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#include <linux/module.h>

#include <linux/spinlock.h>

#include <asm/atomic.h>

/*

 * This is an implementation of the notion of "decrement a

 * reference count, and return locked if it decremented to zero".

 *

 * NOTE NOTE NOTE! This is _not_ equivalent to

 *

 *      if (atomic_dec_and_test(&atomic)) {

 *              spin_lock(&lock);

 *              return 1;

 *      }

 *      return 0;

 *

 * because the spin-lock and the decrement must be

 * "atomic".

 */

int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)

{

#ifdef CONFIG_SMP

        /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */

        if (atomic_add_unless(atomic, -1, 1))

                return 0;

#endif

        /* Otherwise do it the slow way */

        spin_lock(lock);

        if (atomic_dec_and_test(atomic))

                return 1;

        spin_unlock(lock);

        return 0;

}

EXPORT_SYMBOL(_atomic_dec_and_lock);