/*
   * kernel/mutex.c
   *
   * Mutexes: blocking mutual exclusion locks
   *
   * Started by Ingo Molnar:
   *
   *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   *
   * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
   * David Howells for suggestions and improvements.
   *

   *  - Adaptive spinning for mutexes by Peter Zijlstra. (Ported to mainline
   *    from the -rt tree, where it was originally implemented for rtmutexes
   *    by Steven Rostedt, based on work by Gregory Haskins, Peter Morreale
   *    and Sven Dietrich.
   *

   * Also see Documentation/mutex-design.txt.
   */
  #include <linux/mutex.h>
  #include <linux/sched.h>
  #include <linux/module.h>
  #include <linux/spinlock.h>
  #include <linux/interrupt.h>

  #include <linux/debug_locks.h>

  
  /*
   * In the DEBUG case we are using the "NULL fastpath" for mutexes,
   * which forces all calls into the slowpath:
   */
  #ifdef CONFIG_DEBUG_MUTEXES
  # include "mutex-debug.h"
  # include <asm-generic/mutex-null.h>
  #else
  # include "mutex.h"
  # include <asm/mutex.h>
  #endif

  void
  __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)

  {
  	atomic_set(&lock->count, 1);
  	spin_lock_init(&lock->wait_lock);
  	INIT_LIST_HEAD(&lock->wait_list);

  	mutex_clear_owner(lock);

  	debug_mutex_init(lock, name, key);

  }
  
  EXPORT_SYMBOL(__mutex_init);

  #ifndef CONFIG_DEBUG_LOCK_ALLOC

  /*
   * We split the mutex lock/unlock logic into separate fastpath and
   * slowpath functions, to reduce the register pressure on the fastpath.
   * We also put the fastpath first in the kernel image, to make sure the
   * branch is predicted by the CPU as default-untaken.
   */

  static __used noinline void __sched

  __mutex_lock_slowpath(atomic_t *lock_count);

  /**

   * mutex_lock - acquire the mutex
   * @lock: the mutex to be acquired
   *
   * Lock the mutex exclusively for this task. If the mutex is not
   * available right now, it will sleep until it can get it.
   *
   * The mutex must later on be released by the same task that
   * acquired it. Recursive locking is not allowed. The task
   * may not exit without first unlocking the mutex. Also, kernel
   * memory where the mutex resides mutex must not be freed with
   * the mutex still locked. The mutex must first be initialized
   * (or statically defined) before it can be locked. memset()-ing
   * the mutex to 0 is not allowed.
   *
   * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging
   *   checks that will enforce the restrictions and will also do
   *   deadlock debugging. )
   *
   * This function is similar to (but not equivalent to) down().
   */

  void __sched mutex_lock(struct mutex *lock)

  {

  	might_sleep();

  	/*
  	 * The locking fastpath is the 1->0 transition from
  	 * 'unlocked' into 'locked' state.

  	 */
  	__mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);

  	mutex_set_owner(lock);

  }
  
  EXPORT_SYMBOL(mutex_lock);

  #endif

  static __used noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count);

  /**

   * mutex_unlock - release the mutex
   * @lock: the mutex to be released
   *
   * Unlock a mutex that has been locked by this task previously.
   *
   * This function must not be used in interrupt context. Unlocking
   * of a not locked mutex is not allowed.
   *
   * This function is similar to (but not equivalent to) up().
   */

  void __sched mutex_unlock(struct mutex *lock)

  {
  	/*
  	 * The unlocking fastpath is the 0->1 transition from 'locked'
  	 * into 'unlocked' state:

  	 */

  #ifndef CONFIG_DEBUG_MUTEXES
  	/*
  	 * When debugging is enabled we must not clear the owner before time,
  	 * the slow path will always be taken, and that clears the owner field
  	 * after verifying that it was indeed current.
  	 */
  	mutex_clear_owner(lock);
  #endif

  	__mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
  }
  
  EXPORT_SYMBOL(mutex_unlock);
  
  /*
   * Lock a mutex (possibly interruptible), slowpath:
   */
  static inline int __sched

  __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
  	       	unsigned long ip)

  {
  	struct task_struct *task = current;
  	struct mutex_waiter waiter;

  	unsigned long flags;

  	preempt_disable();

  	mutex_acquire(&lock->dep_map, subclass, 0, ip);

  
  #ifdef CONFIG_MUTEX_SPIN_ON_OWNER

  	/*
  	 * Optimistic spinning.
  	 *
  	 * We try to spin for acquisition when we find that there are no
  	 * pending waiters and the lock owner is currently running on a
  	 * (different) CPU.
  	 *
  	 * The rationale is that if the lock owner is running, it is likely to
  	 * release the lock soon.
  	 *
  	 * Since this needs the lock owner, and this mutex implementation
  	 * doesn't track the owner atomically in the lock field, we need to
  	 * track it non-atomically.
  	 *
  	 * We can't do this for DEBUG_MUTEXES because that relies on wait_lock
  	 * to serialize everything.
  	 */
  
  	for (;;) {
  		struct thread_info *owner;
  
  		/*

  		 * If we own the BKL, then don't spin. The owner of
  		 * the mutex might be waiting on us to release the BKL.
  		 */
  		if (unlikely(current->lock_depth >= 0))
  			break;
  
  		/*

  		 * If there's an owner, wait for it to either
  		 * release the lock or go to sleep.
  		 */
  		owner = ACCESS_ONCE(lock->owner);
  		if (owner && !mutex_spin_on_owner(lock, owner))
  			break;

  		if (atomic_cmpxchg(&lock->count, 1, 0) == 1) {
  			lock_acquired(&lock->dep_map, ip);
  			mutex_set_owner(lock);
  			preempt_enable();
  			return 0;
  		}

  		/*
  		 * When there's no owner, we might have preempted between the
  		 * owner acquiring the lock and setting the owner field. If
  		 * we're an RT task that will live-lock because we won't let
  		 * the owner complete.
  		 */
  		if (!owner && (need_resched() || rt_task(task)))
  			break;

  		/*
  		 * The cpu_relax() call is a compiler barrier which forces
  		 * everything in this loop to be re-loaded. We don't need
  		 * memory barriers as we'll eventually observe the right
  		 * values at the cost of a few extra spins.
  		 */

  		arch_mutex_cpu_relax();

  	}
  #endif

  	spin_lock_mutex(&lock->wait_lock, flags);

  	debug_mutex_lock_common(lock, &waiter);

  	debug_mutex_add_waiter(lock, &waiter, task_thread_info(task));

  
  	/* add waiting tasks to the end of the waitqueue (FIFO): */
  	list_add_tail(&waiter.list, &lock->wait_list);
  	waiter.task = task;

  	if (atomic_xchg(&lock->count, -1) == 1)

  		goto done;

  	lock_contended(&lock->dep_map, ip);

  	for (;;) {
  		/*
  		 * Lets try to take the lock again - this is needed even if
  		 * we get here for the first time (shortly after failing to
  		 * acquire the lock), to make sure that we get a wakeup once
  		 * it's unlocked. Later on, if we sleep, this is the
  		 * operation that gives us the lock. We xchg it to -1, so
  		 * that when we release the lock, we properly wake up the
  		 * other waiters:
  		 */

  		if (atomic_xchg(&lock->count, -1) == 1)

  			break;
  
  		/*
  		 * got a signal? (This code gets eliminated in the
  		 * TASK_UNINTERRUPTIBLE case.)
  		 */

  		if (unlikely(signal_pending_state(state, task))) {

  			mutex_remove_waiter(lock, &waiter,
  					    task_thread_info(task));

  			mutex_release(&lock->dep_map, 1, ip);

  			spin_unlock_mutex(&lock->wait_lock, flags);

  
  			debug_mutex_free_waiter(&waiter);

  			preempt_enable();

  			return -EINTR;
  		}
  		__set_task_state(task, state);

  		/* didn't get the lock, go to sleep: */

  		spin_unlock_mutex(&lock->wait_lock, flags);

  		preempt_enable_no_resched();
  		schedule();
  		preempt_disable();

  		spin_lock_mutex(&lock->wait_lock, flags);

  	}

  done:

  	lock_acquired(&lock->dep_map, ip);

  	/* got the lock - rejoice! */

  	mutex_remove_waiter(lock, &waiter, current_thread_info());
  	mutex_set_owner(lock);

  
  	/* set it to 0 if there are no waiters left: */
  	if (likely(list_empty(&lock->wait_list)))
  		atomic_set(&lock->count, 0);

  	spin_unlock_mutex(&lock->wait_lock, flags);

  
  	debug_mutex_free_waiter(&waiter);

  	preempt_enable();

  	return 0;
  }

  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  void __sched
  mutex_lock_nested(struct mutex *lock, unsigned int subclass)
  {
  	might_sleep();

  	__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, _RET_IP_);

  }
  
  EXPORT_SYMBOL_GPL(mutex_lock_nested);

  
  int __sched

  mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
  {
  	might_sleep();
  	return __mutex_lock_common(lock, TASK_KILLABLE, subclass, _RET_IP_);
  }
  EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
  
  int __sched

  mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
  {
  	might_sleep();

  	return __mutex_lock_common(lock, TASK_INTERRUPTIBLE,
  				   subclass, _RET_IP_);

  }
  
  EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);

  #endif

  /*
   * Release the lock, slowpath:
   */

  static inline void

  __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested)

  {

  	struct mutex *lock = container_of(lock_count, struct mutex, count);

  	unsigned long flags;

  	spin_lock_mutex(&lock->wait_lock, flags);

  	mutex_release(&lock->dep_map, nested, _RET_IP_);

  	debug_mutex_unlock(lock);

  
  	/*
  	 * some architectures leave the lock unlocked in the fastpath failure
  	 * case, others need to leave it locked. In the later case we have to
  	 * unlock it here
  	 */
  	if (__mutex_slowpath_needs_to_unlock())
  		atomic_set(&lock->count, 1);

  	if (!list_empty(&lock->wait_list)) {
  		/* get the first entry from the wait-list: */
  		struct mutex_waiter *waiter =
  				list_entry(lock->wait_list.next,
  					   struct mutex_waiter, list);
  
  		debug_mutex_wake_waiter(lock, waiter);
  
  		wake_up_process(waiter->task);
  	}

  	spin_unlock_mutex(&lock->wait_lock, flags);

  }
  
  /*

   * Release the lock, slowpath:
   */

  static __used noinline void

  __mutex_unlock_slowpath(atomic_t *lock_count)
  {

  	__mutex_unlock_common_slowpath(lock_count, 1);

  }

  #ifndef CONFIG_DEBUG_LOCK_ALLOC

  /*

   * Here come the less common (and hence less performance-critical) APIs:
   * mutex_lock_interruptible() and mutex_trylock().
   */

  static noinline int __sched

  __mutex_lock_killable_slowpath(atomic_t *lock_count);

  static noinline int __sched

  __mutex_lock_interruptible_slowpath(atomic_t *lock_count);

  /**
   * mutex_lock_interruptible - acquire the mutex, interruptible

   * @lock: the mutex to be acquired
   *
   * Lock the mutex like mutex_lock(), and return 0 if the mutex has
   * been acquired or sleep until the mutex becomes available. If a
   * signal arrives while waiting for the lock then this function
   * returns -EINTR.
   *
   * This function is similar to (but not equivalent to) down_interruptible().
   */

  int __sched mutex_lock_interruptible(struct mutex *lock)

  {

  	int ret;

  	might_sleep();

  	ret =  __mutex_fastpath_lock_retval

  			(&lock->count, __mutex_lock_interruptible_slowpath);

  	if (!ret)
  		mutex_set_owner(lock);
  
  	return ret;

  }
  
  EXPORT_SYMBOL(mutex_lock_interruptible);

  int __sched mutex_lock_killable(struct mutex *lock)

  {

  	int ret;

  	might_sleep();

  	ret = __mutex_fastpath_lock_retval

  			(&lock->count, __mutex_lock_killable_slowpath);

  	if (!ret)
  		mutex_set_owner(lock);
  
  	return ret;

  }
  EXPORT_SYMBOL(mutex_lock_killable);

  static __used noinline void __sched

  __mutex_lock_slowpath(atomic_t *lock_count)
  {
  	struct mutex *lock = container_of(lock_count, struct mutex, count);
  
  	__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, _RET_IP_);
  }

  static noinline int __sched

  __mutex_lock_killable_slowpath(atomic_t *lock_count)
  {
  	struct mutex *lock = container_of(lock_count, struct mutex, count);
  
  	return __mutex_lock_common(lock, TASK_KILLABLE, 0, _RET_IP_);
  }

  static noinline int __sched

  __mutex_lock_interruptible_slowpath(atomic_t *lock_count)

  {
  	struct mutex *lock = container_of(lock_count, struct mutex, count);

  	return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, _RET_IP_);

  }

  #endif

  
  /*
   * Spinlock based trylock, we take the spinlock and check whether we
   * can get the lock:
   */
  static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
  {
  	struct mutex *lock = container_of(lock_count, struct mutex, count);

  	unsigned long flags;

  	int prev;

  	spin_lock_mutex(&lock->wait_lock, flags);

  
  	prev = atomic_xchg(&lock->count, -1);

  	if (likely(prev == 1)) {

  		mutex_set_owner(lock);

  		mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
  	}

  	/* Set it back to 0 if there are no waiters: */
  	if (likely(list_empty(&lock->wait_list)))
  		atomic_set(&lock->count, 0);

  	spin_unlock_mutex(&lock->wait_lock, flags);

  
  	return prev == 1;
  }

  /**
   * mutex_trylock - try to acquire the mutex, without waiting

   * @lock: the mutex to be acquired
   *
   * Try to acquire the mutex atomically. Returns 1 if the mutex
   * has been acquired successfully, and 0 on contention.
   *
   * NOTE: this function follows the spin_trylock() convention, so

   * it is negated from the down_trylock() return values! Be careful

   * about this when converting semaphore users to mutexes.
   *
   * This function must not be used in interrupt context. The
   * mutex must be released by the same task that acquired it.
   */

  int __sched mutex_trylock(struct mutex *lock)

  {

  	int ret;
  
  	ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath);
  	if (ret)
  		mutex_set_owner(lock);
  
  	return ret;

  }

  EXPORT_SYMBOL(mutex_trylock);

  
  /**
   * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
   * @cnt: the atomic which we are to dec
   * @lock: the mutex to return holding if we dec to 0
   *
   * return true and hold lock if we dec to 0, return false otherwise
   */
  int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
  {
  	/* dec if we can't possibly hit 0 */
  	if (atomic_add_unless(cnt, -1, 1))
  		return 0;
  	/* we might hit 0, so take the lock */
  	mutex_lock(lock);
  	if (!atomic_dec_and_test(cnt)) {
  		/* when we actually did the dec, we didn't hit 0 */
  		mutex_unlock(lock);
  		return 0;
  	}
  	/* we hit 0, and we hold the lock */
  	return 1;
  }
  EXPORT_SYMBOL(atomic_dec_and_mutex_lock);