projects/linux·blob v2.6.13 · refs

799 lines · 19.3 KiB

1/*
2 * Fast Userspace Mutexes (which I call "Futexes!").
3 * (C) Rusty Russell, IBM 2002
4 *
5 * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
6 * (C) Copyright 2003 Red Hat Inc, All Rights Reserved
7 *
8 * Removed page pinning, fix privately mapped COW pages and other cleanups
9 * (C) Copyright 2003, 2004 Jamie Lokier
10 *
11 * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
12 * enough at me, Linus for the original (flawed) idea, Matthew
13 * Kirkwood for proof-of-concept implementation.
14 *
15 * "The futexes are also cursed."
16 * "But they come in a choice of three flavours!"
17 *
18 * This program is free software; you can redistribute it and/or modify
19 * it under the terms of the GNU General Public License as published by
20 * the Free Software Foundation; either version 2 of the License, or
21 * (at your option) any later version.
22 *
23 * This program is distributed in the hope that it will be useful,
24 * but WITHOUT ANY WARRANTY; without even the implied warranty of
25 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
26 * GNU General Public License for more details.
27 *
28 * You should have received a copy of the GNU General Public License
29 * along with this program; if not, write to the Free Software
30 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
31 */
32#include <linux/slab.h>
33#include <linux/poll.h>
34#include <linux/fs.h>
35#include <linux/file.h>
36#include <linux/jhash.h>
37#include <linux/init.h>
38#include <linux/futex.h>
39#include <linux/mount.h>
40#include <linux/pagemap.h>
41#include <linux/syscalls.h>
42#include <linux/signal.h>
43
44#define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
45
46/*
47 * Futexes are matched on equal values of this key.
48 * The key type depends on whether it's a shared or private mapping.
49 * Don't rearrange members without looking at hash_futex().
50 *
51 * offset is aligned to a multiple of sizeof(u32) (== 4) by definition.
52 * We set bit 0 to indicate if it's an inode-based key.
53 */
54union futex_key {
55 struct {
56 unsigned long pgoff;
57 struct inode *inode;
58 int offset;
59 } shared;
60 struct {
61 unsigned long uaddr;
62 struct mm_struct *mm;
63 int offset;
64 } private;
65 struct {
66 unsigned long word;
67 void *ptr;
68 int offset;
69 } both;
70};
71
72/*
73 * We use this hashed waitqueue instead of a normal wait_queue_t, so
74 * we can wake only the relevant ones (hashed queues may be shared).
75 *
76 * A futex_q has a woken state, just like tasks have TASK_RUNNING.
77 * It is considered woken when list_empty(&q->list) || q->lock_ptr == 0.
78 * The order of wakup is always to make the first condition true, then
79 * wake up q->waiters, then make the second condition true.
80 */
81struct futex_q {
82 struct list_head list;
83 wait_queue_head_t waiters;
84
85 /* Which hash list lock to use. */
86 spinlock_t *lock_ptr;
87
88 /* Key which the futex is hashed on. */
89 union futex_key key;
90
91 /* For fd, sigio sent using these. */
92 int fd;
93 struct file *filp;
94};
95
96/*
97 * Split the global futex_lock into every hash list lock.
98 */
99struct futex_hash_bucket {
100 spinlock_t lock;
101 struct list_head chain;
102};
103
104static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
105
106/* Futex-fs vfsmount entry: */
107static struct vfsmount *futex_mnt;
108
109/*
110 * We hash on the keys returned from get_futex_key (see below).
111 */
112static struct futex_hash_bucket *hash_futex(union futex_key *key)
113{
114 u32 hash = jhash2((u32*)&key->both.word,
115 (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
116 key->both.offset);
117 return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
118}
119
120/*
121 * Return 1 if two futex_keys are equal, 0 otherwise.
122 */
123static inline int match_futex(union futex_key *key1, union futex_key *key2)
124{
125 return (key1->both.word == key2->both.word
126 && key1->both.ptr == key2->both.ptr
127 && key1->both.offset == key2->both.offset);
128}
129
130/*
131 * Get parameters which are the keys for a futex.
132 *
133 * For shared mappings, it's (page->index, vma->vm_file->f_dentry->d_inode,
134 * offset_within_page). For private mappings, it's (uaddr, current->mm).
135 * We can usually work out the index without swapping in the page.
136 *
137 * Returns: 0, or negative error code.
138 * The key words are stored in *key on success.
139 *
140 * Should be called with &current->mm->mmap_sem but NOT any spinlocks.
141 */
142static int get_futex_key(unsigned long uaddr, union futex_key *key)
143{
144 struct mm_struct *mm = current->mm;
145 struct vm_area_struct *vma;
146 struct page *page;
147 int err;
148
149 /*
150 * The futex address must be "naturally" aligned.
151 */
152 key->both.offset = uaddr % PAGE_SIZE;
153 if (unlikely((key->both.offset % sizeof(u32)) != 0))
154 return -EINVAL;
155 uaddr -= key->both.offset;
156
157 /*
158 * The futex is hashed differently depending on whether
159 * it's in a shared or private mapping. So check vma first.
160 */
161 vma = find_extend_vma(mm, uaddr);
162 if (unlikely(!vma))
163 return -EFAULT;
164
165 /*
166 * Permissions.
167 */
168 if (unlikely((vma->vm_flags & (VM_IO|VM_READ)) != VM_READ))
169 return (vma->vm_flags & VM_IO) ? -EPERM : -EACCES;
170
171 /*
172 * Private mappings are handled in a simple way.
173 *
174 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
175 * it's a read-only handle, it's expected that futexes attach to
176 * the object not the particular process. Therefore we use
177 * VM_MAYSHARE here, not VM_SHARED which is restricted to shared
178 * mappings of _writable_ handles.
179 */
180 if (likely(!(vma->vm_flags & VM_MAYSHARE))) {
181 key->private.mm = mm;
182 key->private.uaddr = uaddr;
183 return 0;
184 }
185
186 /*
187 * Linear file mappings are also simple.
188 */
189 key->shared.inode = vma->vm_file->f_dentry->d_inode;
190 key->both.offset++; /* Bit 0 of offset indicates inode-based key. */
191 if (likely(!(vma->vm_flags & VM_NONLINEAR))) {
192 key->shared.pgoff = (((uaddr - vma->vm_start) >> PAGE_SHIFT)
193 + vma->vm_pgoff);
194 return 0;
195 }
196
197 /*
198 * We could walk the page table to read the non-linear
199 * pte, and get the page index without fetching the page
200 * from swap. But that's a lot of code to duplicate here
201 * for a rare case, so we simply fetch the page.
202 */
203
204 /*
205 * Do a quick atomic lookup first - this is the fastpath.
206 */
207 spin_lock(&current->mm->page_table_lock);
208 page = follow_page(mm, uaddr, 0);
209 if (likely(page != NULL)) {
210 key->shared.pgoff =
211 page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
212 spin_unlock(&current->mm->page_table_lock);
213 return 0;
214 }
215 spin_unlock(&current->mm->page_table_lock);
216
217 /*
218 * Do it the general way.
219 */
220 err = get_user_pages(current, mm, uaddr, 1, 0, 0, &page, NULL);
221 if (err >= 0) {
222 key->shared.pgoff =
223 page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
224 put_page(page);
225 return 0;
226 }
227 return err;
228}
229
230/*
231 * Take a reference to the resource addressed by a key.
232 * Can be called while holding spinlocks.
233 *
234 * NOTE: mmap_sem MUST be held between get_futex_key() and calling this
235 * function, if it is called at all. mmap_sem keeps key->shared.inode valid.
236 */
237static inline void get_key_refs(union futex_key *key)
238{
239 if (key->both.ptr != 0) {
240 if (key->both.offset & 1)
241 atomic_inc(&key->shared.inode->i_count);
242 else
243 atomic_inc(&key->private.mm->mm_count);
244 }
245}
246
247/*
248 * Drop a reference to the resource addressed by a key.
249 * The hash bucket spinlock must not be held.
250 */
251static void drop_key_refs(union futex_key *key)
252{
253 if (key->both.ptr != 0) {
254 if (key->both.offset & 1)
255 iput(key->shared.inode);
256 else
257 mmdrop(key->private.mm);
258 }
259}
260
261static inline int get_futex_value_locked(int *dest, int __user *from)
262{
263 int ret;
264
265 inc_preempt_count();
266 ret = __copy_from_user_inatomic(dest, from, sizeof(int));
267 dec_preempt_count();
268
269 return ret ? -EFAULT : 0;
270}
271
272/*
273 * The hash bucket lock must be held when this is called.
274 * Afterwards, the futex_q must not be accessed.
275 */
276static void wake_futex(struct futex_q *q)
277{
278 list_del_init(&q->list);
279 if (q->filp)
280 send_sigio(&q->filp->f_owner, q->fd, POLL_IN);
281 /*
282 * The lock in wake_up_all() is a crucial memory barrier after the
283 * list_del_init() and also before assigning to q->lock_ptr.
284 */
285 wake_up_all(&q->waiters);
286 /*
287 * The waiting task can free the futex_q as soon as this is written,
288 * without taking any locks. This must come last.
289 */
290 q->lock_ptr = NULL;
291}
292
293/*
294 * Wake up all waiters hashed on the physical page that is mapped
295 * to this virtual address:
296 */
297static int futex_wake(unsigned long uaddr, int nr_wake)
298{
299 union futex_key key;
300 struct futex_hash_bucket *bh;
301 struct list_head *head;
302 struct futex_q *this, *next;
303 int ret;
304
305 down_read(&current->mm->mmap_sem);
306
307 ret = get_futex_key(uaddr, &key);
308 if (unlikely(ret != 0))
309 goto out;
310
311 bh = hash_futex(&key);
312 spin_lock(&bh->lock);
313 head = &bh->chain;
314
315 list_for_each_entry_safe(this, next, head, list) {
316 if (match_futex (&this->key, &key)) {
317 wake_futex(this);
318 if (++ret >= nr_wake)
319 break;
320 }
321 }
322
323 spin_unlock(&bh->lock);
324out:
325 up_read(&current->mm->mmap_sem);
326 return ret;
327}
328
329/*
330 * Requeue all waiters hashed on one physical page to another
331 * physical page.
332 */
333static int futex_requeue(unsigned long uaddr1, unsigned long uaddr2,
334 int nr_wake, int nr_requeue, int *valp)
335{
336 union futex_key key1, key2;
337 struct futex_hash_bucket *bh1, *bh2;
338 struct list_head *head1;
339 struct futex_q *this, *next;
340 int ret, drop_count = 0;
341
342 retry:
343 down_read(&current->mm->mmap_sem);
344
345 ret = get_futex_key(uaddr1, &key1);
346 if (unlikely(ret != 0))
347 goto out;
348 ret = get_futex_key(uaddr2, &key2);
349 if (unlikely(ret != 0))
350 goto out;
351
352 bh1 = hash_futex(&key1);
353 bh2 = hash_futex(&key2);
354
355 if (bh1 < bh2)
356 spin_lock(&bh1->lock);
357 spin_lock(&bh2->lock);
358 if (bh1 > bh2)
359 spin_lock(&bh1->lock);
360
361 if (likely(valp != NULL)) {
362 int curval;
363
364 ret = get_futex_value_locked(&curval, (int __user *)uaddr1);
365
366 if (unlikely(ret)) {
367 spin_unlock(&bh1->lock);
368 if (bh1 != bh2)
369 spin_unlock(&bh2->lock);
370
371 /* If we would have faulted, release mmap_sem, fault
372 * it in and start all over again.
373 */
374 up_read(&current->mm->mmap_sem);
375
376 ret = get_user(curval, (int __user *)uaddr1);
377
378 if (!ret)
379 goto retry;
380
381 return ret;
382 }
383 if (curval != *valp) {
384 ret = -EAGAIN;
385 goto out_unlock;
386 }
387 }
388
389 head1 = &bh1->chain;
390 list_for_each_entry_safe(this, next, head1, list) {
391 if (!match_futex (&this->key, &key1))
392 continue;
393 if (++ret <= nr_wake) {
394 wake_futex(this);
395 } else {
396 list_move_tail(&this->list, &bh2->chain);
397 this->lock_ptr = &bh2->lock;
398 this->key = key2;
399 get_key_refs(&key2);
400 drop_count++;
401
402 if (ret - nr_wake >= nr_requeue)
403 break;
404 /* Make sure to stop if key1 == key2 */
405 if (head1 == &bh2->chain && head1 != &next->list)
406 head1 = &this->list;
407 }
408 }
409
410out_unlock:
411 spin_unlock(&bh1->lock);
412 if (bh1 != bh2)
413 spin_unlock(&bh2->lock);
414
415 /* drop_key_refs() must be called outside the spinlocks. */
416 while (--drop_count >= 0)
417 drop_key_refs(&key1);
418
419out:
420 up_read(&current->mm->mmap_sem);
421 return ret;
422}
423
424/* The key must be already stored in q->key. */
425static inline struct futex_hash_bucket *
426queue_lock(struct futex_q *q, int fd, struct file *filp)
427{
428 struct futex_hash_bucket *bh;
429
430 q->fd = fd;
431 q->filp = filp;
432
433 init_waitqueue_head(&q->waiters);
434
435 get_key_refs(&q->key);
436 bh = hash_futex(&q->key);
437 q->lock_ptr = &bh->lock;
438
439 spin_lock(&bh->lock);
440 return bh;
441}
442
443static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *bh)
444{
445 list_add_tail(&q->list, &bh->chain);
446 spin_unlock(&bh->lock);
447}
448
449static inline void
450queue_unlock(struct futex_q *q, struct futex_hash_bucket *bh)
451{
452 spin_unlock(&bh->lock);
453 drop_key_refs(&q->key);
454}
455
456/*
457 * queue_me and unqueue_me must be called as a pair, each
458 * exactly once. They are called with the hashed spinlock held.
459 */
460
461/* The key must be already stored in q->key. */
462static void queue_me(struct futex_q *q, int fd, struct file *filp)
463{
464 struct futex_hash_bucket *bh;
465 bh = queue_lock(q, fd, filp);
466 __queue_me(q, bh);
467}
468
469/* Return 1 if we were still queued (ie. 0 means we were woken) */
470static int unqueue_me(struct futex_q *q)
471{
472 int ret = 0;
473 spinlock_t *lock_ptr;
474
475 /* In the common case we don't take the spinlock, which is nice. */
476 retry:
477 lock_ptr = q->lock_ptr;
478 if (lock_ptr != 0) {
479 spin_lock(lock_ptr);
480 /*
481 * q->lock_ptr can change between reading it and
482 * spin_lock(), causing us to take the wrong lock. This
483 * corrects the race condition.
484 *
485 * Reasoning goes like this: if we have the wrong lock,
486 * q->lock_ptr must have changed (maybe several times)
487 * between reading it and the spin_lock(). It can
488 * change again after the spin_lock() but only if it was
489 * already changed before the spin_lock(). It cannot,
490 * however, change back to the original value. Therefore
491 * we can detect whether we acquired the correct lock.
492 */
493 if (unlikely(lock_ptr != q->lock_ptr)) {
494 spin_unlock(lock_ptr);
495 goto retry;
496 }
497 WARN_ON(list_empty(&q->list));
498 list_del(&q->list);
499 spin_unlock(lock_ptr);
500 ret = 1;
501 }
502
503 drop_key_refs(&q->key);
504 return ret;
505}
506
507static int futex_wait(unsigned long uaddr, int val, unsigned long time)
508{
509 DECLARE_WAITQUEUE(wait, current);
510 int ret, curval;
511 struct futex_q q;
512 struct futex_hash_bucket *bh;
513
514 retry:
515 down_read(&current->mm->mmap_sem);
516
517 ret = get_futex_key(uaddr, &q.key);
518 if (unlikely(ret != 0))
519 goto out_release_sem;
520
521 bh = queue_lock(&q, -1, NULL);
522
523 /*
524 * Access the page AFTER the futex is queued.
525 * Order is important:
526 *
527 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
528 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
529 *
530 * The basic logical guarantee of a futex is that it blocks ONLY
531 * if cond(var) is known to be true at the time of blocking, for
532 * any cond. If we queued after testing *uaddr, that would open
533 * a race condition where we could block indefinitely with
534 * cond(var) false, which would violate the guarantee.
535 *
536 * A consequence is that futex_wait() can return zero and absorb
537 * a wakeup when *uaddr != val on entry to the syscall. This is
538 * rare, but normal.
539 *
540 * We hold the mmap semaphore, so the mapping cannot have changed
541 * since we looked it up in get_futex_key.
542 */
543
544 ret = get_futex_value_locked(&curval, (int __user *)uaddr);
545
546 if (unlikely(ret)) {
547 queue_unlock(&q, bh);
548
549 /* If we would have faulted, release mmap_sem, fault it in and
550 * start all over again.
551 */
552 up_read(&current->mm->mmap_sem);
553
554 ret = get_user(curval, (int __user *)uaddr);
555
556 if (!ret)
557 goto retry;
558 return ret;
559 }
560 if (curval != val) {
561 ret = -EWOULDBLOCK;
562 queue_unlock(&q, bh);
563 goto out_release_sem;
564 }
565
566 /* Only actually queue if *uaddr contained val. */
567 __queue_me(&q, bh);
568
569 /*
570 * Now the futex is queued and we have checked the data, we
571 * don't want to hold mmap_sem while we sleep.
572 */
573 up_read(&current->mm->mmap_sem);
574
575 /*
576 * There might have been scheduling since the queue_me(), as we
577 * cannot hold a spinlock across the get_user() in case it
578 * faults, and we cannot just set TASK_INTERRUPTIBLE state when
579 * queueing ourselves into the futex hash. This code thus has to
580 * rely on the futex_wake() code removing us from hash when it
581 * wakes us up.
582 */
583
584 /* add_wait_queue is the barrier after __set_current_state. */
585 __set_current_state(TASK_INTERRUPTIBLE);
586 add_wait_queue(&q.waiters, &wait);
587 /*
588 * !list_empty() is safe here without any lock.
589 * q.lock_ptr != 0 is not safe, because of ordering against wakeup.
590 */
591 if (likely(!list_empty(&q.list)))
592 time = schedule_timeout(time);
593 __set_current_state(TASK_RUNNING);
594
595 /*
596 * NOTE: we don't remove ourselves from the waitqueue because
597 * we are the only user of it.
598 */
599
600 /* If we were woken (and unqueued), we succeeded, whatever. */
601 if (!unqueue_me(&q))
602 return 0;
603 if (time == 0)
604 return -ETIMEDOUT;
605 /* We expect signal_pending(current), but another thread may
606 * have handled it for us already. */
607 return -EINTR;
608
609 out_release_sem:
610 up_read(&current->mm->mmap_sem);
611 return ret;
612}
613
614static int futex_close(struct inode *inode, struct file *filp)
615{
616 struct futex_q *q = filp->private_data;
617
618 unqueue_me(q);
619 kfree(q);
620 return 0;
621}
622
623/* This is one-shot: once it's gone off you need a new fd */
624static unsigned int futex_poll(struct file *filp,
625 struct poll_table_struct *wait)
626{
627 struct futex_q *q = filp->private_data;
628 int ret = 0;
629
630 poll_wait(filp, &q->waiters, wait);
631
632 /*
633 * list_empty() is safe here without any lock.
634 * q->lock_ptr != 0 is not safe, because of ordering against wakeup.
635 */
636 if (list_empty(&q->list))
637 ret = POLLIN | POLLRDNORM;
638
639 return ret;
640}
641
642static struct file_operations futex_fops = {
643 .release = futex_close,
644 .poll = futex_poll,
645};
646
647/*
648 * Signal allows caller to avoid the race which would occur if they
649 * set the sigio stuff up afterwards.
650 */
651static int futex_fd(unsigned long uaddr, int signal)
652{
653 struct futex_q *q;
654 struct file *filp;
655 int ret, err;
656
657 ret = -EINVAL;
658 if (!valid_signal(signal))
659 goto out;
660
661 ret = get_unused_fd();
662 if (ret < 0)
663 goto out;
664 filp = get_empty_filp();
665 if (!filp) {
666 put_unused_fd(ret);
667 ret = -ENFILE;
668 goto out;
669 }
670 filp->f_op = &futex_fops;
671 filp->f_vfsmnt = mntget(futex_mnt);
672 filp->f_dentry = dget(futex_mnt->mnt_root);
673 filp->f_mapping = filp->f_dentry->d_inode->i_mapping;
674
675 if (signal) {
676 int err;
677 err = f_setown(filp, current->pid, 1);
678 if (err < 0) {
679 put_unused_fd(ret);
680 put_filp(filp);
681 ret = err;
682 goto out;
683 }
684 filp->f_owner.signum = signal;
685 }
686
687 q = kmalloc(sizeof(*q), GFP_KERNEL);
688 if (!q) {
689 put_unused_fd(ret);
690 put_filp(filp);
691 ret = -ENOMEM;
692 goto out;
693 }
694
695 down_read(&current->mm->mmap_sem);
696 err = get_futex_key(uaddr, &q->key);
697
698 if (unlikely(err != 0)) {
699 up_read(&current->mm->mmap_sem);
700 put_unused_fd(ret);
701 put_filp(filp);
702 kfree(q);
703 return err;
704 }
705
706 /*
707 * queue_me() must be called before releasing mmap_sem, because
708 * key->shared.inode needs to be referenced while holding it.
709 */
710 filp->private_data = q;
711
712 queue_me(q, ret, filp);
713 up_read(&current->mm->mmap_sem);
714
715 /* Now we map fd to filp, so userspace can access it */
716 fd_install(ret, filp);
717out:
718 return ret;
719}
720
721long do_futex(unsigned long uaddr, int op, int val, unsigned long timeout,
722 unsigned long uaddr2, int val2, int val3)
723{
724 int ret;
725
726 switch (op) {
727 case FUTEX_WAIT:
728 ret = futex_wait(uaddr, val, timeout);
729 break;
730 case FUTEX_WAKE:
731 ret = futex_wake(uaddr, val);
732 break;
733 case FUTEX_FD:
734 /* non-zero val means F_SETOWN(getpid()) & F_SETSIG(val) */
735 ret = futex_fd(uaddr, val);
736 break;
737 case FUTEX_REQUEUE:
738 ret = futex_requeue(uaddr, uaddr2, val, val2, NULL);
739 break;
740 case FUTEX_CMP_REQUEUE:
741 ret = futex_requeue(uaddr, uaddr2, val, val2, &val3);
742 break;
743 default:
744 ret = -ENOSYS;
745 }
746 return ret;
747}
748
749
750asmlinkage long sys_futex(u32 __user *uaddr, int op, int val,
751 struct timespec __user *utime, u32 __user *uaddr2,
752 int val3)
753{
754 struct timespec t;
755 unsigned long timeout = MAX_SCHEDULE_TIMEOUT;
756 int val2 = 0;
757
758 if ((op == FUTEX_WAIT) && utime) {
759 if (copy_from_user(&t, utime, sizeof(t)) != 0)
760 return -EFAULT;
761 timeout = timespec_to_jiffies(&t) + 1;
762 }
763 /*
764 * requeue parameter in 'utime' if op == FUTEX_REQUEUE.
765 */
766 if (op >= FUTEX_REQUEUE)
767 val2 = (int) (unsigned long) utime;
768
769 return do_futex((unsigned long)uaddr, op, val, timeout,
770 (unsigned long)uaddr2, val2, val3);
771}
772
773static struct super_block *
774futexfs_get_sb(struct file_system_type *fs_type,
775 int flags, const char *dev_name, void *data)
776{
777 return get_sb_pseudo(fs_type, "futex", NULL, 0xBAD1DEA);
778}
779
780static struct file_system_type futex_fs_type = {
781 .name = "futexfs",
782 .get_sb = futexfs_get_sb,
783 .kill_sb = kill_anon_super,
784};
785
786static int __init init(void)
787{
788 unsigned int i;
789
790 register_filesystem(&futex_fs_type);
791 futex_mnt = kern_mount(&futex_fs_type);
792
793 for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
794 INIT_LIST_HEAD(&futex_queues[i].chain);
795 spin_lock_init(&futex_queues[i].lock);
796 }
797 return 0;
798}
799__initcall(init);