/*
   * Mutexes: blocking mutual exclusion locks
   *
   * started by Ingo Molnar:
   *
   *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   *
   * This file contains the main data structure and API definitions.
   */
  #ifndef __LINUX_MUTEX_H
  #define __LINUX_MUTEX_H
  
  #include <asm/current.h>
  #include <linux/list.h>
  #include <linux/spinlock_types.h>
  #include <linux/linkage.h>
  #include <linux/lockdep.h>
  #include <linux/atomic.h>
  #include <asm/processor.h>
  
  /*
   * Simple, straightforward mutexes with strict semantics:
   *
   * - only one task can hold the mutex at a time
   * - only the owner can unlock the mutex
   * - multiple unlocks are not permitted
   * - recursive locking is not permitted
   * - a mutex object must be initialized via the API
   * - a mutex object must not be initialized via memset or copying
   * - task may not exit with mutex held
   * - memory areas where held locks reside must not be freed
   * - held mutexes must not be reinitialized
   * - mutexes may not be used in hardware or software interrupt
   *   contexts such as tasklets and timers
   *
   * These semantics are fully enforced when DEBUG_MUTEXES is
   * enabled. Furthermore, besides enforcing the above rules, the mutex
   * debugging code also implements a number of additional features
   * that make lock debugging easier and faster:
   *
   * - uses symbolic names of mutexes, whenever they are printed in debug output
   * - point-of-acquire tracking, symbolic lookup of function names
   * - list of all locks held in the system, printout of them
   * - owner tracking
   * - detects self-recursing locks and prints out all relevant info
   * - detects multi-task circular deadlocks and prints out all affected
   *   locks and tasks (and only those tasks)
   */
  struct mutex {
  	/* 1: unlocked, 0: locked, negative: locked, possible waiters */
  	atomic_t		count;
  	spinlock_t		wait_lock;
  	struct list_head	wait_list;
  #if defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_SMP)
  	struct task_struct	*owner;
  #endif
  #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
  	void			*spin_mlock;	/* Spinner MCS lock */
  #endif
  #ifdef CONFIG_DEBUG_MUTEXES
  	const char 		*name;
  	void			*magic;
  #endif
  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  	struct lockdep_map	dep_map;
  #endif
  };
  
  /*
   * This is the control structure for tasks blocked on mutex,
   * which resides on the blocked task's kernel stack:
   */
  struct mutex_waiter {
  	struct list_head	list;
  	struct task_struct	*task;
  #ifdef CONFIG_DEBUG_MUTEXES
  	void			*magic;
  #endif
  };
  
  #ifdef CONFIG_DEBUG_MUTEXES
  # include <linux/mutex-debug.h>
  #else
  # define __DEBUG_MUTEX_INITIALIZER(lockname)
  /**
   * mutex_init - initialize the mutex
   * @mutex: the mutex to be initialized
   *
   * Initialize the mutex to unlocked state.
   *
   * It is not allowed to initialize an already locked mutex.
   */
  # define mutex_init(mutex) \
  do {							\
  	static struct lock_class_key __key;		\
  							\
  	__mutex_init((mutex), #mutex, &__key);		\
  } while (0)
  static inline void mutex_destroy(struct mutex *lock) {}
  #endif
  
  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  # define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
  		, .dep_map = { .name = #lockname }
  #else
  # define __DEP_MAP_MUTEX_INITIALIZER(lockname)
  #endif
  
  #define __MUTEX_INITIALIZER(lockname) \
  		{ .count = ATOMIC_INIT(1) \
  		, .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
  		, .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
  		__DEBUG_MUTEX_INITIALIZER(lockname) \
  		__DEP_MAP_MUTEX_INITIALIZER(lockname) }
  
  #define DEFINE_MUTEX(mutexname) \
  	struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
  
  extern void __mutex_init(struct mutex *lock, const char *name,
  			 struct lock_class_key *key);
  
  /**
   * mutex_is_locked - is the mutex locked
   * @lock: the mutex to be queried
   *
   * Returns 1 if the mutex is locked, 0 if unlocked.
   */
  static inline int mutex_is_locked(struct mutex *lock)
  {
  	return atomic_read(&lock->count) != 1;
  }
  
  /*
   * See kernel/locking/mutex.c for detailed documentation of these APIs.
   * Also see Documentation/mutex-design.txt.
   */
  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
  extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
  
  extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
  					unsigned int subclass);
  extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
  					unsigned int subclass);
  
  #define mutex_lock(lock) mutex_lock_nested(lock, 0)
  #define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
  #define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
  
  #define mutex_lock_nest_lock(lock, nest_lock)				\
  do {									\
  	typecheck(struct lockdep_map *, &(nest_lock)->dep_map);	\
  	_mutex_lock_nest_lock(lock, &(nest_lock)->dep_map);		\
  } while (0)
  
  #else
  extern void mutex_lock(struct mutex *lock);
  extern int __must_check mutex_lock_interruptible(struct mutex *lock);
  extern int __must_check mutex_lock_killable(struct mutex *lock);
  
  # define mutex_lock_nested(lock, subclass) mutex_lock(lock)
  # define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
  # define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
  # define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
  #endif
  
  /*
   * NOTE: mutex_trylock() follows the spin_trylock() convention,
   *       not the down_trylock() convention!
   *
   * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
   */
  extern int mutex_trylock(struct mutex *lock);
  extern void mutex_unlock(struct mutex *lock);
  
  extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
  
  #ifndef arch_mutex_cpu_relax
  # define arch_mutex_cpu_relax() cpu_relax()
  #endif
  
  #endif