[PATCH] pi-futex: futex_lock_pi/futex_unlock_pi support

This adds the actual pi-futex implementation, based on rt-mutexes.

[dino@in.ibm.com: fix an oops-causing race]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Dinakar Guniguntala <dino@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

5 files changed, 818 insertions, 41 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 3e8a0282e9a5..ab06b9f88f64 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -926,6 +926,14 @@ fastcall NORET_TYPE void do_exit(long code)
         tsk->mempolicy = NULL;
 #endif
         /*
+         * This must happen late, after the PID is not
+         * hashed anymore:
+         */
+        if (unlikely(!list_empty(&tsk->pi_state_list)))
+                exit_pi_state_list(tsk);
+        if (unlikely(current->pi_state_cache))
+                kfree(current->pi_state_cache);
+        /*
          * If DEBUG_MUTEXES is on, make sure we are holding no locks:
          */
         mutex_debug_check_no_locks_held(tsk);
diff --git a/kernel/fork.c b/kernel/fork.c
index b664a081fffa..628198a4f28a 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1092,6 +1092,9 @@ static task_t *copy_process(unsigned long clone_flags,
 #ifdef CONFIG_COMPAT
         p->compat_robust_list = NULL;
 #endif
+        INIT_LIST_HEAD(&p->pi_state_list);
+        p->pi_state_cache = NULL;
+
         /*
          * sigaltstack should be cleared when sharing the same VM
          */
diff --git a/kernel/futex.c b/kernel/futex.c
index 50356fb5d726..b305b7f8dad5 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -12,6 +12,10 @@
  *  (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>
+ *
  *  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.
@@ -46,6 +50,8 @@
 #include <linux/signal.h>
 #include <asm/futex.h>
 
+#include "rtmutex_common.h"
+
 #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
 
 /*
@@ -75,6 +81,27 @@ union futex_key {
 };
 
 /*
+ * Priority Inheritance state:
+ */
+struct futex_pi_state {
+        /*
+         * list of 'owned' pi_state instances - these have to be
+         * cleaned up in do_exit() if the task exits prematurely:
+         */
+        struct list_head list;
+
+        /*
+         * The PI object:
+         */
+        struct rt_mutex pi_mutex;
+
+        struct task_struct *owner;
+        atomic_t refcount;
+
+        union futex_key key;
+};
+
+/*
  * We use this hashed waitqueue instead of a normal wait_queue_t, so
  * we can wake only the relevant ones (hashed queues may be shared).
  *
@@ -96,6 +123,10 @@ struct futex_q {
         /* For fd, sigio sent using these: */
         int fd;
         struct file *filp;
+
+        /* Optional priority inheritance state: */
+        struct futex_pi_state *pi_state;
+        struct task_struct *task;
 };
 
 /*
@@ -259,6 +290,232 @@ static inline int get_futex_value_locked(u32 *dest, u32 __user *from)
 }
 
 /*
+ * Fault handling. Called with current->mm->mmap_sem held.
+ */
+static int futex_handle_fault(unsigned long address, int attempt)
+{
+        struct vm_area_struct * vma;
+        struct mm_struct *mm = current->mm;
+
+        if (attempt >= 2 || !(vma = find_vma(mm, address)) ||
+            vma->vm_start > address || !(vma->vm_flags & VM_WRITE))
+                return -EFAULT;
+
+        switch (handle_mm_fault(mm, vma, address, 1)) {
+        case VM_FAULT_MINOR:
+                current->min_flt++;
+                break;
+        case VM_FAULT_MAJOR:
+                current->maj_flt++;
+                break;
+        default:
+                return -EFAULT;
+        }
+        return 0;
+}
+
+/*
+ * PI code:
+ */
+static int refill_pi_state_cache(void)
+{
+        struct futex_pi_state *pi_state;
+
+        if (likely(current->pi_state_cache))
+                return 0;
+
+        pi_state = kmalloc(sizeof(*pi_state), GFP_KERNEL);
+
+        if (!pi_state)
+                return -ENOMEM;
+
+        memset(pi_state, 0, sizeof(*pi_state));
+        INIT_LIST_HEAD(&pi_state->list);
+        /* pi_mutex gets initialized later */
+        pi_state->owner = NULL;
+        atomic_set(&pi_state->refcount, 1);
+
+        current->pi_state_cache = pi_state;
+
+        return 0;
+}
+
+static struct futex_pi_state * alloc_pi_state(void)
+{
+        struct futex_pi_state *pi_state = current->pi_state_cache;
+
+        WARN_ON(!pi_state);
+        current->pi_state_cache = NULL;
+
+        return pi_state;
+}
+
+static void free_pi_state(struct futex_pi_state *pi_state)
+{
+        if (!atomic_dec_and_test(&pi_state->refcount))
+                return;
+
+        /*
+         * If pi_state->owner is NULL, the owner is most probably dying
+         * and has cleaned up the pi_state already
+         */
+        if (pi_state->owner) {
+                spin_lock_irq(&pi_state->owner->pi_lock);
+                list_del_init(&pi_state->list);
+                spin_unlock_irq(&pi_state->owner->pi_lock);
+
+                rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
+        }
+
+        if (current->pi_state_cache)
+                kfree(pi_state);
+        else {
+                /*
+                 * pi_state->list is already empty.
+                 * clear pi_state->owner.
+                 * refcount is at 0 - put it back to 1.
+                 */
+                pi_state->owner = NULL;
+                atomic_set(&pi_state->refcount, 1);
+                current->pi_state_cache = pi_state;
+        }
+}
+
+/*
+ * Look up the task based on what TID userspace gave us.
+ * We dont trust it.
+ */
+static struct task_struct * futex_find_get_task(pid_t pid)
+{
+        struct task_struct *p;
+
+        read_lock(&tasklist_lock);
+        p = find_task_by_pid(pid);
+        if (!p)
+                goto out_unlock;
+        if ((current->euid != p->euid) && (current->euid != p->uid)) {
+                p = NULL;
+                goto out_unlock;
+        }
+        if (p->state == EXIT_ZOMBIE || p->exit_state == EXIT_ZOMBIE) {
+                p = NULL;
+                goto out_unlock;
+        }
+        get_task_struct(p);
+out_unlock:
+        read_unlock(&tasklist_lock);
+
+        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 futex_hash_bucket *hb;
+        struct list_head *next, *head = &curr->pi_state_list;
+        struct futex_pi_state *pi_state;
+        union futex_key key;
+
+        /*
+         * We are a ZOMBIE and nobody can enqueue itself on
+         * pi_state_list anymore, but we have to be careful
+         * versus waiters unqueueing themselfs
+         */
+        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;
+                spin_unlock_irq(&curr->pi_lock);
+
+                hb = hash_futex(&key);
+                spin_lock(&hb->lock);
+
+                spin_lock_irq(&curr->pi_lock);
+                if (head->next != next) {
+                        spin_unlock(&hb->lock);
+                        continue;
+                }
+
+                list_del_init(&pi_state->list);
+
+                WARN_ON(pi_state->owner != curr);
+
+                pi_state->owner = NULL;
+                spin_unlock_irq(&curr->pi_lock);
+
+                rt_mutex_unlock(&pi_state->pi_mutex);
+
+                spin_unlock(&hb->lock);
+
+                spin_lock_irq(&curr->pi_lock);
+        }
+        spin_unlock_irq(&curr->pi_lock);
+}
+
+static int
+lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, struct futex_q *me)
+{
+        struct futex_pi_state *pi_state = NULL;
+        struct futex_q *this, *next;
+        struct list_head *head;
+        struct task_struct *p;
+        pid_t pid;
+
+        head = &hb->chain;
+
+        list_for_each_entry_safe(this, next, head, list) {
+                if (match_futex (&this->key, &me->key)) {
+                        /*
+                         * Another waiter already exists - bump up
+                         * the refcount and return its pi_state:
+                         */
+                        pi_state = this->pi_state;
+                        atomic_inc(&pi_state->refcount);
+                        me->pi_state = pi_state;
+
+                        return 0;
+                }
+        }
+
+        /*
+         * We are the first waiter - try to look up the real owner and
+         * attach the new pi_state to it:
+         */
+        pid = uval & FUTEX_TID_MASK;
+        p = futex_find_get_task(pid);
+        if (!p)
+                return -ESRCH;
+
+        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 = me->key;
+
+        spin_lock_irq(&p->pi_lock);
+        list_add(&pi_state->list, &p->pi_state_list);
+        pi_state->owner = p;
+        spin_unlock_irq(&p->pi_lock);
+
+        put_task_struct(p);
+
+        me->pi_state = pi_state;
+
+        return 0;
+}
+
+/*
  * The hash bucket lock must be held when this is called.
  * Afterwards, the futex_q must not be accessed.
  */
@@ -285,6 +542,70 @@ static void wake_futex(struct futex_q *q)
         q->lock_ptr = NULL;
 }
 
+static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
+{
+        struct task_struct *new_owner;
+        struct futex_pi_state *pi_state = this->pi_state;
+        u32 curval, newval;
+
+        if (!pi_state)
+                return -EINVAL;
+
+        new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
+
+        /*
+         * This happens when we have stolen the lock and the original
+         * pending owner did not enqueue itself back on the rt_mutex.
+         * Thats not a tragedy. We know that way, that a lock waiter
+         * is on the fly. We make the futex_q waiter the pending owner.
+         */
+        if (!new_owner)
+                new_owner = this->task;
+
+        /*
+         * We pass it to the next owner. (The WAITERS bit is always
+         * kept enabled while there is PI state around. We must also
+         * preserve the owner died bit.)
+         */
+        newval = (uval & FUTEX_OWNER_DIED) | FUTEX_WAITERS | new_owner->pid;
+
+        inc_preempt_count();
+        curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
+        dec_preempt_count();
+
+        if (curval == -EFAULT)
+                return -EFAULT;
+        if (curval != uval)
+                return -EINVAL;
+
+        list_del_init(&pi_state->owner->pi_state_list);
+        list_add(&pi_state->list, &new_owner->pi_state_list);
+        pi_state->owner = new_owner;
+        rt_mutex_unlock(&pi_state->pi_mutex);
+
+        return 0;
+}
+
+static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
+{
+        u32 oldval;
+
+        /*
+         * There is no waiter, so we unlock the futex. The owner died
+         * bit has not to be preserved here. We are the owner:
+         */
+        inc_preempt_count();
+        oldval = futex_atomic_cmpxchg_inatomic(uaddr, uval, 0);
+        dec_preempt_count();
+
+        if (oldval == -EFAULT)
+                return oldval;
+        if (oldval != uval)
+                return -EAGAIN;
+
+        return 0;
+}
+
 /*
  * Wake up all waiters hashed on the physical page that is mapped
  * to this virtual address:
@@ -309,6 +630,8 @@ static int futex_wake(u32 __user *uaddr, int nr_wake)
 
         list_for_each_entry_safe(this, next, head, list) {
                 if (match_futex (&this->key, &key)) {
+                        if (this->pi_state)
+                                return -EINVAL;
                         wake_futex(this);
                         if (++ret >= nr_wake)
                                 break;
@@ -385,27 +708,9 @@ retry:
                  * still holding the mmap_sem.
                  */
                 if (attempt++) {
-                        struct vm_area_struct * vma;
-                        struct mm_struct *mm = current->mm;
-                        unsigned long address = (unsigned long)uaddr2;
-
-                        ret = -EFAULT;
-                        if (attempt >= 2 ||
-                            !(vma = find_vma(mm, address)) ||
-                            vma->vm_start > address ||
-                            !(vma->vm_flags & VM_WRITE))
+                        if (futex_handle_fault((unsigned long)uaddr2,
+                                               attempt))
                                 goto out;
-
-                        switch (handle_mm_fault(mm, vma, address, 1)) {
-                        case VM_FAULT_MINOR:
-                                current->min_flt++;
-                                break;
-                        case VM_FAULT_MAJOR:
-                                current->maj_flt++;
-                                break;
-                        default:
-                                goto out;
-                        }
                         goto retry;
                 }
 
@@ -572,6 +877,7 @@ queue_lock(struct futex_q *q, int fd, struct file *filp)
 static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
 {
         list_add_tail(&q->list, &hb->chain);
+        q->task = current;
         spin_unlock(&hb->lock);
 }
 
@@ -626,6 +932,9 @@ static int unqueue_me(struct futex_q *q)
                 }
                 WARN_ON(list_empty(&q->list));
                 list_del(&q->list);
+
+                BUG_ON(q->pi_state);
+
                 spin_unlock(lock_ptr);
                 ret = 1;
         }
@@ -634,16 +943,36 @@ static int unqueue_me(struct futex_q *q)
         return ret;
 }
 
+/*
+ * 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.
+ */
+static void unqueue_me_pi(struct futex_q *q, struct futex_hash_bucket *hb)
+{
+        WARN_ON(list_empty(&q->list));
+        list_del(&q->list);
+
+        BUG_ON(!q->pi_state);
+        free_pi_state(q->pi_state);
+        q->pi_state = NULL;
+
+        spin_unlock(&hb->lock);
+
+        drop_key_refs(&q->key);
+}
+
 static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time)
 {
-        DECLARE_WAITQUEUE(wait, current);
+        struct task_struct *curr = current;
+        DECLARE_WAITQUEUE(wait, curr);
         struct futex_hash_bucket *hb;
         struct futex_q q;
         u32 uval;
         int ret;
 
+        q.pi_state = NULL;
  retry:
-        down_read(&current->mm->mmap_sem);
+        down_read(&curr->mm->mmap_sem);
 
         ret = get_futex_key(uaddr, &q.key);
         if (unlikely(ret != 0))
@@ -680,7 +1009,7 @@ static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time)
                  * If we would have faulted, release mmap_sem, fault it in and
                  * start all over again.
                  */
-                up_read(&current->mm->mmap_sem);
+                up_read(&curr->mm->mmap_sem);
 
                 ret = get_user(uval, uaddr);
 
@@ -688,11 +1017,9 @@ static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time)
                         goto retry;
                 return ret;
         }
-        if (uval != val) {
-                ret = -EWOULDBLOCK;
-                queue_unlock(&q, hb);
-                goto out_release_sem;
-        }
+        ret = -EWOULDBLOCK;
+        if (uval != val)
+                goto out_unlock_release_sem;
 
         /* Only actually queue if *uaddr contained val.  */
         __queue_me(&q, hb);
@@ -700,8 +1027,8 @@ static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time)
         /*
          * Now the futex is queued and we have checked the data, we
          * don't want to hold mmap_sem while we sleep.
-         */     
-        up_read(&current->mm->mmap_sem);
+         */
+        up_read(&curr->mm->mmap_sem);
 
         /*
          * There might have been scheduling since the queue_me(), as we
@@ -739,8 +1066,415 @@ static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time)
          */
         return -EINTR;
 
+ out_unlock_release_sem:
+        queue_unlock(&q, hb);
+
  out_release_sem:
+        up_read(&curr->mm->mmap_sem);
+        return ret;
+}
+
+/*
+ * Userspace tried a 0 -> TID atomic transition of the futex value
+ * and failed. The kernel side here does the whole locking operation:
+ * if there are waiters then it will block, it does PI, etc. (Due to
+ * races the kernel might see a 0 value of the futex too.)
+ */
+static int do_futex_lock_pi(u32 __user *uaddr, int detect, int trylock,
+                            struct hrtimer_sleeper *to)
+{
+        struct task_struct *curr = current;
+        struct futex_hash_bucket *hb;
+        u32 uval, newval, curval;
+        struct futex_q q;
+        int ret, attempt = 0;
+
+        if (refill_pi_state_cache())
+                return -ENOMEM;
+
+        q.pi_state = NULL;
+ retry:
+        down_read(&curr->mm->mmap_sem);
+
+        ret = get_futex_key(uaddr, &q.key);
+        if (unlikely(ret != 0))
+                goto out_release_sem;
+
+        hb = queue_lock(&q, -1, NULL);
+
+ retry_locked:
+        /*
+         * To avoid races, we attempt to take the lock here again
+         * (by doing a 0 -> TID atomic cmpxchg), while holding all
+         * the locks. It will most likely not succeed.
+         */
+        newval = current->pid;
+
+        inc_preempt_count();
+        curval = futex_atomic_cmpxchg_inatomic(uaddr, 0, newval);
+        dec_preempt_count();
+
+        if (unlikely(curval == -EFAULT))
+                goto uaddr_faulted;
+
+        /* We own the lock already */
+        if (unlikely((curval & FUTEX_TID_MASK) == current->pid)) {
+                if (!detect && 0)
+                        force_sig(SIGKILL, current);
+                ret = -EDEADLK;
+                goto out_unlock_release_sem;
+        }
+
+        /*
+         * Surprise - we got the lock. Just return
+         * to userspace:
+         */
+        if (unlikely(!curval))
+                goto out_unlock_release_sem;
+
+        uval = curval;
+        newval = uval | FUTEX_WAITERS;
+
+        inc_preempt_count();
+        curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
+        dec_preempt_count();
+
+        if (unlikely(curval == -EFAULT))
+                goto uaddr_faulted;
+        if (unlikely(curval != uval))
+                goto retry_locked;
+
+        /*
+         * 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);
+
+        if (unlikely(ret)) {
+                /*
+                 * There were no waiters and the owner task lookup
+                 * failed. When the OWNER_DIED bit is set, then we
+                 * know that this is a robust futex and we actually
+                 * take the lock. This is safe as we are protected by
+                 * the hash bucket lock. We also set the waiters bit
+                 * unconditionally here, to simplify glibc handling of
+                 * multiple tasks racing to acquire the lock and
+                 * cleanup the problems which were left by the dead
+                 * owner.
+                 */
+                if (curval & FUTEX_OWNER_DIED) {
+                        uval = newval;
+                        newval = current->pid |
+                                FUTEX_OWNER_DIED | FUTEX_WAITERS;
+
+                        inc_preempt_count();
+                        curval = futex_atomic_cmpxchg_inatomic(uaddr,
+                                                               uval, newval);
+                        dec_preempt_count();
+
+                        if (unlikely(curval == -EFAULT))
+                                goto uaddr_faulted;
+                        if (unlikely(curval != uval))
+                                goto retry_locked;
+                        ret = 0;
+                }
+                goto out_unlock_release_sem;
+        }
+
+        /*
+         * Only actually queue now that the atomic ops are done:
+         */
+        __queue_me(&q, hb);
+
+        /*
+         * Now the futex is queued and we have checked the data, we
+         * don't want to hold mmap_sem while we sleep.
+         */
+        up_read(&curr->mm->mmap_sem);
+
+        WARN_ON(!q.pi_state);
+        /*
+         * Block on the PI mutex:
+         */
+        if (!trylock)
+                ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
+        else {
+                ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
+                /* Fixup the trylock return value: */
+                ret = ret ? 0 : -EWOULDBLOCK;
+        }
+
+        down_read(&curr->mm->mmap_sem);
+        hb = queue_lock(&q, -1, NULL);
+
+        /*
+         * 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);
+                        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);
+                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 {
+                /*
+                 * 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, hb);
+                up_read(&curr->mm->mmap_sem);
+        }
+
+        if (!detect && ret == -EDEADLK && 0)
+                force_sig(SIGKILL, current);
+
+        return ret;
+
+ out_unlock_release_sem:
+        queue_unlock(&q, hb);
+
+ out_release_sem:
+        up_read(&curr->mm->mmap_sem);
+        return ret;
+
+ uaddr_faulted:
+        /*
+         * We have to r/w  *(int __user *)uaddr, but we can't modify it
+         * non-atomically.  Therefore, if get_user below is not
+         * enough, we need to handle the fault ourselves, while
+         * still holding the mmap_sem.
+         */
+        if (attempt++) {
+                if (futex_handle_fault((unsigned long)uaddr, attempt))
+                        goto out_unlock_release_sem;
+
+                goto retry_locked;
+        }
+
+        queue_unlock(&q, hb);
+        up_read(&curr->mm->mmap_sem);
+
+        ret = get_user(uval, uaddr);
+        if (!ret && (uval != -EFAULT))
+                goto retry;
+
+        return ret;
+}
+
+/*
+ * Restart handler
+ */
+static long futex_lock_pi_restart(struct restart_block *restart)
+{
+        struct hrtimer_sleeper timeout, *to = NULL;
+        int ret;
+
+        restart->fn = do_no_restart_syscall;
+
+        if (restart->arg2 || restart->arg3) {
+                to = &timeout;
+                hrtimer_init(&to->timer, CLOCK_REALTIME, HRTIMER_ABS);
+                hrtimer_init_sleeper(to, current);
+                to->timer.expires.tv64 = ((u64)restart->arg1 << 32) |
+                        (u64) restart->arg0;
+        }
+
+        pr_debug("lock_pi restart: %p, %d (%d)\n",
+                 (u32 __user *)restart->arg0, current->pid);
+
+        ret = do_futex_lock_pi((u32 __user *)restart->arg0, restart->arg1,
+                               0, to);
+
+        if (ret != -EINTR)
+                return ret;
+
+        restart->fn = futex_lock_pi_restart;
+
+        /* The other values are filled in */
+        return -ERESTART_RESTARTBLOCK;
+}
+
+/*
+ * Called from the syscall entry below.
+ */
+static int futex_lock_pi(u32 __user *uaddr, int detect, unsigned long sec,
+                         long nsec, int trylock)
+{
+        struct hrtimer_sleeper timeout, *to = NULL;
+        struct restart_block *restart;
+        int ret;
+
+        if (sec != MAX_SCHEDULE_TIMEOUT) {
+                to = &timeout;
+                hrtimer_init(&to->timer, CLOCK_REALTIME, HRTIMER_ABS);
+                hrtimer_init_sleeper(to, current);
+                to->timer.expires = ktime_set(sec, nsec);
+        }
+
+        ret = do_futex_lock_pi(uaddr, detect, trylock, to);
+
+        if (ret != -EINTR)
+                return ret;
+
+        pr_debug("lock_pi interrupted: %p, %d (%d)\n", uaddr, current->pid);
+
+        restart = &current_thread_info()->restart_block;
+        restart->fn = futex_lock_pi_restart;
+        restart->arg0 = (unsigned long) uaddr;
+        restart->arg1 = detect;
+        if (to) {
+                restart->arg2 = to->timer.expires.tv64 & 0xFFFFFFFF;
+                restart->arg3 = to->timer.expires.tv64 >> 32;
+        } else
+                restart->arg2 = restart->arg3 = 0;
+
+        return -ERESTART_RESTARTBLOCK;
+}
+
+/*
+ * 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)
+{
+        struct futex_hash_bucket *hb;
+        struct futex_q *this, *next;
+        u32 uval;
+        struct list_head *head;
+        union futex_key key;
+        int ret, attempt = 0;
+
+retry:
+        if (get_user(uval, uaddr))
+                return -EFAULT;
+        /*
+         * We release only a lock we actually own:
+         */
+        if ((uval & FUTEX_TID_MASK) != current->pid)
+                return -EPERM;
+        /*
+         * First take all the futex related locks:
+         */
+        down_read(&current->mm->mmap_sem);
+
+        ret = get_futex_key(uaddr, &key);
+        if (unlikely(ret != 0))
+                goto out;
+
+        hb = hash_futex(&key);
+        spin_lock(&hb->lock);
+
+retry_locked:
+        /*
+         * To avoid races, try to do the TID -> 0 atomic transition
+         * again. If it succeeds then we can return without waking
+         * anyone else up:
+         */
+        inc_preempt_count();
+        uval = futex_atomic_cmpxchg_inatomic(uaddr, current->pid, 0);
+        dec_preempt_count();
+
+        if (unlikely(uval == -EFAULT))
+                goto pi_faulted;
+        /*
+         * Rare case: we managed to release the lock atomically,
+         * no need to wake anyone else up:
+         */
+        if (unlikely(uval == current->pid))
+                goto out_unlock;
+
+        /*
+         * Ok, other tasks may need to be woken up - check waiters
+         * and do the wakeup if necessary:
+         */
+        head = &hb->chain;
+
+        list_for_each_entry_safe(this, next, head, list) {
+                if (!match_futex (&this->key, &key))
+                        continue;
+                ret = wake_futex_pi(uaddr, uval, this);
+                /*
+                 * The atomic access to the futex value
+                 * generated a pagefault, so retry the
+                 * user-access and the wakeup:
+                 */
+                if (ret == -EFAULT)
+                        goto pi_faulted;
+                goto out_unlock;
+        }
+        /*
+         * No waiters - kernel unlocks the futex:
+         */
+        ret = unlock_futex_pi(uaddr, uval);
+        if (ret == -EFAULT)
+                goto pi_faulted;
+
+out_unlock:
+        spin_unlock(&hb->lock);
+out:
+        up_read(&current->mm->mmap_sem);
+
+        return ret;
+
+pi_faulted:
+        /*
+         * We have to r/w  *(int __user *)uaddr, but we can't modify it
+         * non-atomically.  Therefore, if get_user below is not
+         * enough, we need to handle the fault ourselves, while
+         * still holding the mmap_sem.
+         */
+        if (attempt++) {
+                if (futex_handle_fault((unsigned long)uaddr, attempt))
+                        goto out_unlock;
+
+                goto retry_locked;
+        }
+
+        spin_unlock(&hb->lock);
         up_read(&current->mm->mmap_sem);
+
+        ret = get_user(uval, uaddr);
+        if (!ret && (uval != -EFAULT))
+                goto retry;
+
         return ret;
 }
 
@@ -819,6 +1553,7 @@ static int futex_fd(u32 __user *uaddr, int signal)
                 err = -ENOMEM;
                 goto error;
         }
+        q->pi_state = NULL;
 
         down_read(&current->mm->mmap_sem);
         err = get_futex_key(uaddr, &q->key);
@@ -856,7 +1591,7 @@ error:
  * Implementation: user-space maintains a per-thread list of locks it
  * is holding. Upon do_exit(), the kernel carefully walks this list,
  * and marks all locks that are owned by this thread with the
- * FUTEX_OWNER_DEAD bit, and wakes up a waiter (if any). The list is
+ * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
  * always manipulated with the lock held, so the list is private and
  * per-thread. Userspace also maintains a per-thread 'list_op_pending'
  * field, to allow the kernel to clean up if the thread dies after
@@ -931,7 +1666,7 @@ err_unlock:
  */
 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr)
 {
-        u32 uval;
+        u32 uval, nval;
 
 retry:
         if (get_user(uval, uaddr))
@@ -948,8 +1683,12 @@ retry:
                  * thread-death.) The rest of the cleanup is done in
                  * userspace.
                  */
-                if (futex_atomic_cmpxchg_inatomic(uaddr, uval,
-                                         uval | FUTEX_OWNER_DIED) != uval)
+                nval = futex_atomic_cmpxchg_inatomic(uaddr, uval,
+                                                     uval | FUTEX_OWNER_DIED);
+                if (nval == -EFAULT)
+                        return -1;
+
+                if (nval != uval)
                         goto retry;
 
                 if (uval & FUTEX_WAITERS)
@@ -994,7 +1733,7 @@ void exit_robust_list(struct task_struct *curr)
         while (entry != &head->list) {
                 /*
                  * A pending lock might already be on the list, so
-                 * dont process it twice:
+                 * don't process it twice:
                  */
                 if (entry != pending)
                         if (handle_futex_death((void *)entry + futex_offset,
@@ -1040,6 +1779,15 @@ long do_futex(u32 __user *uaddr, int op, u32 val, unsigned long timeout,
         case FUTEX_WAKE_OP:
                 ret = futex_wake_op(uaddr, uaddr2, val, val2, val3);
                 break;
+        case FUTEX_LOCK_PI:
+                ret = futex_lock_pi(uaddr, val, timeout, val2, 0);
+                break;
+        case FUTEX_UNLOCK_PI:
+                ret = futex_unlock_pi(uaddr);
+                break;
+        case FUTEX_TRYLOCK_PI:
+                ret = futex_lock_pi(uaddr, 0, timeout, val2, 1);
+                break;
         default:
                 ret = -ENOSYS;
         }
@@ -1055,17 +1803,22 @@ asmlinkage long sys_futex(u32 __user *uaddr, int op, u32 val,
         unsigned long timeout = MAX_SCHEDULE_TIMEOUT;
         u32 val2 = 0;
 
-        if (utime && (op == FUTEX_WAIT)) {
+        if (utime && (op == FUTEX_WAIT || op == FUTEX_LOCK_PI)) {
                 if (copy_from_user(&t, utime, sizeof(t)) != 0)
                         return -EFAULT;
                 if (!timespec_valid(&t))
                         return -EINVAL;
-                timeout = timespec_to_jiffies(&t) + 1;
+                if (op == FUTEX_WAIT)
+                        timeout = timespec_to_jiffies(&t) + 1;
+                else {
+                        timeout = t.tv_sec;
+                        val2 = t.tv_nsec;
+                }
         }
         /*
          * requeue parameter in 'utime' if op == FUTEX_REQUEUE.
          */
-        if (op >= FUTEX_REQUEUE)
+        if (op == FUTEX_REQUEUE || op == FUTEX_CMP_REQUEUE)
                 val2 = (u32) (unsigned long) utime;
 
         return do_futex(uaddr, op, val, timeout, uaddr2, val2, val3);
diff --git a/kernel/futex_compat.c b/kernel/futex_compat.c
index 7e57c31670a3..d1d92b441fb7 100644
--- a/kernel/futex_compat.c
+++ b/kernel/futex_compat.c
@@ -129,14 +129,19 @@ asmlinkage long compat_sys_futex(u32 __user *uaddr, int op, u32 val,
         unsigned long timeout = MAX_SCHEDULE_TIMEOUT;
         int val2 = 0;
 
-        if (utime && (op == FUTEX_WAIT)) {
+        if (utime && (op == FUTEX_WAIT || op == FUTEX_LOCK_PI)) {
                 if (get_compat_timespec(&t, utime))
                         return -EFAULT;
                 if (!timespec_valid(&t))
                         return -EINVAL;
-                timeout = timespec_to_jiffies(&t) + 1;
+                if (op == FUTEX_WAIT)
+                        timeout = timespec_to_jiffies(&t) + 1;
+                else {
+                        timeout = t.tv_sec;
+                        val2 = t.tv_nsec;
+                }
         }
-        if (op >= FUTEX_REQUEUE)
+        if (op == FUTEX_REQUEUE || op == FUTEX_CMP_REQUEUE)
                 val2 = (int) (unsigned long) utime;
 
         return do_futex(uaddr, op, val, timeout, uaddr2, val2, val3);
diff --git a/kernel/rtmutex_common.h b/kernel/rtmutex_common.h
index e068024eeffc..9c75856e791e 100644
--- a/kernel/rtmutex_common.h
+++ b/kernel/rtmutex_common.h
@@ -112,4 +112,12 @@ static inline unsigned long rt_mutex_owner_pending(struct rt_mutex *lock)
         return (unsigned long)lock->owner & RT_MUTEX_OWNER_PENDING;
 }
 
+/*
+ * PI-futex support (proxy locking functions, etc.):
+ */
+extern struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock);
+extern void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
+                                       struct task_struct *proxy_owner);
+extern void rt_mutex_proxy_unlock(struct rt_mutex *lock,
+                                  struct task_struct *proxy_owner);
 #endif