/*
   *  Fast Userspace Mutexes (which I call "Futexes!").
   *  (C) Rusty Russell, IBM 2002
   *
   *  Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
   *  (C) Copyright 2003 Red Hat Inc, All Rights Reserved
   *
   *  Removed page pinning, fix privately mapped COW pages and other cleanups
   *  (C) Copyright 2003, 2004 Jamie Lokier
   *

   *  Robust futex support started by Ingo Molnar
   *  (C) Copyright 2006 Red Hat Inc, All Rights Reserved
   *  Thanks to Thomas Gleixner for suggestions, analysis and fixes.
   *

   *  PI-futex support started by Ingo Molnar and Thomas Gleixner
   *  Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   *  Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
   *

   *  PRIVATE futexes by Eric Dumazet
   *  Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
   *

   *  Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
   *  enough at me, Linus for the original (flawed) idea, Matthew
   *  Kirkwood for proof-of-concept implementation.
   *
   *  "The futexes are also cursed."
   *  "But they come in a choice of three flavours!"
   *
   *  This program is free software; you can redistribute it and/or modify
   *  it under the terms of the GNU General Public License as published by
   *  the Free Software Foundation; either version 2 of the License, or
   *  (at your option) any later version.
   *
   *  This program is distributed in the hope that it will be useful,
   *  but WITHOUT ANY WARRANTY; without even the implied warranty of
   *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   *  GNU General Public License for more details.
   *
   *  You should have received a copy of the GNU General Public License
   *  along with this program; if not, write to the Free Software
   *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
   */
  #include <linux/slab.h>
  #include <linux/poll.h>
  #include <linux/fs.h>
  #include <linux/file.h>
  #include <linux/jhash.h>
  #include <linux/init.h>
  #include <linux/futex.h>
  #include <linux/mount.h>
  #include <linux/pagemap.h>
  #include <linux/syscalls.h>

  #include <linux/signal.h>

  #include <linux/module.h>

  #include <linux/magic.h>

  #include <linux/pid.h>
  #include <linux/nsproxy.h>

  #include <asm/futex.h>

  #include "rtmutex_common.h"

  int __read_mostly futex_cmpxchg_enabled;

  #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
  
  /*

   * Priority Inheritance state:
   */
  struct futex_pi_state {
  	/*
  	 * list of 'owned' pi_state instances - these have to be
  	 * cleaned up in do_exit() if the task exits prematurely:
  	 */
  	struct list_head list;
  
  	/*
  	 * The PI object:
  	 */
  	struct rt_mutex pi_mutex;
  
  	struct task_struct *owner;
  	atomic_t refcount;
  
  	union futex_key key;
  };
  
  /*

   * We use this hashed waitqueue instead of a normal wait_queue_t, so
   * we can wake only the relevant ones (hashed queues may be shared).
   *
   * A futex_q has a woken state, just like tasks have TASK_RUNNING.

   * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.

   * The order of wakup is always to make the first condition true, then

   * wake up q->waiter, then make the second condition true.

   */
  struct futex_q {

  	struct plist_node list;

  	/* There can only be a single waiter */
  	wait_queue_head_t waiter;

  	/* Which hash list lock to use: */

  	spinlock_t *lock_ptr;

  	/* Key which the futex is hashed on: */

  	union futex_key key;

  	/* Optional priority inheritance state: */
  	struct futex_pi_state *pi_state;
  	struct task_struct *task;

  
  	/* Bitset for the optional bitmasked wakeup */
  	u32 bitset;

  };
  
  /*
   * Split the global futex_lock into every hash list lock.
   */
  struct futex_hash_bucket {

  	spinlock_t lock;
  	struct plist_head chain;

  };
  
  static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];

  /*
   * We hash on the keys returned from get_futex_key (see below).
   */
  static struct futex_hash_bucket *hash_futex(union futex_key *key)
  {
  	u32 hash = jhash2((u32*)&key->both.word,
  			  (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
  			  key->both.offset);
  	return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
  }
  
  /*
   * Return 1 if two futex_keys are equal, 0 otherwise.
   */
  static inline int match_futex(union futex_key *key1, union futex_key *key2)
  {
  	return (key1->both.word == key2->both.word
  		&& key1->both.ptr == key2->both.ptr
  		&& key1->both.offset == key2->both.offset);
  }

  /*
   * Take a reference to the resource addressed by a key.
   * Can be called while holding spinlocks.
   *
   */
  static void get_futex_key_refs(union futex_key *key)
  {
  	if (!key->both.ptr)
  		return;
  
  	switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
  	case FUT_OFF_INODE:
  		atomic_inc(&key->shared.inode->i_count);
  		break;
  	case FUT_OFF_MMSHARED:
  		atomic_inc(&key->private.mm->mm_count);
  		break;
  	}
  }
  
  /*
   * Drop a reference to the resource addressed by a key.
   * The hash bucket spinlock must not be held.
   */
  static void drop_futex_key_refs(union futex_key *key)
  {

  	if (!key->both.ptr) {
  		/* If we're here then we tried to put a key we failed to get */
  		WARN_ON_ONCE(1);

  		return;

  	}

  
  	switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
  	case FUT_OFF_INODE:
  		iput(key->shared.inode);
  		break;
  	case FUT_OFF_MMSHARED:
  		mmdrop(key->private.mm);
  		break;
  	}
  }

  /**
   * get_futex_key - Get parameters which are the keys for a futex.
   * @uaddr: virtual address of the futex
   * @shared: NULL for a PROCESS_PRIVATE futex,
   *	&current->mm->mmap_sem for a PROCESS_SHARED futex
   * @key: address where result is stored.
   *
   * Returns a negative error code or 0
   * The key words are stored in *key on success.

   *

   * For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,

   * offset_within_page).  For private mappings, it's (uaddr, current->mm).
   * We can usually work out the index without swapping in the page.
   *

   * fshared is NULL for PROCESS_PRIVATE futexes
   * For other futexes, it points to &current->mm->mmap_sem and
   * caller must have taken the reader lock. but NOT any spinlocks.

   */

  static int get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key)

  {

  	unsigned long address = (unsigned long)uaddr;

  	struct mm_struct *mm = current->mm;

  	struct page *page;
  	int err;
  
  	/*
  	 * The futex address must be "naturally" aligned.
  	 */

  	key->both.offset = address % PAGE_SIZE;

  	if (unlikely((address % sizeof(u32)) != 0))

  		return -EINVAL;

  	address -= key->both.offset;

  
  	/*

  	 * PROCESS_PRIVATE futexes are fast.
  	 * As the mm cannot disappear under us and the 'key' only needs
  	 * virtual address, we dont even have to find the underlying vma.
  	 * Note : We do have to check 'uaddr' is a valid user address,
  	 *        but access_ok() should be faster than find_vma()
  	 */
  	if (!fshared) {
  		if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))))
  			return -EFAULT;
  		key->private.mm = mm;
  		key->private.address = address;

  		get_futex_key_refs(key);

  		return 0;
  	}

  again:

  	err = get_user_pages_fast(address, 1, 0, &page);

  	if (err < 0)
  		return err;
  
  	lock_page(page);
  	if (!page->mapping) {
  		unlock_page(page);
  		put_page(page);
  		goto again;
  	}

  
  	/*
  	 * Private mappings are handled in a simple way.
  	 *
  	 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
  	 * it's a read-only handle, it's expected that futexes attach to

  	 * the object not the particular process.

  	 */

  	if (PageAnon(page)) {
  		key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */

  		key->private.mm = mm;

  		key->private.address = address;

  	} else {
  		key->both.offset |= FUT_OFF_INODE; /* inode-based key */
  		key->shared.inode = page->mapping->host;
  		key->shared.pgoff = page->index;

  	}

  	get_futex_key_refs(key);

  	unlock_page(page);
  	put_page(page);
  	return 0;

  }

  static inline

  void put_futex_key(int fshared, union futex_key *key)

  {

  	drop_futex_key_refs(key);

  }

  static u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval)
  {
  	u32 curval;
  
  	pagefault_disable();
  	curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
  	pagefault_enable();
  
  	return curval;
  }
  
  static int get_futex_value_locked(u32 *dest, u32 __user *from)

  {
  	int ret;

  	pagefault_disable();

  	ret = __copy_from_user_inatomic(dest, from, sizeof(u32));

  	pagefault_enable();

  
  	return ret ? -EFAULT : 0;
  }
  
  /*

   * Fault handling.

   */

  static int futex_handle_fault(unsigned long address, int attempt)

  {
  	struct vm_area_struct * vma;
  	struct mm_struct *mm = current->mm;

  	int ret = -EFAULT;

  	if (attempt > 2)
  		return ret;

  	down_read(&mm->mmap_sem);

  	vma = find_vma(mm, address);
  	if (vma && address >= vma->vm_start &&
  	    (vma->vm_flags & VM_WRITE)) {

  		int fault;
  		fault = handle_mm_fault(mm, vma, address, 1);
  		if (unlikely((fault & VM_FAULT_ERROR))) {
  #if 0
  			/* XXX: let's do this when we verify it is OK */
  			if (ret & VM_FAULT_OOM)
  				ret = -ENOMEM;
  #endif
  		} else {

  			ret = 0;

  			if (fault & VM_FAULT_MAJOR)
  				current->maj_flt++;
  			else
  				current->min_flt++;

  		}

  	}

  	up_read(&mm->mmap_sem);

  	return ret;

  }
  
  /*
   * PI code:
   */
  static int refill_pi_state_cache(void)
  {
  	struct futex_pi_state *pi_state;
  
  	if (likely(current->pi_state_cache))
  		return 0;

  	pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);

  
  	if (!pi_state)
  		return -ENOMEM;

  	INIT_LIST_HEAD(&pi_state->list);
  	/* pi_mutex gets initialized later */
  	pi_state->owner = NULL;
  	atomic_set(&pi_state->refcount, 1);

  	pi_state->key = FUTEX_KEY_INIT;

  
  	current->pi_state_cache = pi_state;
  
  	return 0;
  }
  
  static struct futex_pi_state * alloc_pi_state(void)
  {
  	struct futex_pi_state *pi_state = current->pi_state_cache;
  
  	WARN_ON(!pi_state);
  	current->pi_state_cache = NULL;
  
  	return pi_state;
  }
  
  static void free_pi_state(struct futex_pi_state *pi_state)
  {
  	if (!atomic_dec_and_test(&pi_state->refcount))
  		return;
  
  	/*
  	 * If pi_state->owner is NULL, the owner is most probably dying
  	 * and has cleaned up the pi_state already
  	 */
  	if (pi_state->owner) {
  		spin_lock_irq(&pi_state->owner->pi_lock);
  		list_del_init(&pi_state->list);
  		spin_unlock_irq(&pi_state->owner->pi_lock);
  
  		rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
  	}
  
  	if (current->pi_state_cache)
  		kfree(pi_state);
  	else {
  		/*
  		 * pi_state->list is already empty.
  		 * clear pi_state->owner.
  		 * refcount is at 0 - put it back to 1.
  		 */
  		pi_state->owner = NULL;
  		atomic_set(&pi_state->refcount, 1);
  		current->pi_state_cache = pi_state;
  	}
  }
  
  /*
   * Look up the task based on what TID userspace gave us.
   * We dont trust it.
   */
  static struct task_struct * futex_find_get_task(pid_t pid)
  {
  	struct task_struct *p;

  	const struct cred *cred = current_cred(), *pcred;

  	rcu_read_lock();

  	p = find_task_by_vpid(pid);

  	if (!p) {

  		p = ERR_PTR(-ESRCH);

  	} else {
  		pcred = __task_cred(p);
  		if (cred->euid != pcred->euid &&
  		    cred->euid != pcred->uid)
  			p = ERR_PTR(-ESRCH);
  		else
  			get_task_struct(p);
  	}

  	rcu_read_unlock();

  
  	return p;
  }
  
  /*
   * This task is holding PI mutexes at exit time => bad.
   * Kernel cleans up PI-state, but userspace is likely hosed.
   * (Robust-futex cleanup is separate and might save the day for userspace.)
   */
  void exit_pi_state_list(struct task_struct *curr)
  {

  	struct list_head *next, *head = &curr->pi_state_list;
  	struct futex_pi_state *pi_state;

  	struct futex_hash_bucket *hb;

  	union futex_key key = FUTEX_KEY_INIT;

  	if (!futex_cmpxchg_enabled)
  		return;

  	/*
  	 * We are a ZOMBIE and nobody can enqueue itself on
  	 * pi_state_list anymore, but we have to be careful

  	 * versus waiters unqueueing themselves:

  	 */
  	spin_lock_irq(&curr->pi_lock);
  	while (!list_empty(head)) {
  
  		next = head->next;
  		pi_state = list_entry(next, struct futex_pi_state, list);
  		key = pi_state->key;

  		hb = hash_futex(&key);

  		spin_unlock_irq(&curr->pi_lock);

  		spin_lock(&hb->lock);
  
  		spin_lock_irq(&curr->pi_lock);

  		/*
  		 * We dropped the pi-lock, so re-check whether this
  		 * task still owns the PI-state:
  		 */

  		if (head->next != next) {
  			spin_unlock(&hb->lock);
  			continue;
  		}

  		WARN_ON(pi_state->owner != curr);

  		WARN_ON(list_empty(&pi_state->list));
  		list_del_init(&pi_state->list);

  		pi_state->owner = NULL;
  		spin_unlock_irq(&curr->pi_lock);
  
  		rt_mutex_unlock(&pi_state->pi_mutex);
  
  		spin_unlock(&hb->lock);
  
  		spin_lock_irq(&curr->pi_lock);
  	}
  	spin_unlock_irq(&curr->pi_lock);
  }
  
  static int

  lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
  		union futex_key *key, struct futex_pi_state **ps)

  {
  	struct futex_pi_state *pi_state = NULL;
  	struct futex_q *this, *next;

  	struct plist_head *head;

  	struct task_struct *p;

  	pid_t pid = uval & FUTEX_TID_MASK;

  
  	head = &hb->chain;

  	plist_for_each_entry_safe(this, next, head, list) {

  		if (match_futex(&this->key, key)) {

  			/*
  			 * Another waiter already exists - bump up
  			 * the refcount and return its pi_state:
  			 */
  			pi_state = this->pi_state;

  			/*
  			 * Userspace might have messed up non PI and PI futexes
  			 */
  			if (unlikely(!pi_state))
  				return -EINVAL;

  			WARN_ON(!atomic_read(&pi_state->refcount));

  			WARN_ON(pid && pi_state->owner &&
  				pi_state->owner->pid != pid);

  			atomic_inc(&pi_state->refcount);

  			*ps = pi_state;

  
  			return 0;
  		}
  	}
  
  	/*

  	 * We are the first waiter - try to look up the real owner and attach

  	 * the new pi_state to it, but bail out when TID = 0

  	 */

  	if (!pid)

  		return -ESRCH;

  	p = futex_find_get_task(pid);

  	if (IS_ERR(p))
  		return PTR_ERR(p);
  
  	/*
  	 * We need to look at the task state flags to figure out,
  	 * whether the task is exiting. To protect against the do_exit
  	 * change of the task flags, we do this protected by
  	 * p->pi_lock:
  	 */
  	spin_lock_irq(&p->pi_lock);
  	if (unlikely(p->flags & PF_EXITING)) {
  		/*
  		 * The task is on the way out. When PF_EXITPIDONE is
  		 * set, we know that the task has finished the
  		 * cleanup:
  		 */
  		int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
  
  		spin_unlock_irq(&p->pi_lock);
  		put_task_struct(p);
  		return ret;
  	}

  
  	pi_state = alloc_pi_state();
  
  	/*
  	 * Initialize the pi_mutex in locked state and make 'p'
  	 * the owner of it:
  	 */
  	rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
  
  	/* Store the key for possible exit cleanups: */

  	pi_state->key = *key;

  	WARN_ON(!list_empty(&pi_state->list));

  	list_add(&pi_state->list, &p->pi_state_list);
  	pi_state->owner = p;
  	spin_unlock_irq(&p->pi_lock);
  
  	put_task_struct(p);

  	*ps = pi_state;

  
  	return 0;
  }
  
  /*

   * The hash bucket lock must be held when this is called.
   * Afterwards, the futex_q must not be accessed.
   */
  static void wake_futex(struct futex_q *q)
  {

  	plist_del(&q->list, &q->list.plist);

  	/*
  	 * The lock in wake_up_all() is a crucial memory barrier after the

  	 * plist_del() and also before assigning to q->lock_ptr.

  	 */

  	wake_up(&q->waiter);

  	/*
  	 * The waiting task can free the futex_q as soon as this is written,
  	 * without taking any locks.  This must come last.

  	 *
  	 * A memory barrier is required here to prevent the following store
  	 * to lock_ptr from getting ahead of the wakeup. Clearing the lock
  	 * at the end of wake_up_all() does not prevent this store from
  	 * moving.

  	 */

  	smp_wmb();

  	q->lock_ptr = NULL;
  }

  static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
  {
  	struct task_struct *new_owner;
  	struct futex_pi_state *pi_state = this->pi_state;
  	u32 curval, newval;
  
  	if (!pi_state)
  		return -EINVAL;

  	spin_lock(&pi_state->pi_mutex.wait_lock);

  	new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
  
  	/*
  	 * This happens when we have stolen the lock and the original
  	 * pending owner did not enqueue itself back on the rt_mutex.
  	 * Thats not a tragedy. We know that way, that a lock waiter
  	 * is on the fly. We make the futex_q waiter the pending owner.
  	 */
  	if (!new_owner)
  		new_owner = this->task;
  
  	/*
  	 * We pass it to the next owner. (The WAITERS bit is always
  	 * kept enabled while there is PI state around. We must also
  	 * preserve the owner died bit.)
  	 */

  	if (!(uval & FUTEX_OWNER_DIED)) {

  		int ret = 0;

  		newval = FUTEX_WAITERS | task_pid_vnr(new_owner);

  		curval = cmpxchg_futex_value_locked(uaddr, uval, newval);

  		if (curval == -EFAULT)

  			ret = -EFAULT;

  		else if (curval != uval)

  			ret = -EINVAL;
  		if (ret) {
  			spin_unlock(&pi_state->pi_mutex.wait_lock);
  			return ret;
  		}

  	}

  	spin_lock_irq(&pi_state->owner->pi_lock);
  	WARN_ON(list_empty(&pi_state->list));
  	list_del_init(&pi_state->list);
  	spin_unlock_irq(&pi_state->owner->pi_lock);
  
  	spin_lock_irq(&new_owner->pi_lock);
  	WARN_ON(!list_empty(&pi_state->list));

  	list_add(&pi_state->list, &new_owner->pi_state_list);
  	pi_state->owner = new_owner;

  	spin_unlock_irq(&new_owner->pi_lock);

  	spin_unlock(&pi_state->pi_mutex.wait_lock);

  	rt_mutex_unlock(&pi_state->pi_mutex);
  
  	return 0;
  }
  
  static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
  {
  	u32 oldval;
  
  	/*
  	 * There is no waiter, so we unlock the futex. The owner died
  	 * bit has not to be preserved here. We are the owner:
  	 */

  	oldval = cmpxchg_futex_value_locked(uaddr, uval, 0);

  
  	if (oldval == -EFAULT)
  		return oldval;
  	if (oldval != uval)
  		return -EAGAIN;
  
  	return 0;
  }

  /*

   * Express the locking dependencies for lockdep:
   */
  static inline void
  double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
  {
  	if (hb1 <= hb2) {
  		spin_lock(&hb1->lock);
  		if (hb1 < hb2)
  			spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
  	} else { /* hb1 > hb2 */
  		spin_lock(&hb2->lock);
  		spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
  	}
  }
  
  /*

   * Wake up all waiters hashed on the physical page that is mapped
   * to this virtual address:
   */

  static int futex_wake(u32 __user *uaddr, int fshared, int nr_wake, u32 bitset)

  {

  	struct futex_hash_bucket *hb;

  	struct futex_q *this, *next;

  	struct plist_head *head;

  	union futex_key key = FUTEX_KEY_INIT;

  	int ret;

  	if (!bitset)
  		return -EINVAL;

  	ret = get_futex_key(uaddr, fshared, &key);

  	if (unlikely(ret != 0))
  		goto out;

  	hb = hash_futex(&key);
  	spin_lock(&hb->lock);
  	head = &hb->chain;

  	plist_for_each_entry_safe(this, next, head, list) {

  		if (match_futex (&this->key, &key)) {

  			if (this->pi_state) {
  				ret = -EINVAL;
  				break;
  			}

  
  			/* Check if one of the bits is set in both bitsets */
  			if (!(this->bitset & bitset))
  				continue;

  			wake_futex(this);
  			if (++ret >= nr_wake)
  				break;
  		}
  	}

  	spin_unlock(&hb->lock);

  	put_futex_key(fshared, &key);

  out:

  	return ret;
  }
  
  /*

   * Wake up all waiters hashed on the physical page that is mapped
   * to this virtual address:
   */

  static int

  futex_wake_op(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,

  	      int nr_wake, int nr_wake2, int op)

  {

  	union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;

  	struct futex_hash_bucket *hb1, *hb2;

  	struct plist_head *head;

  	struct futex_q *this, *next;
  	int ret, op_ret, attempt = 0;
  
  retryfull:

  	ret = get_futex_key(uaddr1, fshared, &key1);

  	if (unlikely(ret != 0))
  		goto out;

  	ret = get_futex_key(uaddr2, fshared, &key2);

  	if (unlikely(ret != 0))

  		goto out_put_key1;

  	hb1 = hash_futex(&key1);
  	hb2 = hash_futex(&key2);

  
  retry:

  	double_lock_hb(hb1, hb2);

  	op_ret = futex_atomic_op_inuser(op, uaddr2);

  	if (unlikely(op_ret < 0)) {

  		u32 dummy;

  		spin_unlock(&hb1->lock);
  		if (hb1 != hb2)
  			spin_unlock(&hb2->lock);

  #ifndef CONFIG_MMU

  		/*
  		 * we don't get EFAULT from MMU faults if we don't have an MMU,
  		 * but we might get them from range checking
  		 */

  		ret = op_ret;

  		goto out_put_keys;

  #endif

  		if (unlikely(op_ret != -EFAULT)) {
  			ret = op_ret;

  			goto out_put_keys;

  		}

  		/*
  		 * futex_atomic_op_inuser needs to both read and write

  		 * *(int __user *)uaddr2, but we can't modify it
  		 * non-atomically.  Therefore, if get_user below is not
  		 * enough, we need to handle the fault ourselves, while

  		 * still holding the mmap_sem.
  		 */

  		if (attempt++) {

  			ret = futex_handle_fault((unsigned long)uaddr2,

  						 attempt);

  			if (ret)

  				goto out_put_keys;

  			goto retry;
  		}

  		ret = get_user(dummy, uaddr2);

  		if (ret)
  			return ret;
  
  		goto retryfull;
  	}

  	head = &hb1->chain;

  	plist_for_each_entry_safe(this, next, head, list) {

  		if (match_futex (&this->key, &key1)) {
  			wake_futex(this);
  			if (++ret >= nr_wake)
  				break;
  		}
  	}
  
  	if (op_ret > 0) {

  		head = &hb2->chain;

  
  		op_ret = 0;

  		plist_for_each_entry_safe(this, next, head, list) {

  			if (match_futex (&this->key, &key2)) {
  				wake_futex(this);
  				if (++op_ret >= nr_wake2)
  					break;
  			}
  		}
  		ret += op_ret;
  	}

  	spin_unlock(&hb1->lock);
  	if (hb1 != hb2)
  		spin_unlock(&hb2->lock);

  out_put_keys:

  	put_futex_key(fshared, &key2);

  out_put_key1:

  	put_futex_key(fshared, &key1);

  out:

  	return ret;
  }
  
  /*

   * Requeue all waiters hashed on one physical page to another
   * physical page.
   */

  static int futex_requeue(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,

  			 int nr_wake, int nr_requeue, u32 *cmpval)

  {

  	union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;

  	struct futex_hash_bucket *hb1, *hb2;

  	struct plist_head *head1;

  	struct futex_q *this, *next;
  	int ret, drop_count = 0;

  retry:

  	ret = get_futex_key(uaddr1, fshared, &key1);

  	if (unlikely(ret != 0))
  		goto out;

  	ret = get_futex_key(uaddr2, fshared, &key2);

  	if (unlikely(ret != 0))

  		goto out_put_key1;

  	hb1 = hash_futex(&key1);
  	hb2 = hash_futex(&key2);

  	double_lock_hb(hb1, hb2);

  	if (likely(cmpval != NULL)) {
  		u32 curval;

  		ret = get_futex_value_locked(&curval, uaddr1);

  
  		if (unlikely(ret)) {

  			spin_unlock(&hb1->lock);
  			if (hb1 != hb2)
  				spin_unlock(&hb2->lock);

  			ret = get_user(curval, uaddr1);

  
  			if (!ret)
  				goto retry;

  			goto out_put_keys;

  		}

  		if (curval != *cmpval) {

  			ret = -EAGAIN;
  			goto out_unlock;
  		}
  	}

  	head1 = &hb1->chain;

  	plist_for_each_entry_safe(this, next, head1, list) {

  		if (!match_futex (&this->key, &key1))
  			continue;
  		if (++ret <= nr_wake) {
  			wake_futex(this);
  		} else {

  			/*
  			 * If key1 and key2 hash to the same bucket, no need to
  			 * requeue.
  			 */
  			if (likely(head1 != &hb2->chain)) {

  				plist_del(&this->list, &hb1->chain);
  				plist_add(&this->list, &hb2->chain);

  				this->lock_ptr = &hb2->lock;

  #ifdef CONFIG_DEBUG_PI_LIST
  				this->list.plist.lock = &hb2->lock;
  #endif

  			}

  			this->key = key2;

  			get_futex_key_refs(&key2);

  			drop_count++;
  
  			if (ret - nr_wake >= nr_requeue)
  				break;

  		}
  	}
  
  out_unlock:

  	spin_unlock(&hb1->lock);
  	if (hb1 != hb2)
  		spin_unlock(&hb2->lock);

  	/* drop_futex_key_refs() must be called outside the spinlocks. */

  	while (--drop_count >= 0)

  		drop_futex_key_refs(&key1);

  out_put_keys:

  	put_futex_key(fshared, &key2);

  out_put_key1:

  	put_futex_key(fshared, &key1);

  out:

  	return ret;
  }
  
  /* The key must be already stored in q->key. */

  static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)

  {

  	struct futex_hash_bucket *hb;

  	init_waitqueue_head(&q->waiter);

  	get_futex_key_refs(&q->key);

  	hb = hash_futex(&q->key);
  	q->lock_ptr = &hb->lock;

  	spin_lock(&hb->lock);
  	return hb;

  }

  static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)

  {

  	int prio;
  
  	/*
  	 * The priority used to register this element is
  	 * - either the real thread-priority for the real-time threads
  	 * (i.e. threads with a priority lower than MAX_RT_PRIO)
  	 * - or MAX_RT_PRIO for non-RT threads.
  	 * Thus, all RT-threads are woken first in priority order, and
  	 * the others are woken last, in FIFO order.
  	 */
  	prio = min(current->normal_prio, MAX_RT_PRIO);
  
  	plist_node_init(&q->list, prio);
  #ifdef CONFIG_DEBUG_PI_LIST
  	q->list.plist.lock = &hb->lock;
  #endif
  	plist_add(&q->list, &hb->chain);

  	q->task = current;

  	spin_unlock(&hb->lock);

  }
  
  static inline void

  queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)

  {

  	spin_unlock(&hb->lock);

  	drop_futex_key_refs(&q->key);

  }
  
  /*
   * queue_me and unqueue_me must be called as a pair, each
   * exactly once.  They are called with the hashed spinlock held.
   */

  /* Return 1 if we were still queued (ie. 0 means we were woken) */
  static int unqueue_me(struct futex_q *q)
  {

  	spinlock_t *lock_ptr;

  	int ret = 0;

  
  	/* In the common case we don't take the spinlock, which is nice. */

  retry:

  	lock_ptr = q->lock_ptr;

  	barrier();

  	if (lock_ptr != NULL) {

  		spin_lock(lock_ptr);
  		/*
  		 * q->lock_ptr can change between reading it and
  		 * spin_lock(), causing us to take the wrong lock.  This
  		 * corrects the race condition.
  		 *
  		 * Reasoning goes like this: if we have the wrong lock,
  		 * q->lock_ptr must have changed (maybe several times)
  		 * between reading it and the spin_lock().  It can
  		 * change again after the spin_lock() but only if it was
  		 * already changed before the spin_lock().  It cannot,
  		 * however, change back to the original value.  Therefore
  		 * we can detect whether we acquired the correct lock.
  		 */
  		if (unlikely(lock_ptr != q->lock_ptr)) {
  			spin_unlock(lock_ptr);
  			goto retry;
  		}

  		WARN_ON(plist_node_empty(&q->list));
  		plist_del(&q->list, &q->list.plist);

  
  		BUG_ON(q->pi_state);

  		spin_unlock(lock_ptr);
  		ret = 1;
  	}

  	drop_futex_key_refs(&q->key);

  	return ret;
  }

  /*
   * PI futexes can not be requeued and must remove themself from the

   * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
   * and dropped here.

   */

  static void unqueue_me_pi(struct futex_q *q)

  {

  	WARN_ON(plist_node_empty(&q->list));
  	plist_del(&q->list, &q->list.plist);

  
  	BUG_ON(!q->pi_state);
  	free_pi_state(q->pi_state);
  	q->pi_state = NULL;

  	spin_unlock(q->lock_ptr);

  	drop_futex_key_refs(&q->key);

  }

  /*

   * Fixup the pi_state owner with the new owner.

   *

   * Must be called with hash bucket lock held and mm->sem held for non
   * private futexes.

   */

  static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,

  				struct task_struct *newowner, int fshared)

  {

  	u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;

  	struct futex_pi_state *pi_state = q->pi_state;

  	struct task_struct *oldowner = pi_state->owner;

  	u32 uval, curval, newval;

  	int ret, attempt = 0;

  
  	/* Owner died? */

  	if (!pi_state->owner)
  		newtid |= FUTEX_OWNER_DIED;
  
  	/*
  	 * We are here either because we stole the rtmutex from the
  	 * pending owner or we are the pending owner which failed to
  	 * get the rtmutex. We have to replace the pending owner TID
  	 * in the user space variable. This must be atomic as we have
  	 * to preserve the owner died bit here.
  	 *
  	 * Note: We write the user space value _before_ changing the
  	 * pi_state because we can fault here. Imagine swapped out
  	 * pages or a fork, which was running right before we acquired
  	 * mmap_sem, that marked all the anonymous memory readonly for
  	 * cow.
  	 *
  	 * Modifying pi_state _before_ the user space value would
  	 * leave the pi_state in an inconsistent state when we fault
  	 * here, because we need to drop the hash bucket lock to
  	 * handle the fault. This might be observed in the PID check
  	 * in lookup_pi_state.
  	 */
  retry:
  	if (get_futex_value_locked(&uval, uaddr))
  		goto handle_fault;
  
  	while (1) {
  		newval = (uval & FUTEX_OWNER_DIED) | newtid;
  
  		curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
  
  		if (curval == -EFAULT)
  			goto handle_fault;
  		if (curval == uval)
  			break;
  		uval = curval;
  	}
  
  	/*
  	 * We fixed up user space. Now we need to fix the pi_state
  	 * itself.
  	 */

  	if (pi_state->owner != NULL) {
  		spin_lock_irq(&pi_state->owner->pi_lock);
  		WARN_ON(list_empty(&pi_state->list));
  		list_del_init(&pi_state->list);
  		spin_unlock_irq(&pi_state->owner->pi_lock);

  	}

  	pi_state->owner = newowner;

  	spin_lock_irq(&newowner->pi_lock);

  	WARN_ON(!list_empty(&pi_state->list));

  	list_add(&pi_state->list, &newowner->pi_state_list);
  	spin_unlock_irq(&newowner->pi_lock);

  	return 0;

  	/*

  	 * To handle the page fault we need to drop the hash bucket
  	 * lock here. That gives the other task (either the pending
  	 * owner itself or the task which stole the rtmutex) the
  	 * chance to try the fixup of the pi_state. So once we are
  	 * back from handling the fault we need to check the pi_state
  	 * after reacquiring the hash bucket lock and before trying to
  	 * do another fixup. When the fixup has been done already we
  	 * simply return.

  	 */

  handle_fault:
  	spin_unlock(q->lock_ptr);

  	ret = futex_handle_fault((unsigned long)uaddr, attempt++);

  	spin_lock(q->lock_ptr);

  	/*
  	 * Check if someone else fixed it for us:
  	 */
  	if (pi_state->owner != oldowner)
  		return 0;
  
  	if (ret)
  		return ret;
  
  	goto retry;

  }

  /*
   * In case we must use restart_block to restart a futex_wait,

   * we encode in the 'flags' shared capability

   */

  #define FLAGS_SHARED		0x01
  #define FLAGS_CLOCKRT		0x02

  static long futex_wait_restart(struct restart_block *restart);

  static int futex_wait(u32 __user *uaddr, int fshared,

  		      u32 val, ktime_t *abs_time, u32 bitset, int clockrt)

  {

  	struct task_struct *curr = current;

  	struct restart_block *restart;

  	DECLARE_WAITQUEUE(wait, curr);

  	struct futex_hash_bucket *hb;

  	struct futex_q q;

  	u32 uval;
  	int ret;

  	struct hrtimer_sleeper t;

  	int rem = 0;

  	if (!bitset)
  		return -EINVAL;

  	q.pi_state = NULL;

  	q.bitset = bitset;

  retry:

  	q.key = FUTEX_KEY_INIT;

  	ret = get_futex_key(uaddr, fshared, &q.key);

  	if (unlikely(ret != 0))

  		goto out;

  	hb = queue_lock(&q);

  
  	/*
  	 * Access the page AFTER the futex is queued.
  	 * Order is important:
  	 *
  	 *   Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
  	 *   Userspace waker:  if (cond(var)) { var = new; futex_wake(&var); }
  	 *
  	 * The basic logical guarantee of a futex is that it blocks ONLY
  	 * if cond(var) is known to be true at the time of blocking, for
  	 * any cond.  If we queued after testing *uaddr, that would open
  	 * a race condition where we could block indefinitely with
  	 * cond(var) false, which would violate the guarantee.
  	 *
  	 * A consequence is that futex_wait() can return zero and absorb
  	 * a wakeup when *uaddr != val on entry to the syscall.  This is
  	 * rare, but normal.
  	 *

  	 * for shared futexes, we hold the mmap semaphore, so the mapping
  	 * cannot have changed since we looked it up in get_futex_key.

  	 */

  	ret = get_futex_value_locked(&uval, uaddr);

  
  	if (unlikely(ret)) {

  		queue_unlock(&q, hb);

  		put_futex_key(fshared, &q.key);

  		ret = get_user(uval, uaddr);

  
  		if (!ret)
  			goto retry;

  		goto out;

  	}

  	ret = -EWOULDBLOCK;

  	if (unlikely(uval != val)) {
  		queue_unlock(&q, hb);
  		goto out_put_key;
  	}

  
  	/* Only actually queue if *uaddr contained val.  */

  	queue_me(&q, hb);

  
  	/*

  	 * There might have been scheduling since the queue_me(), as we
  	 * cannot hold a spinlock across the get_user() in case it
  	 * faults, and we cannot just set TASK_INTERRUPTIBLE state when
  	 * queueing ourselves into the futex hash.  This code thus has to
  	 * rely on the futex_wake() code removing us from hash when it
  	 * wakes us up.
  	 */
  
  	/* add_wait_queue is the barrier after __set_current_state. */
  	__set_current_state(TASK_INTERRUPTIBLE);

  	add_wait_queue(&q.waiter, &wait);

  	/*

  	 * !plist_node_empty() is safe here without any lock.

  	 * q.lock_ptr != 0 is not safe, because of ordering against wakeup.
  	 */

  	if (likely(!plist_node_empty(&q.list))) {

  		if (!abs_time)
  			schedule();
  		else {

  			unsigned long slack;
  			slack = current->timer_slack_ns;
  			if (rt_task(current))
  				slack = 0;

  			hrtimer_init_on_stack(&t.timer,
  					      clockrt ? CLOCK_REALTIME :
  					      CLOCK_MONOTONIC,
  					      HRTIMER_MODE_ABS);

  			hrtimer_init_sleeper(&t, current);

  			hrtimer_set_expires_range_ns(&t.timer, *abs_time, slack);

  			hrtimer_start_expires(&t.timer, HRTIMER_MODE_ABS);

  			if (!hrtimer_active(&t.timer))
  				t.task = NULL;

  
  			/*
  			 * the timer could have already expired, in which
  			 * case current would be flagged for rescheduling.
  			 * Don't bother calling schedule.
  			 */
  			if (likely(t.task))
  				schedule();
  
  			hrtimer_cancel(&t.timer);

  			/* Flag if a timeout occured */
  			rem = (t.task == NULL);

  
  			destroy_hrtimer_on_stack(&t.timer);

  		}

  	}

  	__set_current_state(TASK_RUNNING);
  
  	/*
  	 * NOTE: we don't remove ourselves from the waitqueue because
  	 * we are the only user of it.
  	 */
  
  	/* If we were woken (and unqueued), we succeeded, whatever. */

  	ret = 0;

  	if (!unqueue_me(&q))

  		goto out_put_key;
  	ret = -ETIMEDOUT;

  	if (rem)

  		goto out_put_key;

  	/*
  	 * We expect signal_pending(current), but another thread may
  	 * have handled it for us already.
  	 */

  	ret = -ERESTARTSYS;

  	if (!abs_time)

  		goto out_put_key;

  	restart = &current_thread_info()->restart_block;
  	restart->fn = futex_wait_restart;
  	restart->futex.uaddr = (u32 *)uaddr;
  	restart->futex.val = val;
  	restart->futex.time = abs_time->tv64;
  	restart->futex.bitset = bitset;
  	restart->futex.flags = 0;
  
  	if (fshared)
  		restart->futex.flags |= FLAGS_SHARED;
  	if (clockrt)
  		restart->futex.flags |= FLAGS_CLOCKRT;

  	ret = -ERESTART_RESTARTBLOCK;
  
  out_put_key:
  	put_futex_key(fshared, &q.key);

  out:

  	return ret;
  }

  
  static long futex_wait_restart(struct restart_block *restart)
  {

  	u32 __user *uaddr = (u32 __user *)restart->futex.uaddr;

  	int fshared = 0;

  	ktime_t t;

  	t.tv64 = restart->futex.time;

  	restart->fn = do_no_restart_syscall;

  	if (restart->futex.flags & FLAGS_SHARED)

  		fshared = 1;

  	return (long)futex_wait(uaddr, fshared, restart->futex.val, &t,

  				restart->futex.bitset,
  				restart->futex.flags & FLAGS_CLOCKRT);

  }

  /*
   * Userspace tried a 0 -> TID atomic transition of the futex value
   * and failed. The kernel side here does the whole locking operation:
   * if there are waiters then it will block, it does PI, etc. (Due to
   * races the kernel might see a 0 value of the futex too.)
   */

  static int futex_lock_pi(u32 __user *uaddr, int fshared,

  			 int detect, ktime_t *time, int trylock)

  {

  	struct hrtimer_sleeper timeout, *to = NULL;

  	struct task_struct *curr = current;
  	struct futex_hash_bucket *hb;
  	u32 uval, newval, curval;
  	struct futex_q q;

  	int ret, lock_taken, ownerdied = 0, attempt = 0;

  
  	if (refill_pi_state_cache())
  		return -ENOMEM;

  	if (time) {

  		to = &timeout;

  		hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
  				      HRTIMER_MODE_ABS);

  		hrtimer_init_sleeper(to, current);

  		hrtimer_set_expires(&to->timer, *time);

  	}

  	q.pi_state = NULL;

  retry:

  	q.key = FUTEX_KEY_INIT;

  	ret = get_futex_key(uaddr, fshared, &q.key);

  	if (unlikely(ret != 0))

  		goto out;

  retry_unlocked:

  	hb = queue_lock(&q);

  retry_locked:

  	ret = lock_taken = 0;

  	/*
  	 * To avoid races, we attempt to take the lock here again
  	 * (by doing a 0 -> TID atomic cmpxchg), while holding all
  	 * the locks. It will most likely not succeed.
  	 */

  	newval = task_pid_vnr(current);

  	curval = cmpxchg_futex_value_locked(uaddr, 0, newval);

  
  	if (unlikely(curval == -EFAULT))
  		goto uaddr_faulted;

  	/*
  	 * Detect deadlocks. In case of REQUEUE_PI this is a valid
  	 * situation and we return success to user space.
  	 */

  	if (unlikely((curval & FUTEX_TID_MASK) == task_pid_vnr(current))) {

  		ret = -EDEADLK;

  		goto out_unlock_put_key;

  	}
  
  	/*

  	 * Surprise - we got the lock. Just return to userspace:

  	 */
  	if (unlikely(!curval))

  		goto out_unlock_put_key;

  
  	uval = curval;

  	/*

  	 * Set the WAITERS flag, so the owner will know it has someone
  	 * to wake at next unlock

  	 */

  	newval = curval | FUTEX_WAITERS;
  
  	/*
  	 * There are two cases, where a futex might have no owner (the

  	 * owner TID is 0): OWNER_DIED. We take over the futex in this
  	 * case. We also do an unconditional take over, when the owner
  	 * of the futex died.

  	 *
  	 * This is safe as we are protected by the hash bucket lock !
  	 */
  	if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {

  		/* Keep the OWNER_DIED bit */

  		newval = (curval & ~FUTEX_TID_MASK) | task_pid_vnr(current);

  		ownerdied = 0;
  		lock_taken = 1;
  	}

  	curval = cmpxchg_futex_value_locked(uaddr, uval, newval);

  
  	if (unlikely(curval == -EFAULT))
  		goto uaddr_faulted;
  	if (unlikely(curval != uval))
  		goto retry_locked;

  	/*

  	 * We took the lock due to owner died take over.

  	 */

  	if (unlikely(lock_taken))

  		goto out_unlock_put_key;

  	/*
  	 * We dont have the lock. Look up the PI state (or create it if
  	 * we are the first waiter):
  	 */

  	ret = lookup_pi_state(uval, hb, &q.key, &q.pi_state);

  
  	if (unlikely(ret)) {

  		switch (ret) {

  		case -EAGAIN:
  			/*
  			 * Task is exiting and we just wait for the
  			 * exit to complete.
  			 */
  			queue_unlock(&q, hb);

  			cond_resched();
  			goto retry;

  		case -ESRCH:
  			/*
  			 * No owner found for this futex. Check if the
  			 * OWNER_DIED bit is set to figure out whether
  			 * this is a robust futex or not.
  			 */
  			if (get_futex_value_locked(&curval, uaddr))

  				goto uaddr_faulted;

  
  			/*
  			 * We simply start over in case of a robust
  			 * futex. The code above will take the futex
  			 * and return happy.
  			 */
  			if (curval & FUTEX_OWNER_DIED) {
  				ownerdied = 1;

  				goto retry_locked;

  			}
  		default:

  			goto out_unlock_put_key;

  		}

  	}
  
  	/*
  	 * Only actually queue now that the atomic ops are done:
  	 */

  	queue_me(&q, hb);

  	WARN_ON(!q.pi_state);
  	/*
  	 * Block on the PI mutex:
  	 */
  	if (!trylock)
  		ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
  	else {
  		ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
  		/* Fixup the trylock return value: */
  		ret = ret ? 0 : -EWOULDBLOCK;
  	}

  	spin_lock(q.lock_ptr);

  	if (!ret) {
  		/*
  		 * Got the lock. We might not be the anticipated owner
  		 * if we did a lock-steal - fix up the PI-state in
  		 * that case:
  		 */
  		if (q.pi_state->owner != curr)

  			ret = fixup_pi_state_owner(uaddr, &q, curr, fshared);

  	} else {

  		/*
  		 * Catch the rare case, where the lock was released

  		 * when we were on the way back before we locked the
  		 * hash bucket.

  		 */

  		if (q.pi_state->owner == curr) {
  			/*
  			 * Try to get the rt_mutex now. This might
  			 * fail as some other task acquired the
  			 * rt_mutex after we removed ourself from the
  			 * rt_mutex waiters list.
  			 */
  			if (rt_mutex_trylock(&q.pi_state->pi_mutex))
  				ret = 0;
  			else {
  				/*
  				 * pi_state is incorrect, some other
  				 * task did a lock steal and we
  				 * returned due to timeout or signal
  				 * without taking the rt_mutex. Too
  				 * late. We can access the
  				 * rt_mutex_owner without locking, as
  				 * the other task is now blocked on
  				 * the hash bucket lock. Fix the state
  				 * up.
  				 */
  				struct task_struct *owner;
  				int res;
  
  				owner = rt_mutex_owner(&q.pi_state->pi_mutex);

  				res = fixup_pi_state_owner(uaddr, &q, owner,
  							   fshared);

  				/* propagate -EFAULT, if the fixup failed */
  				if (res)
  					ret = res;
  			}

  		} else {
  			/*
  			 * Paranoia check. If we did not take the lock
  			 * in the trylock above, then we should not be
  			 * the owner of the rtmutex, neither the real
  			 * nor the pending one:
  			 */
  			if (rt_mutex_owner(&q.pi_state->pi_mutex) == curr)
  				printk(KERN_ERR "futex_lock_pi: ret = %d "
  				       "pi-mutex: %p pi-state %p
  ", ret,
  				       q.pi_state->pi_mutex.owner,
  				       q.pi_state->owner);

  		}

  	}

  	/* Unqueue and drop the lock */
  	unqueue_me_pi(&q);

  	if (to)
  		destroy_hrtimer_on_stack(&to->timer);

  	return ret != -EINTR ? ret : -ERESTARTNOINTR;

  out_unlock_put_key:

  	queue_unlock(&q, hb);

  out_put_key:

  	put_futex_key(fshared, &q.key);

  out:

  	if (to)
  		destroy_hrtimer_on_stack(&to->timer);

  	return ret;

  uaddr_faulted:

  	/*

  	 * We have to r/w  *(int __user *)uaddr, and we have to modify it
  	 * atomically.  Therefore, if we continue to fault after get_user()
  	 * below, we need to handle the fault ourselves, while still holding
  	 * the mmap_sem.  This can occur if the uaddr is under contention as
  	 * we have to drop the mmap_sem in order to call get_user().

  	 */

  	queue_unlock(&q, hb);

  	if (attempt++) {

  		ret = futex_handle_fault((unsigned long)uaddr, attempt);

  		if (ret)

  			goto out_put_key;

  		goto retry_unlocked;

  	}

  	ret = get_user(uval, uaddr);

  	if (!ret)

  		goto retry;

  	if (to)
  		destroy_hrtimer_on_stack(&to->timer);

  	return ret;
  }
  
  /*

   * Userspace attempted a TID -> 0 atomic transition, and failed.
   * This is the in-kernel slowpath: we look up the PI state (if any),
   * and do the rt-mutex unlock.
   */

  static int futex_unlock_pi(u32 __user *uaddr, int fshared)

  {
  	struct futex_hash_bucket *hb;
  	struct futex_q *this, *next;
  	u32 uval;

  	struct plist_head *head;

  	union futex_key key = FUTEX_KEY_INIT;

  	int ret, attempt = 0;
  
  retry:
  	if (get_user(uval, uaddr))
  		return -EFAULT;
  	/*
  	 * We release only a lock we actually own:
  	 */

  	if ((uval & FUTEX_TID_MASK) != task_pid_vnr(current))

  		return -EPERM;

  	ret = get_futex_key(uaddr, fshared, &key);

  	if (unlikely(ret != 0))
  		goto out;
  
  	hb = hash_futex(&key);

  retry_unlocked:

  	spin_lock(&hb->lock);

  	/*
  	 * To avoid races, try to do the TID -> 0 atomic transition
  	 * again. If it succeeds then we can return without waking
  	 * anyone else up:
  	 */

  	if (!(uval & FUTEX_OWNER_DIED))

  		uval = cmpxchg_futex_value_locked(uaddr, task_pid_vnr(current), 0);

  
  	if (unlikely(uval == -EFAULT))
  		goto pi_faulted;
  	/*
  	 * Rare case: we managed to release the lock atomically,
  	 * no need to wake anyone else up:
  	 */

  	if (unlikely(uval == task_pid_vnr(current)))

  		goto out_unlock;
  
  	/*
  	 * Ok, other tasks may need to be woken up - check waiters
  	 * and do the wakeup if necessary:
  	 */
  	head = &hb->chain;

  	plist_for_each_entry_safe(this, next, head, list) {

  		if (!match_futex (&this->key, &key))
  			continue;
  		ret = wake_futex_pi(uaddr, uval, this);
  		/*
  		 * The atomic access to the futex value
  		 * generated a pagefault, so retry the
  		 * user-access and the wakeup:
  		 */
  		if (ret == -EFAULT)
  			goto pi_faulted;
  		goto out_unlock;
  	}
  	/*
  	 * No waiters - kernel unlocks the futex:
  	 */

  	if (!(uval & FUTEX_OWNER_DIED)) {
  		ret = unlock_futex_pi(uaddr, uval);
  		if (ret == -EFAULT)
  			goto pi_faulted;
  	}

  
  out_unlock:
  	spin_unlock(&hb->lock);

  	put_futex_key(fshared, &key);

  out:

  	return ret;
  
  pi_faulted:
  	/*

  	 * We have to r/w  *(int __user *)uaddr, and we have to modify it
  	 * atomically.  Therefore, if we continue to fault after get_user()
  	 * below, we need to handle the fault ourselves, while still holding
  	 * the mmap_sem.  This can occur if the uaddr is under contention as
  	 * we have to drop the mmap_sem in order to call get_user().