Linux-2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

kernel/futex.c

@@ -0,0 +1,798 @@
+/*
+ *  Fast Userspace Mutexes (which I call "Futexes!").
+ *  (C) Rusty Russell, IBM 2002
+ *
+ *  Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
+ *  (C) Copyright 2003 Red Hat Inc, All Rights Reserved
+ *
+ *  Removed page pinning, fix privately mapped COW pages and other cleanups
+ *  (C) Copyright 2003, 2004 Jamie Lokier
+ *
+ *  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.
+ *
+ *  "The futexes are also cursed."
+ *  "But they come in a choice of three flavours!"
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, write to the Free Software
+ *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+#include <linux/slab.h>
+#include <linux/poll.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/jhash.h>
+#include <linux/init.h>
+#include <linux/futex.h>
+#include <linux/mount.h>
+#include <linux/pagemap.h>
+#include <linux/syscalls.h>
+
+#define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
+
+/*
+ * Futexes are matched on equal values of this key.
+ * The key type depends on whether it's a shared or private mapping.
+ * Don't rearrange members without looking at hash_futex().
+ *
+ * offset is aligned to a multiple of sizeof(u32) (== 4) by definition.
+ * We set bit 0 to indicate if it's an inode-based key.
+ */
+union futex_key {
+	struct {
+		unsigned long pgoff;
+		struct inode *inode;
+		int offset;
+	} shared;
+	struct {
+		unsigned long uaddr;
+		struct mm_struct *mm;
+		int offset;
+	} private;
+	struct {
+		unsigned long word;
+		void *ptr;
+		int offset;
+	} both;
+};
+
+/*
+ * 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).
+ *
+ * A futex_q has a woken state, just like tasks have TASK_RUNNING.
+ * It is considered woken when list_empty(&q->list) || q->lock_ptr == 0.
+ * The order of wakup is always to make the first condition true, then
+ * wake up q->waiters, then make the second condition true.
+ */
+struct futex_q {
+	struct list_head list;
+	wait_queue_head_t waiters;
+
+	/* Which hash list lock to use. */
+	spinlock_t *lock_ptr;
+
+	/* Key which the futex is hashed on. */
+	union futex_key key;
+
+	/* For fd, sigio sent using these. */
+	int fd;
+	struct file *filp;
+};
+
+/*
+ * Split the global futex_lock into every hash list lock.
+ */
+struct futex_hash_bucket {
+       spinlock_t              lock;
+       struct list_head       chain;
+};
+
+static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
+
+/* Futex-fs vfsmount entry: */
+static struct vfsmount *futex_mnt;
+
+/*
+ * We hash on the keys returned from get_futex_key (see below).
+ */
+static struct futex_hash_bucket *hash_futex(union futex_key *key)
+{
+	u32 hash = jhash2((u32*)&key->both.word,
+			  (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
+			  key->both.offset);
+	return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
+}
+
+/*
+ * Return 1 if two futex_keys are equal, 0 otherwise.
+ */
+static inline int match_futex(union futex_key *key1, union futex_key *key2)
+{
+	return (key1->both.word == key2->both.word
+		&& key1->both.ptr == key2->both.ptr
+		&& key1->both.offset == key2->both.offset);
+}
+
+/*
+ * Get parameters which are the keys for a futex.
+ *
+ * For shared mappings, it's (page->index, vma->vm_file->f_dentry->d_inode,
+ * offset_within_page).  For private mappings, it's (uaddr, current->mm).
+ * We can usually work out the index without swapping in the page.
+ *
+ * Returns: 0, or negative error code.
+ * The key words are stored in *key on success.
+ *
+ * Should be called with &current->mm->mmap_sem but NOT any spinlocks.
+ */
+static int get_futex_key(unsigned long uaddr, union futex_key *key)
+{
+	struct mm_struct *mm = current->mm;
+	struct vm_area_struct *vma;
+	struct page *page;
+	int err;
+
+	/*
+	 * The futex address must be "naturally" aligned.
+	 */
+	key->both.offset = uaddr % PAGE_SIZE;
+	if (unlikely((key->both.offset % sizeof(u32)) != 0))
+		return -EINVAL;
+	uaddr -= 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);
+	if (unlikely(!vma))
+		return -EFAULT;
+
+	/*
+	 * Permissions.
+	 */
+	if (unlikely((vma->vm_flags & (VM_IO|VM_READ)) != VM_READ))
+		return (vma->vm_flags & VM_IO) ? -EPERM : -EACCES;
+
+	/*
+	 * Private mappings are handled in a simple way.
+	 *
+	 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
+	 * it's a read-only handle, it's expected that futexes attach to
+	 * the object not the particular process.  Therefore we use
+	 * VM_MAYSHARE here, not VM_SHARED which is restricted to shared
+	 * mappings of _writable_ handles.
+	 */
+	if (likely(!(vma->vm_flags & VM_MAYSHARE))) {
+		key->private.mm = mm;
+		key->private.uaddr = uaddr;
+		return 0;
+	}
+
+	/*
+	 * Linear file mappings are also simple.
+	 */
+	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)
+				     + vma->vm_pgoff);
+		return 0;
+	}
+
+	/*
+	 * We could walk the page table to read the non-linear
+	 * pte, and get the page index without fetching the page
+	 * from swap.  But that's a lot of code to duplicate here
+	 * for a rare case, so we simply fetch the page.
+	 */
+
+	/*
+	 * Do a quick atomic lookup first - this is the fastpath.
+	 */
+	spin_lock(&current->mm->page_table_lock);
+	page = follow_page(mm, uaddr, 0);
+	if (likely(page != NULL)) {
+		key->shared.pgoff =
+			page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
+		spin_unlock(&current->mm->page_table_lock);
+		return 0;
+	}
+	spin_unlock(&current->mm->page_table_lock);
+
+	/*
+	 * Do it the general way.
+	 */
+	err = get_user_pages(current, mm, uaddr, 1, 0, 0, &page, NULL);
+	if (err >= 0) {
+		key->shared.pgoff =
+			page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
+		put_page(page);
+		return 0;
+	}
+	return err;
+}
+
+/*
+ * Take a reference to the resource addressed by a key.
+ * Can be called while holding spinlocks.
+ *
+ * NOTE: mmap_sem MUST be held between get_futex_key() and calling this
+ * function, if it is called at all.  mmap_sem keeps key->shared.inode valid.
+ */
+static inline void get_key_refs(union futex_key *key)
+{
+	if (key->both.ptr != 0) {
+		if (key->both.offset & 1)
+			atomic_inc(&key->shared.inode->i_count);
+		else
+			atomic_inc(&key->private.mm->mm_count);
+	}
+}
+
+/*
+ * Drop a reference to the resource addressed by a key.
+ * The hash bucket spinlock must not be held.
+ */
+static void drop_key_refs(union futex_key *key)
+{
+	if (key->both.ptr != 0) {
+		if (key->both.offset & 1)
+			iput(key->shared.inode);
+		else
+			mmdrop(key->private.mm);
+	}
+}
+
+static inline int get_futex_value_locked(int *dest, int __user *from)
+{
+	int ret;
+
+	inc_preempt_count();
+	ret = __copy_from_user_inatomic(dest, from, sizeof(int));
+	dec_preempt_count();
+
+	return ret ? -EFAULT : 0;
+}
+
+/*
+ * The hash bucket lock must be held when this is called.
+ * Afterwards, the futex_q must not be accessed.
+ */
+static void wake_futex(struct futex_q *q)
+{
+	list_del_init(&q->list);
+	if (q->filp)
+		send_sigio(&q->filp->f_owner, q->fd, POLL_IN);
+	/*
+	 * The lock in wake_up_all() is a crucial memory barrier after the
+	 * list_del_init() and also before assigning to q->lock_ptr.
+	 */
+	wake_up_all(&q->waiters);
+	/*
+	 * The waiting task can free the futex_q as soon as this is written,
+	 * without taking any locks.  This must come last.
+	 */
+	q->lock_ptr = NULL;
+}
+
+/*
+ * 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)
+{
+	union futex_key key;
+	struct futex_hash_bucket *bh;
+	struct list_head *head;
+	struct futex_q *this, *next;
+	int ret;
+
+	down_read(&current->mm->mmap_sem);
+
+	ret = get_futex_key(uaddr, &key);
+	if (unlikely(ret != 0))
+		goto out;
+
+	bh = hash_futex(&key);
+	spin_lock(&bh->lock);
+	head = &bh->chain;
+
+	list_for_each_entry_safe(this, next, head, list) {
+		if (match_futex (&this->key, &key)) {
+			wake_futex(this);
+			if (++ret >= nr_wake)
+				break;
+		}
+	}
+
+	spin_unlock(&bh->lock);
+out:
+	up_read(&current->mm->mmap_sem);
+	return ret;
+}
+
+/*
+ * 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)
+{
+	union futex_key key1, key2;
+	struct futex_hash_bucket *bh1, *bh2;
+	struct list_head *head1;
+	struct futex_q *this, *next;
+	int ret, drop_count = 0;
+
+ retry:
+	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;
+
+	bh1 = hash_futex(&key1);
+	bh2 = hash_futex(&key2);
+
+	if (bh1 < bh2)
+		spin_lock(&bh1->lock);
+	spin_lock(&bh2->lock);
+	if (bh1 > bh2)
+		spin_lock(&bh1->lock);
+
+	if (likely(valp != NULL)) {
+		int curval;
+
+		ret = get_futex_value_locked(&curval, (int __user *)uaddr1);
+
+		if (unlikely(ret)) {
+			spin_unlock(&bh1->lock);
+			if (bh1 != bh2)
+				spin_unlock(&bh2->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, (int __user *)uaddr1);
+
+			if (!ret)
+				goto retry;
+
+			return ret;
+		}
+		if (curval != *valp) {
+			ret = -EAGAIN;
+			goto out_unlock;
+		}
+	}
+
+	head1 = &bh1->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;
+			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)
+				head1 = &this->list;
+		}
+	}
+
+out_unlock:
+	spin_unlock(&bh1->lock);
+	if (bh1 != bh2)
+		spin_unlock(&bh2->lock);
+
+	/* drop_key_refs() must be called outside the spinlocks. */
+	while (--drop_count >= 0)
+		drop_key_refs(&key1);
+
+out:
+	up_read(&current->mm->mmap_sem);
+	return ret;
+}
+
+/* The key must be already stored in q->key. */
+static inline struct futex_hash_bucket *
+queue_lock(struct futex_q *q, int fd, struct file *filp)
+{
+	struct futex_hash_bucket *bh;
+
+	q->fd = fd;
+	q->filp = filp;
+
+	init_waitqueue_head(&q->waiters);
+
+	get_key_refs(&q->key);
+	bh = hash_futex(&q->key);
+	q->lock_ptr = &bh->lock;
+
+	spin_lock(&bh->lock);
+	return bh;
+}
+
+static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *bh)
+{
+	list_add_tail(&q->list, &bh->chain);
+	spin_unlock(&bh->lock);
+}
+
+static inline void
+queue_unlock(struct futex_q *q, struct futex_hash_bucket *bh)
+{
+	spin_unlock(&bh->lock);
+	drop_key_refs(&q->key);
+}
+
+/*
+ * queue_me and unqueue_me must be called as a pair, each
+ * exactly once.  They are called with the hashed spinlock held.
+ */
+
+/* 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);
+}
+
+/* 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;
+
+	/* In the common case we don't take the spinlock, which is nice. */
+ retry:
+	lock_ptr = q->lock_ptr;
+	if (lock_ptr != 0) {
+		spin_lock(lock_ptr);
+		/*
+		 * q->lock_ptr can change between reading it and
+		 * spin_lock(), causing us to take the wrong lock.  This
+		 * corrects the race condition.
+		 *
+		 * Reasoning goes like this: if we have the wrong lock,
+		 * q->lock_ptr must have changed (maybe several times)
+		 * between reading it and the spin_lock().  It can
+		 * change again after the spin_lock() but only if it was
+		 * already changed before the spin_lock().  It cannot,
+		 * however, change back to the original value.  Therefore
+		 * we can detect whether we acquired the correct lock.
+		 */
+		if (unlikely(lock_ptr != q->lock_ptr)) {
+			spin_unlock(lock_ptr);
+			goto retry;
+		}
+		WARN_ON(list_empty(&q->list));
+		list_del(&q->list);
+		spin_unlock(lock_ptr);
+		ret = 1;
+	}
+
+	drop_key_refs(&q->key);
+	return ret;
+}
+
+static int futex_wait(unsigned long uaddr, int val, unsigned long time)
+{
+	DECLARE_WAITQUEUE(wait, current);
+	int ret, curval;
+	struct futex_q q;
+	struct futex_hash_bucket *bh;
+
+ retry:
+	down_read(&current->mm->mmap_sem);
+
+	ret = get_futex_key(uaddr, &q.key);
+	if (unlikely(ret != 0))
+		goto out_release_sem;
+
+	bh = queue_lock(&q, -1, NULL);
+
+	/*
+	 * Access the page AFTER the futex is queued.
+	 * Order is important:
+	 *
+	 *   Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
+	 *   Userspace waker:  if (cond(var)) { var = new; futex_wake(&var); }
+	 *
+	 * The basic logical guarantee of a futex is that it blocks ONLY
+	 * if cond(var) is known to be true at the time of blocking, for
+	 * any cond.  If we queued after testing *uaddr, that would open
+	 * a race condition where we could block indefinitely with
+	 * cond(var) false, which would violate the guarantee.
+	 *
+	 * A consequence is that futex_wait() can return zero and absorb
+	 * a wakeup when *uaddr != val on entry to the syscall.  This is
+	 * rare, but normal.
+	 *
+	 * 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);
+
+	if (unlikely(ret)) {
+		queue_unlock(&q, bh);
+
+		/* 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);
+
+		if (!ret)
+			goto retry;
+		return ret;
+	}
+	if (curval != val) {
+		ret = -EWOULDBLOCK;
+		queue_unlock(&q, bh);
+		goto out_release_sem;
+	}
+
+	/* Only actually queue if *uaddr contained val.  */
+	__queue_me(&q, bh);
+
+	/*
+	 * 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);
+
+	/*
+	 * There might have been scheduling since the queue_me(), as we
+	 * cannot hold a spinlock across the get_user() in case it
+	 * faults, and we cannot just set TASK_INTERRUPTIBLE state when
+	 * queueing ourselves into the futex hash.  This code thus has to
+	 * rely on the futex_wake() code removing us from hash when it
+	 * wakes us up.
+	 */
+
+	/* add_wait_queue is the barrier after __set_current_state. */
+	__set_current_state(TASK_INTERRUPTIBLE);
+	add_wait_queue(&q.waiters, &wait);
+	/*
+	 * !list_empty() is safe here without any lock.
+	 * q.lock_ptr != 0 is not safe, because of ordering against wakeup.
+	 */
+	if (likely(!list_empty(&q.list)))
+		time = schedule_timeout(time);
+	__set_current_state(TASK_RUNNING);
+
+	/*
+	 * NOTE: we don't remove ourselves from the waitqueue because
+	 * we are the only user of it.
+	 */
+
+	/* If we were woken (and unqueued), we succeeded, whatever. */
+	if (!unqueue_me(&q))
+		return 0;
+	if (time == 0)
+		return -ETIMEDOUT;
+	/* We expect signal_pending(current), but another thread may
+	 * have handled it for us already. */
+	return -EINTR;
+
+ out_release_sem:
+	up_read(&current->mm->mmap_sem);
+	return ret;
+}
+
+static int futex_close(struct inode *inode, struct file *filp)
+{
+	struct futex_q *q = filp->private_data;
+
+	unqueue_me(q);
+	kfree(q);
+	return 0;
+}
+
+/* This is one-shot: once it's gone off you need a new fd */
+static unsigned int futex_poll(struct file *filp,
+			       struct poll_table_struct *wait)
+{
+	struct futex_q *q = filp->private_data;
+	int ret = 0;
+
+	poll_wait(filp, &q->waiters, wait);
+
+	/*
+	 * list_empty() is safe here without any lock.
+	 * q->lock_ptr != 0 is not safe, because of ordering against wakeup.
+	 */
+	if (list_empty(&q->list))
+		ret = POLLIN | POLLRDNORM;
+
+	return ret;
+}
+
+static struct file_operations futex_fops = {
+	.release	= futex_close,
+	.poll		= futex_poll,
+};
+
+/*
+ * 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)
+{
+	struct futex_q *q;
+	struct file *filp;
+	int ret, err;
+
+	ret = -EINVAL;
+	if (signal < 0 || signal > _NSIG)
+		goto out;
+
+	ret = get_unused_fd();
+	if (ret < 0)
+		goto out;
+	filp = get_empty_filp();
+	if (!filp) {
+		put_unused_fd(ret);
+		ret = -ENFILE;
+		goto out;
+	}
+	filp->f_op = &futex_fops;
+	filp->f_vfsmnt = mntget(futex_mnt);
+	filp->f_dentry = dget(futex_mnt->mnt_root);
+	filp->f_mapping = filp->f_dentry->d_inode->i_mapping;
+
+	if (signal) {
+		int err;
+		err = f_setown(filp, current->pid, 1);
+		if (err < 0) {
+			put_unused_fd(ret);
+			put_filp(filp);
+			ret = err;
+			goto out;
+		}
+		filp->f_owner.signum = signal;
+	}
+
+	q = kmalloc(sizeof(*q), GFP_KERNEL);
+	if (!q) {
+		put_unused_fd(ret);
+		put_filp(filp);
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	down_read(&current->mm->mmap_sem);
+	err = get_futex_key(uaddr, &q->key);
+
+	if (unlikely(err != 0)) {
+		up_read(&current->mm->mmap_sem);
+		put_unused_fd(ret);
+		put_filp(filp);
+		kfree(q);
+		return err;
+	}
+
+	/*
+	 * queue_me() must be called before releasing mmap_sem, because
+	 * key->shared.inode needs to be referenced while holding it.
+	 */
+	filp->private_data = q;
+
+	queue_me(q, ret, filp);
+	up_read(&current->mm->mmap_sem);
+
+	/* Now we map fd to filp, so userspace can access it */
+	fd_install(ret, filp);
+out:
+	return ret;
+}
+
+long do_futex(unsigned long uaddr, int op, int val, unsigned long timeout,
+		unsigned long uaddr2, int val2, int val3)
+{
+	int ret;
+
+	switch (op) {
+	case FUTEX_WAIT:
+		ret = futex_wait(uaddr, val, timeout);
+		break;
+	case FUTEX_WAKE:
+		ret = futex_wake(uaddr, val);
+		break;
+	case FUTEX_FD:
+		/* non-zero val means F_SETOWN(getpid()) & F_SETSIG(val) */
+		ret = futex_fd(uaddr, val);
+		break;
+	case FUTEX_REQUEUE:
+		ret = futex_requeue(uaddr, uaddr2, val, val2, NULL);
+		break;
+	case FUTEX_CMP_REQUEUE:
+		ret = futex_requeue(uaddr, uaddr2, val, val2, &val3);
+		break;
+	default:
+		ret = -ENOSYS;
+	}
+	return ret;
+}
+
+
+asmlinkage long sys_futex(u32 __user *uaddr, int op, int val,
+			  struct timespec __user *utime, u32 __user *uaddr2,
+			  int val3)
+{
+	struct timespec t;
+	unsigned long timeout = MAX_SCHEDULE_TIMEOUT;
+	int val2 = 0;
+
+	if ((op == FUTEX_WAIT) && utime) {
+		if (copy_from_user(&t, utime, sizeof(t)) != 0)
+			return -EFAULT;
+		timeout = timespec_to_jiffies(&t) + 1;
+	}
+	/*
+	 * requeue parameter in 'utime' if op == FUTEX_REQUEUE.
+	 */
+	if (op >= FUTEX_REQUEUE)
+		val2 = (int) (unsigned long) utime;
+
+	return do_futex((unsigned long)uaddr, op, val, timeout,
+			(unsigned long)uaddr2, val2, val3);
+}
+
+static struct super_block *
+futexfs_get_sb(struct file_system_type *fs_type,
+	       int flags, const char *dev_name, void *data)
+{
+	return get_sb_pseudo(fs_type, "futex", NULL, 0xBAD1DEA);
+}
+
+static struct file_system_type futex_fs_type = {
+	.name		= "futexfs",
+	.get_sb		= futexfs_get_sb,
+	.kill_sb	= kill_anon_super,
+};
+
+static int __init init(void)
+{
+	unsigned int i;
+
+	register_filesystem(&futex_fs_type);
+	futex_mnt = kern_mount(&futex_fs_type);
+
+	for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
+		INIT_LIST_HEAD(&futex_queues[i].chain);
+		spin_lock_init(&futex_queues[i].lock);
+	}
+	return 0;
+}
+__initcall(init);