7ae2f50641ed16c635d17b01ca9773c9ab1747d1
[linux-2.6.git] / kernel / futex.c
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 <mingo@redhat.com>
17  *  Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
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 <linux/module.h>
52 #include <asm/futex.h>
53
54 #include "rtmutex_common.h"
55
56 #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
57
58 /*
59  * Priority Inheritance state:
60  */
61 struct futex_pi_state {
62         /*
63          * list of 'owned' pi_state instances - these have to be
64          * cleaned up in do_exit() if the task exits prematurely:
65          */
66         struct list_head list;
67
68         /*
69          * The PI object:
70          */
71         struct rt_mutex pi_mutex;
72
73         struct task_struct *owner;
74         atomic_t refcount;
75
76         union futex_key key;
77 };
78
79 /*
80  * We use this hashed waitqueue instead of a normal wait_queue_t, so
81  * we can wake only the relevant ones (hashed queues may be shared).
82  *
83  * A futex_q has a woken state, just like tasks have TASK_RUNNING.
84  * It is considered woken when list_empty(&q->list) || q->lock_ptr == 0.
85  * The order of wakup is always to make the first condition true, then
86  * wake up q->waiters, then make the second condition true.
87  */
88 struct futex_q {
89         struct list_head list;
90         wait_queue_head_t waiters;
91
92         /* Which hash list lock to use: */
93         spinlock_t *lock_ptr;
94
95         /* Key which the futex is hashed on: */
96         union futex_key key;
97
98         /* For fd, sigio sent using these: */
99         int fd;
100         struct file *filp;
101
102         /* Optional priority inheritance state: */
103         struct futex_pi_state *pi_state;
104         struct task_struct *task;
105 };
106
107 /*
108  * Split the global futex_lock into every hash list lock.
109  */
110 struct futex_hash_bucket {
111        spinlock_t              lock;
112        struct list_head       chain;
113 };
114
115 static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
116
117 /* Futex-fs vfsmount entry: */
118 static struct vfsmount *futex_mnt;
119
120 /*
121  * We hash on the keys returned from get_futex_key (see below).
122  */
123 static struct futex_hash_bucket *hash_futex(union futex_key *key)
124 {
125         u32 hash = jhash2((u32*)&key->both.word,
126                           (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
127                           key->both.offset);
128         return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
129 }
130
131 /*
132  * Return 1 if two futex_keys are equal, 0 otherwise.
133  */
134 static inline int match_futex(union futex_key *key1, union futex_key *key2)
135 {
136         return (key1->both.word == key2->both.word
137                 && key1->both.ptr == key2->both.ptr
138                 && key1->both.offset == key2->both.offset);
139 }
140
141 /*
142  * Get parameters which are the keys for a futex.
143  *
144  * For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,
145  * offset_within_page).  For private mappings, it's (uaddr, current->mm).
146  * We can usually work out the index without swapping in the page.
147  *
148  * Returns: 0, or negative error code.
149  * The key words are stored in *key on success.
150  *
151  * Should be called with &current->mm->mmap_sem but NOT any spinlocks.
152  */
153 int get_futex_key(u32 __user *uaddr, union futex_key *key)
154 {
155         unsigned long address = (unsigned long)uaddr;
156         struct mm_struct *mm = current->mm;
157         struct vm_area_struct *vma;
158         struct page *page;
159         int err;
160
161         /*
162          * The futex address must be "naturally" aligned.
163          */
164         key->both.offset = address % PAGE_SIZE;
165         if (unlikely((key->both.offset % sizeof(u32)) != 0))
166                 return -EINVAL;
167         address -= key->both.offset;
168
169         /*
170          * The futex is hashed differently depending on whether
171          * it's in a shared or private mapping.  So check vma first.
172          */
173         vma = find_extend_vma(mm, address);
174         if (unlikely(!vma))
175                 return -EFAULT;
176
177         /*
178          * Permissions.
179          */
180         if (unlikely((vma->vm_flags & (VM_IO|VM_READ)) != VM_READ))
181                 return (vma->vm_flags & VM_IO) ? -EPERM : -EACCES;
182
183         /*
184          * Private mappings are handled in a simple way.
185          *
186          * NOTE: When userspace waits on a MAP_SHARED mapping, even if
187          * it's a read-only handle, it's expected that futexes attach to
188          * the object not the particular process.  Therefore we use
189          * VM_MAYSHARE here, not VM_SHARED which is restricted to shared
190          * mappings of _writable_ handles.
191          */
192         if (likely(!(vma->vm_flags & VM_MAYSHARE))) {
193                 key->private.mm = mm;
194                 key->private.address = address;
195                 return 0;
196         }
197
198         /*
199          * Linear file mappings are also simple.
200          */
201         key->shared.inode = vma->vm_file->f_path.dentry->d_inode;
202         key->both.offset++; /* Bit 0 of offset indicates inode-based key. */
203         if (likely(!(vma->vm_flags & VM_NONLINEAR))) {
204                 key->shared.pgoff = (((address - vma->vm_start) >> PAGE_SHIFT)
205                                      + vma->vm_pgoff);
206                 return 0;
207         }
208
209         /*
210          * We could walk the page table to read the non-linear
211          * pte, and get the page index without fetching the page
212          * from swap.  But that's a lot of code to duplicate here
213          * for a rare case, so we simply fetch the page.
214          */
215         err = get_user_pages(current, mm, address, 1, 0, 0, &page, NULL);
216         if (err >= 0) {
217                 key->shared.pgoff =
218                         page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
219                 put_page(page);
220                 return 0;
221         }
222         return err;
223 }
224 EXPORT_SYMBOL_GPL(get_futex_key);
225
226 /*
227  * Take a reference to the resource addressed by a key.
228  * Can be called while holding spinlocks.
229  *
230  * NOTE: mmap_sem MUST be held between get_futex_key() and calling this
231  * function, if it is called at all.  mmap_sem keeps key->shared.inode valid.
232  */
233 inline void get_futex_key_refs(union futex_key *key)
234 {
235         if (key->both.ptr != 0) {
236                 if (key->both.offset & 1)
237                         atomic_inc(&key->shared.inode->i_count);
238                 else
239                         atomic_inc(&key->private.mm->mm_count);
240         }
241 }
242 EXPORT_SYMBOL_GPL(get_futex_key_refs);
243
244 /*
245  * Drop a reference to the resource addressed by a key.
246  * The hash bucket spinlock must not be held.
247  */
248 void drop_futex_key_refs(union futex_key *key)
249 {
250         if (key->both.ptr != 0) {
251                 if (key->both.offset & 1)
252                         iput(key->shared.inode);
253                 else
254                         mmdrop(key->private.mm);
255         }
256 }
257 EXPORT_SYMBOL_GPL(drop_futex_key_refs);
258
259 static inline int get_futex_value_locked(u32 *dest, u32 __user *from)
260 {
261         int ret;
262
263         pagefault_disable();
264         ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
265         pagefault_enable();
266
267         return ret ? -EFAULT : 0;
268 }
269
270 /*
271  * Fault handling. Called with current->mm->mmap_sem held.
272  */
273 static int futex_handle_fault(unsigned long address, int attempt)
274 {
275         struct vm_area_struct * vma;
276         struct mm_struct *mm = current->mm;
277
278         if (attempt > 2 || !(vma = find_vma(mm, address)) ||
279             vma->vm_start > address || !(vma->vm_flags & VM_WRITE))
280                 return -EFAULT;
281
282         switch (handle_mm_fault(mm, vma, address, 1)) {
283         case VM_FAULT_MINOR:
284                 current->min_flt++;
285                 break;
286         case VM_FAULT_MAJOR:
287                 current->maj_flt++;
288                 break;
289         default:
290                 return -EFAULT;
291         }
292         return 0;
293 }
294
295 /*
296  * PI code:
297  */
298 static int refill_pi_state_cache(void)
299 {
300         struct futex_pi_state *pi_state;
301
302         if (likely(current->pi_state_cache))
303                 return 0;
304
305         pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
306
307         if (!pi_state)
308                 return -ENOMEM;
309
310         INIT_LIST_HEAD(&pi_state->list);
311         /* pi_mutex gets initialized later */
312         pi_state->owner = NULL;
313         atomic_set(&pi_state->refcount, 1);
314
315         current->pi_state_cache = pi_state;
316
317         return 0;
318 }
319
320 static struct futex_pi_state * alloc_pi_state(void)
321 {
322         struct futex_pi_state *pi_state = current->pi_state_cache;
323
324         WARN_ON(!pi_state);
325         current->pi_state_cache = NULL;
326
327         return pi_state;
328 }
329
330 static void free_pi_state(struct futex_pi_state *pi_state)
331 {
332         if (!atomic_dec_and_test(&pi_state->refcount))
333                 return;
334
335         /*
336          * If pi_state->owner is NULL, the owner is most probably dying
337          * and has cleaned up the pi_state already
338          */
339         if (pi_state->owner) {
340                 spin_lock_irq(&pi_state->owner->pi_lock);
341                 list_del_init(&pi_state->list);
342                 spin_unlock_irq(&pi_state->owner->pi_lock);
343
344                 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
345         }
346
347         if (current->pi_state_cache)
348                 kfree(pi_state);
349         else {
350                 /*
351                  * pi_state->list is already empty.
352                  * clear pi_state->owner.
353                  * refcount is at 0 - put it back to 1.
354                  */
355                 pi_state->owner = NULL;
356                 atomic_set(&pi_state->refcount, 1);
357                 current->pi_state_cache = pi_state;
358         }
359 }
360
361 /*
362  * Look up the task based on what TID userspace gave us.
363  * We dont trust it.
364  */
365 static struct task_struct * futex_find_get_task(pid_t pid)
366 {
367         struct task_struct *p;
368
369         rcu_read_lock();
370         p = find_task_by_pid(pid);
371         if (!p)
372                 goto out_unlock;
373         if ((current->euid != p->euid) && (current->euid != p->uid)) {
374                 p = NULL;
375                 goto out_unlock;
376         }
377         if (p->exit_state != 0) {
378                 p = NULL;
379                 goto out_unlock;
380         }
381         get_task_struct(p);
382 out_unlock:
383         rcu_read_unlock();
384
385         return p;
386 }
387
388 /*
389  * This task is holding PI mutexes at exit time => bad.
390  * Kernel cleans up PI-state, but userspace is likely hosed.
391  * (Robust-futex cleanup is separate and might save the day for userspace.)
392  */
393 void exit_pi_state_list(struct task_struct *curr)
394 {
395         struct list_head *next, *head = &curr->pi_state_list;
396         struct futex_pi_state *pi_state;
397         struct futex_hash_bucket *hb;
398         union futex_key key;
399
400         /*
401          * We are a ZOMBIE and nobody can enqueue itself on
402          * pi_state_list anymore, but we have to be careful
403          * versus waiters unqueueing themselves:
404          */
405         spin_lock_irq(&curr->pi_lock);
406         while (!list_empty(head)) {
407
408                 next = head->next;
409                 pi_state = list_entry(next, struct futex_pi_state, list);
410                 key = pi_state->key;
411                 hb = hash_futex(&key);
412                 spin_unlock_irq(&curr->pi_lock);
413
414                 spin_lock(&hb->lock);
415
416                 spin_lock_irq(&curr->pi_lock);
417                 /*
418                  * We dropped the pi-lock, so re-check whether this
419                  * task still owns the PI-state:
420                  */
421                 if (head->next != next) {
422                         spin_unlock(&hb->lock);
423                         continue;
424                 }
425
426                 WARN_ON(pi_state->owner != curr);
427                 WARN_ON(list_empty(&pi_state->list));
428                 list_del_init(&pi_state->list);
429                 pi_state->owner = NULL;
430                 spin_unlock_irq(&curr->pi_lock);
431
432                 rt_mutex_unlock(&pi_state->pi_mutex);
433
434                 spin_unlock(&hb->lock);
435
436                 spin_lock_irq(&curr->pi_lock);
437         }
438         spin_unlock_irq(&curr->pi_lock);
439 }
440
441 static int
442 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, struct futex_q *me)
443 {
444         struct futex_pi_state *pi_state = NULL;
445         struct futex_q *this, *next;
446         struct list_head *head;
447         struct task_struct *p;
448         pid_t pid;
449
450         head = &hb->chain;
451
452         list_for_each_entry_safe(this, next, head, list) {
453                 if (match_futex(&this->key, &me->key)) {
454                         /*
455                          * Another waiter already exists - bump up
456                          * the refcount and return its pi_state:
457                          */
458                         pi_state = this->pi_state;
459                         /*
460                          * Userspace might have messed up non PI and PI futexes
461                          */
462                         if (unlikely(!pi_state))
463                                 return -EINVAL;
464
465                         WARN_ON(!atomic_read(&pi_state->refcount));
466
467                         atomic_inc(&pi_state->refcount);
468                         me->pi_state = pi_state;
469
470                         return 0;
471                 }
472         }
473
474         /*
475          * We are the first waiter - try to look up the real owner and attach
476          * the new pi_state to it, but bail out when the owner died bit is set
477          * and TID = 0:
478          */
479         pid = uval & FUTEX_TID_MASK;
480         if (!pid && (uval & FUTEX_OWNER_DIED))
481                 return -ESRCH;
482         p = futex_find_get_task(pid);
483         if (!p)
484                 return -ESRCH;
485
486         pi_state = alloc_pi_state();
487
488         /*
489          * Initialize the pi_mutex in locked state and make 'p'
490          * the owner of it:
491          */
492         rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
493
494         /* Store the key for possible exit cleanups: */
495         pi_state->key = me->key;
496
497         spin_lock_irq(&p->pi_lock);
498         WARN_ON(!list_empty(&pi_state->list));
499         list_add(&pi_state->list, &p->pi_state_list);
500         pi_state->owner = p;
501         spin_unlock_irq(&p->pi_lock);
502
503         put_task_struct(p);
504
505         me->pi_state = pi_state;
506
507         return 0;
508 }
509
510 /*
511  * The hash bucket lock must be held when this is called.
512  * Afterwards, the futex_q must not be accessed.
513  */
514 static void wake_futex(struct futex_q *q)
515 {
516         list_del_init(&q->list);
517         if (q->filp)
518                 send_sigio(&q->filp->f_owner, q->fd, POLL_IN);
519         /*
520          * The lock in wake_up_all() is a crucial memory barrier after the
521          * list_del_init() and also before assigning to q->lock_ptr.
522          */
523         wake_up_all(&q->waiters);
524         /*
525          * The waiting task can free the futex_q as soon as this is written,
526          * without taking any locks.  This must come last.
527          *
528          * A memory barrier is required here to prevent the following store
529          * to lock_ptr from getting ahead of the wakeup. Clearing the lock
530          * at the end of wake_up_all() does not prevent this store from
531          * moving.
532          */
533         smp_wmb();
534         q->lock_ptr = NULL;
535 }
536
537 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
538 {
539         struct task_struct *new_owner;
540         struct futex_pi_state *pi_state = this->pi_state;
541         u32 curval, newval;
542
543         if (!pi_state)
544                 return -EINVAL;
545
546         spin_lock(&pi_state->pi_mutex.wait_lock);
547         new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
548
549         /*
550          * This happens when we have stolen the lock and the original
551          * pending owner did not enqueue itself back on the rt_mutex.
552          * Thats not a tragedy. We know that way, that a lock waiter
553          * is on the fly. We make the futex_q waiter the pending owner.
554          */
555         if (!new_owner)
556                 new_owner = this->task;
557
558         /*
559          * We pass it to the next owner. (The WAITERS bit is always
560          * kept enabled while there is PI state around. We must also
561          * preserve the owner died bit.)
562          */
563         if (!(uval & FUTEX_OWNER_DIED)) {
564                 newval = FUTEX_WAITERS | new_owner->pid;
565
566                 pagefault_disable();
567                 curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
568                 pagefault_enable();
569                 if (curval == -EFAULT)
570                         return -EFAULT;
571                 if (curval != uval)
572                         return -EINVAL;
573         }
574
575         spin_lock_irq(&pi_state->owner->pi_lock);
576         WARN_ON(list_empty(&pi_state->list));
577         list_del_init(&pi_state->list);
578         spin_unlock_irq(&pi_state->owner->pi_lock);
579
580         spin_lock_irq(&new_owner->pi_lock);
581         WARN_ON(!list_empty(&pi_state->list));
582         list_add(&pi_state->list, &new_owner->pi_state_list);
583         pi_state->owner = new_owner;
584         spin_unlock_irq(&new_owner->pi_lock);
585
586         spin_unlock(&pi_state->pi_mutex.wait_lock);
587         rt_mutex_unlock(&pi_state->pi_mutex);
588
589         return 0;
590 }
591
592 static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
593 {
594         u32 oldval;
595
596         /*
597          * There is no waiter, so we unlock the futex. The owner died
598          * bit has not to be preserved here. We are the owner:
599          */
600         pagefault_disable();
601         oldval = futex_atomic_cmpxchg_inatomic(uaddr, uval, 0);
602         pagefault_enable();
603
604         if (oldval == -EFAULT)
605                 return oldval;
606         if (oldval != uval)
607                 return -EAGAIN;
608
609         return 0;
610 }
611
612 /*
613  * Express the locking dependencies for lockdep:
614  */
615 static inline void
616 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
617 {
618         if (hb1 <= hb2) {
619                 spin_lock(&hb1->lock);
620                 if (hb1 < hb2)
621                         spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
622         } else { /* hb1 > hb2 */
623                 spin_lock(&hb2->lock);
624                 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
625         }
626 }
627
628 /*
629  * Wake up all waiters hashed on the physical page that is mapped
630  * to this virtual address:
631  */
632 static int futex_wake(u32 __user *uaddr, int nr_wake)
633 {
634         struct futex_hash_bucket *hb;
635         struct futex_q *this, *next;
636         struct list_head *head;
637         union futex_key key;
638         int ret;
639
640         down_read(&current->mm->mmap_sem);
641
642         ret = get_futex_key(uaddr, &key);
643         if (unlikely(ret != 0))
644                 goto out;
645
646         hb = hash_futex(&key);
647         spin_lock(&hb->lock);
648         head = &hb->chain;
649
650         list_for_each_entry_safe(this, next, head, list) {
651                 if (match_futex (&this->key, &key)) {
652                         if (this->pi_state) {
653                                 ret = -EINVAL;
654                                 break;
655                         }
656                         wake_futex(this);
657                         if (++ret >= nr_wake)
658                                 break;
659                 }
660         }
661
662         spin_unlock(&hb->lock);
663 out:
664         up_read(&current->mm->mmap_sem);
665         return ret;
666 }
667
668 /*
669  * Wake up all waiters hashed on the physical page that is mapped
670  * to this virtual address:
671  */
672 static int
673 futex_wake_op(u32 __user *uaddr1, u32 __user *uaddr2,
674               int nr_wake, int nr_wake2, int op)
675 {
676         union futex_key key1, key2;
677         struct futex_hash_bucket *hb1, *hb2;
678         struct list_head *head;
679         struct futex_q *this, *next;
680         int ret, op_ret, attempt = 0;
681
682 retryfull:
683         down_read(&current->mm->mmap_sem);
684
685         ret = get_futex_key(uaddr1, &key1);
686         if (unlikely(ret != 0))
687                 goto out;
688         ret = get_futex_key(uaddr2, &key2);
689         if (unlikely(ret != 0))
690                 goto out;
691
692         hb1 = hash_futex(&key1);
693         hb2 = hash_futex(&key2);
694
695 retry:
696         double_lock_hb(hb1, hb2);
697
698         op_ret = futex_atomic_op_inuser(op, uaddr2);
699         if (unlikely(op_ret < 0)) {
700                 u32 dummy;
701
702                 spin_unlock(&hb1->lock);
703                 if (hb1 != hb2)
704                         spin_unlock(&hb2->lock);
705
706 #ifndef CONFIG_MMU
707                 /*
708                  * we don't get EFAULT from MMU faults if we don't have an MMU,
709                  * but we might get them from range checking
710                  */
711                 ret = op_ret;
712                 goto out;
713 #endif
714
715                 if (unlikely(op_ret != -EFAULT)) {
716                         ret = op_ret;
717                         goto out;
718                 }
719
720                 /*
721                  * futex_atomic_op_inuser needs to both read and write
722                  * *(int __user *)uaddr2, but we can't modify it
723                  * non-atomically.  Therefore, if get_user below is not
724                  * enough, we need to handle the fault ourselves, while
725                  * still holding the mmap_sem.
726                  */
727                 if (attempt++) {
728                         if (futex_handle_fault((unsigned long)uaddr2,
729                                                 attempt)) {
730                                 ret = -EFAULT;
731                                 goto out;
732                         }
733                         goto retry;
734                 }
735
736                 /*
737                  * If we would have faulted, release mmap_sem,
738                  * fault it in and start all over again.
739                  */
740                 up_read(&current->mm->mmap_sem);
741
742                 ret = get_user(dummy, uaddr2);
743                 if (ret)
744                         return ret;
745
746                 goto retryfull;
747         }
748
749         head = &hb1->chain;
750
751         list_for_each_entry_safe(this, next, head, list) {
752                 if (match_futex (&this->key, &key1)) {
753                         wake_futex(this);
754                         if (++ret >= nr_wake)
755                                 break;
756                 }
757         }
758
759         if (op_ret > 0) {
760                 head = &hb2->chain;
761
762                 op_ret = 0;
763                 list_for_each_entry_safe(this, next, head, list) {
764                         if (match_futex (&this->key, &key2)) {
765                                 wake_futex(this);
766                                 if (++op_ret >= nr_wake2)
767                                         break;
768                         }
769                 }
770                 ret += op_ret;
771         }
772
773         spin_unlock(&hb1->lock);
774         if (hb1 != hb2)
775                 spin_unlock(&hb2->lock);
776 out:
777         up_read(&current->mm->mmap_sem);
778         return ret;
779 }
780
781 /*
782  * Requeue all waiters hashed on one physical page to another
783  * physical page.
784  */
785 static int futex_requeue(u32 __user *uaddr1, u32 __user *uaddr2,
786                          int nr_wake, int nr_requeue, u32 *cmpval)
787 {
788         union futex_key key1, key2;
789         struct futex_hash_bucket *hb1, *hb2;
790         struct list_head *head1;
791         struct futex_q *this, *next;
792         int ret, drop_count = 0;
793
794  retry:
795         down_read(&current->mm->mmap_sem);
796
797         ret = get_futex_key(uaddr1, &key1);
798         if (unlikely(ret != 0))
799                 goto out;
800         ret = get_futex_key(uaddr2, &key2);
801         if (unlikely(ret != 0))
802                 goto out;
803
804         hb1 = hash_futex(&key1);
805         hb2 = hash_futex(&key2);
806
807         double_lock_hb(hb1, hb2);
808
809         if (likely(cmpval != NULL)) {
810                 u32 curval;
811
812                 ret = get_futex_value_locked(&curval, uaddr1);
813
814                 if (unlikely(ret)) {
815                         spin_unlock(&hb1->lock);
816                         if (hb1 != hb2)
817                                 spin_unlock(&hb2->lock);
818
819                         /*
820                          * If we would have faulted, release mmap_sem, fault
821                          * it in and start all over again.
822                          */
823                         up_read(&current->mm->mmap_sem);
824
825                         ret = get_user(curval, uaddr1);
826
827                         if (!ret)
828                                 goto retry;
829
830                         return ret;
831                 }
832                 if (curval != *cmpval) {
833                         ret = -EAGAIN;
834                         goto out_unlock;
835                 }
836         }
837
838         head1 = &hb1->chain;
839         list_for_each_entry_safe(this, next, head1, list) {
840                 if (!match_futex (&this->key, &key1))
841                         continue;
842                 if (++ret <= nr_wake) {
843                         wake_futex(this);
844                 } else {
845                         /*
846                          * If key1 and key2 hash to the same bucket, no need to
847                          * requeue.
848                          */
849                         if (likely(head1 != &hb2->chain)) {
850                                 list_move_tail(&this->list, &hb2->chain);
851                                 this->lock_ptr = &hb2->lock;
852                         }
853                         this->key = key2;
854                         get_futex_key_refs(&key2);
855                         drop_count++;
856
857                         if (ret - nr_wake >= nr_requeue)
858                                 break;
859                 }
860         }
861
862 out_unlock:
863         spin_unlock(&hb1->lock);
864         if (hb1 != hb2)
865                 spin_unlock(&hb2->lock);
866
867         /* drop_futex_key_refs() must be called outside the spinlocks. */
868         while (--drop_count >= 0)
869                 drop_futex_key_refs(&key1);
870
871 out:
872         up_read(&current->mm->mmap_sem);
873         return ret;
874 }
875
876 /* The key must be already stored in q->key. */
877 static inline struct futex_hash_bucket *
878 queue_lock(struct futex_q *q, int fd, struct file *filp)
879 {
880         struct futex_hash_bucket *hb;
881
882         q->fd = fd;
883         q->filp = filp;
884
885         init_waitqueue_head(&q->waiters);
886
887         get_futex_key_refs(&q->key);
888         hb = hash_futex(&q->key);
889         q->lock_ptr = &hb->lock;
890
891         spin_lock(&hb->lock);
892         return hb;
893 }
894
895 static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
896 {
897         list_add_tail(&q->list, &hb->chain);
898         q->task = current;
899         spin_unlock(&hb->lock);
900 }
901
902 static inline void
903 queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
904 {
905         spin_unlock(&hb->lock);
906         drop_futex_key_refs(&q->key);
907 }
908
909 /*
910  * queue_me and unqueue_me must be called as a pair, each
911  * exactly once.  They are called with the hashed spinlock held.
912  */
913
914 /* The key must be already stored in q->key. */
915 static void queue_me(struct futex_q *q, int fd, struct file *filp)
916 {
917         struct futex_hash_bucket *hb;
918
919         hb = queue_lock(q, fd, filp);
920         __queue_me(q, hb);
921 }
922
923 /* Return 1 if we were still queued (ie. 0 means we were woken) */
924 static int unqueue_me(struct futex_q *q)
925 {
926         spinlock_t *lock_ptr;
927         int ret = 0;
928
929         /* In the common case we don't take the spinlock, which is nice. */
930  retry:
931         lock_ptr = q->lock_ptr;
932         barrier();
933         if (lock_ptr != 0) {
934                 spin_lock(lock_ptr);
935                 /*
936                  * q->lock_ptr can change between reading it and
937                  * spin_lock(), causing us to take the wrong lock.  This
938                  * corrects the race condition.
939                  *
940                  * Reasoning goes like this: if we have the wrong lock,
941                  * q->lock_ptr must have changed (maybe several times)
942                  * between reading it and the spin_lock().  It can
943                  * change again after the spin_lock() but only if it was
944                  * already changed before the spin_lock().  It cannot,
945                  * however, change back to the original value.  Therefore
946                  * we can detect whether we acquired the correct lock.
947                  */
948                 if (unlikely(lock_ptr != q->lock_ptr)) {
949                         spin_unlock(lock_ptr);
950                         goto retry;
951                 }
952                 WARN_ON(list_empty(&q->list));
953                 list_del(&q->list);
954
955                 BUG_ON(q->pi_state);
956
957                 spin_unlock(lock_ptr);
958                 ret = 1;
959         }
960
961         drop_futex_key_refs(&q->key);
962         return ret;
963 }
964
965 /*
966  * PI futexes can not be requeued and must remove themself from the
967  * hash bucket. The hash bucket lock is held on entry and dropped here.
968  */
969 static void unqueue_me_pi(struct futex_q *q, struct futex_hash_bucket *hb)
970 {
971         WARN_ON(list_empty(&q->list));
972         list_del(&q->list);
973
974         BUG_ON(!q->pi_state);
975         free_pi_state(q->pi_state);
976         q->pi_state = NULL;
977
978         spin_unlock(&hb->lock);
979
980         drop_futex_key_refs(&q->key);
981 }
982
983 static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time)
984 {
985         struct task_struct *curr = current;
986         DECLARE_WAITQUEUE(wait, curr);
987         struct futex_hash_bucket *hb;
988         struct futex_q q;
989         u32 uval;
990         int ret;
991
992         q.pi_state = NULL;
993  retry:
994         down_read(&curr->mm->mmap_sem);
995
996         ret = get_futex_key(uaddr, &q.key);
997         if (unlikely(ret != 0))
998                 goto out_release_sem;
999
1000         hb = queue_lock(&q, -1, NULL);
1001
1002         /*
1003          * Access the page AFTER the futex is queued.
1004          * Order is important:
1005          *
1006          *   Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1007          *   Userspace waker:  if (cond(var)) { var = new; futex_wake(&var); }
1008          *
1009          * The basic logical guarantee of a futex is that it blocks ONLY
1010          * if cond(var) is known to be true at the time of blocking, for
1011          * any cond.  If we queued after testing *uaddr, that would open
1012          * a race condition where we could block indefinitely with
1013          * cond(var) false, which would violate the guarantee.
1014          *
1015          * A consequence is that futex_wait() can return zero and absorb
1016          * a wakeup when *uaddr != val on entry to the syscall.  This is
1017          * rare, but normal.
1018          *
1019          * We hold the mmap semaphore, so the mapping cannot have changed
1020          * since we looked it up in get_futex_key.
1021          */
1022         ret = get_futex_value_locked(&uval, uaddr);
1023
1024         if (unlikely(ret)) {
1025                 queue_unlock(&q, hb);
1026
1027                 /*
1028                  * If we would have faulted, release mmap_sem, fault it in and
1029                  * start all over again.
1030                  */
1031                 up_read(&curr->mm->mmap_sem);
1032
1033                 ret = get_user(uval, uaddr);
1034
1035                 if (!ret)
1036                         goto retry;
1037                 return ret;
1038         }
1039         ret = -EWOULDBLOCK;
1040         if (uval != val)
1041                 goto out_unlock_release_sem;
1042
1043         /* Only actually queue if *uaddr contained val.  */
1044         __queue_me(&q, hb);
1045
1046         /*
1047          * Now the futex is queued and we have checked the data, we
1048          * don't want to hold mmap_sem while we sleep.
1049          */
1050         up_read(&curr->mm->mmap_sem);
1051
1052         /*
1053          * There might have been scheduling since the queue_me(), as we
1054          * cannot hold a spinlock across the get_user() in case it
1055          * faults, and we cannot just set TASK_INTERRUPTIBLE state when
1056          * queueing ourselves into the futex hash.  This code thus has to
1057          * rely on the futex_wake() code removing us from hash when it
1058          * wakes us up.
1059          */
1060
1061         /* add_wait_queue is the barrier after __set_current_state. */
1062         __set_current_state(TASK_INTERRUPTIBLE);
1063         add_wait_queue(&q.waiters, &wait);
1064         /*
1065          * !list_empty() is safe here without any lock.
1066          * q.lock_ptr != 0 is not safe, because of ordering against wakeup.
1067          */
1068         if (likely(!list_empty(&q.list)))
1069                 time = schedule_timeout(time);
1070         __set_current_state(TASK_RUNNING);
1071
1072         /*
1073          * NOTE: we don't remove ourselves from the waitqueue because
1074          * we are the only user of it.
1075          */
1076
1077         /* If we were woken (and unqueued), we succeeded, whatever. */
1078         if (!unqueue_me(&q))
1079                 return 0;
1080         if (time == 0)
1081                 return -ETIMEDOUT;
1082         /*
1083          * We expect signal_pending(current), but another thread may
1084          * have handled it for us already.
1085          */
1086         return -EINTR;
1087
1088  out_unlock_release_sem:
1089         queue_unlock(&q, hb);
1090
1091  out_release_sem:
1092         up_read(&curr->mm->mmap_sem);
1093         return ret;
1094 }
1095
1096 /*
1097  * Userspace tried a 0 -> TID atomic transition of the futex value
1098  * and failed. The kernel side here does the whole locking operation:
1099  * if there are waiters then it will block, it does PI, etc. (Due to
1100  * races the kernel might see a 0 value of the futex too.)
1101  */
1102 static int futex_lock_pi(u32 __user *uaddr, int detect, unsigned long sec,
1103                          long nsec, int trylock)
1104 {
1105         struct hrtimer_sleeper timeout, *to = NULL;
1106         struct task_struct *curr = current;
1107         struct futex_hash_bucket *hb;
1108         u32 uval, newval, curval;
1109         struct futex_q q;
1110         int ret, attempt = 0;
1111
1112         if (refill_pi_state_cache())
1113                 return -ENOMEM;
1114
1115         if (sec != MAX_SCHEDULE_TIMEOUT) {
1116                 to = &timeout;
1117                 hrtimer_init(&to->timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
1118                 hrtimer_init_sleeper(to, current);
1119                 to->timer.expires = ktime_set(sec, nsec);
1120         }
1121
1122         q.pi_state = NULL;
1123  retry:
1124         down_read(&curr->mm->mmap_sem);
1125
1126         ret = get_futex_key(uaddr, &q.key);
1127         if (unlikely(ret != 0))
1128                 goto out_release_sem;
1129
1130         hb = queue_lock(&q, -1, NULL);
1131
1132  retry_locked:
1133         /*
1134          * To avoid races, we attempt to take the lock here again
1135          * (by doing a 0 -> TID atomic cmpxchg), while holding all
1136          * the locks. It will most likely not succeed.
1137          */
1138         newval = current->pid;
1139
1140         pagefault_disable();
1141         curval = futex_atomic_cmpxchg_inatomic(uaddr, 0, newval);
1142         pagefault_enable();
1143
1144         if (unlikely(curval == -EFAULT))
1145                 goto uaddr_faulted;
1146
1147         /* We own the lock already */
1148         if (unlikely((curval & FUTEX_TID_MASK) == current->pid)) {
1149                 if (!detect && 0)
1150                         force_sig(SIGKILL, current);
1151                 ret = -EDEADLK;
1152                 goto out_unlock_release_sem;
1153         }
1154
1155         /*
1156          * Surprise - we got the lock. Just return
1157          * to userspace:
1158          */
1159         if (unlikely(!curval))
1160                 goto out_unlock_release_sem;
1161
1162         uval = curval;
1163         newval = uval | FUTEX_WAITERS;
1164
1165         pagefault_disable();
1166         curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
1167         pagefault_enable();
1168
1169         if (unlikely(curval == -EFAULT))
1170                 goto uaddr_faulted;
1171         if (unlikely(curval != uval))
1172                 goto retry_locked;
1173
1174         /*
1175          * We dont have the lock. Look up the PI state (or create it if
1176          * we are the first waiter):
1177          */
1178         ret = lookup_pi_state(uval, hb, &q);
1179
1180         if (unlikely(ret)) {
1181                 /*
1182                  * There were no waiters and the owner task lookup
1183                  * failed. When the OWNER_DIED bit is set, then we
1184                  * know that this is a robust futex and we actually
1185                  * take the lock. This is safe as we are protected by
1186                  * the hash bucket lock. We also set the waiters bit
1187                  * unconditionally here, to simplify glibc handling of
1188                  * multiple tasks racing to acquire the lock and
1189                  * cleanup the problems which were left by the dead
1190                  * owner.
1191                  */
1192                 if (curval & FUTEX_OWNER_DIED) {
1193                         uval = newval;
1194                         newval = current->pid |
1195                                 FUTEX_OWNER_DIED | FUTEX_WAITERS;
1196
1197                         pagefault_disable();
1198                         curval = futex_atomic_cmpxchg_inatomic(uaddr,
1199                                                                uval, newval);
1200                         pagefault_enable();
1201
1202                         if (unlikely(curval == -EFAULT))
1203                                 goto uaddr_faulted;
1204                         if (unlikely(curval != uval))
1205                                 goto retry_locked;
1206                         ret = 0;
1207                 }
1208                 goto out_unlock_release_sem;
1209         }
1210
1211         /*
1212          * Only actually queue now that the atomic ops are done:
1213          */
1214         __queue_me(&q, hb);
1215
1216         /*
1217          * Now the futex is queued and we have checked the data, we
1218          * don't want to hold mmap_sem while we sleep.
1219          */
1220         up_read(&curr->mm->mmap_sem);
1221
1222         WARN_ON(!q.pi_state);
1223         /*
1224          * Block on the PI mutex:
1225          */
1226         if (!trylock)
1227                 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
1228         else {
1229                 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
1230                 /* Fixup the trylock return value: */
1231                 ret = ret ? 0 : -EWOULDBLOCK;
1232         }
1233
1234         down_read(&curr->mm->mmap_sem);
1235         spin_lock(q.lock_ptr);
1236
1237         /*
1238          * Got the lock. We might not be the anticipated owner if we
1239          * did a lock-steal - fix up the PI-state in that case.
1240          */
1241         if (!ret && q.pi_state->owner != curr) {
1242                 u32 newtid = current->pid | FUTEX_WAITERS;
1243
1244                 /* Owner died? */
1245                 if (q.pi_state->owner != NULL) {
1246                         spin_lock_irq(&q.pi_state->owner->pi_lock);
1247                         WARN_ON(list_empty(&q.pi_state->list));
1248                         list_del_init(&q.pi_state->list);
1249                         spin_unlock_irq(&q.pi_state->owner->pi_lock);
1250                 } else
1251                         newtid |= FUTEX_OWNER_DIED;
1252
1253                 q.pi_state->owner = current;
1254
1255                 spin_lock_irq(&current->pi_lock);
1256                 WARN_ON(!list_empty(&q.pi_state->list));
1257                 list_add(&q.pi_state->list, &current->pi_state_list);
1258                 spin_unlock_irq(&current->pi_lock);
1259
1260                 /* Unqueue and drop the lock */
1261                 unqueue_me_pi(&q, hb);
1262                 up_read(&curr->mm->mmap_sem);
1263                 /*
1264                  * We own it, so we have to replace the pending owner
1265                  * TID. This must be atomic as we have preserve the
1266                  * owner died bit here.
1267                  */
1268                 ret = get_user(uval, uaddr);
1269                 while (!ret) {
1270                         newval = (uval & FUTEX_OWNER_DIED) | newtid;
1271                         curval = futex_atomic_cmpxchg_inatomic(uaddr,
1272                                                                uval, newval);
1273                         if (curval == -EFAULT)
1274                                 ret = -EFAULT;
1275                         if (curval == uval)
1276                                 break;
1277                         uval = curval;
1278                 }
1279         } else {
1280                 /*
1281                  * Catch the rare case, where the lock was released
1282                  * when we were on the way back before we locked
1283                  * the hash bucket.
1284                  */
1285                 if (ret && q.pi_state->owner == curr) {
1286                         if (rt_mutex_trylock(&q.pi_state->pi_mutex))
1287                                 ret = 0;
1288                 }
1289                 /* Unqueue and drop the lock */
1290                 unqueue_me_pi(&q, hb);
1291                 up_read(&curr->mm->mmap_sem);
1292         }
1293
1294         if (!detect && ret == -EDEADLK && 0)
1295                 force_sig(SIGKILL, current);
1296
1297         return ret != -EINTR ? ret : -ERESTARTNOINTR;
1298
1299  out_unlock_release_sem:
1300         queue_unlock(&q, hb);
1301
1302  out_release_sem:
1303         up_read(&curr->mm->mmap_sem);
1304         return ret;
1305
1306  uaddr_faulted:
1307         /*
1308          * We have to r/w  *(int __user *)uaddr, but we can't modify it
1309          * non-atomically.  Therefore, if get_user below is not
1310          * enough, we need to handle the fault ourselves, while
1311          * still holding the mmap_sem.
1312          */
1313         if (attempt++) {
1314                 if (futex_handle_fault((unsigned long)uaddr, attempt)) {
1315                         ret = -EFAULT;
1316                         goto out_unlock_release_sem;
1317                 }
1318                 goto retry_locked;
1319         }
1320
1321         queue_unlock(&q, hb);
1322         up_read(&curr->mm->mmap_sem);
1323
1324         ret = get_user(uval, uaddr);
1325         if (!ret && (uval != -EFAULT))
1326                 goto retry;
1327
1328         return ret;
1329 }
1330
1331 /*
1332  * Userspace attempted a TID -> 0 atomic transition, and failed.
1333  * This is the in-kernel slowpath: we look up the PI state (if any),
1334  * and do the rt-mutex unlock.
1335  */
1336 static int futex_unlock_pi(u32 __user *uaddr)
1337 {
1338         struct futex_hash_bucket *hb;
1339         struct futex_q *this, *next;
1340         u32 uval;
1341         struct list_head *head;
1342         union futex_key key;
1343         int ret, attempt = 0;
1344
1345 retry:
1346         if (get_user(uval, uaddr))
1347                 return -EFAULT;
1348         /*
1349          * We release only a lock we actually own:
1350          */
1351         if ((uval & FUTEX_TID_MASK) != current->pid)
1352                 return -EPERM;
1353         /*
1354          * First take all the futex related locks:
1355          */
1356         down_read(&current->mm->mmap_sem);
1357
1358         ret = get_futex_key(uaddr, &key);
1359         if (unlikely(ret != 0))
1360                 goto out;
1361
1362         hb = hash_futex(&key);
1363         spin_lock(&hb->lock);
1364
1365 retry_locked:
1366         /*
1367          * To avoid races, try to do the TID -> 0 atomic transition
1368          * again. If it succeeds then we can return without waking
1369          * anyone else up:
1370          */
1371         if (!(uval & FUTEX_OWNER_DIED)) {
1372                 pagefault_disable();
1373                 uval = futex_atomic_cmpxchg_inatomic(uaddr, current->pid, 0);
1374                 pagefault_enable();
1375         }
1376
1377         if (unlikely(uval == -EFAULT))
1378                 goto pi_faulted;
1379         /*
1380          * Rare case: we managed to release the lock atomically,
1381          * no need to wake anyone else up:
1382          */
1383         if (unlikely(uval == current->pid))
1384                 goto out_unlock;
1385
1386         /*
1387          * Ok, other tasks may need to be woken up - check waiters
1388          * and do the wakeup if necessary:
1389          */
1390         head = &hb->chain;
1391
1392         list_for_each_entry_safe(this, next, head, list) {
1393                 if (!match_futex (&this->key, &key))
1394                         continue;
1395                 ret = wake_futex_pi(uaddr, uval, this);
1396                 /*
1397                  * The atomic access to the futex value
1398                  * generated a pagefault, so retry the
1399                  * user-access and the wakeup:
1400                  */
1401                 if (ret == -EFAULT)
1402                         goto pi_faulted;
1403                 goto out_unlock;
1404         }
1405         /*
1406          * No waiters - kernel unlocks the futex:
1407          */
1408         if (!(uval & FUTEX_OWNER_DIED)) {
1409                 ret = unlock_futex_pi(uaddr, uval);
1410                 if (ret == -EFAULT)
1411                         goto pi_faulted;
1412         }
1413
1414 out_unlock:
1415         spin_unlock(&hb->lock);
1416 out:
1417         up_read(&current->mm->mmap_sem);
1418
1419         return ret;
1420
1421 pi_faulted:
1422         /*
1423          * We have to r/w  *(int __user *)uaddr, but we can't modify it
1424          * non-atomically.  Therefore, if get_user below is not
1425          * enough, we need to handle the fault ourselves, while
1426          * still holding the mmap_sem.
1427          */
1428         if (attempt++) {
1429                 if (futex_handle_fault((unsigned long)uaddr, attempt)) {
1430                         ret = -EFAULT;
1431                         goto out_unlock;
1432                 }
1433                 goto retry_locked;
1434         }
1435
1436         spin_unlock(&hb->lock);
1437         up_read(&current->mm->mmap_sem);
1438
1439         ret = get_user(uval, uaddr);
1440         if (!ret && (uval != -EFAULT))
1441                 goto retry;
1442
1443         return ret;
1444 }
1445
1446 static int futex_close(struct inode *inode, struct file *filp)
1447 {
1448         struct futex_q *q = filp->private_data;
1449
1450         unqueue_me(q);
1451         kfree(q);
1452
1453         return 0;
1454 }
1455
1456 /* This is one-shot: once it's gone off you need a new fd */
1457 static unsigned int futex_poll(struct file *filp,
1458                                struct poll_table_struct *wait)
1459 {
1460         struct futex_q *q = filp->private_data;
1461         int ret = 0;
1462
1463         poll_wait(filp, &q->waiters, wait);
1464
1465         /*
1466          * list_empty() is safe here without any lock.
1467          * q->lock_ptr != 0 is not safe, because of ordering against wakeup.
1468          */
1469         if (list_empty(&q->list))
1470                 ret = POLLIN | POLLRDNORM;
1471
1472         return ret;
1473 }
1474
1475 static const struct file_operations futex_fops = {
1476         .release        = futex_close,
1477         .poll           = futex_poll,
1478 };
1479
1480 /*
1481  * Signal allows caller to avoid the race which would occur if they
1482  * set the sigio stuff up afterwards.
1483  */
1484 static int futex_fd(u32 __user *uaddr, int signal)
1485 {
1486         struct futex_q *q;
1487         struct file *filp;
1488         int ret, err;
1489         static unsigned long printk_interval;
1490
1491         if (printk_timed_ratelimit(&printk_interval, 60 * 60 * 1000)) {
1492                 printk(KERN_WARNING "Process `%s' used FUTEX_FD, which "
1493                         "will be removed from the kernel in June 2007\n",
1494                         current->comm);
1495         }
1496
1497         ret = -EINVAL;
1498         if (!valid_signal(signal))
1499                 goto out;
1500
1501         ret = get_unused_fd();
1502         if (ret < 0)
1503                 goto out;
1504         filp = get_empty_filp();
1505         if (!filp) {
1506                 put_unused_fd(ret);
1507                 ret = -ENFILE;
1508                 goto out;
1509         }
1510         filp->f_op = &futex_fops;
1511         filp->f_path.mnt = mntget(futex_mnt);
1512         filp->f_path.dentry = dget(futex_mnt->mnt_root);
1513         filp->f_mapping = filp->f_path.dentry->d_inode->i_mapping;
1514
1515         if (signal) {
1516                 err = __f_setown(filp, task_pid(current), PIDTYPE_PID, 1);
1517                 if (err < 0) {
1518                         goto error;
1519                 }
1520                 filp->f_owner.signum = signal;
1521         }
1522
1523         q = kmalloc(sizeof(*q), GFP_KERNEL);
1524         if (!q) {
1525                 err = -ENOMEM;
1526                 goto error;
1527         }
1528         q->pi_state = NULL;
1529
1530         down_read(&current->mm->mmap_sem);
1531         err = get_futex_key(uaddr, &q->key);
1532
1533         if (unlikely(err != 0)) {
1534                 up_read(&current->mm->mmap_sem);
1535                 kfree(q);
1536                 goto error;
1537         }
1538
1539         /*
1540          * queue_me() must be called before releasing mmap_sem, because
1541          * key->shared.inode needs to be referenced while holding it.
1542          */
1543         filp->private_data = q;
1544
1545         queue_me(q, ret, filp);
1546         up_read(&current->mm->mmap_sem);
1547
1548         /* Now we map fd to filp, so userspace can access it */
1549         fd_install(ret, filp);
1550 out:
1551         return ret;
1552 error:
1553         put_unused_fd(ret);
1554         put_filp(filp);
1555         ret = err;
1556         goto out;
1557 }
1558
1559 /*
1560  * Support for robust futexes: the kernel cleans up held futexes at
1561  * thread exit time.
1562  *
1563  * Implementation: user-space maintains a per-thread list of locks it
1564  * is holding. Upon do_exit(), the kernel carefully walks this list,
1565  * and marks all locks that are owned by this thread with the
1566  * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
1567  * always manipulated with the lock held, so the list is private and
1568  * per-thread. Userspace also maintains a per-thread 'list_op_pending'
1569  * field, to allow the kernel to clean up if the thread dies after
1570  * acquiring the lock, but just before it could have added itself to
1571  * the list. There can only be one such pending lock.
1572  */
1573
1574 /**
1575  * sys_set_robust_list - set the robust-futex list head of a task
1576  * @head: pointer to the list-head
1577  * @len: length of the list-head, as userspace expects
1578  */
1579 asmlinkage long
1580 sys_set_robust_list(struct robust_list_head __user *head,
1581                     size_t len)
1582 {
1583         /*
1584          * The kernel knows only one size for now:
1585          */
1586         if (unlikely(len != sizeof(*head)))
1587                 return -EINVAL;
1588
1589         current->robust_list = head;
1590
1591         return 0;
1592 }
1593
1594 /**
1595  * sys_get_robust_list - get the robust-futex list head of a task
1596  * @pid: pid of the process [zero for current task]
1597  * @head_ptr: pointer to a list-head pointer, the kernel fills it in
1598  * @len_ptr: pointer to a length field, the kernel fills in the header size
1599  */
1600 asmlinkage long
1601 sys_get_robust_list(int pid, struct robust_list_head __user * __user *head_ptr,
1602                     size_t __user *len_ptr)
1603 {
1604         struct robust_list_head __user *head;
1605         unsigned long ret;
1606
1607         if (!pid)
1608                 head = current->robust_list;
1609         else {
1610                 struct task_struct *p;
1611
1612                 ret = -ESRCH;
1613                 rcu_read_lock();
1614                 p = find_task_by_pid(pid);
1615                 if (!p)
1616                         goto err_unlock;
1617                 ret = -EPERM;
1618                 if ((current->euid != p->euid) && (current->euid != p->uid) &&
1619                                 !capable(CAP_SYS_PTRACE))
1620                         goto err_unlock;
1621                 head = p->robust_list;
1622                 rcu_read_unlock();
1623         }
1624
1625         if (put_user(sizeof(*head), len_ptr))
1626                 return -EFAULT;
1627         return put_user(head, head_ptr);
1628
1629 err_unlock:
1630         rcu_read_unlock();
1631
1632         return ret;
1633 }
1634
1635 /*
1636  * Process a futex-list entry, check whether it's owned by the
1637  * dying task, and do notification if so:
1638  */
1639 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
1640 {
1641         u32 uval, nval, mval;
1642
1643 retry:
1644         if (get_user(uval, uaddr))
1645                 return -1;
1646
1647         if ((uval & FUTEX_TID_MASK) == curr->pid) {
1648                 /*
1649                  * Ok, this dying thread is truly holding a futex
1650                  * of interest. Set the OWNER_DIED bit atomically
1651                  * via cmpxchg, and if the value had FUTEX_WAITERS
1652                  * set, wake up a waiter (if any). (We have to do a
1653                  * futex_wake() even if OWNER_DIED is already set -
1654                  * to handle the rare but possible case of recursive
1655                  * thread-death.) The rest of the cleanup is done in
1656                  * userspace.
1657                  */
1658                 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
1659                 nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
1660
1661                 if (nval == -EFAULT)
1662                         return -1;
1663
1664                 if (nval != uval)
1665                         goto retry;
1666
1667                 /*
1668                  * Wake robust non-PI futexes here. The wakeup of
1669                  * PI futexes happens in exit_pi_state():
1670                  */
1671                 if (!pi) {
1672                         if (uval & FUTEX_WAITERS)
1673                                 futex_wake(uaddr, 1);
1674                 }
1675         }
1676         return 0;
1677 }
1678
1679 /*
1680  * Fetch a robust-list pointer. Bit 0 signals PI futexes:
1681  */
1682 static inline int fetch_robust_entry(struct robust_list __user **entry,
1683                                      struct robust_list __user * __user *head,
1684                                      int *pi)
1685 {
1686         unsigned long uentry;
1687
1688         if (get_user(uentry, (unsigned long __user *)head))
1689                 return -EFAULT;
1690
1691         *entry = (void __user *)(uentry & ~1UL);
1692         *pi = uentry & 1;
1693
1694         return 0;
1695 }
1696
1697 /*
1698  * Walk curr->robust_list (very carefully, it's a userspace list!)
1699  * and mark any locks found there dead, and notify any waiters.
1700  *
1701  * We silently return on any sign of list-walking problem.
1702  */
1703 void exit_robust_list(struct task_struct *curr)
1704 {
1705         struct robust_list_head __user *head = curr->robust_list;
1706         struct robust_list __user *entry, *pending;
1707         unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
1708         unsigned long futex_offset;
1709
1710         /*
1711          * Fetch the list head (which was registered earlier, via
1712          * sys_set_robust_list()):
1713          */
1714         if (fetch_robust_entry(&entry, &head->list.next, &pi))
1715                 return;
1716         /*
1717          * Fetch the relative futex offset:
1718          */
1719         if (get_user(futex_offset, &head->futex_offset))
1720                 return;
1721         /*
1722          * Fetch any possibly pending lock-add first, and handle it
1723          * if it exists:
1724          */
1725         if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
1726                 return;
1727
1728         if (pending)
1729                 handle_futex_death((void __user *)pending + futex_offset, curr, pip);
1730
1731         while (entry != &head->list) {
1732                 /*
1733                  * A pending lock might already be on the list, so
1734                  * don't process it twice:
1735                  */
1736                 if (entry != pending)
1737                         if (handle_futex_death((void __user *)entry + futex_offset,
1738                                                 curr, pi))
1739                                 return;
1740                 /*
1741                  * Fetch the next entry in the list:
1742                  */
1743                 if (fetch_robust_entry(&entry, &entry->next, &pi))
1744                         return;
1745                 /*
1746                  * Avoid excessively long or circular lists:
1747                  */
1748                 if (!--limit)
1749                         break;
1750
1751                 cond_resched();
1752         }
1753 }
1754
1755 long do_futex(u32 __user *uaddr, int op, u32 val, unsigned long timeout,
1756                 u32 __user *uaddr2, u32 val2, u32 val3)
1757 {
1758         int ret;
1759
1760         switch (op) {
1761         case FUTEX_WAIT:
1762                 ret = futex_wait(uaddr, val, timeout);
1763                 break;
1764         case FUTEX_WAKE:
1765                 ret = futex_wake(uaddr, val);
1766                 break;
1767         case FUTEX_FD:
1768                 /* non-zero val means F_SETOWN(getpid()) & F_SETSIG(val) */
1769                 ret = futex_fd(uaddr, val);
1770                 break;
1771         case FUTEX_REQUEUE:
1772                 ret = futex_requeue(uaddr, uaddr2, val, val2, NULL);
1773                 break;
1774         case FUTEX_CMP_REQUEUE:
1775                 ret = futex_requeue(uaddr, uaddr2, val, val2, &val3);
1776                 break;
1777         case FUTEX_WAKE_OP:
1778                 ret = futex_wake_op(uaddr, uaddr2, val, val2, val3);
1779                 break;
1780         case FUTEX_LOCK_PI:
1781                 ret = futex_lock_pi(uaddr, val, timeout, val2, 0);
1782                 break;
1783         case FUTEX_UNLOCK_PI:
1784                 ret = futex_unlock_pi(uaddr);
1785                 break;
1786         case FUTEX_TRYLOCK_PI:
1787                 ret = futex_lock_pi(uaddr, 0, timeout, val2, 1);
1788                 break;
1789         default:
1790                 ret = -ENOSYS;
1791         }
1792         return ret;
1793 }
1794
1795
1796 asmlinkage long sys_futex(u32 __user *uaddr, int op, u32 val,
1797                           struct timespec __user *utime, u32 __user *uaddr2,
1798                           u32 val3)
1799 {
1800         struct timespec t;
1801         unsigned long timeout = MAX_SCHEDULE_TIMEOUT;
1802         u32 val2 = 0;
1803
1804         if (utime && (op == FUTEX_WAIT || op == FUTEX_LOCK_PI)) {
1805                 if (copy_from_user(&t, utime, sizeof(t)) != 0)
1806                         return -EFAULT;
1807                 if (!timespec_valid(&t))
1808                         return -EINVAL;
1809                 if (op == FUTEX_WAIT)
1810                         timeout = timespec_to_jiffies(&t) + 1;
1811                 else {
1812                         timeout = t.tv_sec;
1813                         val2 = t.tv_nsec;
1814                 }
1815         }
1816         /*
1817          * requeue parameter in 'utime' if op == FUTEX_REQUEUE.
1818          */
1819         if (op == FUTEX_REQUEUE || op == FUTEX_CMP_REQUEUE)
1820                 val2 = (u32) (unsigned long) utime;
1821
1822         return do_futex(uaddr, op, val, timeout, uaddr2, val2, val3);
1823 }
1824
1825 static int futexfs_get_sb(struct file_system_type *fs_type,
1826                           int flags, const char *dev_name, void *data,
1827                           struct vfsmount *mnt)
1828 {
1829         return get_sb_pseudo(fs_type, "futex", NULL, 0xBAD1DEA, mnt);
1830 }
1831
1832 static struct file_system_type futex_fs_type = {
1833         .name           = "futexfs",
1834         .get_sb         = futexfs_get_sb,
1835         .kill_sb        = kill_anon_super,
1836 };
1837
1838 static int __init init(void)
1839 {
1840         int i = register_filesystem(&futex_fs_type);
1841
1842         if (i)
1843                 return i;
1844
1845         futex_mnt = kern_mount(&futex_fs_type);
1846         if (IS_ERR(futex_mnt)) {
1847                 unregister_filesystem(&futex_fs_type);
1848                 return PTR_ERR(futex_mnt);
1849         }
1850
1851         for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
1852                 INIT_LIST_HEAD(&futex_queues[i].chain);
1853                 spin_lock_init(&futex_queues[i].lock);
1854         }
1855         return 0;
1856 }
1857 __initcall(init);