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