hung_task: fix false positive during vfork
[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  *  PRIVATE futexes by Eric Dumazet
20  *  Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
21  *
22  *  Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
23  *  Copyright (C) IBM Corporation, 2009
24  *  Thanks to Thomas Gleixner for conceptual design and careful reviews.
25  *
26  *  Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
27  *  enough at me, Linus for the original (flawed) idea, Matthew
28  *  Kirkwood for proof-of-concept implementation.
29  *
30  *  "The futexes are also cursed."
31  *  "But they come in a choice of three flavours!"
32  *
33  *  This program is free software; you can redistribute it and/or modify
34  *  it under the terms of the GNU General Public License as published by
35  *  the Free Software Foundation; either version 2 of the License, or
36  *  (at your option) any later version.
37  *
38  *  This program is distributed in the hope that it will be useful,
39  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
40  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
41  *  GNU General Public License for more details.
42  *
43  *  You should have received a copy of the GNU General Public License
44  *  along with this program; if not, write to the Free Software
45  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
46  */
47 #include <linux/slab.h>
48 #include <linux/poll.h>
49 #include <linux/fs.h>
50 #include <linux/file.h>
51 #include <linux/jhash.h>
52 #include <linux/init.h>
53 #include <linux/futex.h>
54 #include <linux/mount.h>
55 #include <linux/pagemap.h>
56 #include <linux/syscalls.h>
57 #include <linux/signal.h>
58 #include <linux/module.h>
59 #include <linux/magic.h>
60 #include <linux/pid.h>
61 #include <linux/nsproxy.h>
62
63 #include <asm/futex.h>
64
65 #include "rtmutex_common.h"
66
67 int __read_mostly futex_cmpxchg_enabled;
68
69 #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
70
71 /*
72  * Futex flags used to encode options to functions and preserve them across
73  * restarts.
74  */
75 #define FLAGS_SHARED            0x01
76 #define FLAGS_CLOCKRT           0x02
77 #define FLAGS_HAS_TIMEOUT       0x04
78
79 /*
80  * Priority Inheritance state:
81  */
82 struct futex_pi_state {
83         /*
84          * list of 'owned' pi_state instances - these have to be
85          * cleaned up in do_exit() if the task exits prematurely:
86          */
87         struct list_head list;
88
89         /*
90          * The PI object:
91          */
92         struct rt_mutex pi_mutex;
93
94         struct task_struct *owner;
95         atomic_t refcount;
96
97         union futex_key key;
98 };
99
100 /**
101  * struct futex_q - The hashed futex queue entry, one per waiting task
102  * @list:               priority-sorted list of tasks waiting on this futex
103  * @task:               the task waiting on the futex
104  * @lock_ptr:           the hash bucket lock
105  * @key:                the key the futex is hashed on
106  * @pi_state:           optional priority inheritance state
107  * @rt_waiter:          rt_waiter storage for use with requeue_pi
108  * @requeue_pi_key:     the requeue_pi target futex key
109  * @bitset:             bitset for the optional bitmasked wakeup
110  *
111  * We use this hashed waitqueue, instead of a normal wait_queue_t, so
112  * we can wake only the relevant ones (hashed queues may be shared).
113  *
114  * A futex_q has a woken state, just like tasks have TASK_RUNNING.
115  * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
116  * The order of wakeup is always to make the first condition true, then
117  * the second.
118  *
119  * PI futexes are typically woken before they are removed from the hash list via
120  * the rt_mutex code. See unqueue_me_pi().
121  */
122 struct futex_q {
123         struct plist_node list;
124
125         struct task_struct *task;
126         spinlock_t *lock_ptr;
127         union futex_key key;
128         struct futex_pi_state *pi_state;
129         struct rt_mutex_waiter *rt_waiter;
130         union futex_key *requeue_pi_key;
131         u32 bitset;
132 };
133
134 static const struct futex_q futex_q_init = {
135         /* list gets initialized in queue_me()*/
136         .key = FUTEX_KEY_INIT,
137         .bitset = FUTEX_BITSET_MATCH_ANY
138 };
139
140 /*
141  * Hash buckets are shared by all the futex_keys that hash to the same
142  * location.  Each key may have multiple futex_q structures, one for each task
143  * waiting on a futex.
144  */
145 struct futex_hash_bucket {
146         spinlock_t lock;
147         struct plist_head chain;
148 };
149
150 static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
151
152 /*
153  * We hash on the keys returned from get_futex_key (see below).
154  */
155 static struct futex_hash_bucket *hash_futex(union futex_key *key)
156 {
157         u32 hash = jhash2((u32*)&key->both.word,
158                           (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
159                           key->both.offset);
160         return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
161 }
162
163 /*
164  * Return 1 if two futex_keys are equal, 0 otherwise.
165  */
166 static inline int match_futex(union futex_key *key1, union futex_key *key2)
167 {
168         return (key1 && key2
169                 && key1->both.word == key2->both.word
170                 && key1->both.ptr == key2->both.ptr
171                 && key1->both.offset == key2->both.offset);
172 }
173
174 /*
175  * Take a reference to the resource addressed by a key.
176  * Can be called while holding spinlocks.
177  *
178  */
179 static void get_futex_key_refs(union futex_key *key)
180 {
181         if (!key->both.ptr)
182                 return;
183
184         switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
185         case FUT_OFF_INODE:
186                 ihold(key->shared.inode);
187                 break;
188         case FUT_OFF_MMSHARED:
189                 atomic_inc(&key->private.mm->mm_count);
190                 break;
191         }
192 }
193
194 /*
195  * Drop a reference to the resource addressed by a key.
196  * The hash bucket spinlock must not be held.
197  */
198 static void drop_futex_key_refs(union futex_key *key)
199 {
200         if (!key->both.ptr) {
201                 /* If we're here then we tried to put a key we failed to get */
202                 WARN_ON_ONCE(1);
203                 return;
204         }
205
206         switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
207         case FUT_OFF_INODE:
208                 iput(key->shared.inode);
209                 break;
210         case FUT_OFF_MMSHARED:
211                 mmdrop(key->private.mm);
212                 break;
213         }
214 }
215
216 /**
217  * get_futex_key() - Get parameters which are the keys for a futex
218  * @uaddr:      virtual address of the futex
219  * @fshared:    0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
220  * @key:        address where result is stored.
221  * @rw:         mapping needs to be read/write (values: VERIFY_READ,
222  *              VERIFY_WRITE)
223  *
224  * Returns a negative error code or 0
225  * The key words are stored in *key on success.
226  *
227  * For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,
228  * offset_within_page).  For private mappings, it's (uaddr, current->mm).
229  * We can usually work out the index without swapping in the page.
230  *
231  * lock_page() might sleep, the caller should not hold a spinlock.
232  */
233 static int
234 get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
235 {
236         unsigned long address = (unsigned long)uaddr;
237         struct mm_struct *mm = current->mm;
238         struct page *page, *page_head;
239         int err, ro = 0;
240
241         /*
242          * The futex address must be "naturally" aligned.
243          */
244         key->both.offset = address % PAGE_SIZE;
245         if (unlikely((address % sizeof(u32)) != 0))
246                 return -EINVAL;
247         address -= key->both.offset;
248
249         /*
250          * PROCESS_PRIVATE futexes are fast.
251          * As the mm cannot disappear under us and the 'key' only needs
252          * virtual address, we dont even have to find the underlying vma.
253          * Note : We do have to check 'uaddr' is a valid user address,
254          *        but access_ok() should be faster than find_vma()
255          */
256         if (!fshared) {
257                 if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))))
258                         return -EFAULT;
259                 key->private.mm = mm;
260                 key->private.address = address;
261                 get_futex_key_refs(key);
262                 return 0;
263         }
264
265 again:
266         err = get_user_pages_fast(address, 1, 1, &page);
267         /*
268          * If write access is not required (eg. FUTEX_WAIT), try
269          * and get read-only access.
270          */
271         if (err == -EFAULT && rw == VERIFY_READ) {
272                 err = get_user_pages_fast(address, 1, 0, &page);
273                 ro = 1;
274         }
275         if (err < 0)
276                 return err;
277         else
278                 err = 0;
279
280 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
281         page_head = page;
282         if (unlikely(PageTail(page))) {
283                 put_page(page);
284                 /* serialize against __split_huge_page_splitting() */
285                 local_irq_disable();
286                 if (likely(__get_user_pages_fast(address, 1, 1, &page) == 1)) {
287                         page_head = compound_head(page);
288                         /*
289                          * page_head is valid pointer but we must pin
290                          * it before taking the PG_lock and/or
291                          * PG_compound_lock. The moment we re-enable
292                          * irqs __split_huge_page_splitting() can
293                          * return and the head page can be freed from
294                          * under us. We can't take the PG_lock and/or
295                          * PG_compound_lock on a page that could be
296                          * freed from under us.
297                          */
298                         if (page != page_head) {
299                                 get_page(page_head);
300                                 put_page(page);
301                         }
302                         local_irq_enable();
303                 } else {
304                         local_irq_enable();
305                         goto again;
306                 }
307         }
308 #else
309         page_head = compound_head(page);
310         if (page != page_head) {
311                 get_page(page_head);
312                 put_page(page);
313         }
314 #endif
315
316         lock_page(page_head);
317
318         /*
319          * If page_head->mapping is NULL, then it cannot be a PageAnon
320          * page; but it might be the ZERO_PAGE or in the gate area or
321          * in a special mapping (all cases which we are happy to fail);
322          * or it may have been a good file page when get_user_pages_fast
323          * found it, but truncated or holepunched or subjected to
324          * invalidate_complete_page2 before we got the page lock (also
325          * cases which we are happy to fail).  And we hold a reference,
326          * so refcount care in invalidate_complete_page's remove_mapping
327          * prevents drop_caches from setting mapping to NULL beneath us.
328          *
329          * The case we do have to guard against is when memory pressure made
330          * shmem_writepage move it from filecache to swapcache beneath us:
331          * an unlikely race, but we do need to retry for page_head->mapping.
332          */
333         if (!page_head->mapping) {
334                 int shmem_swizzled = PageSwapCache(page_head);
335                 unlock_page(page_head);
336                 put_page(page_head);
337                 if (shmem_swizzled)
338                         goto again;
339                 return -EFAULT;
340         }
341
342         /*
343          * Private mappings are handled in a simple way.
344          *
345          * NOTE: When userspace waits on a MAP_SHARED mapping, even if
346          * it's a read-only handle, it's expected that futexes attach to
347          * the object not the particular process.
348          */
349         if (PageAnon(page_head)) {
350                 /*
351                  * A RO anonymous page will never change and thus doesn't make
352                  * sense for futex operations.
353                  */
354                 if (ro) {
355                         err = -EFAULT;
356                         goto out;
357                 }
358
359                 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
360                 key->private.mm = mm;
361                 key->private.address = address;
362         } else {
363                 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
364                 key->shared.inode = page_head->mapping->host;
365                 key->shared.pgoff = page_head->index;
366         }
367
368         get_futex_key_refs(key);
369
370 out:
371         unlock_page(page_head);
372         put_page(page_head);
373         return err;
374 }
375
376 static inline void put_futex_key(union futex_key *key)
377 {
378         drop_futex_key_refs(key);
379 }
380
381 /**
382  * fault_in_user_writeable() - Fault in user address and verify RW access
383  * @uaddr:      pointer to faulting user space address
384  *
385  * Slow path to fixup the fault we just took in the atomic write
386  * access to @uaddr.
387  *
388  * We have no generic implementation of a non-destructive write to the
389  * user address. We know that we faulted in the atomic pagefault
390  * disabled section so we can as well avoid the #PF overhead by
391  * calling get_user_pages() right away.
392  */
393 static int fault_in_user_writeable(u32 __user *uaddr)
394 {
395         struct mm_struct *mm = current->mm;
396         int ret;
397
398         down_read(&mm->mmap_sem);
399         ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
400                                FAULT_FLAG_WRITE);
401         up_read(&mm->mmap_sem);
402
403         return ret < 0 ? ret : 0;
404 }
405
406 /**
407  * futex_top_waiter() - Return the highest priority waiter on a futex
408  * @hb:         the hash bucket the futex_q's reside in
409  * @key:        the futex key (to distinguish it from other futex futex_q's)
410  *
411  * Must be called with the hb lock held.
412  */
413 static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
414                                         union futex_key *key)
415 {
416         struct futex_q *this;
417
418         plist_for_each_entry(this, &hb->chain, list) {
419                 if (match_futex(&this->key, key))
420                         return this;
421         }
422         return NULL;
423 }
424
425 static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
426                                       u32 uval, u32 newval)
427 {
428         int ret;
429
430         pagefault_disable();
431         ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
432         pagefault_enable();
433
434         return ret;
435 }
436
437 static int get_futex_value_locked(u32 *dest, u32 __user *from)
438 {
439         int ret;
440
441         pagefault_disable();
442         ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
443         pagefault_enable();
444
445         return ret ? -EFAULT : 0;
446 }
447
448
449 /*
450  * PI code:
451  */
452 static int refill_pi_state_cache(void)
453 {
454         struct futex_pi_state *pi_state;
455
456         if (likely(current->pi_state_cache))
457                 return 0;
458
459         pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
460
461         if (!pi_state)
462                 return -ENOMEM;
463
464         INIT_LIST_HEAD(&pi_state->list);
465         /* pi_mutex gets initialized later */
466         pi_state->owner = NULL;
467         atomic_set(&pi_state->refcount, 1);
468         pi_state->key = FUTEX_KEY_INIT;
469
470         current->pi_state_cache = pi_state;
471
472         return 0;
473 }
474
475 static struct futex_pi_state * alloc_pi_state(void)
476 {
477         struct futex_pi_state *pi_state = current->pi_state_cache;
478
479         WARN_ON(!pi_state);
480         current->pi_state_cache = NULL;
481
482         return pi_state;
483 }
484
485 static void free_pi_state(struct futex_pi_state *pi_state)
486 {
487         if (!atomic_dec_and_test(&pi_state->refcount))
488                 return;
489
490         /*
491          * If pi_state->owner is NULL, the owner is most probably dying
492          * and has cleaned up the pi_state already
493          */
494         if (pi_state->owner) {
495                 raw_spin_lock_irq(&pi_state->owner->pi_lock);
496                 list_del_init(&pi_state->list);
497                 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
498
499                 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
500         }
501
502         if (current->pi_state_cache)
503                 kfree(pi_state);
504         else {
505                 /*
506                  * pi_state->list is already empty.
507                  * clear pi_state->owner.
508                  * refcount is at 0 - put it back to 1.
509                  */
510                 pi_state->owner = NULL;
511                 atomic_set(&pi_state->refcount, 1);
512                 current->pi_state_cache = pi_state;
513         }
514 }
515
516 /*
517  * Look up the task based on what TID userspace gave us.
518  * We dont trust it.
519  */
520 static struct task_struct * futex_find_get_task(pid_t pid)
521 {
522         struct task_struct *p;
523
524         rcu_read_lock();
525         p = find_task_by_vpid(pid);
526         if (p)
527                 get_task_struct(p);
528
529         rcu_read_unlock();
530
531         return p;
532 }
533
534 /*
535  * This task is holding PI mutexes at exit time => bad.
536  * Kernel cleans up PI-state, but userspace is likely hosed.
537  * (Robust-futex cleanup is separate and might save the day for userspace.)
538  */
539 void exit_pi_state_list(struct task_struct *curr)
540 {
541         struct list_head *next, *head = &curr->pi_state_list;
542         struct futex_pi_state *pi_state;
543         struct futex_hash_bucket *hb;
544         union futex_key key = FUTEX_KEY_INIT;
545
546         if (!futex_cmpxchg_enabled)
547                 return;
548         /*
549          * We are a ZOMBIE and nobody can enqueue itself on
550          * pi_state_list anymore, but we have to be careful
551          * versus waiters unqueueing themselves:
552          */
553         raw_spin_lock_irq(&curr->pi_lock);
554         while (!list_empty(head)) {
555
556                 next = head->next;
557                 pi_state = list_entry(next, struct futex_pi_state, list);
558                 key = pi_state->key;
559                 hb = hash_futex(&key);
560                 raw_spin_unlock_irq(&curr->pi_lock);
561
562                 spin_lock(&hb->lock);
563
564                 raw_spin_lock_irq(&curr->pi_lock);
565                 /*
566                  * We dropped the pi-lock, so re-check whether this
567                  * task still owns the PI-state:
568                  */
569                 if (head->next != next) {
570                         spin_unlock(&hb->lock);
571                         continue;
572                 }
573
574                 WARN_ON(pi_state->owner != curr);
575                 WARN_ON(list_empty(&pi_state->list));
576                 list_del_init(&pi_state->list);
577                 pi_state->owner = NULL;
578                 raw_spin_unlock_irq(&curr->pi_lock);
579
580                 rt_mutex_unlock(&pi_state->pi_mutex);
581
582                 spin_unlock(&hb->lock);
583
584                 raw_spin_lock_irq(&curr->pi_lock);
585         }
586         raw_spin_unlock_irq(&curr->pi_lock);
587 }
588
589 static int
590 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
591                 union futex_key *key, struct futex_pi_state **ps)
592 {
593         struct futex_pi_state *pi_state = NULL;
594         struct futex_q *this, *next;
595         struct plist_head *head;
596         struct task_struct *p;
597         pid_t pid = uval & FUTEX_TID_MASK;
598
599         head = &hb->chain;
600
601         plist_for_each_entry_safe(this, next, head, list) {
602                 if (match_futex(&this->key, key)) {
603                         /*
604                          * Another waiter already exists - bump up
605                          * the refcount and return its pi_state:
606                          */
607                         pi_state = this->pi_state;
608                         /*
609                          * Userspace might have messed up non-PI and PI futexes
610                          */
611                         if (unlikely(!pi_state))
612                                 return -EINVAL;
613
614                         WARN_ON(!atomic_read(&pi_state->refcount));
615
616                         /*
617                          * When pi_state->owner is NULL then the owner died
618                          * and another waiter is on the fly. pi_state->owner
619                          * is fixed up by the task which acquires
620                          * pi_state->rt_mutex.
621                          *
622                          * We do not check for pid == 0 which can happen when
623                          * the owner died and robust_list_exit() cleared the
624                          * TID.
625                          */
626                         if (pid && pi_state->owner) {
627                                 /*
628                                  * Bail out if user space manipulated the
629                                  * futex value.
630                                  */
631                                 if (pid != task_pid_vnr(pi_state->owner))
632                                         return -EINVAL;
633                         }
634
635                         atomic_inc(&pi_state->refcount);
636                         *ps = pi_state;
637
638                         return 0;
639                 }
640         }
641
642         /*
643          * We are the first waiter - try to look up the real owner and attach
644          * the new pi_state to it, but bail out when TID = 0
645          */
646         if (!pid)
647                 return -ESRCH;
648         p = futex_find_get_task(pid);
649         if (!p)
650                 return -ESRCH;
651
652         /*
653          * We need to look at the task state flags to figure out,
654          * whether the task is exiting. To protect against the do_exit
655          * change of the task flags, we do this protected by
656          * p->pi_lock:
657          */
658         raw_spin_lock_irq(&p->pi_lock);
659         if (unlikely(p->flags & PF_EXITING)) {
660                 /*
661                  * The task is on the way out. When PF_EXITPIDONE is
662                  * set, we know that the task has finished the
663                  * cleanup:
664                  */
665                 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
666
667                 raw_spin_unlock_irq(&p->pi_lock);
668                 put_task_struct(p);
669                 return ret;
670         }
671
672         pi_state = alloc_pi_state();
673
674         /*
675          * Initialize the pi_mutex in locked state and make 'p'
676          * the owner of it:
677          */
678         rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
679
680         /* Store the key for possible exit cleanups: */
681         pi_state->key = *key;
682
683         WARN_ON(!list_empty(&pi_state->list));
684         list_add(&pi_state->list, &p->pi_state_list);
685         pi_state->owner = p;
686         raw_spin_unlock_irq(&p->pi_lock);
687
688         put_task_struct(p);
689
690         *ps = pi_state;
691
692         return 0;
693 }
694
695 /**
696  * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
697  * @uaddr:              the pi futex user address
698  * @hb:                 the pi futex hash bucket
699  * @key:                the futex key associated with uaddr and hb
700  * @ps:                 the pi_state pointer where we store the result of the
701  *                      lookup
702  * @task:               the task to perform the atomic lock work for.  This will
703  *                      be "current" except in the case of requeue pi.
704  * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
705  *
706  * Returns:
707  *  0 - ready to wait
708  *  1 - acquired the lock
709  * <0 - error
710  *
711  * The hb->lock and futex_key refs shall be held by the caller.
712  */
713 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
714                                 union futex_key *key,
715                                 struct futex_pi_state **ps,
716                                 struct task_struct *task, int set_waiters)
717 {
718         int lock_taken, ret, ownerdied = 0;
719         u32 uval, newval, curval, vpid = task_pid_vnr(task);
720
721 retry:
722         ret = lock_taken = 0;
723
724         /*
725          * To avoid races, we attempt to take the lock here again
726          * (by doing a 0 -> TID atomic cmpxchg), while holding all
727          * the locks. It will most likely not succeed.
728          */
729         newval = vpid;
730         if (set_waiters)
731                 newval |= FUTEX_WAITERS;
732
733         if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval)))
734                 return -EFAULT;
735
736         /*
737          * Detect deadlocks.
738          */
739         if ((unlikely((curval & FUTEX_TID_MASK) == vpid)))
740                 return -EDEADLK;
741
742         /*
743          * Surprise - we got the lock. Just return to userspace:
744          */
745         if (unlikely(!curval))
746                 return 1;
747
748         uval = curval;
749
750         /*
751          * Set the FUTEX_WAITERS flag, so the owner will know it has someone
752          * to wake at the next unlock.
753          */
754         newval = curval | FUTEX_WAITERS;
755
756         /*
757          * There are two cases, where a futex might have no owner (the
758          * owner TID is 0): OWNER_DIED. We take over the futex in this
759          * case. We also do an unconditional take over, when the owner
760          * of the futex died.
761          *
762          * This is safe as we are protected by the hash bucket lock !
763          */
764         if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
765                 /* Keep the OWNER_DIED bit */
766                 newval = (curval & ~FUTEX_TID_MASK) | vpid;
767                 ownerdied = 0;
768                 lock_taken = 1;
769         }
770
771         if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
772                 return -EFAULT;
773         if (unlikely(curval != uval))
774                 goto retry;
775
776         /*
777          * We took the lock due to owner died take over.
778          */
779         if (unlikely(lock_taken))
780                 return 1;
781
782         /*
783          * We dont have the lock. Look up the PI state (or create it if
784          * we are the first waiter):
785          */
786         ret = lookup_pi_state(uval, hb, key, ps);
787
788         if (unlikely(ret)) {
789                 switch (ret) {
790                 case -ESRCH:
791                         /*
792                          * No owner found for this futex. Check if the
793                          * OWNER_DIED bit is set to figure out whether
794                          * this is a robust futex or not.
795                          */
796                         if (get_futex_value_locked(&curval, uaddr))
797                                 return -EFAULT;
798
799                         /*
800                          * We simply start over in case of a robust
801                          * futex. The code above will take the futex
802                          * and return happy.
803                          */
804                         if (curval & FUTEX_OWNER_DIED) {
805                                 ownerdied = 1;
806                                 goto retry;
807                         }
808                 default:
809                         break;
810                 }
811         }
812
813         return ret;
814 }
815
816 /**
817  * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
818  * @q:  The futex_q to unqueue
819  *
820  * The q->lock_ptr must not be NULL and must be held by the caller.
821  */
822 static void __unqueue_futex(struct futex_q *q)
823 {
824         struct futex_hash_bucket *hb;
825
826         if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
827             || WARN_ON(plist_node_empty(&q->list)))
828                 return;
829
830         hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
831         plist_del(&q->list, &hb->chain);
832 }
833
834 /*
835  * The hash bucket lock must be held when this is called.
836  * Afterwards, the futex_q must not be accessed.
837  */
838 static void wake_futex(struct futex_q *q)
839 {
840         struct task_struct *p = q->task;
841
842         /*
843          * We set q->lock_ptr = NULL _before_ we wake up the task. If
844          * a non-futex wake up happens on another CPU then the task
845          * might exit and p would dereference a non-existing task
846          * struct. Prevent this by holding a reference on p across the
847          * wake up.
848          */
849         get_task_struct(p);
850
851         __unqueue_futex(q);
852         /*
853          * The waiting task can free the futex_q as soon as
854          * q->lock_ptr = NULL is written, without taking any locks. A
855          * memory barrier is required here to prevent the following
856          * store to lock_ptr from getting ahead of the plist_del.
857          */
858         smp_wmb();
859         q->lock_ptr = NULL;
860
861         wake_up_state(p, TASK_NORMAL);
862         put_task_struct(p);
863 }
864
865 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
866 {
867         struct task_struct *new_owner;
868         struct futex_pi_state *pi_state = this->pi_state;
869         u32 curval, newval;
870
871         if (!pi_state)
872                 return -EINVAL;
873
874         /*
875          * If current does not own the pi_state then the futex is
876          * inconsistent and user space fiddled with the futex value.
877          */
878         if (pi_state->owner != current)
879                 return -EINVAL;
880
881         raw_spin_lock(&pi_state->pi_mutex.wait_lock);
882         new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
883
884         /*
885          * It is possible that the next waiter (the one that brought
886          * this owner to the kernel) timed out and is no longer
887          * waiting on the lock.
888          */
889         if (!new_owner)
890                 new_owner = this->task;
891
892         /*
893          * We pass it to the next owner. (The WAITERS bit is always
894          * kept enabled while there is PI state around. We must also
895          * preserve the owner died bit.)
896          */
897         if (!(uval & FUTEX_OWNER_DIED)) {
898                 int ret = 0;
899
900                 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
901
902                 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
903                         ret = -EFAULT;
904                 else if (curval != uval)
905                         ret = -EINVAL;
906                 if (ret) {
907                         raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
908                         return ret;
909                 }
910         }
911
912         raw_spin_lock_irq(&pi_state->owner->pi_lock);
913         WARN_ON(list_empty(&pi_state->list));
914         list_del_init(&pi_state->list);
915         raw_spin_unlock_irq(&pi_state->owner->pi_lock);
916
917         raw_spin_lock_irq(&new_owner->pi_lock);
918         WARN_ON(!list_empty(&pi_state->list));
919         list_add(&pi_state->list, &new_owner->pi_state_list);
920         pi_state->owner = new_owner;
921         raw_spin_unlock_irq(&new_owner->pi_lock);
922
923         raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
924         rt_mutex_unlock(&pi_state->pi_mutex);
925
926         return 0;
927 }
928
929 static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
930 {
931         u32 oldval;
932
933         /*
934          * There is no waiter, so we unlock the futex. The owner died
935          * bit has not to be preserved here. We are the owner:
936          */
937         if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0))
938                 return -EFAULT;
939         if (oldval != uval)
940                 return -EAGAIN;
941
942         return 0;
943 }
944
945 /*
946  * Express the locking dependencies for lockdep:
947  */
948 static inline void
949 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
950 {
951         if (hb1 <= hb2) {
952                 spin_lock(&hb1->lock);
953                 if (hb1 < hb2)
954                         spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
955         } else { /* hb1 > hb2 */
956                 spin_lock(&hb2->lock);
957                 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
958         }
959 }
960
961 static inline void
962 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
963 {
964         spin_unlock(&hb1->lock);
965         if (hb1 != hb2)
966                 spin_unlock(&hb2->lock);
967 }
968
969 /*
970  * Wake up waiters matching bitset queued on this futex (uaddr).
971  */
972 static int
973 futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
974 {
975         struct futex_hash_bucket *hb;
976         struct futex_q *this, *next;
977         struct plist_head *head;
978         union futex_key key = FUTEX_KEY_INIT;
979         int ret;
980
981         if (!bitset)
982                 return -EINVAL;
983
984         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
985         if (unlikely(ret != 0))
986                 goto out;
987
988         hb = hash_futex(&key);
989         spin_lock(&hb->lock);
990         head = &hb->chain;
991
992         plist_for_each_entry_safe(this, next, head, list) {
993                 if (match_futex (&this->key, &key)) {
994                         if (this->pi_state || this->rt_waiter) {
995                                 ret = -EINVAL;
996                                 break;
997                         }
998
999                         /* Check if one of the bits is set in both bitsets */
1000                         if (!(this->bitset & bitset))
1001                                 continue;
1002
1003                         wake_futex(this);
1004                         if (++ret >= nr_wake)
1005                                 break;
1006                 }
1007         }
1008
1009         spin_unlock(&hb->lock);
1010         put_futex_key(&key);
1011 out:
1012         return ret;
1013 }
1014
1015 /*
1016  * Wake up all waiters hashed on the physical page that is mapped
1017  * to this virtual address:
1018  */
1019 static int
1020 futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
1021               int nr_wake, int nr_wake2, int op)
1022 {
1023         union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1024         struct futex_hash_bucket *hb1, *hb2;
1025         struct plist_head *head;
1026         struct futex_q *this, *next;
1027         int ret, op_ret;
1028
1029 retry:
1030         ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1031         if (unlikely(ret != 0))
1032                 goto out;
1033         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
1034         if (unlikely(ret != 0))
1035                 goto out_put_key1;
1036
1037         hb1 = hash_futex(&key1);
1038         hb2 = hash_futex(&key2);
1039
1040 retry_private:
1041         double_lock_hb(hb1, hb2);
1042         op_ret = futex_atomic_op_inuser(op, uaddr2);
1043         if (unlikely(op_ret < 0)) {
1044
1045                 double_unlock_hb(hb1, hb2);
1046
1047 #ifndef CONFIG_MMU
1048                 /*
1049                  * we don't get EFAULT from MMU faults if we don't have an MMU,
1050                  * but we might get them from range checking
1051                  */
1052                 ret = op_ret;
1053                 goto out_put_keys;
1054 #endif
1055
1056                 if (unlikely(op_ret != -EFAULT)) {
1057                         ret = op_ret;
1058                         goto out_put_keys;
1059                 }
1060
1061                 ret = fault_in_user_writeable(uaddr2);
1062                 if (ret)
1063                         goto out_put_keys;
1064
1065                 if (!(flags & FLAGS_SHARED))
1066                         goto retry_private;
1067
1068                 put_futex_key(&key2);
1069                 put_futex_key(&key1);
1070                 goto retry;
1071         }
1072
1073         head = &hb1->chain;
1074
1075         plist_for_each_entry_safe(this, next, head, list) {
1076                 if (match_futex (&this->key, &key1)) {
1077                         wake_futex(this);
1078                         if (++ret >= nr_wake)
1079                                 break;
1080                 }
1081         }
1082
1083         if (op_ret > 0) {
1084                 head = &hb2->chain;
1085
1086                 op_ret = 0;
1087                 plist_for_each_entry_safe(this, next, head, list) {
1088                         if (match_futex (&this->key, &key2)) {
1089                                 wake_futex(this);
1090                                 if (++op_ret >= nr_wake2)
1091                                         break;
1092                         }
1093                 }
1094                 ret += op_ret;
1095         }
1096
1097         double_unlock_hb(hb1, hb2);
1098 out_put_keys:
1099         put_futex_key(&key2);
1100 out_put_key1:
1101         put_futex_key(&key1);
1102 out:
1103         return ret;
1104 }
1105
1106 /**
1107  * requeue_futex() - Requeue a futex_q from one hb to another
1108  * @q:          the futex_q to requeue
1109  * @hb1:        the source hash_bucket
1110  * @hb2:        the target hash_bucket
1111  * @key2:       the new key for the requeued futex_q
1112  */
1113 static inline
1114 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1115                    struct futex_hash_bucket *hb2, union futex_key *key2)
1116 {
1117
1118         /*
1119          * If key1 and key2 hash to the same bucket, no need to
1120          * requeue.
1121          */
1122         if (likely(&hb1->chain != &hb2->chain)) {
1123                 plist_del(&q->list, &hb1->chain);
1124                 plist_add(&q->list, &hb2->chain);
1125                 q->lock_ptr = &hb2->lock;
1126         }
1127         get_futex_key_refs(key2);
1128         q->key = *key2;
1129 }
1130
1131 /**
1132  * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1133  * @q:          the futex_q
1134  * @key:        the key of the requeue target futex
1135  * @hb:         the hash_bucket of the requeue target futex
1136  *
1137  * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1138  * target futex if it is uncontended or via a lock steal.  Set the futex_q key
1139  * to the requeue target futex so the waiter can detect the wakeup on the right
1140  * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1141  * atomic lock acquisition.  Set the q->lock_ptr to the requeue target hb->lock
1142  * to protect access to the pi_state to fixup the owner later.  Must be called
1143  * with both q->lock_ptr and hb->lock held.
1144  */
1145 static inline
1146 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1147                            struct futex_hash_bucket *hb)
1148 {
1149         get_futex_key_refs(key);
1150         q->key = *key;
1151
1152         __unqueue_futex(q);
1153
1154         WARN_ON(!q->rt_waiter);
1155         q->rt_waiter = NULL;
1156
1157         q->lock_ptr = &hb->lock;
1158
1159         wake_up_state(q->task, TASK_NORMAL);
1160 }
1161
1162 /**
1163  * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1164  * @pifutex:            the user address of the to futex
1165  * @hb1:                the from futex hash bucket, must be locked by the caller
1166  * @hb2:                the to futex hash bucket, must be locked by the caller
1167  * @key1:               the from futex key
1168  * @key2:               the to futex key
1169  * @ps:                 address to store the pi_state pointer
1170  * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
1171  *
1172  * Try and get the lock on behalf of the top waiter if we can do it atomically.
1173  * Wake the top waiter if we succeed.  If the caller specified set_waiters,
1174  * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1175  * hb1 and hb2 must be held by the caller.
1176  *
1177  * Returns:
1178  *  0 - failed to acquire the lock atomicly
1179  *  1 - acquired the lock
1180  * <0 - error
1181  */
1182 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1183                                  struct futex_hash_bucket *hb1,
1184                                  struct futex_hash_bucket *hb2,
1185                                  union futex_key *key1, union futex_key *key2,
1186                                  struct futex_pi_state **ps, int set_waiters)
1187 {
1188         struct futex_q *top_waiter = NULL;
1189         u32 curval;
1190         int ret;
1191
1192         if (get_futex_value_locked(&curval, pifutex))
1193                 return -EFAULT;
1194
1195         /*
1196          * Find the top_waiter and determine if there are additional waiters.
1197          * If the caller intends to requeue more than 1 waiter to pifutex,
1198          * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1199          * as we have means to handle the possible fault.  If not, don't set
1200          * the bit unecessarily as it will force the subsequent unlock to enter
1201          * the kernel.
1202          */
1203         top_waiter = futex_top_waiter(hb1, key1);
1204
1205         /* There are no waiters, nothing for us to do. */
1206         if (!top_waiter)
1207                 return 0;
1208
1209         /* Ensure we requeue to the expected futex. */
1210         if (!match_futex(top_waiter->requeue_pi_key, key2))
1211                 return -EINVAL;
1212
1213         /*
1214          * Try to take the lock for top_waiter.  Set the FUTEX_WAITERS bit in
1215          * the contended case or if set_waiters is 1.  The pi_state is returned
1216          * in ps in contended cases.
1217          */
1218         ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1219                                    set_waiters);
1220         if (ret == 1)
1221                 requeue_pi_wake_futex(top_waiter, key2, hb2);
1222
1223         return ret;
1224 }
1225
1226 /**
1227  * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1228  * @uaddr1:     source futex user address
1229  * @flags:      futex flags (FLAGS_SHARED, etc.)
1230  * @uaddr2:     target futex user address
1231  * @nr_wake:    number of waiters to wake (must be 1 for requeue_pi)
1232  * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1233  * @cmpval:     @uaddr1 expected value (or %NULL)
1234  * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1235  *              pi futex (pi to pi requeue is not supported)
1236  *
1237  * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1238  * uaddr2 atomically on behalf of the top waiter.
1239  *
1240  * Returns:
1241  * >=0 - on success, the number of tasks requeued or woken
1242  *  <0 - on error
1243  */
1244 static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1245                          u32 __user *uaddr2, int nr_wake, int nr_requeue,
1246                          u32 *cmpval, int requeue_pi)
1247 {
1248         union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1249         int drop_count = 0, task_count = 0, ret;
1250         struct futex_pi_state *pi_state = NULL;
1251         struct futex_hash_bucket *hb1, *hb2;
1252         struct plist_head *head1;
1253         struct futex_q *this, *next;
1254         u32 curval2;
1255
1256         if (requeue_pi) {
1257                 /*
1258                  * requeue_pi requires a pi_state, try to allocate it now
1259                  * without any locks in case it fails.
1260                  */
1261                 if (refill_pi_state_cache())
1262                         return -ENOMEM;
1263                 /*
1264                  * requeue_pi must wake as many tasks as it can, up to nr_wake
1265                  * + nr_requeue, since it acquires the rt_mutex prior to
1266                  * returning to userspace, so as to not leave the rt_mutex with
1267                  * waiters and no owner.  However, second and third wake-ups
1268                  * cannot be predicted as they involve race conditions with the
1269                  * first wake and a fault while looking up the pi_state.  Both
1270                  * pthread_cond_signal() and pthread_cond_broadcast() should
1271                  * use nr_wake=1.
1272                  */
1273                 if (nr_wake != 1)
1274                         return -EINVAL;
1275         }
1276
1277 retry:
1278         if (pi_state != NULL) {
1279                 /*
1280                  * We will have to lookup the pi_state again, so free this one
1281                  * to keep the accounting correct.
1282                  */
1283                 free_pi_state(pi_state);
1284                 pi_state = NULL;
1285         }
1286
1287         ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1288         if (unlikely(ret != 0))
1289                 goto out;
1290         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
1291                             requeue_pi ? VERIFY_WRITE : VERIFY_READ);
1292         if (unlikely(ret != 0))
1293                 goto out_put_key1;
1294
1295         hb1 = hash_futex(&key1);
1296         hb2 = hash_futex(&key2);
1297
1298 retry_private:
1299         double_lock_hb(hb1, hb2);
1300
1301         if (likely(cmpval != NULL)) {
1302                 u32 curval;
1303
1304                 ret = get_futex_value_locked(&curval, uaddr1);
1305
1306                 if (unlikely(ret)) {
1307                         double_unlock_hb(hb1, hb2);
1308
1309                         ret = get_user(curval, uaddr1);
1310                         if (ret)
1311                                 goto out_put_keys;
1312
1313                         if (!(flags & FLAGS_SHARED))
1314                                 goto retry_private;
1315
1316                         put_futex_key(&key2);
1317                         put_futex_key(&key1);
1318                         goto retry;
1319                 }
1320                 if (curval != *cmpval) {
1321                         ret = -EAGAIN;
1322                         goto out_unlock;
1323                 }
1324         }
1325
1326         if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1327                 /*
1328                  * Attempt to acquire uaddr2 and wake the top waiter. If we
1329                  * intend to requeue waiters, force setting the FUTEX_WAITERS
1330                  * bit.  We force this here where we are able to easily handle
1331                  * faults rather in the requeue loop below.
1332                  */
1333                 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1334                                                  &key2, &pi_state, nr_requeue);
1335
1336                 /*
1337                  * At this point the top_waiter has either taken uaddr2 or is
1338                  * waiting on it.  If the former, then the pi_state will not
1339                  * exist yet, look it up one more time to ensure we have a
1340                  * reference to it.
1341                  */
1342                 if (ret == 1) {
1343                         WARN_ON(pi_state);
1344                         drop_count++;
1345                         task_count++;
1346                         ret = get_futex_value_locked(&curval2, uaddr2);
1347                         if (!ret)
1348                                 ret = lookup_pi_state(curval2, hb2, &key2,
1349                                                       &pi_state);
1350                 }
1351
1352                 switch (ret) {
1353                 case 0:
1354                         break;
1355                 case -EFAULT:
1356                         double_unlock_hb(hb1, hb2);
1357                         put_futex_key(&key2);
1358                         put_futex_key(&key1);
1359                         ret = fault_in_user_writeable(uaddr2);
1360                         if (!ret)
1361                                 goto retry;
1362                         goto out;
1363                 case -EAGAIN:
1364                         /* The owner was exiting, try again. */
1365                         double_unlock_hb(hb1, hb2);
1366                         put_futex_key(&key2);
1367                         put_futex_key(&key1);
1368                         cond_resched();
1369                         goto retry;
1370                 default:
1371                         goto out_unlock;
1372                 }
1373         }
1374
1375         head1 = &hb1->chain;
1376         plist_for_each_entry_safe(this, next, head1, list) {
1377                 if (task_count - nr_wake >= nr_requeue)
1378                         break;
1379
1380                 if (!match_futex(&this->key, &key1))
1381                         continue;
1382
1383                 /*
1384                  * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1385                  * be paired with each other and no other futex ops.
1386                  */
1387                 if ((requeue_pi && !this->rt_waiter) ||
1388                     (!requeue_pi && this->rt_waiter)) {
1389                         ret = -EINVAL;
1390                         break;
1391                 }
1392
1393                 /*
1394                  * Wake nr_wake waiters.  For requeue_pi, if we acquired the
1395                  * lock, we already woke the top_waiter.  If not, it will be
1396                  * woken by futex_unlock_pi().
1397                  */
1398                 if (++task_count <= nr_wake && !requeue_pi) {
1399                         wake_futex(this);
1400                         continue;
1401                 }
1402
1403                 /* Ensure we requeue to the expected futex for requeue_pi. */
1404                 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1405                         ret = -EINVAL;
1406                         break;
1407                 }
1408
1409                 /*
1410                  * Requeue nr_requeue waiters and possibly one more in the case
1411                  * of requeue_pi if we couldn't acquire the lock atomically.
1412                  */
1413                 if (requeue_pi) {
1414                         /* Prepare the waiter to take the rt_mutex. */
1415                         atomic_inc(&pi_state->refcount);
1416                         this->pi_state = pi_state;
1417                         ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1418                                                         this->rt_waiter,
1419                                                         this->task, 1);
1420                         if (ret == 1) {
1421                                 /* We got the lock. */
1422                                 requeue_pi_wake_futex(this, &key2, hb2);
1423                                 drop_count++;
1424                                 continue;
1425                         } else if (ret) {
1426                                 /* -EDEADLK */
1427                                 this->pi_state = NULL;
1428                                 free_pi_state(pi_state);
1429                                 goto out_unlock;
1430                         }
1431                 }
1432                 requeue_futex(this, hb1, hb2, &key2);
1433                 drop_count++;
1434         }
1435
1436 out_unlock:
1437         double_unlock_hb(hb1, hb2);
1438
1439         /*
1440          * drop_futex_key_refs() must be called outside the spinlocks. During
1441          * the requeue we moved futex_q's from the hash bucket at key1 to the
1442          * one at key2 and updated their key pointer.  We no longer need to
1443          * hold the references to key1.
1444          */
1445         while (--drop_count >= 0)
1446                 drop_futex_key_refs(&key1);
1447
1448 out_put_keys:
1449         put_futex_key(&key2);
1450 out_put_key1:
1451         put_futex_key(&key1);
1452 out:
1453         if (pi_state != NULL)
1454                 free_pi_state(pi_state);
1455         return ret ? ret : task_count;
1456 }
1457
1458 /* The key must be already stored in q->key. */
1459 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
1460         __acquires(&hb->lock)
1461 {
1462         struct futex_hash_bucket *hb;
1463
1464         hb = hash_futex(&q->key);
1465         q->lock_ptr = &hb->lock;
1466
1467         spin_lock(&hb->lock);
1468         return hb;
1469 }
1470
1471 static inline void
1472 queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
1473         __releases(&hb->lock)
1474 {
1475         spin_unlock(&hb->lock);
1476 }
1477
1478 /**
1479  * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1480  * @q:  The futex_q to enqueue
1481  * @hb: The destination hash bucket
1482  *
1483  * The hb->lock must be held by the caller, and is released here. A call to
1484  * queue_me() is typically paired with exactly one call to unqueue_me().  The
1485  * exceptions involve the PI related operations, which may use unqueue_me_pi()
1486  * or nothing if the unqueue is done as part of the wake process and the unqueue
1487  * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1488  * an example).
1489  */
1490 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1491         __releases(&hb->lock)
1492 {
1493         int prio;
1494
1495         /*
1496          * The priority used to register this element is
1497          * - either the real thread-priority for the real-time threads
1498          * (i.e. threads with a priority lower than MAX_RT_PRIO)
1499          * - or MAX_RT_PRIO for non-RT threads.
1500          * Thus, all RT-threads are woken first in priority order, and
1501          * the others are woken last, in FIFO order.
1502          */
1503         prio = min(current->normal_prio, MAX_RT_PRIO);
1504
1505         plist_node_init(&q->list, prio);
1506         plist_add(&q->list, &hb->chain);
1507         q->task = current;
1508         spin_unlock(&hb->lock);
1509 }
1510
1511 /**
1512  * unqueue_me() - Remove the futex_q from its futex_hash_bucket
1513  * @q:  The futex_q to unqueue
1514  *
1515  * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
1516  * be paired with exactly one earlier call to queue_me().
1517  *
1518  * Returns:
1519  *   1 - if the futex_q was still queued (and we removed unqueued it)
1520  *   0 - if the futex_q was already removed by the waking thread
1521  */
1522 static int unqueue_me(struct futex_q *q)
1523 {
1524         spinlock_t *lock_ptr;
1525         int ret = 0;
1526
1527         /* In the common case we don't take the spinlock, which is nice. */
1528 retry:
1529         lock_ptr = q->lock_ptr;
1530         barrier();
1531         if (lock_ptr != NULL) {
1532                 spin_lock(lock_ptr);
1533                 /*
1534                  * q->lock_ptr can change between reading it and
1535                  * spin_lock(), causing us to take the wrong lock.  This
1536                  * corrects the race condition.
1537                  *
1538                  * Reasoning goes like this: if we have the wrong lock,
1539                  * q->lock_ptr must have changed (maybe several times)
1540                  * between reading it and the spin_lock().  It can
1541                  * change again after the spin_lock() but only if it was
1542                  * already changed before the spin_lock().  It cannot,
1543                  * however, change back to the original value.  Therefore
1544                  * we can detect whether we acquired the correct lock.
1545                  */
1546                 if (unlikely(lock_ptr != q->lock_ptr)) {
1547                         spin_unlock(lock_ptr);
1548                         goto retry;
1549                 }
1550                 __unqueue_futex(q);
1551
1552                 BUG_ON(q->pi_state);
1553
1554                 spin_unlock(lock_ptr);
1555                 ret = 1;
1556         }
1557
1558         drop_futex_key_refs(&q->key);
1559         return ret;
1560 }
1561
1562 /*
1563  * PI futexes can not be requeued and must remove themself from the
1564  * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1565  * and dropped here.
1566  */
1567 static void unqueue_me_pi(struct futex_q *q)
1568         __releases(q->lock_ptr)
1569 {
1570         __unqueue_futex(q);
1571
1572         BUG_ON(!q->pi_state);
1573         free_pi_state(q->pi_state);
1574         q->pi_state = NULL;
1575
1576         spin_unlock(q->lock_ptr);
1577 }
1578
1579 /*
1580  * Fixup the pi_state owner with the new owner.
1581  *
1582  * Must be called with hash bucket lock held and mm->sem held for non
1583  * private futexes.
1584  */
1585 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1586                                 struct task_struct *newowner)
1587 {
1588         u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
1589         struct futex_pi_state *pi_state = q->pi_state;
1590         struct task_struct *oldowner = pi_state->owner;
1591         u32 uval, curval, newval;
1592         int ret;
1593
1594         /* Owner died? */
1595         if (!pi_state->owner)
1596                 newtid |= FUTEX_OWNER_DIED;
1597
1598         /*
1599          * We are here either because we stole the rtmutex from the
1600          * previous highest priority waiter or we are the highest priority
1601          * waiter but failed to get the rtmutex the first time.
1602          * We have to replace the newowner TID in the user space variable.
1603          * This must be atomic as we have to preserve the owner died bit here.
1604          *
1605          * Note: We write the user space value _before_ changing the pi_state
1606          * because we can fault here. Imagine swapped out pages or a fork
1607          * that marked all the anonymous memory readonly for cow.
1608          *
1609          * Modifying pi_state _before_ the user space value would
1610          * leave the pi_state in an inconsistent state when we fault
1611          * here, because we need to drop the hash bucket lock to
1612          * handle the fault. This might be observed in the PID check
1613          * in lookup_pi_state.
1614          */
1615 retry:
1616         if (get_futex_value_locked(&uval, uaddr))
1617                 goto handle_fault;
1618
1619         while (1) {
1620                 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1621
1622                 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
1623                         goto handle_fault;
1624                 if (curval == uval)
1625                         break;
1626                 uval = curval;
1627         }
1628
1629         /*
1630          * We fixed up user space. Now we need to fix the pi_state
1631          * itself.
1632          */
1633         if (pi_state->owner != NULL) {
1634                 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1635                 WARN_ON(list_empty(&pi_state->list));
1636                 list_del_init(&pi_state->list);
1637                 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1638         }
1639
1640         pi_state->owner = newowner;
1641
1642         raw_spin_lock_irq(&newowner->pi_lock);
1643         WARN_ON(!list_empty(&pi_state->list));
1644         list_add(&pi_state->list, &newowner->pi_state_list);
1645         raw_spin_unlock_irq(&newowner->pi_lock);
1646         return 0;
1647
1648         /*
1649          * To handle the page fault we need to drop the hash bucket
1650          * lock here. That gives the other task (either the highest priority
1651          * waiter itself or the task which stole the rtmutex) the
1652          * chance to try the fixup of the pi_state. So once we are
1653          * back from handling the fault we need to check the pi_state
1654          * after reacquiring the hash bucket lock and before trying to
1655          * do another fixup. When the fixup has been done already we
1656          * simply return.
1657          */
1658 handle_fault:
1659         spin_unlock(q->lock_ptr);
1660
1661         ret = fault_in_user_writeable(uaddr);
1662
1663         spin_lock(q->lock_ptr);
1664
1665         /*
1666          * Check if someone else fixed it for us:
1667          */
1668         if (pi_state->owner != oldowner)
1669                 return 0;
1670
1671         if (ret)
1672                 return ret;
1673
1674         goto retry;
1675 }
1676
1677 static long futex_wait_restart(struct restart_block *restart);
1678
1679 /**
1680  * fixup_owner() - Post lock pi_state and corner case management
1681  * @uaddr:      user address of the futex
1682  * @q:          futex_q (contains pi_state and access to the rt_mutex)
1683  * @locked:     if the attempt to take the rt_mutex succeeded (1) or not (0)
1684  *
1685  * After attempting to lock an rt_mutex, this function is called to cleanup
1686  * the pi_state owner as well as handle race conditions that may allow us to
1687  * acquire the lock. Must be called with the hb lock held.
1688  *
1689  * Returns:
1690  *  1 - success, lock taken
1691  *  0 - success, lock not taken
1692  * <0 - on error (-EFAULT)
1693  */
1694 static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
1695 {
1696         struct task_struct *owner;
1697         int ret = 0;
1698
1699         if (locked) {
1700                 /*
1701                  * Got the lock. We might not be the anticipated owner if we
1702                  * did a lock-steal - fix up the PI-state in that case:
1703                  */
1704                 if (q->pi_state->owner != current)
1705                         ret = fixup_pi_state_owner(uaddr, q, current);
1706                 goto out;
1707         }
1708
1709         /*
1710          * Catch the rare case, where the lock was released when we were on the
1711          * way back before we locked the hash bucket.
1712          */
1713         if (q->pi_state->owner == current) {
1714                 /*
1715                  * Try to get the rt_mutex now. This might fail as some other
1716                  * task acquired the rt_mutex after we removed ourself from the
1717                  * rt_mutex waiters list.
1718                  */
1719                 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
1720                         locked = 1;
1721                         goto out;
1722                 }
1723
1724                 /*
1725                  * pi_state is incorrect, some other task did a lock steal and
1726                  * we returned due to timeout or signal without taking the
1727                  * rt_mutex. Too late.
1728                  */
1729                 raw_spin_lock(&q->pi_state->pi_mutex.wait_lock);
1730                 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
1731                 if (!owner)
1732                         owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
1733                 raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock);
1734                 ret = fixup_pi_state_owner(uaddr, q, owner);
1735                 goto out;
1736         }
1737
1738         /*
1739          * Paranoia check. If we did not take the lock, then we should not be
1740          * the owner of the rt_mutex.
1741          */
1742         if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
1743                 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
1744                                 "pi-state %p\n", ret,
1745                                 q->pi_state->pi_mutex.owner,
1746                                 q->pi_state->owner);
1747
1748 out:
1749         return ret ? ret : locked;
1750 }
1751
1752 /**
1753  * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
1754  * @hb:         the futex hash bucket, must be locked by the caller
1755  * @q:          the futex_q to queue up on
1756  * @timeout:    the prepared hrtimer_sleeper, or null for no timeout
1757  */
1758 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
1759                                 struct hrtimer_sleeper *timeout)
1760 {
1761         /*
1762          * The task state is guaranteed to be set before another task can
1763          * wake it. set_current_state() is implemented using set_mb() and
1764          * queue_me() calls spin_unlock() upon completion, both serializing
1765          * access to the hash list and forcing another memory barrier.
1766          */
1767         set_current_state(TASK_INTERRUPTIBLE);
1768         queue_me(q, hb);
1769
1770         /* Arm the timer */
1771         if (timeout) {
1772                 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1773                 if (!hrtimer_active(&timeout->timer))
1774                         timeout->task = NULL;
1775         }
1776
1777         /*
1778          * If we have been removed from the hash list, then another task
1779          * has tried to wake us, and we can skip the call to schedule().
1780          */
1781         if (likely(!plist_node_empty(&q->list))) {
1782                 /*
1783                  * If the timer has already expired, current will already be
1784                  * flagged for rescheduling. Only call schedule if there
1785                  * is no timeout, or if it has yet to expire.
1786                  */
1787                 if (!timeout || timeout->task)
1788                         schedule();
1789         }
1790         __set_current_state(TASK_RUNNING);
1791 }
1792
1793 /**
1794  * futex_wait_setup() - Prepare to wait on a futex
1795  * @uaddr:      the futex userspace address
1796  * @val:        the expected value
1797  * @flags:      futex flags (FLAGS_SHARED, etc.)
1798  * @q:          the associated futex_q
1799  * @hb:         storage for hash_bucket pointer to be returned to caller
1800  *
1801  * Setup the futex_q and locate the hash_bucket.  Get the futex value and
1802  * compare it with the expected value.  Handle atomic faults internally.
1803  * Return with the hb lock held and a q.key reference on success, and unlocked
1804  * with no q.key reference on failure.
1805  *
1806  * Returns:
1807  *  0 - uaddr contains val and hb has been locked
1808  * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlcoked
1809  */
1810 static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
1811                            struct futex_q *q, struct futex_hash_bucket **hb)
1812 {
1813         u32 uval;
1814         int ret;
1815
1816         /*
1817          * Access the page AFTER the hash-bucket is locked.
1818          * Order is important:
1819          *
1820          *   Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1821          *   Userspace waker:  if (cond(var)) { var = new; futex_wake(&var); }
1822          *
1823          * The basic logical guarantee of a futex is that it blocks ONLY
1824          * if cond(var) is known to be true at the time of blocking, for
1825          * any cond.  If we locked the hash-bucket after testing *uaddr, that
1826          * would open a race condition where we could block indefinitely with
1827          * cond(var) false, which would violate the guarantee.
1828          *
1829          * On the other hand, we insert q and release the hash-bucket only
1830          * after testing *uaddr.  This guarantees that futex_wait() will NOT
1831          * absorb a wakeup if *uaddr does not match the desired values
1832          * while the syscall executes.
1833          */
1834 retry:
1835         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
1836         if (unlikely(ret != 0))
1837                 return ret;
1838
1839 retry_private:
1840         *hb = queue_lock(q);
1841
1842         ret = get_futex_value_locked(&uval, uaddr);
1843
1844         if (ret) {
1845                 queue_unlock(q, *hb);
1846
1847                 ret = get_user(uval, uaddr);
1848                 if (ret)
1849                         goto out;
1850
1851                 if (!(flags & FLAGS_SHARED))
1852                         goto retry_private;
1853
1854                 put_futex_key(&q->key);
1855                 goto retry;
1856         }
1857
1858         if (uval != val) {
1859                 queue_unlock(q, *hb);
1860                 ret = -EWOULDBLOCK;
1861         }
1862
1863 out:
1864         if (ret)
1865                 put_futex_key(&q->key);
1866         return ret;
1867 }
1868
1869 static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
1870                       ktime_t *abs_time, u32 bitset)
1871 {
1872         struct hrtimer_sleeper timeout, *to = NULL;
1873         struct restart_block *restart;
1874         struct futex_hash_bucket *hb;
1875         struct futex_q q = futex_q_init;
1876         int ret;
1877
1878         if (!bitset)
1879                 return -EINVAL;
1880         q.bitset = bitset;
1881
1882         if (abs_time) {
1883                 to = &timeout;
1884
1885                 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
1886                                       CLOCK_REALTIME : CLOCK_MONOTONIC,
1887                                       HRTIMER_MODE_ABS);
1888                 hrtimer_init_sleeper(to, current);
1889                 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
1890                                              current->timer_slack_ns);
1891         }
1892
1893 retry:
1894         /*
1895          * Prepare to wait on uaddr. On success, holds hb lock and increments
1896          * q.key refs.
1897          */
1898         ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
1899         if (ret)
1900                 goto out;
1901
1902         /* queue_me and wait for wakeup, timeout, or a signal. */
1903         futex_wait_queue_me(hb, &q, to);
1904
1905         /* If we were woken (and unqueued), we succeeded, whatever. */
1906         ret = 0;
1907         /* unqueue_me() drops q.key ref */
1908         if (!unqueue_me(&q))
1909                 goto out;
1910         ret = -ETIMEDOUT;
1911         if (to && !to->task)
1912                 goto out;
1913
1914         /*
1915          * We expect signal_pending(current), but we might be the
1916          * victim of a spurious wakeup as well.
1917          */
1918         if (!signal_pending(current))
1919                 goto retry;
1920
1921         ret = -ERESTARTSYS;
1922         if (!abs_time)
1923                 goto out;
1924
1925         restart = &current_thread_info()->restart_block;
1926         restart->fn = futex_wait_restart;
1927         restart->futex.uaddr = uaddr;
1928         restart->futex.val = val;
1929         restart->futex.time = abs_time->tv64;
1930         restart->futex.bitset = bitset;
1931         restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
1932
1933         ret = -ERESTART_RESTARTBLOCK;
1934
1935 out:
1936         if (to) {
1937                 hrtimer_cancel(&to->timer);
1938                 destroy_hrtimer_on_stack(&to->timer);
1939         }
1940         return ret;
1941 }
1942
1943
1944 static long futex_wait_restart(struct restart_block *restart)
1945 {
1946         u32 __user *uaddr = restart->futex.uaddr;
1947         ktime_t t, *tp = NULL;
1948
1949         if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
1950                 t.tv64 = restart->futex.time;
1951                 tp = &t;
1952         }
1953         restart->fn = do_no_restart_syscall;
1954
1955         return (long)futex_wait(uaddr, restart->futex.flags,
1956                                 restart->futex.val, tp, restart->futex.bitset);
1957 }
1958
1959
1960 /*
1961  * Userspace tried a 0 -> TID atomic transition of the futex value
1962  * and failed. The kernel side here does the whole locking operation:
1963  * if there are waiters then it will block, it does PI, etc. (Due to
1964  * races the kernel might see a 0 value of the futex too.)
1965  */
1966 static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect,
1967                          ktime_t *time, int trylock)
1968 {
1969         struct hrtimer_sleeper timeout, *to = NULL;
1970         struct futex_hash_bucket *hb;
1971         struct futex_q q = futex_q_init;
1972         int res, ret;
1973
1974         if (refill_pi_state_cache())
1975                 return -ENOMEM;
1976
1977         if (time) {
1978                 to = &timeout;
1979                 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
1980                                       HRTIMER_MODE_ABS);
1981                 hrtimer_init_sleeper(to, current);
1982                 hrtimer_set_expires(&to->timer, *time);
1983         }
1984
1985 retry:
1986         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
1987         if (unlikely(ret != 0))
1988                 goto out;
1989
1990 retry_private:
1991         hb = queue_lock(&q);
1992
1993         ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
1994         if (unlikely(ret)) {
1995                 switch (ret) {
1996                 case 1:
1997                         /* We got the lock. */
1998                         ret = 0;
1999                         goto out_unlock_put_key;
2000                 case -EFAULT:
2001                         goto uaddr_faulted;
2002                 case -EAGAIN:
2003                         /*
2004                          * Task is exiting and we just wait for the
2005                          * exit to complete.
2006                          */
2007                         queue_unlock(&q, hb);
2008                         put_futex_key(&q.key);
2009                         cond_resched();
2010                         goto retry;
2011                 default:
2012                         goto out_unlock_put_key;
2013                 }
2014         }
2015
2016         /*
2017          * Only actually queue now that the atomic ops are done:
2018          */
2019         queue_me(&q, hb);
2020
2021         WARN_ON(!q.pi_state);
2022         /*
2023          * Block on the PI mutex:
2024          */
2025         if (!trylock)
2026                 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
2027         else {
2028                 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
2029                 /* Fixup the trylock return value: */
2030                 ret = ret ? 0 : -EWOULDBLOCK;
2031         }
2032
2033         spin_lock(q.lock_ptr);
2034         /*
2035          * Fixup the pi_state owner and possibly acquire the lock if we
2036          * haven't already.
2037          */
2038         res = fixup_owner(uaddr, &q, !ret);
2039         /*
2040          * If fixup_owner() returned an error, proprogate that.  If it acquired
2041          * the lock, clear our -ETIMEDOUT or -EINTR.
2042          */
2043         if (res)
2044                 ret = (res < 0) ? res : 0;
2045
2046         /*
2047          * If fixup_owner() faulted and was unable to handle the fault, unlock
2048          * it and return the fault to userspace.
2049          */
2050         if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
2051                 rt_mutex_unlock(&q.pi_state->pi_mutex);
2052
2053         /* Unqueue and drop the lock */
2054         unqueue_me_pi(&q);
2055
2056         goto out_put_key;
2057
2058 out_unlock_put_key:
2059         queue_unlock(&q, hb);
2060
2061 out_put_key:
2062         put_futex_key(&q.key);
2063 out:
2064         if (to)
2065                 destroy_hrtimer_on_stack(&to->timer);
2066         return ret != -EINTR ? ret : -ERESTARTNOINTR;
2067
2068 uaddr_faulted:
2069         queue_unlock(&q, hb);
2070
2071         ret = fault_in_user_writeable(uaddr);
2072         if (ret)
2073                 goto out_put_key;
2074
2075         if (!(flags & FLAGS_SHARED))
2076                 goto retry_private;
2077
2078         put_futex_key(&q.key);
2079         goto retry;
2080 }
2081
2082 /*
2083  * Userspace attempted a TID -> 0 atomic transition, and failed.
2084  * This is the in-kernel slowpath: we look up the PI state (if any),
2085  * and do the rt-mutex unlock.
2086  */
2087 static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
2088 {
2089         struct futex_hash_bucket *hb;
2090         struct futex_q *this, *next;
2091         struct plist_head *head;
2092         union futex_key key = FUTEX_KEY_INIT;
2093         u32 uval, vpid = task_pid_vnr(current);
2094         int ret;
2095
2096 retry:
2097         if (get_user(uval, uaddr))
2098                 return -EFAULT;
2099         /*
2100          * We release only a lock we actually own:
2101          */
2102         if ((uval & FUTEX_TID_MASK) != vpid)
2103                 return -EPERM;
2104
2105         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
2106         if (unlikely(ret != 0))
2107                 goto out;
2108
2109         hb = hash_futex(&key);
2110         spin_lock(&hb->lock);
2111
2112         /*
2113          * To avoid races, try to do the TID -> 0 atomic transition
2114          * again. If it succeeds then we can return without waking
2115          * anyone else up:
2116          */
2117         if (!(uval & FUTEX_OWNER_DIED) &&
2118             cmpxchg_futex_value_locked(&uval, uaddr, vpid, 0))
2119                 goto pi_faulted;
2120         /*
2121          * Rare case: we managed to release the lock atomically,
2122          * no need to wake anyone else up:
2123          */
2124         if (unlikely(uval == vpid))
2125                 goto out_unlock;
2126
2127         /*
2128          * Ok, other tasks may need to be woken up - check waiters
2129          * and do the wakeup if necessary:
2130          */
2131         head = &hb->chain;
2132
2133         plist_for_each_entry_safe(this, next, head, list) {
2134                 if (!match_futex (&this->key, &key))
2135                         continue;
2136                 ret = wake_futex_pi(uaddr, uval, this);
2137                 /*
2138                  * The atomic access to the futex value
2139                  * generated a pagefault, so retry the
2140                  * user-access and the wakeup:
2141                  */
2142                 if (ret == -EFAULT)
2143                         goto pi_faulted;
2144                 goto out_unlock;
2145         }
2146         /*
2147          * No waiters - kernel unlocks the futex:
2148          */
2149         if (!(uval & FUTEX_OWNER_DIED)) {
2150                 ret = unlock_futex_pi(uaddr, uval);
2151                 if (ret == -EFAULT)
2152                         goto pi_faulted;
2153         }
2154
2155 out_unlock:
2156         spin_unlock(&hb->lock);
2157         put_futex_key(&key);
2158
2159 out:
2160         return ret;
2161
2162 pi_faulted:
2163         spin_unlock(&hb->lock);
2164         put_futex_key(&key);
2165
2166         ret = fault_in_user_writeable(uaddr);
2167         if (!ret)
2168                 goto retry;
2169
2170         return ret;
2171 }
2172
2173 /**
2174  * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2175  * @hb:         the hash_bucket futex_q was original enqueued on
2176  * @q:          the futex_q woken while waiting to be requeued
2177  * @key2:       the futex_key of the requeue target futex
2178  * @timeout:    the timeout associated with the wait (NULL if none)
2179  *
2180  * Detect if the task was woken on the initial futex as opposed to the requeue
2181  * target futex.  If so, determine if it was a timeout or a signal that caused
2182  * the wakeup and return the appropriate error code to the caller.  Must be
2183  * called with the hb lock held.
2184  *
2185  * Returns
2186  *  0 - no early wakeup detected
2187  * <0 - -ETIMEDOUT or -ERESTARTNOINTR
2188  */
2189 static inline
2190 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2191                                    struct futex_q *q, union futex_key *key2,
2192                                    struct hrtimer_sleeper *timeout)
2193 {
2194         int ret = 0;
2195
2196         /*
2197          * With the hb lock held, we avoid races while we process the wakeup.
2198          * We only need to hold hb (and not hb2) to ensure atomicity as the
2199          * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2200          * It can't be requeued from uaddr2 to something else since we don't
2201          * support a PI aware source futex for requeue.
2202          */
2203         if (!match_futex(&q->key, key2)) {
2204                 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2205                 /*
2206                  * We were woken prior to requeue by a timeout or a signal.
2207                  * Unqueue the futex_q and determine which it was.
2208                  */
2209                 plist_del(&q->list, &hb->chain);
2210
2211                 /* Handle spurious wakeups gracefully */
2212                 ret = -EWOULDBLOCK;
2213                 if (timeout && !timeout->task)
2214                         ret = -ETIMEDOUT;
2215                 else if (signal_pending(current))
2216                         ret = -ERESTARTNOINTR;
2217         }
2218         return ret;
2219 }
2220
2221 /**
2222  * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2223  * @uaddr:      the futex we initially wait on (non-pi)
2224  * @flags:      futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
2225  *              the same type, no requeueing from private to shared, etc.
2226  * @val:        the expected value of uaddr
2227  * @abs_time:   absolute timeout
2228  * @bitset:     32 bit wakeup bitset set by userspace, defaults to all
2229  * @clockrt:    whether to use CLOCK_REALTIME (1) or CLOCK_MONOTONIC (0)
2230  * @uaddr2:     the pi futex we will take prior to returning to user-space
2231  *
2232  * The caller will wait on uaddr and will be requeued by futex_requeue() to
2233  * uaddr2 which must be PI aware.  Normal wakeup will wake on uaddr2 and
2234  * complete the acquisition of the rt_mutex prior to returning to userspace.
2235  * This ensures the rt_mutex maintains an owner when it has waiters; without
2236  * one, the pi logic wouldn't know which task to boost/deboost, if there was a
2237  * need to.
2238  *
2239  * We call schedule in futex_wait_queue_me() when we enqueue and return there
2240  * via the following:
2241  * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2242  * 2) wakeup on uaddr2 after a requeue
2243  * 3) signal
2244  * 4) timeout
2245  *
2246  * If 3, cleanup and return -ERESTARTNOINTR.
2247  *
2248  * If 2, we may then block on trying to take the rt_mutex and return via:
2249  * 5) successful lock
2250  * 6) signal
2251  * 7) timeout
2252  * 8) other lock acquisition failure
2253  *
2254  * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2255  *
2256  * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2257  *
2258  * Returns:
2259  *  0 - On success
2260  * <0 - On error
2261  */
2262 static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
2263                                  u32 val, ktime_t *abs_time, u32 bitset,
2264                                  u32 __user *uaddr2)
2265 {
2266         struct hrtimer_sleeper timeout, *to = NULL;
2267         struct rt_mutex_waiter rt_waiter;
2268         struct rt_mutex *pi_mutex = NULL;
2269         struct futex_hash_bucket *hb;
2270         union futex_key key2 = FUTEX_KEY_INIT;
2271         struct futex_q q = futex_q_init;
2272         int res, ret;
2273
2274         if (!bitset)
2275                 return -EINVAL;
2276
2277         if (abs_time) {
2278                 to = &timeout;
2279                 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2280                                       CLOCK_REALTIME : CLOCK_MONOTONIC,
2281                                       HRTIMER_MODE_ABS);
2282                 hrtimer_init_sleeper(to, current);
2283                 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2284                                              current->timer_slack_ns);
2285         }
2286
2287         /*
2288          * The waiter is allocated on our stack, manipulated by the requeue
2289          * code while we sleep on uaddr.
2290          */
2291         debug_rt_mutex_init_waiter(&rt_waiter);
2292         rt_waiter.task = NULL;
2293
2294         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
2295         if (unlikely(ret != 0))
2296                 goto out;
2297
2298         q.bitset = bitset;
2299         q.rt_waiter = &rt_waiter;
2300         q.requeue_pi_key = &key2;
2301
2302         /*
2303          * Prepare to wait on uaddr. On success, increments q.key (key1) ref
2304          * count.
2305          */
2306         ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2307         if (ret)
2308                 goto out_key2;
2309
2310         /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2311         futex_wait_queue_me(hb, &q, to);
2312
2313         spin_lock(&hb->lock);
2314         ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2315         spin_unlock(&hb->lock);
2316         if (ret)
2317                 goto out_put_keys;
2318
2319         /*
2320          * In order for us to be here, we know our q.key == key2, and since
2321          * we took the hb->lock above, we also know that futex_requeue() has
2322          * completed and we no longer have to concern ourselves with a wakeup
2323          * race with the atomic proxy lock acquisition by the requeue code. The
2324          * futex_requeue dropped our key1 reference and incremented our key2
2325          * reference count.
2326          */
2327
2328         /* Check if the requeue code acquired the second futex for us. */
2329         if (!q.rt_waiter) {
2330                 /*
2331                  * Got the lock. We might not be the anticipated owner if we
2332                  * did a lock-steal - fix up the PI-state in that case.
2333                  */
2334                 if (q.pi_state && (q.pi_state->owner != current)) {
2335                         spin_lock(q.lock_ptr);
2336                         ret = fixup_pi_state_owner(uaddr2, &q, current);
2337                         spin_unlock(q.lock_ptr);
2338                 }
2339         } else {
2340                 /*
2341                  * We have been woken up by futex_unlock_pi(), a timeout, or a
2342                  * signal.  futex_unlock_pi() will not destroy the lock_ptr nor
2343                  * the pi_state.
2344                  */
2345                 WARN_ON(!&q.pi_state);
2346                 pi_mutex = &q.pi_state->pi_mutex;
2347                 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
2348                 debug_rt_mutex_free_waiter(&rt_waiter);
2349
2350                 spin_lock(q.lock_ptr);
2351                 /*
2352                  * Fixup the pi_state owner and possibly acquire the lock if we
2353                  * haven't already.
2354                  */
2355                 res = fixup_owner(uaddr2, &q, !ret);
2356                 /*
2357                  * If fixup_owner() returned an error, proprogate that.  If it
2358                  * acquired the lock, clear -ETIMEDOUT or -EINTR.
2359                  */
2360                 if (res)
2361                         ret = (res < 0) ? res : 0;
2362
2363                 /* Unqueue and drop the lock. */
2364                 unqueue_me_pi(&q);
2365         }
2366
2367         /*
2368          * If fixup_pi_state_owner() faulted and was unable to handle the
2369          * fault, unlock the rt_mutex and return the fault to userspace.
2370          */
2371         if (ret == -EFAULT) {
2372                 if (rt_mutex_owner(pi_mutex) == current)
2373                         rt_mutex_unlock(pi_mutex);
2374         } else if (ret == -EINTR) {
2375                 /*
2376                  * We've already been requeued, but cannot restart by calling
2377                  * futex_lock_pi() directly. We could restart this syscall, but
2378                  * it would detect that the user space "val" changed and return
2379                  * -EWOULDBLOCK.  Save the overhead of the restart and return
2380                  * -EWOULDBLOCK directly.
2381                  */
2382                 ret = -EWOULDBLOCK;
2383         }
2384
2385 out_put_keys:
2386         put_futex_key(&q.key);
2387 out_key2:
2388         put_futex_key(&key2);
2389
2390 out:
2391         if (to) {
2392                 hrtimer_cancel(&to->timer);
2393                 destroy_hrtimer_on_stack(&to->timer);
2394         }
2395         return ret;
2396 }
2397
2398 /*
2399  * Support for robust futexes: the kernel cleans up held futexes at
2400  * thread exit time.
2401  *
2402  * Implementation: user-space maintains a per-thread list of locks it
2403  * is holding. Upon do_exit(), the kernel carefully walks this list,
2404  * and marks all locks that are owned by this thread with the
2405  * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2406  * always manipulated with the lock held, so the list is private and
2407  * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2408  * field, to allow the kernel to clean up if the thread dies after
2409  * acquiring the lock, but just before it could have added itself to
2410  * the list. There can only be one such pending lock.
2411  */
2412
2413 /**
2414  * sys_set_robust_list() - Set the robust-futex list head of a task
2415  * @head:       pointer to the list-head
2416  * @len:        length of the list-head, as userspace expects
2417  */
2418 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2419                 size_t, len)
2420 {
2421         if (!futex_cmpxchg_enabled)
2422                 return -ENOSYS;
2423         /*
2424          * The kernel knows only one size for now:
2425          */
2426         if (unlikely(len != sizeof(*head)))
2427                 return -EINVAL;
2428
2429         current->robust_list = head;
2430
2431         return 0;
2432 }
2433
2434 /**
2435  * sys_get_robust_list() - Get the robust-futex list head of a task
2436  * @pid:        pid of the process [zero for current task]
2437  * @head_ptr:   pointer to a list-head pointer, the kernel fills it in
2438  * @len_ptr:    pointer to a length field, the kernel fills in the header size
2439  */
2440 SYSCALL_DEFINE3(get_robust_list, int, pid,
2441                 struct robust_list_head __user * __user *, head_ptr,
2442                 size_t __user *, len_ptr)
2443 {
2444         struct robust_list_head __user *head;
2445         unsigned long ret;
2446         const struct cred *cred = current_cred(), *pcred;
2447
2448         if (!futex_cmpxchg_enabled)
2449                 return -ENOSYS;
2450
2451         if (!pid)
2452                 head = current->robust_list;
2453         else {
2454                 struct task_struct *p;
2455
2456                 ret = -ESRCH;
2457                 rcu_read_lock();
2458                 p = find_task_by_vpid(pid);
2459                 if (!p)
2460                         goto err_unlock;
2461                 ret = -EPERM;
2462                 pcred = __task_cred(p);
2463                 /* If victim is in different user_ns, then uids are not
2464                    comparable, so we must have CAP_SYS_PTRACE */
2465                 if (cred->user->user_ns != pcred->user->user_ns) {
2466                         if (!ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE))
2467                                 goto err_unlock;
2468                         goto ok;
2469                 }
2470                 /* If victim is in same user_ns, then uids are comparable */
2471                 if (cred->euid != pcred->euid &&
2472                     cred->euid != pcred->uid &&
2473                     !ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE))
2474                         goto err_unlock;
2475 ok:
2476                 head = p->robust_list;
2477                 rcu_read_unlock();
2478         }
2479
2480         if (put_user(sizeof(*head), len_ptr))
2481                 return -EFAULT;
2482         return put_user(head, head_ptr);
2483
2484 err_unlock:
2485         rcu_read_unlock();
2486
2487         return ret;
2488 }
2489
2490 /*
2491  * Process a futex-list entry, check whether it's owned by the
2492  * dying task, and do notification if so:
2493  */
2494 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
2495 {
2496         u32 uval, nval, mval;
2497
2498 retry:
2499         if (get_user(uval, uaddr))
2500                 return -1;
2501
2502         if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
2503                 /*
2504                  * Ok, this dying thread is truly holding a futex
2505                  * of interest. Set the OWNER_DIED bit atomically
2506                  * via cmpxchg, and if the value had FUTEX_WAITERS
2507                  * set, wake up a waiter (if any). (We have to do a
2508                  * futex_wake() even if OWNER_DIED is already set -
2509                  * to handle the rare but possible case of recursive
2510                  * thread-death.) The rest of the cleanup is done in
2511                  * userspace.
2512                  */
2513                 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
2514                 /*
2515                  * We are not holding a lock here, but we want to have
2516                  * the pagefault_disable/enable() protection because
2517                  * we want to handle the fault gracefully. If the
2518                  * access fails we try to fault in the futex with R/W
2519                  * verification via get_user_pages. get_user() above
2520                  * does not guarantee R/W access. If that fails we
2521                  * give up and leave the futex locked.
2522                  */
2523                 if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
2524                         if (fault_in_user_writeable(uaddr))
2525                                 return -1;
2526                         goto retry;
2527                 }
2528                 if (nval != uval)
2529                         goto retry;
2530
2531                 /*
2532                  * Wake robust non-PI futexes here. The wakeup of
2533                  * PI futexes happens in exit_pi_state():
2534                  */
2535                 if (!pi && (uval & FUTEX_WAITERS))
2536                         futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
2537         }
2538         return 0;
2539 }
2540
2541 /*
2542  * Fetch a robust-list pointer. Bit 0 signals PI futexes:
2543  */
2544 static inline int fetch_robust_entry(struct robust_list __user **entry,
2545                                      struct robust_list __user * __user *head,
2546                                      unsigned int *pi)
2547 {
2548         unsigned long uentry;
2549
2550         if (get_user(uentry, (unsigned long __user *)head))
2551                 return -EFAULT;
2552
2553         *entry = (void __user *)(uentry & ~1UL);
2554         *pi = uentry & 1;
2555
2556         return 0;
2557 }
2558
2559 /*
2560  * Walk curr->robust_list (very carefully, it's a userspace list!)
2561  * and mark any locks found there dead, and notify any waiters.
2562  *
2563  * We silently return on any sign of list-walking problem.
2564  */
2565 void exit_robust_list(struct task_struct *curr)
2566 {
2567         struct robust_list_head __user *head = curr->robust_list;
2568         struct robust_list __user *entry, *next_entry, *pending;
2569         unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
2570         unsigned int uninitialized_var(next_pi);
2571         unsigned long futex_offset;
2572         int rc;
2573
2574         if (!futex_cmpxchg_enabled)
2575                 return;
2576
2577         /*
2578          * Fetch the list head (which was registered earlier, via
2579          * sys_set_robust_list()):
2580          */
2581         if (fetch_robust_entry(&entry, &head->list.next, &pi))
2582                 return;
2583         /*
2584          * Fetch the relative futex offset:
2585          */
2586         if (get_user(futex_offset, &head->futex_offset))
2587                 return;
2588         /*
2589          * Fetch any possibly pending lock-add first, and handle it
2590          * if it exists:
2591          */
2592         if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
2593                 return;
2594
2595         next_entry = NULL;      /* avoid warning with gcc */
2596         while (entry != &head->list) {
2597                 /*
2598                  * Fetch the next entry in the list before calling
2599                  * handle_futex_death:
2600                  */
2601                 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
2602                 /*
2603                  * A pending lock might already be on the list, so
2604                  * don't process it twice:
2605                  */
2606                 if (entry != pending)
2607                         if (handle_futex_death((void __user *)entry + futex_offset,
2608                                                 curr, pi))
2609                                 return;
2610                 if (rc)
2611                         return;
2612                 entry = next_entry;
2613                 pi = next_pi;
2614                 /*
2615                  * Avoid excessively long or circular lists:
2616                  */
2617                 if (!--limit)
2618                         break;
2619
2620                 cond_resched();
2621         }
2622
2623         if (pending)
2624                 handle_futex_death((void __user *)pending + futex_offset,
2625                                    curr, pip);
2626 }
2627
2628 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
2629                 u32 __user *uaddr2, u32 val2, u32 val3)
2630 {
2631         int ret = -ENOSYS, cmd = op & FUTEX_CMD_MASK;
2632         unsigned int flags = 0;
2633
2634         if (!(op & FUTEX_PRIVATE_FLAG))
2635                 flags |= FLAGS_SHARED;
2636
2637         if (op & FUTEX_CLOCK_REALTIME) {
2638                 flags |= FLAGS_CLOCKRT;
2639                 if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
2640                         return -ENOSYS;
2641         }
2642
2643         switch (cmd) {
2644         case FUTEX_WAIT:
2645                 val3 = FUTEX_BITSET_MATCH_ANY;
2646         case FUTEX_WAIT_BITSET:
2647                 ret = futex_wait(uaddr, flags, val, timeout, val3);
2648                 break;
2649         case FUTEX_WAKE:
2650                 val3 = FUTEX_BITSET_MATCH_ANY;
2651         case FUTEX_WAKE_BITSET:
2652                 ret = futex_wake(uaddr, flags, val, val3);
2653                 break;
2654         case FUTEX_REQUEUE:
2655                 ret = futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
2656                 break;
2657         case FUTEX_CMP_REQUEUE:
2658                 ret = futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
2659                 break;
2660         case FUTEX_WAKE_OP:
2661                 ret = futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
2662                 break;
2663         case FUTEX_LOCK_PI:
2664                 if (futex_cmpxchg_enabled)
2665                         ret = futex_lock_pi(uaddr, flags, val, timeout, 0);
2666                 break;
2667         case FUTEX_UNLOCK_PI:
2668                 if (futex_cmpxchg_enabled)
2669                         ret = futex_unlock_pi(uaddr, flags);
2670                 break;
2671         case FUTEX_TRYLOCK_PI:
2672                 if (futex_cmpxchg_enabled)
2673                         ret = futex_lock_pi(uaddr, flags, 0, timeout, 1);
2674                 break;
2675         case FUTEX_WAIT_REQUEUE_PI:
2676                 val3 = FUTEX_BITSET_MATCH_ANY;
2677                 ret = futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
2678                                             uaddr2);
2679                 break;
2680         case FUTEX_CMP_REQUEUE_PI:
2681                 ret = futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
2682                 break;
2683         default:
2684                 ret = -ENOSYS;
2685         }
2686         return ret;
2687 }
2688
2689
2690 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
2691                 struct timespec __user *, utime, u32 __user *, uaddr2,
2692                 u32, val3)
2693 {
2694         struct timespec ts;
2695         ktime_t t, *tp = NULL;
2696         u32 val2 = 0;
2697         int cmd = op & FUTEX_CMD_MASK;
2698
2699         if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
2700                       cmd == FUTEX_WAIT_BITSET ||
2701                       cmd == FUTEX_WAIT_REQUEUE_PI)) {
2702                 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
2703                         return -EFAULT;
2704                 if (!timespec_valid(&ts))
2705                         return -EINVAL;
2706
2707                 t = timespec_to_ktime(ts);
2708                 if (cmd == FUTEX_WAIT)
2709                         t = ktime_add_safe(ktime_get(), t);
2710                 tp = &t;
2711         }
2712         /*
2713          * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
2714          * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
2715          */
2716         if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
2717             cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
2718                 val2 = (u32) (unsigned long) utime;
2719
2720         return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
2721 }
2722
2723 static int __init futex_init(void)
2724 {
2725         u32 curval;
2726         int i;
2727
2728         /*
2729          * This will fail and we want it. Some arch implementations do
2730          * runtime detection of the futex_atomic_cmpxchg_inatomic()
2731          * functionality. We want to know that before we call in any
2732          * of the complex code paths. Also we want to prevent
2733          * registration of robust lists in that case. NULL is
2734          * guaranteed to fault and we get -EFAULT on functional
2735          * implementation, the non-functional ones will return
2736          * -ENOSYS.
2737          */
2738         if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
2739                 futex_cmpxchg_enabled = 1;
2740
2741         for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
2742                 plist_head_init(&futex_queues[i].chain);
2743                 spin_lock_init(&futex_queues[i].lock);
2744         }
2745
2746         return 0;
2747 }
2748 __initcall(futex_init);