137 lines
3.6 KiB
C
137 lines
3.6 KiB
C
/*
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*
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*
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* PowerPC-specific semaphore code.
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*
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* Copyright (C) 1999 Cort Dougan <cort@cs.nmt.edu>
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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 License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*
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* April 2001 - Reworked by Paul Mackerras <paulus@samba.org>
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* to eliminate the SMP races in the old version between the updates
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* of `count' and `waking'. Now we use negative `count' values to
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* indicate that some process(es) are waiting for the semaphore.
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*/
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#include <linux/sched.h>
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#include <linux/init.h>
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#include <linux/module.h>
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#include <asm/atomic.h>
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#include <asm/semaphore.h>
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#include <asm/errno.h>
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/*
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* Atomically update sem->count.
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* This does the equivalent of the following:
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*
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* old_count = sem->count;
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* tmp = MAX(old_count, 0) + incr;
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* sem->count = tmp;
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* return old_count;
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*/
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static inline int __sem_update_count(struct semaphore *sem, int incr)
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{
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int old_count, tmp;
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__asm__ __volatile__("\n"
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"1: lwarx %0,0,%3\n"
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" srawi %1,%0,31\n"
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" andc %1,%0,%1\n"
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" add %1,%1,%4\n"
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" stwcx. %1,0,%3\n"
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" bne 1b"
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: "=&r" (old_count), "=&r" (tmp), "=m" (sem->count)
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: "r" (&sem->count), "r" (incr), "m" (sem->count)
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: "cc");
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return old_count;
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}
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void __up(struct semaphore *sem)
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{
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/*
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* Note that we incremented count in up() before we came here,
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* but that was ineffective since the result was <= 0, and
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* any negative value of count is equivalent to 0.
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* This ends up setting count to 1, unless count is now > 0
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* (i.e. because some other cpu has called up() in the meantime),
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* in which case we just increment count.
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*/
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__sem_update_count(sem, 1);
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wake_up(&sem->wait);
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}
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EXPORT_SYMBOL(__up);
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/*
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* Note that when we come in to __down or __down_interruptible,
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* we have already decremented count, but that decrement was
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* ineffective since the result was < 0, and any negative value
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* of count is equivalent to 0.
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* Thus it is only when we decrement count from some value > 0
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* that we have actually got the semaphore.
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*/
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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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__set_task_state(tsk, TASK_UNINTERRUPTIBLE);
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add_wait_queue_exclusive(&sem->wait, &wait);
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/*
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* Try to get the semaphore. If the count is > 0, then we've
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* got the semaphore; we decrement count and exit the loop.
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* If the count is 0 or negative, we set it to -1, indicating
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* that we are asleep, and then sleep.
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*/
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while (__sem_update_count(sem, -1) <= 0) {
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schedule();
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set_task_state(tsk, TASK_UNINTERRUPTIBLE);
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}
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remove_wait_queue(&sem->wait, &wait);
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__set_task_state(tsk, TASK_RUNNING);
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/*
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* If there are any more sleepers, wake one of them up so
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* that it can either get the semaphore, or set count to -1
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* indicating that there are still processes sleeping.
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*/
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wake_up(&sem->wait);
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}
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EXPORT_SYMBOL(__down);
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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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__set_task_state(tsk, TASK_INTERRUPTIBLE);
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add_wait_queue_exclusive(&sem->wait, &wait);
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while (__sem_update_count(sem, -1) <= 0) {
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if (signal_pending(current)) {
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/*
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* A signal is pending - give up trying.
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* Set sem->count to 0 if it is negative,
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* since we are no longer sleeping.
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*/
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__sem_update_count(sem, 0);
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retval = -EINTR;
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break;
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}
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schedule();
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set_task_state(tsk, TASK_INTERRUPTIBLE);
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}
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remove_wait_queue(&sem->wait, &wait);
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__set_task_state(tsk, TASK_RUNNING);
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wake_up(&sem->wait);
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return retval;
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}
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EXPORT_SYMBOL(__down_interruptible);
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