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 e1246ccbf89a..4a60ef55dab4 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);