150 lines
3.5 KiB
C
150 lines
3.5 KiB
C
/* MN10300 Semaphore implementation
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*
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* Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public Licence
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* as published by the Free Software Foundation; either version
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* 2 of the Licence, or (at your option) any later version.
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*/
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#include <linux/sched.h>
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#include <linux/module.h>
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#include <asm/semaphore.h>
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struct sem_waiter {
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struct list_head list;
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struct task_struct *task;
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};
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#if SEMAPHORE_DEBUG
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void semtrace(struct semaphore *sem, const char *str)
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{
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if (sem->debug)
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printk(KERN_DEBUG "[%d] %s({%d,%d})\n",
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current->pid,
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str,
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atomic_read(&sem->count),
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list_empty(&sem->wait_list) ? 0 : 1);
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}
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#else
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#define semtrace(SEM, STR) do { } while (0)
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#endif
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/*
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* wait for a token to be granted from a semaphore
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* - entered with lock held and interrupts disabled
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*/
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void __down(struct semaphore *sem, unsigned long flags)
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{
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struct task_struct *tsk = current;
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struct sem_waiter waiter;
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semtrace(sem, "Entering __down");
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/* set up my own style of waitqueue */
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waiter.task = tsk;
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get_task_struct(tsk);
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list_add_tail(&waiter.list, &sem->wait_list);
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/* we don't need to touch the semaphore struct anymore */
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spin_unlock_irqrestore(&sem->wait_lock, flags);
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/* wait to be given the semaphore */
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set_task_state(tsk, TASK_UNINTERRUPTIBLE);
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for (;;) {
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if (!waiter.task)
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break;
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schedule();
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set_task_state(tsk, TASK_UNINTERRUPTIBLE);
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}
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tsk->state = TASK_RUNNING;
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semtrace(sem, "Leaving __down");
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}
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EXPORT_SYMBOL(__down);
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/*
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* interruptibly wait for a token to be granted from a semaphore
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* - entered with lock held and interrupts disabled
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*/
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int __down_interruptible(struct semaphore *sem, unsigned long flags)
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{
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struct task_struct *tsk = current;
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struct sem_waiter waiter;
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int ret;
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semtrace(sem, "Entering __down_interruptible");
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/* set up my own style of waitqueue */
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waiter.task = tsk;
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get_task_struct(tsk);
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list_add_tail(&waiter.list, &sem->wait_list);
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/* we don't need to touch the semaphore struct anymore */
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set_task_state(tsk, TASK_INTERRUPTIBLE);
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spin_unlock_irqrestore(&sem->wait_lock, flags);
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/* wait to be given the semaphore */
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ret = 0;
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for (;;) {
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if (!waiter.task)
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break;
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if (unlikely(signal_pending(current)))
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goto interrupted;
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schedule();
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set_task_state(tsk, TASK_INTERRUPTIBLE);
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}
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out:
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tsk->state = TASK_RUNNING;
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semtrace(sem, "Leaving __down_interruptible");
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return ret;
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interrupted:
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spin_lock_irqsave(&sem->wait_lock, flags);
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list_del(&waiter.list);
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spin_unlock_irqrestore(&sem->wait_lock, flags);
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ret = 0;
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if (!waiter.task) {
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put_task_struct(current);
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ret = -EINTR;
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}
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goto out;
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}
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EXPORT_SYMBOL(__down_interruptible);
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/*
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* release a single token back to a semaphore
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* - entered with lock held and interrupts disabled
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*/
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void __up(struct semaphore *sem)
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{
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struct task_struct *tsk;
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struct sem_waiter *waiter;
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semtrace(sem, "Entering __up");
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/* grant the token to the process at the front of the queue */
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waiter = list_entry(sem->wait_list.next, struct sem_waiter, list);
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/* We must be careful not to touch 'waiter' after we set ->task = NULL.
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* It is an allocated on the waiter's stack and may become invalid at
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* any time after that point (due to a wakeup from another source).
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*/
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list_del_init(&waiter->list);
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tsk = waiter->task;
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smp_mb();
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waiter->task = NULL;
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wake_up_process(tsk);
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put_task_struct(tsk);
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semtrace(sem, "Leaving __up");
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}
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EXPORT_SYMBOL(__up);
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