Viewing file:  dec_and_lock.c (1.17 KB) -rw-r--r--
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#include <linux/module.h>
#include <linux/spinlock.h>
#include <asm/atomic.h>
#include <asm/system.h>
/*
* This is an implementation of the notion of "decrement a
* reference count, and return locked if it decremented to zero".
*
* This implementation can be used on any architecture that
* has a cmpxchg, and where atomic->value is an int holding
* the value of the atomic (i.e. the high bits aren't used
* for a lock or anything like that).
*
* N.B. ATOMIC_DEC_AND_LOCK gets defined in include/linux/spinlock.h
* if spinlocks are empty and thus atomic_dec_and_lock is defined
* to be atomic_dec_and_test - in that case we don't need it
* defined here as well.
*/
#ifndef ATOMIC_DEC_AND_LOCK
int atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
{
int counter;
int newcount;
for (;;) {
counter = atomic_read(atomic);
newcount = counter - 1;
if (!newcount)
break; /* do it the slow way */
newcount = cmpxchg(&atomic->counter, counter, newcount);
if (newcount == counter)
return 0;
}
spin_lock(lock);
if (atomic_dec_and_test(atomic))
return 1;
spin_unlock(lock);
return 0;
}
EXPORT_SYMBOL(atomic_dec_and_lock);
#endif /* ATOMIC_DEC_AND_LOCK */
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