/*

   * kernel/locking/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/locking/mutex-design.txt.

   */
  #include <linux/mutex.h>

  #include <linux/ww_mutex.h>

  #include <linux/sched.h>

  #include <linux/sched/rt.h>

  #include <linux/export.h>

  #include <linux/spinlock.h>
  #include <linux/interrupt.h>

  #include <linux/debug_locks.h>

  #include <linux/osq_lock.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>

  /*
   * Must be 0 for the debug case so we do not do the unlock outside of the
   * wait_lock region. debug_mutex_unlock() will do the actual unlock in this
   * case.
   */
  # undef __mutex_slowpath_needs_to_unlock
  # define  __mutex_slowpath_needs_to_unlock()	0

  #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);

  #ifdef CONFIG_MUTEX_SPIN_ON_OWNER

  	osq_lock_init(&lock->osq);

  #endif

  	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.
   */

  __visible 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 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 __always_inline void ww_mutex_lock_acquired(struct ww_mutex *ww,
  						   struct ww_acquire_ctx *ww_ctx)
  {
  #ifdef CONFIG_DEBUG_MUTEXES
  	/*
  	 * If this WARN_ON triggers, you used ww_mutex_lock to acquire,
  	 * but released with a normal mutex_unlock in this call.
  	 *
  	 * This should never happen, always use ww_mutex_unlock.
  	 */
  	DEBUG_LOCKS_WARN_ON(ww->ctx);
  
  	/*
  	 * Not quite done after calling ww_acquire_done() ?
  	 */
  	DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
  
  	if (ww_ctx->contending_lock) {
  		/*
  		 * After -EDEADLK you tried to
  		 * acquire a different ww_mutex? Bad!
  		 */
  		DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
  
  		/*
  		 * You called ww_mutex_lock after receiving -EDEADLK,
  		 * but 'forgot' to unlock everything else first?
  		 */
  		DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
  		ww_ctx->contending_lock = NULL;
  	}
  
  	/*
  	 * Naughty, using a different class will lead to undefined behavior!
  	 */
  	DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
  #endif
  	ww_ctx->acquired++;
  }
  
  /*

   * After acquiring lock with fastpath or when we lost out in contested

   * slowpath, set ctx and wake up any waiters so they can recheck.
   *
   * This function is never called when CONFIG_DEBUG_LOCK_ALLOC is set,
   * as the fastpath and opportunistic spinning are disabled in that case.
   */
  static __always_inline void
  ww_mutex_set_context_fastpath(struct ww_mutex *lock,
  			       struct ww_acquire_ctx *ctx)
  {
  	unsigned long flags;
  	struct mutex_waiter *cur;
  
  	ww_mutex_lock_acquired(lock, ctx);
  
  	lock->ctx = ctx;
  
  	/*
  	 * The lock->ctx update should be visible on all cores before
  	 * the atomic read is done, otherwise contended waiters might be
  	 * missed. The contended waiters will either see ww_ctx == NULL
  	 * and keep spinning, or it will acquire wait_lock, add itself
  	 * to waiter list and sleep.
  	 */
  	smp_mb(); /* ^^^ */
  
  	/*
  	 * Check if lock is contended, if not there is nobody to wake up
  	 */
  	if (likely(atomic_read(&lock->base.count) == 0))
  		return;
  
  	/*
  	 * Uh oh, we raced in fastpath, wake up everyone in this case,
  	 * so they can see the new lock->ctx.
  	 */
  	spin_lock_mutex(&lock->base.wait_lock, flags);
  	list_for_each_entry(cur, &lock->base.wait_list, list) {
  		debug_mutex_wake_waiter(&lock->base, cur);
  		wake_up_process(cur->task);
  	}
  	spin_unlock_mutex(&lock->base.wait_lock, flags);
  }

  /*
   * After acquiring lock in the slowpath set ctx and wake up any
   * waiters so they can recheck.
   *
   * Callers must hold the mutex wait_lock.
   */
  static __always_inline void
  ww_mutex_set_context_slowpath(struct ww_mutex *lock,
  			      struct ww_acquire_ctx *ctx)
  {
  	struct mutex_waiter *cur;
  
  	ww_mutex_lock_acquired(lock, ctx);
  	lock->ctx = ctx;
  
  	/*
  	 * Give any possible sleeping processes the chance to wake up,
  	 * so they can recheck if they have to back off.
  	 */
  	list_for_each_entry(cur, &lock->base.wait_list, list) {
  		debug_mutex_wake_waiter(&lock->base, cur);
  		wake_up_process(cur->task);
  	}
  }

  #ifdef CONFIG_MUTEX_SPIN_ON_OWNER

  /*
   * Look out! "owner" is an entirely speculative pointer
   * access and not reliable.
   */
  static noinline

  bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)

  {

  	bool ret = true;

  	rcu_read_lock();

  	while (lock->owner == owner) {

  		/*
  		 * Ensure we emit the owner->on_cpu, dereference _after_

  		 * checking lock->owner still matches owner. If that fails,
  		 * owner might point to freed memory. If it still matches,

  		 * the rcu_read_lock() ensures the memory stays valid.
  		 */
  		barrier();
  
  		if (!owner->on_cpu || need_resched()) {
  			ret = false;
  			break;
  		}

  		cpu_relax_lowlatency();

  	}
  	rcu_read_unlock();

  	return ret;

  }

  
  /*
   * Initial check for entering the mutex spinning loop
   */
  static inline int mutex_can_spin_on_owner(struct mutex *lock)
  {

  	struct task_struct *owner;

  	int retval = 1;

  	if (need_resched())
  		return 0;

  	rcu_read_lock();

  	owner = READ_ONCE(lock->owner);

  	if (owner)
  		retval = owner->on_cpu;

  	rcu_read_unlock();
  	/*
  	 * if lock->owner is not set, the mutex owner may have just acquired
  	 * it and not set the owner yet or the mutex has been released.
  	 */
  	return retval;
  }

  
  /*
   * Atomically try to take the lock when it is available
   */
  static inline bool mutex_try_to_acquire(struct mutex *lock)
  {
  	return !mutex_is_locked(lock) &&

  		(atomic_cmpxchg_acquire(&lock->count, 1, 0) == 1);

  }
  
  /*
   * Optimistic spinning.
   *
   * We try to spin for acquisition when we find that the lock owner
   * is currently running on a (different) CPU and while we don't
   * need to reschedule. 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.
   *
   * The mutex spinners are queued up using MCS lock so that only one
   * spinner can compete for the mutex. However, if mutex spinning isn't
   * going to happen, there is no point in going through the lock/unlock
   * overhead.
   *
   * Returns true when the lock was taken, otherwise false, indicating
   * that we need to jump to the slowpath and sleep.
   */
  static bool mutex_optimistic_spin(struct mutex *lock,
  				  struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
  {
  	struct task_struct *task = current;
  
  	if (!mutex_can_spin_on_owner(lock))
  		goto done;

  	/*
  	 * In order to avoid a stampede of mutex spinners trying to
  	 * acquire the mutex all at once, the spinners need to take a
  	 * MCS (queued) lock first before spinning on the owner field.
  	 */

  	if (!osq_lock(&lock->osq))
  		goto done;
  
  	while (true) {
  		struct task_struct *owner;
  
  		if (use_ww_ctx && ww_ctx->acquired > 0) {
  			struct ww_mutex *ww;
  
  			ww = container_of(lock, struct ww_mutex, base);
  			/*
  			 * If ww->ctx is set the contents are undefined, only
  			 * by acquiring wait_lock there is a guarantee that
  			 * they are not invalid when reading.
  			 *
  			 * As such, when deadlock detection needs to be
  			 * performed the optimistic spinning cannot be done.
  			 */

  			if (READ_ONCE(ww->ctx))

  				break;
  		}
  
  		/*
  		 * If there's an owner, wait for it to either
  		 * release the lock or go to sleep.
  		 */

  		owner = READ_ONCE(lock->owner);

  		if (owner && !mutex_spin_on_owner(lock, owner))
  			break;
  
  		/* Try to acquire the mutex if it is unlocked. */
  		if (mutex_try_to_acquire(lock)) {
  			lock_acquired(&lock->dep_map, ip);
  
  			if (use_ww_ctx) {
  				struct ww_mutex *ww;
  				ww = container_of(lock, struct ww_mutex, base);
  
  				ww_mutex_set_context_fastpath(ww, ww_ctx);
  			}
  
  			mutex_set_owner(lock);
  			osq_unlock(&lock->osq);
  			return true;
  		}
  
  		/*
  		 * 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.
  		 */
  		cpu_relax_lowlatency();
  	}
  
  	osq_unlock(&lock->osq);
  done:
  	/*
  	 * If we fell out of the spin path because of need_resched(),
  	 * reschedule now, before we try-lock the mutex. This avoids getting
  	 * scheduled out right after we obtained the mutex.
  	 */

  	if (need_resched()) {
  		/*
  		 * We _should_ have TASK_RUNNING here, but just in case
  		 * we do not, make it so, otherwise we might get stuck.
  		 */
  		__set_current_state(TASK_RUNNING);

  		schedule_preempt_disabled();

  	}

  
  	return false;
  }
  #else
  static bool mutex_optimistic_spin(struct mutex *lock,
  				  struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
  {
  	return false;
  }

  #endif

  __visible __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);

  /**
   * ww_mutex_unlock - release the w/w mutex
   * @lock: the mutex to be released
   *
   * Unlock a mutex that has been locked by this task previously with any of the
   * ww_mutex_lock* functions (with or without an acquire context). It is
   * forbidden to release the locks after releasing the acquire context.
   *
   * This function must not be used in interrupt context. Unlocking
   * of a unlocked mutex is not allowed.
   */
  void __sched ww_mutex_unlock(struct ww_mutex *lock)
  {
  	/*
  	 * The unlocking fastpath is the 0->1 transition from 'locked'
  	 * into 'unlocked' state:
  	 */
  	if (lock->ctx) {
  #ifdef CONFIG_DEBUG_MUTEXES
  		DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
  #endif
  		if (lock->ctx->acquired > 0)
  			lock->ctx->acquired--;
  		lock->ctx = NULL;
  	}
  
  #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->base);
  #endif
  	__mutex_fastpath_unlock(&lock->base.count, __mutex_unlock_slowpath);
  }
  EXPORT_SYMBOL(ww_mutex_unlock);
  
  static inline int __sched

  __ww_mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx)

  {
  	struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);

  	struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);

  
  	if (!hold_ctx)
  		return 0;

  	if (ctx->stamp - hold_ctx->stamp <= LONG_MAX &&
  	    (ctx->stamp != hold_ctx->stamp || ctx > hold_ctx)) {
  #ifdef CONFIG_DEBUG_MUTEXES
  		DEBUG_LOCKS_WARN_ON(ctx->contending_lock);
  		ctx->contending_lock = ww;
  #endif
  		return -EDEADLK;
  	}
  
  	return 0;
  }

  /*
   * Lock a mutex (possibly interruptible), slowpath:
   */

  static __always_inline int __sched

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

  		    struct lockdep_map *nest_lock, unsigned long ip,

  		    struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)

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

  	unsigned long flags;

  	int ret;

  	if (use_ww_ctx) {
  		struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
  		if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
  			return -EALREADY;
  	}

  	preempt_disable();

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

  	if (mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx)) {
  		/* got the lock, yay! */
  		preempt_enable();
  		return 0;

  	}

  	spin_lock_mutex(&lock->wait_lock, flags);

  	/*
  	 * Once more, try to acquire the lock. Only try-lock the mutex if

  	 * it is unlocked to reduce unnecessary xchg() operations.

  	 */

  	if (!mutex_is_locked(lock) &&
  	    (atomic_xchg_acquire(&lock->count, 0) == 1))

  		goto skip_wait;

  	debug_mutex_lock_common(lock, &waiter);

  	debug_mutex_add_waiter(lock, &waiter, task);

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

  	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. We only attempt the xchg if the count is
  		 * non-negative in order to avoid unnecessary xchg operations:

  		 */

  		if (atomic_read(&lock->count) >= 0 &&

  		    (atomic_xchg_acquire(&lock->count, -1) == 1))

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

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

  			ret = -EINTR;
  			goto err;
  		}

  		if (use_ww_ctx && ww_ctx->acquired > 0) {

  			ret = __ww_mutex_lock_check_stamp(lock, ww_ctx);

  			if (ret)
  				goto err;

  		}

  		__set_task_state(task, state);

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

  		spin_unlock_mutex(&lock->wait_lock, flags);

  		schedule_preempt_disabled();

  		spin_lock_mutex(&lock->wait_lock, flags);

  	}

  	__set_task_state(task, TASK_RUNNING);

  	mutex_remove_waiter(lock, &waiter, task);

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

  skip_wait:
  	/* got the lock - cleanup and rejoice! */

  	lock_acquired(&lock->dep_map, ip);

  	mutex_set_owner(lock);

  	if (use_ww_ctx) {

  		struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);

  		ww_mutex_set_context_slowpath(ww, ww_ctx);

  	}

  	spin_unlock_mutex(&lock->wait_lock, flags);

  	preempt_enable();

  	return 0;

  
  err:

  	mutex_remove_waiter(lock, &waiter, task);

  	spin_unlock_mutex(&lock->wait_lock, flags);
  	debug_mutex_free_waiter(&waiter);
  	mutex_release(&lock->dep_map, 1, ip);
  	preempt_enable();
  	return ret;

  }

  #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, NULL, _RET_IP_, NULL, 0);

  }
  
  EXPORT_SYMBOL_GPL(mutex_lock_nested);

  void __sched
  _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
  {
  	might_sleep();

  	__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,

  			    0, nest, _RET_IP_, NULL, 0);

  }
  
  EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);

  int __sched

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

  	return __mutex_lock_common(lock, TASK_KILLABLE,

  				   subclass, NULL, _RET_IP_, NULL, 0);

  }
  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, NULL, _RET_IP_, NULL, 0);

  }
  
  EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);

  static inline int
  ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
  {
  #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
  	unsigned tmp;
  
  	if (ctx->deadlock_inject_countdown-- == 0) {
  		tmp = ctx->deadlock_inject_interval;
  		if (tmp > UINT_MAX/4)
  			tmp = UINT_MAX;
  		else
  			tmp = tmp*2 + tmp + tmp/2;
  
  		ctx->deadlock_inject_interval = tmp;
  		ctx->deadlock_inject_countdown = tmp;
  		ctx->contending_lock = lock;
  
  		ww_mutex_unlock(lock);
  
  		return -EDEADLK;
  	}
  #endif
  
  	return 0;
  }

  
  int __sched
  __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
  {

  	int ret;

  	might_sleep();

  	ret =  __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE,

  				   0, &ctx->dep_map, _RET_IP_, ctx, 1);

  	if (!ret && ctx->acquired > 1)

  		return ww_mutex_deadlock_injection(lock, ctx);
  
  	return ret;

  }
  EXPORT_SYMBOL_GPL(__ww_mutex_lock);
  
  int __sched
  __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
  {

  	int ret;

  	might_sleep();

  	ret = __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE,

  				  0, &ctx->dep_map, _RET_IP_, ctx, 1);

  	if (!ret && ctx->acquired > 1)

  		return ww_mutex_deadlock_injection(lock, ctx);
  
  	return ret;

  }
  EXPORT_SYMBOL_GPL(__ww_mutex_lock_interruptible);

  #endif

  /*
   * Release the lock, slowpath:
   */

  static inline void

  __mutex_unlock_common_slowpath(struct mutex *lock, int nested)

  {

  	unsigned long flags;

  	WAKE_Q(wake_q);

  	/*

  	 * As a performance measurement, release the lock before doing other
  	 * wakeup related duties to follow. This allows other tasks to acquire
  	 * the lock sooner, while still handling cleanups in past unlock calls.
  	 * This can be done as we do not enforce strict equivalence between the
  	 * mutex counter and wait_list.
  	 *
  	 *
  	 * 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 - as the lock counter is currently 0 or negative.

  	 */
  	if (__mutex_slowpath_needs_to_unlock())
  		atomic_set(&lock->count, 1);

  	spin_lock_mutex(&lock->wait_lock, flags);
  	mutex_release(&lock->dep_map, nested, _RET_IP_);
  	debug_mutex_unlock(lock);

  	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_q_add(&wake_q, waiter->task);

  	}

  	spin_unlock_mutex(&lock->wait_lock, flags);

  	wake_up_q(&wake_q);

  }
  
  /*

   * Release the lock, slowpath:
   */

  __visible void

  __mutex_unlock_slowpath(atomic_t *lock_count)
  {

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

  static noinline int __sched

  __mutex_lock_interruptible_slowpath(struct mutex *lock);

  /**
   * 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);
  	if (likely(!ret)) {

  		mutex_set_owner(lock);

  		return 0;
  	} else
  		return __mutex_lock_interruptible_slowpath(lock);

  }
  
  EXPORT_SYMBOL(mutex_lock_interruptible);

  int __sched mutex_lock_killable(struct mutex *lock)

  {

  	int ret;

  	might_sleep();

  	ret = __mutex_fastpath_lock_retval(&lock->count);
  	if (likely(!ret)) {

  		mutex_set_owner(lock);

  		return 0;
  	} else
  		return __mutex_lock_killable_slowpath(lock);

  }
  EXPORT_SYMBOL(mutex_lock_killable);

  __visible 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,

  			    NULL, _RET_IP_, NULL, 0);

  }

  static noinline int __sched

  __mutex_lock_killable_slowpath(struct mutex *lock)

  {

  	return __mutex_lock_common(lock, TASK_KILLABLE, 0,

  				   NULL, _RET_IP_, NULL, 0);

  }

  static noinline int __sched

  __mutex_lock_interruptible_slowpath(struct mutex *lock)

  {

  	return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0,

  				   NULL, _RET_IP_, NULL, 0);

  }
  
  static noinline int __sched
  __ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
  {
  	return __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, 0,

  				   NULL, _RET_IP_, ctx, 1);

  }

  
  static noinline int __sched
  __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
  					    struct ww_acquire_ctx *ctx)
  {
  	return __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, 0,

  				   NULL, _RET_IP_, ctx, 1);

  }

  #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;

  	/* No need to trylock if the mutex is locked. */
  	if (mutex_is_locked(lock))
  		return 0;

  	spin_lock_mutex(&lock->wait_lock, flags);

  	prev = atomic_xchg_acquire(&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);

  #ifndef CONFIG_DEBUG_LOCK_ALLOC
  int __sched
  __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
  {
  	int ret;
  
  	might_sleep();
  
  	ret = __mutex_fastpath_lock_retval(&lock->base.count);
  
  	if (likely(!ret)) {
  		ww_mutex_set_context_fastpath(lock, ctx);
  		mutex_set_owner(&lock->base);
  	} else
  		ret = __ww_mutex_lock_slowpath(lock, ctx);
  	return ret;
  }
  EXPORT_SYMBOL(__ww_mutex_lock);
  
  int __sched
  __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
  {
  	int ret;
  
  	might_sleep();
  
  	ret = __mutex_fastpath_lock_retval(&lock->base.count);
  
  	if (likely(!ret)) {
  		ww_mutex_set_context_fastpath(lock, ctx);
  		mutex_set_owner(&lock->base);
  	} else
  		ret = __ww_mutex_lock_interruptible_slowpath(lock, ctx);
  	return ret;
  }
  EXPORT_SYMBOL(__ww_mutex_lock_interruptible);
  
  #endif

  /**
   * 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);