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>
   *
   *  Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
   *  Copyright (C) IBM Corporation, 2009
   *  Thanks to Thomas Gleixner for conceptual design and careful reviews.
   *
   *  Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
   *  enough at me, Linus for the original (flawed) idea, Matthew
   *  Kirkwood for proof-of-concept implementation.
   *
   *  "The futexes are also cursed."
   *  "But they come in a choice of three flavours!"
   *
   *  This program is free software; you can redistribute it and/or modify
   *  it under the terms of the GNU General Public License as published by
   *  the Free Software Foundation; either version 2 of the License, or
   *  (at your option) any later version.
   *
   *  This program is distributed in the hope that it will be useful,
   *  but WITHOUT ANY WARRANTY; without even the implied warranty of
   *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   *  GNU General Public License for more details.
   *
   *  You should have received a copy of the GNU General Public License
   *  along with this program; if not, write to the Free Software
   *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
   */
  #include <linux/slab.h>
  #include <linux/poll.h>
  #include <linux/fs.h>
  #include <linux/file.h>
  #include <linux/jhash.h>
  #include <linux/init.h>
  #include <linux/futex.h>
  #include <linux/mount.h>
  #include <linux/pagemap.h>
  #include <linux/syscalls.h>
  #include <linux/signal.h>
  #include <linux/module.h>
  #include <linux/magic.h>
  #include <linux/pid.h>
  #include <linux/nsproxy.h>
  
  #include <asm/futex.h>
  
  #include "rtmutex_common.h"
  
  int __read_mostly futex_cmpxchg_enabled;
  
  #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
  
  /*
   * Priority Inheritance state:
   */
  struct futex_pi_state {
          /*
           * list of 'owned' pi_state instances - these have to be
           * cleaned up in do_exit() if the task exits prematurely:
           */
          struct list_head list;
  
          /*
           * The PI object:
           */
          struct rt_mutex pi_mutex;
  
          struct task_struct *owner;
          atomic_t refcount;
  
          union futex_key key;
  };
  
  /*
   * We use this hashed waitqueue instead of a normal wait_queue_t, so
   * we can wake only the relevant ones (hashed queues may be shared).
   *
   * A futex_q has a woken state, just like tasks have TASK_RUNNING.
   * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
   * The order of wakup is always to make the first condition true, then
   * wake up q->waiter, then make the second condition true.
  */
 struct futex_q {
         struct plist_node list;
         /* Waiter reference */
         struct task_struct *task;
 
         /* Which hash list lock to use: */
         spinlock_t *lock_ptr;
 
         /* Key which the futex is hashed on: */
         union futex_key key;
 
         /* Optional priority inheritance state: */
         struct futex_pi_state *pi_state;
 
         /* rt_waiter storage for requeue_pi: */
         struct rt_mutex_waiter *rt_waiter;
 
         /* The expected requeue pi target futex key: */
         union futex_key *requeue_pi_key;
 
         /* Bitset for the optional bitmasked wakeup */
         u32 bitset;
 };
 
 /*
  * Hash buckets are shared by all the futex_keys that hash to the same
  * location.  Each key may have multiple futex_q structures, one for each task
  * waiting on a futex.
  */
 struct futex_hash_bucket {
         spinlock_t lock;
         struct plist_head chain;
 };
 
 static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
 
 /*
  * We hash on the keys returned from get_futex_key (see below).
  */
 static struct futex_hash_bucket *hash_futex(union futex_key *key)
 {
         u32 hash = jhash2((u32*)&key->both.word,
                           (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
                           key->both.offset);
         return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
 }
 
 /*
  * Return 1 if two futex_keys are equal, 0 otherwise.
  */
 static inline int match_futex(union futex_key *key1, union futex_key *key2)
 {
         return (key1 && key2
                 && key1->both.word == key2->both.word
                 && key1->both.ptr == key2->both.ptr
                 && key1->both.offset == key2->both.offset);
 }
 
 /*
  * Take a reference to the resource addressed by a key.
  * Can be called while holding spinlocks.
  *
  */
 static void get_futex_key_refs(union futex_key *key)
 {
         if (!key->both.ptr)
                 return;
 
         switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
         case FUT_OFF_INODE:
                 atomic_inc(&key->shared.inode->i_count);
                 break;
         case FUT_OFF_MMSHARED:
                 atomic_inc(&key->private.mm->mm_count);
                 break;
         }
 }
 
 /*
  * Drop a reference to the resource addressed by a key.
  * The hash bucket spinlock must not be held.
  */
 static void drop_futex_key_refs(union futex_key *key)
 {
         if (!key->both.ptr) {
                 /* If we're here then we tried to put a key we failed to get */
                 WARN_ON_ONCE(1);
                 return;
         }
 
         switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
         case FUT_OFF_INODE:
                 iput(key->shared.inode);
                 break;
         case FUT_OFF_MMSHARED:
                 mmdrop(key->private.mm);
                 break;
         }
 }
 
 /**
  * get_futex_key - Get parameters which are the keys for a futex.
  * @uaddr: virtual address of the futex
  * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
  * @key: address where result is stored.
  * @rw: mapping needs to be read/write (values: VERIFY_READ, VERIFY_WRITE)
  *
  * Returns a negative error code or 0
  * The key words are stored in *key on success.
  *
  * For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,
  * offset_within_page).  For private mappings, it's (uaddr, current->mm).
  * We can usually work out the index without swapping in the page.
  *
  * lock_page() might sleep, the caller should not hold a spinlock.
  */
 static int
 get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
 {
         unsigned long address = (unsigned long)uaddr;
         struct mm_struct *mm = current->mm;
         struct page *page;
         int err;
 
         /*
          * The futex address must be "naturally" aligned.
          */
         key->both.offset = address % PAGE_SIZE;
         if (unlikely((address % sizeof(u32)) != 0))
                 return -EINVAL;
         address -= key->both.offset;
 
         /*
          * PROCESS_PRIVATE futexes are fast.
          * As the mm cannot disappear under us and the 'key' only needs
          * virtual address, we dont even have to find the underlying vma.
          * Note : We do have to check 'uaddr' is a valid user address,
          *        but access_ok() should be faster than find_vma()
          */
         if (!fshared) {
                 if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
                         return -EFAULT;
                 key->private.mm = mm;
                 key->private.address = address;
                 get_futex_key_refs(key);
                 return 0;
         }
 
 again:
         err = get_user_pages_fast(address, 1, rw == VERIFY_WRITE, &page);
         if (err < 0)
                 return err;
 
         page = compound_head(page);
         lock_page(page);
         if (!page->mapping) {
                 unlock_page(page);
                 put_page(page);
                 goto again;
         }
 
         /*
          * Private mappings are handled in a simple way.
          *
          * NOTE: When userspace waits on a MAP_SHARED mapping, even if
          * it's a read-only handle, it's expected that futexes attach to
          * the object not the particular process.
          */
         if (PageAnon(page)) {
                 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
                 key->private.mm = mm;
                 key->private.address = address;
         } else {
                 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
                 key->shared.inode = page->mapping->host;
                 key->shared.pgoff = page->index;
         }
 
         get_futex_key_refs(key);
 
         unlock_page(page);
         put_page(page);
         return 0;
 }
 
 static inline
 void put_futex_key(int fshared, union futex_key *key)
 {
         drop_futex_key_refs(key);
 }
 
 /*
  * fault_in_user_writeable - fault in user address and verify RW access
  * @uaddr:      pointer to faulting user space address
  *
  * Slow path to fixup the fault we just took in the atomic write
  * access to @uaddr.
  *
  * We have no generic implementation of a non destructive write to the
  * user address. We know that we faulted in the atomic pagefault
  * disabled section so we can as well avoid the #PF overhead by
  * calling get_user_pages() right away.
  */
 static int fault_in_user_writeable(u32 __user *uaddr)
 {
         struct mm_struct *mm = current->mm;
         int ret;
 
         down_read(&mm->mmap_sem);
         ret = get_user_pages(current, mm, (unsigned long)uaddr,
                              1, 1, 0, NULL, NULL);
         up_read(&mm->mmap_sem);
 
         return ret < 0 ? ret : 0;
 }
 
 /**
  * futex_top_waiter() - Return the highest priority waiter on a futex
  * @hb:     the hash bucket the futex_q's reside in
  * @key:    the futex key (to distinguish it from other futex futex_q's)
  *
  * Must be called with the hb lock held.
  */
 static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
                                         union futex_key *key)
 {
         struct futex_q *this;
 
         plist_for_each_entry(this, &hb->chain, list) {
                 if (match_futex(&this->key, key))
                         return this;
         }
         return NULL;
 }
 
 static u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval)
 {
         u32 curval;
 
         pagefault_disable();
         curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
         pagefault_enable();
 
         return curval;
 }
 
 static int get_futex_value_locked(u32 *dest, u32 __user *from)
 {
         int ret;
 
         pagefault_disable();
         ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
         pagefault_enable();
 
         return ret ? -EFAULT : 0;
 }
 
 
 /*
  * PI code:
  */
 static int refill_pi_state_cache(void)
 {
         struct futex_pi_state *pi_state;
 
         if (likely(current->pi_state_cache))
                 return 0;
 
         pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
 
         if (!pi_state)
                 return -ENOMEM;
 
         INIT_LIST_HEAD(&pi_state->list);
         /* pi_mutex gets initialized later */
         pi_state->owner = NULL;
         atomic_set(&pi_state->refcount, 1);
         pi_state->key = FUTEX_KEY_INIT;
 
         current->pi_state_cache = pi_state;
 
         return 0;
 }
 
 static struct futex_pi_state * alloc_pi_state(void)
 {
         struct futex_pi_state *pi_state = current->pi_state_cache;
 
         WARN_ON(!pi_state);
         current->pi_state_cache = NULL;
 
         return pi_state;
 }
 
 static void free_pi_state(struct futex_pi_state *pi_state)
 {
         if (!atomic_dec_and_test(&pi_state->refcount))
                 return;
 
         /*
          * If pi_state->owner is NULL, the owner is most probably dying
          * and has cleaned up the pi_state already
          */
         if (pi_state->owner) {
                 spin_lock_irq(&pi_state->owner->pi_lock);
                 list_del_init(&pi_state->list);
                 spin_unlock_irq(&pi_state->owner->pi_lock);
 
                 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
         }
 
         if (current->pi_state_cache)
                 kfree(pi_state);
         else {
                 /*
                  * pi_state->list is already empty.
                  * clear pi_state->owner.
                  * refcount is at 0 - put it back to 1.
                  */
                 pi_state->owner = NULL;
                 atomic_set(&pi_state->refcount, 1);
                 current->pi_state_cache = pi_state;
         }
 }
 
 /*
  * Look up the task based on what TID userspace gave us.
  * We dont trust it.
  */
 static struct task_struct * futex_find_get_task(pid_t pid)
 {
         struct task_struct *p;
         const struct cred *cred = current_cred(), *pcred;
 
         rcu_read_lock();
         p = find_task_by_vpid(pid);
         if (!p) {
                 p = ERR_PTR(-ESRCH);
         } else {
                 pcred = __task_cred(p);
                 if (cred->euid != pcred->euid &&
                     cred->euid != pcred->uid)
                         p = ERR_PTR(-ESRCH);
                 else
                         get_task_struct(p);
         }
 
         rcu_read_unlock();
 
         return p;
 }
 
 /*
  * This task is holding PI mutexes at exit time => bad.
  * Kernel cleans up PI-state, but userspace is likely hosed.
  * (Robust-futex cleanup is separate and might save the day for userspace.)
  */
 void exit_pi_state_list(struct task_struct *curr)
 {
         struct list_head *next, *head = &curr->pi_state_list;
         struct futex_pi_state *pi_state;
         struct futex_hash_bucket *hb;
         union futex_key key = FUTEX_KEY_INIT;
 
         if (!futex_cmpxchg_enabled)
                 return;
         /*
          * We are a ZOMBIE and nobody can enqueue itself on
          * pi_state_list anymore, but we have to be careful
          * versus waiters unqueueing themselves:
          */
         spin_lock_irq(&curr->pi_lock);
         while (!list_empty(head)) {
 
                 next = head->next;
                 pi_state = list_entry(next, struct futex_pi_state, list);
                 key = pi_state->key;
                 hb = hash_futex(&key);
                 spin_unlock_irq(&curr->pi_lock);
 
                 spin_lock(&hb->lock);
 
                 spin_lock_irq(&curr->pi_lock);
                 /*
                  * We dropped the pi-lock, so re-check whether this
                  * task still owns the PI-state:
                  */
                 if (head->next != next) {
                         spin_unlock(&hb->lock);
                         continue;
                 }
 
                 WARN_ON(pi_state->owner != curr);
                 WARN_ON(list_empty(&pi_state->list));
                 list_del_init(&pi_state->list);
                 pi_state->owner = NULL;
                 spin_unlock_irq(&curr->pi_lock);
 
                 rt_mutex_unlock(&pi_state->pi_mutex);
 
                 spin_unlock(&hb->lock);
 
                 spin_lock_irq(&curr->pi_lock);
         }
         spin_unlock_irq(&curr->pi_lock);
 }
 
 static int
 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
                 union futex_key *key, struct futex_pi_state **ps)
 {
         struct futex_pi_state *pi_state = NULL;
         struct futex_q *this, *next;
         struct plist_head *head;
         struct task_struct *p;
         pid_t pid = uval & FUTEX_TID_MASK;
 
         head = &hb->chain;
 
         plist_for_each_entry_safe(this, next, head, list) {
                 if (match_futex(&this->key, key)) {
                         /*
                          * Another waiter already exists - bump up
                          * the refcount and return its pi_state:
                          */
                         pi_state = this->pi_state;
                         /*
                          * Userspace might have messed up non PI and PI futexes
                          */
                         if (unlikely(!pi_state))
                                 return -EINVAL;
 
                         WARN_ON(!atomic_read(&pi_state->refcount));
 
                         /*
                          * When pi_state->owner is NULL then the owner died
                          * and another waiter is on the fly. pi_state->owner
                          * is fixed up by the task which acquires
                          * pi_state->rt_mutex.
                          *
                          * We do not check for pid == 0 which can happen when
                          * the owner died and robust_list_exit() cleared the
                          * TID.
                          */
                         if (pid && pi_state->owner) {
                                 /*
                                  * Bail out if user space manipulated the
                                  * futex value.
                                  */
                                 if (pid != task_pid_vnr(pi_state->owner))
                                         return -EINVAL;
                         }
 
                         atomic_inc(&pi_state->refcount);
                         *ps = pi_state;
 
                         return 0;
                 }
         }
 
         /*
          * We are the first waiter - try to look up the real owner and attach
          * the new pi_state to it, but bail out when TID = 0
          */
         if (!pid)
                 return -ESRCH;
         p = futex_find_get_task(pid);
         if (IS_ERR(p))
                 return PTR_ERR(p);
 
         /*
          * We need to look at the task state flags to figure out,
          * whether the task is exiting. To protect against the do_exit
          * change of the task flags, we do this protected by
          * p->pi_lock:
          */
         spin_lock_irq(&p->pi_lock);
         if (unlikely(p->flags & PF_EXITING)) {
                 /*
                  * The task is on the way out. When PF_EXITPIDONE is
                  * set, we know that the task has finished the
                  * cleanup:
                  */
                 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
 
                 spin_unlock_irq(&p->pi_lock);
                 put_task_struct(p);
                 return ret;
         }
 
         pi_state = alloc_pi_state();
 
         /*
          * Initialize the pi_mutex in locked state and make 'p'
          * the owner of it:
          */
         rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
 
         /* Store the key for possible exit cleanups: */
         pi_state->key = *key;
 
         WARN_ON(!list_empty(&pi_state->list));
         list_add(&pi_state->list, &p->pi_state_list);
         pi_state->owner = p;
         spin_unlock_irq(&p->pi_lock);
 
         put_task_struct(p);
 
         *ps = pi_state;
 
         return 0;
 }
 
 /**
  * futex_lock_pi_atomic() - atomic work required to acquire a pi aware futex
  * @uaddr:              the pi futex user address
  * @hb:                 the pi futex hash bucket
  * @key:                the futex key associated with uaddr and hb
  * @ps:                 the pi_state pointer where we store the result of the
  *                      lookup
  * @task:               the task to perform the atomic lock work for.  This will
  *                      be "current" except in the case of requeue pi.
  * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
  *
  * Returns:
  *  0 - ready to wait
  *  1 - acquired the lock
  * <0 - error
  *
  * The hb->lock and futex_key refs shall be held by the caller.
  */
 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
                                 union futex_key *key,
                                 struct futex_pi_state **ps,
                                 struct task_struct *task, int set_waiters)
 {
         int lock_taken, ret, ownerdied = 0;
         u32 uval, newval, curval;
 
 retry:
         ret = lock_taken = 0;
 
         /*
          * To avoid races, we attempt to take the lock here again
          * (by doing a 0 -> TID atomic cmpxchg), while holding all
          * the locks. It will most likely not succeed.
          */
         newval = task_pid_vnr(task);
         if (set_waiters)
                 newval |= FUTEX_WAITERS;
 
         curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
 
         if (unlikely(curval == -EFAULT))
                 return -EFAULT;
 
         /*
          * Detect deadlocks.
          */
         if ((unlikely((curval & FUTEX_TID_MASK) == task_pid_vnr(task))))
                 return -EDEADLK;
 
         /*
          * Surprise - we got the lock. Just return to userspace:
          */
         if (unlikely(!curval))
                 return 1;
 
         uval = curval;
 
         /*
          * Set the FUTEX_WAITERS flag, so the owner will know it has someone
          * to wake at the next unlock.
          */
         newval = curval | FUTEX_WAITERS;
 
         /*
          * There are two cases, where a futex might have no owner (the
          * owner TID is 0): OWNER_DIED. We take over the futex in this
          * case. We also do an unconditional take over, when the owner
          * of the futex died.
          *
          * This is safe as we are protected by the hash bucket lock !
          */
         if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
                 /* Keep the OWNER_DIED bit */
                 newval = (curval & ~FUTEX_TID_MASK) | task_pid_vnr(task);
                 ownerdied = 0;
                 lock_taken = 1;
         }
 
         curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
 
         if (unlikely(curval == -EFAULT))
                 return -EFAULT;
         if (unlikely(curval != uval))
                 goto retry;
 
         /*
          * We took the lock due to owner died take over.
          */
         if (unlikely(lock_taken))
                 return 1;
 
         /*
          * We dont have the lock. Look up the PI state (or create it if
          * we are the first waiter):
          */
         ret = lookup_pi_state(uval, hb, key, ps);
 
         if (unlikely(ret)) {
                 switch (ret) {
                 case -ESRCH:
                         /*
                          * No owner found for this futex. Check if the
                          * OWNER_DIED bit is set to figure out whether
                          * this is a robust futex or not.
                          */
                         if (get_futex_value_locked(&curval, uaddr))
                                 return -EFAULT;
 
                         /*
                          * We simply start over in case of a robust
                          * futex. The code above will take the futex
                          * and return happy.
                          */
                         if (curval & FUTEX_OWNER_DIED) {
                                 ownerdied = 1;
                                 goto retry;
                         }
                 default:
                         break;
                 }
         }
 
         return ret;
 }
 
 /*
  * The hash bucket lock must be held when this is called.
  * Afterwards, the futex_q must not be accessed.
  */
 static void wake_futex(struct futex_q *q)
 {
         struct task_struct *p = q->task;
 
         /*
          * We set q->lock_ptr = NULL _before_ we wake up the task. If
          * a non futex wake up happens on another CPU then the task
          * might exit and p would dereference a non existing task
          * struct. Prevent this by holding a reference on p across the
          * wake up.
          */
         get_task_struct(p);
 
         plist_del(&q->list, &q->list.plist);
         /*
          * The waiting task can free the futex_q as soon as
          * q->lock_ptr = NULL is written, without taking any locks. A
          * memory barrier is required here to prevent the following
          * store to lock_ptr from getting ahead of the plist_del.
          */
         smp_wmb();
         q->lock_ptr = NULL;
 
         wake_up_state(p, TASK_NORMAL);
         put_task_struct(p);
 }
 
 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
 {
         struct task_struct *new_owner;
         struct futex_pi_state *pi_state = this->pi_state;
         u32 curval, newval;
 
         if (!pi_state)
                 return -EINVAL;
 
         /*
          * If current does not own the pi_state then the futex is
          * inconsistent and user space fiddled with the futex value.
          */
         if (pi_state->owner != current)
                 return -EINVAL;
 
         spin_lock(&pi_state->pi_mutex.wait_lock);
         new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
 
         /*
          * This happens when we have stolen the lock and the original
          * pending owner did not enqueue itself back on the rt_mutex.
          * Thats not a tragedy. We know that way, that a lock waiter
          * is on the fly. We make the futex_q waiter the pending owner.
          */
         if (!new_owner)
                 new_owner = this->task;
 
         /*
          * We pass it to the next owner. (The WAITERS bit is always
          * kept enabled while there is PI state around. We must also
          * preserve the owner died bit.)
          */
         if (!(uval & FUTEX_OWNER_DIED)) {
                 int ret = 0;
 
                 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
 
                 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
 
                 if (curval == -EFAULT)
                         ret = -EFAULT;
                 else if (curval != uval)
                         ret = -EINVAL;
                 if (ret) {
                         spin_unlock(&pi_state->pi_mutex.wait_lock);
                         return ret;
                 }
         }
 
         spin_lock_irq(&pi_state->owner->pi_lock);
         WARN_ON(list_empty(&pi_state->list));
         list_del_init(&pi_state->list);
         spin_unlock_irq(&pi_state->owner->pi_lock);
 
         spin_lock_irq(&new_owner->pi_lock);
         WARN_ON(!list_empty(&pi_state->list));
         list_add(&pi_state->list, &new_owner->pi_state_list);
         pi_state->owner = new_owner;
         spin_unlock_irq(&new_owner->pi_lock);
 
         spin_unlock(&pi_state->pi_mutex.wait_lock);
         rt_mutex_unlock(&pi_state->pi_mutex);
 
         return 0;
 }
 
 static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
 {
         u32 oldval;
 
         /*
          * There is no waiter, so we unlock the futex. The owner died
          * bit has not to be preserved here. We are the owner:
          */
         oldval = cmpxchg_futex_value_locked(uaddr, uval, 0);
 
         if (oldval == -EFAULT)
                 return oldval;
         if (oldval != uval)
                 return -EAGAIN;
 
         return 0;
 }
 
 /*
  * Express the locking dependencies for lockdep:
  */
 static inline void
 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
 {
         if (hb1 <= hb2) {
                 spin_lock(&hb1->lock);
                 if (hb1 < hb2)
                         spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
         } else { /* hb1 > hb2 */
                 spin_lock(&hb2->lock);
                 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
         }
 }
 
 static inline void
 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
 {
         spin_unlock(&hb1->lock);
         if (hb1 != hb2)
                 spin_unlock(&hb2->lock);
 }
 
 /*
  * Wake up waiters matching bitset queued on this futex (uaddr).
  */
 static int futex_wake(u32 __user *uaddr, int fshared, int nr_wake, u32 bitset)
 {
         struct futex_hash_bucket *hb;
         struct futex_q *this, *next;
         struct plist_head *head;
         union futex_key key = FUTEX_KEY_INIT;
         int ret;
 
         if (!bitset)
                 return -EINVAL;
 
         ret = get_futex_key(uaddr, fshared, &key, VERIFY_READ);
         if (unlikely(ret != 0))
                 goto out;
 
         hb = hash_futex(&key);
         spin_lock(&hb->lock);
         head = &hb->chain;
 
         plist_for_each_entry_safe(this, next, head, list) {
                 if (match_futex (&this->key, &key)) {
                         if (this->pi_state || this->rt_waiter) {
                                 ret = -EINVAL;
                                 break;
                         }
 
                         /* Check if one of the bits is set in both bitsets */
                         if (!(this->bitset & bitset))
                                 continue;
 
                         wake_futex(this);
                         if (++ret >= nr_wake)
                                 break;
                 }
         }
 
         spin_unlock(&hb->lock);
         put_futex_key(fshared, &key);
 out:
         return ret;
 }
 
 /*
  * Wake up all waiters hashed on the physical page that is mapped
  * to this virtual address:
  */
 static int
 futex_wake_op(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
               int nr_wake, int nr_wake2, int op)
 {
         union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
         struct futex_hash_bucket *hb1, *hb2;
         struct plist_head *head;
         struct futex_q *this, *next;
         int ret, op_ret;
 
 retry:
         ret = get_futex_key(uaddr1, fshared, &key1, VERIFY_READ);
         if (unlikely(ret != 0))
                 goto out;
         ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE);
         if (unlikely(ret != 0))
                 goto out_put_key1;
 
         hb1 = hash_futex(&key1);
         hb2 = hash_futex(&key2);
 
 retry_private:
         double_lock_hb(hb1, hb2);
         op_ret = futex_atomic_op_inuser(op, uaddr2);
         if (unlikely(op_ret < 0)) {
 
                 double_unlock_hb(hb1, hb2);
 
 #ifndef CONFIG_MMU
                 /*
                  * we don't get EFAULT from MMU faults if we don't have an MMU,
                  * but we might get them from range checking
                  */
                 ret = op_ret;
                 goto out_put_keys;
 #endif
 
                 if (unlikely(op_ret != -EFAULT)) {
                         ret = op_ret;
                         goto out_put_keys;
                 }
 
                 ret = fault_in_user_writeable(uaddr2);
                 if (ret)
                         goto out_put_keys;
 
                 if (!fshared)
                         goto retry_private;
 
                 put_futex_key(fshared, &key2);
                 put_futex_key(fshared, &key1);
                 goto retry;
         }
 
         head = &hb1->chain;
 
         plist_for_each_entry_safe(this, next, head, list) {
                 if (match_futex (&this->key, &key1)) {
                         wake_futex(this);
                         if (++ret >= nr_wake)
                                 break;
                 }
         }
 
         if (op_ret > 0) {
                 head = &hb2->chain;
 
                 op_ret = 0;
                 plist_for_each_entry_safe(this, next, head, list) {
                         if (match_futex (&this->key, &key2)) {
                                 wake_futex(this);
                                 if (++op_ret >= nr_wake2)
                                         break;
                         }
                 }
                 ret += op_ret;
         }
 
         double_unlock_hb(hb1, hb2);
 out_put_keys:
         put_futex_key(fshared, &key2);
 out_put_key1:
         put_futex_key(fshared, &key1);
 out:
         return ret;
 }
 
 /**
  * requeue_futex() - Requeue a futex_q from one hb to another
  * @q:          the futex_q to requeue
  * @hb1:        the source hash_bucket
  * @hb2:        the target hash_bucket
  * @key2:       the new key for the requeued futex_q
  */
 static inline
 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
                    struct futex_hash_bucket *hb2, union futex_key *key2)
 {
 
         /*
          * If key1 and key2 hash to the same bucket, no need to
          * requeue.
          */
         if (likely(&hb1->chain != &hb2->chain)) {
                 plist_del(&q->list, &hb1->chain);
                 plist_add(&q->list, &hb2->chain);
                 q->lock_ptr = &hb2->lock;
 #ifdef CONFIG_DEBUG_PI_LIST
                 q->list.plist.lock = &hb2->lock;
 #endif
         }
         get_futex_key_refs(key2);
         q->key = *key2;
 }
 
 /**
  * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
  * q:   the futex_q
  * key: the key of the requeue target futex
  * hb:  the hash_bucket of the requeue target futex
  *
  * During futex_requeue, with requeue_pi=1, it is possible to acquire the
  * target futex if it is uncontended or via a lock steal.  Set the futex_q key
  * to the requeue target futex so the waiter can detect the wakeup on the right
  * futex, but remove it from the hb and NULL the rt_waiter so it can detect
  * atomic lock acquisition.  Set the q->lock_ptr to the requeue target hb->lock
  * to protect access to the pi_state to fixup the owner later.  Must be called
  * with both q->lock_ptr and hb->lock held.
  */
 static inline
 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
                            struct futex_hash_bucket *hb)
 {
         get_futex_key_refs(key);
         q->key = *key;
 
         WARN_ON(plist_node_empty(&q->list));
         plist_del(&q->list, &q->list.plist);
 
         WARN_ON(!q->rt_waiter);
         q->rt_waiter = NULL;
 
         q->lock_ptr = &hb->lock;
 #ifdef CONFIG_DEBUG_PI_LIST
         q->list.plist.lock = &hb->lock;
 #endif
 
         wake_up_state(q->task, TASK_NORMAL);
 }
 
 /**
  * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
  * @pifutex:            the user address of the to futex
  * @hb1:                the from futex hash bucket, must be locked by the caller
  * @hb2:                the to futex hash bucket, must be locked by the caller
  * @key1:               the from futex key
  * @key2:               the to futex key
  * @ps:                 address to store the pi_state pointer
  * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
  *
  * Try and get the lock on behalf of the top waiter if we can do it atomically.
  * Wake the top waiter if we succeed.  If the caller specified set_waiters,
  * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
  * hb1 and hb2 must be held by the caller.
  *
  * Returns:
  *  0 - failed to acquire the lock atomicly
  *  1 - acquired the lock
  * <0 - error
  */
 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
                                  struct futex_hash_bucket *hb1,
                                  struct futex_hash_bucket *hb2,
                                  union futex_key *key1, union futex_key *key2,
                                  struct futex_pi_state **ps, int set_waiters)
 {
         struct futex_q *top_waiter = NULL;
         u32 curval;
         int ret;
 
         if (get_futex_value_locked(&curval, pifutex))
                 return -EFAULT;
 
         /*
          * Find the top_waiter and determine if there are additional waiters.
          * If the caller intends to requeue more than 1 waiter to pifutex,
          * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
          * as we have means to handle the possible fault.  If not, don't set
          * the bit unecessarily as it will force the subsequent unlock to enter
          * the kernel.
          */
         top_waiter = futex_top_waiter(hb1, key1);
 
         /* There are no waiters, nothing for us to do. */
         if (!top_waiter)
                 return 0;
 
         /* Ensure we requeue to the expected futex. */
         if (!match_futex(top_waiter->requeue_pi_key, key2))
                 return -EINVAL;
 
         /*
          * Try to take the lock for top_waiter.  Set the FUTEX_WAITERS bit in
          * the contended case or if set_waiters is 1.  The pi_state is returned
          * in ps in contended cases.
          */
         ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
                                    set_waiters);
         if (ret == 1)
                 requeue_pi_wake_futex(top_waiter, key2, hb2);
 
         return ret;
 }
 
 /**
  * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
  * uaddr1:      source futex user address
  * uaddr2:      target futex user address
  * nr_wake:     number of waiters to wake (must be 1 for requeue_pi)
  * nr_requeue:  number of waiters to requeue (0-INT_MAX)
  * requeue_pi:  if we are attempting to requeue from a non-pi futex to a
  *              pi futex (pi to pi requeue is not supported)
  *
  * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
  * uaddr2 atomically on behalf of the top waiter.
  *
  * Returns:
  * >=0 - on success, the number of tasks requeued or woken
  *  <0 - on error
  */
 static int futex_requeue(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
                          int nr_wake, int nr_requeue, u32 *cmpval,
                          int requeue_pi)
 {
         union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
         int drop_count = 0, task_count = 0, ret;
         struct futex_pi_state *pi_state = NULL;
         struct futex_hash_bucket *hb1, *hb2;
         struct plist_head *head1;
         struct futex_q *this, *next;
         u32 curval2;
 
         if (requeue_pi) {
                 /*
                  * requeue_pi requires a pi_state, try to allocate it now
                  * without any locks in case it fails.
                  */
                 if (refill_pi_state_cache())
                         return -ENOMEM;
                 /*
                  * requeue_pi must wake as many tasks as it can, up to nr_wake
                  * + nr_requeue, since it acquires the rt_mutex prior to
                  * returning to userspace, so as to not leave the rt_mutex with
                  * waiters and no owner.  However, second and third wake-ups
                  * cannot be predicted as they involve race conditions with the
                  * first wake and a fault while looking up the pi_state.  Both
                  * pthread_cond_signal() and pthread_cond_broadcast() should
                  * use nr_wake=1.
                  */
                 if (nr_wake != 1)
                         return -EINVAL;
         }
 
 retry:
         if (pi_state != NULL) {
                 /*
                  * We will have to lookup the pi_state again, so free this one
                  * to keep the accounting correct.
                  */
                 free_pi_state(pi_state);
                 pi_state = NULL;
         }
 
         ret = get_futex_key(uaddr1, fshared, &key1, VERIFY_READ);
         if (unlikely(ret != 0))
                 goto out;
         ret = get_futex_key(uaddr2, fshared, &key2,
                             requeue_pi ? VERIFY_WRITE : VERIFY_READ);
         if (unlikely(ret != 0))
                 goto out_put_key1;
 
         hb1 = hash_futex(&key1);
         hb2 = hash_futex(&key2);
 
 retry_private:
         double_lock_hb(hb1, hb2);
 
         if (likely(cmpval != NULL)) {
                 u32 curval;
 
                 ret = get_futex_value_locked(&curval, uaddr1);
 
                 if (unlikely(ret)) {
                         double_unlock_hb(hb1, hb2);
 
                         ret = get_user(curval, uaddr1);
                         if (ret)
                                 goto out_put_keys;
 
                         if (!fshared)
                                 goto retry_private;
 
                         put_futex_key(fshared, &key2);
                         put_futex_key(fshared, &key1);
                         goto retry;
                 }
                 if (curval != *cmpval) {
                         ret = -EAGAIN;
                         goto out_unlock;
                 }
         }
 
         if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
                 /*
                  * Attempt to acquire uaddr2 and wake the top waiter. If we
                  * intend to requeue waiters, force setting the FUTEX_WAITERS
                  * bit.  We force this here where we are able to easily handle
                  * faults rather in the requeue loop below.
                  */
                 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
                                                  &key2, &pi_state, nr_requeue);
 
                 /*
                  * At this point the top_waiter has either taken uaddr2 or is
                  * waiting on it.  If the former, then the pi_state will not
                  * exist yet, look it up one more time to ensure we have a
                  * reference to it.
                  */
                 if (ret == 1) {
                         WARN_ON(pi_state);
                         drop_count++;
                         task_count++;
                         ret = get_futex_value_locked(&curval2, uaddr2);
                         if (!ret)
                                 ret = lookup_pi_state(curval2, hb2, &key2,
                                                       &pi_state);
                 }
 
                 switch (ret) {
                 case 0:
                         break;
                 case -EFAULT:
                         double_unlock_hb(hb1, hb2);
                         put_futex_key(fshared, &key2);
                         put_futex_key(fshared, &key1);
                         ret = fault_in_user_writeable(uaddr2);
                         if (!ret)
                                 goto retry;
                         goto out;
                 case -EAGAIN:
                         /* The owner was exiting, try again. */
                         double_unlock_hb(hb1, hb2);
                         put_futex_key(fshared, &key2);
                         put_futex_key(fshared, &key1);
                         cond_resched();
                         goto retry;
                 default:
                         goto out_unlock;
                 }
         }
 
         head1 = &hb1->chain;
         plist_for_each_entry_safe(this, next, head1, list) {
                 if (task_count - nr_wake >= nr_requeue)
                         break;
 
                 if (!match_futex(&this->key, &key1))
                         continue;
 
                 /*
                  * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
                  * be paired with each other and no other futex ops.
                  */
                 if ((requeue_pi && !this->rt_waiter) ||
                     (!requeue_pi && this->rt_waiter)) {
                         ret = -EINVAL;
                         break;
                 }
 
                 /*
                  * Wake nr_wake waiters.  For requeue_pi, if we acquired the
                  * lock, we already woke the top_waiter.  If not, it will be
                  * woken by futex_unlock_pi().
                  */
                 if (++task_count <= nr_wake && !requeue_pi) {
                         wake_futex(this);
                         continue;
                 }
 
                 /* Ensure we requeue to the expected futex for requeue_pi. */
                 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
                         ret = -EINVAL;
                         break;
                 }
 
                 /*
                  * Requeue nr_requeue waiters and possibly one more in the case
                  * of requeue_pi if we couldn't acquire the lock atomically.
                  */
                 if (requeue_pi) {
                         /* Prepare the waiter to take the rt_mutex. */
                         atomic_inc(&pi_state->refcount);
                         this->pi_state = pi_state;
                         ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
                                                         this->rt_waiter,
                                                         this->task, 1);
                         if (ret == 1) {
                                 /* We got the lock. */
                                 requeue_pi_wake_futex(this, &key2, hb2);
                                 drop_count++;
                                 continue;
                         } else if (ret) {
                                 /* -EDEADLK */
                                 this->pi_state = NULL;
                                 free_pi_state(pi_state);
                                 goto out_unlock;
                         }
                 }
                 requeue_futex(this, hb1, hb2, &key2);
                 drop_count++;
         }
 
 out_unlock:
         double_unlock_hb(hb1, hb2);
 
         /*
          * drop_futex_key_refs() must be called outside the spinlocks. During
          * the requeue we moved futex_q's from the hash bucket at key1 to the
          * one at key2 and updated their key pointer.  We no longer need to
          * hold the references to key1.
          */
         while (--drop_count >= 0)
                 drop_futex_key_refs(&key1);
 
 out_put_keys:
         put_futex_key(fshared, &key2);
 out_put_key1:
         put_futex_key(fshared, &key1);
 out:
         if (pi_state != NULL)
                 free_pi_state(pi_state);
         return ret ? ret : task_count;
 }
 
 /* The key must be already stored in q->key. */
 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
 {
         struct futex_hash_bucket *hb;
 
         get_futex_key_refs(&q->key);
         hb = hash_futex(&q->key);
         q->lock_ptr = &hb->lock;
 
         spin_lock(&hb->lock);
         return hb;
 }
 
 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
 {
         int prio;
 
         /*
          * The priority used to register this element is
          * - either the real thread-priority for the real-time threads
          * (i.e. threads with a priority lower than MAX_RT_PRIO)
          * - or MAX_RT_PRIO for non-RT threads.
          * Thus, all RT-threads are woken first in priority order, and
          * the others are woken last, in FIFO order.
          */
         prio = min(current->normal_prio, MAX_RT_PRIO);
 
         plist_node_init(&q->list, prio);
 #ifdef CONFIG_DEBUG_PI_LIST
         q->list.plist.lock = &hb->lock;
 #endif
         plist_add(&q->list, &hb->chain);
         q->task = current;
         spin_unlock(&hb->lock);
 }
 
 static inline void
 queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
 {
         spin_unlock(&hb->lock);
         drop_futex_key_refs(&q->key);
 }
 
 /*
  * queue_me and unqueue_me must be called as a pair, each
  * exactly once.  They are called with the hashed spinlock held.
  */
 
 /* Return 1 if we were still queued (ie. 0 means we were woken) */
 static int unqueue_me(struct futex_q *q)
 {
         spinlock_t *lock_ptr;
         int ret = 0;
 
         /* In the common case we don't take the spinlock, which is nice. */
 retry:
         lock_ptr = q->lock_ptr;
         barrier();
         if (lock_ptr != NULL) {
                 spin_lock(lock_ptr);
                 /*
                  * q->lock_ptr can change between reading it and
                  * spin_lock(), causing us to take the wrong lock.  This
                  * corrects the race condition.
                  *
                  * Reasoning goes like this: if we have the wrong lock,
                  * q->lock_ptr must have changed (maybe several times)
                  * between reading it and the spin_lock().  It can
                  * change again after the spin_lock() but only if it was
                  * already changed before the spin_lock().  It cannot,
                  * however, change back to the original value.  Therefore
                  * we can detect whether we acquired the correct lock.
                  */
                 if (unlikely(lock_ptr != q->lock_ptr)) {
                         spin_unlock(lock_ptr);
                         goto retry;
                 }
                 WARN_ON(plist_node_empty(&q->list));
                 plist_del(&q->list, &q->list.plist);
 
                 BUG_ON(q->pi_state);
 
                 spin_unlock(lock_ptr);
                 ret = 1;
         }
 
         drop_futex_key_refs(&q->key);
         return ret;
 }
 
 /*
  * PI futexes can not be requeued and must remove themself from the
  * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
  * and dropped here.
  */
 static void unqueue_me_pi(struct futex_q *q)
 {
         WARN_ON(plist_node_empty(&q->list));
         plist_del(&q->list, &q->list.plist);
 
         BUG_ON(!q->pi_state);
         free_pi_state(q->pi_state);
         q->pi_state = NULL;
 
         spin_unlock(q->lock_ptr);
 
         drop_futex_key_refs(&q->key);
 }
 
 /*
  * Fixup the pi_state owner with the new owner.
  *
  * Must be called with hash bucket lock held and mm->sem held for non
  * private futexes.
  */
 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
                                 struct task_struct *newowner, int fshared)
 {
         u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
         struct futex_pi_state *pi_state = q->pi_state;
         struct task_struct *oldowner = pi_state->owner;
         u32 uval, curval, newval;
         int ret;
 
         /* Owner died? */
         if (!pi_state->owner)
                 newtid |= FUTEX_OWNER_DIED;
 
         /*
          * We are here either because we stole the rtmutex from the
          * pending owner or we are the pending owner which failed to
          * get the rtmutex. We have to replace the pending owner TID
          * in the user space variable. This must be atomic as we have
          * to preserve the owner died bit here.
          *
          * Note: We write the user space value _before_ changing the pi_state
          * because we can fault here. Imagine swapped out pages or a fork
          * that marked all the anonymous memory readonly for cow.
          *
          * Modifying pi_state _before_ the user space value would
          * leave the pi_state in an inconsistent state when we fault
          * here, because we need to drop the hash bucket lock to
          * handle the fault. This might be observed in the PID check
          * in lookup_pi_state.
          */
 retry:
         if (get_futex_value_locked(&uval, uaddr))
                 goto handle_fault;
 
         while (1) {
                 newval = (uval & FUTEX_OWNER_DIED) | newtid;
 
                 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
 
                 if (curval == -EFAULT)
                         goto handle_fault;
                 if (curval == uval)
                         break;
                 uval = curval;
         }
 
         /*
          * We fixed up user space. Now we need to fix the pi_state
          * itself.
          */
         if (pi_state->owner != NULL) {
                 spin_lock_irq(&pi_state->owner->pi_lock);
                 WARN_ON(list_empty(&pi_state->list));
                 list_del_init(&pi_state->list);
                 spin_unlock_irq(&pi_state->owner->pi_lock);
         }
 
         pi_state->owner = newowner;
 
         spin_lock_irq(&newowner->pi_lock);
         WARN_ON(!list_empty(&pi_state->list));
         list_add(&pi_state->list, &newowner->pi_state_list);
         spin_unlock_irq(&newowner->pi_lock);
         return 0;
 
         /*
          * To handle the page fault we need to drop the hash bucket
          * lock here. That gives the other task (either the pending
          * owner itself or the task which stole the rtmutex) the
          * chance to try the fixup of the pi_state. So once we are
          * back from handling the fault we need to check the pi_state
          * after reacquiring the hash bucket lock and before trying to
          * do another fixup. When the fixup has been done already we
          * simply return.
          */
 handle_fault:
         spin_unlock(q->lock_ptr);
 
         ret = fault_in_user_writeable(uaddr);
 
         spin_lock(q->lock_ptr);
 
         /*
          * Check if someone else fixed it for us:
          */
         if (pi_state->owner != oldowner)
                 return 0;
 
         if (ret)
                 return ret;
 
         goto retry;
 }
 
 /*
  * In case we must use restart_block to restart a futex_wait,
  * we encode in the 'flags' shared capability
  */
 #define FLAGS_SHARED            0x01
 #define FLAGS_CLOCKRT           0x02
 #define FLAGS_HAS_TIMEOUT       0x04
 
 static long futex_wait_restart(struct restart_block *restart);
 
 /**
  * fixup_owner() - Post lock pi_state and corner case management
  * @uaddr:      user address of the futex
  * @fshared:    whether the futex is shared (1) or not (0)
  * @q:          futex_q (contains pi_state and access to the rt_mutex)
  * @locked:     if the attempt to take the rt_mutex succeeded (1) or not (0)
  *
  * After attempting to lock an rt_mutex, this function is called to cleanup
  * the pi_state owner as well as handle race conditions that may allow us to
  * acquire the lock. Must be called with the hb lock held.
  *
  * Returns:
  *  1 - success, lock taken
  *  0 - success, lock not taken
  * <0 - on error (-EFAULT)
  */
 static int fixup_owner(u32 __user *uaddr, int fshared, struct futex_q *q,
                        int locked)
 {
         struct task_struct *owner;
         int ret = 0;
 
         if (locked) {
                 /*
                  * Got the lock. We might not be the anticipated owner if we
                  * did a lock-steal - fix up the PI-state in that case:
                  */
                 if (q->pi_state->owner != current)
                         ret = fixup_pi_state_owner(uaddr, q, current, fshared);
                 goto out;
         }
 
         /*
          * Catch the rare case, where the lock was released when we were on the
          * way back before we locked the hash bucket.
          */
         if (q->pi_state->owner == current) {
                 /*
                  * Try to get the rt_mutex now. This might fail as some other
                  * task acquired the rt_mutex after we removed ourself from the
                  * rt_mutex waiters list.
                  */
                 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
                         locked = 1;
                         goto out;
                 }
 
                 /*
                  * pi_state is incorrect, some other task did a lock steal and
                  * we returned due to timeout or signal without taking the
                  * rt_mutex. Too late. We can access the rt_mutex_owner without
                  * locking, as the other task is now blocked on the hash bucket
                  * lock. Fix the state up.
                  */
                 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
                 ret = fixup_pi_state_owner(uaddr, q, owner, fshared);
                 goto out;
         }
 
         /*
          * Paranoia check. If we did not take the lock, then we should not be
          * the owner, nor the pending owner, of the rt_mutex.
          */
         if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
                 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
                                 "pi-state %p\n", ret,
                                 q->pi_state->pi_mutex.owner,
                                 q->pi_state->owner);
 
 out:
         return ret ? ret : locked;
 }
 
 /**
  * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
  * @hb:         the futex hash bucket, must be locked by the caller
  * @q:          the futex_q to queue up on
  * @timeout:    the prepared hrtimer_sleeper, or null for no timeout
  */
 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
                                 struct hrtimer_sleeper *timeout)
 {
         set_current_state(TASK_INTERRUPTIBLE);
         queue_me(q, hb);
 
         /* Arm the timer */
         if (timeout) {
                 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
                 if (!hrtimer_active(&timeout->timer))
                         timeout->task = NULL;
         }
 
         /*
          * If we have been removed from the hash list, then another task
          * has tried to wake us, and we can skip the call to schedule().
          */
         if (likely(!plist_node_empty(&q->list))) {
                 /*
                  * If the timer has already expired, current will already be
                  * flagged for rescheduling. Only call schedule if there
                  * is no timeout, or if it has yet to expire.
                  */
                 if (!timeout || timeout->task)
                         schedule();
         }
         __set_current_state(TASK_RUNNING);
 }
 
 /**
  * futex_wait_setup() - Prepare to wait on a futex
  * @uaddr:      the futex userspace address
  * @val:        the expected value
  * @fshared:    whether the futex is shared (1) or not (0)
  * @q:          the associated futex_q
  * @hb:         storage for hash_bucket pointer to be returned to caller
  *
  * Setup the futex_q and locate the hash_bucket.  Get the futex value and
  * compare it with the expected value.  Handle atomic faults internally.
  * Return with the hb lock held and a q.key reference on success, and unlocked
  * with no q.key reference on failure.
  *
  * Returns:
  *  0 - uaddr contains val and hb has been locked
  * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlcoked
  */
 static int futex_wait_setup(u32 __user *uaddr, u32 val, int fshared,
                            struct futex_q *q, struct futex_hash_bucket **hb)
 {
         u32 uval;
         int ret;
 
         /*
          * Access the page AFTER the hash-bucket is locked.
          * Order is important:
          *
          *   Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
          *   Userspace waker:  if (cond(var)) { var = new; futex_wake(&var); }
          *
          * The basic logical guarantee of a futex is that it blocks ONLY
          * if cond(var) is known to be true at the time of blocking, for
          * any cond.  If we queued after testing *uaddr, that would open
          * a race condition where we could block indefinitely with
          * cond(var) false, which would violate the guarantee.
          *
          * A consequence is that futex_wait() can return zero and absorb
          * a wakeup when *uaddr != val on entry to the syscall.  This is
          * rare, but normal.
          */
 retry:
         q->key = FUTEX_KEY_INIT;
         ret = get_futex_key(uaddr, fshared, &q->key, VERIFY_READ);
         if (unlikely(ret != 0))
                 return ret;
 
 retry_private:
         *hb = queue_lock(q);
 
         ret = get_futex_value_locked(&uval, uaddr);
 
         if (ret) {
                 queue_unlock(q, *hb);
 
                 ret = get_user(uval, uaddr);
                 if (ret)
                         goto out;
 
                 if (!fshared)
                         goto retry_private;
 
                 put_futex_key(fshared, &q->key);
                 goto retry;
         }
 
         if (uval != val) {
                 queue_unlock(q, *hb);
                 ret = -EWOULDBLOCK;
         }
 
 out:
         if (ret)
                 put_futex_key(fshared, &q->key);
         return ret;
 }
 
 static int futex_wait(u32 __user *uaddr, int fshared,
                       u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
 {
         struct hrtimer_sleeper timeout, *to = NULL;
         struct restart_block *restart;
         struct futex_hash_bucket *hb;
         struct futex_q q;
         int ret;
 
         if (!bitset)
                 return -EINVAL;
 
         q.pi_state = NULL;
         q.bitset = bitset;
         q.rt_waiter = NULL;
         q.requeue_pi_key = NULL;
 
         if (abs_time) {
                 to = &timeout;
 
                 hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
                                       CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
                 hrtimer_init_sleeper(to, current);
                 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
                                              current->timer_slack_ns);
         }
 
 retry:
         /* Prepare to wait on uaddr. */
         ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
         if (ret)
                 goto out;
 
         /* queue_me and wait for wakeup, timeout, or a signal. */
         futex_wait_queue_me(hb, &q, to);
 
         /* If we were woken (and unqueued), we succeeded, whatever. */
         ret = 0;
         if (!unqueue_me(&q))
                 goto out_put_key;
         ret = -ETIMEDOUT;
         if (to && !to->task)
                 goto out_put_key;
 
         /*
          * We expect signal_pending(current), but we might be the
          * victim of a spurious wakeup as well.
          */
         if (!signal_pending(current)) {
                 put_futex_key(fshared, &q.key);
                 goto retry;
         }
 
         ret = -ERESTARTSYS;
         if (!abs_time)
                 goto out_put_key;
 
         restart = &current_thread_info()->restart_block;
         restart->fn = futex_wait_restart;
         restart->futex.uaddr = (u32 *)uaddr;
         restart->futex.val = val;
         restart->futex.time = abs_time->tv64;
         restart->futex.bitset = bitset;
         restart->futex.flags = FLAGS_HAS_TIMEOUT;
 
         if (fshared)
                 restart->futex.flags |= FLAGS_SHARED;
         if (clockrt)
                 restart->futex.flags |= FLAGS_CLOCKRT;
 
         ret = -ERESTART_RESTARTBLOCK;
 
 out_put_key:
         put_futex_key(fshared, &q.key);
 out:
         if (to) {
                 hrtimer_cancel(&to->timer);
                 destroy_hrtimer_on_stack(&to->timer);
         }
         return ret;
 }
 
 
 static long futex_wait_restart(struct restart_block *restart)
 {
         u32 __user *uaddr = (u32 __user *)restart->futex.uaddr;
         int fshared = 0;
         ktime_t t, *tp = NULL;
 
         if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
                 t.tv64 = restart->futex.time;
                 tp = &t;
         }
         restart->fn = do_no_restart_syscall;
         if (restart->futex.flags & FLAGS_SHARED)
                 fshared = 1;
         return (long)futex_wait(uaddr, fshared, restart->futex.val, tp,
                                 restart->futex.bitset,
                                 restart->futex.flags & FLAGS_CLOCKRT);
 }
 
 
 /*
  * Userspace tried a 0 -> TID atomic transition of the futex value
  * and failed. The kernel side here does the whole locking operation:
  * if there are waiters then it will block, it does PI, etc. (Due to
  * races the kernel might see a 0 value of the futex too.)
  */
 static int futex_lock_pi(u32 __user *uaddr, int fshared,
                          int detect, ktime_t *time, int trylock)
 {
         struct hrtimer_sleeper timeout, *to = NULL;
         struct futex_hash_bucket *hb;
         struct futex_q q;
         int res, ret;
 
         if (refill_pi_state_cache())
                 return -ENOMEM;
 
         if (time) {
                 to = &timeout;
                 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
                                       HRTIMER_MODE_ABS);
                 hrtimer_init_sleeper(to, current);
                 hrtimer_set_expires(&to->timer, *time);
         }
 
         q.pi_state = NULL;
         q.rt_waiter = NULL;
         q.requeue_pi_key = NULL;
 retry:
         q.key = FUTEX_KEY_INIT;
         ret = get_futex_key(uaddr, fshared, &q.key, VERIFY_WRITE);
         if (unlikely(ret != 0))
                 goto out;
 
 retry_private:
         hb = queue_lock(&q);
 
         ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
         if (unlikely(ret)) {
                 switch (ret) {
                 case 1:
                         /* We got the lock. */
                         ret = 0;
                         goto out_unlock_put_key;
                 case -EFAULT:
                         goto uaddr_faulted;
                 case -EAGAIN:
                         /*
                          * Task is exiting and we just wait for the
                          * exit to complete.
                          */
                         queue_unlock(&q, hb);
                         put_futex_key(fshared, &q.key);
                         cond_resched();
                         goto retry;
                 default:
                         goto out_unlock_put_key;
                 }
         }
 
         /*
          * Only actually queue now that the atomic ops are done:
          */
         queue_me(&q, hb);
 
         WARN_ON(!q.pi_state);
         /*
          * Block on the PI mutex:
          */
         if (!trylock)
                 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
         else {
                 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
                 /* Fixup the trylock return value: */
                 ret = ret ? 0 : -EWOULDBLOCK;
         }
 
         spin_lock(q.lock_ptr);
         /*
          * Fixup the pi_state owner and possibly acquire the lock if we
          * haven't already.
          */
         res = fixup_owner(uaddr, fshared, &q, !ret);
         /*
          * If fixup_owner() returned an error, proprogate that.  If it acquired
          * the lock, clear our -ETIMEDOUT or -EINTR.
          */
         if (res)
                 ret = (res < 0) ? res : 0;
 
         /*
          * If fixup_owner() faulted and was unable to handle the fault, unlock
          * it and return the fault to userspace.
          */
         if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
                 rt_mutex_unlock(&q.pi_state->pi_mutex);
 
         /* Unqueue and drop the lock */
         unqueue_me_pi(&q);
 
         goto out_put_key;
 
 out_unlock_put_key:
         queue_unlock(&q, hb);
 
 out_put_key:
         put_futex_key(fshared, &q.key);
 out:
         if (to)
                 destroy_hrtimer_on_stack(&to->timer);
         return ret != -EINTR ? ret : -ERESTARTNOINTR;
 
 uaddr_faulted:
         queue_unlock(&q, hb);
 
         ret = fault_in_user_writeable(uaddr);
         if (ret)
                 goto out_put_key;
 
         if (!fshared)
                 goto retry_private;
 
         put_futex_key(fshared, &q.key);
         goto retry;
 }
 
 /*
  * Userspace attempted a TID -> 0 atomic transition, and failed.
  * This is the in-kernel slowpath: we look up the PI state (if any),
  * and do the rt-mutex unlock.
  */
 static int futex_unlock_pi(u32 __user *uaddr, int fshared)
 {
         struct futex_hash_bucket *hb;
         struct futex_q *this, *next;
         u32 uval;
         struct plist_head *head;
         union futex_key key = FUTEX_KEY_INIT;
         int ret;
 
 retry:
         if (get_user(uval, uaddr))
                 return -EFAULT;
         /*
          * We release only a lock we actually own:
          */
         if ((uval & FUTEX_TID_MASK) != task_pid_vnr(current))
                 return -EPERM;
 
         ret = get_futex_key(uaddr, fshared, &key, VERIFY_WRITE);
         if (unlikely(ret != 0))
                 goto out;
 
         hb = hash_futex(&key);
         spin_lock(&hb->lock);
 
         /*
          * To avoid races, try to do the TID -> 0 atomic transition
          * again. If it succeeds then we can return without waking
          * anyone else up:
          */
         if (!(uval & FUTEX_OWNER_DIED))
                 uval = cmpxchg_futex_value_locked(uaddr, task_pid_vnr(current), 0);
 
 
         if (unlikely(uval == -EFAULT))
                 goto pi_faulted;
         /*
          * Rare case: we managed to release the lock atomically,
          * no need to wake anyone else up:
          */
         if (unlikely(uval == task_pid_vnr(current)))
                 goto out_unlock;
 
         /*
          * Ok, other tasks may need to be woken up - check waiters
          * and do the wakeup if necessary:
          */
         head = &hb->chain;
 
         plist_for_each_entry_safe(this, next, head, list) {
                 if (!match_futex (&this->key, &key))
                         continue;
                 ret = wake_futex_pi(uaddr, uval, this);
                 /*
                  * The atomic access to the futex value
                  * generated a pagefault, so retry the
                  * user-access and the wakeup:
                  */
                 if (ret == -EFAULT)
                         goto pi_faulted;
                 goto out_unlock;
         }
         /*
          * No waiters - kernel unlocks the futex:
          */
         if (!(uval & FUTEX_OWNER_DIED)) {
                 ret = unlock_futex_pi(uaddr, uval);
                 if (ret == -EFAULT)
                         goto pi_faulted;
         }
 
 out_unlock:
         spin_unlock(&hb->lock);
         put_futex_key(fshared, &key);
 
 out:
         return ret;
 
 pi_faulted:
         spin_unlock(&hb->lock);
         put_futex_key(fshared, &key);
 
         ret = fault_in_user_writeable(uaddr);
         if (!ret)
                 goto retry;
 
         return ret;
 }
 
 /**
  * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
  * @hb:         the hash_bucket futex_q was original enqueued on
  * @q:          the futex_q woken while waiting to be requeued
  * @key2:       the futex_key of the requeue target futex
  * @timeout:    the timeout associated with the wait (NULL if none)
  *
  * Detect if the task was woken on the initial futex as opposed to the requeue
  * target futex.  If so, determine if it was a timeout or a signal that caused
  * the wakeup and return the appropriate error code to the caller.  Must be
  * called with the hb lock held.
  *
  * Returns
  *  0 - no early wakeup detected
  * <0 - -ETIMEDOUT or -ERESTARTNOINTR
  */
 static inline
 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
                                    struct futex_q *q, union futex_key *key2,
                                    struct hrtimer_sleeper *timeout)
 {
         int ret = 0;
 
         /*
          * With the hb lock held, we avoid races while we process the wakeup.
          * We only need to hold hb (and not hb2) to ensure atomicity as the
          * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
          * It can't be requeued from uaddr2 to something else since we don't
          * support a PI aware source futex for requeue.
          */
         if (!match_futex(&q->key, key2)) {
                 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
                 /*
                  * We were woken prior to requeue by a timeout or a signal.
                  * Unqueue the futex_q and determine which it was.
                  */
                 plist_del(&q->list, &q->list.plist);
 
                 /* Handle spurious wakeups gracefully */
                 ret = -EWOULDBLOCK;
                 if (timeout && !timeout->task)
                         ret = -ETIMEDOUT;
                 else if (signal_pending(current))
                         ret = -ERESTARTNOINTR;
         }
         return ret;
 }
 
 /**
  * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
  * @uaddr:      the futex we initialyl wait on (non-pi)
  * @fshared:    whether the futexes are shared (1) or not (0).  They must be
  *              the same type, no requeueing from private to shared, etc.
  * @val:        the expected value of uaddr
  * @abs_time:   absolute timeout
  * @bitset:     32 bit wakeup bitset set by userspace, defaults to all.
  * @clockrt:    whether to use CLOCK_REALTIME (1) or CLOCK_MONOTONIC (0)
  * @uaddr2:     the pi futex we will take prior to returning to user-space
  *
  * The caller will wait on uaddr and will be requeued by futex_requeue() to
  * uaddr2 which must be PI aware.  Normal wakeup will wake on uaddr2 and
  * complete the acquisition of the rt_mutex prior to returning to userspace.
  * This ensures the rt_mutex maintains an owner when it has waiters; without
  * one, the pi logic wouldn't know which task to boost/deboost, if there was a
  * need to.
  *
  * We call schedule in futex_wait_queue_me() when we enqueue and return there
  * via the following:
  * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
  * 2) wakeup on uaddr2 after a requeue and subsequent unlock
  * 3) signal (before or after requeue)
  * 4) timeout (before or after requeue)
  *
  * If 3, we setup a restart_block with futex_wait_requeue_pi() as the function.
  *
  * If 2, we may then block on trying to take the rt_mutex and return via:
  * 5) successful lock
  * 6) signal
  * 7) timeout
  * 8) other lock acquisition failure
  *
  * If 6, we setup a restart_block with futex_lock_pi() as the function.
  *
  * If 4 or 7, we cleanup and return with -ETIMEDOUT.
  *
  * Returns:
  *  0 - On success
  * <0 - On error
  */
 static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
                                  u32 val, ktime_t *abs_time, u32 bitset,
                                  int clockrt, u32 __user *uaddr2)
 {
         struct hrtimer_sleeper timeout, *to = NULL;
         struct rt_mutex_waiter rt_waiter;
         struct rt_mutex *pi_mutex = NULL;
         struct futex_hash_bucket *hb;
         union futex_key key2;
         struct futex_q q;
         int res, ret;
 
         if (!bitset)
                 return -EINVAL;
 
         if (abs_time) {
                 to = &timeout;
                 hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
                                       CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
                 hrtimer_init_sleeper(to, current);
                 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
                                              current->timer_slack_ns);
         }
 
         /*
          * The waiter is allocated on our stack, manipulated by the requeue
          * code while we sleep on uaddr.
          */
         debug_rt_mutex_init_waiter(&rt_waiter);
         rt_waiter.task = NULL;
 
         key2 = FUTEX_KEY_INIT;
         ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE);
         if (unlikely(ret != 0))
                 goto out;
 
         q.pi_state = NULL;
         q.bitset = bitset;
         q.rt_waiter = &rt_waiter;
         q.requeue_pi_key = &key2;
 
         /* Prepare to wait on uaddr. */
         ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
         if (ret)
                 goto out_key2;
 
         /* Queue the futex_q, drop the hb lock, wait for wakeup. */
         futex_wait_queue_me(hb, &q, to);
 
         spin_lock(&hb->lock);
         ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
         spin_unlock(&hb->lock);
         if (ret)
                 goto out_put_keys;
 
         /*
          * In order for us to be here, we know our q.key == key2, and since
          * we took the hb->lock above, we also know that futex_requeue() has
          * completed and we no longer have to concern ourselves with a wakeup
          * race with the atomic proxy lock acquition by the requeue code.
          */
 
         /* Check if the requeue code acquired the second futex for us. */
         if (!q.rt_waiter) {
                 /*
                  * Got the lock. We might not be the anticipated owner if we
                  * did a lock-steal - fix up the PI-state in that case.
                  */
                 if (q.pi_state && (q.pi_state->owner != current)) {
                         spin_lock(q.lock_ptr);
                         ret = fixup_pi_state_owner(uaddr2, &q, current,
                                                    fshared);
                         spin_unlock(q.lock_ptr);
                 }
         } else {
                 /*
                  * We have been woken up by futex_unlock_pi(), a timeout, or a
                  * signal.  futex_unlock_pi() will not destroy the lock_ptr nor
                  * the pi_state.
                  */
                 WARN_ON(!&q.pi_state);
                 pi_mutex = &q.pi_state->pi_mutex;
                 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
                 debug_rt_mutex_free_waiter(&rt_waiter);
 
                 spin_lock(q.lock_ptr);
                 /*
                  * Fixup the pi_state owner and possibly acquire the lock if we
                  * haven't already.
                  */
                 res = fixup_owner(uaddr2, fshared, &q, !ret);
                 /*
                  * If fixup_owner() returned an error, proprogate that.  If it
                  * acquired the lock, clear our -ETIMEDOUT or -EINTR.
                  */
                 if (res)
                         ret = (res < 0) ? res : 0;
 
                 /* Unqueue and drop the lock. */
                 unqueue_me_pi(&q);
         }
 
         /*
          * If fixup_pi_state_owner() faulted and was unable to handle the
          * fault, unlock the rt_mutex and return the fault to userspace.
          */
         if (ret == -EFAULT) {
                 if (rt_mutex_owner(pi_mutex) == current)
                         rt_mutex_unlock(pi_mutex);
         } else if (ret == -EINTR) {
                 /*
                  * We've already been requeued, but we have no way to
                  * restart by calling futex_lock_pi() directly. We
                  * could restart the syscall, but that will look at
                  * the user space value and return right away. So we
                  * drop back with EWOULDBLOCK to tell user space that
                  * "val" has been changed. That's the same what the
                  * restart of the syscall would do in
                  * futex_wait_setup().
                  */
                 ret = -EWOULDBLOCK;
         }
 
 out_put_keys:
         put_futex_key(fshared, &q.key);
 out_key2:
         put_futex_key(fshared, &key2);
 
 out:
         if (to) {
                 hrtimer_cancel(&to->timer);
                 destroy_hrtimer_on_stack(&to->timer);
         }
         return ret;
 }
 
 /*
  * Support for robust futexes: the kernel cleans up held futexes at
  * thread exit time.
  *
  * Implementation: user-space maintains a per-thread list of locks it
  * is holding. Upon do_exit(), the kernel carefully walks this list,
  * and marks all locks that are owned by this thread with the
  * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
  * always manipulated with the lock held, so the list is private and
  * per-thread. Userspace also maintains a per-thread 'list_op_pending'
  * field, to allow the kernel to clean up if the thread dies after
  * acquiring the lock, but just before it could have added itself to
  * the list. There can only be one such pending lock.
  */
 
 /**
  * sys_set_robust_list - set the robust-futex list head of a task
  * @head: pointer to the list-head
  * @len: length of the list-head, as userspace expects
  */
 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
                 size_t, len)
 {
         if (!futex_cmpxchg_enabled)
                 return -ENOSYS;
         /*
          * The kernel knows only one size for now:
          */
         if (unlikely(len != sizeof(*head)))
                 return -EINVAL;
 
         current->robust_list = head;
 
         return 0;
 }
 
 /**
  * sys_get_robust_list - get the robust-futex list head of a task
  * @pid: pid of the process [zero for current task]
  * @head_ptr: pointer to a list-head pointer, the kernel fills it in
  * @len_ptr: pointer to a length field, the kernel fills in the header size
  */
 SYSCALL_DEFINE3(get_robust_list, int, pid,
                 struct robust_list_head __user * __user *, head_ptr,
                 size_t __user *, len_ptr)
 {
         struct robust_list_head __user *head;
         unsigned long ret;
         const struct cred *cred = current_cred(), *pcred;
 
         if (!futex_cmpxchg_enabled)
                 return -ENOSYS;
 
         if (!pid)
                 head = current->robust_list;
         else {
                 struct task_struct *p;
 
                 ret = -ESRCH;
                 rcu_read_lock();
                 p = find_task_by_vpid(pid);
                 if (!p)
                         goto err_unlock;
                 ret = -EPERM;
                 pcred = __task_cred(p);
                 if (cred->euid != pcred->euid &&
                     cred->euid != pcred->uid &&
                     !capable(CAP_SYS_PTRACE))
                         goto err_unlock;
                 head = p->robust_list;
                 rcu_read_unlock();
         }
 
         if (put_user(sizeof(*head), len_ptr))
                 return -EFAULT;
         return put_user(head, head_ptr);
 
 err_unlock:
         rcu_read_unlock();
 
         return ret;
 }
 
 /*
  * Process a futex-list entry, check whether it's owned by the
  * dying task, and do notification if so:
  */
 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
 {
         u32 uval, nval, mval;
 
 retry:
         if (get_user(uval, uaddr))
                 return -1;
 
         if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
                 /*
                  * Ok, this dying thread is truly holding a futex
                  * of interest. Set the OWNER_DIED bit atomically
                  * via cmpxchg, and if the value had FUTEX_WAITERS
                  * set, wake up a waiter (if any). (We have to do a
                  * futex_wake() even if OWNER_DIED is already set -
                  * to handle the rare but possible case of recursive
                  * thread-death.) The rest of the cleanup is done in
                  * userspace.
                  */
                 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
                 nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
 
                 if (nval == -EFAULT)
                         return -1;
 
                 if (nval != uval)
                         goto retry;
 
                 /*
                  * Wake robust non-PI futexes here. The wakeup of
                  * PI futexes happens in exit_pi_state():
                  */
                 if (!pi && (uval & FUTEX_WAITERS))
                         futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
         }
         return 0;
 }
 
 /*
  * Fetch a robust-list pointer. Bit 0 signals PI futexes:
  */
 static inline int fetch_robust_entry(struct robust_list __user **entry,
                                      struct robust_list __user * __user *head,
                                      int *pi)
 {
         unsigned long uentry;
 
         if (get_user(uentry, (unsigned long __user *)head))
                 return -EFAULT;
 
         *entry = (void __user *)(uentry & ~1UL);
         *pi = uentry & 1;
 
         return 0;
 }
 
 /*
  * Walk curr->robust_list (very carefully, it's a userspace list!)
  * and mark any locks found there dead, and notify any waiters.
  *
  * We silently return on any sign of list-walking problem.
  */
 void exit_robust_list(struct task_struct *curr)
 {
         struct robust_list_head __user *head = curr->robust_list;
         struct robust_list __user *entry, *next_entry, *pending;
         unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
         unsigned long futex_offset;
         int rc;
 
         if (!futex_cmpxchg_enabled)
                 return;
 
         /*
          * Fetch the list head (which was registered earlier, via
          * sys_set_robust_list()):
          */
         if (fetch_robust_entry(&entry, &head->list.next, &pi))
                 return;
         /*
          * Fetch the relative futex offset:
          */
         if (get_user(futex_offset, &head->futex_offset))
                 return;
         /*
          * Fetch any possibly pending lock-add first, and handle it
          * if it exists:
          */
         if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
                 return;
 
         next_entry = NULL;      /* avoid warning with gcc */
         while (entry != &head->list) {
                 /*
                  * Fetch the next entry in the list before calling
                  * handle_futex_death:
                  */
                 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
                 /*
                  * A pending lock might already be on the list, so
                  * don't process it twice:
                  */
                 if (entry != pending)
                         if (handle_futex_death((void __user *)entry + futex_offset,
                                                 curr, pi))
                                 return;
                 if (rc)
                         return;
                 entry = next_entry;
                 pi = next_pi;
                 /*
                  * Avoid excessively long or circular lists:
                  */
                 if (!--limit)
                         break;
 
                 cond_resched();
         }
 
         if (pending)
                 handle_futex_death((void __user *)pending + futex_offset,
                                    curr, pip);
 }
 
 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
                 u32 __user *uaddr2, u32 val2, u32 val3)
 {
         int clockrt, ret = -ENOSYS;
         int cmd = op & FUTEX_CMD_MASK;
         int fshared = 0;
 
         if (!(op & FUTEX_PRIVATE_FLAG))
                 fshared = 1;
 
         clockrt = op & FUTEX_CLOCK_REALTIME;
         if (clockrt && cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
                 return -ENOSYS;
 
         switch (cmd) {
         case FUTEX_WAIT:
                 val3 = FUTEX_BITSET_MATCH_ANY;
         case FUTEX_WAIT_BITSET:
                 ret = futex_wait(uaddr, fshared, val, timeout, val3, clockrt);
                 break;
         case FUTEX_WAKE:
                 val3 = FUTEX_BITSET_MATCH_ANY;
         case FUTEX_WAKE_BITSET:
                 ret = futex_wake(uaddr, fshared, val, val3);
                 break;
         case FUTEX_REQUEUE:
                 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL, 0);
                 break;
         case FUTEX_CMP_REQUEUE:
                 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
                                     0);
                 break;
         case FUTEX_WAKE_OP:
                 ret = futex_wake_op(uaddr, fshared, uaddr2, val, val2, val3);
                 break;
         case FUTEX_LOCK_PI:
                 if (futex_cmpxchg_enabled)
                         ret = futex_lock_pi(uaddr, fshared, val, timeout, 0);
                 break;
         case FUTEX_UNLOCK_PI:
                 if (futex_cmpxchg_enabled)
                         ret = futex_unlock_pi(uaddr, fshared);
                 break;
         case FUTEX_TRYLOCK_PI:
                 if (futex_cmpxchg_enabled)
                         ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1);
                 break;
         case FUTEX_WAIT_REQUEUE_PI:
                 val3 = FUTEX_BITSET_MATCH_ANY;
                 ret = futex_wait_requeue_pi(uaddr, fshared, val, timeout, val3,
                                             clockrt, uaddr2);
                 break;
         case FUTEX_CMP_REQUEUE_PI:
                 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
                                     1);
                 break;
         default:
                 ret = -ENOSYS;
         }
         return ret;
 }
 
 
 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
                 struct timespec __user *, utime, u32 __user *, uaddr2,
                 u32, val3)
 {
         struct timespec ts;
         ktime_t t, *tp = NULL;
         u32 val2 = 0;
         int cmd = op & FUTEX_CMD_MASK;
 
         if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
                       cmd == FUTEX_WAIT_BITSET ||
                       cmd == FUTEX_WAIT_REQUEUE_PI)) {
                 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
                         return -EFAULT;
                 if (!timespec_valid(&ts))
                         return -EINVAL;
 
                 t = timespec_to_ktime(ts);
                 if (cmd == FUTEX_WAIT)
                         t = ktime_add_safe(ktime_get(), t);
                 tp = &t;
         }
         /*
          * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
          * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
          */
         if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
             cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
                 val2 = (u32) (unsigned long) utime;
 
         return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
 }
 
 static int __init futex_init(void)
 {
         u32 curval;
         int i;
 
         /*
          * This will fail and we want it. Some arch implementations do
          * runtime detection of the futex_atomic_cmpxchg_inatomic()
          * functionality. We want to know that before we call in any
          * of the complex code paths. Also we want to prevent
          * registration of robust lists in that case. NULL is
          * guaranteed to fault and we get -EFAULT on functional
          * implementation, the non functional ones will return
          * -ENOSYS.
          */
         curval = cmpxchg_futex_value_locked(NULL, 0, 0);
         if (curval == -EFAULT)
                 futex_cmpxchg_enabled = 1;
 
         for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
                 plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock);
                 spin_lock_init(&futex_queues[i].lock);
         }
 
         return 0;
 }
 __initcall(futex_init);