root/include/linux/bit_spinlock.h

INCLUDED FROM

DEFINITIONS

1. bit_spin_lock
2. bit_spin_trylock
3. bit_spin_unlock
4. __bit_spin_unlock
5. bit_spin_is_locked

#ifndef __LINUX_BIT_SPINLOCK_H
#define __LINUX_BIT_SPINLOCK_H

/*
 *  bit-based spin_lock()
 *
 * Don't use this unless you really need to: spin_lock() and spin_unlock()
 * are significantly faster.
 */
static inline void bit_spin_lock(int bitnum, unsigned long *addr)
{
        /*
         * Assuming the lock is uncontended, this never enters
         * the body of the outer loop. If it is contended, then
         * within the inner loop a non-atomic test is used to
         * busywait with less bus contention for a good time to
         * attempt to acquire the lock bit.
         */
        preempt_disable();
#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
        while (unlikely(test_and_set_bit_lock(bitnum, addr))) {
                while (test_bit(bitnum, addr)) {
                        preempt_enable();
                        cpu_relax();
                        preempt_disable();
                }
        }
#endif
        __acquire(bitlock);
}

/*
 * Return true if it was acquired
 */
static inline int bit_spin_trylock(int bitnum, unsigned long *addr)
{
        preempt_disable();
#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
        if (unlikely(test_and_set_bit_lock(bitnum, addr))) {
                preempt_enable();
                return 0;
        }
#endif
        __acquire(bitlock);
        return 1;
}

/*
 *  bit-based spin_unlock()
 */
static inline void bit_spin_unlock(int bitnum, unsigned long *addr)
{
#ifdef CONFIG_DEBUG_SPINLOCK
        BUG_ON(!test_bit(bitnum, addr));
#endif
#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
        clear_bit_unlock(bitnum, addr);
#endif
        preempt_enable();
        __release(bitlock);
}

/*
 *  bit-based spin_unlock()
 *  non-atomic version, which can be used eg. if the bit lock itself is
 *  protecting the rest of the flags in the word.
 */
static inline void __bit_spin_unlock(int bitnum, unsigned long *addr)
{
#ifdef CONFIG_DEBUG_SPINLOCK
        BUG_ON(!test_bit(bitnum, addr));
#endif
#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
        __clear_bit_unlock(bitnum, addr);
#endif
        preempt_enable();
        __release(bitlock);
}

/*
 * Return true if the lock is held.
 */
static inline int bit_spin_is_locked(int bitnum, unsigned long *addr)
{
#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
        return test_bit(bitnum, addr);
#elif defined CONFIG_PREEMPT
        return preempt_count();
#else
        return 1;
#endif
}

#endif /* __LINUX_BIT_SPINLOCK_H */