[PATCH] pi-futex: futex code cleanups

We are pleased to announce "lightweight userspace priority inheritance" (PI)
support for futexes.  The following patchset and glibc patch implements it,
ontop of the robust-futexes patchset which is included in 2.6.16-mm1.

We are calling it lightweight for 3 reasons:

 - in the user-space fastpath a PI-enabled futex involves no kernel work
   (or any other PI complexity) at all.  No registration, no extra kernel
   calls - just pure fast atomic ops in userspace.

 - in the slowpath (in the lock-contention case), the system call and
   scheduling pattern is in fact better than that of normal futexes, due to
   the 'integrated' nature of FUTEX_LOCK_PI.  [more about that further down]

 - the in-kernel PI implementation is streamlined around the mutex
   abstraction, with strict rules that keep the implementation relatively
   simple: only a single owner may own a lock (i.e.  no read-write lock
   support), only the owner may unlock a lock, no recursive locking, etc.

  Priority Inheritance - why, oh why???
  -------------------------------------

Many of you heard the horror stories about the evil PI code circling Linux for
years, which makes no real sense at all and is only used by buggy applications
and which has horrible overhead.  Some of you have dreaded this very moment,
when someone actually submits working PI code ;-)

So why would we like to see PI support for futexes?

We'd like to see it done purely for technological reasons.  We dont think it's
a buggy concept, we think it's useful functionality to offer to applications,
which functionality cannot be achieved in other ways.  We also think it's the
right thing to do, and we think we've got the right arguments and the right
numbers to prove that.  We also believe that we can address all the
counter-arguments as well.  For these reasons (and the reasons outlined below)
we are submitting this patch-set for upstream kernel inclusion.

What are the benefits of PI?

  The short reply:
  ----------------

User-space PI helps achieving/improving determinism for user-space
applications.  In the best-case, it can help achieve determinism and
well-bound latencies.  Even in the worst-case, PI will improve the statistical
distribution of locking related application delays.

  The longer reply:
  -----------------

Firstly, sharing locks between multiple tasks is a common programming
technique that often cannot be replaced with lockless algorithms.  As we can
see it in the kernel [which is a quite complex program in itself], lockless
structures are rather the exception than the norm - the current ratio of
lockless vs.  locky code for shared data structures is somewhere between 1:10
and 1:100.  Lockless is hard, and the complexity of lockless algorithms often
endangers to ability to do robust reviews of said code.  I.e.  critical RT
apps often choose lock structures to protect critical data structures, instead
of lockless algorithms.  Furthermore, there are cases (like shared hardware,
or other resource limits) where lockless access is mathematically impossible.

Media players (such as Jack) are an example of reasonable application design
with multiple tasks (with multiple priority levels) sharing short-held locks:
for example, a highprio audio playback thread is combined with medium-prio
construct-audio-data threads and low-prio display-colory-stuff threads.  Add
video and decoding to the mix and we've got even more priority levels.

So once we accept that synchronization objects (locks) are an unavoidable fact
of life, and once we accept that multi-task userspace apps have a very fair
expectation of being able to use locks, we've got to think about how to offer
the option of a deterministic locking implementation to user-space.

Most of the technical counter-arguments against doing priority inheritance
only apply to kernel-space locks.  But user-space locks are different, there
we cannot disable interrupts or make the task non-preemptible in a critical
section, so the 'use spinlocks' argument does not apply (user-space spinlocks
have the same priority inversion problems as other user-space locking
constructs).  Fact is, pretty much the only technique that currently enables
good determinism for userspace locks (such as futex-based pthread mutexes) is
priority inheritance:

Currently (without PI), if a high-prio and a low-prio task shares a lock [this
is a quite common scenario for most non-trivial RT applications], even if all
critical sections are coded carefully to be deterministic (i.e.  all critical
sections are short in duration and only execute a limited number of
instructions), the kernel cannot guarantee any deterministic execution of the
high-prio task: any medium-priority task could preempt the low-prio task while
it holds the shared lock and executes the critical section, and could delay it
indefinitely.

  Implementation:
  ---------------

As mentioned before, the userspace fastpath of PI-enabled pthread mutexes
involves no kernel work at all - they behave quite similarly to normal
futex-based locks: a 0 value means unlocked, and a value==TID means locked.
(This is the same method as used by list-based robust futexes.) Userspace uses
atomic ops to lock/unlock these mutexes without entering the kernel.

To handle the slowpath, we have added two new futex ops:

  FUTEX_LOCK_PI
  FUTEX_UNLOCK_PI

If the lock-acquire fastpath fails, [i.e.  an atomic transition from 0 to TID
fails], then FUTEX_LOCK_PI is called.  The kernel does all the remaining work:
if there is no futex-queue attached to the futex address yet then the code
looks up the task that owns the futex [it has put its own TID into the futex
value], and attaches a 'PI state' structure to the futex-queue.  The pi_state
includes an rt-mutex, which is a PI-aware, kernel-based synchronization
object.  The 'other' task is made the owner of the rt-mutex, and the
FUTEX_WAITERS bit is atomically set in the futex value.  Then this task tries
to lock the rt-mutex, on which it blocks.  Once it returns, it has the mutex
acquired, and it sets the futex value to its own TID and returns.  Userspace
has no other work to perform - it now owns the lock, and futex value contains
FUTEX_WAITERS|TID.

If the unlock side fastpath succeeds, [i.e.  userspace manages to do a TID ->
0 atomic transition of the futex value], then no kernel work is triggered.

If the unlock fastpath fails (because the FUTEX_WAITERS bit is set), then
FUTEX_UNLOCK_PI is called, and the kernel unlocks the futex on the behalf of
userspace - and it also unlocks the attached pi_state->rt_mutex and thus wakes
up any potential waiters.

Note that under this approach, contrary to other PI-futex approaches, there is
no prior 'registration' of a PI-futex.  [which is not quite possible anyway,
due to existing ABI properties of pthread mutexes.]

Also, under this scheme, 'robustness' and 'PI' are two orthogonal properties
of futexes, and all four combinations are possible: futex, robust-futex,
PI-futex, robust+PI-futex.

  glibc support:
  --------------

Ulrich Drepper and Jakub Jelinek have written glibc support for PI-futexes
(and robust futexes), enabling robust and PI (PTHREAD_PRIO_INHERIT) POSIX
mutexes.  (PTHREAD_PRIO_PROTECT support will be added later on too, no
additional kernel changes are needed for that).  [NOTE: The glibc patch is
obviously inofficial and unsupported without matching upstream kernel
functionality.]

the patch-queue and the glibc patch can also be downloaded from:

  http://redhat.com/~mingo/PI-futex-patches/

Many thanks go to the people who helped us create this kernel feature: Steven
Rostedt, Esben Nielsen, Benedikt Spranger, Daniel Walker, John Cooper, Arjan
van de Ven, Oleg Nesterov and others.  Credits for related prior projects goes
to Dirk Grambow, Inaky Perez-Gonzalez, Bill Huey and many others.

Clean up the futex code, before adding more features to it:

 - use u32 as the futex field type - that's the ABI
 - use __user and pointers to u32 instead of unsigned long
 - code style / comment style cleanups
 - rename hash-bucket name from 'bh' to 'hb'.

I checked the pre and post futex.o object files to make sure this
patch has no code effects.

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>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Jakub Jelinek <jakub@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/futex.h

@@ -90,9 +90,8 @@ struct robust_list_head {
  */
 #define ROBUST_LIST_LIMIT	2048
 
-long do_futex(unsigned long uaddr, int op, int val,
-		unsigned long timeout, unsigned long uaddr2, int val2,
-		int val3);
+long do_futex(u32 __user *uaddr, int op, u32 val, unsigned long timeout,
+	      u32 __user *uaddr2, u32 val2, u32 val3);
 
 extern int handle_futex_death(u32 __user *uaddr, struct task_struct *curr);
 

include/linux/syscalls.h

@@ -174,9 +174,9 @@ asmlinkage long sys_waitid(int which, pid_t pid,
 			   int options, struct rusage __user *ru);
 asmlinkage long sys_waitpid(pid_t pid, int __user *stat_addr, int options);
 asmlinkage long sys_set_tid_address(int __user *tidptr);
-asmlinkage long sys_futex(u32 __user *uaddr, int op, int val,
+asmlinkage long sys_futex(u32 __user *uaddr, int op, u32 val,
 			struct timespec __user *utime, u32 __user *uaddr2,
-			int val3);
+			u32 val3);
 
 asmlinkage long sys_init_module(void __user *umod, unsigned long len,
 				const char __user *uargs);

kernel/futex.c

@@ -63,7 +63,7 @@ union futex_key {
 		int offset;
 	} shared;
 	struct {
-		unsigned long uaddr;
+		unsigned long address;
 		struct mm_struct *mm;
 		int offset;
 	} private;
@@ -87,13 +87,13 @@ struct futex_q {
 	struct list_head list;
 	wait_queue_head_t waiters;
 
-	/* Which hash list lock to use. */
+	/* Which hash list lock to use: */
 	spinlock_t *lock_ptr;
 
-	/* Key which the futex is hashed on. */
+	/* Key which the futex is hashed on: */
 	union futex_key key;
 
-	/* For fd, sigio sent using these. */
+	/* For fd, sigio sent using these: */
 	int fd;
 	struct file *filp;
 };
@@ -144,8 +144,9 @@ static inline int match_futex(union futex_key *key1, union futex_key *key2)
  *
  * Should be called with &current->mm->mmap_sem but NOT any spinlocks.
  */
-static int get_futex_key(unsigned long uaddr, union futex_key *key)
+static int get_futex_key(u32 __user *uaddr, union futex_key *key)
 {
+	unsigned long address = (unsigned long)uaddr;
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma;
 	struct page *page;
@@ -154,16 +155,16 @@ static int get_futex_key(unsigned long uaddr, union futex_key *key)
 	/*
 	 * The futex address must be "naturally" aligned.
 	 */
-	key->both.offset = uaddr % PAGE_SIZE;
+	key->both.offset = address % PAGE_SIZE;
 	if (unlikely((key->both.offset % sizeof(u32)) != 0))
 		return -EINVAL;
-	uaddr -= key->both.offset;
+	address -= key->both.offset;
 
 	/*
 	 * The futex is hashed differently depending on whether
 	 * it's in a shared or private mapping.  So check vma first.
 	 */
-	vma = find_extend_vma(mm, uaddr);
+	vma = find_extend_vma(mm, address);
 	if (unlikely(!vma))
 		return -EFAULT;
 
@@ -184,7 +185,7 @@ static int get_futex_key(unsigned long uaddr, union futex_key *key)
 	 */
 	if (likely(!(vma->vm_flags & VM_MAYSHARE))) {
 		key->private.mm = mm;
-		key->private.uaddr = uaddr;
+		key->private.address = address;
 		return 0;
 	}
 
@@ -194,7 +195,7 @@ static int get_futex_key(unsigned long uaddr, union futex_key *key)
 	key->shared.inode = vma->vm_file->f_dentry->d_inode;
 	key->both.offset++; /* Bit 0 of offset indicates inode-based key. */
 	if (likely(!(vma->vm_flags & VM_NONLINEAR))) {
-		key->shared.pgoff = (((uaddr - vma->vm_start) >> PAGE_SHIFT)
+		key->shared.pgoff = (((address - vma->vm_start) >> PAGE_SHIFT)
 				     + vma->vm_pgoff);
 		return 0;
 	}
@@ -205,7 +206,7 @@ static int get_futex_key(unsigned long uaddr, union futex_key *key)
 	 * from swap.  But that's a lot of code to duplicate here
 	 * for a rare case, so we simply fetch the page.
 	 */
-	err = get_user_pages(current, mm, uaddr, 1, 0, 0, &page, NULL);
+	err = get_user_pages(current, mm, address, 1, 0, 0, &page, NULL);
 	if (err >= 0) {
 		key->shared.pgoff =
 			page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
@@ -246,12 +247,12 @@ static void drop_key_refs(union futex_key *key)
 	}
 }
 
-static inline int get_futex_value_locked(int *dest, int __user *from)
+static inline int get_futex_value_locked(u32 *dest, u32 __user *from)
 {
 	int ret;
 
 	inc_preempt_count();
-	ret = __copy_from_user_inatomic(dest, from, sizeof(int));
+	ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
 	dec_preempt_count();
 
 	return ret ? -EFAULT : 0;
@@ -288,12 +289,12 @@ static void wake_futex(struct futex_q *q)
  * Wake up all waiters hashed on the physical page that is mapped
  * to this virtual address:
  */
-static int futex_wake(unsigned long uaddr, int nr_wake)
+static int futex_wake(u32 __user *uaddr, int nr_wake)
 {
-	union futex_key key;
-	struct futex_hash_bucket *bh;
-	struct list_head *head;
+	struct futex_hash_bucket *hb;
 	struct futex_q *this, *next;
+	struct list_head *head;
+	union futex_key key;
 	int ret;
 
 	down_read(&current->mm->mmap_sem);
@@ -302,9 +303,9 @@ static int futex_wake(unsigned long uaddr, int nr_wake)
 	if (unlikely(ret != 0))
 		goto out;
 
-	bh = hash_futex(&key);
-	spin_lock(&bh->lock);
-	head = &bh->chain;
+	hb = hash_futex(&key);
+	spin_lock(&hb->lock);
+	head = &hb->chain;
 
 	list_for_each_entry_safe(this, next, head, list) {
 		if (match_futex (&this->key, &key)) {
@@ -314,7 +315,7 @@ static int futex_wake(unsigned long uaddr, int nr_wake)
 		}
 	}
 
-	spin_unlock(&bh->lock);
+	spin_unlock(&hb->lock);
 out:
 	up_read(&current->mm->mmap_sem);
 	return ret;
@@ -324,10 +325,12 @@ out:
  * Wake up all waiters hashed on the physical page that is mapped
  * to this virtual address:
  */
-static int futex_wake_op(unsigned long uaddr1, unsigned long uaddr2, int nr_wake, int nr_wake2, int op)
+static int
+futex_wake_op(u32 __user *uaddr1, u32 __user *uaddr2,
+	      int nr_wake, int nr_wake2, int op)
 {
 	union futex_key key1, key2;
-	struct futex_hash_bucket *bh1, *bh2;
+	struct futex_hash_bucket *hb1, *hb2;
 	struct list_head *head;
 	struct futex_q *this, *next;
 	int ret, op_ret, attempt = 0;
@@ -342,27 +345,29 @@ retryfull:
 	if (unlikely(ret != 0))
 		goto out;
 
-	bh1 = hash_futex(&key1);
-	bh2 = hash_futex(&key2);
+	hb1 = hash_futex(&key1);
+	hb2 = hash_futex(&key2);
 
 retry:
-	if (bh1 < bh2)
-		spin_lock(&bh1->lock);
-	spin_lock(&bh2->lock);
-	if (bh1 > bh2)
-		spin_lock(&bh1->lock);
+	if (hb1 < hb2)
+		spin_lock(&hb1->lock);
+	spin_lock(&hb2->lock);
+	if (hb1 > hb2)
+		spin_lock(&hb1->lock);
 
-	op_ret = futex_atomic_op_inuser(op, (int __user *)uaddr2);
+	op_ret = futex_atomic_op_inuser(op, uaddr2);
 	if (unlikely(op_ret < 0)) {
-		int dummy;
+		u32 dummy;
 
-		spin_unlock(&bh1->lock);
-		if (bh1 != bh2)
-			spin_unlock(&bh2->lock);
+		spin_unlock(&hb1->lock);
+		if (hb1 != hb2)
+			spin_unlock(&hb2->lock);
 
 #ifndef CONFIG_MMU
-		/* we don't get EFAULT from MMU faults if we don't have an MMU,
-		 * but we might get them from range checking */
+		/*
+		 * we don't get EFAULT from MMU faults if we don't have an MMU,
+		 * but we might get them from range checking
+		 */
 		ret = op_ret;
 		goto out;
 #endif
@@ -372,23 +377,26 @@ retry:
 			goto out;
 		}
 
-		/* futex_atomic_op_inuser needs to both read and write
+		/*
+		 * futex_atomic_op_inuser needs to both read and write
 		 * *(int __user *)uaddr2, 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.  */
+		 * 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, uaddr2)) ||
-			    vma->vm_start > uaddr2 ||
+			    !(vma = find_vma(mm, address)) ||
+			    vma->vm_start > address ||
 			    !(vma->vm_flags & VM_WRITE))
 				goto out;
 
-			switch (handle_mm_fault(mm, vma, uaddr2, 1)) {
+			switch (handle_mm_fault(mm, vma, address, 1)) {
 			case VM_FAULT_MINOR:
 				current->min_flt++;
 				break;
@@ -401,18 +409,20 @@ retry:
 			goto retry;
 		}
 
-		/* If we would have faulted, release mmap_sem,
-		 * fault it in and start all over again.  */
+		/*
+		 * 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(dummy, (int __user *)uaddr2);
+		ret = get_user(dummy, uaddr2);
 		if (ret)
 			return ret;
 
 		goto retryfull;
 	}
 
-	head = &bh1->chain;
+	head = &hb1->chain;
 
 	list_for_each_entry_safe(this, next, head, list) {
 		if (match_futex (&this->key, &key1)) {
@@ -423,7 +433,7 @@ retry:
 	}
 
 	if (op_ret > 0) {
-		head = &bh2->chain;
+		head = &hb2->chain;
 
 		op_ret = 0;
 		list_for_each_entry_safe(this, next, head, list) {
@@ -436,9 +446,9 @@ retry:
 		ret += op_ret;
 	}
 
-	spin_unlock(&bh1->lock);
-	if (bh1 != bh2)
-		spin_unlock(&bh2->lock);
+	spin_unlock(&hb1->lock);
+	if (hb1 != hb2)
+		spin_unlock(&hb2->lock);
 out:
 	up_read(&current->mm->mmap_sem);
 	return ret;
@@ -448,11 +458,11 @@ out:
  * Requeue all waiters hashed on one physical page to another
  * physical page.
  */
-static int futex_requeue(unsigned long uaddr1, unsigned long uaddr2,
-			 int nr_wake, int nr_requeue, int *valp)
+static int futex_requeue(u32 __user *uaddr1, u32 __user *uaddr2,
+			 int nr_wake, int nr_requeue, u32 *cmpval)
 {
 	union futex_key key1, key2;
-	struct futex_hash_bucket *bh1, *bh2;
+	struct futex_hash_bucket *hb1, *hb2;
 	struct list_head *head1;
 	struct futex_q *this, *next;
 	int ret, drop_count = 0;
@@ -467,68 +477,69 @@ static int futex_requeue(unsigned long uaddr1, unsigned long uaddr2,
 	if (unlikely(ret != 0))
 		goto out;
 
-	bh1 = hash_futex(&key1);
-	bh2 = hash_futex(&key2);
+	hb1 = hash_futex(&key1);
+	hb2 = hash_futex(&key2);
 
-	if (bh1 < bh2)
-		spin_lock(&bh1->lock);
-	spin_lock(&bh2->lock);
-	if (bh1 > bh2)
-		spin_lock(&bh1->lock);
+	if (hb1 < hb2)
+		spin_lock(&hb1->lock);
+	spin_lock(&hb2->lock);
+	if (hb1 > hb2)
+		spin_lock(&hb1->lock);
 
-	if (likely(valp != NULL)) {
-		int curval;
+	if (likely(cmpval != NULL)) {
+		u32 curval;
 
-		ret = get_futex_value_locked(&curval, (int __user *)uaddr1);
+		ret = get_futex_value_locked(&curval, uaddr1);
 
 		if (unlikely(ret)) {
-			spin_unlock(&bh1->lock);
-			if (bh1 != bh2)
-				spin_unlock(&bh2->lock);
+			spin_unlock(&hb1->lock);
+			if (hb1 != hb2)
+				spin_unlock(&hb2->lock);
 
-			/* If we would have faulted, release mmap_sem, fault
+			/*
+			 * 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, (int __user *)uaddr1);
+			ret = get_user(curval, uaddr1);
 
 			if (!ret)
 				goto retry;
 
 			return ret;
 		}
-		if (curval != *valp) {
+		if (curval != *cmpval) {
 			ret = -EAGAIN;
 			goto out_unlock;
 		}
 	}
 
-	head1 = &bh1->chain;
+	head1 = &hb1->chain;
 	list_for_each_entry_safe(this, next, head1, list) {
 		if (!match_futex (&this->key, &key1))
 			continue;
 		if (++ret <= nr_wake) {
 			wake_futex(this);
 		} else {
-			list_move_tail(&this->list, &bh2->chain);
-			this->lock_ptr = &bh2->lock;
+			list_move_tail(&this->list, &hb2->chain);
+			this->lock_ptr = &hb2->lock;
 			this->key = key2;
 			get_key_refs(&key2);
 			drop_count++;
 
 			if (ret - nr_wake >= nr_requeue)
 				break;
-			/* Make sure to stop if key1 == key2 */
-			if (head1 == &bh2->chain && head1 != &next->list)
+			/* Make sure to stop if key1 == key2: */
+			if (head1 == &hb2->chain && head1 != &next->list)
 				head1 = &this->list;
 		}
 	}
 
 out_unlock:
-	spin_unlock(&bh1->lock);
-	if (bh1 != bh2)
-		spin_unlock(&bh2->lock);
+	spin_unlock(&hb1->lock);
+	if (hb1 != hb2)
+		spin_unlock(&hb2->lock);
 
 	/* drop_key_refs() must be called outside the spinlocks. */
 	while (--drop_count >= 0)
@@ -543,7 +554,7 @@ out:
 static inline struct futex_hash_bucket *
 queue_lock(struct futex_q *q, int fd, struct file *filp)
 {
-	struct futex_hash_bucket *bh;
+	struct futex_hash_bucket *hb;
 
 	q->fd = fd;
 	q->filp = filp;
@@ -551,23 +562,23 @@ queue_lock(struct futex_q *q, int fd, struct file *filp)
 	init_waitqueue_head(&q->waiters);
 
 	get_key_refs(&q->key);
-	bh = hash_futex(&q->key);
-	q->lock_ptr = &bh->lock;
+	hb = hash_futex(&q->key);
+	q->lock_ptr = &hb->lock;
 
-	spin_lock(&bh->lock);
-	return bh;
+	spin_lock(&hb->lock);
+	return hb;
 }
 
-static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *bh)
+static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
 {
-	list_add_tail(&q->list, &bh->chain);
-	spin_unlock(&bh->lock);
+	list_add_tail(&q->list, &hb->chain);
+	spin_unlock(&hb->lock);
 }
 
 static inline void
-queue_unlock(struct futex_q *q, struct futex_hash_bucket *bh)
+queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
 {
-	spin_unlock(&bh->lock);
+	spin_unlock(&hb->lock);
 	drop_key_refs(&q->key);
 }
 
@@ -579,16 +590,17 @@ queue_unlock(struct futex_q *q, struct futex_hash_bucket *bh)
 /* The key must be already stored in q->key. */
 static void queue_me(struct futex_q *q, int fd, struct file *filp)
 {
-	struct futex_hash_bucket *bh;
-	bh = queue_lock(q, fd, filp);
-	__queue_me(q, bh);
+	struct futex_hash_bucket *hb;
+
+	hb = queue_lock(q, fd, filp);
+	__queue_me(q, hb);
 }
 
 /* Return 1 if we were still queued (ie. 0 means we were woken) */
 static int unqueue_me(struct futex_q *q)
 {
-	int ret = 0;
 	spinlock_t *lock_ptr;
+	int ret = 0;
 
 	/* In the common case we don't take the spinlock, which is nice. */
  retry:
@@ -622,12 +634,13 @@ static int unqueue_me(struct futex_q *q)
 	return ret;
 }
 
-static int futex_wait(unsigned long uaddr, int val, unsigned long time)
+static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time)
 {
 	DECLARE_WAITQUEUE(wait, current);
-	int ret, curval;
+	struct futex_hash_bucket *hb;
 	struct futex_q q;
-	struct futex_hash_bucket *bh;
+	u32 uval;
+	int ret;
 
  retry:
 	down_read(&current->mm->mmap_sem);
@@ -636,7 +649,7 @@ static int futex_wait(unsigned long uaddr, int val, unsigned long time)
 	if (unlikely(ret != 0))
 		goto out_release_sem;
 
-	bh = queue_lock(&q, -1, NULL);
+	hb = queue_lock(&q, -1, NULL);
 
 	/*
 	 * Access the page AFTER the futex is queued.
@@ -658,31 +671,31 @@ static int futex_wait(unsigned long uaddr, int val, unsigned long time)
 	 * We hold the mmap semaphore, so the mapping cannot have changed
 	 * since we looked it up in get_futex_key.
 	 */
-
-	ret = get_futex_value_locked(&curval, (int __user *)uaddr);
+	ret = get_futex_value_locked(&uval, uaddr);
 
 	if (unlikely(ret)) {
-		queue_unlock(&q, bh);
+		queue_unlock(&q, hb);
 
-		/* If we would have faulted, release mmap_sem, fault it in and
+		/*
+		 * 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, (int __user *)uaddr);
+		ret = get_user(uval, uaddr);
 
 		if (!ret)
 			goto retry;
 		return ret;
 	}
-	if (curval != val) {
+	if (uval != val) {
 		ret = -EWOULDBLOCK;
-		queue_unlock(&q, bh);
+		queue_unlock(&q, hb);
 		goto out_release_sem;
 	}
 
 	/* Only actually queue if *uaddr contained val.  */
-	__queue_me(&q, bh);
+	__queue_me(&q, hb);
 
 	/*
 	 * Now the futex is queued and we have checked the data, we
@@ -720,8 +733,10 @@ static int futex_wait(unsigned long uaddr, int val, unsigned long time)
 		return 0;
 	if (time == 0)
 		return -ETIMEDOUT;
-	/* We expect signal_pending(current), but another thread may
-	 * have handled it for us already. */
+	/*
+	 * We expect signal_pending(current), but another thread may
+	 * have handled it for us already.
+	 */
 	return -EINTR;
 
  out_release_sem:
@@ -735,6 +750,7 @@ static int futex_close(struct inode *inode, struct file *filp)
 
 	unqueue_me(q);
 	kfree(q);
+
 	return 0;
 }
 
@@ -766,7 +782,7 @@ static struct file_operations futex_fops = {
  * Signal allows caller to avoid the race which would occur if they
  * set the sigio stuff up afterwards.
  */
-static int futex_fd(unsigned long uaddr, int signal)
+static int futex_fd(u32 __user *uaddr, int signal)
 {
 	struct futex_q *q;
 	struct file *filp;
@@ -937,7 +953,7 @@ retry:
 			goto retry;
 
 		if (uval & FUTEX_WAITERS)
-			futex_wake((unsigned long)uaddr, 1);
+			futex_wake(uaddr, 1);
 	}
 	return 0;
 }
@@ -999,8 +1015,8 @@ void exit_robust_list(struct task_struct *curr)
 	}
 }
 
-long do_futex(unsigned long uaddr, int op, int val, unsigned long timeout,
-		unsigned long uaddr2, int val2, int val3)
+long do_futex(u32 __user *uaddr, int op, u32 val, unsigned long timeout,
+		u32 __user *uaddr2, u32 val2, u32 val3)
 {
 	int ret;
 
@@ -1031,13 +1047,13 @@ long do_futex(unsigned long uaddr, int op, int val, unsigned long timeout,
 }
 
 
-asmlinkage long sys_futex(u32 __user *uaddr, int op, int val,
+asmlinkage long sys_futex(u32 __user *uaddr, int op, u32 val,
 			  struct timespec __user *utime, u32 __user *uaddr2,
-			  int val3)
+			  u32 val3)
 {
 	struct timespec t;
 	unsigned long timeout = MAX_SCHEDULE_TIMEOUT;
-	int val2 = 0;
+	u32 val2 = 0;
 
 	if (utime && (op == FUTEX_WAIT)) {
 		if (copy_from_user(&t, utime, sizeof(t)) != 0)
@@ -1050,10 +1066,9 @@ asmlinkage long sys_futex(u32 __user *uaddr, int op, int val,
 	 * requeue parameter in 'utime' if op == FUTEX_REQUEUE.
 	 */
 	if (op >= FUTEX_REQUEUE)
-		val2 = (int) (unsigned long) utime;
+		val2 = (u32) (unsigned long) utime;
 
-	return do_futex((unsigned long)uaddr, op, val, timeout,
-			(unsigned long)uaddr2, val2, val3);
+	return do_futex(uaddr, op, val, timeout, uaddr2, val2, val3);
 }
 
 static int futexfs_get_sb(struct file_system_type *fs_type,

kernel/futex_compat.c

@@ -139,6 +139,5 @@ asmlinkage long compat_sys_futex(u32 __user *uaddr, int op, u32 val,
 	if (op >= FUTEX_REQUEUE)
 		val2 = (int) (unsigned long) utime;
 
-	return do_futex((unsigned long)uaddr, op, val, timeout,
-			(unsigned long)uaddr2, val2, val3);
+	return do_futex(uaddr, op, val, timeout, uaddr2, val2, val3);
 }