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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>
 *
 *  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"

#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->waiters, then make the second condition true.
 */
struct futex_q {
      struct plist_node list;
      wait_queue_head_t waiters;

      /* Which hash list lock to use: */
      spinlock_t *lock_ptr;

      /* Key which the futex is hashed on: */
      union futex_key key;

      /* For fd, sigio sent using these: */
      int fd;
      struct file *filp;

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

/*
 * 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];

/* Futex-fs vfsmount entry: */
static struct vfsmount *futex_mnt;

/*
 * Take mm->mmap_sem, when futex is shared
 */
static inline void futex_lock_mm(struct rw_semaphore *fshared)
{
      if (fshared)
            down_read(fshared);
}

/*
 * Release mm->mmap_sem, when the futex is shared
 */
static inline void futex_unlock_mm(struct rw_semaphore *fshared)
{
      if (fshared)
            up_read(fshared);
}

/*
 * 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);
}

/**
 * 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, struct rw_semaphore *fshared,
                   union futex_key *key)
{
      unsigned long address = (unsigned long)uaddr;
      struct mm_struct *mm = current->mm;
      struct vm_area_struct *vma;
      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;
            return 0;
      }
      /*
       * The futex is hashed differently depending on whether
       * it's in a shared or private mapping.  So check vma first.
       */
      vma = find_extend_vma(mm, address);
      if (unlikely(!vma))
            return -EFAULT;

      /*
       * Permissions.
       */
      if (unlikely((vma->vm_flags & (VM_IO|VM_READ)) != VM_READ))
            return (vma->vm_flags & VM_IO) ? -EPERM : -EACCES;

      /*
       * 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.  Therefore we use
       * VM_MAYSHARE here, not VM_SHARED which is restricted to shared
       * mappings of _writable_ handles.
       */
      if (likely(!(vma->vm_flags & VM_MAYSHARE))) {
            key->both.offset |= FUT_OFF_MMSHARED; /* reference taken on mm */
            key->private.mm = mm;
            key->private.address = address;
            return 0;
      }

      /*
       * Linear file mappings are also simple.
       */
      key->shared.inode = vma->vm_file->f_path.dentry->d_inode;
      key->both.offset |= FUT_OFF_INODE; /* inode-based key. */
      if (likely(!(vma->vm_flags & VM_NONLINEAR))) {
            key->shared.pgoff = (((address - vma->vm_start) >> PAGE_SHIFT)
                             + vma->vm_pgoff);
            return 0;
      }

      /*
       * We could walk the page table to read the non-linear
       * pte, and get the page index without fetching the page
       * from swap.  But that's a lot of code to duplicate here
       * for a rare case, so we simply fetch the page.
       */
      err = get_user_pages(current, mm, address, 1, 0, 0, &page, NULL);
      if (err >= 0) {
            key->shared.pgoff =
                  page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
            put_page(page);
            return 0;
      }
      return err;
}

/*
 * 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 == 0)
            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)
            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;
      }
}

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.
 * if fshared is non NULL, current->mm->mmap_sem is already held
 */
static int futex_handle_fault(unsigned long address,
                        struct rw_semaphore *fshared, int attempt)
{
      struct vm_area_struct * vma;
      struct mm_struct *mm = current->mm;
      int ret = -EFAULT;

      if (attempt > 2)
            return ret;

      if (!fshared)
            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++;
            }
      }
      if (!fshared)
            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);

      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;

      rcu_read_lock();
      p = find_task_by_vpid(pid);
      if (!p || ((current->euid != p->euid) && (current->euid != p->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;

      /*
       * 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);
      if (q->filp)
            send_sigio(&q->filp->f_owner, q->fd, POLL_IN);
      /*
       * 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_all(&q->waiters);
      /*
       * 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, struct rw_semaphore *fshared,
                  int nr_wake)
{
      struct futex_hash_bucket *hb;
      struct futex_q *this, *next;
      struct plist_head *head;
      union futex_key key;
      int ret;

      futex_lock_mm(fshared);

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

      spin_unlock(&hb->lock);
out:
      futex_unlock_mm(fshared);
      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, struct rw_semaphore *fshared,
            u32 __user *uaddr2,
            int nr_wake, int nr_wake2, int op)
{
      union futex_key key1, key2;
      struct futex_hash_bucket *hb1, *hb2;
      struct plist_head *head;
      struct futex_q *this, *next;
      int ret, op_ret, attempt = 0;

retryfull:
      futex_lock_mm(fshared);

      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;

      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;
#endif

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

            /*
             * 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,
                                     fshared, attempt);
                  if (ret)
                        goto out;
                  goto retry;
            }

            /*
             * If we would have faulted, release mmap_sem,
             * fault it in and start all over again.
             */
            futex_unlock_mm(fshared);

            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:
      futex_unlock_mm(fshared);

      return ret;
}

/*
 * Requeue all waiters hashed on one physical page to another
 * physical page.
 */
static int futex_requeue(u32 __user *uaddr1, struct rw_semaphore *fshared,
                   u32 __user *uaddr2,
                   int nr_wake, int nr_requeue, u32 *cmpval)
{
      union futex_key key1, key2;
      struct futex_hash_bucket *hb1, *hb2;
      struct plist_head *head1;
      struct futex_q *this, *next;
      int ret, drop_count = 0;

 retry:
      futex_lock_mm(fshared);

      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;

      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);

                  /*
                   * If we would have faulted, release mmap_sem, fault
                   * it in and start all over again.
                   */
                  futex_unlock_mm(fshared);

                  ret = get_user(curval, uaddr1);

                  if (!ret)
                        goto retry;

                  return ret;
            }
            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:
      futex_unlock_mm(fshared);
      return ret;
}

/* The key must be already stored in q->key. */
static inline struct futex_hash_bucket *
queue_lock(struct futex_q *q, int fd, struct file *filp)
{
      struct futex_hash_bucket *hb;

      q->fd = fd;
      q->filp = filp;

      init_waitqueue_head(&q->waiters);

      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.
 */

/* The key must be already stored in q->key. */
static void queue_me(struct futex_q *q, int fd, struct file *filp)
{
      struct futex_hash_bucket *hb;

      hb = queue_lock(q, fd, filp);
      __queue_me(q, hb);
}

/* 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)
{
      u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
      struct futex_pi_state *pi_state = q->pi_state;
      u32 uval, curval, newval;
      int ret;

      /* Owner died? */
      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);
      } else
            newtid |= FUTEX_OWNER_DIED;

      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);

      /*
       * We own it, so we have to replace the pending owner
       * TID. This must be atomic as we have preserve the
       * owner died bit here.
       */
      ret = get_futex_value_locked(&uval, uaddr);

      while (!ret) {
            newval = (uval & FUTEX_OWNER_DIED) | newtid;

            curval = cmpxchg_futex_value_locked(uaddr, uval, newval);

            if (curval == -EFAULT)
                  ret = -EFAULT;
            if (curval == uval)
                  break;
            uval = curval;
      }
      return ret;
}

/*
 * In case we must use restart_block to restart a futex_wait,
 * we encode in the 'flags' shared capability
 */
#define FLAGS_SHARED  1

static long futex_wait_restart(struct restart_block *restart);

static int futex_wait(u32 __user *uaddr, struct rw_semaphore *fshared,
                  u32 val, ktime_t *abs_time)
{
      struct task_struct *curr = current;
      DECLARE_WAITQUEUE(wait, curr);
      struct futex_hash_bucket *hb;
      struct futex_q q;
      u32 uval;
      int ret;
      struct hrtimer_sleeper t;
      int rem = 0;

      q.pi_state = NULL;
 retry:
      futex_lock_mm(fshared);

      ret = get_futex_key(uaddr, fshared, &q.key);
      if (unlikely(ret != 0))
            goto out_release_sem;

      hb = queue_lock(&q, -1, NULL);

      /*
       * 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);

            /*
             * If we would have faulted, release mmap_sem, fault it in and
             * start all over again.
             */
            futex_unlock_mm(fshared);

            ret = get_user(uval, uaddr);

            if (!ret)
                  goto retry;
            return ret;
      }
      ret = -EWOULDBLOCK;
      if (uval != val)
            goto out_unlock_release_sem;

      /* Only actually queue if *uaddr contained val.  */
      __queue_me(&q, hb);

      /*
       * Now the futex is queued and we have checked the data, we
       * don't want to hold mmap_sem while we sleep.
       */
      futex_unlock_mm(fshared);

      /*
       * 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.waiters, &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 {
                  hrtimer_init(&t.timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
                  hrtimer_init_sleeper(&t, current);
                  t.timer.expires = *abs_time;

                  hrtimer_start(&t.timer, t.timer.expires, HRTIMER_MODE_ABS);

                  /*
                   * 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);
            }
      }
      __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. */
      if (!unqueue_me(&q))
            return 0;
      if (rem)
            return -ETIMEDOUT;

      /*
       * We expect signal_pending(current), but another thread may
       * have handled it for us already.
       */
      if (!abs_time)
            return -ERESTARTSYS;
      else {
            struct restart_block *restart;
            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.flags = 0;

            if (fshared)
                  restart->futex.flags |= FLAGS_SHARED;
            return -ERESTART_RESTARTBLOCK;
      }

 out_unlock_release_sem:
      queue_unlock(&q, hb);

 out_release_sem:
      futex_unlock_mm(fshared);
      return ret;
}


static long futex_wait_restart(struct restart_block *restart)
{
      u32 __user *uaddr = (u32 __user *)restart->futex.uaddr;
      struct rw_semaphore *fshared = NULL;
      ktime_t t;

      t.tv64 = restart->futex.time;
      restart->fn = do_no_restart_syscall;
      if (restart->futex.flags & FLAGS_SHARED)
            fshared = &current->mm->mmap_sem;
      return (long)futex_wait(uaddr, fshared, restart->futex.val, &t);
}


/*
 * 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, struct rw_semaphore *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(&to->timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
            hrtimer_init_sleeper(to, current);
            to->timer.expires = *time;
      }

      q.pi_state = NULL;
 retry:
      futex_lock_mm(fshared);

      ret = get_futex_key(uaddr, fshared, &q.key);
      if (unlikely(ret != 0))
            goto out_release_sem;

 retry_unlocked:
      hb = queue_lock(&q, -1, NULL);

 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_release_sem;
      }

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

      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_release_sem;

      /*
       * 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);
                  futex_unlock_mm(fshared);
                  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_release_sem;
            }
      }

      /*
       * Only actually queue now that the atomic ops are done:
       */
      __queue_me(&q, hb);

      /*
       * Now the futex is queued and we have checked the data, we
       * don't want to hold mmap_sem while we sleep.
       */
      futex_unlock_mm(fshared);

      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;
      }

      futex_lock_mm(fshared);
      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);
      } 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);

                        WARN_ON(rt_mutex_owner(&q.pi_state->pi_mutex) !=
                              owner);

                        /* 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\n", ret,
                               q.pi_state->pi_mutex.owner,
                               q.pi_state->owner);
            }
      }

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

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

 out_unlock_release_sem:
      queue_unlock(&q, hb);

 out_release_sem:
      futex_unlock_mm(fshared);
      return ret;

 uaddr_faulted:
      /*
       * We have to r/w  *(int __user *)uaddr, 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.
       *
       * ... and hb->lock. :-) --ANK
       */
      queue_unlock(&q, hb);

      if (attempt++) {
            ret = futex_handle_fault((unsigned long)uaddr, fshared,
                               attempt);
            if (ret)
                  goto out_release_sem;
            goto retry_unlocked;
      }

      futex_unlock_mm(fshared);

      ret = get_user(uval, uaddr);
      if (!ret && (uval != -EFAULT))
            goto retry;

      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, struct rw_semaphore *fshared)
{
      struct futex_hash_bucket *hb;
      struct futex_q *this, *next;
      u32 uval;
      struct plist_head *head;
      union futex_key key;
      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;
      /*
       * First take all the futex related locks:
       */
      futex_lock_mm(fshared);

      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);
out:
      futex_unlock_mm(fshared);

      return ret;

pi_faulted:
      /*
       * We have to r/w  *(int __user *)uaddr, 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.
       *
       * ... and hb->lock. --ANK
       */
      spin_unlock(&hb->lock);

      if (attempt++) {
            ret = futex_handle_fault((unsigned long)uaddr, fshared,
                               attempt);
            if (ret)
                  goto out;
            uval = 0;
            goto retry_unlocked;
      }

      futex_unlock_mm(fshared);

      ret = get_user(uval, uaddr);
      if (!ret && (uval != -EFAULT))
            goto retry;

      return ret;
}

static int futex_close(struct inode *inode, struct file *filp)
{
      struct futex_q *q = filp->private_data;

      unqueue_me(q);
      kfree(q);

      return 0;
}

/* This is one-shot: once it's gone off you need a new fd */
static unsigned int futex_poll(struct file *filp,
                         struct poll_table_struct *wait)
{
      struct futex_q *q = filp->private_data;
      int ret = 0;

      poll_wait(filp, &q->waiters, wait);

      /*
       * plist_node_empty() is safe here without any lock.
       * q->lock_ptr != 0 is not safe, because of ordering against wakeup.
       */
      if (plist_node_empty(&q->list))
            ret = POLLIN | POLLRDNORM;

      return ret;
}

static const struct file_operations futex_fops = {
      .release    = futex_close,
      .poll       = futex_poll,
};

/*
 * Signal allows caller to avoid the race which would occur if they
 * set the sigio stuff up afterwards.
 */
static int futex_fd(u32 __user *uaddr, int signal)
{
      struct futex_q *q;
      struct file *filp;
      int ret, err;
      struct rw_semaphore *fshared;
      static unsigned long printk_interval;

      if (printk_timed_ratelimit(&printk_interval, 60 * 60 * 1000)) {
            printk(KERN_WARNING "Process `%s' used FUTEX_FD, which "
                   "will be removed from the kernel in June 2007\n",
                   current->comm);
      }

      ret = -EINVAL;
      if (!valid_signal(signal))
            goto out;

      ret = get_unused_fd();
      if (ret < 0)
            goto out;
      filp = get_empty_filp();
      if (!filp) {
            put_unused_fd(ret);
            ret = -ENFILE;
            goto out;
      }
      filp->f_op = &futex_fops;
      filp->f_path.mnt = mntget(futex_mnt);
      filp->f_path.dentry = dget(futex_mnt->mnt_root);
      filp->f_mapping = filp->f_path.dentry->d_inode->i_mapping;

      if (signal) {
            err = __f_setown(filp, task_pid(current), PIDTYPE_PID, 1);
            if (err < 0) {
                  goto error;
            }
            filp->f_owner.signum = signal;
      }

      q = kmalloc(sizeof(*q), GFP_KERNEL);
      if (!q) {
            err = -ENOMEM;
            goto error;
      }
      q->pi_state = NULL;

      fshared = &current->mm->mmap_sem;
      down_read(fshared);
      err = get_futex_key(uaddr, fshared, &q->key);

      if (unlikely(err != 0)) {
            up_read(fshared);
            kfree(q);
            goto error;
      }

      /*
       * queue_me() must be called before releasing mmap_sem, because
       * key->shared.inode needs to be referenced while holding it.
       */
      filp->private_data = q;

      queue_me(q, ret, filp);
      up_read(fshared);

      /* Now we map fd to filp, so userspace can access it */
      fd_install(ret, filp);
out:
      return ret;
error:
      put_unused_fd(ret);
      put_filp(filp);
      ret = err;
      goto out;
}

/*
 * 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
 */
asmlinkage long
sys_set_robust_list(struct robust_list_head __user *head,
                size_t len)
{
      /*
       * 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
 */
asmlinkage long
sys_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;

      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;
            if ((current->euid != p->euid) && (current->euid != p->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, &curr->mm->mmap_sem, 1);
      }
      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;

      /*
       * 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 ret;
      int cmd = op & FUTEX_CMD_MASK;
      struct rw_semaphore *fshared = NULL;

      if (!(op & FUTEX_PRIVATE_FLAG))
            fshared = &current->mm->mmap_sem;

      switch (cmd) {
      case FUTEX_WAIT:
            ret = futex_wait(uaddr, fshared, val, timeout);
            break;
      case FUTEX_WAKE:
            ret = futex_wake(uaddr, fshared, val);
            break;
      case FUTEX_FD:
            /* non-zero val means F_SETOWN(getpid()) & F_SETSIG(val) */
            ret = futex_fd(uaddr, val);
            break;
      case FUTEX_REQUEUE:
            ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL);
            break;
      case FUTEX_CMP_REQUEUE:
            ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3);
            break;
      case FUTEX_WAKE_OP:
            ret = futex_wake_op(uaddr, fshared, uaddr2, val, val2, val3);
            break;
      case FUTEX_LOCK_PI:
            ret = futex_lock_pi(uaddr, fshared, val, timeout, 0);
            break;
      case FUTEX_UNLOCK_PI:
            ret = futex_unlock_pi(uaddr, fshared);
            break;
      case FUTEX_TRYLOCK_PI:
            ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1);
            break;
      default:
            ret = -ENOSYS;
      }
      return ret;
}


asmlinkage long sys_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)) {
            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(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_WAKE_OP)
            val2 = (u32) (unsigned long) utime;

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

static int futexfs_get_sb(struct file_system_type *fs_type,
                    int flags, const char *dev_name, void *data,
                    struct vfsmount *mnt)
{
      return get_sb_pseudo(fs_type, "futex", NULL, FUTEXFS_SUPER_MAGIC, mnt);
}

static struct file_system_type futex_fs_type = {
      .name       = "futexfs",
      .get_sb           = futexfs_get_sb,
      .kill_sb    = kill_anon_super,
};

static int __init init(void)
{
      int i = register_filesystem(&futex_fs_type);

      if (i)
            return i;

      futex_mnt = kern_mount(&futex_fs_type);
      if (IS_ERR(futex_mnt)) {
            unregister_filesystem(&futex_fs_type);
            return PTR_ERR(futex_mnt);
      }

      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(init);

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