text: #ifndef __LINUX_BIT_SPINLOCK_H
  #define __LINUX_BIT_SPINLOCK_H
  
  #include <linux/kernel.h>
  #include <linux/preempt.h>
  #include <asm/atomic.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))) {
  		preempt_enable();
  		do {
  			cpu_relax();
  		} while (test_bit(bitnum, addr));
  		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 */
  