Cross-Referenced Linux and Device Driver Code

   /*
    *  Fast Userspace Mutexes (which I call "Futexes!").
    *  (C) Rusty Russell, IBM 2002
    *
    *  Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
    *  (C) Copyright 2003 Red Hat Inc, All Rights Reserved
    *
    *  Removed page pinning, fix privately mapped COW pages and other cleanups
    *  (C) Copyright 2003, 2004 Jamie Lokier
   *
   *  Robust futex support started by Ingo Molnar
   *  (C) Copyright 2006 Red Hat Inc, All Rights Reserved
   *  Thanks to Thomas Gleixner for suggestions, analysis and fixes.
   *
   *  PI-futex support started by Ingo Molnar and Thomas Gleixner
   *  Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   *  Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
   *
   *  PRIVATE futexes by Eric Dumazet
   *  Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
   *
   *  Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
   *  enough at me, Linus for the original (flawed) idea, Matthew
   *  Kirkwood for proof-of-concept implementation.
   *
   *  "The futexes are also cursed."
   *  "But they come in a choice of three flavours!"
   *
   *  This program is free software; you can redistribute it and/or modify
   *  it under the terms of the GNU General Public License as published by
   *  the Free Software Foundation; either version 2 of the License, or
   *  (at your option) any later version.
   *
   *  This program is distributed in the hope that it will be useful,
   *  but WITHOUT ANY WARRANTY; without even the implied warranty of
   *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   *  GNU General Public License for more details.
   *
   *  You should have received a copy of the GNU General Public License
   *  along with this program; if not, write to the Free Software
   *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
   */
  #include <linux/slab.h>
  #include <linux/poll.h>
  #include <linux/fs.h>
  #include <linux/file.h>
  #include <linux/jhash.h>
  #include <linux/init.h>
  #include <linux/futex.h>
  #include <linux/mount.h>
  #include <linux/pagemap.h>
  #include <linux/syscalls.h>
  #include <linux/signal.h>
  #include <linux/module.h>
  #include <linux/magic.h>
  #include <linux/pid.h>
  #include <linux/nsproxy.h>
  
  #include <asm/futex.h>
  
  #include "rtmutex_common.h"
  
  int __read_mostly futex_cmpxchg_enabled;
  
  #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
  
  /*
   * Priority Inheritance state:
   */
  struct futex_pi_state {
          /*
           * list of 'owned' pi_state instances - these have to be
           * cleaned up in do_exit() if the task exits prematurely:
           */
          struct list_head list;
  
          /*
           * The PI object:
           */
          struct rt_mutex pi_mutex;
  
          struct task_struct *owner;
          atomic_t refcount;
  
          union futex_key key;
  };
  
  /*
   * We use this hashed waitqueue instead of a normal wait_queue_t, so
   * we can wake only the relevant ones (hashed queues may be shared).
   *
   * A futex_q has a woken state, just like tasks have TASK_RUNNING.
   * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
   * The order of wakup is always to make the first condition true, then
   * wake up q->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;
 
         /* Bitset for the optional bitmasked wakeup */
         u32 bitset;
 };
 
 /*
  * Split the global futex_lock into every hash list lock.
  */
 struct futex_hash_bucket {
         spinlock_t lock;
         struct plist_head chain;
 };
 
 static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
 
 /* Futex-fs vfsmount entry: */
 static struct vfsmount *futex_mnt;
 
 int futex_performance_hack;
 
 /*
  * Take mm->mmap_sem, when futex is shared
  */
 static inline void futex_lock_mm(struct rw_semaphore *fshared)
 {
         if (fshared && !futex_performance_hack)
                 down_read(fshared);
 }
 
 /*
  * Release mm->mmap_sem, when the futex is shared
  */
 static inline void futex_unlock_mm(struct rw_semaphore *fshared)
 {
         if (fshared && !futex_performance_hack)
                 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 == NULL)
                 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;
 
         if (!futex_cmpxchg_enabled)
                 return;
         /*
          * We are a ZOMBIE and nobody can enqueue itself on
          * pi_state_list anymore, but we have to be careful
          * versus waiters unqueueing themselves:
          */
         spin_lock_irq(&curr->pi_lock);
         while (!list_empty(head)) {
 
                 next = head->next;
                 pi_state = list_entry(next, struct futex_pi_state, list);
                 key = pi_state->key;
                 hb = hash_futex(&key);
                 spin_unlock_irq(&curr->pi_lock);
 
                 spin_lock(&hb->lock);
 
                 spin_lock_irq(&curr->pi_lock);
                 /*
                  * We dropped the pi-lock, so re-check whether this
                  * task still owns the PI-state:
                  */
                 if (head->next != next) {
                         spin_unlock(&hb->lock);
                         continue;
                 }
 
                 WARN_ON(pi_state->owner != curr);
                 WARN_ON(list_empty(&pi_state->list));
                 list_del_init(&pi_state->list);
                 pi_state->owner = NULL;
                 spin_unlock_irq(&curr->pi_lock);
 
                 rt_mutex_unlock(&pi_state->pi_mutex);
 
                 spin_unlock(&hb->lock);
 
                 spin_lock_irq(&curr->pi_lock);
         }
         spin_unlock_irq(&curr->pi_lock);
 }
 
 static int
 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
                 union futex_key *key, struct futex_pi_state **ps)
 {
         struct futex_pi_state *pi_state = NULL;
         struct futex_q *this, *next;
         struct plist_head *head;
         struct task_struct *p;
         pid_t pid = uval & FUTEX_TID_MASK;
 
         head = &hb->chain;
 
         plist_for_each_entry_safe(this, next, head, list) {
                 if (match_futex(&this->key, key)) {
                         /*
                          * Another waiter already exists - bump up
                          * the refcount and return its pi_state:
                          */
                         pi_state = this->pi_state;
                         /*
                          * Userspace might have messed up non PI and PI futexes
                          */
                         if (unlikely(!pi_state))
                                 return -EINVAL;
 
                         WARN_ON(!atomic_read(&pi_state->refcount));
                         WARN_ON(pid && pi_state->owner &&
                                 pi_state->owner->pid != pid);
 
                         atomic_inc(&pi_state->refcount);
                         *ps = pi_state;
 
                         return 0;
                 }
         }
 
         /*
          * We are the first waiter - try to look up the real owner and attach
          * the new pi_state to it, but bail out when TID = 0
          */
         if (!pid)
                 return -ESRCH;
         p = futex_find_get_task(pid);
         if (IS_ERR(p))
                 return PTR_ERR(p);
 
         /*
          * We need to look at the task state flags to figure out,
          * whether the task is exiting. To protect against the do_exit
          * change of the task flags, we do this protected by
          * p->pi_lock:
          */
         spin_lock_irq(&p->pi_lock);
         if (unlikely(p->flags & PF_EXITING)) {
                 /*
                  * The task is on the way out. When PF_EXITPIDONE is
                  * set, we know that the task has finished the
                  * cleanup:
                  */
                 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
 
                 spin_unlock_irq(&p->pi_lock);
                 put_task_struct(p);
                 return ret;
         }
 
         pi_state = alloc_pi_state();
 
         /*
          * Initialize the pi_mutex in locked state and make 'p'
          * the owner of it:
          */
         rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
 
         /* Store the key for possible exit cleanups: */
         pi_state->key = *key;
 
         WARN_ON(!list_empty(&pi_state->list));
         list_add(&pi_state->list, &p->pi_state_list);
         pi_state->owner = p;
         spin_unlock_irq(&p->pi_lock);
 
         put_task_struct(p);
 
         *ps = pi_state;
 
         return 0;
 }
 
 /*
  * The hash bucket lock must be held when this is called.
  * Afterwards, the futex_q must not be accessed.
  */
 static void wake_futex(struct futex_q *q)
 {
         plist_del(&q->list, &q->list.plist);
         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, u32 bitset)
 {
         struct futex_hash_bucket *hb;
         struct futex_q *this, *next;
         struct plist_head *head;
         union futex_key key;
         int ret;
 
         if (!bitset)
                 return -EINVAL;
 
         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;
                         }
 
                         /* 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);
 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
 #ifdef CONFIG_PREEMPT_RT
                                 this->list.plist.lock = NULL;
 #else
                                 this->list.plist.lock = &hb2->lock;
 #endif
 #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
 #ifdef CONFIG_PREEMPT_RT
         q->list.plist.lock = NULL;
 #else
         q->list.plist.lock = &hb->lock;
 #endif
 #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,
                                 struct rw_semaphore *fshared)
 {
         u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
         struct futex_pi_state *pi_state = q->pi_state;
         struct task_struct *oldowner = pi_state->owner;
         u32 uval, curval, newval;
         int ret, attempt = 0;
 
         /* Owner died? */
         if (!pi_state->owner)
                 newtid |= FUTEX_OWNER_DIED;
 
         /*
          * We are here either because we stole the rtmutex from the
          * pending owner or we are the pending owner which failed to
          * get the rtmutex. We have to replace the pending owner TID
          * in the user space variable. This must be atomic as we have
          * preserve the owner died bit here.
          *
          * Note: We write the user space value _before_ changing the
          * pi_state because we can fault here. Imagine swapped out
          * pages or a fork, which was running right before we acquired
          * mmap_sem, that marked all the anonymous memory readonly for
          * cow.
          *
          * Modifying pi_state _before_ the user space value would
          * leave the pi_state in an inconsistent state when we fault
          * here, because we need to drop the hash bucket lock to
          * handle the fault. This might be observed in the PID check
          * in lookup_pi_state.
          */
 retry:
         if (get_futex_value_locked(&uval, uaddr))
                 goto handle_fault;
 
         while (1) {
                 newval = (uval & FUTEX_OWNER_DIED) | newtid;
 
                 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
 
                 if (curval == -EFAULT)
                         goto handle_fault;
                 if (curval == uval)
                         break;
                 uval = curval;
         }
 
         /*
          * We fixed up user space. Now we need to fix the pi_state
          * itself.
          */
         if (pi_state->owner != NULL) {
                 spin_lock_irq(&pi_state->owner->pi_lock);
                 WARN_ON(list_empty(&pi_state->list));
                 list_del_init(&pi_state->list);
                 spin_unlock_irq(&pi_state->owner->pi_lock);
         }
 
         pi_state->owner = newowner;
 
         spin_lock_irq(&newowner->pi_lock);
         WARN_ON(!list_empty(&pi_state->list));
         list_add(&pi_state->list, &newowner->pi_state_list);
         spin_unlock_irq(&newowner->pi_lock);
         return 0;
 
         /*
          * To handle the page fault we need to drop the hash bucket
          * lock here. That gives the other task (either the pending
          * owner itself or the task which stole the rtmutex) the
          * chance to try the fixup of the pi_state. So once we are
          * back from handling the fault we need to check the pi_state
          * after reacquiring the hash bucket lock and before trying to
          * do another fixup. When the fixup has been done already we
          * simply return.
          */
 handle_fault:
         spin_unlock(q->lock_ptr);
 
         ret = futex_handle_fault((unsigned long)uaddr, fshared, attempt++);
 
         spin_lock(q->lock_ptr);
 
         /*
          * Check if someone else fixed it for us:
          */
         if (pi_state->owner != oldowner)
                 return 0;
 
         if (ret)
                 return ret;
 
         goto retry;
 }
 
 /*
  * In case we must use restart_block to restart a futex_wait,
  * we encode in the 'flags' shared capability
  */
 #define FLAGS_SHARED  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, u32 bitset)
 {
         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;
 
         if (!bitset)
                 return -EINVAL;
 
         q.pi_state = NULL;
         q.bitset = bitset;
  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))) {
                 unsigned long nosched_flag = current->flags & PF_NOSCHED;
 
                 current->flags &= ~PF_NOSCHED;
 
                 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);
                         if (!hrtimer_active(&t.timer))
                                 t.task = NULL;
 
                         /*
                          * the timer could have already expired, in which
                          * case current would be flagged for rescheduling.
                          * Don't bother calling schedule.
                          */
                         if (likely(t.task))
                                 schedule();
 
                         hrtimer_cancel(&t.timer);
 
                         /* Flag if a timeout occured */
                         rem = (t.task == NULL);
                 }
 
                 current->flags |= nosched_flag;
         }
         __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.bitset = bitset;
                 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,
                                 restart->futex.bitset);
 }
 
 
 /*
  * 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, fshared);
         } else {
                 /*
                  * Catch the rare case, where the lock was released
                  * when we were on the way back before we locked the
                  * hash bucket.
                  */
                 if (q.pi_state->owner == curr) {
                         /*
                          * Try to get the rt_mutex now. This might
                          * fail as some other task acquired the
                          * rt_mutex after we removed ourself from the
                          * rt_mutex waiters list.
                          */
                         if (rt_mutex_trylock(&q.pi_state->pi_mutex))
                                 ret = 0;
                         else {
                                 /*
                                  * pi_state is incorrect, some other
                                  * task did a lock steal and we
                                  * returned due to timeout or signal
                                  * without taking the rt_mutex. Too
                                  * late. We can access the
                                  * rt_mutex_owner without locking, as
                                  * the other task is now blocked on
                                  * the hash bucket lock. Fix the state
                                  * up.
                                  */
                                 struct task_struct *owner;
                                 int res;
 
                                 owner = rt_mutex_owner(&q.pi_state->pi_mutex);
                                 res = fixup_pi_state_owner(uaddr, &q, owner,
                                                            fshared);
 
                                 /* propagate -EFAULT, if the fixup failed */
                                 if (res)
                                         ret = res;
                         }
                 } else {
                         /*
                          * Paranoia check. If we did not take the lock
                          * in the trylock above, then we should not be
                          * the owner of the rtmutex, neither the real
                          * nor the pending one:
                          */
                         if (rt_mutex_owner(&q.pi_state->pi_mutex) == curr)
                                 printk(KERN_ERR "futex_lock_pi: ret = %d "
                                        "pi-mutex: %p pi-state %p\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)
 {
         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
  */
 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 (!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;
                 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,
                                    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 ret = -ENOSYS;
         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:
                 val3 = FUTEX_BITSET_MATCH_ANY;
         case FUTEX_WAIT_BITSET:
                 ret = futex_wait(uaddr, fshared, val, timeout, val3);
                 break;
         case FUTEX_WAKE:
                 val3 = FUTEX_BITSET_MATCH_ANY;
         case FUTEX_WAKE_BITSET:
                 ret = futex_wake(uaddr, fshared, val, val3);
                 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:
                 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;
         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 ||
                       cmd == FUTEX_WAIT_BITSET)) {
                 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_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 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++) {
 #ifdef CONFIG_PREEMPT_RT
                 plist_head_init(&futex_queues[i].chain, NULL);
 #else
                 plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock);
 #endif
                 spin_lock_init(&futex_queues[i].lock);
         }
 
         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);
         }
 
         return 0;
 }
 __initcall(futex_init);