// SPDX-License-Identifier: GPL-2.0-only

  /*

   * 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.rst.

   */
  #include <linux/mutex.h>

  #include <linux/ww_mutex.h>

  #include <linux/sched/signal.h>

  #include <linux/sched/rt.h>

  #include <linux/sched/wake_q.h>

  #include <linux/sched/debug.h>

  #include <linux/export.h>

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

  #include <linux/debug_locks.h>

  #include <linux/osq_lock.h>

  #ifdef CONFIG_DEBUG_MUTEXES
  # include "mutex-debug.h"

  #else
  # include "mutex.h"

  #endif

  #include <trace/hooks/dtask.h>

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

  {

  	atomic_long_set(&lock->owner, 0);

  	spin_lock_init(&lock->wait_lock);
  	INIT_LIST_HEAD(&lock->wait_list);

  #ifdef CONFIG_MUTEX_SPIN_ON_OWNER

  	osq_lock_init(&lock->osq);

  #endif

  	debug_mutex_init(lock, name, key);

  }

  EXPORT_SYMBOL(__mutex_init);

  /*
   * @owner: contains: 'struct task_struct *' to the current lock owner,
   * NULL means not owned. Since task_struct pointers are aligned at

   * at least L1_CACHE_BYTES, we have low bits to store extra state.

   *
   * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.

   * Bit1 indicates unlock needs to hand the lock to the top-waiter

   * Bit2 indicates handoff has been done and we're waiting for pickup.

   */
  #define MUTEX_FLAG_WAITERS	0x01

  #define MUTEX_FLAG_HANDOFF	0x02

  #define MUTEX_FLAG_PICKUP	0x04

  #define MUTEX_FLAGS		0x07

  /*
   * Internal helper function; C doesn't allow us to hide it :/
   *
   * DO NOT USE (outside of mutex code).
   */
  static inline struct task_struct *__mutex_owner(struct mutex *lock)
  {

  	return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);

  }

  static inline struct task_struct *__owner_task(unsigned long owner)
  {
  	return (struct task_struct *)(owner & ~MUTEX_FLAGS);
  }

  bool mutex_is_locked(struct mutex *lock)
  {
  	return __mutex_owner(lock) != NULL;
  }
  EXPORT_SYMBOL(mutex_is_locked);
  
  __must_check enum mutex_trylock_recursive_enum
  mutex_trylock_recursive(struct mutex *lock)
  {
  	if (unlikely(__mutex_owner(lock) == current))
  		return MUTEX_TRYLOCK_RECURSIVE;
  
  	return mutex_trylock(lock);
  }
  EXPORT_SYMBOL(mutex_trylock_recursive);

  static inline unsigned long __owner_flags(unsigned long owner)
  {
  	return owner & MUTEX_FLAGS;
  }
  
  /*

   * Trylock variant that retuns the owning task on failure.

   */

  static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)

  {
  	unsigned long owner, curr = (unsigned long)current;
  
  	owner = atomic_long_read(&lock->owner);
  	for (;;) { /* must loop, can race against a flag */

  		unsigned long old, flags = __owner_flags(owner);

  		unsigned long task = owner & ~MUTEX_FLAGS;

  		if (task) {
  			if (likely(task != curr))
  				break;

  			if (likely(!(flags & MUTEX_FLAG_PICKUP)))
  				break;

  			flags &= ~MUTEX_FLAG_PICKUP;
  		} else {
  #ifdef CONFIG_DEBUG_MUTEXES
  			DEBUG_LOCKS_WARN_ON(flags & MUTEX_FLAG_PICKUP);
  #endif

  		}
  
  		/*
  		 * We set the HANDOFF bit, we must make sure it doesn't live
  		 * past the point where we acquire it. This would be possible
  		 * if we (accidentally) set the bit on an unlocked mutex.
  		 */

  		flags &= ~MUTEX_FLAG_HANDOFF;

  		old = atomic_long_cmpxchg_acquire(&lock->owner, owner, curr | flags);

  		if (old == owner)

  			return NULL;

  
  		owner = old;
  	}

  
  	return __owner_task(owner);
  }
  
  /*
   * Actual trylock that will work on any unlocked state.
   */
  static inline bool __mutex_trylock(struct mutex *lock)
  {
  	return !__mutex_trylock_or_owner(lock);

  }
  
  #ifndef CONFIG_DEBUG_LOCK_ALLOC
  /*
   * Lockdep annotations are contained to the slow paths for simplicity.
   * There is nothing that would stop spreading the lockdep annotations outwards
   * except more code.
   */
  
  /*
   * Optimistic trylock that only works in the uncontended case. Make sure to
   * follow with a __mutex_trylock() before failing.
   */
  static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
  {
  	unsigned long curr = (unsigned long)current;

  	unsigned long zero = 0UL;

  	if (atomic_long_try_cmpxchg_acquire(&lock->owner, &zero, curr))

  		return true;
  
  	return false;
  }
  
  static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
  {
  	unsigned long curr = (unsigned long)current;
  
  	if (atomic_long_cmpxchg_release(&lock->owner, curr, 0UL) == curr)
  		return true;
  
  	return false;
  }
  #endif
  
  static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag)
  {
  	atomic_long_or(flag, &lock->owner);
  }
  
  static inline void __mutex_clear_flag(struct mutex *lock, unsigned long flag)
  {
  	atomic_long_andnot(flag, &lock->owner);
  }

  static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_waiter *waiter)
  {
  	return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter;
  }
  
  /*

   * Add @waiter to a given location in the lock wait_list and set the
   * FLAG_WAITERS flag if it's the first waiter.
   */
  static void __sched
  __mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
  		   struct list_head *list)
  {
  	debug_mutex_add_waiter(lock, waiter, current);
  
  	list_add_tail(&waiter->list, list);
  	if (__mutex_waiter_is_first(lock, waiter))
  		__mutex_set_flag(lock, MUTEX_FLAG_WAITERS);
  }
  
  /*

   * Give up ownership to a specific task, when @task = NULL, this is equivalent

   * to a regular unlock. Sets PICKUP on a handoff, clears HANDOF, preserves
   * WAITERS. Provides RELEASE semantics like a regular unlock, the
   * __mutex_trylock() provides a matching ACQUIRE semantics for the handoff.

   */
  static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
  {
  	unsigned long owner = atomic_long_read(&lock->owner);
  
  	for (;;) {
  		unsigned long old, new;
  
  #ifdef CONFIG_DEBUG_MUTEXES
  		DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);

  		DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);

  #endif
  
  		new = (owner & MUTEX_FLAG_WAITERS);
  		new |= (unsigned long)task;

  		if (task)
  			new |= MUTEX_FLAG_PICKUP;

  
  		old = atomic_long_cmpxchg_release(&lock->owner, owner, new);
  		if (old == owner)
  			break;
  
  		owner = old;
  	}
  }

  #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 void __sched __mutex_lock_slowpath(struct mutex *lock);

  /**

   * 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();

  	if (!__mutex_trylock_fast(lock))
  		__mutex_lock_slowpath(lock);
  }

  EXPORT_SYMBOL(mutex_lock);

  #endif

  /*
   * Wait-Die:
   *   The newer transactions are killed when:
   *     It (the new transaction) makes a request for a lock being held
   *     by an older transaction.

   *
   * Wound-Wait:
   *   The newer transactions are wounded when:
   *     An older transaction makes a request for a lock being held by
   *     the newer transaction.

   */
  
  /*
   * Associate the ww_mutex @ww with the context @ww_ctx under which we acquired
   * it.
   */

  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++;

  	ww->ctx = ww_ctx;

  }

  /*
   * Determine if context @a is 'after' context @b. IOW, @a is a younger
   * transaction than @b and depending on algorithm either needs to wait for
   * @b or die.
   */

  static inline bool __sched
  __ww_ctx_stamp_after(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
  {

  
  	return (signed long)(a->stamp - b->stamp) > 0;
  }
  
  /*
   * Wait-Die; wake a younger waiter context (when locks held) such that it can
   * die.
   *
   * Among waiters with context, only the first one can have other locks acquired
   * already (ctx->acquired > 0), because __ww_mutex_add_waiter() and
   * __ww_mutex_check_kill() wake any but the earliest context.
   */
  static bool __sched
  __ww_mutex_die(struct mutex *lock, struct mutex_waiter *waiter,
  	       struct ww_acquire_ctx *ww_ctx)
  {

  	if (!ww_ctx->is_wait_die)
  		return false;

  	if (waiter->ww_ctx->acquired > 0 &&
  			__ww_ctx_stamp_after(waiter->ww_ctx, ww_ctx)) {
  		debug_mutex_wake_waiter(lock, waiter);
  		wake_up_process(waiter->task);
  	}
  
  	return true;

  }

  /*

   * Wound-Wait; wound a younger @hold_ctx if it holds the lock.
   *
   * Wound the lock holder if there are waiters with older transactions than
   * the lock holders. Even if multiple waiters may wound the lock holder,
   * it's sufficient that only one does.
   */
  static bool __ww_mutex_wound(struct mutex *lock,
  			     struct ww_acquire_ctx *ww_ctx,
  			     struct ww_acquire_ctx *hold_ctx)
  {
  	struct task_struct *owner = __mutex_owner(lock);
  
  	lockdep_assert_held(&lock->wait_lock);
  
  	/*
  	 * Possible through __ww_mutex_add_waiter() when we race with
  	 * ww_mutex_set_context_fastpath(). In that case we'll get here again
  	 * through __ww_mutex_check_waiters().
  	 */
  	if (!hold_ctx)
  		return false;
  
  	/*
  	 * Can have !owner because of __mutex_unlock_slowpath(), but if owner,
  	 * it cannot go away because we'll have FLAG_WAITERS set and hold
  	 * wait_lock.
  	 */
  	if (!owner)
  		return false;
  
  	if (ww_ctx->acquired > 0 && __ww_ctx_stamp_after(hold_ctx, ww_ctx)) {
  		hold_ctx->wounded = 1;
  
  		/*
  		 * wake_up_process() paired with set_current_state()
  		 * inserts sufficient barriers to make sure @owner either sees

  		 * it's wounded in __ww_mutex_check_kill() or has a

  		 * wakeup pending to re-read the wounded state.
  		 */
  		if (owner != current)
  			wake_up_process(owner);
  
  		return true;
  	}
  
  	return false;
  }
  
  /*

   * We just acquired @lock under @ww_ctx, if there are later contexts waiting

   * behind us on the wait-list, check if they need to die, or wound us.

   *

   * See __ww_mutex_add_waiter() for the list-order construction; basically the
   * list is ordered by stamp, smallest (oldest) first.

   *

   * This relies on never mixing wait-die/wound-wait on the same wait-list;
   * which is currently ensured by that being a ww_class property.
   *

   * The current task must not be on the wait list.
   */
  static void __sched

  __ww_mutex_check_waiters(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)

  {
  	struct mutex_waiter *cur;
  
  	lockdep_assert_held(&lock->wait_lock);
  
  	list_for_each_entry(cur, &lock->wait_list, list) {
  		if (!cur->ww_ctx)
  			continue;

  		if (__ww_mutex_die(lock, cur, ww_ctx) ||
  		    __ww_mutex_wound(lock, cur->ww_ctx, ww_ctx))

  			break;

  	}
  }

  /*

   * After acquiring lock with fastpath, where we do not hold wait_lock, set ctx
   * and wake up any waiters so they can recheck.

   */
  static __always_inline void

  ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)

  {

  	ww_mutex_lock_acquired(lock, ctx);

  	/*
  	 * The lock->ctx update should be visible on all cores before

  	 * the WAITERS check 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(); /* See comments above and below. */

  
  	/*

  	 * [W] ww->ctx = ctx	    [W] MUTEX_FLAG_WAITERS
  	 *     MB		        MB
  	 * [R] MUTEX_FLAG_WAITERS   [R] ww->ctx
  	 *
  	 * The memory barrier above pairs with the memory barrier in
  	 * __ww_mutex_add_waiter() and makes sure we either observe ww->ctx
  	 * and/or !empty list.

  	 */

  	if (likely(!(atomic_long_read(&lock->base.owner) & MUTEX_FLAG_WAITERS)))

  		return;
  
  	/*

  	 * Uh oh, we raced in fastpath, check if any of the waiters need to

  	 * die or wound us.

  	 */

  	spin_lock(&lock->base.wait_lock);

  	__ww_mutex_check_waiters(&lock->base, ctx);

  	spin_unlock(&lock->base.wait_lock);

  }

  #ifdef CONFIG_MUTEX_SPIN_ON_OWNER

  
  static inline
  bool ww_mutex_spin_on_owner(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
  			    struct mutex_waiter *waiter)
  {
  	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.
  	 *
  	 * Check this in every inner iteration because we may
  	 * be racing against another thread's ww_mutex_lock.

  	 */

  	if (ww_ctx->acquired > 0 && READ_ONCE(ww->ctx))
  		return false;
  
  	/*
  	 * If we aren't on the wait list yet, cancel the spin
  	 * if there are waiters. We want  to avoid stealing the
  	 * lock from a waiter with an earlier stamp, since the
  	 * other thread may already own a lock that we also
  	 * need.
  	 */
  	if (!waiter && (atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS))
  		return false;
  
  	/*
  	 * Similarly, stop spinning if we are no longer the
  	 * first waiter.
  	 */
  	if (waiter && !__mutex_waiter_is_first(lock, waiter))
  		return false;
  
  	return true;

  }

  /*

   * Look out! "owner" is an entirely speculative pointer access and not
   * reliable.
   *
   * "noinline" so that this function shows up on perf profiles.

   */
  static noinline

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

  			 struct ww_acquire_ctx *ww_ctx, struct mutex_waiter *waiter)

  {

  	bool ret = true;

  	rcu_read_lock();

  	while (__mutex_owner(lock) == 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();

  		/*
  		 * Use vcpu_is_preempted to detect lock holder preemption issue.
  		 */
  		if (!owner->on_cpu || need_resched() ||
  				vcpu_is_preempted(task_cpu(owner))) {

  			ret = false;
  			break;
  		}

  		if (ww_ctx && !ww_mutex_spin_on_owner(lock, ww_ctx, waiter)) {
  			ret = false;
  			break;

  		}

  		cpu_relax();

  	}
  	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 = __mutex_owner(lock);

  
  	/*
  	 * As lock holder preemption issue, we both skip spinning if task is not
  	 * on cpu or its cpu is preempted
  	 */

  	if (owner)

  		retval = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));

  	rcu_read_unlock();

  	/*

  	 * If lock->owner is not set, the mutex has been released. Return true
  	 * such that we'll trylock in the spin path, which is a faster option
  	 * than the blocking slow path.

  	 */
  	return retval;
  }

  
  /*

   * 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.
   *

   * 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.

   *
   * The waiter flag is set to true if the spinner is a waiter in the wait
   * queue. The waiter-spinner will spin on the lock directly and concurrently
   * with the spinner at the head of the OSQ, if present, until the owner is
   * changed to itself.

   */

  static __always_inline bool
  mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,

  		      const bool use_ww_ctx, struct mutex_waiter *waiter)

  {

  	if (!waiter) {
  		/*
  		 * The purpose of the mutex_can_spin_on_owner() function is
  		 * to eliminate the overhead of osq_lock() and osq_unlock()
  		 * in case spinning isn't possible. As a waiter-spinner
  		 * is not going to take OSQ lock anyway, there is no need
  		 * to call mutex_can_spin_on_owner().
  		 */
  		if (!mutex_can_spin_on_owner(lock))
  			goto fail;

  		/*
  		 * 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 fail;
  	}

  	for (;;) {

  		struct task_struct *owner;

  		/* Try to acquire the mutex... */
  		owner = __mutex_trylock_or_owner(lock);
  		if (!owner)
  			break;

  
  		/*

  		 * There's an owner, wait for it to either

  		 * release the lock or go to sleep.
  		 */

  		if (!mutex_spin_on_owner(lock, owner, ww_ctx, waiter))

  			goto fail_unlock;

  		/*

  		 * 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();

  	}

  	if (!waiter)
  		osq_unlock(&lock->osq);
  
  	return true;
  
  
  fail_unlock:
  	if (!waiter)
  		osq_unlock(&lock->osq);
  
  fail:

  	/*
  	 * 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 __always_inline bool
  mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,

  		      const bool use_ww_ctx, struct mutex_waiter *waiter)

  {
  	return false;
  }

  #endif

  static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip);

  /**

   * 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)

  {

  #ifndef CONFIG_DEBUG_LOCK_ALLOC
  	if (__mutex_unlock_fast(lock))
  		return;

  #endif

  	__mutex_unlock_slowpath(lock, _RET_IP_);

  }

  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;
  	}

  	mutex_unlock(&lock->base);

  }
  EXPORT_SYMBOL(ww_mutex_unlock);

  
  static __always_inline int __sched
  __ww_mutex_kill(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
  {
  	if (ww_ctx->acquired > 0) {
  #ifdef CONFIG_DEBUG_MUTEXES
  		struct ww_mutex *ww;
  
  		ww = container_of(lock, struct ww_mutex, base);
  		DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock);
  		ww_ctx->contending_lock = ww;
  #endif
  		return -EDEADLK;
  	}
  
  	return 0;
  }
  
  
  /*

   * Check the wound condition for the current lock acquire.
   *
   * Wound-Wait: If we're wounded, kill ourself.

   *
   * Wait-Die: If we're trying to acquire a lock already held by an older
   *           context, kill ourselves.
   *
   * Since __ww_mutex_add_waiter() orders the wait-list on stamp, we only have to
   * look at waiters before us in the wait-list.
   */

  static inline int __sched

  __ww_mutex_check_kill(struct mutex *lock, struct mutex_waiter *waiter,
  		      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);

  	struct mutex_waiter *cur;

  	if (ctx->acquired == 0)
  		return 0;

  	if (!ctx->is_wait_die) {
  		if (ctx->wounded)
  			return __ww_mutex_kill(lock, ctx);
  
  		return 0;
  	}

  	if (hold_ctx && __ww_ctx_stamp_after(ctx, hold_ctx))

  		return __ww_mutex_kill(lock, ctx);

  	/*
  	 * If there is a waiter in front of us that has a context, then its

  	 * stamp is earlier than ours and we must kill ourself.

  	 */
  	cur = waiter;
  	list_for_each_entry_continue_reverse(cur, &lock->wait_list, list) {

  		if (!cur->ww_ctx)
  			continue;
  
  		return __ww_mutex_kill(lock, ctx);

  	}
  
  	return 0;
  }

  /*
   * Add @waiter to the wait-list, keep the wait-list ordered by stamp, smallest
   * first. Such that older contexts are preferred to acquire the lock over
   * younger contexts.
   *
   * Waiters without context are interspersed in FIFO order.
   *
   * Furthermore, for Wait-Die kill ourself immediately when possible (there are

   * older contexts already waiting) to avoid unnecessary waiting and for
   * Wound-Wait ensure we wound the owning context when it is younger.

   */

  static inline int __sched
  __ww_mutex_add_waiter(struct mutex_waiter *waiter,
  		      struct mutex *lock,
  		      struct ww_acquire_ctx *ww_ctx)
  {
  	struct mutex_waiter *cur;
  	struct list_head *pos;

  	bool is_wait_die;

  
  	if (!ww_ctx) {

  		__mutex_add_waiter(lock, waiter, &lock->wait_list);

  		return 0;

  	}

  	is_wait_die = ww_ctx->is_wait_die;

  	/*
  	 * Add the waiter before the first waiter with a higher stamp.
  	 * Waiters without a context are skipped to avoid starving

  	 * them. Wait-Die waiters may die here. Wound-Wait waiters
  	 * never die here, but they are sorted in stamp order and
  	 * may wound the lock holder.

  	 */
  	pos = &lock->wait_list;
  	list_for_each_entry_reverse(cur, &lock->wait_list, list) {
  		if (!cur->ww_ctx)
  			continue;
  
  		if (__ww_ctx_stamp_after(ww_ctx, cur->ww_ctx)) {

  			/*
  			 * Wait-Die: if we find an older context waiting, there
  			 * is no point in queueing behind it, as we'd have to
  			 * die the moment it would acquire the lock.
  			 */

  			if (is_wait_die) {
  				int ret = __ww_mutex_kill(lock, ww_ctx);

  				if (ret)
  					return ret;
  			}

  
  			break;
  		}
  
  		pos = &cur->list;

  		/* Wait-Die: ensure younger waiters die. */
  		__ww_mutex_die(lock, cur, ww_ctx);

  	}

  	__mutex_add_waiter(lock, waiter, pos);
  
  	/*
  	 * Wound-Wait: if we're blocking on a mutex owned by a younger context,
  	 * wound that such that we might proceed.
  	 */
  	if (!is_wait_die) {
  		struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
  
  		/*
  		 * See ww_mutex_set_context_fastpath(). Orders setting
  		 * MUTEX_FLAG_WAITERS vs the ww->ctx load,
  		 * such that either we or the fastpath will wound @ww->ctx.
  		 */
  		smp_mb();
  		__ww_mutex_wound(lock, ww_ctx, ww->ctx);
  	}

  	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 mutex_waiter waiter;

  	bool first = false;

  	struct ww_mutex *ww;

  	int ret;

  	might_sleep();

  #ifdef CONFIG_DEBUG_MUTEXES
  	DEBUG_LOCKS_WARN_ON(lock->magic != lock);
  #endif

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

  	if (use_ww_ctx && ww_ctx) {

  		if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
  			return -EALREADY;

  
  		/*
  		 * Reset the wounded flag after a kill. No other process can
  		 * race and wound us here since they can't have a valid owner
  		 * pointer if we don't have any locks held.
  		 */
  		if (ww_ctx->acquired == 0)
  			ww_ctx->wounded = 0;

  	}

  	preempt_disable();

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

  	if (__mutex_trylock(lock) ||

  	    mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, NULL)) {

  		/* got the lock, yay! */

  		lock_acquired(&lock->dep_map, ip);

  		if (use_ww_ctx && ww_ctx)

  			ww_mutex_set_context_fastpath(ww, ww_ctx);

  		preempt_enable();
  		return 0;

  	}

  	spin_lock(&lock->wait_lock);

  	/*

  	 * After waiting to acquire the wait_lock, try again.

  	 */

  	if (__mutex_trylock(lock)) {
  		if (use_ww_ctx && ww_ctx)

  			__ww_mutex_check_waiters(lock, ww_ctx);

  		goto skip_wait;

  	}

  	debug_mutex_lock_common(lock, &waiter);

  	lock_contended(&lock->dep_map, ip);
  
  	if (!use_ww_ctx) {
  		/* add waiting tasks to the end of the waitqueue (FIFO): */

  		__mutex_add_waiter(lock, &waiter, &lock->wait_list);

  
  #ifdef CONFIG_DEBUG_MUTEXES
  		waiter.ww_ctx = MUTEX_POISON_WW_CTX;
  #endif

  	} else {

  		/*
  		 * Add in stamp order, waking up waiters that must kill
  		 * themselves.
  		 */

  		ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
  		if (ret)

  			goto err_early_kill;

  
  		waiter.ww_ctx = ww_ctx;
  	}

  	waiter.task = current;

  	trace_android_vh_mutex_wait_start(lock);

  	set_current_state(state);

  	for (;;) {

  		/*
  		 * Once we hold wait_lock, we're serialized against
  		 * mutex_unlock() handing the lock off to us, do a trylock
  		 * before testing the error conditions to make sure we pick up
  		 * the handoff.
  		 */

  		if (__mutex_trylock(lock))

  			goto acquired;

  
  		/*

  		 * Check for signals and kill conditions while holding

  		 * wait_lock. This ensures the lock cancellation is ordered
  		 * against mutex_unlock() and wake-ups do not go missing.

  		 */

  		if (signal_pending_state(state, current)) {

  			ret = -EINTR;
  			goto err;
  		}

  		if (use_ww_ctx && ww_ctx) {
  			ret = __ww_mutex_check_kill(lock, &waiter, ww_ctx);

  			if (ret)
  				goto err;

  		}

  		spin_unlock(&lock->wait_lock);

  		schedule_preempt_disabled();

  		/*
  		 * ww_mutex needs to always recheck its position since its waiter
  		 * list is not FIFO ordered.
  		 */
  		if ((use_ww_ctx && ww_ctx) || !first) {
  			first = __mutex_waiter_is_first(lock, &waiter);
  			if (first)
  				__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);

  		}

  		set_current_state(state);

  		/*
  		 * Here we order against unlock; we must either see it change
  		 * state back to RUNNING and fall through the next schedule(),
  		 * or we must see its unlock and acquire.
  		 */

  		if (__mutex_trylock(lock) ||

  		    (first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, &waiter)))

  			break;

  		spin_lock(&lock->wait_lock);

  	}

  	spin_lock(&lock->wait_lock);

  acquired:

  	__set_current_state(TASK_RUNNING);

  	trace_android_vh_mutex_wait_finish(lock);

  	if (use_ww_ctx && ww_ctx) {
  		/*
  		 * Wound-Wait; we stole the lock (!first_waiter), check the
  		 * waiters as anyone might want to wound us.
  		 */
  		if (!ww_ctx->is_wait_die &&
  		    !__mutex_waiter_is_first(lock, &waiter))
  			__ww_mutex_check_waiters(lock, ww_ctx);
  	}

  	mutex_remove_waiter(lock, &waiter, current);

  	if (likely(list_empty(&lock->wait_list)))

  		__mutex_clear_flag(lock, MUTEX_FLAGS);

  	debug_mutex_free_waiter(&waiter);

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

  	lock_acquired(&lock->dep_map, ip);

  	if (use_ww_ctx && ww_ctx)

  		ww_mutex_lock_acquired(ww, ww_ctx);

  	spin_unlock(&lock->wait_lock);

  	preempt_enable();

  	return 0;

  
  err:

  	__set_current_state(TASK_RUNNING);

  	trace_android_vh_mutex_wait_finish(lock);

  	mutex_remove_waiter(lock, &waiter, current);

  err_early_kill:

  	spin_unlock(&lock->wait_lock);

  	debug_mutex_free_waiter(&waiter);

  	mutex_release(&lock->dep_map, ip);

  	preempt_enable();
  	return ret;

  }

  static int __sched
  __mutex_lock(struct mutex *lock, long state, unsigned int subclass,
  	     struct lockdep_map *nest_lock, unsigned long ip)
  {
  	return __mutex_lock_common(lock, state, subclass, nest_lock, ip, NULL, false);
  }
  
  static int __sched
  __ww_mutex_lock(struct mutex *lock, long state, unsigned int subclass,
  		struct lockdep_map *nest_lock, unsigned long ip,
  		struct ww_acquire_ctx *ww_ctx)
  {
  	return __mutex_lock_common(lock, state, subclass, nest_lock, ip, ww_ctx, true);
  }

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

  	__mutex_lock(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);

  }
  
  EXPORT_SYMBOL_GPL(mutex_lock_nested);

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

  	__mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_);

  }

  EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);

  int __sched

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

  	return __mutex_lock(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_);

  }
  EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
  
  int __sched

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

  	return __mutex_lock(lock, TASK_INTERRUPTIBLE, subclass, NULL, _RET_IP_);

  }

  EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);

  void __sched
  mutex_lock_io_nested(struct mutex *lock, unsigned int subclass)
  {
  	int token;
  
  	might_sleep();
  
  	token = io_schedule_prepare();
  	__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
  			    subclass, NULL, _RET_IP_, NULL, 0);
  	io_schedule_finish(token);
  }
  EXPORT_SYMBOL_GPL(mutex_lock_io_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 =  __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE,
  			       0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
  			       ctx);

  	if (!ret && ctx && 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 = __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE,
  			      0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
  			      ctx);

  	if (!ret && ctx && 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 noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)

  {

  	struct task_struct *next = NULL;

  	DEFINE_WAKE_Q(wake_q);

  	unsigned long owner;

  	mutex_release(&lock->dep_map, ip);

  	/*

  	 * Release the lock before (potentially) taking the spinlock such that
  	 * other contenders can get on with things ASAP.
  	 *
  	 * Except when HANDOFF, in that case we must not clear the owner field,
  	 * but instead set it to the top waiter.

  	 */

  	owner = atomic_long_read(&lock->owner);
  	for (;;) {
  		unsigned long old;
  
  #ifdef CONFIG_DEBUG_MUTEXES
  		DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);

  		DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);

  #endif
  
  		if (owner & MUTEX_FLAG_HANDOFF)
  			break;
  
  		old = atomic_long_cmpxchg_release(&lock->owner, owner,
  						  __owner_flags(owner));
  		if (old == owner) {
  			if (owner & MUTEX_FLAG_WAITERS)
  				break;
  
  			return;
  		}
  
  		owner = old;
  	}

  	spin_lock(&lock->wait_lock);

  	debug_mutex_unlock(lock);

  	if (!list_empty(&lock->wait_list)) {
  		/* get the first entry from the wait-list: */
  		struct mutex_waiter *waiter =

  			list_first_entry(&lock->wait_list,
  					 struct mutex_waiter, list);
  
  		next = waiter->task;

  
  		debug_mutex_wake_waiter(lock, waiter);

  		wake_q_add(&wake_q, next);

  	}

  	if (owner & MUTEX_FLAG_HANDOFF)
  		__mutex_handoff(lock, next);

  	spin_unlock(&lock->wait_lock);

  	wake_up_q(&wake_q);

  }

  #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 by signals.
   * @lock: The mutex to be acquired.

   *

   * Lock the mutex like mutex_lock().  If a signal is delivered while the
   * process is sleeping, this function will return without acquiring the
   * mutex.

   *

   * Context: Process context.
   * Return: 0 if the lock was successfully acquired or %-EINTR if a
   * signal arrived.

   */

  int __sched mutex_lock_interruptible(struct mutex *lock)

  {

  	might_sleep();

  
  	if (__mutex_trylock_fast(lock))

  		return 0;

  
  	return __mutex_lock_interruptible_slowpath(lock);

  }
  
  EXPORT_SYMBOL(mutex_lock_interruptible);

  /**
   * mutex_lock_killable() - Acquire the mutex, interruptible by fatal signals.
   * @lock: The mutex to be acquired.
   *
   * Lock the mutex like mutex_lock().  If a signal which will be fatal to
   * the current process is delivered while the process is sleeping, this
   * function will return without acquiring the mutex.
   *
   * Context: Process context.
   * Return: 0 if the lock was successfully acquired or %-EINTR if a
   * fatal signal arrived.
   */

  int __sched mutex_lock_killable(struct mutex *lock)

  {
  	might_sleep();

  
  	if (__mutex_trylock_fast(lock))

  		return 0;

  
  	return __mutex_lock_killable_slowpath(lock);

  }
  EXPORT_SYMBOL(mutex_lock_killable);

  /**
   * mutex_lock_io() - Acquire the mutex and mark the process as waiting for I/O
   * @lock: The mutex to be acquired.
   *
   * Lock the mutex like mutex_lock().  While the task is waiting for this
   * mutex, it will be accounted as being in the IO wait state by the
   * scheduler.
   *
   * Context: Process context.
   */

  void __sched mutex_lock_io(struct mutex *lock)
  {
  	int token;
  
  	token = io_schedule_prepare();
  	mutex_lock(lock);
  	io_schedule_finish(token);
  }
  EXPORT_SYMBOL_GPL(mutex_lock_io);

  static noinline void __sched
  __mutex_lock_slowpath(struct mutex *lock)

  {

  	__mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);

  }

  static noinline int __sched

  __mutex_lock_killable_slowpath(struct mutex *lock)

  {

  	return __mutex_lock(lock, TASK_KILLABLE, 0, NULL, _RET_IP_);

  }

  static noinline int __sched

  __mutex_lock_interruptible_slowpath(struct mutex *lock)

  {

  	return __mutex_lock(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_);

  }
  
  static noinline int __sched
  __ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
  {

  	return __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, 0, NULL,
  			       _RET_IP_, ctx);

  }

  
  static noinline int __sched
  __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
  					    struct ww_acquire_ctx *ctx)
  {

  	return __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, 0, NULL,
  			       _RET_IP_, ctx);

  }

  #endif

  /**
   * 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)

  {

  	bool locked;
  
  #ifdef CONFIG_DEBUG_MUTEXES
  	DEBUG_LOCKS_WARN_ON(lock->magic != lock);
  #endif

  	locked = __mutex_trylock(lock);

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

  	return locked;

  }

  EXPORT_SYMBOL(mutex_trylock);

  #ifndef CONFIG_DEBUG_LOCK_ALLOC
  int __sched

  ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)

  {

  	might_sleep();

  	if (__mutex_trylock_fast(&lock->base)) {

  		if (ctx)
  			ww_mutex_set_context_fastpath(lock, ctx);

  		return 0;
  	}
  
  	return __ww_mutex_lock_slowpath(lock, ctx);

  }

  EXPORT_SYMBOL(ww_mutex_lock);

  
  int __sched

  ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)

  {

  	might_sleep();

  	if (__mutex_trylock_fast(&lock->base)) {

  		if (ctx)
  			ww_mutex_set_context_fastpath(lock, ctx);

  		return 0;
  	}
  
  	return __ww_mutex_lock_interruptible_slowpath(lock, ctx);

  }

  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);