up(&sem->wait);
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}
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int __sched __down_interruptible(struct semaphore * sem)
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{
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int retval = 0;
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struct task_struct *tsk = current;
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DECLARE_WAITQUEUE(wait, tsk);
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tsk->state = TASK_INTERRUPTIBLE;
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add_wait_queue_exclusive(&sem->wait, &wait);
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spin_lock_irq(&semaphore_lock);
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sem->sleepers ++;
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for (;;) {
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int sleepers = sem->sleepers;
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/*
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* With signals pending, this turns into
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* the trylock failure case - we won't be
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* sleeping, and we* can't get the lock as
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* it has contention. Just correct the count
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* and exit.
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*/
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if (signal_pending(current)) {
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retval = -EINTR;
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sem->sleepers = 0;
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atomic24_add(sleepers, &sem->count);
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break;
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}
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/*
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* Add "everybody else" into it. They aren't
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* playing, because we own the spinlock. The
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* "-1" is because we're still hoping to get
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* the lock.
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*/
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if (!atomic24_add_negative(sleepers - 1, &sem->count)) {
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sem->sleepers = 0;
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break;
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}
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sem->sleepers = 1; /* us - see -1 above */
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spin_unlock_irq(&semaphore_lock);
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schedule();
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tsk->state = TASK_INTERRUPTIBLE;
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spin_lock_irq(&semaphore_lock);
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}
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spin_unlock_irq(&semaphore_lock);
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tsk->state = TASK_RUNNING;
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remove_wait_queue(&sem->wait, &wait);
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wake_up(&sem->wait);
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return retval;
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}
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/*
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* Trylock failed - make sure we correct for
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* having decremented the count.
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*/
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int __down_trylock(struct semaphore * sem)
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{
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int sleepers;
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unsigned long flags;
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spin_lock_irqsave(&semaphore_lock, flags);
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sleepers = sem->sleepers + 1;
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sem->sleepers = 0;
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/*
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* Add "everybody else" and us into it. They aren't
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* playing, because we own the spinlock.
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*/
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if (!atomic24_add_negative(sleepers, &sem->count))
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wake_up(&sem->wait);
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spin_unlock_irqrestore(&semaphore_lock, flags);
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return 1;
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}
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