[v2,3/8] futex: make PI support optional

Message ID 20170606232450.30278-4-nicolas.pitre@linaro.org
State New
Headers show
Series
  • scheduler tinification
Related show

Commit Message

Nicolas Pitre June 6, 2017, 11:24 p.m.
Split out the priority inheritance support to a file of its own
to make futex.c easier to understand and, hopefully, to maintain.
This also makes it possible to compile out the PI support when RT
task support is not available.

Signed-off-by: Nicolas Pitre <nico@linaro.org>

---
 include/linux/futex.h |    7 +-
 init/Kconfig          |    7 +-
 kernel/futex.c        | 2829 ++++++++++++-------------------------------------
 kernel/futex_pi.c     | 1563 +++++++++++++++++++++++++++
 4 files changed, 2233 insertions(+), 2173 deletions(-)
 create mode 100644 kernel/futex_pi.c

-- 
2.9.4

Patch

diff --git a/include/linux/futex.h b/include/linux/futex.h
index 7c5b694864..f36bfd26f9 100644
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -54,7 +54,6 @@  union futex_key {
 
 #ifdef CONFIG_FUTEX
 extern void exit_robust_list(struct task_struct *curr);
-extern void exit_pi_state_list(struct task_struct *curr);
 #ifdef CONFIG_HAVE_FUTEX_CMPXCHG
 #define futex_cmpxchg_enabled 1
 #else
@@ -64,8 +63,14 @@  extern int futex_cmpxchg_enabled;
 static inline void exit_robust_list(struct task_struct *curr)
 {
 }
+#endif
+
+#ifdef CONFIG_FUTEX_PI
+extern void exit_pi_state_list(struct task_struct *curr);
+#else
 static inline void exit_pi_state_list(struct task_struct *curr)
 {
 }
 #endif
+
 #endif
diff --git a/init/Kconfig b/init/Kconfig
index b9aed60cac..ad91724f75 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1624,12 +1624,17 @@  config BASE_FULL
 config FUTEX
 	bool "Enable futex support" if EXPERT
 	default y
-	select RT_MUTEXES
+	imply RT_MUTEXES
 	help
 	  Disabling this option will cause the kernel to be built without
 	  support for "fast userspace mutexes".  The resulting kernel may not
 	  run glibc-based applications correctly.
 
+config FUTEX_PI
+	bool
+	depends on FUTEX && RT_MUTEXES
+	default y
+
 config HAVE_FUTEX_CMPXCHG
 	bool
 	depends on FUTEX
diff --git a/kernel/futex.c b/kernel/futex.c
index 357348a6cf..c82ea0098f 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -12,17 +12,9 @@ 
  *  (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.
@@ -70,8 +62,6 @@ 
 
 #include <asm/futex.h>
 
-#include "locking/rtmutex_common.h"
-
 /*
  * READ this before attempting to hack on futexes!
  *
@@ -193,26 +183,7 @@  int __read_mostly futex_cmpxchg_enabled;
 #define FLAGS_CLOCKRT		0x02
 #define FLAGS_HAS_TIMEOUT	0x04
 
-/*
- * 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;
-};
+struct futex_pi_state;
 
 /**
  * struct futex_q - The hashed futex queue entry, one per waiting task
@@ -733,25 +704,6 @@  static int fault_in_user_writeable(u32 __user *uaddr)
 	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 int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
 				      u32 uval, u32 newval)
 {
@@ -779,1114 +731,395 @@  static int get_futex_value_locked(u32 *dest, u32 __user *from)
 /*
  * 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;
+#ifdef CONFIG_FUTEX_PI
+#include "futex_pi.c"
+#else
+#define get_pi_state(...)
+#define put_pi_state(...)
+#define refill_pi_state_cache()		false
+#define lookup_pi_state(...)		-ENOSYS
+#define rt_mutex_start_proxy_lock(...)	-ENOSYS
+#define requeue_pi_wake_futex(...)
+#define futex_proxy_trylock_atomic(...)	-ENOSYS
+#define futex_lock_pi(...)		-ENOSYS
+#define futex_unlock_pi(...)		-ENOSYS
+#define futex_wait_requeue_pi(...)	-ENOSYS
+#endif
 
-	return 0;
-}
 
-static struct futex_pi_state *alloc_pi_state(void)
+/**
+ * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
+ * @q:	The futex_q to unqueue
+ *
+ * The q->lock_ptr must not be NULL and must be held by the caller.
+ */
+static void __unqueue_futex(struct futex_q *q)
 {
-	struct futex_pi_state *pi_state = current->pi_state_cache;
-
-	WARN_ON(!pi_state);
-	current->pi_state_cache = NULL;
+	struct futex_hash_bucket *hb;
 
-	return pi_state;
-}
+	if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
+	    || WARN_ON(plist_node_empty(&q->list)))
+		return;
 
-static void get_pi_state(struct futex_pi_state *pi_state)
-{
-	WARN_ON_ONCE(!atomic_inc_not_zero(&pi_state->refcount));
+	hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
+	plist_del(&q->list, &hb->chain);
+	hb_waiters_dec(hb);
 }
 
 /*
- * Drops a reference to the pi_state object and frees or caches it
- * when the last reference is gone.
- *
- * Must be called with the hb lock held.
+ * The hash bucket lock must be held when this is called.
+ * Afterwards, the futex_q must not be accessed. Callers
+ * must ensure to later call wake_up_q() for the actual
+ * wakeups to occur.
  */
-static void put_pi_state(struct futex_pi_state *pi_state)
+static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
 {
-	if (!pi_state)
-		return;
+	struct task_struct *p = q->task;
 
-	if (!atomic_dec_and_test(&pi_state->refcount))
+	if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
 		return;
 
 	/*
-	 * If pi_state->owner is NULL, the owner is most probably dying
-	 * and has cleaned up the pi_state already
+	 * Queue the task for later wakeup for after we've released
+	 * the hb->lock. wake_q_add() grabs reference to p.
 	 */
-	if (pi_state->owner) {
-		raw_spin_lock_irq(&pi_state->owner->pi_lock);
-		list_del_init(&pi_state->list);
-		raw_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;
-	}
+	wake_q_add(wake_q, p);
+	__unqueue_futex(q);
+	/*
+	 * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
+	 * is written, without taking any locks. This is possible in the event
+	 * of a spurious wakeup, for example. A memory barrier is required here
+	 * to prevent the following store to lock_ptr from getting ahead of the
+	 * plist_del in __unqueue_futex().
+	 */
+	smp_store_release(&q->lock_ptr, NULL);
 }
 
 /*
- * Look up the task based on what TID userspace gave us.
- * We dont trust it.
+ * Express the locking dependencies for lockdep:
  */
-static struct task_struct *futex_find_get_task(pid_t pid)
+static inline void
+double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
 {
-	struct task_struct *p;
-
-	rcu_read_lock();
-	p = find_task_by_vpid(pid);
-	if (p)
-		get_task_struct(p);
-
-	rcu_read_unlock();
+	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);
+	}
+}
 
-	return p;
+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);
 }
 
 /*
- * 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.)
+ * Wake up waiters matching bitset queued on this futex (uaddr).
  */
-void exit_pi_state_list(struct task_struct *curr)
+static int
+futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
 {
-	struct list_head *next, *head = &curr->pi_state_list;
-	struct futex_pi_state *pi_state;
 	struct futex_hash_bucket *hb;
+	struct futex_q *this, *next;
 	union futex_key key = FUTEX_KEY_INIT;
+	int ret;
+	DEFINE_WAKE_Q(wake_q);
 
-	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:
-	 */
-	raw_spin_lock_irq(&curr->pi_lock);
-	while (!list_empty(head)) {
+	if (!bitset)
+		return -EINVAL;
 
-		next = head->next;
-		pi_state = list_entry(next, struct futex_pi_state, list);
-		key = pi_state->key;
-		hb = hash_futex(&key);
-		raw_spin_unlock_irq(&curr->pi_lock);
+	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
+	if (unlikely(ret != 0))
+		goto out;
 
-		spin_lock(&hb->lock);
+	hb = hash_futex(&key);
 
-		raw_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;
-		}
+	/* Make sure we really have tasks to wakeup */
+	if (!hb_waiters_pending(hb))
+		goto out_put_key;
 
-		WARN_ON(pi_state->owner != curr);
-		WARN_ON(list_empty(&pi_state->list));
-		list_del_init(&pi_state->list);
-		pi_state->owner = NULL;
-		raw_spin_unlock_irq(&curr->pi_lock);
+	spin_lock(&hb->lock);
 
-		get_pi_state(pi_state);
-		spin_unlock(&hb->lock);
+	plist_for_each_entry_safe(this, next, &hb->chain, list) {
+		if (match_futex (&this->key, &key)) {
+			if (this->pi_state || this->rt_waiter) {
+				ret = -EINVAL;
+				break;
+			}
 
-		rt_mutex_futex_unlock(&pi_state->pi_mutex);
-		put_pi_state(pi_state);
+			/* Check if one of the bits is set in both bitsets */
+			if (!(this->bitset & bitset))
+				continue;
 
-		raw_spin_lock_irq(&curr->pi_lock);
+			mark_wake_futex(&wake_q, this);
+			if (++ret >= nr_wake)
+				break;
+		}
 	}
-	raw_spin_unlock_irq(&curr->pi_lock);
-}
 
-/*
- * We need to check the following states:
- *
- *      Waiter | pi_state | pi->owner | uTID      | uODIED | ?
- *
- * [1]  NULL   | ---      | ---       | 0         | 0/1    | Valid
- * [2]  NULL   | ---      | ---       | >0        | 0/1    | Valid
- *
- * [3]  Found  | NULL     | --        | Any       | 0/1    | Invalid
- *
- * [4]  Found  | Found    | NULL      | 0         | 1      | Valid
- * [5]  Found  | Found    | NULL      | >0        | 1      | Invalid
- *
- * [6]  Found  | Found    | task      | 0         | 1      | Valid
- *
- * [7]  Found  | Found    | NULL      | Any       | 0      | Invalid
- *
- * [8]  Found  | Found    | task      | ==taskTID | 0/1    | Valid
- * [9]  Found  | Found    | task      | 0         | 0      | Invalid
- * [10] Found  | Found    | task      | !=taskTID | 0/1    | Invalid
- *
- * [1]	Indicates that the kernel can acquire the futex atomically. We
- *	came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
- *
- * [2]	Valid, if TID does not belong to a kernel thread. If no matching
- *      thread is found then it indicates that the owner TID has died.
- *
- * [3]	Invalid. The waiter is queued on a non PI futex
- *
- * [4]	Valid state after exit_robust_list(), which sets the user space
- *	value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
- *
- * [5]	The user space value got manipulated between exit_robust_list()
- *	and exit_pi_state_list()
- *
- * [6]	Valid state after exit_pi_state_list() which sets the new owner in
- *	the pi_state but cannot access the user space value.
- *
- * [7]	pi_state->owner can only be NULL when the OWNER_DIED bit is set.
- *
- * [8]	Owner and user space value match
- *
- * [9]	There is no transient state which sets the user space TID to 0
- *	except exit_robust_list(), but this is indicated by the
- *	FUTEX_OWNER_DIED bit. See [4]
- *
- * [10] There is no transient state which leaves owner and user space
- *	TID out of sync.
- *
- *
- * Serialization and lifetime rules:
- *
- * hb->lock:
- *
- *	hb -> futex_q, relation
- *	futex_q -> pi_state, relation
- *
- *	(cannot be raw because hb can contain arbitrary amount
- *	 of futex_q's)
- *
- * pi_mutex->wait_lock:
- *
- *	{uval, pi_state}
- *
- *	(and pi_mutex 'obviously')
- *
- * p->pi_lock:
- *
- *	p->pi_state_list -> pi_state->list, relation
- *
- * pi_state->refcount:
- *
- *	pi_state lifetime
- *
- *
- * Lock order:
- *
- *   hb->lock
- *     pi_mutex->wait_lock
- *       p->pi_lock
- *
- */
+	spin_unlock(&hb->lock);
+	wake_up_q(&wake_q);
+out_put_key:
+	put_futex_key(&key);
+out:
+	return ret;
+}
 
 /*
- * Validate that the existing waiter has a pi_state and sanity check
- * the pi_state against the user space value. If correct, attach to
- * it.
+ * Wake up all waiters hashed on the physical page that is mapped
+ * to this virtual address:
  */
-static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
-			      struct futex_pi_state *pi_state,
-			      struct futex_pi_state **ps)
+static int
+futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
+	      int nr_wake, int nr_wake2, int op)
 {
-	pid_t pid = uval & FUTEX_TID_MASK;
-	u32 uval2;
-	int ret;
-
-	/*
-	 * Userspace might have messed up non-PI and PI futexes [3]
-	 */
-	if (unlikely(!pi_state))
-		return -EINVAL;
+	union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
+	struct futex_hash_bucket *hb1, *hb2;
+	struct futex_q *this, *next;
+	int ret, op_ret;
+	DEFINE_WAKE_Q(wake_q);
 
-	/*
-	 * We get here with hb->lock held, and having found a
-	 * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
-	 * has dropped the hb->lock in between queue_me() and unqueue_me_pi(),
-	 * which in turn means that futex_lock_pi() still has a reference on
-	 * our pi_state.
-	 *
-	 * The waiter holding a reference on @pi_state also protects against
-	 * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
-	 * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
-	 * free pi_state before we can take a reference ourselves.
-	 */
-	WARN_ON(!atomic_read(&pi_state->refcount));
+retry:
+	ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
+	if (unlikely(ret != 0))
+		goto out;
+	ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
+	if (unlikely(ret != 0))
+		goto out_put_key1;
 
-	/*
-	 * Now that we have a pi_state, we can acquire wait_lock
-	 * and do the state validation.
-	 */
-	raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+	hb1 = hash_futex(&key1);
+	hb2 = hash_futex(&key2);
 
-	/*
-	 * Since {uval, pi_state} is serialized by wait_lock, and our current
-	 * uval was read without holding it, it can have changed. Verify it
-	 * still is what we expect it to be, otherwise retry the entire
-	 * operation.
-	 */
-	if (get_futex_value_locked(&uval2, uaddr))
-		goto out_efault;
+retry_private:
+	double_lock_hb(hb1, hb2);
+	op_ret = futex_atomic_op_inuser(op, uaddr2);
+	if (unlikely(op_ret < 0)) {
 
-	if (uval != uval2)
-		goto out_eagain;
+		double_unlock_hb(hb1, hb2);
 
-	/*
-	 * Handle the owner died case:
-	 */
-	if (uval & FUTEX_OWNER_DIED) {
+#ifndef CONFIG_MMU
 		/*
-		 * exit_pi_state_list sets owner to NULL and wakes the
-		 * topmost waiter. The task which acquires the
-		 * pi_state->rt_mutex will fixup owner.
+		 * we don't get EFAULT from MMU faults if we don't have an MMU,
+		 * but we might get them from range checking
 		 */
-		if (!pi_state->owner) {
-			/*
-			 * No pi state owner, but the user space TID
-			 * is not 0. Inconsistent state. [5]
-			 */
-			if (pid)
-				goto out_einval;
-			/*
-			 * Take a ref on the state and return success. [4]
-			 */
-			goto out_attach;
-		}
+		ret = op_ret;
+		goto out_put_keys;
+#endif
 
-		/*
-		 * If TID is 0, then either the dying owner has not
-		 * yet executed exit_pi_state_list() or some waiter
-		 * acquired the rtmutex in the pi state, but did not
-		 * yet fixup the TID in user space.
-		 *
-		 * Take a ref on the state and return success. [6]
-		 */
-		if (!pid)
-			goto out_attach;
-	} else {
-		/*
-		 * If the owner died bit is not set, then the pi_state
-		 * must have an owner. [7]
-		 */
-		if (!pi_state->owner)
-			goto out_einval;
-	}
+		if (unlikely(op_ret != -EFAULT)) {
+			ret = op_ret;
+			goto out_put_keys;
+		}
 
-	/*
-	 * Bail out if user space manipulated the futex value. If pi
-	 * state exists then the owner TID must be the same as the
-	 * user space TID. [9/10]
-	 */
-	if (pid != task_pid_vnr(pi_state->owner))
-		goto out_einval;
+		ret = fault_in_user_writeable(uaddr2);
+		if (ret)
+			goto out_put_keys;
 
-out_attach:
-	get_pi_state(pi_state);
-	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
-	*ps = pi_state;
-	return 0;
+		if (!(flags & FLAGS_SHARED))
+			goto retry_private;
 
-out_einval:
-	ret = -EINVAL;
-	goto out_error;
+		put_futex_key(&key2);
+		put_futex_key(&key1);
+		goto retry;
+	}
 
-out_eagain:
-	ret = -EAGAIN;
-	goto out_error;
+	plist_for_each_entry_safe(this, next, &hb1->chain, list) {
+		if (match_futex (&this->key, &key1)) {
+			if (this->pi_state || this->rt_waiter) {
+				ret = -EINVAL;
+				goto out_unlock;
+			}
+			mark_wake_futex(&wake_q, this);
+			if (++ret >= nr_wake)
+				break;
+		}
+	}
 
-out_efault:
-	ret = -EFAULT;
-	goto out_error;
+	if (op_ret > 0) {
+		op_ret = 0;
+		plist_for_each_entry_safe(this, next, &hb2->chain, list) {
+			if (match_futex (&this->key, &key2)) {
+				if (this->pi_state || this->rt_waiter) {
+					ret = -EINVAL;
+					goto out_unlock;
+				}
+				mark_wake_futex(&wake_q, this);
+				if (++op_ret >= nr_wake2)
+					break;
+			}
+		}
+		ret += op_ret;
+	}
 
-out_error:
-	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+out_unlock:
+	double_unlock_hb(hb1, hb2);
+	wake_up_q(&wake_q);
+out_put_keys:
+	put_futex_key(&key2);
+out_put_key1:
+	put_futex_key(&key1);
+out:
 	return ret;
 }
 
-/*
- * Lookup the task for the TID provided from user space and attach to
- * it after doing proper sanity checks.
+/**
+ * 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 int attach_to_pi_owner(u32 uval, union futex_key *key,
-			      struct futex_pi_state **ps)
+static inline
+void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
+		   struct futex_hash_bucket *hb2, union futex_key *key2)
 {
-	pid_t pid = uval & FUTEX_TID_MASK;
-	struct futex_pi_state *pi_state;
-	struct task_struct *p;
-
-	/*
-	 * 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 [1]
-	 */
-	if (!pid)
-		return -ESRCH;
-	p = futex_find_get_task(pid);
-	if (!p)
-		return -ESRCH;
-
-	if (unlikely(p->flags & PF_KTHREAD)) {
-		put_task_struct(p);
-		return -EPERM;
-	}
 
 	/*
-	 * 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:
+	 * If key1 and key2 hash to the same bucket, no need to
+	 * requeue.
 	 */
-	raw_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;
-
-		raw_spin_unlock_irq(&p->pi_lock);
-		put_task_struct(p);
-		return ret;
+	if (likely(&hb1->chain != &hb2->chain)) {
+		plist_del(&q->list, &hb1->chain);
+		hb_waiters_dec(hb1);
+		hb_waiters_inc(hb2);
+		plist_add(&q->list, &hb2->chain);
+		q->lock_ptr = &hb2->lock;
 	}
-
-	/*
-	 * No existing pi state. First waiter. [2]
-	 *
-	 * This creates pi_state, we have hb->lock held, this means nothing can
-	 * observe this state, wait_lock is irrelevant.
-	 */
-	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;
-	raw_spin_unlock_irq(&p->pi_lock);
-
-	put_task_struct(p);
-
-	*ps = pi_state;
-
-	return 0;
-}
-
-static int lookup_pi_state(u32 __user *uaddr, u32 uval,
-			   struct futex_hash_bucket *hb,
-			   union futex_key *key, struct futex_pi_state **ps)
-{
-	struct futex_q *top_waiter = futex_top_waiter(hb, key);
-
-	/*
-	 * If there is a waiter on that futex, validate it and
-	 * attach to the pi_state when the validation succeeds.
-	 */
-	if (top_waiter)
-		return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
-
-	/*
-	 * We are the first waiter - try to look up the owner based on
-	 * @uval and attach to it.
-	 */
-	return attach_to_pi_owner(uval, key, ps);
-}
-
-static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
-{
-	u32 uninitialized_var(curval);
-
-	if (unlikely(should_fail_futex(true)))
-		return -EFAULT;
-
-	if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
-		return -EFAULT;
-
-	/* If user space value changed, let the caller retry */
-	return curval != uval ? -EAGAIN : 0;
+	get_futex_key_refs(key2);
+	q->key = *key2;
 }
 
 /**
- * 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)
+ * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
+ * @uaddr1:	source futex user address
+ * @flags:	futex flags (FLAGS_SHARED, etc.)
+ * @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)
+ * @cmpval:	@uaddr1 expected value (or %NULL)
+ * @requeue_pi:	if we are attempting to requeue from a non-pi futex to a
+ *		pi futex (pi to pi requeue is not supported)
  *
- * Return:
- *  0 - ready to wait;
- *  1 - acquired the lock;
- * <0 - error
+ * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
+ * uaddr2 atomically on behalf of the top waiter.
  *
- * The hb->lock and futex_key refs shall be held by the caller.
+ * Return:
+ * >=0 - on success, the number of tasks requeued or woken;
+ *  <0 - on error
  */
-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)
+static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
+			 u32 __user *uaddr2, int nr_wake, int nr_requeue,
+			 u32 *cmpval, int requeue_pi)
 {
-	u32 uval, newval, vpid = task_pid_vnr(task);
-	struct futex_q *top_waiter;
-	int ret;
-
-	/*
-	 * Read the user space value first so we can validate a few
-	 * things before proceeding further.
-	 */
-	if (get_futex_value_locked(&uval, uaddr))
-		return -EFAULT;
-
-	if (unlikely(should_fail_futex(true)))
-		return -EFAULT;
-
-	/*
-	 * Detect deadlocks.
-	 */
-	if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
-		return -EDEADLK;
-
-	if ((unlikely(should_fail_futex(true))))
-		return -EDEADLK;
+	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 futex_q *this, *next;
+	DEFINE_WAKE_Q(wake_q);
 
 	/*
-	 * Lookup existing state first. If it exists, try to attach to
-	 * its pi_state.
+	 * When PI not supported, return -ENOSYS if requeue_pi is true,
+	 * otherwise this will let the compiler assume requeue_pi is false
+	 * which shoud optimize away all the conditional code further down.
 	 */
-	top_waiter = futex_top_waiter(hb, key);
-	if (top_waiter)
-		return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
+	if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi)
+		return -ENOSYS;
 
-	/*
-	 * No waiter and user TID is 0. We are here because the
-	 * waiters or the owner died bit is set or called from
-	 * requeue_cmp_pi or for whatever reason something took the
-	 * syscall.
-	 */
-	if (!(uval & FUTEX_TID_MASK)) {
+	if (requeue_pi) {
 		/*
-		 * We take over the futex. No other waiters and the user space
-		 * TID is 0. We preserve the owner died bit.
+		 * Requeue PI only works on two distinct uaddrs. This
+		 * check is only valid for private futexes. See below.
 		 */
-		newval = uval & FUTEX_OWNER_DIED;
-		newval |= vpid;
-
-		/* The futex requeue_pi code can enforce the waiters bit */
-		if (set_waiters)
-			newval |= FUTEX_WAITERS;
-
-		ret = lock_pi_update_atomic(uaddr, uval, newval);
-		/* If the take over worked, return 1 */
-		return ret < 0 ? ret : 1;
-	}
-
-	/*
-	 * First waiter. Set the waiters bit before attaching ourself to
-	 * the owner. If owner tries to unlock, it will be forced into
-	 * the kernel and blocked on hb->lock.
-	 */
-	newval = uval | FUTEX_WAITERS;
-	ret = lock_pi_update_atomic(uaddr, uval, newval);
-	if (ret)
-		return ret;
-	/*
-	 * If the update of the user space value succeeded, we try to
-	 * attach to the owner. If that fails, no harm done, we only
-	 * set the FUTEX_WAITERS bit in the user space variable.
-	 */
-	return attach_to_pi_owner(uval, key, ps);
-}
-
-/**
- * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
- * @q:	The futex_q to unqueue
- *
- * The q->lock_ptr must not be NULL and must be held by the caller.
- */
-static void __unqueue_futex(struct futex_q *q)
-{
-	struct futex_hash_bucket *hb;
-
-	if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
-	    || WARN_ON(plist_node_empty(&q->list)))
-		return;
-
-	hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
-	plist_del(&q->list, &hb->chain);
-	hb_waiters_dec(hb);
-}
-
-/*
- * The hash bucket lock must be held when this is called.
- * Afterwards, the futex_q must not be accessed. Callers
- * must ensure to later call wake_up_q() for the actual
- * wakeups to occur.
- */
-static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
-{
-	struct task_struct *p = q->task;
-
-	if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
-		return;
-
-	/*
-	 * Queue the task for later wakeup for after we've released
-	 * the hb->lock. wake_q_add() grabs reference to p.
-	 */
-	wake_q_add(wake_q, p);
-	__unqueue_futex(q);
-	/*
-	 * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
-	 * is written, without taking any locks. This is possible in the event
-	 * of a spurious wakeup, for example. A memory barrier is required here
-	 * to prevent the following store to lock_ptr from getting ahead of the
-	 * plist_del in __unqueue_futex().
-	 */
-	smp_store_release(&q->lock_ptr, NULL);
-}
-
-/*
- * Caller must hold a reference on @pi_state.
- */
-static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
-{
-	u32 uninitialized_var(curval), newval;
-	struct task_struct *new_owner;
-	bool postunlock = false;
-	DEFINE_WAKE_Q(wake_q);
-	int ret = 0;
+		if (uaddr1 == uaddr2)
+			return -EINVAL;
 
-	new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
-	if (WARN_ON_ONCE(!new_owner)) {
 		/*
-		 * As per the comment in futex_unlock_pi() this should not happen.
-		 *
-		 * When this happens, give up our locks and try again, giving
-		 * the futex_lock_pi() instance time to complete, either by
-		 * waiting on the rtmutex or removing itself from the futex
-		 * queue.
+		 * requeue_pi requires a pi_state, try to allocate it now
+		 * without any locks in case it fails.
 		 */
-		ret = -EAGAIN;
-		goto out_unlock;
-	}
-
-	/*
-	 * We pass it to the next owner. The WAITERS bit is always kept
-	 * enabled while there is PI state around. We cleanup the owner
-	 * died bit, because we are the owner.
-	 */
-	newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
-
-	if (unlikely(should_fail_futex(true)))
-		ret = -EFAULT;
-
-	if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) {
-		ret = -EFAULT;
-
-	} else if (curval != uval) {
+		if (refill_pi_state_cache())
+			return -ENOMEM;
 		/*
-		 * If a unconditional UNLOCK_PI operation (user space did not
-		 * try the TID->0 transition) raced with a waiter setting the
-		 * FUTEX_WAITERS flag between get_user() and locking the hash
-		 * bucket lock, retry the operation.
+		 * 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 ((FUTEX_TID_MASK & curval) == uval)
-			ret = -EAGAIN;
-		else
-			ret = -EINVAL;
+		if (nr_wake != 1)
+			return -EINVAL;
 	}
 
-	if (ret)
-		goto out_unlock;
+retry:
+	ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
+	if (unlikely(ret != 0))
+		goto out;
+	ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
+			    requeue_pi ? VERIFY_WRITE : VERIFY_READ);
+	if (unlikely(ret != 0))
+		goto out_put_key1;
 
 	/*
-	 * This is a point of no return; once we modify the uval there is no
-	 * going back and subsequent operations must not fail.
+	 * The check above which compares uaddrs is not sufficient for
+	 * shared futexes. We need to compare the keys:
 	 */
+	if (requeue_pi && match_futex(&key1, &key2)) {
+		ret = -EINVAL;
+		goto out_put_keys;
+	}
 
-	raw_spin_lock(&pi_state->owner->pi_lock);
-	WARN_ON(list_empty(&pi_state->list));
-	list_del_init(&pi_state->list);
-	raw_spin_unlock(&pi_state->owner->pi_lock);
+	hb1 = hash_futex(&key1);
+	hb2 = hash_futex(&key2);
 
-	raw_spin_lock(&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;
-	raw_spin_unlock(&new_owner->pi_lock);
+retry_private:
+	hb_waiters_inc(hb2);
+	double_lock_hb(hb1, hb2);
 
-	postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
+	if (likely(cmpval != NULL)) {
+		u32 curval;
 
-out_unlock:
-	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+		ret = get_futex_value_locked(&curval, uaddr1);
 
-	if (postunlock)
-		rt_mutex_postunlock(&wake_q);
+		if (unlikely(ret)) {
+			double_unlock_hb(hb1, hb2);
+			hb_waiters_dec(hb2);
 
-	return ret;
-}
-
-/*
- * 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, unsigned int flags, int nr_wake, u32 bitset)
-{
-	struct futex_hash_bucket *hb;
-	struct futex_q *this, *next;
-	union futex_key key = FUTEX_KEY_INIT;
-	int ret;
-	DEFINE_WAKE_Q(wake_q);
-
-	if (!bitset)
-		return -EINVAL;
-
-	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
-	if (unlikely(ret != 0))
-		goto out;
-
-	hb = hash_futex(&key);
-
-	/* Make sure we really have tasks to wakeup */
-	if (!hb_waiters_pending(hb))
-		goto out_put_key;
-
-	spin_lock(&hb->lock);
-
-	plist_for_each_entry_safe(this, next, &hb->chain, list) {
-		if (match_futex (&this->key, &key)) {
-			if (this->pi_state || this->rt_waiter) {
-				ret = -EINVAL;
-				break;
-			}
+			ret = get_user(curval, uaddr1);
+			if (ret)
+				goto out_put_keys;
 
-			/* Check if one of the bits is set in both bitsets */
-			if (!(this->bitset & bitset))
-				continue;
+			if (!(flags & FLAGS_SHARED))
+				goto retry_private;
 
-			mark_wake_futex(&wake_q, this);
-			if (++ret >= nr_wake)
-				break;
+			put_futex_key(&key2);
+			put_futex_key(&key1);
+			goto retry;
+		}
+		if (curval != *cmpval) {
+			ret = -EAGAIN;
+			goto out_unlock;
 		}
 	}
 
-	spin_unlock(&hb->lock);
-	wake_up_q(&wake_q);
-out_put_key:
-	put_futex_key(&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, unsigned int flags, 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 futex_q *this, *next;
-	int ret, op_ret;
-	DEFINE_WAKE_Q(wake_q);
-
-retry:
-	ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
-	if (unlikely(ret != 0))
-		goto out;
-	ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &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
+	if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
 		/*
-		 * we don't get EFAULT from MMU faults if we don't have an MMU,
-		 * but we might get them from range checking
+		 * 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 = 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 (!(flags & FLAGS_SHARED))
-			goto retry_private;
-
-		put_futex_key(&key2);
-		put_futex_key(&key1);
-		goto retry;
-	}
-
-	plist_for_each_entry_safe(this, next, &hb1->chain, list) {
-		if (match_futex (&this->key, &key1)) {
-			if (this->pi_state || this->rt_waiter) {
-				ret = -EINVAL;
-				goto out_unlock;
-			}
-			mark_wake_futex(&wake_q, this);
-			if (++ret >= nr_wake)
-				break;
-		}
-	}
-
-	if (op_ret > 0) {
-		op_ret = 0;
-		plist_for_each_entry_safe(this, next, &hb2->chain, list) {
-			if (match_futex (&this->key, &key2)) {
-				if (this->pi_state || this->rt_waiter) {
-					ret = -EINVAL;
-					goto out_unlock;
-				}
-				mark_wake_futex(&wake_q, this);
-				if (++op_ret >= nr_wake2)
-					break;
-			}
-		}
-		ret += op_ret;
-	}
-
-out_unlock:
-	double_unlock_hb(hb1, hb2);
-	wake_up_q(&wake_q);
-out_put_keys:
-	put_futex_key(&key2);
-out_put_key1:
-	put_futex_key(&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);
-		hb_waiters_dec(hb1);
-		hb_waiters_inc(hb2);
-		plist_add(&q->list, &hb2->chain);
-		q->lock_ptr = &hb2->lock;
-	}
-	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;
-
-	__unqueue_futex(q);
-
-	WARN_ON(!q->rt_waiter);
-	q->rt_waiter = NULL;
-
-	q->lock_ptr = &hb->lock;
-
-	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.
- *
- * Return:
- *  0 - failed to acquire the lock atomically;
- * >0 - acquired the lock, return value is vpid of the top_waiter
- * <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, vpid;
-
-	if (get_futex_value_locked(&curval, pifutex))
-		return -EFAULT;
-
-	if (unlikely(should_fail_futex(true)))
-		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.
-	 */
-	vpid = task_pid_vnr(top_waiter->task);
-	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 vpid;
-	}
-	return ret;
-}
-
-/**
- * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
- * @uaddr1:	source futex user address
- * @flags:	futex flags (FLAGS_SHARED, etc.)
- * @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)
- * @cmpval:	@uaddr1 expected value (or %NULL)
- * @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.
- *
- * Return:
- * >=0 - on success, the number of tasks requeued or woken;
- *  <0 - on error
- */
-static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
-			 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 futex_q *this, *next;
-	DEFINE_WAKE_Q(wake_q);
-
-	if (requeue_pi) {
-		/*
-		 * Requeue PI only works on two distinct uaddrs. This
-		 * check is only valid for private futexes. See below.
-		 */
-		if (uaddr1 == uaddr2)
-			return -EINVAL;
-
-		/*
-		 * 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:
-	ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
-	if (unlikely(ret != 0))
-		goto out;
-	ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
-			    requeue_pi ? VERIFY_WRITE : VERIFY_READ);
-	if (unlikely(ret != 0))
-		goto out_put_key1;
-
-	/*
-	 * The check above which compares uaddrs is not sufficient for
-	 * shared futexes. We need to compare the keys:
-	 */
-	if (requeue_pi && match_futex(&key1, &key2)) {
-		ret = -EINVAL;
-		goto out_put_keys;
-	}
-
-	hb1 = hash_futex(&key1);
-	hb2 = hash_futex(&key2);
-
-retry_private:
-	hb_waiters_inc(hb2);
-	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);
-			hb_waiters_dec(hb2);
-
-			ret = get_user(curval, uaddr1);
-			if (ret)
-				goto out_put_keys;
-
-			if (!(flags & FLAGS_SHARED))
-				goto retry_private;
-
-			put_futex_key(&key2);
-			put_futex_key(&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);
+		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
@@ -1912,1085 +1145,415 @@  static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
 			 *
 			 * If that call succeeds then we have pi_state and an
 			 * initial refcount on it.
-			 */
-			ret = lookup_pi_state(uaddr2, ret, hb2, &key2, &pi_state);
-		}
-
-		switch (ret) {
-		case 0:
-			/* We hold a reference on the pi state. */
-			break;
-
-			/* If the above failed, then pi_state is NULL */
-		case -EFAULT:
-			double_unlock_hb(hb1, hb2);
-			hb_waiters_dec(hb2);
-			put_futex_key(&key2);
-			put_futex_key(&key1);
-			ret = fault_in_user_writeable(uaddr2);
-			if (!ret)
-				goto retry;
-			goto out;
-		case -EAGAIN:
-			/*
-			 * Two reasons for this:
-			 * - Owner is exiting and we just wait for the
-			 *   exit to complete.
-			 * - The user space value changed.
-			 */
-			double_unlock_hb(hb1, hb2);
-			hb_waiters_dec(hb2);
-			put_futex_key(&key2);
-			put_futex_key(&key1);
-			cond_resched();
-			goto retry;
-		default:
-			goto out_unlock;
-		}
-	}
-
-	plist_for_each_entry_safe(this, next, &hb1->chain, 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.
-		 *
-		 * We should never be requeueing a futex_q with a pi_state,
-		 * which is awaiting a futex_unlock_pi().
-		 */
-		if ((requeue_pi && !this->rt_waiter) ||
-		    (!requeue_pi && this->rt_waiter) ||
-		    this->pi_state) {
-			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) {
-			mark_wake_futex(&wake_q, 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. Take a
-			 * refcount on the pi_state and store the pointer in
-			 * the futex_q object of the waiter.
-			 */
-			get_pi_state(pi_state);
-			this->pi_state = pi_state;
-			ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
-							this->rt_waiter,
-							this->task);
-			if (ret == 1) {
-				/*
-				 * We got the lock. We do neither drop the
-				 * refcount on pi_state nor clear
-				 * this->pi_state because the waiter needs the
-				 * pi_state for cleaning up the user space
-				 * value. It will drop the refcount after
-				 * doing so.
-				 */
-				requeue_pi_wake_futex(this, &key2, hb2);
-				drop_count++;
-				continue;
-			} else if (ret) {
-				/*
-				 * rt_mutex_start_proxy_lock() detected a
-				 * potential deadlock when we tried to queue
-				 * that waiter. Drop the pi_state reference
-				 * which we took above and remove the pointer
-				 * to the state from the waiters futex_q
-				 * object.
-				 */
-				this->pi_state = NULL;
-				put_pi_state(pi_state);
-				/*
-				 * We stop queueing more waiters and let user
-				 * space deal with the mess.
-				 */
-				break;
-			}
-		}
-		requeue_futex(this, hb1, hb2, &key2);
-		drop_count++;
-	}
-
-	/*
-	 * We took an extra initial reference to the pi_state either
-	 * in futex_proxy_trylock_atomic() or in lookup_pi_state(). We
-	 * need to drop it here again.
-	 */
-	put_pi_state(pi_state);
-
-out_unlock:
-	double_unlock_hb(hb1, hb2);
-	wake_up_q(&wake_q);
-	hb_waiters_dec(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(&key2);
-out_put_key1:
-	put_futex_key(&key1);
-out:
-	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)
-	__acquires(&hb->lock)
-{
-	struct futex_hash_bucket *hb;
-
-	hb = hash_futex(&q->key);
-
-	/*
-	 * Increment the counter before taking the lock so that
-	 * a potential waker won't miss a to-be-slept task that is
-	 * waiting for the spinlock. This is safe as all queue_lock()
-	 * users end up calling queue_me(). Similarly, for housekeeping,
-	 * decrement the counter at queue_unlock() when some error has
-	 * occurred and we don't end up adding the task to the list.
-	 */
-	hb_waiters_inc(hb);
-
-	q->lock_ptr = &hb->lock;
-
-	spin_lock(&hb->lock); /* implies smp_mb(); (A) */
-	return hb;
-}
-
-static inline void
-queue_unlock(struct futex_hash_bucket *hb)
-	__releases(&hb->lock)
-{
-	spin_unlock(&hb->lock);
-	hb_waiters_dec(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);
-	plist_add(&q->list, &hb->chain);
-	q->task = current;
-}
-
-/**
- * queue_me() - Enqueue the futex_q on the futex_hash_bucket
- * @q:	The futex_q to enqueue
- * @hb:	The destination hash bucket
- *
- * The hb->lock must be held by the caller, and is released here. A call to
- * queue_me() is typically paired with exactly one call to unqueue_me().  The
- * exceptions involve the PI related operations, which may use unqueue_me_pi()
- * or nothing if the unqueue is done as part of the wake process and the unqueue
- * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
- * an example).
- */
-static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
-	__releases(&hb->lock)
-{
-	__queue_me(q, hb);
-	spin_unlock(&hb->lock);
-}
-
-/**
- * unqueue_me() - Remove the futex_q from its futex_hash_bucket
- * @q:	The futex_q to unqueue
- *
- * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
- * be paired with exactly one earlier call to queue_me().
- *
- * Return:
- *   1 - if the futex_q was still queued (and we removed unqueued it);
- *   0 - if the futex_q was already removed by the waking thread
- */
-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:
-	/*
-	 * q->lock_ptr can change between this read and the following spin_lock.
-	 * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
-	 * optimizing lock_ptr out of the logic below.
-	 */
-	lock_ptr = READ_ONCE(q->lock_ptr);
-	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;
-		}
-		__unqueue_futex(q);
-
-		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)
-	__releases(q->lock_ptr)
-{
-	__unqueue_futex(q);
-
-	BUG_ON(!q->pi_state);
-	put_pi_state(q->pi_state);
-	q->pi_state = NULL;
-
-	spin_unlock(q->lock_ptr);
-}
-
-/*
- * Fixup the pi_state owner with the new owner.
- *
- * Must be called with hash bucket lock held and mm->sem held for non
- * private futexes.
- */
-static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
-				struct task_struct *newowner)
-{
-	u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
-	struct futex_pi_state *pi_state = q->pi_state;
-	u32 uval, uninitialized_var(curval), newval;
-	struct task_struct *oldowner;
-	int ret;
-
-	raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
-
-	oldowner = pi_state->owner;
-	/* Owner died? */
-	if (!pi_state->owner)
-		newtid |= FUTEX_OWNER_DIED;
-
-	/*
-	 * We are here either because we stole the rtmutex from the
-	 * previous highest priority waiter or we are the highest priority
-	 * waiter but have failed to get the rtmutex the first time.
-	 *
-	 * We have to replace the newowner 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 locks 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;
-
-	for (;;) {
-		newval = (uval & FUTEX_OWNER_DIED) | newtid;
-
-		if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
-			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) {
-		raw_spin_lock(&pi_state->owner->pi_lock);
-		WARN_ON(list_empty(&pi_state->list));
-		list_del_init(&pi_state->list);
-		raw_spin_unlock(&pi_state->owner->pi_lock);
-	}
-
-	pi_state->owner = newowner;
-
-	raw_spin_lock(&newowner->pi_lock);
-	WARN_ON(!list_empty(&pi_state->list));
-	list_add(&pi_state->list, &newowner->pi_state_list);
-	raw_spin_unlock(&newowner->pi_lock);
-	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
-
-	return 0;
-
-	/*
-	 * To handle the page fault we need to drop the locks here. That gives
-	 * the other task (either the highest priority waiter 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 locks and before trying to
-	 * do another fixup. When the fixup has been done already we simply
-	 * return.
-	 *
-	 * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
-	 * drop hb->lock since the caller owns the hb -> futex_q relation.
-	 * Dropping the pi_mutex->wait_lock requires the state revalidate.
-	 */
-handle_fault:
-	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
-	spin_unlock(q->lock_ptr);
-
-	ret = fault_in_user_writeable(uaddr);
-
-	spin_lock(q->lock_ptr);
-	raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
-
-	/*
-	 * Check if someone else fixed it for us:
-	 */
-	if (pi_state->owner != oldowner) {
-		ret = 0;
-		goto out_unlock;
-	}
-
-	if (ret)
-		goto out_unlock;
-
-	goto retry;
-
-out_unlock:
-	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
-	return ret;
-}
-
-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
- * @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.
- *
- * Return:
- *  1 - success, lock taken;
- *  0 - success, lock not taken;
- * <0 - on error (-EFAULT)
- */
-static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
-{
-	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:
-		 *
-		 * We can safely read pi_state->owner without holding wait_lock
-		 * because we now own the rt_mutex, only the owner will attempt
-		 * to change it.
-		 */
-		if (q->pi_state->owner != current)
-			ret = fixup_pi_state_owner(uaddr, q, current);
-		goto out;
-	}
-
-	/*
-	 * Paranoia check. If we did not take the lock, then we should not be
-	 * the 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)
-{
-	/*
-	 * The task state is guaranteed to be set before another task can
-	 * wake it. set_current_state() is implemented using smp_store_mb() and
-	 * queue_me() calls spin_unlock() upon completion, both serializing
-	 * access to the hash list and forcing another memory barrier.
-	 */
-	set_current_state(TASK_INTERRUPTIBLE);
-	queue_me(q, hb);
-
-	/* Arm the timer */
-	if (timeout)
-		hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
-
-	/*
-	 * 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)
-			freezable_schedule();
-	}
-	__set_current_state(TASK_RUNNING);
-}
-
-/**
- * futex_wait_setup() - Prepare to wait on a futex
- * @uaddr:	the futex userspace address
- * @val:	the expected value
- * @flags:	futex flags (FLAGS_SHARED, etc.)
- * @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.
- *
- * Return:
- *  0 - uaddr contains val and hb has been locked;
- * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
- */
-static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
-			   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 locked the hash-bucket after testing *uaddr, that
-	 * would open a race condition where we could block indefinitely with
-	 * cond(var) false, which would violate the guarantee.
-	 *
-	 * On the other hand, we insert q and release the hash-bucket only
-	 * after testing *uaddr.  This guarantees that futex_wait() will NOT
-	 * absorb a wakeup if *uaddr does not match the desired values
-	 * while the syscall executes.
-	 */
-retry:
-	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &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(*hb);
-
-		ret = get_user(uval, uaddr);
-		if (ret)
-			goto out;
-
-		if (!(flags & FLAGS_SHARED))
-			goto retry_private;
-
-		put_futex_key(&q->key);
-		goto retry;
-	}
-
-	if (uval != val) {
-		queue_unlock(*hb);
-		ret = -EWOULDBLOCK;
-	}
-
-out:
-	if (ret)
-		put_futex_key(&q->key);
-	return ret;
-}
-
-static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
-		      ktime_t *abs_time, u32 bitset)
-{
-	struct hrtimer_sleeper timeout, *to = NULL;
-	struct restart_block *restart;
-	struct futex_hash_bucket *hb;
-	struct futex_q q = futex_q_init;
-	int ret;
-
-	if (!bitset)
-		return -EINVAL;
-	q.bitset = bitset;
-
-	if (abs_time) {
-		to = &timeout;
-
-		hrtimer_init_on_stack(&to->timer, (flags & FLAGS_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. On success, holds hb lock and increments
-	 * q.key refs.
-	 */
-	ret = futex_wait_setup(uaddr, val, flags, &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;
-	/* unqueue_me() drops q.key ref */
-	if (!unqueue_me(&q))
-		goto out;
-	ret = -ETIMEDOUT;
-	if (to && !to->task)
-		goto out;
-
-	/*
-	 * We expect signal_pending(current), but we might be the
-	 * victim of a spurious wakeup as well.
-	 */
-	if (!signal_pending(current))
-		goto retry;
-
-	ret = -ERESTARTSYS;
-	if (!abs_time)
-		goto out;
-
-	restart = &current->restart_block;
-	restart->fn = futex_wait_restart;
-	restart->futex.uaddr = uaddr;
-	restart->futex.val = val;
-	restart->futex.time = *abs_time;
-	restart->futex.bitset = bitset;
-	restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
-
-	ret = -ERESTART_RESTARTBLOCK;
-
-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 = restart->futex.uaddr;
-	ktime_t t, *tp = NULL;
-
-	if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
-		t = restart->futex.time;
-		tp = &t;
-	}
-	restart->fn = do_no_restart_syscall;
-
-	return (long)futex_wait(uaddr, restart->futex.flags,
-				restart->futex.val, tp, restart->futex.bitset);
-}
-
-
-/*
- * Userspace tried a 0 -> TID atomic transition of the futex value
- * and failed. The kernel side here does the whole locking operation:
- * if there are waiters then it will block as a consequence of relying
- * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
- * a 0 value of the futex too.).
- *
- * Also serves as futex trylock_pi()'ing, and due semantics.
- */
-static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
-			 ktime_t *time, int trylock)
-{
-	struct hrtimer_sleeper timeout, *to = NULL;
-	struct futex_pi_state *pi_state = NULL;
-	struct rt_mutex_waiter rt_waiter;
-	struct futex_hash_bucket *hb;
-	struct futex_q q = futex_q_init;
-	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);
-	}
-
-retry:
-	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
-	if (unlikely(ret != 0))
-		goto out;
-
-retry_private:
-	hb = queue_lock(&q);
+			 */
+			ret = lookup_pi_state(uaddr2, ret, hb2, &key2, &pi_state);
+		}
 
-	ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
-	if (unlikely(ret)) {
-		/*
-		 * Atomic work succeeded and we got the lock,
-		 * or failed. Either way, we do _not_ block.
-		 */
 		switch (ret) {
-		case 1:
-			/* We got the lock. */
-			ret = 0;
-			goto out_unlock_put_key;
+		case 0:
+			/* We hold a reference on the pi state. */
+			break;
+
+			/* If the above failed, then pi_state is NULL */
 		case -EFAULT:
-			goto uaddr_faulted;
+			double_unlock_hb(hb1, hb2);
+			hb_waiters_dec(hb2);
+			put_futex_key(&key2);
+			put_futex_key(&key1);
+			ret = fault_in_user_writeable(uaddr2);
+			if (!ret)
+				goto retry;
+			goto out;
 		case -EAGAIN:
 			/*
 			 * Two reasons for this:
-			 * - Task is exiting and we just wait for the
+			 * - Owner is exiting and we just wait for the
 			 *   exit to complete.
 			 * - The user space value changed.
 			 */
-			queue_unlock(hb);
-			put_futex_key(&q.key);
+			double_unlock_hb(hb1, hb2);
+			hb_waiters_dec(hb2);
+			put_futex_key(&key2);
+			put_futex_key(&key1);
 			cond_resched();
 			goto retry;
 		default:
-			goto out_unlock_put_key;
+			goto out_unlock;
 		}
 	}
 
-	WARN_ON(!q.pi_state);
-
-	/*
-	 * Only actually queue now that the atomic ops are done:
-	 */
-	__queue_me(&q, hb);
+	plist_for_each_entry_safe(this, next, &hb1->chain, list) {
+		if (task_count - nr_wake >= nr_requeue)
+			break;
 
-	if (trylock) {
-		ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
-		/* Fixup the trylock return value: */
-		ret = ret ? 0 : -EWOULDBLOCK;
-		goto no_block;
-	}
+		if (!match_futex(&this->key, &key1))
+			continue;
 
-	rt_mutex_init_waiter(&rt_waiter);
+		/*
+		 * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
+		 * be paired with each other and no other futex ops.
+		 *
+		 * We should never be requeueing a futex_q with a pi_state,
+		 * which is awaiting a futex_unlock_pi().
+		 */
+		if ((requeue_pi && !this->rt_waiter) ||
+		    (!requeue_pi && this->rt_waiter) ||
+		    this->pi_state) {
+			ret = -EINVAL;
+			break;
+		}
 
-	/*
-	 * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
-	 * hold it while doing rt_mutex_start_proxy(), because then it will
-	 * include hb->lock in the blocking chain, even through we'll not in
-	 * fact hold it while blocking. This will lead it to report -EDEADLK
-	 * and BUG when futex_unlock_pi() interleaves with this.
-	 *
-	 * Therefore acquire wait_lock while holding hb->lock, but drop the
-	 * latter before calling rt_mutex_start_proxy_lock(). This still fully
-	 * serializes against futex_unlock_pi() as that does the exact same
-	 * lock handoff sequence.
-	 */
-	raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
-	spin_unlock(q.lock_ptr);
-	ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
-	raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
+		/*
+		 * 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) {
+			mark_wake_futex(&wake_q, this);
+			continue;
+		}
 
-	if (ret) {
-		if (ret == 1)
-			ret = 0;
+		/* Ensure we requeue to the expected futex for requeue_pi. */
+		if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
+			ret = -EINVAL;
+			break;
+		}
 
-		spin_lock(q.lock_ptr);
-		goto no_block;
+		/*
+		 * 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. Take a
+			 * refcount on the pi_state and store the pointer in
+			 * the futex_q object of the waiter.
+			 */
+			get_pi_state(pi_state);
+			this->pi_state = pi_state;
+			ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
+							this->rt_waiter,
+							this->task);
+			if (ret == 1) {
+				/*
+				 * We got the lock. We do neither drop the
+				 * refcount on pi_state nor clear
+				 * this->pi_state because the waiter needs the
+				 * pi_state for cleaning up the user space
+				 * value. It will drop the refcount after
+				 * doing so.
+				 */
+				requeue_pi_wake_futex(this, &key2, hb2);
+				drop_count++;
+				continue;
+			} else if (ret) {
+				/*
+				 * rt_mutex_start_proxy_lock() detected a
+				 * potential deadlock when we tried to queue
+				 * that waiter. Drop the pi_state reference
+				 * which we took above and remove the pointer
+				 * to the state from the waiters futex_q
+				 * object.
+				 */
+				this->pi_state = NULL;
+				put_pi_state(pi_state);
+				/*
+				 * We stop queueing more waiters and let user
+				 * space deal with the mess.
+				 */
+				break;
+			}
+		}
+		requeue_futex(this, hb1, hb2, &key2);
+		drop_count++;
 	}
 
-
-	if (unlikely(to))
-		hrtimer_start_expires(&to->timer, HRTIMER_MODE_ABS);
-
-	ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
-
-	spin_lock(q.lock_ptr);
 	/*
-	 * If we failed to acquire the lock (signal/timeout), we must
-	 * first acquire the hb->lock before removing the lock from the
-	 * rt_mutex waitqueue, such that we can keep the hb and rt_mutex
-	 * wait lists consistent.
-	 *
-	 * In particular; it is important that futex_unlock_pi() can not
-	 * observe this inconsistency.
+	 * We took an extra initial reference to the pi_state either
+	 * in futex_proxy_trylock_atomic() or in lookup_pi_state(). We
+	 * need to drop it here again.
 	 */
-	if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
-		ret = 0;
+	put_pi_state(pi_state);
 
-no_block:
-	/*
-	 * Fixup the pi_state owner and possibly acquire the lock if we
-	 * haven't already.
-	 */
-	res = fixup_owner(uaddr, &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;
+out_unlock:
+	double_unlock_hb(hb1, hb2);
+	wake_up_q(&wake_q);
+	hb_waiters_dec(hb2);
 
 	/*
-	 * If fixup_owner() faulted and was unable to handle the fault, unlock
-	 * it and return the fault to userspace.
+	 * 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.
 	 */
-	if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) {
-		pi_state = q.pi_state;
-		get_pi_state(pi_state);
-	}
-
-	/* Unqueue and drop the lock */
-	unqueue_me_pi(&q);
-
-	if (pi_state) {
-		rt_mutex_futex_unlock(&pi_state->pi_mutex);
-		put_pi_state(pi_state);
-	}
-
-	goto out_put_key;
-
-out_unlock_put_key:
-	queue_unlock(hb);
+	while (--drop_count >= 0)
+		drop_futex_key_refs(&key1);
 
-out_put_key:
-	put_futex_key(&q.key);
+out_put_keys:
+	put_futex_key(&key2);
+out_put_key1:
+	put_futex_key(&key1);
 out:
-	if (to) {
-		hrtimer_cancel(&to->timer);
-		destroy_hrtimer_on_stack(&to->timer);
-	}
-	return ret != -EINTR ? ret : -ERESTARTNOINTR;
-
-uaddr_faulted:
-	queue_unlock(hb);
-
-	ret = fault_in_user_writeable(uaddr);
-	if (ret)
-		goto out_put_key;
-
-	if (!(flags & FLAGS_SHARED))
-		goto retry_private;
-
-	put_futex_key(&q.key);
-	goto retry;
+	return ret ? ret : task_count;
 }
 
-/*
- * 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, unsigned int flags)
+/* The key must be already stored in q->key. */
+static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
+	__acquires(&hb->lock)
 {
-	u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current);
-	union futex_key key = FUTEX_KEY_INIT;
 	struct futex_hash_bucket *hb;
-	struct futex_q *top_waiter;
-	int ret;
 
-retry:
-	if (get_user(uval, uaddr))
-		return -EFAULT;
+	hb = hash_futex(&q->key);
+
 	/*
-	 * We release only a lock we actually own:
+	 * Increment the counter before taking the lock so that
+	 * a potential waker won't miss a to-be-slept task that is
+	 * waiting for the spinlock. This is safe as all queue_lock()
+	 * users end up calling queue_me(). Similarly, for housekeeping,
+	 * decrement the counter at queue_unlock() when some error has
+	 * occurred and we don't end up adding the task to the list.
 	 */
-	if ((uval & FUTEX_TID_MASK) != vpid)
-		return -EPERM;
+	hb_waiters_inc(hb);
 
-	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
-	if (ret)
-		return ret;
+	q->lock_ptr = &hb->lock;
 
-	hb = hash_futex(&key);
-	spin_lock(&hb->lock);
+	spin_lock(&hb->lock); /* implies smp_mb(); (A) */
+	return hb;
+}
 
-	/*
-	 * Check waiters first. We do not trust user space values at
-	 * all and we at least want to know if user space fiddled
-	 * with the futex value instead of blindly unlocking.
-	 */
-	top_waiter = futex_top_waiter(hb, &key);
-	if (top_waiter) {
-		struct futex_pi_state *pi_state = top_waiter->pi_state;
+static inline void
+queue_unlock(struct futex_hash_bucket *hb)
+	__releases(&hb->lock)
+{
+	spin_unlock(&hb->lock);
+	hb_waiters_dec(hb);
+}
 
-		ret = -EINVAL;
-		if (!pi_state)
-			goto out_unlock;
+static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
+{
+	int prio;
 
-		/*
-		 * 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)
-			goto out_unlock;
+	/*
+	 * 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);
 
-		get_pi_state(pi_state);
-		/*
-		 * By taking wait_lock while still holding hb->lock, we ensure
-		 * there is no point where we hold neither; and therefore
-		 * wake_futex_pi() must observe a state consistent with what we
-		 * observed.
-		 */
-		raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
-		spin_unlock(&hb->lock);
+	plist_node_init(&q->list, prio);
+	plist_add(&q->list, &hb->chain);
+	q->task = current;
+}
 
-		ret = wake_futex_pi(uaddr, uval, pi_state);
+/**
+ * queue_me() - Enqueue the futex_q on the futex_hash_bucket
+ * @q:	The futex_q to enqueue
+ * @hb:	The destination hash bucket
+ *
+ * The hb->lock must be held by the caller, and is released here. A call to
+ * queue_me() is typically paired with exactly one call to unqueue_me().  The
+ * exceptions involve the PI related operations, which may use unqueue_me_pi()
+ * or nothing if the unqueue is done as part of the wake process and the unqueue
+ * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
+ * an example).
+ */
+static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
+	__releases(&hb->lock)
+{
+	__queue_me(q, hb);
+	spin_unlock(&hb->lock);
+}
 
-		put_pi_state(pi_state);
+/**
+ * unqueue_me() - Remove the futex_q from its futex_hash_bucket
+ * @q:	The futex_q to unqueue
+ *
+ * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
+ * be paired with exactly one earlier call to queue_me().
+ *
+ * Return:
+ *   1 - if the futex_q was still queued (and we removed unqueued it);
+ *   0 - if the futex_q was already removed by the waking thread
+ */
+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:
+	/*
+	 * q->lock_ptr can change between this read and the following spin_lock.
+	 * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
+	 * optimizing lock_ptr out of the logic below.
+	 */
+	lock_ptr = READ_ONCE(q->lock_ptr);
+	if (lock_ptr != NULL) {
+		spin_lock(lock_ptr);
 		/*
-		 * Success, we're done! No tricky corner cases.
-		 */
-		if (!ret)
-			goto out_putkey;
-		/*
-		 * The atomic access to the futex value generated a
-		 * pagefault, so retry the user-access and the wakeup:
-		 */
-		if (ret == -EFAULT)
-			goto pi_faulted;
-		/*
-		 * A unconditional UNLOCK_PI op raced against a waiter
-		 * setting the FUTEX_WAITERS bit. Try again.
+		 * 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 (ret == -EAGAIN) {
-			put_futex_key(&key);
+		if (unlikely(lock_ptr != q->lock_ptr)) {
+			spin_unlock(lock_ptr);
 			goto retry;
 		}
-		/*
-		 * wake_futex_pi has detected invalid state. Tell user
-		 * space.
-		 */
-		goto out_putkey;
-	}
+		__unqueue_futex(q);
 
-	/*
-	 * We have no kernel internal state, i.e. no waiters in the
-	 * kernel. Waiters which are about to queue themselves are stuck
-	 * on hb->lock. So we can safely ignore them. We do neither
-	 * preserve the WAITERS bit not the OWNER_DIED one. We are the
-	 * owner.
-	 */
-	if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0)) {
-		spin_unlock(&hb->lock);
-		goto pi_faulted;
-	}
+		BUG_ON(q->pi_state);
 
-	/*
-	 * If uval has changed, let user space handle it.
-	 */
-	ret = (curval == uval) ? 0 : -EAGAIN;
+		spin_unlock(lock_ptr);
+		ret = 1;
+	}
 
-out_unlock:
-	spin_unlock(&hb->lock);
-out_putkey:
-	put_futex_key(&key);
+	drop_futex_key_refs(&q->key);
 	return ret;
+}
 
-pi_faulted:
-	put_futex_key(&key);
+static long futex_wait_restart(struct restart_block *restart);
 
-	ret = fault_in_user_writeable(uaddr);
-	if (!ret)
-		goto retry;
+/**
+ * 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)
+{
+	/*
+	 * The task state is guaranteed to be set before another task can
+	 * wake it. set_current_state() is implemented using smp_store_mb() and
+	 * queue_me() calls spin_unlock() upon completion, both serializing
+	 * access to the hash list and forcing another memory barrier.
+	 */
+	set_current_state(TASK_INTERRUPTIBLE);
+	queue_me(q, hb);
 
-	return ret;
+	/* Arm the timer */
+	if (timeout)
+		hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
+
+	/*
+	 * 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)
+			freezable_schedule();
+	}
+	__set_current_state(TASK_RUNNING);
 }
 
 /**
- * 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)
+ * futex_wait_setup() - Prepare to wait on a futex
+ * @uaddr:	the futex userspace address
+ * @val:	the expected value
+ * @flags:	futex flags (FLAGS_SHARED, etc.)
+ * @q:		the associated futex_q
+ * @hb:		storage for hash_bucket pointer to be returned to caller
  *
- * 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.
+ * 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.
  *
  * Return:
- *  0 = no early wakeup detected;
- * <0 = -ETIMEDOUT or -ERESTARTNOINTR
+ *  0 - uaddr contains val and hb has been locked;
+ * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
  */
-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)
+static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
+			   struct futex_q *q, struct futex_hash_bucket **hb)
 {
-	int ret = 0;
+	u32 uval;
+	int ret;
 
 	/*
-	 * 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.
+	 * 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 locked the hash-bucket after testing *uaddr, that
+	 * would open a race condition where we could block indefinitely with
+	 * cond(var) false, which would violate the guarantee.
+	 *
+	 * On the other hand, we insert q and release the hash-bucket only
+	 * after testing *uaddr.  This guarantees that futex_wait() will NOT
+	 * absorb a wakeup if *uaddr does not match the desired values
+	 * while the syscall executes.
 	 */
-	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, &hb->chain);
-		hb_waiters_dec(hb);
+retry:
+	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &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(*hb);
+
+		ret = get_user(uval, uaddr);
+		if (ret)
+			goto out;
+
+		if (!(flags & FLAGS_SHARED))
+			goto retry_private;
+
+		put_futex_key(&q->key);
+		goto retry;
+	}
 
-		/* Handle spurious wakeups gracefully */
+	if (uval != val) {
+		queue_unlock(*hb);
 		ret = -EWOULDBLOCK;
-		if (timeout && !timeout->task)
-			ret = -ETIMEDOUT;
-		else if (signal_pending(current))
-			ret = -ERESTARTNOINTR;
 	}
+
+out:
+	if (ret)
+		put_futex_key(&q->key);
 	return ret;
 }
 
-/**
- * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
- * @uaddr:	the futex we initially wait on (non-pi)
- * @flags:	futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), 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
- * @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 and unique from uaddr.  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 would not 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
- * 3) signal
- * 4) timeout
- *
- * If 3, cleanup and return -ERESTARTNOINTR.
- *
- * 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, return -EWOULDBLOCK (restarting the syscall would do the same).
- *
- * If 4 or 7, we cleanup and return with -ETIMEDOUT.
- *
- * Return:
- *  0 - On success;
- * <0 - On error
- */
-static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
-				 u32 val, ktime_t *abs_time, u32 bitset,
-				 u32 __user *uaddr2)
+static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
+		      ktime_t *abs_time, u32 bitset)
 {
 	struct hrtimer_sleeper timeout, *to = NULL;
-	struct futex_pi_state *pi_state = NULL;
-	struct rt_mutex_waiter rt_waiter;
+	struct restart_block *restart;
 	struct futex_hash_bucket *hb;
-	union futex_key key2 = FUTEX_KEY_INIT;
 	struct futex_q q = futex_q_init;
-	int res, ret;
-
-	if (uaddr == uaddr2)
-		return -EINVAL;
+	int ret;
 
 	if (!bitset)
 		return -EINVAL;
+	q.bitset = bitset;
 
 	if (abs_time) {
 		to = &timeout;
+
 		hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
 				      CLOCK_REALTIME : CLOCK_MONOTONIC,
 				      HRTIMER_MODE_ABS);
@@ -2999,139 +1562,47 @@  static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
 					     current->timer_slack_ns);
 	}
 
+retry:
 	/*
-	 * The waiter is allocated on our stack, manipulated by the requeue
-	 * code while we sleep on uaddr.
-	 */
-	rt_mutex_init_waiter(&rt_waiter);
-
-	ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
-	if (unlikely(ret != 0))
-		goto out;
-
-	q.bitset = bitset;
-	q.rt_waiter = &rt_waiter;
-	q.requeue_pi_key = &key2;
-
-	/*
-	 * Prepare to wait on uaddr. On success, increments q.key (key1) ref
-	 * count.
+	 * Prepare to wait on uaddr. On success, holds hb lock and increments
+	 * q.key refs.
 	 */
 	ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
 	if (ret)
-		goto out_key2;
-
-	/*
-	 * The check above which compares uaddrs is not sufficient for
-	 * shared futexes. We need to compare the keys:
-	 */
-	if (match_futex(&q.key, &key2)) {
-		queue_unlock(hb);
-		ret = -EINVAL;
-		goto out_put_keys;
-	}
+		goto out;
 
-	/* Queue the futex_q, drop the hb lock, wait for wakeup. */
+	/* queue_me and wait for wakeup, timeout, or a signal. */
 	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;
+	/* If we were woken (and unqueued), we succeeded, whatever. */
+	ret = 0;
+	/* unqueue_me() drops q.key ref */
+	if (!unqueue_me(&q))
+		goto out;
+	ret = -ETIMEDOUT;
+	if (to && !to->task)
+		goto out;
 
 	/*
-	 * 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 acquisition by the requeue code. The
-	 * futex_requeue dropped our key1 reference and incremented our key2
-	 * reference count.
+	 * We expect signal_pending(current), but we might be the
+	 * victim of a spurious wakeup as well.
 	 */
+	if (!signal_pending(current))
+		goto retry;
 
-	/* 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);
-			if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
-				pi_state = q.pi_state;
-				get_pi_state(pi_state);
-			}
-			/*
-			 * Drop the reference to the pi state which
-			 * the requeue_pi() code acquired for us.
-			 */
-			put_pi_state(q.pi_state);
-			spin_unlock(q.lock_ptr);
-		}
-	} else {
-		struct rt_mutex *pi_mutex;
-
-		/*
-		 * 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_wait_proxy_lock(pi_mutex, to, &rt_waiter);
-
-		spin_lock(q.lock_ptr);
-		if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
-			ret = 0;
-
-		debug_rt_mutex_free_waiter(&rt_waiter);
-		/*
-		 * Fixup the pi_state owner and possibly acquire the lock if we
-		 * haven't already.
-		 */
-		res = fixup_owner(uaddr2, &q, !ret);
-		/*
-		 * If fixup_owner() returned an error, proprogate that.  If it
-		 * acquired the lock, clear -ETIMEDOUT or -EINTR.
-		 */
-		if (res)
-			ret = (res < 0) ? res : 0;
-
-		/*
-		 * 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 && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
-			pi_state = q.pi_state;
-			get_pi_state(pi_state);
-		}
-
-		/* Unqueue and drop the lock. */
-		unqueue_me_pi(&q);
-	}
-
-	if (pi_state) {
-		rt_mutex_futex_unlock(&pi_state->pi_mutex);
-		put_pi_state(pi_state);
-	}
+	ret = -ERESTARTSYS;
+	if (!abs_time)
+		goto out;
 
-	if (ret == -EINTR) {
-		/*
-		 * We've already been requeued, but cannot restart by calling
-		 * futex_lock_pi() directly. We could restart this syscall, but
-		 * it would detect that the user space "val" changed and return
-		 * -EWOULDBLOCK.  Save the overhead of the restart and return
-		 * -EWOULDBLOCK directly.
-		 */
-		ret = -EWOULDBLOCK;
-	}
+	restart = &current->restart_block;
+	restart->fn = futex_wait_restart;
+	restart->futex.uaddr = uaddr;
+	restart->futex.val = val;
+	restart->futex.time = *abs_time;
+	restart->futex.bitset = bitset;
+	restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
 
-out_put_keys:
-	put_futex_key(&q.key);
-out_key2:
-	put_futex_key(&key2);
+	ret = -ERESTART_RESTARTBLOCK;
 
 out:
 	if (to) {
@@ -3141,6 +1612,22 @@  static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
 	return ret;
 }
 
+
+static long futex_wait_restart(struct restart_block *restart)
+{
+	u32 __user *uaddr = restart->futex.uaddr;
+	ktime_t t, *tp = NULL;
+
+	if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
+		t = restart->futex.time;
+		tp = &t;
+	}
+	restart->fn = do_no_restart_syscall;
+
+	return (long)futex_wait(uaddr, restart->futex.flags,
+				restart->futex.val, tp, restart->futex.bitset);
+}
+
 /*
  * Support for robust futexes: the kernel cleans up held futexes at
  * thread exit time.
diff --git a/kernel/futex_pi.c b/kernel/futex_pi.c
new file mode 100644
index 0000000000..a10c962aa2
--- /dev/null
+++ b/kernel/futex_pi.c
@@ -0,0 +1,1563 @@ 
+/*
+ *  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>
+ *
+ *  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.
+ *
+ *  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 "locking/rtmutex_common.h"
+
+/* from futex.c: */
+static void __unqueue_futex(struct futex_q *q);
+static inline struct futex_hash_bucket *queue_lock(struct futex_q *q);
+static inline void queue_unlock(struct futex_hash_bucket *hb);
+static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb);
+static void futex_wait_queue_me(struct futex_hash_bucket *hb,
+		struct futex_q *q, struct hrtimer_sleeper *timeout);
+static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
+		struct futex_q *q, struct futex_hash_bucket **hb);
+
+/*
+ * 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;
+};
+
+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 get_pi_state(struct futex_pi_state *pi_state)
+{
+	WARN_ON_ONCE(!atomic_inc_not_zero(&pi_state->refcount));
+}
+
+/*
+ * Drops a reference to the pi_state object and frees or caches it
+ * when the last reference is gone.
+ *
+ * Must be called with the hb lock held.
+ */
+static void put_pi_state(struct futex_pi_state *pi_state)
+{
+	if (!pi_state)
+		return;
+
+	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) {
+		raw_spin_lock_irq(&pi_state->owner->pi_lock);
+		list_del_init(&pi_state->list);
+		raw_spin_unlock_irq(&pi_state->owner->pi_lock);
+
+		rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
+	}
+
+	if (current->pi_state_cache)
+		kfree(pi_state);
+	else {
+		/*
+		 * pi_state->list is already empty.
+		 * clear pi_state->owner.
+		 * refcount is at 0 - put it back to 1.
+		 */
+		pi_state->owner = NULL;
+		atomic_set(&pi_state->refcount, 1);
+		current->pi_state_cache = pi_state;
+	}
+}
+
+/*
+ * Look up the task based on what TID userspace gave us.
+ * We dont trust it.
+ */
+static struct task_struct *futex_find_get_task(pid_t pid)
+{
+	struct task_struct *p;
+
+	rcu_read_lock();
+	p = find_task_by_vpid(pid);
+	if (p)
+		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:
+	 */
+	raw_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);
+		raw_spin_unlock_irq(&curr->pi_lock);
+
+		spin_lock(&hb->lock);
+
+		raw_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;
+		raw_spin_unlock_irq(&curr->pi_lock);
+
+		get_pi_state(pi_state);
+		spin_unlock(&hb->lock);
+
+		rt_mutex_futex_unlock(&pi_state->pi_mutex);
+		put_pi_state(pi_state);
+
+		raw_spin_lock_irq(&curr->pi_lock);
+	}
+	raw_spin_unlock_irq(&curr->pi_lock);
+}
+
+/**
+ * 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;
+}
+
+/*
+ * We need to check the following states:
+ *
+ *      Waiter | pi_state | pi->owner | uTID      | uODIED | ?
+ *
+ * [1]  NULL   | ---      | ---       | 0         | 0/1    | Valid
+ * [2]  NULL   | ---      | ---       | >0        | 0/1    | Valid
+ *
+ * [3]  Found  | NULL     | --        | Any       | 0/1    | Invalid
+ *
+ * [4]  Found  | Found    | NULL      | 0         | 1      | Valid
+ * [5]  Found  | Found    | NULL      | >0        | 1      | Invalid
+ *
+ * [6]  Found  | Found    | task      | 0         | 1      | Valid
+ *
+ * [7]  Found  | Found    | NULL      | Any       | 0      | Invalid
+ *
+ * [8]  Found  | Found    | task      | ==taskTID | 0/1    | Valid
+ * [9]  Found  | Found    | task      | 0         | 0      | Invalid
+ * [10] Found  | Found    | task      | !=taskTID | 0/1    | Invalid
+ *
+ * [1]	Indicates that the kernel can acquire the futex atomically. We
+ *	came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
+ *
+ * [2]	Valid, if TID does not belong to a kernel thread. If no matching
+ *      thread is found then it indicates that the owner TID has died.
+ *
+ * [3]	Invalid. The waiter is queued on a non PI futex
+ *
+ * [4]	Valid state after exit_robust_list(), which sets the user space
+ *	value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
+ *
+ * [5]	The user space value got manipulated between exit_robust_list()
+ *	and exit_pi_state_list()
+ *
+ * [6]	Valid state after exit_pi_state_list() which sets the new owner in
+ *	the pi_state but cannot access the user space value.
+ *
+ * [7]	pi_state->owner can only be NULL when the OWNER_DIED bit is set.
+ *
+ * [8]	Owner and user space value match
+ *
+ * [9]	There is no transient state which sets the user space TID to 0
+ *	except exit_robust_list(), but this is indicated by the
+ *	FUTEX_OWNER_DIED bit. See [4]
+ *
+ * [10] There is no transient state which leaves owner and user space
+ *	TID out of sync.
+ *
+ *
+ * Serialization and lifetime rules:
+ *
+ * hb->lock:
+ *
+ *	hb -> futex_q, relation
+ *	futex_q -> pi_state, relation
+ *
+ *	(cannot be raw because hb can contain arbitrary amount
+ *	 of futex_q's)
+ *
+ * pi_mutex->wait_lock:
+ *
+ *	{uval, pi_state}
+ *
+ *	(and pi_mutex 'obviously')
+ *
+ * p->pi_lock:
+ *
+ *	p->pi_state_list -> pi_state->list, relation
+ *
+ * pi_state->refcount:
+ *
+ *	pi_state lifetime
+ *
+ *
+ * Lock order:
+ *
+ *   hb->lock
+ *     pi_mutex->wait_lock
+ *       p->pi_lock
+ *
+ */
+
+/*
+ * Validate that the existing waiter has a pi_state and sanity check
+ * the pi_state against the user space value. If correct, attach to
+ * it.
+ */
+static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
+			      struct futex_pi_state *pi_state,
+			      struct futex_pi_state **ps)
+{
+	pid_t pid = uval & FUTEX_TID_MASK;
+	u32 uval2;
+	int ret;
+
+	/*
+	 * Userspace might have messed up non-PI and PI futexes [3]
+	 */
+	if (unlikely(!pi_state))
+		return -EINVAL;
+
+	/*
+	 * We get here with hb->lock held, and having found a
+	 * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
+	 * has dropped the hb->lock in between queue_me() and unqueue_me_pi(),
+	 * which in turn means that futex_lock_pi() still has a reference on
+	 * our pi_state.
+	 *
+	 * The waiter holding a reference on @pi_state also protects against
+	 * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
+	 * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
+	 * free pi_state before we can take a reference ourselves.
+	 */
+	WARN_ON(!atomic_read(&pi_state->refcount));
+
+	/*
+	 * Now that we have a pi_state, we can acquire wait_lock
+	 * and do the state validation.
+	 */
+	raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+
+	/*
+	 * Since {uval, pi_state} is serialized by wait_lock, and our current
+	 * uval was read without holding it, it can have changed. Verify it
+	 * still is what we expect it to be, otherwise retry the entire
+	 * operation.
+	 */
+	if (get_futex_value_locked(&uval2, uaddr))
+		goto out_efault;
+
+	if (uval != uval2)
+		goto out_eagain;
+
+	/*
+	 * Handle the owner died case:
+	 */
+	if (uval & FUTEX_OWNER_DIED) {
+		/*
+		 * exit_pi_state_list sets owner to NULL and wakes the
+		 * topmost waiter. The task which acquires the
+		 * pi_state->rt_mutex will fixup owner.
+		 */
+		if (!pi_state->owner) {
+			/*
+			 * No pi state owner, but the user space TID
+			 * is not 0. Inconsistent state. [5]
+			 */
+			if (pid)
+				goto out_einval;
+			/*
+			 * Take a ref on the state and return success. [4]
+			 */
+			goto out_attach;
+		}
+
+		/*
+		 * If TID is 0, then either the dying owner has not
+		 * yet executed exit_pi_state_list() or some waiter
+		 * acquired the rtmutex in the pi state, but did not
+		 * yet fixup the TID in user space.
+		 *
+		 * Take a ref on the state and return success. [6]
+		 */
+		if (!pid)
+			goto out_attach;
+	} else {
+		/*
+		 * If the owner died bit is not set, then the pi_state
+		 * must have an owner. [7]
+		 */
+		if (!pi_state->owner)
+			goto out_einval;
+	}
+
+	/*
+	 * Bail out if user space manipulated the futex value. If pi
+	 * state exists then the owner TID must be the same as the
+	 * user space TID. [9/10]
+	 */
+	if (pid != task_pid_vnr(pi_state->owner))
+		goto out_einval;
+
+out_attach:
+	get_pi_state(pi_state);
+	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+	*ps = pi_state;
+	return 0;
+
+out_einval:
+	ret = -EINVAL;
+	goto out_error;
+
+out_eagain:
+	ret = -EAGAIN;
+	goto out_error;
+
+out_efault:
+	ret = -EFAULT;
+	goto out_error;
+
+out_error:
+	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+	return ret;
+}
+
+/*
+ * Lookup the task for the TID provided from user space and attach to
+ * it after doing proper sanity checks.
+ */
+static int attach_to_pi_owner(u32 uval, union futex_key *key,
+			      struct futex_pi_state **ps)
+{
+	pid_t pid = uval & FUTEX_TID_MASK;
+	struct futex_pi_state *pi_state;
+	struct task_struct *p;
+
+	/*
+	 * 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 [1]
+	 */
+	if (!pid)
+		return -ESRCH;
+	p = futex_find_get_task(pid);
+	if (!p)
+		return -ESRCH;
+
+	if (unlikely(p->flags & PF_KTHREAD)) {
+		put_task_struct(p);
+		return -EPERM;
+	}
+
+	/*
+	 * 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:
+	 */
+	raw_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;
+
+		raw_spin_unlock_irq(&p->pi_lock);
+		put_task_struct(p);
+		return ret;
+	}
+
+	/*
+	 * No existing pi state. First waiter. [2]
+	 *
+	 * This creates pi_state, we have hb->lock held, this means nothing can
+	 * observe this state, wait_lock is irrelevant.
+	 */
+	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;
+	raw_spin_unlock_irq(&p->pi_lock);
+
+	put_task_struct(p);
+
+	*ps = pi_state;
+
+	return 0;
+}
+
+static int lookup_pi_state(u32 __user *uaddr, u32 uval,
+			   struct futex_hash_bucket *hb,
+			   union futex_key *key, struct futex_pi_state **ps)
+{
+	struct futex_q *top_waiter = futex_top_waiter(hb, key);
+
+	/*
+	 * If there is a waiter on that futex, validate it and
+	 * attach to the pi_state when the validation succeeds.
+	 */
+	if (top_waiter)
+		return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
+
+	/*
+	 * We are the first waiter - try to look up the owner based on
+	 * @uval and attach to it.
+	 */
+	return attach_to_pi_owner(uval, key, ps);
+}
+
+static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
+{
+	u32 uninitialized_var(curval);
+
+	if (unlikely(should_fail_futex(true)))
+		return -EFAULT;
+
+	if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
+		return -EFAULT;
+
+	/* If user space value changed, let the caller retry */
+	return curval != uval ? -EAGAIN : 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)
+ *
+ * Return:
+ *  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)
+{
+	u32 uval, newval, vpid = task_pid_vnr(task);
+	struct futex_q *top_waiter;
+	int ret;
+
+	/*
+	 * Read the user space value first so we can validate a few
+	 * things before proceeding further.
+	 */
+	if (get_futex_value_locked(&uval, uaddr))
+		return -EFAULT;
+
+	if (unlikely(should_fail_futex(true)))
+		return -EFAULT;
+
+	/*
+	 * Detect deadlocks.
+	 */
+	if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
+		return -EDEADLK;
+
+	if ((unlikely(should_fail_futex(true))))
+		return -EDEADLK;
+
+	/*
+	 * Lookup existing state first. If it exists, try to attach to
+	 * its pi_state.
+	 */
+	top_waiter = futex_top_waiter(hb, key);
+	if (top_waiter)
+		return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
+
+	/*
+	 * No waiter and user TID is 0. We are here because the
+	 * waiters or the owner died bit is set or called from
+	 * requeue_cmp_pi or for whatever reason something took the
+	 * syscall.
+	 */
+	if (!(uval & FUTEX_TID_MASK)) {
+		/*
+		 * We take over the futex. No other waiters and the user space
+		 * TID is 0. We preserve the owner died bit.
+		 */
+		newval = uval & FUTEX_OWNER_DIED;
+		newval |= vpid;
+
+		/* The futex requeue_pi code can enforce the waiters bit */
+		if (set_waiters)
+			newval |= FUTEX_WAITERS;
+
+		ret = lock_pi_update_atomic(uaddr, uval, newval);
+		/* If the take over worked, return 1 */
+		return ret < 0 ? ret : 1;
+	}
+
+	/*
+	 * First waiter. Set the waiters bit before attaching ourself to
+	 * the owner. If owner tries to unlock, it will be forced into
+	 * the kernel and blocked on hb->lock.
+	 */
+	newval = uval | FUTEX_WAITERS;
+	ret = lock_pi_update_atomic(uaddr, uval, newval);
+	if (ret)
+		return ret;
+	/*
+	 * If the update of the user space value succeeded, we try to
+	 * attach to the owner. If that fails, no harm done, we only
+	 * set the FUTEX_WAITERS bit in the user space variable.
+	 */
+	return attach_to_pi_owner(uval, key, ps);
+}
+
+/*
+ * Caller must hold a reference on @pi_state.
+ */
+static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
+{
+	u32 uninitialized_var(curval), newval;
+	struct task_struct *new_owner;
+	bool postunlock = false;
+	DEFINE_WAKE_Q(wake_q);
+	int ret = 0;
+
+	new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
+	if (WARN_ON_ONCE(!new_owner)) {
+		/*
+		 * As per the comment in futex_unlock_pi() this should not happen.
+		 *
+		 * When this happens, give up our locks and try again, giving
+		 * the futex_lock_pi() instance time to complete, either by
+		 * waiting on the rtmutex or removing itself from the futex
+		 * queue.
+		 */
+		ret = -EAGAIN;
+		goto out_unlock;
+	}
+
+	/*
+	 * We pass it to the next owner. The WAITERS bit is always kept
+	 * enabled while there is PI state around. We cleanup the owner
+	 * died bit, because we are the owner.
+	 */
+	newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
+
+	if (unlikely(should_fail_futex(true)))
+		ret = -EFAULT;
+
+	if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) {
+		ret = -EFAULT;
+
+	} else if (curval != uval) {
+		/*
+		 * If a unconditional UNLOCK_PI operation (user space did not
+		 * try the TID->0 transition) raced with a waiter setting the
+		 * FUTEX_WAITERS flag between get_user() and locking the hash
+		 * bucket lock, retry the operation.
+		 */
+		if ((FUTEX_TID_MASK & curval) == uval)
+			ret = -EAGAIN;
+		else
+			ret = -EINVAL;
+	}
+
+	if (ret)
+		goto out_unlock;
+
+	/*
+	 * This is a point of no return; once we modify the uval there is no
+	 * going back and subsequent operations must not fail.
+	 */
+
+	raw_spin_lock(&pi_state->owner->pi_lock);
+	WARN_ON(list_empty(&pi_state->list));
+	list_del_init(&pi_state->list);
+	raw_spin_unlock(&pi_state->owner->pi_lock);
+
+	raw_spin_lock(&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;
+	raw_spin_unlock(&new_owner->pi_lock);
+
+	postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
+
+out_unlock:
+	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+
+	if (postunlock)
+		rt_mutex_postunlock(&wake_q);
+
+	return ret;
+}
+
+/**
+ * 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;
+
+	__unqueue_futex(q);
+
+	WARN_ON(!q->rt_waiter);
+	q->rt_waiter = NULL;
+
+	q->lock_ptr = &hb->lock;
+
+	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.
+ *
+ * Return:
+ *  0 - failed to acquire the lock atomically;
+ * >0 - acquired the lock, return value is vpid of the top_waiter
+ * <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, vpid;
+
+	if (get_futex_value_locked(&curval, pifutex))
+		return -EFAULT;
+
+	if (unlikely(should_fail_futex(true)))
+		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.
+	 */
+	vpid = task_pid_vnr(top_waiter->task);
+	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 vpid;
+	}
+	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)
+	__releases(q->lock_ptr)
+{
+	__unqueue_futex(q);
+
+	BUG_ON(!q->pi_state);
+	put_pi_state(q->pi_state);
+	q->pi_state = NULL;
+
+	spin_unlock(q->lock_ptr);
+}
+
+/*
+ * Fixup the pi_state owner with the new owner.
+ *
+ * Must be called with hash bucket lock held and mm->sem held for non
+ * private futexes.
+ */
+static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
+				struct task_struct *newowner)
+{
+	u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
+	struct futex_pi_state *pi_state = q->pi_state;
+	u32 uval, uninitialized_var(curval), newval;
+	struct task_struct *oldowner;
+	int ret;
+
+	raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+
+	oldowner = pi_state->owner;
+	/* Owner died? */
+	if (!pi_state->owner)
+		newtid |= FUTEX_OWNER_DIED;
+
+	/*
+	 * We are here either because we stole the rtmutex from the
+	 * previous highest priority waiter or we are the highest priority
+	 * waiter but have failed to get the rtmutex the first time.
+	 *
+	 * We have to replace the newowner 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 locks 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;
+
+	for (;;) {
+		newval = (uval & FUTEX_OWNER_DIED) | newtid;
+
+		if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
+			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) {
+		raw_spin_lock(&pi_state->owner->pi_lock);
+		WARN_ON(list_empty(&pi_state->list));
+		list_del_init(&pi_state->list);
+		raw_spin_unlock(&pi_state->owner->pi_lock);
+	}
+
+	pi_state->owner = newowner;
+
+	raw_spin_lock(&newowner->pi_lock);
+	WARN_ON(!list_empty(&pi_state->list));
+	list_add(&pi_state->list, &newowner->pi_state_list);
+	raw_spin_unlock(&newowner->pi_lock);
+	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+
+	return 0;
+
+	/*
+	 * To handle the page fault we need to drop the locks here. That gives
+	 * the other task (either the highest priority waiter 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 locks and before trying to
+	 * do another fixup. When the fixup has been done already we simply
+	 * return.
+	 *
+	 * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
+	 * drop hb->lock since the caller owns the hb -> futex_q relation.
+	 * Dropping the pi_mutex->wait_lock requires the state revalidate.
+	 */
+handle_fault:
+	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+	spin_unlock(q->lock_ptr);
+
+	ret = fault_in_user_writeable(uaddr);
+
+	spin_lock(q->lock_ptr);
+	raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+
+	/*
+	 * Check if someone else fixed it for us:
+	 */
+	if (pi_state->owner != oldowner) {
+		ret = 0;
+		goto out_unlock;
+	}
+
+	if (ret)
+		goto out_unlock;
+
+	goto retry;
+
+out_unlock:
+	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+	return ret;
+}
+
+/**
+ * fixup_owner() - Post lock pi_state and corner case management
+ * @uaddr:	user address of the futex
+ * @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.
+ *
+ * Return:
+ *  1 - success, lock taken;
+ *  0 - success, lock not taken;
+ * <0 - on error (-EFAULT)
+ */
+static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
+{
+	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:
+		 *
+		 * We can safely read pi_state->owner without holding wait_lock
+		 * because we now own the rt_mutex, only the owner will attempt
+		 * to change it.
+		 */
+		if (q->pi_state->owner != current)
+			ret = fixup_pi_state_owner(uaddr, q, current);
+		goto out;
+	}
+
+	/*
+	 * Paranoia check. If we did not take the lock, then we should not be
+	 * the 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;
+}
+
+/*
+ * 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 as a consequence of relying
+ * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
+ * a 0 value of the futex too.).
+ *
+ * Also serves as futex trylock_pi()'ing, and due semantics.
+ */
+static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
+			 ktime_t *time, int trylock)
+{
+	struct hrtimer_sleeper timeout, *to = NULL;
+	struct futex_pi_state *pi_state = NULL;
+	struct rt_mutex_waiter rt_waiter;
+	struct futex_hash_bucket *hb;
+	struct futex_q q = futex_q_init;
+	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);
+	}
+
+retry:
+	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &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)) {
+		/*
+		 * Atomic work succeeded and we got the lock,
+		 * or failed. Either way, we do _not_ block.
+		 */
+		switch (ret) {
+		case 1:
+			/* We got the lock. */
+			ret = 0;
+			goto out_unlock_put_key;
+		case -EFAULT:
+			goto uaddr_faulted;
+		case -EAGAIN:
+			/*
+			 * Two reasons for this:
+			 * - Task is exiting and we just wait for the
+			 *   exit to complete.
+			 * - The user space value changed.
+			 */
+			queue_unlock(hb);
+			put_futex_key(&q.key);
+			cond_resched();
+			goto retry;
+		default:
+			goto out_unlock_put_key;
+		}
+	}
+
+	WARN_ON(!q.pi_state);
+
+	/*
+	 * Only actually queue now that the atomic ops are done:
+	 */
+	__queue_me(&q, hb);
+
+	if (trylock) {
+		ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
+		/* Fixup the trylock return value: */
+		ret = ret ? 0 : -EWOULDBLOCK;
+		goto no_block;
+	}
+
+	rt_mutex_init_waiter(&rt_waiter);
+
+	/*
+	 * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
+	 * hold it while doing rt_mutex_start_proxy(), because then it will
+	 * include hb->lock in the blocking chain, even through we'll not in
+	 * fact hold it while blocking. This will lead it to report -EDEADLK
+	 * and BUG when futex_unlock_pi() interleaves with this.
+	 *
+	 * Therefore acquire wait_lock while holding hb->lock, but drop the
+	 * latter before calling rt_mutex_start_proxy_lock(). This still fully
+	 * serializes against futex_unlock_pi() as that does the exact same
+	 * lock handoff sequence.
+	 */
+	raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
+	spin_unlock(q.lock_ptr);
+	ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
+	raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
+
+	if (ret) {
+		if (ret == 1)
+			ret = 0;
+
+		spin_lock(q.lock_ptr);
+		goto no_block;
+	}
+
+
+	if (unlikely(to))
+		hrtimer_start_expires(&to->timer, HRTIMER_MODE_ABS);
+
+	ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
+
+	spin_lock(q.lock_ptr);
+	/*
+	 * If we failed to acquire the lock (signal/timeout), we must
+	 * first acquire the hb->lock before removing the lock from the
+	 * rt_mutex waitqueue, such that we can keep the hb and rt_mutex
+	 * wait lists consistent.
+	 *
+	 * In particular; it is important that futex_unlock_pi() can not
+	 * observe this inconsistency.
+	 */
+	if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
+		ret = 0;
+
+no_block:
+	/*
+	 * Fixup the pi_state owner and possibly acquire the lock if we
+	 * haven't already.
+	 */
+	res = fixup_owner(uaddr, &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)) {
+		pi_state = q.pi_state;
+		get_pi_state(pi_state);
+	}
+
+	/* Unqueue and drop the lock */
+	unqueue_me_pi(&q);
+
+	if (pi_state) {
+		rt_mutex_futex_unlock(&pi_state->pi_mutex);
+		put_pi_state(pi_state);
+	}
+
+	goto out_put_key;
+
+out_unlock_put_key:
+	queue_unlock(hb);
+
+out_put_key:
+	put_futex_key(&q.key);
+out:
+	if (to) {
+		hrtimer_cancel(&to->timer);
+		destroy_hrtimer_on_stack(&to->timer);
+	}
+	return ret != -EINTR ? ret : -ERESTARTNOINTR;
+
+uaddr_faulted:
+	queue_unlock(hb);
+
+	ret = fault_in_user_writeable(uaddr);
+	if (ret)
+		goto out_put_key;
+
+	if (!(flags & FLAGS_SHARED))
+		goto retry_private;
+
+	put_futex_key(&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, unsigned int flags)
+{
+	u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current);
+	union futex_key key = FUTEX_KEY_INIT;
+	struct futex_hash_bucket *hb;
+	struct futex_q *top_waiter;
+	int ret;
+
+retry:
+	if (get_user(uval, uaddr))
+		return -EFAULT;
+	/*
+	 * We release only a lock we actually own:
+	 */
+	if ((uval & FUTEX_TID_MASK) != vpid)
+		return -EPERM;
+
+	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
+	if (ret)
+		return ret;
+
+	hb = hash_futex(&key);
+	spin_lock(&hb->lock);
+
+	/*
+	 * Check waiters first. We do not trust user space values at
+	 * all and we at least want to know if user space fiddled
+	 * with the futex value instead of blindly unlocking.
+	 */
+	top_waiter = futex_top_waiter(hb, &key);
+	if (top_waiter) {
+		struct futex_pi_state *pi_state = top_waiter->pi_state;
+
+		ret = -EINVAL;
+		if (!pi_state)
+			goto out_unlock;
+
+		/*
+		 * 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)
+			goto out_unlock;
+
+		get_pi_state(pi_state);
+		/*
+		 * By taking wait_lock while still holding hb->lock, we ensure
+		 * there is no point where we hold neither; and therefore
+		 * wake_futex_pi() must observe a state consistent with what we
+		 * observed.
+		 */
+		raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+		spin_unlock(&hb->lock);
+
+		ret = wake_futex_pi(uaddr, uval, pi_state);
+
+		put_pi_state(pi_state);
+
+		/*
+		 * Success, we're done! No tricky corner cases.
+		 */
+		if (!ret)
+			goto out_putkey;
+		/*
+		 * The atomic access to the futex value generated a
+		 * pagefault, so retry the user-access and the wakeup:
+		 */
+		if (ret == -EFAULT)
+			goto pi_faulted;
+		/*
+		 * A unconditional UNLOCK_PI op raced against a waiter
+		 * setting the FUTEX_WAITERS bit. Try again.
+		 */
+		if (ret == -EAGAIN) {
+			put_futex_key(&key);
+			goto retry;
+		}
+		/*
+		 * wake_futex_pi has detected invalid state. Tell user
+		 * space.
+		 */
+		goto out_putkey;
+	}
+
+	/*
+	 * We have no kernel internal state, i.e. no waiters in the
+	 * kernel. Waiters which are about to queue themselves are stuck
+	 * on hb->lock. So we can safely ignore them. We do neither
+	 * preserve the WAITERS bit not the OWNER_DIED one. We are the
+	 * owner.
+	 */
+	if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0)) {
+		spin_unlock(&hb->lock);
+		goto pi_faulted;
+	}
+
+	/*
+	 * If uval has changed, let user space handle it.
+	 */
+	ret = (curval == uval) ? 0 : -EAGAIN;
+
+out_unlock:
+	spin_unlock(&hb->lock);
+out_putkey:
+	put_futex_key(&key);
+	return ret;
+
+pi_faulted:
+	put_futex_key(&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.
+ *
+ * Return:
+ *  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, &hb->chain);
+		hb_waiters_dec(hb);
+
+		/* 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 initially wait on (non-pi)
+ * @flags:	futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), 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
+ * @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 and unique from uaddr.  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 would not 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
+ * 3) signal
+ * 4) timeout
+ *
+ * If 3, cleanup and return -ERESTARTNOINTR.
+ *
+ * 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, return -EWOULDBLOCK (restarting the syscall would do the same).
+ *
+ * If 4 or 7, we cleanup and return with -ETIMEDOUT.
+ *
+ * Return:
+ *  0 - On success;
+ * <0 - On error
+ */
+static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
+				 u32 val, ktime_t *abs_time, u32 bitset,
+				 u32 __user *uaddr2)
+{
+	struct hrtimer_sleeper timeout, *to = NULL;
+	struct futex_pi_state *pi_state = NULL;
+	struct rt_mutex_waiter rt_waiter;
+	struct futex_hash_bucket *hb;
+	union futex_key key2 = FUTEX_KEY_INIT;
+	struct futex_q q = futex_q_init;
+	int res, ret;
+
+	if (uaddr == uaddr2)
+		return -EINVAL;
+
+	if (!bitset)
+		return -EINVAL;
+
+	if (abs_time) {
+		to = &timeout;
+		hrtimer_init_on_stack(&to->timer, (flags & FLAGS_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.
+	 */
+	rt_mutex_init_waiter(&rt_waiter);
+
+	ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
+	if (unlikely(ret != 0))
+		goto out;
+
+	q.bitset = bitset;
+	q.rt_waiter = &rt_waiter;
+	q.requeue_pi_key = &key2;
+
+	/*
+	 * Prepare to wait on uaddr. On success, increments q.key (key1) ref
+	 * count.
+	 */
+	ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
+	if (ret)
+		goto out_key2;
+
+	/*
+	 * The check above which compares uaddrs is not sufficient for
+	 * shared futexes. We need to compare the keys:
+	 */
+	if (match_futex(&q.key, &key2)) {
+		queue_unlock(hb);
+		ret = -EINVAL;
+		goto out_put_keys;
+	}
+
+	/* 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 acquisition by the requeue code. The
+	 * futex_requeue dropped our key1 reference and incremented our key2
+	 * reference count.
+	 */
+
+	/* 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);
+			if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
+				pi_state = q.pi_state;
+				get_pi_state(pi_state);
+			}
+			/*
+			 * Drop the reference to the pi state which
+			 * the requeue_pi() code acquired for us.
+			 */
+			put_pi_state(q.pi_state);
+			spin_unlock(q.lock_ptr);
+		}
+	} else {
+		struct rt_mutex *pi_mutex;
+
+		/*
+		 * 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_wait_proxy_lock(pi_mutex, to, &rt_waiter);
+
+		spin_lock(q.lock_ptr);
+		if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
+			ret = 0;
+
+		debug_rt_mutex_free_waiter(&rt_waiter);
+		/*
+		 * Fixup the pi_state owner and possibly acquire the lock if we
+		 * haven't already.
+		 */
+		res = fixup_owner(uaddr2, &q, !ret);
+		/*
+		 * If fixup_owner() returned an error, proprogate that.  If it
+		 * acquired the lock, clear -ETIMEDOUT or -EINTR.
+		 */
+		if (res)
+			ret = (res < 0) ? res : 0;
+
+		/*
+		 * 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 && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
+			pi_state = q.pi_state;
+			get_pi_state(pi_state);
+		}
+
+		/* Unqueue and drop the lock. */
+		unqueue_me_pi(&q);
+	}
+
+	if (pi_state) {
+		rt_mutex_futex_unlock(&pi_state->pi_mutex);
+		put_pi_state(pi_state);
+	}
+
+	if (ret == -EINTR) {
+		/*
+		 * We've already been requeued, but cannot restart by calling
+		 * futex_lock_pi() directly. We could restart this syscall, but
+		 * it would detect that the user space "val" changed and return
+		 * -EWOULDBLOCK.  Save the overhead of the restart and return
+		 * -EWOULDBLOCK directly.
+		 */
+		ret = -EWOULDBLOCK;
+	}
+
+out_put_keys:
+	put_futex_key(&q.key);
+out_key2:
+	put_futex_key(&key2);
+
+out:
+	if (to) {
+		hrtimer_cancel(&to->timer);
+		destroy_hrtimer_on_stack(&to->timer);
+	}
+	return ret;
+}