// SPDX-License-Identifier: GPL-2.0
#include <linux/export.h>
#include <linux/lockref.h>

#if USE_CMPXCHG_LOCKREF

/*
 * Note that the "cmpxchg()" reloads the "old" value for the
 * failure case.
 */
#define CMPXCHG_LOOP(CODE, SUCCESS) do {                                        \
        int retry = 100;                                                        \
        struct lockref old;                                                     \
        BUILD_BUG_ON(sizeof(old) != 8);                                         \
        old.lock_count = READ_ONCE(lockref->lock_count);                        \
        while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) {     \
                struct lockref new = old;                                       \
                CODE                                                            \
                if (likely(try_cmpxchg64_relaxed(&lockref->lock_count,          \
                                                 &old.lock_count,               \
                                                 new.lock_count))) {            \
                        SUCCESS;                                                \
                }                                                               \
                if (!--retry)                                                   \
                        break;                                                  \
        }                                                                       \
} while (0)

#else

#define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0)

#endif

/**
 * lockref_get - Increments reference count unconditionally
 * @lockref: pointer to lockref structure
 *
 * This operation is only valid if you already hold a reference
 * to the object, so you know the count cannot be zero.
 */
void lockref_get(struct lockref *lockref)
{
        CMPXCHG_LOOP(
                new.count++;
        ,
                return;
        );

        spin_lock(&lockref->lock);
        lockref->count++;
        spin_unlock(&lockref->lock);
}
EXPORT_SYMBOL(lockref_get);

/**
 * lockref_get_not_zero - Increments count unless the count is 0 or dead
 * @lockref: pointer to lockref structure
 * Return: 1 if count updated successfully or 0 if count was zero
 */
bool lockref_get_not_zero(struct lockref *lockref)
{
        bool retval = false;

        CMPXCHG_LOOP(
                new.count++;
                if (old.count <= 0)
                        return false;
        ,
                return true;
        );

        spin_lock(&lockref->lock);
        if (lockref->count > 0) {
                lockref->count++;
                retval = true;
        }
        spin_unlock(&lockref->lock);
        return retval;
}
EXPORT_SYMBOL(lockref_get_not_zero);

/**
 * lockref_put_return - Decrement reference count if possible
 * @lockref: pointer to lockref structure
 *
 * Decrement the reference count and return the new value.
 * If the lockref was dead or locked, return -1.
 */
int lockref_put_return(struct lockref *lockref)
{
        CMPXCHG_LOOP(
                new.count--;
                if (old.count <= 0)
                        return -1;
        ,
                return new.count;
        );
        return -1;
}
EXPORT_SYMBOL(lockref_put_return);

/**
 * lockref_put_or_lock - decrements count unless count <= 1 before decrement
 * @lockref: pointer to lockref structure
 * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
 */
bool lockref_put_or_lock(struct lockref *lockref)
{
        CMPXCHG_LOOP(
                new.count--;
                if (old.count <= 1)
                        break;
        ,
                return true;
        );

        spin_lock(&lockref->lock);
        if (lockref->count <= 1)
                return false;
        lockref->count--;
        spin_unlock(&lockref->lock);
        return true;
}
EXPORT_SYMBOL(lockref_put_or_lock);

/**
 * lockref_mark_dead - mark lockref dead
 * @lockref: pointer to lockref structure
 */
void lockref_mark_dead(struct lockref *lockref)
{
        assert_spin_locked(&lockref->lock);
        lockref->count = -128;
}
EXPORT_SYMBOL(lockref_mark_dead);

/**
 * lockref_get_not_dead - Increments count unless the ref is dead
 * @lockref: pointer to lockref structure
 * Return: 1 if count updated successfully or 0 if lockref was dead
 */
bool lockref_get_not_dead(struct lockref *lockref)
{
        bool retval = false;

        CMPXCHG_LOOP(
                new.count++;
                if (old.count < 0)
                        return false;
        ,
                return true;
        );

        spin_lock(&lockref->lock);
        if (lockref->count >= 0) {
                lockref->count++;
                retval = true;
        }
        spin_unlock(&lockref->lock);
        return retval;
}
EXPORT_SYMBOL(lockref_get_not_dead);