Merge branch 'futexes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'futexes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  futex: fix restart in wait_requeue_pi
  futex: fix restart for early wakeup in futex_wait_requeue_pi()
  futex: cleanup error exit
  futex: remove the wait queue
  futex: add requeue-pi documentation
  futex: remove FUTEX_REQUEUE_PI (non CMP)
  futex: fix futex_wait_setup key handling
  sparc64: extend TI_RESTART_BLOCK space by 8 bytes
  futex: fixup unlocked requeue pi case
  futex: add requeue_pi functionality
  futex: split out futex value validation code
  futex: distangle futex_requeue()
  futex: add FUTEX_HAS_TIMEOUT flag to restart.futex.flags
  rt_mutex: add proxy lock routines
  futex: split out fixup owner logic from futex_lock_pi()
  futex: split out atomic logic from futex_lock_pi()
  futex: add helper to find the top prio waiter of a futex
  futex: separate futex_wait_queue_me() logic from futex_wait()

3 files changed, 1084 insertions, 352 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index d546b2d53a62..80b5ce716596 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -19,6 +19,10 @@
  *  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.
@@ -96,8 +100,8 @@ struct futex_pi_state {
  */
 struct futex_q {
         struct plist_node list;
-        /* There can only be a single waiter */
-        wait_queue_head_t waiter;
+        /* Waiter reference */
+        struct task_struct *task;
 
         /* Which hash list lock to use: */
         spinlock_t *lock_ptr;
@@ -107,7 +111,9 @@ struct futex_q {
 
         /* Optional priority inheritance state: */
         struct futex_pi_state *pi_state;
-        struct task_struct *task;
+
+        /* rt_waiter storage for requeue_pi: */
+        struct rt_mutex_waiter *rt_waiter;
 
         /* Bitset for the optional bitmasked wakeup */
         u32 bitset;
@@ -278,6 +284,25 @@ void put_futex_key(int fshared, union futex_key *key)
         drop_futex_key_refs(key);
 }
 
+/**
+ * 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;
@@ -539,28 +564,160 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
         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)
 {
-        plist_del(&q->list, &q->list.plist);
+        struct task_struct *p = q->task;
+
         /*
-         * The lock in wake_up_all() is a crucial memory barrier after the
-         * plist_del() and also before assigning to q->lock_ptr.
+         * 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.
          */
-        wake_up(&q->waiter);
+        get_task_struct(p);
+
+        plist_del(&q->list, &q->list.plist);
         /*
-         * 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() does not prevent this store from moving.
+         * 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)
@@ -689,7 +846,7 @@ static int futex_wake(u32 __user *uaddr, int fshared, int nr_wake, u32 bitset)
 
         plist_for_each_entry_safe(this, next, head, list) {
                 if (match_futex (&this->key, &key)) {
-                        if (this->pi_state) {
+                        if (this->pi_state || this->rt_waiter) {
                                 ret = -EINVAL;
                                 break;
                         }
@@ -802,24 +959,185 @@ out:
         return ret;
 }
 
-/*
- * Requeue all waiters hashed on one physical page to another
- * physical page.
+/**
+ * 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
+ *
+ * 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.  Must be called with the q->lock_ptr held.
+ */
+static inline
+void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key)
+{
+        drop_futex_key_refs(&q->key);
+        get_futex_key_refs(key);
+        q->key = *key;
+
+        WARN_ON(plist_node_empty(&q->list));
+        plist_del(&q->list, &q->list.plist);
+
+        WARN_ON(!q->rt_waiter);
+        q->rt_waiter = NULL;
+
+        wake_up_state(q->task, TASK_NORMAL);
+}
+
+/**
+ * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
+ * @pifutex:            the user address of the to futex
+ * @hb1:                the from futex hash bucket, must be locked by the caller
+ * @hb2:                the to futex hash bucket, must be locked by the caller
+ * @key1:               the from futex key
+ * @key2:               the to futex key
+ * @ps:                 address to store the pi_state pointer
+ * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
+ *
+ * Try and get the lock on behalf of the top waiter if we can do it atomically.
+ * Wake the top waiter if we succeed.  If the caller specified set_waiters,
+ * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
+ * hb1 and hb2 must be held by the caller.
+ *
+ * Returns:
+ *  0 - failed to acquire the lock atomicly
+ *  1 - acquired the lock
+ * <0 - error
+ */
+static int futex_proxy_trylock_atomic(u32 __user *pifutex,
+                                 struct futex_hash_bucket *hb1,
+                                 struct futex_hash_bucket *hb2,
+                                 union futex_key *key1, union futex_key *key2,
+                                 struct futex_pi_state **ps, int set_waiters)
+{
+        struct futex_q *top_waiter = NULL;
+        u32 curval;
+        int ret;
+
+        if (get_futex_value_locked(&curval, pifutex))
+                return -EFAULT;
+
+        /*
+         * Find the top_waiter and determine if there are additional waiters.
+         * If the caller intends to requeue more than 1 waiter to pifutex,
+         * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
+         * as we have means to handle the possible fault.  If not, don't set
+         * the bit unecessarily as it will force the subsequent unlock to enter
+         * the kernel.
+         */
+        top_waiter = futex_top_waiter(hb1, key1);
+
+        /* There are no waiters, nothing for us to do. */
+        if (!top_waiter)
+                return 0;
+
+        /*
+         * Try to take the lock for top_waiter.  Set the FUTEX_WAITERS bit in
+         * the contended case or if set_waiters is 1.  The pi_state is returned
+         * in ps in contended cases.
+         */
+        ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
+                                   set_waiters);
+        if (ret == 1)
+                requeue_pi_wake_futex(top_waiter, key2);
+
+        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 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;
-        int ret, drop_count = 0;
+        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, VERIFY_READ);
+        ret = get_futex_key(uaddr2, fshared, &key2,
+                            requeue_pi ? VERIFY_WRITE : VERIFY_READ);
         if (unlikely(ret != 0))
                 goto out_put_key1;
 
@@ -854,32 +1172,99 @@ retry_private:
                 }
         }
 
+        if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
+                /*
+                 * Attempt to acquire uaddr2 and wake the top waiter. If we
+                 * intend to requeue waiters, force setting the FUTEX_WAITERS
+                 * bit.  We force this here where we are able to easily handle
+                 * faults rather in the requeue loop below.
+                 */
+                ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
+                                                 &key2, &pi_state, nr_requeue);
+
+                /*
+                 * At this point the top_waiter has either taken uaddr2 or is
+                 * waiting on it.  If the former, then the pi_state will not
+                 * exist yet, look it up one more time to ensure we have a
+                 * reference to it.
+                 */
+                if (ret == 1) {
+                        WARN_ON(pi_state);
+                        task_count++;
+                        ret = get_futex_value_locked(&curval2, uaddr2);
+                        if (!ret)
+                                ret = lookup_pi_state(curval2, hb2, &key2,
+                                                      &pi_state);
+                }
+
+                switch (ret) {
+                case 0:
+                        break;
+                case -EFAULT:
+                        double_unlock_hb(hb1, hb2);
+                        put_futex_key(fshared, &key2);
+                        put_futex_key(fshared, &key1);
+                        ret = get_user(curval2, 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 (!match_futex (&this->key, &key1))
+                if (task_count - nr_wake >= nr_requeue)
+                        break;
+
+                if (!match_futex(&this->key, &key1))
                         continue;
-                if (++ret <= nr_wake) {
+
+                WARN_ON(!requeue_pi && this->rt_waiter);
+                WARN_ON(requeue_pi && !this->rt_waiter);
+
+                /*
+                 * 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);
-                } else {
-                        /*
-                         * If key1 and key2 hash to the same bucket, no need to
-                         * requeue.
-                         */
-                        if (likely(head1 != &hb2->chain)) {
-                                plist_del(&this->list, &hb1->chain);
-                                plist_add(&this->list, &hb2->chain);
-                                this->lock_ptr = &hb2->lock;
-#ifdef CONFIG_DEBUG_PI_LIST
-                                this->list.plist.lock = &hb2->lock;
-#endif
-                        }
-                        this->key = key2;
-                        get_futex_key_refs(&key2);
-                        drop_count++;
+                        continue;
+                }
 
-                        if (ret - nr_wake >= nr_requeue)
-                                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);
+                                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:
@@ -899,7 +1284,9 @@ out_put_keys:
 out_put_key1:
         put_futex_key(fshared, &key1);
 out:
-        return ret;
+        if (pi_state != NULL)
+                free_pi_state(pi_state);
+        return ret ? ret : task_count;
 }
 
 /* The key must be already stored in q->key. */
@@ -907,8 +1294,6 @@ static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
 {
         struct futex_hash_bucket *hb;
 
-        init_waitqueue_head(&q->waiter);
-
         get_futex_key_refs(&q->key);
         hb = hash_futex(&q->key);
         q->lock_ptr = &hb->lock;
@@ -1119,35 +1504,149 @@ handle_fault:
  */
 #define FLAGS_SHARED            0x01
 #define FLAGS_CLOCKRT           0x02
+#define FLAGS_HAS_TIMEOUT       0x04
 
 static long futex_wait_restart(struct restart_block *restart);
 
-static int futex_wait(u32 __user *uaddr, int fshared,
-                      u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
+/**
+ * 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 *curr = current;
-        struct restart_block *restart;
-        DECLARE_WAITQUEUE(wait, curr);
-        struct futex_hash_bucket *hb;
-        struct futex_q q;
-        u32 uval;
-        int ret;
-        struct hrtimer_sleeper t;
-        int rem = 0;
+        struct task_struct *owner;
+        int ret = 0;
 
-        if (!bitset)
-                return -EINVAL;
+        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;
+        }
 
-        q.pi_state = NULL;
-        q.bitset = bitset;
-retry:
-        q.key = FUTEX_KEY_INIT;
-        ret = get_futex_key(uaddr, fshared, &q.key, VERIFY_READ);
-        if (unlikely(ret != 0))
+        /*
+         * 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;
+        }
 
-retry_private:
-        hb = queue_lock(&q);
+        /*
+         * Paranoia check. If we did not take the lock, then we should not be
+         * the owner, nor the pending owner, of the rt_mutex.
+         */
+        if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
+                printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
+                                "pi-state %p\n", ret,
+                                q->pi_state->pi_mutex.owner,
+                                q->pi_state->owner);
+
+out:
+        return ret ? ret : locked;
+}
+
+/**
+ * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
+ * @hb:         the futex hash bucket, must be locked by the caller
+ * @q:          the futex_q to queue up on
+ * @timeout:    the prepared hrtimer_sleeper, or null for no timeout
+ */
+static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
+                                struct hrtimer_sleeper *timeout)
+{
+        queue_me(q, hb);
+
+        /*
+         * There might have been scheduling since the queue_me(), as we
+         * cannot hold a spinlock across the get_user() in case it
+         * faults, and we cannot just set TASK_INTERRUPTIBLE state when
+         * queueing ourselves into the futex hash. This code thus has to
+         * rely on the futex_wake() code removing us from hash when it
+         * wakes us up.
+         */
+        set_current_state(TASK_INTERRUPTIBLE);
+
+        /* Arm the timer */
+        if (timeout) {
+                hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
+                if (!hrtimer_active(&timeout->timer))
+                        timeout->task = NULL;
+        }
+
+        /*
+         * !plist_node_empty() is safe here without any lock.
+         * q.lock_ptr != 0 is not safe, because of ordering against wakeup.
+         */
+        if (likely(!plist_node_empty(&q->list))) {
+                /*
+                 * If the timer has already expired, current will already be
+                 * flagged for rescheduling. Only call schedule if there
+                 * is no timeout, or if it has yet to expire.
+                 */
+                if (!timeout || timeout->task)
+                        schedule();
+        }
+        __set_current_state(TASK_RUNNING);
+}
+
+/**
+ * futex_wait_setup() - Prepare to wait on a futex
+ * @uaddr:      the futex userspace address
+ * @val:        the expected value
+ * @fshared:    whether the futex is shared (1) or not (0)
+ * @q:          the associated futex_q
+ * @hb:         storage for hash_bucket pointer to be returned to caller
+ *
+ * Setup the futex_q and locate the hash_bucket.  Get the futex value and
+ * compare it with the expected value.  Handle atomic faults internally.
+ * Return with the hb lock held and a q.key reference on success, and unlocked
+ * with no q.key reference on failure.
+ *
+ * Returns:
+ *  0 - uaddr contains val and hb has been locked
+ * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlcoked
+ */
+static int futex_wait_setup(u32 __user *uaddr, u32 val, int fshared,
+                           struct futex_q *q, struct futex_hash_bucket **hb)
+{
+        u32 uval;
+        int ret;
 
         /*
          * Access the page AFTER the hash-bucket is locked.
@@ -1165,95 +1664,83 @@ retry_private:
          * 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.
          */
+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 (unlikely(ret)) {
-                queue_unlock(&q, hb);
+        if (ret) {
+                queue_unlock(q, *hb);
 
                 ret = get_user(uval, uaddr);
                 if (ret)
-                        goto out_put_key;
+                        goto out;
 
                 if (!fshared)
                         goto retry_private;
 
-                put_futex_key(fshared, &q.key);
+                put_futex_key(fshared, &q->key);
                 goto retry;
         }
-        ret = -EWOULDBLOCK;
-        if (unlikely(uval != val)) {
-                queue_unlock(&q, hb);
-                goto out_put_key;
-        }
 
-        /* Only actually queue if *uaddr contained val.  */
-        queue_me(&q, hb);
+        if (uval != val) {
+                queue_unlock(q, *hb);
+                ret = -EWOULDBLOCK;
+        }
 
-        /*
-         * 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.
-         */
+out:
+        if (ret)
+                put_futex_key(fshared, &q->key);
+        return ret;
+}
 
-        /* add_wait_queue is the barrier after __set_current_state. */
-        __set_current_state(TASK_INTERRUPTIBLE);
-        add_wait_queue(&q.waiter, &wait);
-        /*
-         * !plist_node_empty() is safe here without any lock.
-         * q.lock_ptr != 0 is not safe, because of ordering against wakeup.
-         */
-        if (likely(!plist_node_empty(&q.list))) {
-                if (!abs_time)
-                        schedule();
-                else {
-                        hrtimer_init_on_stack(&t.timer,
-                                              clockrt ? CLOCK_REALTIME :
-                                              CLOCK_MONOTONIC,
-                                              HRTIMER_MODE_ABS);
-                        hrtimer_init_sleeper(&t, current);
-                        hrtimer_set_expires_range_ns(&t.timer, *abs_time,
-                                                     current->timer_slack_ns);
-
-                        hrtimer_start_expires(&t.timer, HRTIMER_MODE_ABS);
-                        if (!hrtimer_active(&t.timer))
-                                t.task = NULL;
+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;
 
-                        /*
-                         * 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();
+        if (!bitset)
+                return -EINVAL;
 
-                        hrtimer_cancel(&t.timer);
+        q.pi_state = NULL;
+        q.bitset = bitset;
+        q.rt_waiter = NULL;
 
-                        /* Flag if a timeout occured */
-                        rem = (t.task == NULL);
+        if (abs_time) {
+                to = &timeout;
 
-                        destroy_hrtimer_on_stack(&t.timer);
-                }
+                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);
         }
-        __set_current_state(TASK_RUNNING);
 
-        /*
-         * NOTE: we don't remove ourselves from the waitqueue because
-         * we are the only user of it.
-         */
+        /* 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 (rem)
+        if (to && !to->task)
                 goto out_put_key;
 
         /*
@@ -1270,7 +1757,7 @@ retry_private:
         restart->futex.val = val;
         restart->futex.time = abs_time->tv64;
         restart->futex.bitset = bitset;
-        restart->futex.flags = 0;
+        restart->futex.flags = FLAGS_HAS_TIMEOUT;
 
         if (fshared)
                 restart->futex.flags |= FLAGS_SHARED;
@@ -1282,6 +1769,10 @@ retry_private:
 out_put_key:
         put_futex_key(fshared, &q.key);
 out:
+        if (to) {
+                hrtimer_cancel(&to->timer);
+                destroy_hrtimer_on_stack(&to->timer);
+        }
         return ret;
 }
 
@@ -1290,13 +1781,16 @@ static long futex_wait_restart(struct restart_block *restart)
 {
         u32 __user *uaddr = (u32 __user *)restart->futex.uaddr;
         int fshared = 0;
-        ktime_t t;
+        ktime_t t, *tp = NULL;
 
-        t.tv64 = restart->futex.time;
+        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, &t,
+        return (long)futex_wait(uaddr, fshared, restart->futex.val, tp,
                                 restart->futex.bitset,
                                 restart->futex.flags & FLAGS_CLOCKRT);
 }
@@ -1312,11 +1806,10 @@ static int futex_lock_pi(u32 __user *uaddr, int fshared,
                          int detect, ktime_t *time, int trylock)
 {
         struct hrtimer_sleeper timeout, *to = NULL;
-        struct task_struct *curr = current;
         struct futex_hash_bucket *hb;
-        u32 uval, newval, curval;
+        u32 uval;
         struct futex_q q;
-        int ret, lock_taken, ownerdied = 0;
+        int res, ret;
 
         if (refill_pi_state_cache())
                 return -ENOMEM;
@@ -1330,6 +1823,7 @@ static int futex_lock_pi(u32 __user *uaddr, int fshared,
         }
 
         q.pi_state = NULL;
+        q.rt_waiter = NULL;
 retry:
         q.key = FUTEX_KEY_INIT;
         ret = get_futex_key(uaddr, fshared, &q.key, VERIFY_WRITE);
@@ -1339,81 +1833,15 @@ retry:
 retry_private:
         hb = queue_lock(&q);
 
-retry_locked:
-        ret = lock_taken = 0;
-
-        /*
-         * To avoid races, we attempt to take the lock here again
-         * (by doing a 0 -> TID atomic cmpxchg), while holding all
-         * the locks. It will most likely not succeed.
-         */
-        newval = task_pid_vnr(current);
-
-        curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
-
-        if (unlikely(curval == -EFAULT))
-                goto uaddr_faulted;
-
-        /*
-         * Detect deadlocks. In case of REQUEUE_PI this is a valid
-         * situation and we return success to user space.
-         */
-        if (unlikely((curval & FUTEX_TID_MASK) == task_pid_vnr(current))) {
-                ret = -EDEADLK;
-                goto out_unlock_put_key;
-        }
-
-        /*
-         * Surprise - we got the lock. Just return to userspace:
-         */
-        if (unlikely(!curval))
-                goto out_unlock_put_key;
-
-        uval = curval;
-
-        /*
-         * Set the WAITERS flag, so the owner will know it has someone
-         * to wake at next unlock
-         */
-        newval = curval | FUTEX_WAITERS;
-
-        /*
-         * There are two cases, where a futex might have no owner (the
-         * owner TID is 0): OWNER_DIED. We take over the futex in this
-         * case. We also do an unconditional take over, when the owner
-         * of the futex died.
-         *
-         * This is safe as we are protected by the hash bucket lock !
-         */
-        if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
-                /* Keep the OWNER_DIED bit */
-                newval = (curval & ~FUTEX_TID_MASK) | task_pid_vnr(current);
-                ownerdied = 0;
-                lock_taken = 1;
-        }
-
-        curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
-
-        if (unlikely(curval == -EFAULT))
-                goto uaddr_faulted;
-        if (unlikely(curval != uval))
-                goto retry_locked;
-
-        /*
-         * We took the lock due to owner died take over.
-         */
-        if (unlikely(lock_taken))
-                goto out_unlock_put_key;
-
-        /*
-         * We dont have the lock. Look up the PI state (or create it if
-         * we are the first waiter):
-         */
-        ret = lookup_pi_state(uval, hb, &q.key, &q.pi_state);
-
+        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
@@ -1423,25 +1851,6 @@ retry_locked:
                         put_futex_key(fshared, &q.key);
                         cond_resched();
                         goto retry;
-
-                case -ESRCH:
-                        /*
-                         * No owner found for this futex. Check if the
-                         * OWNER_DIED bit is set to figure out whether
-                         * this is a robust futex or not.
-                         */
-                        if (get_futex_value_locked(&curval, uaddr))
-                                goto uaddr_faulted;
-
-                        /*
-                         * We simply start over in case of a robust
-                         * futex. The code above will take the futex
-                         * and return happy.
-                         */
-                        if (curval & FUTEX_OWNER_DIED) {
-                                ownerdied = 1;
-                                goto retry_locked;
-                        }
                 default:
                         goto out_unlock_put_key;
                 }
@@ -1465,71 +1874,21 @@ retry_locked:
         }
 
         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);
-                }
-        }
+        /*
+         * 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_pi_state_owner() faulted and was unable to handle the
-         * fault, unlock it and return the fault to userspace.
+         * 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);
@@ -1537,9 +1896,7 @@ retry_locked:
         /* Unqueue and drop the lock */
         unqueue_me_pi(&q);
 
-        if (to)
-                destroy_hrtimer_on_stack(&to->timer);
-        return ret != -EINTR ? ret : -ERESTARTNOINTR;
+        goto out;
 
 out_unlock_put_key:
         queue_unlock(&q, hb);
@@ -1549,7 +1906,7 @@ out_put_key:
 out:
         if (to)
                 destroy_hrtimer_on_stack(&to->timer);
-        return ret;
+        return ret != -EINTR ? ret : -ERESTARTNOINTR;
 
 uaddr_faulted:
         /*
@@ -1572,7 +1929,6 @@ uaddr_faulted:
         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),
@@ -1674,6 +2030,229 @@ pi_faulted:
         return ret;
 }
 
+/**
+ * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
+ * @hb:         the hash_bucket futex_q was original enqueued on
+ * @q:          the futex_q woken while waiting to be requeued
+ * @key2:       the futex_key of the requeue target futex
+ * @timeout:    the timeout associated with the wait (NULL if none)
+ *
+ * Detect if the task was woken on the initial futex as opposed to the requeue
+ * target futex.  If so, determine if it was a timeout or a signal that caused
+ * the wakeup and return the appropriate error code to the caller.  Must be
+ * called with the hb lock held.
+ *
+ * Returns
+ *  0 - no early wakeup detected
+ * <0 - -ETIMEDOUT or -ERESTARTNOINTR
+ */
+static inline
+int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
+                                   struct futex_q *q, union futex_key *key2,
+                                   struct hrtimer_sleeper *timeout)
+{
+        int ret = 0;
+
+        /*
+         * With the hb lock held, we avoid races while we process the wakeup.
+         * We only need to hold hb (and not hb2) to ensure atomicity as the
+         * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
+         * It can't be requeued from uaddr2 to something else since we don't
+         * support a PI aware source futex for requeue.
+         */
+        if (!match_futex(&q->key, key2)) {
+                WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
+                /*
+                 * We were woken prior to requeue by a timeout or a signal.
+                 * Unqueue the futex_q and determine which it was.
+                 */
+                plist_del(&q->list, &q->list.plist);
+                drop_futex_key_refs(&q->key);
+
+                if (timeout && !timeout->task)
+                        ret = -ETIMEDOUT;
+                else
+                        ret = -ERESTARTNOINTR;
+        }
+        return ret;
+}
+
+/**
+ * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
+ * @uaddr:      the futex we initialyl wait on (non-pi)
+ * @fshared:    whether the futexes are shared (1) or not (0).  They must be
+ *              the same type, no requeueing from private to shared, etc.
+ * @val:        the expected value of uaddr
+ * @abs_time:   absolute timeout
+ * @bitset:     32 bit wakeup bitset set by userspace, defaults to all.
+ * @clockrt:    whether to use CLOCK_REALTIME (1) or CLOCK_MONOTONIC (0)
+ * @uaddr2:     the pi futex we will take prior to returning to user-space
+ *
+ * The caller will wait on uaddr and will be requeued by futex_requeue() to
+ * uaddr2 which must be PI aware.  Normal wakeup will wake on uaddr2 and
+ * complete the acquisition of the rt_mutex prior to returning to userspace.
+ * This ensures the rt_mutex maintains an owner when it has waiters; without
+ * one, the pi logic wouldn't know which task to boost/deboost, if there was a
+ * need to.
+ *
+ * We call schedule in futex_wait_queue_me() when we enqueue and return there
+ * via the following:
+ * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
+ * 2) wakeup on uaddr2 after a requeue and subsequent unlock
+ * 3) signal (before or after requeue)
+ * 4) timeout (before or after requeue)
+ *
+ * If 3, we setup a restart_block with futex_wait_requeue_pi() as the function.
+ *
+ * If 2, we may then block on trying to take the rt_mutex and return via:
+ * 5) successful lock
+ * 6) signal
+ * 7) timeout
+ * 8) other lock acquisition failure
+ *
+ * If 6, we setup a restart_block with futex_lock_pi() as the function.
+ *
+ * If 4 or 7, we cleanup and return with -ETIMEDOUT.
+ *
+ * Returns:
+ *  0 - On success
+ * <0 - On error
+ */
+static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
+                                 u32 val, ktime_t *abs_time, u32 bitset,
+                                 int clockrt, u32 __user *uaddr2)
+{
+        struct hrtimer_sleeper timeout, *to = NULL;
+        struct rt_mutex_waiter rt_waiter;
+        struct rt_mutex *pi_mutex = NULL;
+        struct futex_hash_bucket *hb;
+        union futex_key key2;
+        struct futex_q q;
+        int res, ret;
+
+        if (!bitset)
+                return -EINVAL;
+
+        if (abs_time) {
+                to = &timeout;
+                hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
+                                      CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+                hrtimer_init_sleeper(to, current);
+                hrtimer_set_expires_range_ns(&to->timer, *abs_time,
+                                             current->timer_slack_ns);
+        }
+
+        /*
+         * The waiter is allocated on our stack, manipulated by the requeue
+         * code while we sleep on uaddr.
+         */
+        debug_rt_mutex_init_waiter(&rt_waiter);
+        rt_waiter.task = NULL;
+
+        q.pi_state = NULL;
+        q.bitset = bitset;
+        q.rt_waiter = &rt_waiter;
+
+        key2 = FUTEX_KEY_INIT;
+        ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE);
+        if (unlikely(ret != 0))
+                goto out;
+
+        /* Prepare to wait on uaddr. */
+        ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
+        if (ret)
+                goto out_key2;
+
+        /* Queue the futex_q, drop the hb lock, wait for wakeup. */
+        futex_wait_queue_me(hb, &q, to);
+
+        spin_lock(&hb->lock);
+        ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
+        spin_unlock(&hb->lock);
+        if (ret)
+                goto out_put_keys;
+
+        /*
+         * In order for us to be here, we know our q.key == key2, and since
+         * we took the hb->lock above, we also know that futex_requeue() has
+         * completed and we no longer have to concern ourselves with a wakeup
+         * race with the atomic proxy lock acquition by the requeue code.
+         */
+
+        /* Check if the requeue code acquired the second futex for us. */
+        if (!q.rt_waiter) {
+                /*
+                 * Got the lock. We might not be the anticipated owner if we
+                 * did a lock-steal - fix up the PI-state in that case.
+                 */
+                if (q.pi_state && (q.pi_state->owner != current)) {
+                        spin_lock(q.lock_ptr);
+                        ret = fixup_pi_state_owner(uaddr2, &q, current,
+                                                   fshared);
+                        spin_unlock(q.lock_ptr);
+                }
+        } else {
+                /*
+                 * We have been woken up by futex_unlock_pi(), a timeout, or a
+                 * signal.  futex_unlock_pi() will not destroy the lock_ptr nor
+                 * the pi_state.
+                 */
+                WARN_ON(!&q.pi_state);
+                pi_mutex = &q.pi_state->pi_mutex;
+                ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
+                debug_rt_mutex_free_waiter(&rt_waiter);
+
+                spin_lock(q.lock_ptr);
+                /*
+                 * Fixup the pi_state owner and possibly acquire the lock if we
+                 * haven't already.
+                 */
+                res = fixup_owner(uaddr2, fshared, &q, !ret);
+                /*
+                 * If fixup_owner() returned an error, proprogate that.  If it
+                 * acquired the lock, clear our -ETIMEDOUT or -EINTR.
+                 */
+                if (res)
+                        ret = (res < 0) ? res : 0;
+
+                /* Unqueue and drop the lock. */
+                unqueue_me_pi(&q);
+        }
+
+        /*
+         * If fixup_pi_state_owner() faulted and was unable to handle the
+         * fault, unlock the rt_mutex and return the fault to userspace.
+         */
+        if (ret == -EFAULT) {
+                if (rt_mutex_owner(pi_mutex) == current)
+                        rt_mutex_unlock(pi_mutex);
+        } else if (ret == -EINTR) {
+                /*
+                 * We've already been requeued, but we have no way to
+                 * restart by calling futex_lock_pi() directly. We
+                 * could restart the syscall, but that will look at
+                 * the user space value and return right away. So we
+                 * drop back with EWOULDBLOCK to tell user space that
+                 * "val" has been changed. That's the same what the
+                 * restart of the syscall would do in
+                 * futex_wait_setup().
+                 */
+                ret = -EWOULDBLOCK;
+        }
+
+out_put_keys:
+        put_futex_key(fshared, &q.key);
+out_key2:
+        put_futex_key(fshared, &key2);
+
+out:
+        if (to) {
+                hrtimer_cancel(&to->timer);
+                destroy_hrtimer_on_stack(&to->timer);
+        }
+        return ret;
+}
+
 /*
  * Support for robust futexes: the kernel cleans up held futexes at
  * thread exit time.
@@ -1896,7 +2475,7 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
                 fshared = 1;
 
         clockrt = op & FUTEX_CLOCK_REALTIME;
-        if (clockrt && cmd != FUTEX_WAIT_BITSET)
+        if (clockrt && cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
                 return -ENOSYS;
 
         switch (cmd) {
@@ -1911,10 +2490,11 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
                 ret = futex_wake(uaddr, fshared, val, val3);
                 break;
         case FUTEX_REQUEUE:
-                ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL);
+                ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL, 0);
                 break;
         case FUTEX_CMP_REQUEUE:
-                ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3);
+                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);
@@ -1931,6 +2511,15 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
                 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;
         }
@@ -1948,7 +2537,8 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
         int cmd = op & FUTEX_CMD_MASK;
 
         if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
-                      cmd == FUTEX_WAIT_BITSET)) {
+                      cmd == FUTEX_WAIT_BITSET ||
+                      cmd == FUTEX_WAIT_REQUEUE_PI)) {
                 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
                         return -EFAULT;
                 if (!timespec_valid(&ts))
@@ -1960,11 +2550,11 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
                 tp = &t;
         }
         /*
-         * requeue parameter in 'utime' if cmd == FUTEX_REQUEUE.
+         * 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)
+            cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
                 val2 = (u32) (unsigned long) utime;
 
         return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
index 69d9cb921ffa..fec77e7e0562 100644
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -300,7 +300,8 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
  * assigned pending owner [which might not have taken the
  * lock yet]:
  */
-static inline int try_to_steal_lock(struct rt_mutex *lock)
+static inline int try_to_steal_lock(struct rt_mutex *lock,
+                                    struct task_struct *task)
 {
         struct task_struct *pendowner = rt_mutex_owner(lock);
         struct rt_mutex_waiter *next;
@@ -309,11 +310,11 @@ static inline int try_to_steal_lock(struct rt_mutex *lock)
         if (!rt_mutex_owner_pending(lock))
                 return 0;
 
-        if (pendowner == current)
+        if (pendowner == task)
                 return 1;
 
         spin_lock_irqsave(&pendowner->pi_lock, flags);
-        if (current->prio >= pendowner->prio) {
+        if (task->prio >= pendowner->prio) {
                 spin_unlock_irqrestore(&pendowner->pi_lock, flags);
                 return 0;
         }
@@ -338,21 +339,21 @@ static inline int try_to_steal_lock(struct rt_mutex *lock)
          * We are going to steal the lock and a waiter was
          * enqueued on the pending owners pi_waiters queue. So
          * we have to enqueue this waiter into
-         * current->pi_waiters list. This covers the case,
-         * where current is boosted because it holds another
+         * task->pi_waiters list. This covers the case,
+         * where task is boosted because it holds another
          * lock and gets unboosted because the booster is
          * interrupted, so we would delay a waiter with higher
-         * priority as current->normal_prio.
+         * priority as task->normal_prio.
          *
          * Note: in the rare case of a SCHED_OTHER task changing
          * its priority and thus stealing the lock, next->task
-         * might be current:
+         * might be task:
          */
-        if (likely(next->task != current)) {
-                spin_lock_irqsave(&current->pi_lock, flags);
-                plist_add(&next->pi_list_entry, &current->pi_waiters);
-                __rt_mutex_adjust_prio(current);
-                spin_unlock_irqrestore(&current->pi_lock, flags);
+        if (likely(next->task != task)) {
+                spin_lock_irqsave(&task->pi_lock, flags);
+                plist_add(&next->pi_list_entry, &task->pi_waiters);
+                __rt_mutex_adjust_prio(task);
+                spin_unlock_irqrestore(&task->pi_lock, flags);
         }
         return 1;
 }
@@ -389,7 +390,7 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock)
          */
         mark_rt_mutex_waiters(lock);
 
-        if (rt_mutex_owner(lock) && !try_to_steal_lock(lock))
+        if (rt_mutex_owner(lock) && !try_to_steal_lock(lock, current))
                 return 0;
 
         /* We got the lock. */
@@ -411,6 +412,7 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock)
  */
 static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
                                    struct rt_mutex_waiter *waiter,
+                                   struct task_struct *task,
                                    int detect_deadlock)
 {
         struct task_struct *owner = rt_mutex_owner(lock);
@@ -418,21 +420,21 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
         unsigned long flags;
         int chain_walk = 0, res;
 
-        spin_lock_irqsave(&current->pi_lock, flags);
-        __rt_mutex_adjust_prio(current);
-        waiter->task = current;
+        spin_lock_irqsave(&task->pi_lock, flags);
+        __rt_mutex_adjust_prio(task);
+        waiter->task = task;
         waiter->lock = lock;
-        plist_node_init(&waiter->list_entry, current->prio);
-        plist_node_init(&waiter->pi_list_entry, current->prio);
+        plist_node_init(&waiter->list_entry, task->prio);
+        plist_node_init(&waiter->pi_list_entry, task->prio);
 
         /* Get the top priority waiter on the lock */
         if (rt_mutex_has_waiters(lock))
                 top_waiter = rt_mutex_top_waiter(lock);
         plist_add(&waiter->list_entry, &lock->wait_list);
 
-        current->pi_blocked_on = waiter;
+        task->pi_blocked_on = waiter;
 
-        spin_unlock_irqrestore(&current->pi_lock, flags);
+        spin_unlock_irqrestore(&task->pi_lock, flags);
 
         if (waiter == rt_mutex_top_waiter(lock)) {
                 spin_lock_irqsave(&owner->pi_lock, flags);
@@ -460,7 +462,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
         spin_unlock(&lock->wait_lock);
 
         res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
-                                         current);
+                                         task);
 
         spin_lock(&lock->wait_lock);
 
@@ -605,37 +607,25 @@ void rt_mutex_adjust_pi(struct task_struct *task)
         rt_mutex_adjust_prio_chain(task, 0, NULL, NULL, task);
 }
 
-/*
- * Slow path lock function:
+/**
+ * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
+ * @lock:                the rt_mutex to take
+ * @state:               the state the task should block in (TASK_INTERRUPTIBLE
+ *                       or TASK_UNINTERRUPTIBLE)
+ * @timeout:             the pre-initialized and started timer, or NULL for none
+ * @waiter:              the pre-initialized rt_mutex_waiter
+ * @detect_deadlock:     passed to task_blocks_on_rt_mutex
+ *
+ * lock->wait_lock must be held by the caller.
  */
 static int __sched
-rt_mutex_slowlock(struct rt_mutex *lock, int state,
-                  struct hrtimer_sleeper *timeout,
-                  int detect_deadlock)
+__rt_mutex_slowlock(struct rt_mutex *lock, int state,
+                    struct hrtimer_sleeper *timeout,
+                    struct rt_mutex_waiter *waiter,
+                    int detect_deadlock)
 {
-        struct rt_mutex_waiter waiter;
         int ret = 0;
 
-        debug_rt_mutex_init_waiter(&waiter);
-        waiter.task = NULL;
-
-        spin_lock(&lock->wait_lock);
-
-        /* Try to acquire the lock again: */
-        if (try_to_take_rt_mutex(lock)) {
-                spin_unlock(&lock->wait_lock);
-                return 0;
-        }
-
-        set_current_state(state);
-
-        /* Setup the timer, when timeout != NULL */
-        if (unlikely(timeout)) {
-                hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
-                if (!hrtimer_active(&timeout->timer))
-                        timeout->task = NULL;
-        }
-
         for (;;) {
                 /* Try to acquire the lock: */
                 if (try_to_take_rt_mutex(lock))
@@ -656,19 +646,19 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
                 }
 
                 /*
-                 * waiter.task is NULL the first time we come here and
+                 * waiter->task is NULL the first time we come here and
                  * when we have been woken up by the previous owner
                  * but the lock got stolen by a higher prio task.
                  */
-                if (!waiter.task) {
-                        ret = task_blocks_on_rt_mutex(lock, &waiter,
+                if (!waiter->task) {
+                        ret = task_blocks_on_rt_mutex(lock, waiter, current,
                                                       detect_deadlock);
                         /*
                          * If we got woken up by the owner then start loop
                          * all over without going into schedule to try
                          * to get the lock now:
                          */
-                        if (unlikely(!waiter.task)) {
+                        if (unlikely(!waiter->task)) {
                                 /*
                                  * Reset the return value. We might
                                  * have returned with -EDEADLK and the
@@ -684,15 +674,52 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
 
                 spin_unlock(&lock->wait_lock);
 
-                debug_rt_mutex_print_deadlock(&waiter);
+                debug_rt_mutex_print_deadlock(waiter);
 
-                if (waiter.task)
+                if (waiter->task)
                         schedule_rt_mutex(lock);
 
                 spin_lock(&lock->wait_lock);
                 set_current_state(state);
         }
 
+        return ret;
+}
+
+/*
+ * Slow path lock function:
+ */
+static int __sched
+rt_mutex_slowlock(struct rt_mutex *lock, int state,
+                  struct hrtimer_sleeper *timeout,
+                  int detect_deadlock)
+{
+        struct rt_mutex_waiter waiter;
+        int ret = 0;
+
+        debug_rt_mutex_init_waiter(&waiter);
+        waiter.task = NULL;
+
+        spin_lock(&lock->wait_lock);
+
+        /* Try to acquire the lock again: */
+        if (try_to_take_rt_mutex(lock)) {
+                spin_unlock(&lock->wait_lock);
+                return 0;
+        }
+
+        set_current_state(state);
+
+        /* Setup the timer, when timeout != NULL */
+        if (unlikely(timeout)) {
+                hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
+                if (!hrtimer_active(&timeout->timer))
+                        timeout->task = NULL;
+        }
+
+        ret = __rt_mutex_slowlock(lock, state, timeout, &waiter,
+                                  detect_deadlock);
+
         set_current_state(TASK_RUNNING);
 
         if (unlikely(waiter.task))
@@ -986,6 +1013,59 @@ void rt_mutex_proxy_unlock(struct rt_mutex *lock,
 }
 
 /**
+ * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
+ * @lock:               the rt_mutex to take
+ * @waiter:             the pre-initialized rt_mutex_waiter
+ * @task:               the task to prepare
+ * @detect_deadlock:    perform deadlock detection (1) or not (0)
+ *
+ * Returns:
+ *  0 - task blocked on lock
+ *  1 - acquired the lock for task, caller should wake it up
+ * <0 - error
+ *
+ * Special API call for FUTEX_REQUEUE_PI support.
+ */
+int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
+                              struct rt_mutex_waiter *waiter,
+                              struct task_struct *task, int detect_deadlock)
+{
+        int ret;
+
+        spin_lock(&lock->wait_lock);
+
+        mark_rt_mutex_waiters(lock);
+
+        if (!rt_mutex_owner(lock) || try_to_steal_lock(lock, task)) {
+                /* We got the lock for task. */
+                debug_rt_mutex_lock(lock);
+
+                rt_mutex_set_owner(lock, task, 0);
+
+                rt_mutex_deadlock_account_lock(lock, task);
+                return 1;
+        }
+
+        ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);
+
+
+        if (ret && !waiter->task) {
+                /*
+                 * Reset the return value. We might have
+                 * returned with -EDEADLK and the owner
+                 * released the lock while we were walking the
+                 * pi chain.  Let the waiter sort it out.
+                 */
+                ret = 0;
+        }
+        spin_unlock(&lock->wait_lock);
+
+        debug_rt_mutex_print_deadlock(waiter);
+
+        return ret;
+}
+
+/**
  * rt_mutex_next_owner - return the next owner of the lock
  *
  * @lock: the rt lock query
@@ -1004,3 +1084,57 @@ struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
 
         return rt_mutex_top_waiter(lock)->task;
 }
+
+/**
+ * rt_mutex_finish_proxy_lock() - Complete lock acquisition
+ * @lock:               the rt_mutex we were woken on
+ * @to:                 the timeout, null if none. hrtimer should already have
+ *                      been started.
+ * @waiter:             the pre-initialized rt_mutex_waiter
+ * @detect_deadlock:    perform deadlock detection (1) or not (0)
+ *
+ * Complete the lock acquisition started our behalf by another thread.
+ *
+ * Returns:
+ *  0 - success
+ * <0 - error, one of -EINTR, -ETIMEDOUT, or -EDEADLK
+ *
+ * Special API call for PI-futex requeue support
+ */
+int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
+                               struct hrtimer_sleeper *to,
+                               struct rt_mutex_waiter *waiter,
+                               int detect_deadlock)
+{
+        int ret;
+
+        spin_lock(&lock->wait_lock);
+
+        set_current_state(TASK_INTERRUPTIBLE);
+
+        ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter,
+                                  detect_deadlock);
+
+        set_current_state(TASK_RUNNING);
+
+        if (unlikely(waiter->task))
+                remove_waiter(lock, waiter);
+
+        /*
+         * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
+         * have to fix that up.
+         */
+        fixup_rt_mutex_waiters(lock);
+
+        spin_unlock(&lock->wait_lock);
+
+        /*
+         * Readjust priority, when we did not get the lock. We might have been
+         * the pending owner and boosted. Since we did not take the lock, the
+         * PI boost has to go.
+         */
+        if (unlikely(ret))
+                rt_mutex_adjust_prio(current);
+
+        return ret;
+}
diff --git a/kernel/rtmutex_common.h b/kernel/rtmutex_common.h
index e124bf5800ea..97a2f81866af 100644
--- a/kernel/rtmutex_common.h
+++ b/kernel/rtmutex_common.h
@@ -120,6 +120,14 @@ extern void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
                                        struct task_struct *proxy_owner);
 extern void rt_mutex_proxy_unlock(struct rt_mutex *lock,
                                   struct task_struct *proxy_owner);
+extern int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
+                                     struct rt_mutex_waiter *waiter,
+                                     struct task_struct *task,
+                                     int detect_deadlock);
+extern int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
+                                      struct hrtimer_sleeper *to,
+                                      struct rt_mutex_waiter *waiter,
+                                      int detect_deadlock);
 
 #ifdef CONFIG_DEBUG_RT_MUTEXES
 # include "rtmutex-debug.h"