projects/linux·blob v2.6.21 · refs

1879 lines · 43.9 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 * Robust futex support started by Ingo Molnar
12 * (C) Copyright 2006 Red Hat Inc, All Rights Reserved
13 * Thanks to Thomas Gleixner for suggestions, analysis and fixes.
14 *
15 * PI-futex support started by Ingo Molnar and Thomas Gleixner
16 * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <[email protected]>
17 * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <[email protected]>
18 *
19 * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
20 * enough at me, Linus for the original (flawed) idea, Matthew
21 * Kirkwood for proof-of-concept implementation.
22 *
23 * "The futexes are also cursed."
24 * "But they come in a choice of three flavours!"
25 *
26 * This program is free software; you can redistribute it and/or modify
27 * it under the terms of the GNU General Public License as published by
28 * the Free Software Foundation; either version 2 of the License, or
29 * (at your option) any later version.
30 *
31 * This program is distributed in the hope that it will be useful,
32 * but WITHOUT ANY WARRANTY; without even the implied warranty of
33 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
34 * GNU General Public License for more details.
35 *
36 * You should have received a copy of the GNU General Public License
37 * along with this program; if not, write to the Free Software
38 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
39 */
40#include <linux/slab.h>
41#include <linux/poll.h>
42#include <linux/fs.h>
43#include <linux/file.h>
44#include <linux/jhash.h>
45#include <linux/init.h>
46#include <linux/futex.h>
47#include <linux/mount.h>
48#include <linux/pagemap.h>
49#include <linux/syscalls.h>
50#include <linux/signal.h>
51#include <asm/futex.h>
52
53#include "rtmutex_common.h"
54
55#define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
56
57/*
58 * Futexes are matched on equal values of this key.
59 * The key type depends on whether it's a shared or private mapping.
60 * Don't rearrange members without looking at hash_futex().
61 *
62 * offset is aligned to a multiple of sizeof(u32) (== 4) by definition.
63 * We set bit 0 to indicate if it's an inode-based key.
64 */
65union futex_key {
66 struct {
67 unsigned long pgoff;
68 struct inode *inode;
69 int offset;
70 } shared;
71 struct {
72 unsigned long address;
73 struct mm_struct *mm;
74 int offset;
75 } private;
76 struct {
77 unsigned long word;
78 void *ptr;
79 int offset;
80 } both;
81};
82
83/*
84 * Priority Inheritance state:
85 */
86struct futex_pi_state {
87 /*
88 * list of 'owned' pi_state instances - these have to be
89 * cleaned up in do_exit() if the task exits prematurely:
90 */
91 struct list_head list;
92
93 /*
94 * The PI object:
95 */
96 struct rt_mutex pi_mutex;
97
98 struct task_struct *owner;
99 atomic_t refcount;
100
101 union futex_key key;
102};
103
104/*
105 * We use this hashed waitqueue instead of a normal wait_queue_t, so
106 * we can wake only the relevant ones (hashed queues may be shared).
107 *
108 * A futex_q has a woken state, just like tasks have TASK_RUNNING.
109 * It is considered woken when list_empty(&q->list) || q->lock_ptr == 0.
110 * The order of wakup is always to make the first condition true, then
111 * wake up q->waiters, then make the second condition true.
112 */
113struct futex_q {
114 struct list_head list;
115 wait_queue_head_t waiters;
116
117 /* Which hash list lock to use: */
118 spinlock_t *lock_ptr;
119
120 /* Key which the futex is hashed on: */
121 union futex_key key;
122
123 /* For fd, sigio sent using these: */
124 int fd;
125 struct file *filp;
126
127 /* Optional priority inheritance state: */
128 struct futex_pi_state *pi_state;
129 struct task_struct *task;
130};
131
132/*
133 * Split the global futex_lock into every hash list lock.
134 */
135struct futex_hash_bucket {
136 spinlock_t lock;
137 struct list_head chain;
138};
139
140static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
141
142/* Futex-fs vfsmount entry: */
143static struct vfsmount *futex_mnt;
144
145/*
146 * We hash on the keys returned from get_futex_key (see below).
147 */
148static struct futex_hash_bucket *hash_futex(union futex_key *key)
149{
150 u32 hash = jhash2((u32*)&key->both.word,
151 (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
152 key->both.offset);
153 return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
154}
155
156/*
157 * Return 1 if two futex_keys are equal, 0 otherwise.
158 */
159static inline int match_futex(union futex_key *key1, union futex_key *key2)
160{
161 return (key1->both.word == key2->both.word
162 && key1->both.ptr == key2->both.ptr
163 && key1->both.offset == key2->both.offset);
164}
165
166/*
167 * Get parameters which are the keys for a futex.
168 *
169 * For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,
170 * offset_within_page). For private mappings, it's (uaddr, current->mm).
171 * We can usually work out the index without swapping in the page.
172 *
173 * Returns: 0, or negative error code.
174 * The key words are stored in *key on success.
175 *
176 * Should be called with &current->mm->mmap_sem but NOT any spinlocks.
177 */
178static int get_futex_key(u32 __user *uaddr, union futex_key *key)
179{
180 unsigned long address = (unsigned long)uaddr;
181 struct mm_struct *mm = current->mm;
182 struct vm_area_struct *vma;
183 struct page *page;
184 int err;
185
186 /*
187 * The futex address must be "naturally" aligned.
188 */
189 key->both.offset = address % PAGE_SIZE;
190 if (unlikely((key->both.offset % sizeof(u32)) != 0))
191 return -EINVAL;
192 address -= key->both.offset;
193
194 /*
195 * The futex is hashed differently depending on whether
196 * it's in a shared or private mapping. So check vma first.
197 */
198 vma = find_extend_vma(mm, address);
199 if (unlikely(!vma))
200 return -EFAULT;
201
202 /*
203 * Permissions.
204 */
205 if (unlikely((vma->vm_flags & (VM_IO|VM_READ)) != VM_READ))
206 return (vma->vm_flags & VM_IO) ? -EPERM : -EACCES;
207
208 /*
209 * Private mappings are handled in a simple way.
210 *
211 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
212 * it's a read-only handle, it's expected that futexes attach to
213 * the object not the particular process. Therefore we use
214 * VM_MAYSHARE here, not VM_SHARED which is restricted to shared
215 * mappings of _writable_ handles.
216 */
217 if (likely(!(vma->vm_flags & VM_MAYSHARE))) {
218 key->private.mm = mm;
219 key->private.address = address;
220 return 0;
221 }
222
223 /*
224 * Linear file mappings are also simple.
225 */
226 key->shared.inode = vma->vm_file->f_path.dentry->d_inode;
227 key->both.offset++; /* Bit 0 of offset indicates inode-based key. */
228 if (likely(!(vma->vm_flags & VM_NONLINEAR))) {
229 key->shared.pgoff = (((address - vma->vm_start) >> PAGE_SHIFT)
230 + vma->vm_pgoff);
231 return 0;
232 }
233
234 /*
235 * We could walk the page table to read the non-linear
236 * pte, and get the page index without fetching the page
237 * from swap. But that's a lot of code to duplicate here
238 * for a rare case, so we simply fetch the page.
239 */
240 err = get_user_pages(current, mm, address, 1, 0, 0, &page, NULL);
241 if (err >= 0) {
242 key->shared.pgoff =
243 page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
244 put_page(page);
245 return 0;
246 }
247 return err;
248}
249
250/*
251 * Take a reference to the resource addressed by a key.
252 * Can be called while holding spinlocks.
253 *
254 * NOTE: mmap_sem MUST be held between get_futex_key() and calling this
255 * function, if it is called at all. mmap_sem keeps key->shared.inode valid.
256 */
257static inline void get_key_refs(union futex_key *key)
258{
259 if (key->both.ptr != 0) {
260 if (key->both.offset & 1)
261 atomic_inc(&key->shared.inode->i_count);
262 else
263 atomic_inc(&key->private.mm->mm_count);
264 }
265}
266
267/*
268 * Drop a reference to the resource addressed by a key.
269 * The hash bucket spinlock must not be held.
270 */
271static void drop_key_refs(union futex_key *key)
272{
273 if (key->both.ptr != 0) {
274 if (key->both.offset & 1)
275 iput(key->shared.inode);
276 else
277 mmdrop(key->private.mm);
278 }
279}
280
281static inline int get_futex_value_locked(u32 *dest, u32 __user *from)
282{
283 int ret;
284
285 pagefault_disable();
286 ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
287 pagefault_enable();
288
289 return ret ? -EFAULT : 0;
290}
291
292/*
293 * Fault handling. Called with current->mm->mmap_sem held.
294 */
295static int futex_handle_fault(unsigned long address, int attempt)
296{
297 struct vm_area_struct * vma;
298 struct mm_struct *mm = current->mm;
299
300 if (attempt > 2 || !(vma = find_vma(mm, address)) ||
301 vma->vm_start > address || !(vma->vm_flags & VM_WRITE))
302 return -EFAULT;
303
304 switch (handle_mm_fault(mm, vma, address, 1)) {
305 case VM_FAULT_MINOR:
306 current->min_flt++;
307 break;
308 case VM_FAULT_MAJOR:
309 current->maj_flt++;
310 break;
311 default:
312 return -EFAULT;
313 }
314 return 0;
315}
316
317/*
318 * PI code:
319 */
320static int refill_pi_state_cache(void)
321{
322 struct futex_pi_state *pi_state;
323
324 if (likely(current->pi_state_cache))
325 return 0;
326
327 pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
328
329 if (!pi_state)
330 return -ENOMEM;
331
332 INIT_LIST_HEAD(&pi_state->list);
333 /* pi_mutex gets initialized later */
334 pi_state->owner = NULL;
335 atomic_set(&pi_state->refcount, 1);
336
337 current->pi_state_cache = pi_state;
338
339 return 0;
340}
341
342static struct futex_pi_state * alloc_pi_state(void)
343{
344 struct futex_pi_state *pi_state = current->pi_state_cache;
345
346 WARN_ON(!pi_state);
347 current->pi_state_cache = NULL;
348
349 return pi_state;
350}
351
352static void free_pi_state(struct futex_pi_state *pi_state)
353{
354 if (!atomic_dec_and_test(&pi_state->refcount))
355 return;
356
357 /*
358 * If pi_state->owner is NULL, the owner is most probably dying
359 * and has cleaned up the pi_state already
360 */
361 if (pi_state->owner) {
362 spin_lock_irq(&pi_state->owner->pi_lock);
363 list_del_init(&pi_state->list);
364 spin_unlock_irq(&pi_state->owner->pi_lock);
365
366 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
367 }
368
369 if (current->pi_state_cache)
370 kfree(pi_state);
371 else {
372 /*
373 * pi_state->list is already empty.
374 * clear pi_state->owner.
375 * refcount is at 0 - put it back to 1.
376 */
377 pi_state->owner = NULL;
378 atomic_set(&pi_state->refcount, 1);
379 current->pi_state_cache = pi_state;
380 }
381}
382
383/*
384 * Look up the task based on what TID userspace gave us.
385 * We dont trust it.
386 */
387static struct task_struct * futex_find_get_task(pid_t pid)
388{
389 struct task_struct *p;
390
391 rcu_read_lock();
392 p = find_task_by_pid(pid);
393 if (!p)
394 goto out_unlock;
395 if ((current->euid != p->euid) && (current->euid != p->uid)) {
396 p = NULL;
397 goto out_unlock;
398 }
399 if (p->exit_state != 0) {
400 p = NULL;
401 goto out_unlock;
402 }
403 get_task_struct(p);
404out_unlock:
405 rcu_read_unlock();
406
407 return p;
408}
409
410/*
411 * This task is holding PI mutexes at exit time => bad.
412 * Kernel cleans up PI-state, but userspace is likely hosed.
413 * (Robust-futex cleanup is separate and might save the day for userspace.)
414 */
415void exit_pi_state_list(struct task_struct *curr)
416{
417 struct list_head *next, *head = &curr->pi_state_list;
418 struct futex_pi_state *pi_state;
419 struct futex_hash_bucket *hb;
420 union futex_key key;
421
422 /*
423 * We are a ZOMBIE and nobody can enqueue itself on
424 * pi_state_list anymore, but we have to be careful
425 * versus waiters unqueueing themselves:
426 */
427 spin_lock_irq(&curr->pi_lock);
428 while (!list_empty(head)) {
429
430 next = head->next;
431 pi_state = list_entry(next, struct futex_pi_state, list);
432 key = pi_state->key;
433 hb = hash_futex(&key);
434 spin_unlock_irq(&curr->pi_lock);
435
436 spin_lock(&hb->lock);
437
438 spin_lock_irq(&curr->pi_lock);
439 /*
440 * We dropped the pi-lock, so re-check whether this
441 * task still owns the PI-state:
442 */
443 if (head->next != next) {
444 spin_unlock(&hb->lock);
445 continue;
446 }
447
448 WARN_ON(pi_state->owner != curr);
449 WARN_ON(list_empty(&pi_state->list));
450 list_del_init(&pi_state->list);
451 pi_state->owner = NULL;
452 spin_unlock_irq(&curr->pi_lock);
453
454 rt_mutex_unlock(&pi_state->pi_mutex);
455
456 spin_unlock(&hb->lock);
457
458 spin_lock_irq(&curr->pi_lock);
459 }
460 spin_unlock_irq(&curr->pi_lock);
461}
462
463static int
464lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, struct futex_q *me)
465{
466 struct futex_pi_state *pi_state = NULL;
467 struct futex_q *this, *next;
468 struct list_head *head;
469 struct task_struct *p;
470 pid_t pid;
471
472 head = &hb->chain;
473
474 list_for_each_entry_safe(this, next, head, list) {
475 if (match_futex(&this->key, &me->key)) {
476 /*
477 * Another waiter already exists - bump up
478 * the refcount and return its pi_state:
479 */
480 pi_state = this->pi_state;
481 /*
482 * Userspace might have messed up non PI and PI futexes
483 */
484 if (unlikely(!pi_state))
485 return -EINVAL;
486
487 WARN_ON(!atomic_read(&pi_state->refcount));
488
489 atomic_inc(&pi_state->refcount);
490 me->pi_state = pi_state;
491
492 return 0;
493 }
494 }
495
496 /*
497 * We are the first waiter - try to look up the real owner and attach
498 * the new pi_state to it, but bail out when the owner died bit is set
499 * and TID = 0:
500 */
501 pid = uval & FUTEX_TID_MASK;
502 if (!pid && (uval & FUTEX_OWNER_DIED))
503 return -ESRCH;
504 p = futex_find_get_task(pid);
505 if (!p)
506 return -ESRCH;
507
508 pi_state = alloc_pi_state();
509
510 /*
511 * Initialize the pi_mutex in locked state and make 'p'
512 * the owner of it:
513 */
514 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
515
516 /* Store the key for possible exit cleanups: */
517 pi_state->key = me->key;
518
519 spin_lock_irq(&p->pi_lock);
520 WARN_ON(!list_empty(&pi_state->list));
521 list_add(&pi_state->list, &p->pi_state_list);
522 pi_state->owner = p;
523 spin_unlock_irq(&p->pi_lock);
524
525 put_task_struct(p);
526
527 me->pi_state = pi_state;
528
529 return 0;
530}
531
532/*
533 * The hash bucket lock must be held when this is called.
534 * Afterwards, the futex_q must not be accessed.
535 */
536static void wake_futex(struct futex_q *q)
537{
538 list_del_init(&q->list);
539 if (q->filp)
540 send_sigio(&q->filp->f_owner, q->fd, POLL_IN);
541 /*
542 * The lock in wake_up_all() is a crucial memory barrier after the
543 * list_del_init() and also before assigning to q->lock_ptr.
544 */
545 wake_up_all(&q->waiters);
546 /*
547 * The waiting task can free the futex_q as soon as this is written,
548 * without taking any locks. This must come last.
549 *
550 * A memory barrier is required here to prevent the following store
551 * to lock_ptr from getting ahead of the wakeup. Clearing the lock
552 * at the end of wake_up_all() does not prevent this store from
553 * moving.
554 */
555 smp_wmb();
556 q->lock_ptr = NULL;
557}
558
559static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
560{
561 struct task_struct *new_owner;
562 struct futex_pi_state *pi_state = this->pi_state;
563 u32 curval, newval;
564
565 if (!pi_state)
566 return -EINVAL;
567
568 spin_lock(&pi_state->pi_mutex.wait_lock);
569 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
570
571 /*
572 * This happens when we have stolen the lock and the original
573 * pending owner did not enqueue itself back on the rt_mutex.
574 * Thats not a tragedy. We know that way, that a lock waiter
575 * is on the fly. We make the futex_q waiter the pending owner.
576 */
577 if (!new_owner)
578 new_owner = this->task;
579
580 /*
581 * We pass it to the next owner. (The WAITERS bit is always
582 * kept enabled while there is PI state around. We must also
583 * preserve the owner died bit.)
584 */
585 if (!(uval & FUTEX_OWNER_DIED)) {
586 newval = FUTEX_WAITERS | new_owner->pid;
587
588 pagefault_disable();
589 curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
590 pagefault_enable();
591 if (curval == -EFAULT)
592 return -EFAULT;
593 if (curval != uval)
594 return -EINVAL;
595 }
596
597 spin_lock_irq(&pi_state->owner->pi_lock);
598 WARN_ON(list_empty(&pi_state->list));
599 list_del_init(&pi_state->list);
600 spin_unlock_irq(&pi_state->owner->pi_lock);
601
602 spin_lock_irq(&new_owner->pi_lock);
603 WARN_ON(!list_empty(&pi_state->list));
604 list_add(&pi_state->list, &new_owner->pi_state_list);
605 pi_state->owner = new_owner;
606 spin_unlock_irq(&new_owner->pi_lock);
607
608 spin_unlock(&pi_state->pi_mutex.wait_lock);
609 rt_mutex_unlock(&pi_state->pi_mutex);
610
611 return 0;
612}
613
614static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
615{
616 u32 oldval;
617
618 /*
619 * There is no waiter, so we unlock the futex. The owner died
620 * bit has not to be preserved here. We are the owner:
621 */
622 pagefault_disable();
623 oldval = futex_atomic_cmpxchg_inatomic(uaddr, uval, 0);
624 pagefault_enable();
625
626 if (oldval == -EFAULT)
627 return oldval;
628 if (oldval != uval)
629 return -EAGAIN;
630
631 return 0;
632}
633
634/*
635 * Express the locking dependencies for lockdep:
636 */
637static inline void
638double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
639{
640 if (hb1 <= hb2) {
641 spin_lock(&hb1->lock);
642 if (hb1 < hb2)
643 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
644 } else { /* hb1 > hb2 */
645 spin_lock(&hb2->lock);
646 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
647 }
648}
649
650/*
651 * Wake up all waiters hashed on the physical page that is mapped
652 * to this virtual address:
653 */
654static int futex_wake(u32 __user *uaddr, int nr_wake)
655{
656 struct futex_hash_bucket *hb;
657 struct futex_q *this, *next;
658 struct list_head *head;
659 union futex_key key;
660 int ret;
661
662 down_read(&current->mm->mmap_sem);
663
664 ret = get_futex_key(uaddr, &key);
665 if (unlikely(ret != 0))
666 goto out;
667
668 hb = hash_futex(&key);
669 spin_lock(&hb->lock);
670 head = &hb->chain;
671
672 list_for_each_entry_safe(this, next, head, list) {
673 if (match_futex (&this->key, &key)) {
674 if (this->pi_state) {
675 ret = -EINVAL;
676 break;
677 }
678 wake_futex(this);
679 if (++ret >= nr_wake)
680 break;
681 }
682 }
683
684 spin_unlock(&hb->lock);
685out:
686 up_read(&current->mm->mmap_sem);
687 return ret;
688}
689
690/*
691 * Wake up all waiters hashed on the physical page that is mapped
692 * to this virtual address:
693 */
694static int
695futex_wake_op(u32 __user *uaddr1, u32 __user *uaddr2,
696 int nr_wake, int nr_wake2, int op)
697{
698 union futex_key key1, key2;
699 struct futex_hash_bucket *hb1, *hb2;
700 struct list_head *head;
701 struct futex_q *this, *next;
702 int ret, op_ret, attempt = 0;
703
704retryfull:
705 down_read(&current->mm->mmap_sem);
706
707 ret = get_futex_key(uaddr1, &key1);
708 if (unlikely(ret != 0))
709 goto out;
710 ret = get_futex_key(uaddr2, &key2);
711 if (unlikely(ret != 0))
712 goto out;
713
714 hb1 = hash_futex(&key1);
715 hb2 = hash_futex(&key2);
716
717retry:
718 double_lock_hb(hb1, hb2);
719
720 op_ret = futex_atomic_op_inuser(op, uaddr2);
721 if (unlikely(op_ret < 0)) {
722 u32 dummy;
723
724 spin_unlock(&hb1->lock);
725 if (hb1 != hb2)
726 spin_unlock(&hb2->lock);
727
728#ifndef CONFIG_MMU
729 /*
730 * we don't get EFAULT from MMU faults if we don't have an MMU,
731 * but we might get them from range checking
732 */
733 ret = op_ret;
734 goto out;
735#endif
736
737 if (unlikely(op_ret != -EFAULT)) {
738 ret = op_ret;
739 goto out;
740 }
741
742 /*
743 * futex_atomic_op_inuser needs to both read and write
744 * *(int __user *)uaddr2, but we can't modify it
745 * non-atomically. Therefore, if get_user below is not
746 * enough, we need to handle the fault ourselves, while
747 * still holding the mmap_sem.
748 */
749 if (attempt++) {
750 if (futex_handle_fault((unsigned long)uaddr2,
751 attempt)) {
752 ret = -EFAULT;
753 goto out;
754 }
755 goto retry;
756 }
757
758 /*
759 * If we would have faulted, release mmap_sem,
760 * fault it in and start all over again.
761 */
762 up_read(&current->mm->mmap_sem);
763
764 ret = get_user(dummy, uaddr2);
765 if (ret)
766 return ret;
767
768 goto retryfull;
769 }
770
771 head = &hb1->chain;
772
773 list_for_each_entry_safe(this, next, head, list) {
774 if (match_futex (&this->key, &key1)) {
775 wake_futex(this);
776 if (++ret >= nr_wake)
777 break;
778 }
779 }
780
781 if (op_ret > 0) {
782 head = &hb2->chain;
783
784 op_ret = 0;
785 list_for_each_entry_safe(this, next, head, list) {
786 if (match_futex (&this->key, &key2)) {
787 wake_futex(this);
788 if (++op_ret >= nr_wake2)
789 break;
790 }
791 }
792 ret += op_ret;
793 }
794
795 spin_unlock(&hb1->lock);
796 if (hb1 != hb2)
797 spin_unlock(&hb2->lock);
798out:
799 up_read(&current->mm->mmap_sem);
800 return ret;
801}
802
803/*
804 * Requeue all waiters hashed on one physical page to another
805 * physical page.
806 */
807static int futex_requeue(u32 __user *uaddr1, u32 __user *uaddr2,
808 int nr_wake, int nr_requeue, u32 *cmpval)
809{
810 union futex_key key1, key2;
811 struct futex_hash_bucket *hb1, *hb2;
812 struct list_head *head1;
813 struct futex_q *this, *next;
814 int ret, drop_count = 0;
815
816 retry:
817 down_read(&current->mm->mmap_sem);
818
819 ret = get_futex_key(uaddr1, &key1);
820 if (unlikely(ret != 0))
821 goto out;
822 ret = get_futex_key(uaddr2, &key2);
823 if (unlikely(ret != 0))
824 goto out;
825
826 hb1 = hash_futex(&key1);
827 hb2 = hash_futex(&key2);
828
829 double_lock_hb(hb1, hb2);
830
831 if (likely(cmpval != NULL)) {
832 u32 curval;
833
834 ret = get_futex_value_locked(&curval, uaddr1);
835
836 if (unlikely(ret)) {
837 spin_unlock(&hb1->lock);
838 if (hb1 != hb2)
839 spin_unlock(&hb2->lock);
840
841 /*
842 * If we would have faulted, release mmap_sem, fault
843 * it in and start all over again.
844 */
845 up_read(&current->mm->mmap_sem);
846
847 ret = get_user(curval, uaddr1);
848
849 if (!ret)
850 goto retry;
851
852 return ret;
853 }
854 if (curval != *cmpval) {
855 ret = -EAGAIN;
856 goto out_unlock;
857 }
858 }
859
860 head1 = &hb1->chain;
861 list_for_each_entry_safe(this, next, head1, list) {
862 if (!match_futex (&this->key, &key1))
863 continue;
864 if (++ret <= nr_wake) {
865 wake_futex(this);
866 } else {
867 /*
868 * If key1 and key2 hash to the same bucket, no need to
869 * requeue.
870 */
871 if (likely(head1 != &hb2->chain)) {
872 list_move_tail(&this->list, &hb2->chain);
873 this->lock_ptr = &hb2->lock;
874 }
875 this->key = key2;
876 get_key_refs(&key2);
877 drop_count++;
878
879 if (ret - nr_wake >= nr_requeue)
880 break;
881 }
882 }
883
884out_unlock:
885 spin_unlock(&hb1->lock);
886 if (hb1 != hb2)
887 spin_unlock(&hb2->lock);
888
889 /* drop_key_refs() must be called outside the spinlocks. */
890 while (--drop_count >= 0)
891 drop_key_refs(&key1);
892
893out:
894 up_read(&current->mm->mmap_sem);
895 return ret;
896}
897
898/* The key must be already stored in q->key. */
899static inline struct futex_hash_bucket *
900queue_lock(struct futex_q *q, int fd, struct file *filp)
901{
902 struct futex_hash_bucket *hb;
903
904 q->fd = fd;
905 q->filp = filp;
906
907 init_waitqueue_head(&q->waiters);
908
909 get_key_refs(&q->key);
910 hb = hash_futex(&q->key);
911 q->lock_ptr = &hb->lock;
912
913 spin_lock(&hb->lock);
914 return hb;
915}
916
917static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
918{
919 list_add_tail(&q->list, &hb->chain);
920 q->task = current;
921 spin_unlock(&hb->lock);
922}
923
924static inline void
925queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
926{
927 spin_unlock(&hb->lock);
928 drop_key_refs(&q->key);
929}
930
931/*
932 * queue_me and unqueue_me must be called as a pair, each
933 * exactly once. They are called with the hashed spinlock held.
934 */
935
936/* The key must be already stored in q->key. */
937static void queue_me(struct futex_q *q, int fd, struct file *filp)
938{
939 struct futex_hash_bucket *hb;
940
941 hb = queue_lock(q, fd, filp);
942 __queue_me(q, hb);
943}
944
945/* Return 1 if we were still queued (ie. 0 means we were woken) */
946static int unqueue_me(struct futex_q *q)
947{
948 spinlock_t *lock_ptr;
949 int ret = 0;
950
951 /* In the common case we don't take the spinlock, which is nice. */
952 retry:
953 lock_ptr = q->lock_ptr;
954 barrier();
955 if (lock_ptr != 0) {
956 spin_lock(lock_ptr);
957 /*
958 * q->lock_ptr can change between reading it and
959 * spin_lock(), causing us to take the wrong lock. This
960 * corrects the race condition.
961 *
962 * Reasoning goes like this: if we have the wrong lock,
963 * q->lock_ptr must have changed (maybe several times)
964 * between reading it and the spin_lock(). It can
965 * change again after the spin_lock() but only if it was
966 * already changed before the spin_lock(). It cannot,
967 * however, change back to the original value. Therefore
968 * we can detect whether we acquired the correct lock.
969 */
970 if (unlikely(lock_ptr != q->lock_ptr)) {
971 spin_unlock(lock_ptr);
972 goto retry;
973 }
974 WARN_ON(list_empty(&q->list));
975 list_del(&q->list);
976
977 BUG_ON(q->pi_state);
978
979 spin_unlock(lock_ptr);
980 ret = 1;
981 }
982
983 drop_key_refs(&q->key);
984 return ret;
985}
986
987/*
988 * PI futexes can not be requeued and must remove themself from the
989 * hash bucket. The hash bucket lock is held on entry and dropped here.
990 */
991static void unqueue_me_pi(struct futex_q *q, struct futex_hash_bucket *hb)
992{
993 WARN_ON(list_empty(&q->list));
994 list_del(&q->list);
995
996 BUG_ON(!q->pi_state);
997 free_pi_state(q->pi_state);
998 q->pi_state = NULL;
999
1000 spin_unlock(&hb->lock);
1001
1002 drop_key_refs(&q->key);
1003}
1004
1005static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time)
1006{
1007 struct task_struct *curr = current;
1008 DECLARE_WAITQUEUE(wait, curr);
1009 struct futex_hash_bucket *hb;
1010 struct futex_q q;
1011 u32 uval;
1012 int ret;
1013
1014 q.pi_state = NULL;
1015 retry:
1016 down_read(&curr->mm->mmap_sem);
1017
1018 ret = get_futex_key(uaddr, &q.key);
1019 if (unlikely(ret != 0))
1020 goto out_release_sem;
1021
1022 hb = queue_lock(&q, -1, NULL);
1023
1024 /*
1025 * Access the page AFTER the futex is queued.
1026 * Order is important:
1027 *
1028 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1029 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
1030 *
1031 * The basic logical guarantee of a futex is that it blocks ONLY
1032 * if cond(var) is known to be true at the time of blocking, for
1033 * any cond. If we queued after testing *uaddr, that would open
1034 * a race condition where we could block indefinitely with
1035 * cond(var) false, which would violate the guarantee.
1036 *
1037 * A consequence is that futex_wait() can return zero and absorb
1038 * a wakeup when *uaddr != val on entry to the syscall. This is
1039 * rare, but normal.
1040 *
1041 * We hold the mmap semaphore, so the mapping cannot have changed
1042 * since we looked it up in get_futex_key.
1043 */
1044 ret = get_futex_value_locked(&uval, uaddr);
1045
1046 if (unlikely(ret)) {
1047 queue_unlock(&q, hb);
1048
1049 /*
1050 * If we would have faulted, release mmap_sem, fault it in and
1051 * start all over again.
1052 */
1053 up_read(&curr->mm->mmap_sem);
1054
1055 ret = get_user(uval, uaddr);
1056
1057 if (!ret)
1058 goto retry;
1059 return ret;
1060 }
1061 ret = -EWOULDBLOCK;
1062 if (uval != val)
1063 goto out_unlock_release_sem;
1064
1065 /* Only actually queue if *uaddr contained val. */
1066 __queue_me(&q, hb);
1067
1068 /*
1069 * Now the futex is queued and we have checked the data, we
1070 * don't want to hold mmap_sem while we sleep.
1071 */
1072 up_read(&curr->mm->mmap_sem);
1073
1074 /*
1075 * There might have been scheduling since the queue_me(), as we
1076 * cannot hold a spinlock across the get_user() in case it
1077 * faults, and we cannot just set TASK_INTERRUPTIBLE state when
1078 * queueing ourselves into the futex hash. This code thus has to
1079 * rely on the futex_wake() code removing us from hash when it
1080 * wakes us up.
1081 */
1082
1083 /* add_wait_queue is the barrier after __set_current_state. */
1084 __set_current_state(TASK_INTERRUPTIBLE);
1085 add_wait_queue(&q.waiters, &wait);
1086 /*
1087 * !list_empty() is safe here without any lock.
1088 * q.lock_ptr != 0 is not safe, because of ordering against wakeup.
1089 */
1090 if (likely(!list_empty(&q.list)))
1091 time = schedule_timeout(time);
1092 __set_current_state(TASK_RUNNING);
1093
1094 /*
1095 * NOTE: we don't remove ourselves from the waitqueue because
1096 * we are the only user of it.
1097 */
1098
1099 /* If we were woken (and unqueued), we succeeded, whatever. */
1100 if (!unqueue_me(&q))
1101 return 0;
1102 if (time == 0)
1103 return -ETIMEDOUT;
1104 /*
1105 * We expect signal_pending(current), but another thread may
1106 * have handled it for us already.
1107 */
1108 return -EINTR;
1109
1110 out_unlock_release_sem:
1111 queue_unlock(&q, hb);
1112
1113 out_release_sem:
1114 up_read(&curr->mm->mmap_sem);
1115 return ret;
1116}
1117
1118/*
1119 * Userspace tried a 0 -> TID atomic transition of the futex value
1120 * and failed. The kernel side here does the whole locking operation:
1121 * if there are waiters then it will block, it does PI, etc. (Due to
1122 * races the kernel might see a 0 value of the futex too.)
1123 */
1124static int futex_lock_pi(u32 __user *uaddr, int detect, unsigned long sec,
1125 long nsec, int trylock)
1126{
1127 struct hrtimer_sleeper timeout, *to = NULL;
1128 struct task_struct *curr = current;
1129 struct futex_hash_bucket *hb;
1130 u32 uval, newval, curval;
1131 struct futex_q q;
1132 int ret, attempt = 0;
1133
1134 if (refill_pi_state_cache())
1135 return -ENOMEM;
1136
1137 if (sec != MAX_SCHEDULE_TIMEOUT) {
1138 to = &timeout;
1139 hrtimer_init(&to->timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
1140 hrtimer_init_sleeper(to, current);
1141 to->timer.expires = ktime_set(sec, nsec);
1142 }
1143
1144 q.pi_state = NULL;
1145 retry:
1146 down_read(&curr->mm->mmap_sem);
1147
1148 ret = get_futex_key(uaddr, &q.key);
1149 if (unlikely(ret != 0))
1150 goto out_release_sem;
1151
1152 hb = queue_lock(&q, -1, NULL);
1153
1154 retry_locked:
1155 /*
1156 * To avoid races, we attempt to take the lock here again
1157 * (by doing a 0 -> TID atomic cmpxchg), while holding all
1158 * the locks. It will most likely not succeed.
1159 */
1160 newval = current->pid;
1161
1162 pagefault_disable();
1163 curval = futex_atomic_cmpxchg_inatomic(uaddr, 0, newval);
1164 pagefault_enable();
1165
1166 if (unlikely(curval == -EFAULT))
1167 goto uaddr_faulted;
1168
1169 /* We own the lock already */
1170 if (unlikely((curval & FUTEX_TID_MASK) == current->pid)) {
1171 if (!detect && 0)
1172 force_sig(SIGKILL, current);
1173 ret = -EDEADLK;
1174 goto out_unlock_release_sem;
1175 }
1176
1177 /*
1178 * Surprise - we got the lock. Just return
1179 * to userspace:
1180 */
1181 if (unlikely(!curval))
1182 goto out_unlock_release_sem;
1183
1184 uval = curval;
1185 newval = uval | FUTEX_WAITERS;
1186
1187 pagefault_disable();
1188 curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
1189 pagefault_enable();
1190
1191 if (unlikely(curval == -EFAULT))
1192 goto uaddr_faulted;
1193 if (unlikely(curval != uval))
1194 goto retry_locked;
1195
1196 /*
1197 * We dont have the lock. Look up the PI state (or create it if
1198 * we are the first waiter):
1199 */
1200 ret = lookup_pi_state(uval, hb, &q);
1201
1202 if (unlikely(ret)) {
1203 /*
1204 * There were no waiters and the owner task lookup
1205 * failed. When the OWNER_DIED bit is set, then we
1206 * know that this is a robust futex and we actually
1207 * take the lock. This is safe as we are protected by
1208 * the hash bucket lock. We also set the waiters bit
1209 * unconditionally here, to simplify glibc handling of
1210 * multiple tasks racing to acquire the lock and
1211 * cleanup the problems which were left by the dead
1212 * owner.
1213 */
1214 if (curval & FUTEX_OWNER_DIED) {
1215 uval = newval;
1216 newval = current->pid |
1217 FUTEX_OWNER_DIED | FUTEX_WAITERS;
1218
1219 pagefault_disable();
1220 curval = futex_atomic_cmpxchg_inatomic(uaddr,
1221 uval, newval);
1222 pagefault_enable();
1223
1224 if (unlikely(curval == -EFAULT))
1225 goto uaddr_faulted;
1226 if (unlikely(curval != uval))
1227 goto retry_locked;
1228 ret = 0;
1229 }
1230 goto out_unlock_release_sem;
1231 }
1232
1233 /*
1234 * Only actually queue now that the atomic ops are done:
1235 */
1236 __queue_me(&q, hb);
1237
1238 /*
1239 * Now the futex is queued and we have checked the data, we
1240 * don't want to hold mmap_sem while we sleep.
1241 */
1242 up_read(&curr->mm->mmap_sem);
1243
1244 WARN_ON(!q.pi_state);
1245 /*
1246 * Block on the PI mutex:
1247 */
1248 if (!trylock)
1249 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
1250 else {
1251 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
1252 /* Fixup the trylock return value: */
1253 ret = ret ? 0 : -EWOULDBLOCK;
1254 }
1255
1256 down_read(&curr->mm->mmap_sem);
1257 spin_lock(q.lock_ptr);
1258
1259 /*
1260 * Got the lock. We might not be the anticipated owner if we
1261 * did a lock-steal - fix up the PI-state in that case.
1262 */
1263 if (!ret && q.pi_state->owner != curr) {
1264 u32 newtid = current->pid | FUTEX_WAITERS;
1265
1266 /* Owner died? */
1267 if (q.pi_state->owner != NULL) {
1268 spin_lock_irq(&q.pi_state->owner->pi_lock);
1269 WARN_ON(list_empty(&q.pi_state->list));
1270 list_del_init(&q.pi_state->list);
1271 spin_unlock_irq(&q.pi_state->owner->pi_lock);
1272 } else
1273 newtid |= FUTEX_OWNER_DIED;
1274
1275 q.pi_state->owner = current;
1276
1277 spin_lock_irq(&current->pi_lock);
1278 WARN_ON(!list_empty(&q.pi_state->list));
1279 list_add(&q.pi_state->list, &current->pi_state_list);
1280 spin_unlock_irq(&current->pi_lock);
1281
1282 /* Unqueue and drop the lock */
1283 unqueue_me_pi(&q, hb);
1284 up_read(&curr->mm->mmap_sem);
1285 /*
1286 * We own it, so we have to replace the pending owner
1287 * TID. This must be atomic as we have preserve the
1288 * owner died bit here.
1289 */
1290 ret = get_user(uval, uaddr);
1291 while (!ret) {
1292 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1293 curval = futex_atomic_cmpxchg_inatomic(uaddr,
1294 uval, newval);
1295 if (curval == -EFAULT)
1296 ret = -EFAULT;
1297 if (curval == uval)
1298 break;
1299 uval = curval;
1300 }
1301 } else {
1302 /*
1303 * Catch the rare case, where the lock was released
1304 * when we were on the way back before we locked
1305 * the hash bucket.
1306 */
1307 if (ret && q.pi_state->owner == curr) {
1308 if (rt_mutex_trylock(&q.pi_state->pi_mutex))
1309 ret = 0;
1310 }
1311 /* Unqueue and drop the lock */
1312 unqueue_me_pi(&q, hb);
1313 up_read(&curr->mm->mmap_sem);
1314 }
1315
1316 if (!detect && ret == -EDEADLK && 0)
1317 force_sig(SIGKILL, current);
1318
1319 return ret != -EINTR ? ret : -ERESTARTNOINTR;
1320
1321 out_unlock_release_sem:
1322 queue_unlock(&q, hb);
1323
1324 out_release_sem:
1325 up_read(&curr->mm->mmap_sem);
1326 return ret;
1327
1328 uaddr_faulted:
1329 /*
1330 * We have to r/w *(int __user *)uaddr, but we can't modify it
1331 * non-atomically. Therefore, if get_user below is not
1332 * enough, we need to handle the fault ourselves, while
1333 * still holding the mmap_sem.
1334 */
1335 if (attempt++) {
1336 if (futex_handle_fault((unsigned long)uaddr, attempt)) {
1337 ret = -EFAULT;
1338 goto out_unlock_release_sem;
1339 }
1340 goto retry_locked;
1341 }
1342
1343 queue_unlock(&q, hb);
1344 up_read(&curr->mm->mmap_sem);
1345
1346 ret = get_user(uval, uaddr);
1347 if (!ret && (uval != -EFAULT))
1348 goto retry;
1349
1350 return ret;
1351}
1352
1353/*
1354 * Userspace attempted a TID -> 0 atomic transition, and failed.
1355 * This is the in-kernel slowpath: we look up the PI state (if any),
1356 * and do the rt-mutex unlock.
1357 */
1358static int futex_unlock_pi(u32 __user *uaddr)
1359{
1360 struct futex_hash_bucket *hb;
1361 struct futex_q *this, *next;
1362 u32 uval;
1363 struct list_head *head;
1364 union futex_key key;
1365 int ret, attempt = 0;
1366
1367retry:
1368 if (get_user(uval, uaddr))
1369 return -EFAULT;
1370 /*
1371 * We release only a lock we actually own:
1372 */
1373 if ((uval & FUTEX_TID_MASK) != current->pid)
1374 return -EPERM;
1375 /*
1376 * First take all the futex related locks:
1377 */
1378 down_read(&current->mm->mmap_sem);
1379
1380 ret = get_futex_key(uaddr, &key);
1381 if (unlikely(ret != 0))
1382 goto out;
1383
1384 hb = hash_futex(&key);
1385 spin_lock(&hb->lock);
1386
1387retry_locked:
1388 /*
1389 * To avoid races, try to do the TID -> 0 atomic transition
1390 * again. If it succeeds then we can return without waking
1391 * anyone else up:
1392 */
1393 if (!(uval & FUTEX_OWNER_DIED)) {
1394 pagefault_disable();
1395 uval = futex_atomic_cmpxchg_inatomic(uaddr, current->pid, 0);
1396 pagefault_enable();
1397 }
1398
1399 if (unlikely(uval == -EFAULT))
1400 goto pi_faulted;
1401 /*
1402 * Rare case: we managed to release the lock atomically,
1403 * no need to wake anyone else up:
1404 */
1405 if (unlikely(uval == current->pid))
1406 goto out_unlock;
1407
1408 /*
1409 * Ok, other tasks may need to be woken up - check waiters
1410 * and do the wakeup if necessary:
1411 */
1412 head = &hb->chain;
1413
1414 list_for_each_entry_safe(this, next, head, list) {
1415 if (!match_futex (&this->key, &key))
1416 continue;
1417 ret = wake_futex_pi(uaddr, uval, this);
1418 /*
1419 * The atomic access to the futex value
1420 * generated a pagefault, so retry the
1421 * user-access and the wakeup:
1422 */
1423 if (ret == -EFAULT)
1424 goto pi_faulted;
1425 goto out_unlock;
1426 }
1427 /*
1428 * No waiters - kernel unlocks the futex:
1429 */
1430 if (!(uval & FUTEX_OWNER_DIED)) {
1431 ret = unlock_futex_pi(uaddr, uval);
1432 if (ret == -EFAULT)
1433 goto pi_faulted;
1434 }
1435
1436out_unlock:
1437 spin_unlock(&hb->lock);
1438out:
1439 up_read(&current->mm->mmap_sem);
1440
1441 return ret;
1442
1443pi_faulted:
1444 /*
1445 * We have to r/w *(int __user *)uaddr, but we can't modify it
1446 * non-atomically. Therefore, if get_user below is not
1447 * enough, we need to handle the fault ourselves, while
1448 * still holding the mmap_sem.
1449 */
1450 if (attempt++) {
1451 if (futex_handle_fault((unsigned long)uaddr, attempt)) {
1452 ret = -EFAULT;
1453 goto out_unlock;
1454 }
1455 goto retry_locked;
1456 }
1457
1458 spin_unlock(&hb->lock);
1459 up_read(&current->mm->mmap_sem);
1460
1461 ret = get_user(uval, uaddr);
1462 if (!ret && (uval != -EFAULT))
1463 goto retry;
1464
1465 return ret;
1466}
1467
1468static int futex_close(struct inode *inode, struct file *filp)
1469{
1470 struct futex_q *q = filp->private_data;
1471
1472 unqueue_me(q);
1473 kfree(q);
1474
1475 return 0;
1476}
1477
1478/* This is one-shot: once it's gone off you need a new fd */
1479static unsigned int futex_poll(struct file *filp,
1480 struct poll_table_struct *wait)
1481{
1482 struct futex_q *q = filp->private_data;
1483 int ret = 0;
1484
1485 poll_wait(filp, &q->waiters, wait);
1486
1487 /*
1488 * list_empty() is safe here without any lock.
1489 * q->lock_ptr != 0 is not safe, because of ordering against wakeup.
1490 */
1491 if (list_empty(&q->list))
1492 ret = POLLIN | POLLRDNORM;
1493
1494 return ret;
1495}
1496
1497static const struct file_operations futex_fops = {
1498 .release = futex_close,
1499 .poll = futex_poll,
1500};
1501
1502/*
1503 * Signal allows caller to avoid the race which would occur if they
1504 * set the sigio stuff up afterwards.
1505 */
1506static int futex_fd(u32 __user *uaddr, int signal)
1507{
1508 struct futex_q *q;
1509 struct file *filp;
1510 int ret, err;
1511 static unsigned long printk_interval;
1512
1513 if (printk_timed_ratelimit(&printk_interval, 60 * 60 * 1000)) {
1514 printk(KERN_WARNING "Process `%s' used FUTEX_FD, which "
1515 "will be removed from the kernel in June 2007\n",
1516 current->comm);
1517 }
1518
1519 ret = -EINVAL;
1520 if (!valid_signal(signal))
1521 goto out;
1522
1523 ret = get_unused_fd();
1524 if (ret < 0)
1525 goto out;
1526 filp = get_empty_filp();
1527 if (!filp) {
1528 put_unused_fd(ret);
1529 ret = -ENFILE;
1530 goto out;
1531 }
1532 filp->f_op = &futex_fops;
1533 filp->f_path.mnt = mntget(futex_mnt);
1534 filp->f_path.dentry = dget(futex_mnt->mnt_root);
1535 filp->f_mapping = filp->f_path.dentry->d_inode->i_mapping;
1536
1537 if (signal) {
1538 err = __f_setown(filp, task_pid(current), PIDTYPE_PID, 1);
1539 if (err < 0) {
1540 goto error;
1541 }
1542 filp->f_owner.signum = signal;
1543 }
1544
1545 q = kmalloc(sizeof(*q), GFP_KERNEL);
1546 if (!q) {
1547 err = -ENOMEM;
1548 goto error;
1549 }
1550 q->pi_state = NULL;
1551
1552 down_read(&current->mm->mmap_sem);
1553 err = get_futex_key(uaddr, &q->key);
1554
1555 if (unlikely(err != 0)) {
1556 up_read(&current->mm->mmap_sem);
1557 kfree(q);
1558 goto error;
1559 }
1560
1561 /*
1562 * queue_me() must be called before releasing mmap_sem, because
1563 * key->shared.inode needs to be referenced while holding it.
1564 */
1565 filp->private_data = q;
1566
1567 queue_me(q, ret, filp);
1568 up_read(&current->mm->mmap_sem);
1569
1570 /* Now we map fd to filp, so userspace can access it */
1571 fd_install(ret, filp);
1572out:
1573 return ret;
1574error:
1575 put_unused_fd(ret);
1576 put_filp(filp);
1577 ret = err;
1578 goto out;
1579}
1580
1581/*
1582 * Support for robust futexes: the kernel cleans up held futexes at
1583 * thread exit time.
1584 *
1585 * Implementation: user-space maintains a per-thread list of locks it
1586 * is holding. Upon do_exit(), the kernel carefully walks this list,
1587 * and marks all locks that are owned by this thread with the
1588 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
1589 * always manipulated with the lock held, so the list is private and
1590 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
1591 * field, to allow the kernel to clean up if the thread dies after
1592 * acquiring the lock, but just before it could have added itself to
1593 * the list. There can only be one such pending lock.
1594 */
1595
1596/**
1597 * sys_set_robust_list - set the robust-futex list head of a task
1598 * @head: pointer to the list-head
1599 * @len: length of the list-head, as userspace expects
1600 */
1601asmlinkage long
1602sys_set_robust_list(struct robust_list_head __user *head,
1603 size_t len)
1604{
1605 /*
1606 * The kernel knows only one size for now:
1607 */
1608 if (unlikely(len != sizeof(*head)))
1609 return -EINVAL;
1610
1611 current->robust_list = head;
1612
1613 return 0;
1614}
1615
1616/**
1617 * sys_get_robust_list - get the robust-futex list head of a task
1618 * @pid: pid of the process [zero for current task]
1619 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
1620 * @len_ptr: pointer to a length field, the kernel fills in the header size
1621 */
1622asmlinkage long
1623sys_get_robust_list(int pid, struct robust_list_head __user * __user *head_ptr,
1624 size_t __user *len_ptr)
1625{
1626 struct robust_list_head __user *head;
1627 unsigned long ret;
1628
1629 if (!pid)
1630 head = current->robust_list;
1631 else {
1632 struct task_struct *p;
1633
1634 ret = -ESRCH;
1635 rcu_read_lock();
1636 p = find_task_by_pid(pid);
1637 if (!p)
1638 goto err_unlock;
1639 ret = -EPERM;
1640 if ((current->euid != p->euid) && (current->euid != p->uid) &&
1641 !capable(CAP_SYS_PTRACE))
1642 goto err_unlock;
1643 head = p->robust_list;
1644 rcu_read_unlock();
1645 }
1646
1647 if (put_user(sizeof(*head), len_ptr))
1648 return -EFAULT;
1649 return put_user(head, head_ptr);
1650
1651err_unlock:
1652 rcu_read_unlock();
1653
1654 return ret;
1655}
1656
1657/*
1658 * Process a futex-list entry, check whether it's owned by the
1659 * dying task, and do notification if so:
1660 */
1661int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
1662{
1663 u32 uval, nval, mval;
1664
1665retry:
1666 if (get_user(uval, uaddr))
1667 return -1;
1668
1669 if ((uval & FUTEX_TID_MASK) == curr->pid) {
1670 /*
1671 * Ok, this dying thread is truly holding a futex
1672 * of interest. Set the OWNER_DIED bit atomically
1673 * via cmpxchg, and if the value had FUTEX_WAITERS
1674 * set, wake up a waiter (if any). (We have to do a
1675 * futex_wake() even if OWNER_DIED is already set -
1676 * to handle the rare but possible case of recursive
1677 * thread-death.) The rest of the cleanup is done in
1678 * userspace.
1679 */
1680 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
1681 nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
1682
1683 if (nval == -EFAULT)
1684 return -1;
1685
1686 if (nval != uval)
1687 goto retry;
1688
1689 /*
1690 * Wake robust non-PI futexes here. The wakeup of
1691 * PI futexes happens in exit_pi_state():
1692 */
1693 if (!pi) {
1694 if (uval & FUTEX_WAITERS)
1695 futex_wake(uaddr, 1);
1696 }
1697 }
1698 return 0;
1699}
1700
1701/*
1702 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
1703 */
1704static inline int fetch_robust_entry(struct robust_list __user **entry,
1705 struct robust_list __user * __user *head,
1706 int *pi)
1707{
1708 unsigned long uentry;
1709
1710 if (get_user(uentry, (unsigned long __user *)head))
1711 return -EFAULT;
1712
1713 *entry = (void __user *)(uentry & ~1UL);
1714 *pi = uentry & 1;
1715
1716 return 0;
1717}
1718
1719/*
1720 * Walk curr->robust_list (very carefully, it's a userspace list!)
1721 * and mark any locks found there dead, and notify any waiters.
1722 *
1723 * We silently return on any sign of list-walking problem.
1724 */
1725void exit_robust_list(struct task_struct *curr)
1726{
1727 struct robust_list_head __user *head = curr->robust_list;
1728 struct robust_list __user *entry, *pending;
1729 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
1730 unsigned long futex_offset;
1731
1732 /*
1733 * Fetch the list head (which was registered earlier, via
1734 * sys_set_robust_list()):
1735 */
1736 if (fetch_robust_entry(&entry, &head->list.next, &pi))
1737 return;
1738 /*
1739 * Fetch the relative futex offset:
1740 */
1741 if (get_user(futex_offset, &head->futex_offset))
1742 return;
1743 /*
1744 * Fetch any possibly pending lock-add first, and handle it
1745 * if it exists:
1746 */
1747 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
1748 return;
1749
1750 if (pending)
1751 handle_futex_death((void __user *)pending + futex_offset, curr, pip);
1752
1753 while (entry != &head->list) {
1754 /*
1755 * A pending lock might already be on the list, so
1756 * don't process it twice:
1757 */
1758 if (entry != pending)
1759 if (handle_futex_death((void __user *)entry + futex_offset,
1760 curr, pi))
1761 return;
1762 /*
1763 * Fetch the next entry in the list:
1764 */
1765 if (fetch_robust_entry(&entry, &entry->next, &pi))
1766 return;
1767 /*
1768 * Avoid excessively long or circular lists:
1769 */
1770 if (!--limit)
1771 break;
1772
1773 cond_resched();
1774 }
1775}
1776
1777long do_futex(u32 __user *uaddr, int op, u32 val, unsigned long timeout,
1778 u32 __user *uaddr2, u32 val2, u32 val3)
1779{
1780 int ret;
1781
1782 switch (op) {
1783 case FUTEX_WAIT:
1784 ret = futex_wait(uaddr, val, timeout);
1785 break;
1786 case FUTEX_WAKE:
1787 ret = futex_wake(uaddr, val);
1788 break;
1789 case FUTEX_FD:
1790 /* non-zero val means F_SETOWN(getpid()) & F_SETSIG(val) */
1791 ret = futex_fd(uaddr, val);
1792 break;
1793 case FUTEX_REQUEUE:
1794 ret = futex_requeue(uaddr, uaddr2, val, val2, NULL);
1795 break;
1796 case FUTEX_CMP_REQUEUE:
1797 ret = futex_requeue(uaddr, uaddr2, val, val2, &val3);
1798 break;
1799 case FUTEX_WAKE_OP:
1800 ret = futex_wake_op(uaddr, uaddr2, val, val2, val3);
1801 break;
1802 case FUTEX_LOCK_PI:
1803 ret = futex_lock_pi(uaddr, val, timeout, val2, 0);
1804 break;
1805 case FUTEX_UNLOCK_PI:
1806 ret = futex_unlock_pi(uaddr);
1807 break;
1808 case FUTEX_TRYLOCK_PI:
1809 ret = futex_lock_pi(uaddr, 0, timeout, val2, 1);
1810 break;
1811 default:
1812 ret = -ENOSYS;
1813 }
1814 return ret;
1815}
1816
1817
1818asmlinkage long sys_futex(u32 __user *uaddr, int op, u32 val,
1819 struct timespec __user *utime, u32 __user *uaddr2,
1820 u32 val3)
1821{
1822 struct timespec t;
1823 unsigned long timeout = MAX_SCHEDULE_TIMEOUT;
1824 u32 val2 = 0;
1825
1826 if (utime && (op == FUTEX_WAIT || op == FUTEX_LOCK_PI)) {
1827 if (copy_from_user(&t, utime, sizeof(t)) != 0)
1828 return -EFAULT;
1829 if (!timespec_valid(&t))
1830 return -EINVAL;
1831 if (op == FUTEX_WAIT)
1832 timeout = timespec_to_jiffies(&t) + 1;
1833 else {
1834 timeout = t.tv_sec;
1835 val2 = t.tv_nsec;
1836 }
1837 }
1838 /*
1839 * requeue parameter in 'utime' if op == FUTEX_REQUEUE.
1840 */
1841 if (op == FUTEX_REQUEUE || op == FUTEX_CMP_REQUEUE)
1842 val2 = (u32) (unsigned long) utime;
1843
1844 return do_futex(uaddr, op, val, timeout, uaddr2, val2, val3);
1845}
1846
1847static int futexfs_get_sb(struct file_system_type *fs_type,
1848 int flags, const char *dev_name, void *data,
1849 struct vfsmount *mnt)
1850{
1851 return get_sb_pseudo(fs_type, "futex", NULL, 0xBAD1DEA, mnt);
1852}
1853
1854static struct file_system_type futex_fs_type = {
1855 .name = "futexfs",
1856 .get_sb = futexfs_get_sb,
1857 .kill_sb = kill_anon_super,
1858};
1859
1860static int __init init(void)
1861{
1862 int i = register_filesystem(&futex_fs_type);
1863
1864 if (i)
1865 return i;
1866
1867 futex_mnt = kern_mount(&futex_fs_type);
1868 if (IS_ERR(futex_mnt)) {
1869 unregister_filesystem(&futex_fs_type);
1870 return PTR_ERR(futex_mnt);
1871 }
1872
1873 for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
1874 INIT_LIST_HEAD(&futex_queues[i].chain);
1875 spin_lock_init(&futex_queues[i].lock);
1876 }
1877 return 0;
1878}
1879__initcall(init);