futex_requeue_pi optimization

This patch provides the futex_requeue_pi functionality, which allows some
threads waiting on a normal futex to be requeued on the wait-queue of a
PI-futex.

This provides an optimization, already used for (normal) futexes, to be used
with the PI-futexes.

This optimization is currently used by the glibc in pthread_broadcast, when
using "normal" mutexes.  With futex_requeue_pi, it can be used with
PRIO_INHERIT mutexes too.

Signed-off-by: Pierre Peiffer <pierre.peiffer@bull.net>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Ulrich Drepper <drepper@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 487 insertions, 54 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index e1246ccbf89..4a60ef55dab 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -53,6 +53,12 @@
 
 #include "rtmutex_common.h"
 
+#ifdef CONFIG_DEBUG_RT_MUTEXES
+# include "rtmutex-debug.h"
+#else
+# include "rtmutex.h"
+#endif
+
 #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
 
 /*
@@ -102,6 +108,12 @@ struct futex_q {
 	/* Optional priority inheritance state: */
 	struct futex_pi_state *pi_state;
 	struct task_struct *task;
+
+	/*
+	 * This waiter is used in case of requeue from a
+	 * normal futex to a PI-futex
+	 */
+	struct rt_mutex_waiter waiter;
 };
 
 /*
@@ -180,6 +192,9 @@ int get_futex_key(u32 __user *uaddr, union futex_key *key)
 	if (unlikely((vma->vm_flags & (VM_IO|VM_READ)) != VM_READ))
 		return (vma->vm_flags & VM_IO) ? -EPERM : -EACCES;
 
+	/* Save the user address in the ley */
+	key->uaddr = uaddr;
+
 	/*
 	 * Private mappings are handled in a simple way.
 	 *
@@ -439,7 +454,8 @@ void exit_pi_state_list(struct task_struct *curr)
 }
 
 static int
-lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, struct futex_q *me)
+lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
+		union futex_key *key, struct futex_pi_state **ps)
 {
 	struct futex_pi_state *pi_state = NULL;
 	struct futex_q *this, *next;
@@ -450,7 +466,7 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, struct futex_q *me)
 	head = &hb->chain;
 
 	plist_for_each_entry_safe(this, next, head, list) {
-		if (match_futex(&this->key, &me->key)) {
+		if (match_futex(&this->key, key)) {
 			/*
 			 * Another waiter already exists - bump up
 			 * the refcount and return its pi_state:
@@ -465,7 +481,7 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, struct futex_q *me)
 			WARN_ON(!atomic_read(&pi_state->refcount));
 
 			atomic_inc(&pi_state->refcount);
-			me->pi_state = pi_state;
+			*ps = pi_state;
 
 			return 0;
 		}
@@ -492,7 +508,7 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, struct futex_q *me)
 	rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
 
 	/* Store the key for possible exit cleanups: */
-	pi_state->key = me->key;
+	pi_state->key = *key;
 
 	spin_lock_irq(&p->pi_lock);
 	WARN_ON(!list_empty(&pi_state->list));
@@ -502,7 +518,7 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, struct futex_q *me)
 
 	put_task_struct(p);
 
-	me->pi_state = pi_state;
+	*ps = pi_state;
 
 	return 0;
 }
@@ -562,6 +578,8 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
 	 */
 	if (!(uval & FUTEX_OWNER_DIED)) {
 		newval = FUTEX_WAITERS | new_owner->pid;
+		/* Keep the FUTEX_WAITER_REQUEUED flag if it was set */
+		newval |= (uval & FUTEX_WAITER_REQUEUED);
 
 		pagefault_disable();
 		curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
@@ -666,6 +684,254 @@ out:
 }
 
 /*
+ * Called from futex_requeue_pi.
+ * Set FUTEX_WAITERS and FUTEX_WAITER_REQUEUED flags on the
+ * PI-futex value; search its associated pi_state if an owner exist
+ * or create a new one without owner.
+ */
+static inline int
+lookup_pi_state_for_requeue(u32 __user *uaddr, struct futex_hash_bucket *hb,
+			    union futex_key *key,
+			    struct futex_pi_state **pi_state)
+{
+	u32 curval, uval, newval;
+
+retry:
+	/*
+	 * We can't handle a fault cleanly because we can't
+	 * release the locks here. Simply return the fault.
+	 */
+	if (get_futex_value_locked(&curval, uaddr))
+		return -EFAULT;
+
+	/* set the flags FUTEX_WAITERS and FUTEX_WAITER_REQUEUED */
+	if ((curval & (FUTEX_WAITERS | FUTEX_WAITER_REQUEUED))
+	    != (FUTEX_WAITERS | FUTEX_WAITER_REQUEUED)) {
+		/*
+		 * No waiters yet, we prepare the futex to have some waiters.
+		 */
+
+		uval = curval;
+		newval = uval | FUTEX_WAITERS | FUTEX_WAITER_REQUEUED;
+
+		pagefault_disable();
+		curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
+		pagefault_enable();
+
+		if (unlikely(curval == -EFAULT))
+			return -EFAULT;
+		if (unlikely(curval != uval))
+			goto retry;
+	}
+
+	if (!(curval & FUTEX_TID_MASK)
+	    || lookup_pi_state(curval, hb, key, pi_state)) {
+		/* the futex has no owner (yet) or the lookup failed:
+		   allocate one pi_state without owner */
+
+		*pi_state = alloc_pi_state();
+
+		/* Already stores the key: */
+		(*pi_state)->key = *key;
+
+		/* init the mutex without owner */
+		__rt_mutex_init(&(*pi_state)->pi_mutex, NULL);
+	}
+
+	return 0;
+}
+
+/*
+ * Keep the first nr_wake waiter from futex1, wake up one,
+ * and requeue the next nr_requeue waiters following hashed on
+ * one physical page to another physical page (PI-futex uaddr2)
+ */
+static int futex_requeue_pi(u32 __user *uaddr1, u32 __user *uaddr2,
+			    int nr_wake, int nr_requeue, u32 *cmpval)
+{
+	union futex_key key1, key2;
+	struct futex_hash_bucket *hb1, *hb2;
+	struct plist_head *head1;
+	struct futex_q *this, *next;
+	struct futex_pi_state *pi_state2 = NULL;
+	struct rt_mutex_waiter *waiter, *top_waiter = NULL;
+	struct rt_mutex *lock2 = NULL;
+	int ret, drop_count = 0;
+
+	if (refill_pi_state_cache())
+		return -ENOMEM;
+
+retry:
+	/*
+	 * First take all the futex related locks:
+	 */
+	down_read(&current->mm->mmap_sem);
+
+	ret = get_futex_key(uaddr1, &key1);
+	if (unlikely(ret != 0))
+		goto out;
+	ret = get_futex_key(uaddr2, &key2);
+	if (unlikely(ret != 0))
+		goto out;
+
+	hb1 = hash_futex(&key1);
+	hb2 = hash_futex(&key2);
+
+	double_lock_hb(hb1, hb2);
+
+	if (likely(cmpval != NULL)) {
+		u32 curval;
+
+		ret = get_futex_value_locked(&curval, uaddr1);
+
+		if (unlikely(ret)) {
+			spin_unlock(&hb1->lock);
+			if (hb1 != hb2)
+				spin_unlock(&hb2->lock);
+
+			/*
+			 * If we would have faulted, release mmap_sem, fault
+			 * it in and start all over again.
+			 */
+			up_read(&current->mm->mmap_sem);
+
+			ret = get_user(curval, uaddr1);
+
+			if (!ret)
+				goto retry;
+
+			return ret;
+		}
+		if (curval != *cmpval) {
+			ret = -EAGAIN;
+			goto out_unlock;
+		}
+	}
+
+	head1 = &hb1->chain;
+	plist_for_each_entry_safe(this, next, head1, list) {
+		if (!match_futex (&this->key, &key1))
+			continue;
+		if (++ret <= nr_wake) {
+			wake_futex(this);
+		} else {
+			/*
+			 * FIRST: get and set the pi_state
+			 */
+			if (!pi_state2) {
+				int s;
+				/* do this only the first time we requeue someone */
+				s = lookup_pi_state_for_requeue(uaddr2, hb2,
+								&key2, &pi_state2);
+				if (s) {
+					ret = s;
+					goto out_unlock;
+				}
+
+				lock2 = &pi_state2->pi_mutex;
+				spin_lock(&lock2->wait_lock);
+
+				/* Save the top waiter of the wait_list */
+				if (rt_mutex_has_waiters(lock2))
+					top_waiter = rt_mutex_top_waiter(lock2);
+			} else
+				atomic_inc(&pi_state2->refcount);
+
+
+			this->pi_state = pi_state2;
+
+			/*
+			 * SECOND: requeue futex_q to the correct hashbucket
+			 */
+
+			/*
+			 * If key1 and key2 hash to the same bucket, no need to
+			 * requeue.
+			 */
+			if (likely(head1 != &hb2->chain)) {
+				plist_del(&this->list, &hb1->chain);
+				plist_add(&this->list, &hb2->chain);
+				this->lock_ptr = &hb2->lock;
+#ifdef CONFIG_DEBUG_PI_LIST
+				this->list.plist.lock = &hb2->lock;
+#endif
+			}
+			this->key = key2;
+			get_futex_key_refs(&key2);
+			drop_count++;
+
+
+			/*
+			 * THIRD: queue it to lock2
+			 */
+			spin_lock_irq(&this->task->pi_lock);
+			waiter = &this->waiter;
+			waiter->task = this->task;
+			waiter->lock = lock2;
+			plist_node_init(&waiter->list_entry, this->task->prio);
+			plist_node_init(&waiter->pi_list_entry, this->task->prio);
+			plist_add(&waiter->list_entry, &lock2->wait_list);
+			this->task->pi_blocked_on = waiter;
+			spin_unlock_irq(&this->task->pi_lock);
+
+			if (ret - nr_wake >= nr_requeue)
+				break;
+		}
+	}
+
+	/* If we've requeued some tasks and the top_waiter of the rt_mutex
+	   has changed, we must adjust the priority of the owner, if any */
+	if (drop_count) {
+		struct task_struct *owner = rt_mutex_owner(lock2);
+		if (owner &&
+		    (top_waiter != (waiter = rt_mutex_top_waiter(lock2)))) {
+			int chain_walk = 0;
+
+			spin_lock_irq(&owner->pi_lock);
+			if (top_waiter)
+				plist_del(&top_waiter->pi_list_entry, &owner->pi_waiters);
+			else
+				/*
+				 * There was no waiters before the requeue,
+				 * the flag must be updated
+				 */
+				mark_rt_mutex_waiters(lock2);
+
+			plist_add(&waiter->pi_list_entry, &owner->pi_waiters);
+			__rt_mutex_adjust_prio(owner);
+			if (owner->pi_blocked_on) {
+				chain_walk = 1;
+				get_task_struct(owner);
+			}
+
+			spin_unlock_irq(&owner->pi_lock);
+			spin_unlock(&lock2->wait_lock);
+
+			if (chain_walk)
+				rt_mutex_adjust_prio_chain(owner, 0, lock2, NULL,
+							   current);
+		} else {
+			/* No owner or the top_waiter does not change */
+			mark_rt_mutex_waiters(lock2);
+			spin_unlock(&lock2->wait_lock);
+		}
+	}
+
+out_unlock:
+	spin_unlock(&hb1->lock);
+	if (hb1 != hb2)
+		spin_unlock(&hb2->lock);
+
+	/* drop_futex_key_refs() must be called outside the spinlocks. */
+	while (--drop_count >= 0)
+		drop_futex_key_refs(&key1);
+
+out:
+	up_read(&current->mm->mmap_sem);
+	return ret;
+}
+
+/*
  * Wake up all waiters hashed on the physical page that is mapped
  * to this virtual address:
  */
@@ -984,9 +1250,10 @@ static int unqueue_me(struct futex_q *q)
 
 /*
  * PI futexes can not be requeued and must remove themself from the
- * hash bucket. The hash bucket lock is held on entry and dropped here.
+ * 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, struct futex_hash_bucket *hb)
+static void unqueue_me_pi(struct futex_q *q)
 {
 	WARN_ON(plist_node_empty(&q->list));
 	plist_del(&q->list, &q->list.plist);
@@ -995,11 +1262,65 @@ static void unqueue_me_pi(struct futex_q *q, struct futex_hash_bucket *hb)
 	free_pi_state(q->pi_state);
 	q->pi_state = NULL;
 
-	spin_unlock(&hb->lock);
+	spin_unlock(q->lock_ptr);
 
 	drop_futex_key_refs(&q->key);
 }
 
+/*
+ * Fixup the pi_state owner with current.
+ *
+ * The cur->mm semaphore must be  held, it is released at return of this
+ * function.
+ */
+static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
+				struct futex_hash_bucket *hb,
+				struct task_struct *curr)
+{
+	u32 newtid = curr->pid | FUTEX_WAITERS;
+	struct futex_pi_state *pi_state = q->pi_state;
+	u32 uval, curval, newval;
+	int ret;
+
+	/* Owner died? */
+	if (pi_state->owner != NULL) {
+		spin_lock_irq(&pi_state->owner->pi_lock);
+		WARN_ON(list_empty(&pi_state->list));
+		list_del_init(&pi_state->list);
+		spin_unlock_irq(&pi_state->owner->pi_lock);
+	} else
+		newtid |= FUTEX_OWNER_DIED;
+
+	pi_state->owner = curr;
+
+	spin_lock_irq(&curr->pi_lock);
+	WARN_ON(!list_empty(&pi_state->list));
+	list_add(&pi_state->list, &curr->pi_state_list);
+	spin_unlock_irq(&curr->pi_lock);
+
+	/* Unqueue and drop the lock */
+	unqueue_me_pi(q);
+	up_read(&curr->mm->mmap_sem);
+	/*
+	 * We own it, so we have to replace the pending owner
+	 * TID. This must be atomic as we have preserve the
+	 * owner died bit here.
+	 */
+	ret = get_user(uval, uaddr);
+	while (!ret) {
+		newval = (uval & FUTEX_OWNER_DIED) | newtid;
+		newval |= (uval & FUTEX_WAITER_REQUEUED);
+		curval = futex_atomic_cmpxchg_inatomic(uaddr,
+						       uval, newval);
+		if (curval == -EFAULT)
+ 			ret = -EFAULT;
+		if (curval == uval)
+			break;
+		uval = curval;
+	}
+	return ret;
+}
+
 static long futex_wait_restart(struct restart_block *restart);
 static int futex_wait(u32 __user *uaddr, u32 val, ktime_t *abs_time)
 {
@@ -1009,7 +1330,7 @@ static int futex_wait(u32 __user *uaddr, u32 val, ktime_t *abs_time)
 	struct futex_q q;
 	u32 uval;
 	int ret;
-	struct hrtimer_sleeper t;
+	struct hrtimer_sleeper t, *to = NULL;
 	int rem = 0;
 
 	q.pi_state = NULL;
@@ -1063,6 +1384,14 @@ static int futex_wait(u32 __user *uaddr, u32 val, ktime_t *abs_time)
 	if (uval != val)
 		goto out_unlock_release_sem;
 
+	/*
+	 * This rt_mutex_waiter structure is prepared here and will
+	 * be used only if this task is requeued from a normal futex to
+	 * a PI-futex with futex_requeue_pi.
+	 */
+	debug_rt_mutex_init_waiter(&q.waiter);
+	q.waiter.task = NULL;
+
 	/* Only actually queue if *uaddr contained val.  */
 	__queue_me(&q, hb);
 
@@ -1092,6 +1421,7 @@ static int futex_wait(u32 __user *uaddr, u32 val, ktime_t *abs_time)
 		if (!abs_time)
 			schedule();
 		else {
+			to = &t;
 			hrtimer_init(&t.timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
 			hrtimer_init_sleeper(&t, current);
 			t.timer.expires = *abs_time;
@@ -1119,6 +1449,66 @@ static int futex_wait(u32 __user *uaddr, u32 val, ktime_t *abs_time)
 	 * we are the only user of it.
 	 */
 
+	if (q.pi_state) {
+		/*
+		 * We were woken but have been requeued on a PI-futex.
+		 * We have to complete the lock acquisition by taking
+		 * the rtmutex.
+		 */
+
+		struct rt_mutex *lock = &q.pi_state->pi_mutex;
+
+		spin_lock(&lock->wait_lock);
+		if (unlikely(q.waiter.task)) {
+			remove_waiter(lock, &q.waiter);
+		}
+		spin_unlock(&lock->wait_lock);
+
+		if (rem)
+			ret = -ETIMEDOUT;
+		else
+			ret = rt_mutex_timed_lock(lock, to, 1);
+
+		down_read(&curr->mm->mmap_sem);
+		spin_lock(q.lock_ptr);
+
+		/*
+		 * 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 (!ret && q.pi_state->owner != curr) {
+			/*
+			 * We MUST play with the futex we were requeued on,
+			 * NOT the current futex.
+			 * We can retrieve it from the key of the pi_state
+			 */
+			uaddr = q.pi_state->key.uaddr;
+
+			/* mmap_sem and hash_bucket lock are unlocked at
+			   return of this function */
+			ret = fixup_pi_state_owner(uaddr, &q, hb, curr);
+		} else {
+			/*
+			 * Catch the rare case, where the lock was released
+			 * when we were on the way back before we locked
+			 * the hash bucket.
+			 */
+			if (ret && q.pi_state->owner == curr) {
+				if (rt_mutex_trylock(&q.pi_state->pi_mutex))
+					ret = 0;
+			}
+			/* Unqueue and drop the lock */
+			unqueue_me_pi(&q);
+			up_read(&curr->mm->mmap_sem);
+		}
+
+		debug_rt_mutex_free_waiter(&q.waiter);
+
+		return ret;
+	}
+
+	debug_rt_mutex_free_waiter(&q.waiter);
+
 	/* If we were woken (and unqueued), we succeeded, whatever. */
 	if (!unqueue_me(&q))
 		return 0;
@@ -1161,6 +1551,51 @@ static long futex_wait_restart(struct restart_block *restart)
 }
 
 
+static void set_pi_futex_owner(struct futex_hash_bucket *hb,
+			       union futex_key *key, struct task_struct *p)
+{
+	struct plist_head *head;
+	struct futex_q *this, *next;
+	struct futex_pi_state *pi_state = NULL;
+	struct rt_mutex *lock;
+
+	/* Search a waiter that should already exists */
+
+	head = &hb->chain;
+
+	plist_for_each_entry_safe(this, next, head, list) {
+		if (match_futex (&this->key, key)) {
+			pi_state = this->pi_state;
+			break;
+		}
+	}
+
+	BUG_ON(!pi_state);
+
+	/* set p as pi_state's owner */
+	lock = &pi_state->pi_mutex;
+
+	spin_lock(&lock->wait_lock);
+	spin_lock_irq(&p->pi_lock);
+
+	list_add(&pi_state->list, &p->pi_state_list);
+	pi_state->owner = p;
+
+
+	/* set p as pi_mutex's owner */
+	debug_rt_mutex_proxy_lock(lock, p);
+	WARN_ON(rt_mutex_owner(lock));
+	rt_mutex_set_owner(lock, p, 0);
+	rt_mutex_deadlock_account_lock(lock, p);
+
+	plist_add(&rt_mutex_top_waiter(lock)->pi_list_entry,
+		  &p->pi_waiters);
+	__rt_mutex_adjust_prio(p);
+
+	spin_unlock_irq(&p->pi_lock);
+	spin_unlock(&lock->wait_lock);
+}
+
 /*
  * Userspace tried a 0 -> TID atomic transition of the futex value
  * and failed. The kernel side here does the whole locking operation:
@@ -1175,7 +1610,7 @@ static int futex_lock_pi(u32 __user *uaddr, int detect, ktime_t *time,
 	struct futex_hash_bucket *hb;
 	u32 uval, newval, curval;
 	struct futex_q q;
-	int ret, attempt = 0;
+	int ret, lock_held, attempt = 0;
 
 	if (refill_pi_state_cache())
 		return -ENOMEM;
@@ -1198,6 +1633,8 @@ static int futex_lock_pi(u32 __user *uaddr, int detect, ktime_t *time,
 	hb = queue_lock(&q, -1, NULL);
 
  retry_locked:
+	lock_held = 0;
+
 	/*
 	 * To avoid races, we attempt to take the lock here again
 	 * (by doing a 0 -> TID atomic cmpxchg), while holding all
@@ -1216,7 +1653,16 @@ static int futex_lock_pi(u32 __user *uaddr, int detect, ktime_t *time,
 	if (unlikely((curval & FUTEX_TID_MASK) == current->pid)) {
 		if (!detect && 0)
 			force_sig(SIGKILL, current);
-		ret = -EDEADLK;
+		/*
+		 * Normally, this check is done in user space.
+		 * In case of requeue, the owner may attempt to lock this futex,
+		 * even if the ownership has already been given by the previous
+		 * waker.
+		 * In the usual case, this is a case of deadlock, but not in case
+		 * of REQUEUE_PI.
+		 */
+		if (!(curval & FUTEX_WAITER_REQUEUED))
+			ret = -EDEADLK;
 		goto out_unlock_release_sem;
 	}
 
@@ -1228,7 +1674,18 @@ static int futex_lock_pi(u32 __user *uaddr, int detect, ktime_t *time,
 		goto out_unlock_release_sem;
 
 	uval = curval;
-	newval = uval | FUTEX_WAITERS;
+	/*
+	 * In case of a requeue, check if there already is an owner
+	 * If not, just take the futex.
+	 */
+	if ((curval & FUTEX_WAITER_REQUEUED) && !(curval & FUTEX_TID_MASK)) {
+		/* set current as futex owner */
+		newval = curval | current->pid;
+		lock_held = 1;
+	} else
+		/* Set the WAITERS flag, so the owner will know it has someone
+		   to wake at next unlock */
+		newval = curval | FUTEX_WAITERS;
 
 	pagefault_disable();
 	curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
@@ -1239,11 +1696,16 @@ static int futex_lock_pi(u32 __user *uaddr, int detect, ktime_t *time,
 	if (unlikely(curval != uval))
 		goto retry_locked;
 
+	if (lock_held) {
+		set_pi_futex_owner(hb, &q.key, curr);
+		goto out_unlock_release_sem;
+	}
+
 	/*
 	 * We dont have the lock. Look up the PI state (or create it if
 	 * we are the first waiter):
 	 */
-	ret = lookup_pi_state(uval, hb, &q);
+	ret = lookup_pi_state(uval, hb, &q.key, &q.pi_state);
 
 	if (unlikely(ret)) {
 		/*
@@ -1306,45 +1768,10 @@ static int futex_lock_pi(u32 __user *uaddr, int detect, ktime_t *time,
 	 * 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 (!ret && q.pi_state->owner != curr) {
-		u32 newtid = current->pid | FUTEX_WAITERS;
-
-		/* Owner died? */
-		if (q.pi_state->owner != NULL) {
-			spin_lock_irq(&q.pi_state->owner->pi_lock);
-			WARN_ON(list_empty(&q.pi_state->list));
-			list_del_init(&q.pi_state->list);
-			spin_unlock_irq(&q.pi_state->owner->pi_lock);
-		} else
-			newtid |= FUTEX_OWNER_DIED;
-
-		q.pi_state->owner = current;
-
-		spin_lock_irq(&current->pi_lock);
-		WARN_ON(!list_empty(&q.pi_state->list));
-		list_add(&q.pi_state->list, &current->pi_state_list);
-		spin_unlock_irq(&current->pi_lock);
-
-		/* Unqueue and drop the lock */
-		unqueue_me_pi(&q, hb);
-		up_read(&curr->mm->mmap_sem);
-		/*
-		 * We own it, so we have to replace the pending owner
-		 * TID. This must be atomic as we have preserve the
-		 * owner died bit here.
-		 */
-		ret = get_user(uval, uaddr);
-		while (!ret) {
-			newval = (uval & FUTEX_OWNER_DIED) | newtid;
-			curval = futex_atomic_cmpxchg_inatomic(uaddr,
-							       uval, newval);
-			if (curval == -EFAULT)
-				ret = -EFAULT;
-			if (curval == uval)
-				break;
-			uval = curval;
-		}
-	} else {
+	if (!ret && q.pi_state->owner != curr)
+		/* mmap_sem is unlocked at return of this function */
+		ret = fixup_pi_state_owner(uaddr, &q, hb, curr);
+	else {
 		/*
 		 * Catch the rare case, where the lock was released
 		 * when we were on the way back before we locked
@@ -1355,7 +1782,7 @@ static int futex_lock_pi(u32 __user *uaddr, int detect, ktime_t *time,
 				ret = 0;
 		}
 		/* Unqueue and drop the lock */
-		unqueue_me_pi(&q, hb);
+		unqueue_me_pi(&q);
 		up_read(&curr->mm->mmap_sem);
 	}
 
@@ -1724,6 +2151,8 @@ retry:
 		 * userspace.
 		 */
 		mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
+		/* Also keep the FUTEX_WAITER_REQUEUED flag if set */
+		mval |= (uval & FUTEX_WAITER_REQUEUED);
 		nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
 
 		if (nval == -EFAULT)
@@ -1854,6 +2283,9 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
 	case FUTEX_TRYLOCK_PI:
 		ret = futex_lock_pi(uaddr, 0, timeout, 1);
 		break;
+	case FUTEX_CMP_REQUEUE_PI:
+		ret = futex_requeue_pi(uaddr, uaddr2, val, val2, &val3);
+		break;
 	default:
 		ret = -ENOSYS;
 	}
@@ -1883,7 +2315,8 @@ asmlinkage long sys_futex(u32 __user *uaddr, int op, u32 val,
 	/*
 	 * requeue parameter in 'utime' if op == FUTEX_REQUEUE.
 	 */
-	if (op == FUTEX_REQUEUE || op == FUTEX_CMP_REQUEUE)
+	if (op == FUTEX_REQUEUE || op == FUTEX_CMP_REQUEUE
+	    || op == FUTEX_CMP_REQUEUE_PI)
 		val2 = (u32) (unsigned long) utime;
 
 	return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);