// SPDX-License-Identifier: GPL-2.0
#include <linux/export.h>
#include <linux/spinlock.h>
#include <linux/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)
{
        /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
        if (atomic_add_unless(atomic, -1, 1))
                return 0;

        /* 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);

int _atomic_dec_and_lock_irqsave(atomic_t *atomic, spinlock_t *lock,
                                 unsigned long *flags)
{
        /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
        if (atomic_add_unless(atomic, -1, 1))
                return 0;

        /* Otherwise do it the slow way */
        spin_lock_irqsave(lock, *flags);
        if (atomic_dec_and_test(atomic))
                return 1;
        spin_unlock_irqrestore(lock, *flags);
        return 0;
}
EXPORT_SYMBOL(_atomic_dec_and_lock_irqsave);

int atomic_dec_and_raw_lock(atomic_t *atomic, raw_spinlock_t *lock)
{
        /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
        if (atomic_add_unless(atomic, -1, 1))
                return 0;

        /* Otherwise do it the slow way */
        raw_spin_lock(lock);
        if (atomic_dec_and_test(atomic))
                return 1;
        raw_spin_unlock(lock);
        return 0;
}
EXPORT_SYMBOL(atomic_dec_and_raw_lock);

int _atomic_dec_and_raw_lock_irqsave(atomic_t *atomic, raw_spinlock_t *lock,
                                     unsigned long *flags)
{
        /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
        if (atomic_add_unless(atomic, -1, 1))
                return 0;

        /* Otherwise do it the slow way */
        raw_spin_lock_irqsave(lock, *flags);
        if (atomic_dec_and_test(atomic))
                return 1;
        raw_spin_unlock_irqrestore(lock, *flags);
        return 0;
}
EXPORT_SYMBOL(_atomic_dec_and_raw_lock_irqsave);