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futex.c

/*
 *  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>
 *
 *  Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
 *  Copyright (C) IBM Corporation, 2009
 *  Thanks to Thomas Gleixner for conceptual design and careful reviews.
 *
 *  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:
 */
00074 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.
 */
00101 struct futex_q {
      struct plist_node list;
      /* Waiter reference */
      struct task_struct *task;

      /* 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;

      /* rt_waiter storage for requeue_pi: */
      struct rt_mutex_waiter *rt_waiter;

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

/*
 * Hash buckets are shared by all the futex_keys that hash to the same
 * location.  Each key may have multiple futex_q structures, one for each task
 * waiting on a futex.
 */
00127 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
 * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
 * @key: address where result is stored.
 * @rw: mapping needs to be read/write (values: VERIFY_READ, VERIFY_WRITE)
 *
 * 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.
 *
 * lock_page() might sleep, the caller should not hold a spinlock.
 */
static int
get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
{
      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(rw, 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, rw == VERIFY_WRITE, &page);
      if (err < 0)
            return err;

      page = compound_head(page);
      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);
}

/*
 * fault_in_user_writeable - fault in user address and verify RW access
 * @uaddr:  pointer to faulting user space address
 *
 * Slow path to fixup the fault we just took in the atomic write
 * access to @uaddr.
 *
 * We have no generic implementation of a non destructive write to the
 * user address. We know that we faulted in the atomic pagefault
 * disabled section so we can as well avoid the #PF overhead by
 * calling get_user_pages() right away.
 */
static int fault_in_user_writeable(u32 __user *uaddr)
{
      int ret = get_user_pages(current, current->mm, (unsigned long)uaddr,
                         1, 1, 0, NULL, NULL);
      return ret < 0 ? ret : 0;
}

/**
 * futex_top_waiter() - Return the highest priority waiter on a futex
 * @hb:     the hash bucket the futex_q's reside in
 * @key:    the futex key (to distinguish it from other futex futex_q's)
 *
 * Must be called with the hb lock held.
 */
static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
                              union futex_key *key)
{
      struct futex_q *this;

      plist_for_each_entry(this, &hb->chain, list) {
            if (match_futex(&this->key, key))
                  return this;
      }
      return NULL;
}

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;
}


/*
 * 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;
}

/**
 * futex_lock_pi_atomic() - atomic work required to acquire a pi aware futex
 * @uaddr:        the pi futex user address
 * @hb:                 the pi futex hash bucket
 * @key:          the futex key associated with uaddr and hb
 * @ps:                 the pi_state pointer where we store the result of the
 *                lookup
 * @task:         the task to perform the atomic lock work for.  This will
 *                be "current" except in the case of requeue pi.
 * @set_waiters:  force setting the FUTEX_WAITERS bit (1) or not (0)
 *
 * Returns:
 *  0 - ready to wait
 *  1 - acquired the lock
 * <0 - error
 *
 * The hb->lock and futex_key refs shall be held by the caller.
 */
static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
                        union futex_key *key,
                        struct futex_pi_state **ps,
                        struct task_struct *task, int set_waiters)
{
      int lock_taken, ret, ownerdied = 0;
      u32 uval, newval, curval;

retry:
      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(task);
      if (set_waiters)
            newval |= FUTEX_WAITERS;

      curval = cmpxchg_futex_value_locked(uaddr, 0, newval);

      if (unlikely(curval == -EFAULT))
            return -EFAULT;

      /*
       * Detect deadlocks.
       */
      if ((unlikely((curval & FUTEX_TID_MASK) == task_pid_vnr(task))))
            return -EDEADLK;

      /*
       * Surprise - we got the lock. Just return to userspace:
       */
      if (unlikely(!curval))
            return 1;

      uval = curval;

      /*
       * Set the FUTEX_WAITERS flag, so the owner will know it has someone
       * to wake at the 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(task);
            ownerdied = 0;
            lock_taken = 1;
      }

      curval = cmpxchg_futex_value_locked(uaddr, uval, newval);

      if (unlikely(curval == -EFAULT))
            return -EFAULT;
      if (unlikely(curval != uval))
            goto retry;

      /*
       * We took the lock due to owner died take over.
       */
      if (unlikely(lock_taken))
            return 1;

      /*
       * 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, key, ps);

      if (unlikely(ret)) {
            switch (ret) {
            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))
                        return -EFAULT;

                  /*
                   * 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;
                  }
            default:
                  break;
            }
      }

      return ret;
}

/*
 * 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)
{
      struct task_struct *p = q->task;

      /*
       * We set q->lock_ptr = NULL _before_ we wake up the task. If
       * a non futex wake up happens on another CPU then the task
       * might exit and p would dereference a non existing task
       * struct. Prevent this by holding a reference on p across the
       * wake up.
       */
      get_task_struct(p);

      plist_del(&q->list, &q->list.plist);
      /*
       * The waiting task can free the futex_q as soon as
       * q->lock_ptr = NULL is written, without taking any locks. A
       * memory barrier is required here to prevent the following
       * store to lock_ptr from getting ahead of the plist_del.
       */
      smp_wmb();
      q->lock_ptr = NULL;

      wake_up_state(p, TASK_NORMAL);
      put_task_struct(p);
}

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);
      }
}

static inline void
double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
{
      spin_unlock(&hb1->lock);
      if (hb1 != hb2)
            spin_unlock(&hb2->lock);
}

/*
 * Wake up waiters matching bitset queued on this futex (uaddr).
 */
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, VERIFY_READ);
      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 || this->rt_waiter) {
                        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;

retry:
      ret = get_futex_key(uaddr1, fshared, &key1, VERIFY_READ);
      if (unlikely(ret != 0))
            goto out;
      ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE);
      if (unlikely(ret != 0))
            goto out_put_key1;

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

      double_lock_hb(hb1, hb2);
retry_private:
      op_ret = futex_atomic_op_inuser(op, uaddr2);
      if (unlikely(op_ret < 0)) {

            double_unlock_hb(hb1, hb2);

#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;
            }

            ret = fault_in_user_writeable(uaddr2);
            if (ret)
                  goto out_put_keys;

            if (!fshared)
                  goto retry_private;

            put_futex_key(fshared, &key2);
            put_futex_key(fshared, &key1);
            goto retry;
      }

      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;
      }

      double_unlock_hb(hb1, hb2);
out_put_keys:
      put_futex_key(fshared, &key2);
out_put_key1:
      put_futex_key(fshared, &key1);
out:
      return ret;
}

/**
 * requeue_futex() - Requeue a futex_q from one hb to another
 * @q:            the futex_q to requeue
 * @hb1:    the source hash_bucket
 * @hb2:    the target hash_bucket
 * @key2:   the new key for the requeued futex_q
 */
static inline
void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
               struct futex_hash_bucket *hb2, union futex_key *key2)
{

      /*
       * If key1 and key2 hash to the same bucket, no need to
       * requeue.
       */
      if (likely(&hb1->chain != &hb2->chain)) {
            plist_del(&q->list, &hb1->chain);
            plist_add(&q->list, &hb2->chain);
            q->lock_ptr = &hb2->lock;
#ifdef CONFIG_DEBUG_PI_LIST
            q->list.plist.lock = &hb2->lock;
#endif
      }
      get_futex_key_refs(key2);
      q->key = *key2;
}

/**
 * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
 * q: the futex_q
 * key:     the key of the requeue target futex
 * hb:  the hash_bucket of the requeue target futex
 *
 * During futex_requeue, with requeue_pi=1, it is possible to acquire the
 * target futex if it is uncontended or via a lock steal.  Set the futex_q key
 * to the requeue target futex so the waiter can detect the wakeup on the right
 * futex, but remove it from the hb and NULL the rt_waiter so it can detect
 * atomic lock acquisition.  Set the q->lock_ptr to the requeue target hb->lock
 * to protect access to the pi_state to fixup the owner later.  Must be called
 * with both q->lock_ptr and hb->lock held.
 */
static inline
void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
                     struct futex_hash_bucket *hb)
{
      drop_futex_key_refs(&q->key);
      get_futex_key_refs(key);
      q->key = *key;

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

      WARN_ON(!q->rt_waiter);
      q->rt_waiter = NULL;

      q->lock_ptr = &hb->lock;
#ifdef CONFIG_DEBUG_PI_LIST
      q->list.plist.lock = &hb->lock;
#endif

      wake_up_state(q->task, TASK_NORMAL);
}

/**
 * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
 * @pifutex:            the user address of the to futex
 * @hb1:          the from futex hash bucket, must be locked by the caller
 * @hb2:          the to futex hash bucket, must be locked by the caller
 * @key1:         the from futex key
 * @key2:         the to futex key
 * @ps:                 address to store the pi_state pointer
 * @set_waiters:  force setting the FUTEX_WAITERS bit (1) or not (0)
 *
 * Try and get the lock on behalf of the top waiter if we can do it atomically.
 * Wake the top waiter if we succeed.  If the caller specified set_waiters,
 * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
 * hb1 and hb2 must be held by the caller.
 *
 * Returns:
 *  0 - failed to acquire the lock atomicly
 *  1 - acquired the lock
 * <0 - error
 */
static int futex_proxy_trylock_atomic(u32 __user *pifutex,
                         struct futex_hash_bucket *hb1,
                         struct futex_hash_bucket *hb2,
                         union futex_key *key1, union futex_key *key2,
                         struct futex_pi_state **ps, int set_waiters)
{
      struct futex_q *top_waiter = NULL;
      u32 curval;
      int ret;

      if (get_futex_value_locked(&curval, pifutex))
            return -EFAULT;

      /*
       * Find the top_waiter and determine if there are additional waiters.
       * If the caller intends to requeue more than 1 waiter to pifutex,
       * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
       * as we have means to handle the possible fault.  If not, don't set
       * the bit unecessarily as it will force the subsequent unlock to enter
       * the kernel.
       */
      top_waiter = futex_top_waiter(hb1, key1);

      /* There are no waiters, nothing for us to do. */
      if (!top_waiter)
            return 0;

      /*
       * Try to take the lock for top_waiter.  Set the FUTEX_WAITERS bit in
       * the contended case or if set_waiters is 1.  The pi_state is returned
       * in ps in contended cases.
       */
      ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
                           set_waiters);
      if (ret == 1)
            requeue_pi_wake_futex(top_waiter, key2, hb2);

      return ret;
}

/**
 * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
 * uaddr1:  source futex user address
 * uaddr2:  target futex user address
 * nr_wake: number of waiters to wake (must be 1 for requeue_pi)
 * nr_requeue:    number of waiters to requeue (0-INT_MAX)
 * requeue_pi:    if we are attempting to requeue from a non-pi futex to a
 *          pi futex (pi to pi requeue is not supported)
 *
 * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
 * uaddr2 atomically on behalf of the top waiter.
 *
 * Returns:
 * >=0 - on success, the number of tasks requeued or woken
 *  <0 - on error
 */
static int futex_requeue(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
                   int nr_wake, int nr_requeue, u32 *cmpval,
                   int requeue_pi)
{
      union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
      int drop_count = 0, task_count = 0, ret;
      struct futex_pi_state *pi_state = NULL;
      struct futex_hash_bucket *hb1, *hb2;
      struct plist_head *head1;
      struct futex_q *this, *next;
      u32 curval2;

      if (requeue_pi) {
            /*
             * requeue_pi requires a pi_state, try to allocate it now
             * without any locks in case it fails.
             */
            if (refill_pi_state_cache())
                  return -ENOMEM;
            /*
             * requeue_pi must wake as many tasks as it can, up to nr_wake
             * + nr_requeue, since it acquires the rt_mutex prior to
             * returning to userspace, so as to not leave the rt_mutex with
             * waiters and no owner.  However, second and third wake-ups
             * cannot be predicted as they involve race conditions with the
             * first wake and a fault while looking up the pi_state.  Both
             * pthread_cond_signal() and pthread_cond_broadcast() should
             * use nr_wake=1.
             */
            if (nr_wake != 1)
                  return -EINVAL;
      }

retry:
      if (pi_state != NULL) {
            /*
             * We will have to lookup the pi_state again, so free this one
             * to keep the accounting correct.
             */
            free_pi_state(pi_state);
            pi_state = NULL;
      }

      ret = get_futex_key(uaddr1, fshared, &key1, VERIFY_READ);
      if (unlikely(ret != 0))
            goto out;
      ret = get_futex_key(uaddr2, fshared, &key2,
                      requeue_pi ? VERIFY_WRITE : VERIFY_READ);
      if (unlikely(ret != 0))
            goto out_put_key1;

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

retry_private:
      double_lock_hb(hb1, hb2);

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

            ret = get_futex_value_locked(&curval, uaddr1);

            if (unlikely(ret)) {
                  double_unlock_hb(hb1, hb2);

                  ret = get_user(curval, uaddr1);
                  if (ret)
                        goto out_put_keys;

                  if (!fshared)
                        goto retry_private;

                  put_futex_key(fshared, &key2);
                  put_futex_key(fshared, &key1);
                  goto retry;
            }
            if (curval != *cmpval) {
                  ret = -EAGAIN;
                  goto out_unlock;
            }
      }

      if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
            /*
             * Attempt to acquire uaddr2 and wake the top waiter. If we
             * intend to requeue waiters, force setting the FUTEX_WAITERS
             * bit.  We force this here where we are able to easily handle
             * faults rather in the requeue loop below.
             */
            ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
                                     &key2, &pi_state, nr_requeue);

            /*
             * At this point the top_waiter has either taken uaddr2 or is
             * waiting on it.  If the former, then the pi_state will not
             * exist yet, look it up one more time to ensure we have a
             * reference to it.
             */
            if (ret == 1) {
                  WARN_ON(pi_state);
                  task_count++;
                  ret = get_futex_value_locked(&curval2, uaddr2);
                  if (!ret)
                        ret = lookup_pi_state(curval2, hb2, &key2,
                                          &pi_state);
            }

            switch (ret) {
            case 0:
                  break;
            case -EFAULT:
                  double_unlock_hb(hb1, hb2);
                  put_futex_key(fshared, &key2);
                  put_futex_key(fshared, &key1);
                  ret = fault_in_user_writeable(uaddr2);
                  if (!ret)
                        goto retry;
                  goto out;
            case -EAGAIN:
                  /* The owner was exiting, try again. */
                  double_unlock_hb(hb1, hb2);
                  put_futex_key(fshared, &key2);
                  put_futex_key(fshared, &key1);
                  cond_resched();
                  goto retry;
            default:
                  goto out_unlock;
            }
      }

      head1 = &hb1->chain;
      plist_for_each_entry_safe(this, next, head1, list) {
            if (task_count - nr_wake >= nr_requeue)
                  break;

            if (!match_futex(&this->key, &key1))
                  continue;

            /*
             * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
             * be paired with each other and no other futex ops.
             */
            if ((requeue_pi && !this->rt_waiter) ||
                (!requeue_pi && this->rt_waiter)) {
                  ret = -EINVAL;
                  break;
            }

            /*
             * Wake nr_wake waiters.  For requeue_pi, if we acquired the
             * lock, we already woke the top_waiter.  If not, it will be
             * woken by futex_unlock_pi().
             */
            if (++task_count <= nr_wake && !requeue_pi) {
                  wake_futex(this);
                  continue;
            }

            /*
             * Requeue nr_requeue waiters and possibly one more in the case
             * of requeue_pi if we couldn't acquire the lock atomically.
             */
            if (requeue_pi) {
                  /* Prepare the waiter to take the rt_mutex. */
                  atomic_inc(&pi_state->refcount);
                  this->pi_state = pi_state;
                  ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
                                          this->rt_waiter,
                                          this->task, 1);
                  if (ret == 1) {
                        /* We got the lock. */
                        requeue_pi_wake_futex(this, &key2, hb2);
                        continue;
                  } else if (ret) {
                        /* -EDEADLK */
                        this->pi_state = NULL;
                        free_pi_state(pi_state);
                        goto out_unlock;
                  }
            }
            requeue_futex(this, hb1, hb2, &key2);
            drop_count++;
      }

out_unlock:
      double_unlock_hb(hb1, hb2);

      /*
       * drop_futex_key_refs() must be called outside the spinlocks. During
       * the requeue we moved futex_q's from the hash bucket at key1 to the
       * one at key2 and updated their key pointer.  We no longer need to
       * hold the references to key1.
       */
      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:
      if (pi_state != NULL)
            free_pi_state(pi_state);
      return ret ? ret : task_count;
}

/* 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;

      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;

      /* 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
       * 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 = fault_in_user_writeable(uaddr);

      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
#define FLAGS_HAS_TIMEOUT     0x04

static long futex_wait_restart(struct restart_block *restart);

/**
 * fixup_owner() - Post lock pi_state and corner case management
 * @uaddr:  user address of the futex
 * @fshared:      whether the futex is shared (1) or not (0)
 * @q:            futex_q (contains pi_state and access to the rt_mutex)
 * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
 *
 * After attempting to lock an rt_mutex, this function is called to cleanup
 * the pi_state owner as well as handle race conditions that may allow us to
 * acquire the lock. Must be called with the hb lock held.
 *
 * Returns:
 *  1 - success, lock taken
 *  0 - success, lock not taken
 * <0 - on error (-EFAULT)
 */
static int fixup_owner(u32 __user *uaddr, int fshared, struct futex_q *q,
                   int locked)
{
      struct task_struct *owner;
      int ret = 0;

      if (locked) {
            /*
             * 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 != current)
                  ret = fixup_pi_state_owner(uaddr, q, current, fshared);
            goto out;
      }

      /*
       * 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 == current) {
            /*
             * 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)) {
                  locked = 1;
                  goto out;
            }

            /*
             * 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.
             */
            owner = rt_mutex_owner(&q->pi_state->pi_mutex);
            ret = fixup_pi_state_owner(uaddr, q, owner, fshared);
            goto out;
      }

      /*
       * Paranoia check. If we did not take the lock, then we should not be
       * the owner, nor the pending owner, of the rt_mutex.
       */
      if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
            printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
                        "pi-state %p\n", ret,
                        q->pi_state->pi_mutex.owner,
                        q->pi_state->owner);

out:
      return ret ? ret : locked;
}

/**
 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
 * @hb:           the futex hash bucket, must be locked by the caller
 * @q:            the futex_q to queue up on
 * @timeout:      the prepared hrtimer_sleeper, or null for no timeout
 */
static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
                        struct hrtimer_sleeper *timeout)
{
      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.
       */
      set_current_state(TASK_INTERRUPTIBLE);

      /* Arm the timer */
      if (timeout) {
            hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
            if (!hrtimer_active(&timeout->timer))
                  timeout->task = NULL;
      }

      /*
       * !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 the timer has already expired, current will already be
             * flagged for rescheduling. Only call schedule if there
             * is no timeout, or if it has yet to expire.
             */
            if (!timeout || timeout->task)
                  schedule();
      }
      __set_current_state(TASK_RUNNING);
}

/**
 * futex_wait_setup() - Prepare to wait on a futex
 * @uaddr:  the futex userspace address
 * @val:    the expected value
 * @fshared:      whether the futex is shared (1) or not (0)
 * @q:            the associated futex_q
 * @hb:           storage for hash_bucket pointer to be returned to caller
 *
 * Setup the futex_q and locate the hash_bucket.  Get the futex value and
 * compare it with the expected value.  Handle atomic faults internally.
 * Return with the hb lock held and a q.key reference on success, and unlocked
 * with no q.key reference on failure.
 *
 * Returns:
 *  0 - uaddr contains val and hb has been locked
 * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlcoked
 */
static int futex_wait_setup(u32 __user *uaddr, u32 val, int fshared,
                     struct futex_q *q, struct futex_hash_bucket **hb)
{
      u32 uval;
      int ret;

      /*
       * Access the page AFTER the hash-bucket is locked.
       * 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.
       */
retry:
      q->key = FUTEX_KEY_INIT;
      ret = get_futex_key(uaddr, fshared, &q->key, VERIFY_READ);
      if (unlikely(ret != 0))
            return ret;

retry_private:
      *hb = queue_lock(q);

      ret = get_futex_value_locked(&uval, uaddr);

      if (ret) {
            queue_unlock(q, *hb);

            ret = get_user(uval, uaddr);
            if (ret)
                  goto out;

            if (!fshared)
                  goto retry_private;

            put_futex_key(fshared, &q->key);
            goto retry;
      }

      if (uval != val) {
            queue_unlock(q, *hb);
            ret = -EWOULDBLOCK;
      }

out:
      if (ret)
            put_futex_key(fshared, &q->key);
      return ret;
}

static int futex_wait(u32 __user *uaddr, int fshared,
                  u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
{
      struct hrtimer_sleeper timeout, *to = NULL;
      struct restart_block *restart;
      struct futex_hash_bucket *hb;
      struct futex_q q;
      int ret;

      if (!bitset)
            return -EINVAL;

      q.pi_state = NULL;
      q.bitset = bitset;
      q.rt_waiter = NULL;

      if (abs_time) {
            to = &timeout;

            hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
                              CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
            hrtimer_init_sleeper(to, current);
            hrtimer_set_expires_range_ns(&to->timer, *abs_time,
                                   current->timer_slack_ns);
      }

      /* Prepare to wait on uaddr. */
      ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
      if (ret)
            goto out;

      /* queue_me and wait for wakeup, timeout, or a signal. */
      futex_wait_queue_me(hb, &q, to);

      /* If we were woken (and unqueued), we succeeded, whatever. */
      ret = 0;
      if (!unqueue_me(&q))
            goto out_put_key;
      ret = -ETIMEDOUT;
      if (to && !to->task)
            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 = FLAGS_HAS_TIMEOUT;

      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:
      if (to) {
            hrtimer_cancel(&to->timer);
            destroy_hrtimer_on_stack(&to->timer);
      }
      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, *tp = NULL;

      if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
            t.tv64 = restart->futex.time;
            tp = &t;
      }
      restart->fn = do_no_restart_syscall;
      if (restart->futex.flags & FLAGS_SHARED)
            fshared = 1;
      return (long)futex_wait(uaddr, fshared, restart->futex.val, tp,
                        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 futex_hash_bucket *hb;
      struct futex_q q;
      int res, ret;

      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;
      q.rt_waiter = NULL;
retry:
      q.key = FUTEX_KEY_INIT;
      ret = get_futex_key(uaddr, fshared, &q.key, VERIFY_WRITE);
      if (unlikely(ret != 0))
            goto out;

retry_private:
      hb = queue_lock(&q);

      ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
      if (unlikely(ret)) {
            switch (ret) {
            case 1:
                  /* We got the lock. */
                  ret = 0;
                  goto out_unlock_put_key;
            case -EFAULT:
                  goto uaddr_faulted;
            case -EAGAIN:
                  /*
                   * Task is exiting and we just wait for the
                   * exit to complete.
                   */
                  queue_unlock(&q, hb);
                  put_futex_key(fshared, &q.key);
                  cond_resched();
                  goto retry;
            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);
      /*
       * Fixup the pi_state owner and possibly acquire the lock if we
       * haven't already.
       */
      res = fixup_owner(uaddr, fshared, &q, !ret);
      /*
       * If fixup_owner() returned an error, proprogate that.  If it acquired
       * the lock, clear our -ETIMEDOUT or -EINTR.
       */
      if (res)
            ret = (res < 0) ? res : 0;

      /*
       * If fixup_owner() faulted and was unable to handle the fault, unlock
       * it and return the fault to userspace.
       */
      if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
            rt_mutex_unlock(&q.pi_state->pi_mutex);

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

      goto out;

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 != -EINTR ? ret : -ERESTARTNOINTR;

uaddr_faulted:
      queue_unlock(&q, hb);

      ret = fault_in_user_writeable(uaddr);
      if (ret)
            goto out_put_key;

      if (!fshared)
            goto retry_private;

      put_futex_key(fshared, &q.key);
      goto retry;
}

/*
 * 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;

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

      hb = hash_futex(&key);
      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:
      spin_unlock(&hb->lock);
      put_futex_key(fshared, &key);

      ret = fault_in_user_writeable(uaddr);
      if (!ret)
            goto retry;

      return ret;
}

/**
 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
 * @hb:           the hash_bucket futex_q was original enqueued on
 * @q:            the futex_q woken while waiting to be requeued
 * @key2:   the futex_key of the requeue target futex
 * @timeout:      the timeout associated with the wait (NULL if none)
 *
 * Detect if the task was woken on the initial futex as opposed to the requeue
 * target futex.  If so, determine if it was a timeout or a signal that caused
 * the wakeup and return the appropriate error code to the caller.  Must be
 * called with the hb lock held.
 *
 * Returns
 *  0 - no early wakeup detected
 * <0 - -ETIMEDOUT or -ERESTARTNOINTR
 */
static inline
int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
                           struct futex_q *q, union futex_key *key2,
                           struct hrtimer_sleeper *timeout)
{
      int ret = 0;

      /*
       * With the hb lock held, we avoid races while we process the wakeup.
       * We only need to hold hb (and not hb2) to ensure atomicity as the
       * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
       * It can't be requeued from uaddr2 to something else since we don't
       * support a PI aware source futex for requeue.
       */
      if (!match_futex(&q->key, key2)) {
            WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
            /*
             * We were woken prior to requeue by a timeout or a signal.
             * Unqueue the futex_q and determine which it was.
             */
            plist_del(&q->list, &q->list.plist);
            drop_futex_key_refs(&q->key);

            if (timeout && !timeout->task)
                  ret = -ETIMEDOUT;
            else
                  ret = -ERESTARTNOINTR;
      }
      return ret;
}

/**
 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
 * @uaddr:  the futex we initialyl wait on (non-pi)
 * @fshared:      whether the futexes are shared (1) or not (0).  They must be
 *          the same type, no requeueing from private to shared, etc.
 * @val:    the expected value of uaddr
 * @abs_time:     absolute timeout
 * @bitset: 32 bit wakeup bitset set by userspace, defaults to all.
 * @clockrt:      whether to use CLOCK_REALTIME (1) or CLOCK_MONOTONIC (0)
 * @uaddr2: the pi futex we will take prior to returning to user-space
 *
 * The caller will wait on uaddr and will be requeued by futex_requeue() to
 * uaddr2 which must be PI aware.  Normal wakeup will wake on uaddr2 and
 * complete the acquisition of the rt_mutex prior to returning to userspace.
 * This ensures the rt_mutex maintains an owner when it has waiters; without
 * one, the pi logic wouldn't know which task to boost/deboost, if there was a
 * need to.
 *
 * We call schedule in futex_wait_queue_me() when we enqueue and return there
 * via the following:
 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
 * 2) wakeup on uaddr2 after a requeue and subsequent unlock
 * 3) signal (before or after requeue)
 * 4) timeout (before or after requeue)
 *
 * If 3, we setup a restart_block with futex_wait_requeue_pi() as the function.
 *
 * If 2, we may then block on trying to take the rt_mutex and return via:
 * 5) successful lock
 * 6) signal
 * 7) timeout
 * 8) other lock acquisition failure
 *
 * If 6, we setup a restart_block with futex_lock_pi() as the function.
 *
 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
 *
 * Returns:
 *  0 - On success
 * <0 - On error
 */
static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
                         u32 val, ktime_t *abs_time, u32 bitset,
                         int clockrt, u32 __user *uaddr2)
{
      struct hrtimer_sleeper timeout, *to = NULL;
      struct rt_mutex_waiter rt_waiter;
      struct rt_mutex *pi_mutex = NULL;
      struct futex_hash_bucket *hb;
      union futex_key key2;
      struct futex_q q;
      int res, ret;

      if (!bitset)
            return -EINVAL;

      if (abs_time) {
            to = &timeout;
            hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
                              CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
            hrtimer_init_sleeper(to, current);
            hrtimer_set_expires_range_ns(&to->timer, *abs_time,
                                   current->timer_slack_ns);
      }

      /*
       * The waiter is allocated on our stack, manipulated by the requeue
       * code while we sleep on uaddr.
       */
      debug_rt_mutex_init_waiter(&rt_waiter);
      rt_waiter.task = NULL;

      q.pi_state = NULL;
      q.bitset = bitset;
      q.rt_waiter = &rt_waiter;

      key2 = FUTEX_KEY_INIT;
      ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE);
      if (unlikely(ret != 0))
            goto out;

      /* Prepare to wait on uaddr. */
      ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
      if (ret)
            goto out_key2;

      /* Queue the futex_q, drop the hb lock, wait for wakeup. */
      futex_wait_queue_me(hb, &q, to);

      spin_lock(&hb->lock);
      ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
      spin_unlock(&hb->lock);
      if (ret)
            goto out_put_keys;

      /*
       * In order for us to be here, we know our q.key == key2, and since
       * we took the hb->lock above, we also know that futex_requeue() has
       * completed and we no longer have to concern ourselves with a wakeup
       * race with the atomic proxy lock acquition by the requeue code.
       */

      /* Check if the requeue code acquired the second futex for us. */
      if (!q.rt_waiter) {
            /*
             * 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 && (q.pi_state->owner != current)) {
                  spin_lock(q.lock_ptr);
                  ret = fixup_pi_state_owner(uaddr2, &q, current,
                                       fshared);
                  spin_unlock(q.lock_ptr);
            }
      } else {
            /*
             * We have been woken up by futex_unlock_pi(), a timeout, or a
             * signal.  futex_unlock_pi() will not destroy the lock_ptr nor
             * the pi_state.
             */
            WARN_ON(!&q.pi_state);
            pi_mutex = &q.pi_state->pi_mutex;
            ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
            debug_rt_mutex_free_waiter(&rt_waiter);

            spin_lock(q.lock_ptr);
            /*
             * Fixup the pi_state owner and possibly acquire the lock if we
             * haven't already.
             */
            res = fixup_owner(uaddr2, fshared, &q, !ret);
            /*
             * If fixup_owner() returned an error, proprogate that.  If it
             * acquired the lock, clear our -ETIMEDOUT or -EINTR.
             */
            if (res)
                  ret = (res < 0) ? res : 0;

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

      /*
       * If fixup_pi_state_owner() faulted and was unable to handle the
       * fault, unlock the rt_mutex and return the fault to userspace.
       */
      if (ret == -EFAULT) {
            if (rt_mutex_owner(pi_mutex) == current)
                  rt_mutex_unlock(pi_mutex);
      } else if (ret == -EINTR) {
            /*
             * We've already been requeued, but we have no way to
             * restart by calling futex_lock_pi() directly. We
             * could restart the syscall, but that will look at
             * the user space value and return right away. So we
             * drop back with EWOULDBLOCK to tell user space that
             * "val" has been changed. That's the same what the
             * restart of the syscall would do in
             * futex_wait_setup().
             */
            ret = -EWOULDBLOCK;
      }

out_put_keys:
      put_futex_key(fshared, &q.key);
out_key2:
      put_futex_key(fshared, &key2);

out:
      if (to) {
            hrtimer_cancel(&to->timer);
            destroy_hrtimer_on_stack(&to->timer);
      }
      return ret;
}

/*
 * Support for robust futexes: the kernel cleans up held futexes at
 * thread exit time.
 *
 * Implementation: user-space maintains a per-thread list of locks it
 * is holding. Upon do_exit(), the kernel carefully walks this list,
 * and marks all locks that are owned by this thread with the
 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
 * always manipulated with the lock held, so the list is private and
 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
 * field, to allow the kernel to clean up if the thread dies after
 * acquiring the lock, but just before it could have added itself to
 * the list. There can only be one such pending lock.
 */

/**
 * sys_set_robust_list - set the robust-futex list head of a task
 * @head: pointer to the list-head
 * @len: length of the list-head, as userspace expects
 */
SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
            size_t, len)
{
      if (!futex_cmpxchg_enabled)
            return -ENOSYS;
      /*
       * The kernel knows only one size for now:
       */
      if (unlikely(len != sizeof(*head)))
            return -EINVAL;

      current->robust_list = head;

      return 0;
}

/**
 * sys_get_robust_list - get the robust-futex list head of a task
 * @pid: pid of the process [zero for current task]
 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
 * @len_ptr: pointer to a length field, the kernel fills in the header size
 */
SYSCALL_DEFINE3(get_robust_list, int, pid,
            struct robust_list_head __user * __user *, head_ptr,
            size_t __user *, len_ptr)
{
      struct robust_list_head __user *head;
      unsigned long ret;
      const struct cred *cred = current_cred(), *pcred;

      if (!futex_cmpxchg_enabled)
            return -ENOSYS;

      if (!pid)
            head = current->robust_list;
      else {
            struct task_struct *p;

            ret = -ESRCH;
            rcu_read_lock();
            p = find_task_by_vpid(pid);
            if (!p)
                  goto err_unlock;
            ret = -EPERM;
            pcred = __task_cred(p);
            if (cred->euid != pcred->euid &&
                cred->euid != pcred->uid &&
                !capable(CAP_SYS_PTRACE))
                  goto err_unlock;
            head = p->robust_list;
            rcu_read_unlock();
      }

      if (put_user(sizeof(*head), len_ptr))
            return -EFAULT;
      return put_user(head, head_ptr);

err_unlock:
      rcu_read_unlock();

      return ret;
}

/*
 * Process a futex-list entry, check whether it's owned by the
 * dying task, and do notification if so:
 */
int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
{
      u32 uval, nval, mval;

retry:
      if (get_user(uval, uaddr))
            return -1;

      if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
            /*
             * Ok, this dying thread is truly holding a futex
             * of interest. Set the OWNER_DIED bit atomically
             * via cmpxchg, and if the value had FUTEX_WAITERS
             * set, wake up a waiter (if any). (We have to do a
             * futex_wake() even if OWNER_DIED is already set -
             * to handle the rare but possible case of recursive
             * thread-death.) The rest of the cleanup is done in
             * userspace.
             */
            mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
            nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);

            if (nval == -EFAULT)
                  return -1;

            if (nval != uval)
                  goto retry;

            /*
             * Wake robust non-PI futexes here. The wakeup of
             * PI futexes happens in exit_pi_state():
             */
            if (!pi && (uval & FUTEX_WAITERS))
                  futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
      }
      return 0;
}

/*
 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
 */
static inline int fetch_robust_entry(struct robust_list __user **entry,
                             struct robust_list __user * __user *head,
                             int *pi)
{
      unsigned long uentry;

      if (get_user(uentry, (unsigned long __user *)head))
            return -EFAULT;

      *entry = (void __user *)(uentry & ~1UL);
      *pi = uentry & 1;

      return 0;
}

/*
 * Walk curr->robust_list (very carefully, it's a userspace list!)
 * and mark any locks found there dead, and notify any waiters.
 *
 * We silently return on any sign of list-walking problem.
 */
void exit_robust_list(struct task_struct *curr)
{
      struct robust_list_head __user *head = curr->robust_list;
      struct robust_list __user *entry, *next_entry, *pending;
      unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
      unsigned long futex_offset;
      int rc;

      if (!futex_cmpxchg_enabled)
            return;

      /*
       * Fetch the list head (which was registered earlier, via
       * sys_set_robust_list()):
       */
      if (fetch_robust_entry(&entry, &head->list.next, &pi))
            return;
      /*
       * Fetch the relative futex offset:
       */
      if (get_user(futex_offset, &head->futex_offset))
            return;
      /*
       * Fetch any possibly pending lock-add first, and handle it
       * if it exists:
       */
      if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
            return;

      next_entry = NULL;      /* avoid warning with gcc */
      while (entry != &head->list) {
            /*
             * Fetch the next entry in the list before calling
             * handle_futex_death:
             */
            rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
            /*
             * A pending lock might already be on the list, so
             * don't process it twice:
             */
            if (entry != pending)
                  if (handle_futex_death((void __user *)entry + futex_offset,
                                    curr, pi))
                        return;
            if (rc)
                  return;
            entry = next_entry;
            pi = next_pi;
            /*
             * Avoid excessively long or circular lists:
             */
            if (!--limit)
                  break;

            cond_resched();
      }

      if (pending)
            handle_futex_death((void __user *)pending + futex_offset,
                           curr, pip);
}

long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
            u32 __user *uaddr2, u32 val2, u32 val3)
{
      int clockrt, ret = -ENOSYS;
      int cmd = op & FUTEX_CMD_MASK;
      int fshared = 0;

      if (!(op & FUTEX_PRIVATE_FLAG))
            fshared = 1;

      clockrt = op & FUTEX_CLOCK_REALTIME;
      if (clockrt && cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
            return -ENOSYS;

      switch (cmd) {
      case FUTEX_WAIT:
            val3 = FUTEX_BITSET_MATCH_ANY;
      case FUTEX_WAIT_BITSET:
            ret = futex_wait(uaddr, fshared, val, timeout, val3, clockrt);
            break;
      case FUTEX_WAKE:
            val3 = FUTEX_BITSET_MATCH_ANY;
      case FUTEX_WAKE_BITSET:
            ret = futex_wake(uaddr, fshared, val, val3);
            break;
      case FUTEX_REQUEUE:
            ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL, 0);
            break;
      case FUTEX_CMP_REQUEUE:
            ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
                            0);
            break;
      case FUTEX_WAKE_OP:
            ret = futex_wake_op(uaddr, fshared, uaddr2, val, val2, val3);
            break;
      case FUTEX_LOCK_PI:
            if (futex_cmpxchg_enabled)
                  ret = futex_lock_pi(uaddr, fshared, val, timeout, 0);
            break;
      case FUTEX_UNLOCK_PI:
            if (futex_cmpxchg_enabled)
                  ret = futex_unlock_pi(uaddr, fshared);
            break;
      case FUTEX_TRYLOCK_PI:
            if (futex_cmpxchg_enabled)
                  ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1);
            break;
      case FUTEX_WAIT_REQUEUE_PI:
            val3 = FUTEX_BITSET_MATCH_ANY;
            ret = futex_wait_requeue_pi(uaddr, fshared, val, timeout, val3,
                                  clockrt, uaddr2);
            break;
      case FUTEX_CMP_REQUEUE_PI:
            ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
                            1);
            break;
      default:
            ret = -ENOSYS;
      }
      return ret;
}


SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
            struct timespec __user *, utime, u32 __user *, uaddr2,
            u32, val3)
{
      struct timespec ts;
      ktime_t t, *tp = NULL;
      u32 val2 = 0;
      int cmd = op & FUTEX_CMD_MASK;

      if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
                  cmd == FUTEX_WAIT_BITSET ||
                  cmd == FUTEX_WAIT_REQUEUE_PI)) {
            if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
                  return -EFAULT;
            if (!timespec_valid(&ts))
                  return -EINVAL;

            t = timespec_to_ktime(ts);
            if (cmd == FUTEX_WAIT)
                  t = ktime_add_safe(ktime_get(), t);
            tp = &t;
      }
      /*
       * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
       * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
       */
      if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
          cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
            val2 = (u32) (unsigned long) utime;

      return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
}

static int __init futex_init(void)
{
      u32 curval;
      int i;

      /*
       * This will fail and we want it. Some arch implementations do
       * runtime detection of the futex_atomic_cmpxchg_inatomic()
       * functionality. We want to know that before we call in any
       * of the complex code paths. Also we want to prevent
       * registration of robust lists in that case. NULL is
       * guaranteed to fault and we get -EFAULT on functional
       * implementation, the non functional ones will return
       * -ENOSYS.
       */
      curval = cmpxchg_futex_value_locked(NULL, 0, 0);
      if (curval == -EFAULT)
            futex_cmpxchg_enabled = 1;

      for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
            plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock);
            spin_lock_init(&futex_queues[i].lock);
      }

      return 0;
}
__initcall(futex_init);

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