usermodehelper: check subprocess_info->path != NULL
[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/export.h>
59 #include <linux/magic.h>
60 #include <linux/pid.h>
61 #include <linux/nsproxy.h>
62 #include <linux/ptrace.h>
63
64 #include <asm/futex.h>
65
66 #include "rtmutex_common.h"
67
68 int __read_mostly futex_cmpxchg_enabled;
69
70 #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
71
72 /*
73  * Futex flags used to encode options to functions and preserve them across
74  * restarts.
75  */
76 #define FLAGS_SHARED            0x01
77 #define FLAGS_CLOCKRT           0x02
78 #define FLAGS_HAS_TIMEOUT       0x04
79
80 /*
81  * Priority Inheritance state:
82  */
83 struct futex_pi_state {
84         /*
85          * list of 'owned' pi_state instances - these have to be
86          * cleaned up in do_exit() if the task exits prematurely:
87          */
88         struct list_head list;
89
90         /*
91          * The PI object:
92          */
93         struct rt_mutex pi_mutex;
94
95         struct task_struct *owner;
96         atomic_t refcount;
97
98         union futex_key key;
99 };
100
101 /**
102  * struct futex_q - The hashed futex queue entry, one per waiting task
103  * @list:               priority-sorted list of tasks waiting on this futex
104  * @task:               the task waiting on the futex
105  * @lock_ptr:           the hash bucket lock
106  * @key:                the key the futex is hashed on
107  * @pi_state:           optional priority inheritance state
108  * @rt_waiter:          rt_waiter storage for use with requeue_pi
109  * @requeue_pi_key:     the requeue_pi target futex key
110  * @bitset:             bitset for the optional bitmasked wakeup
111  *
112  * We use this hashed waitqueue, instead of a normal wait_queue_t, so
113  * we can wake only the relevant ones (hashed queues may be shared).
114  *
115  * A futex_q has a woken state, just like tasks have TASK_RUNNING.
116  * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
117  * The order of wakeup is always to make the first condition true, then
118  * the second.
119  *
120  * PI futexes are typically woken before they are removed from the hash list via
121  * the rt_mutex code. See unqueue_me_pi().
122  */
123 struct futex_q {
124         struct plist_node list;
125
126         struct task_struct *task;
127         spinlock_t *lock_ptr;
128         union futex_key key;
129         struct futex_pi_state *pi_state;
130         struct rt_mutex_waiter *rt_waiter;
131         union futex_key *requeue_pi_key;
132         u32 bitset;
133 };
134
135 static const struct futex_q futex_q_init = {
136         /* list gets initialized in queue_me()*/
137         .key = FUTEX_KEY_INIT,
138         .bitset = FUTEX_BITSET_MATCH_ANY
139 };
140
141 /*
142  * Hash buckets are shared by all the futex_keys that hash to the same
143  * location.  Each key may have multiple futex_q structures, one for each task
144  * waiting on a futex.
145  */
146 struct futex_hash_bucket {
147         spinlock_t lock;
148         struct plist_head chain;
149 };
150
151 static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
152
153 /*
154  * We hash on the keys returned from get_futex_key (see below).
155  */
156 static struct futex_hash_bucket *hash_futex(union futex_key *key)
157 {
158         u32 hash = jhash2((u32*)&key->both.word,
159                           (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
160                           key->both.offset);
161         return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
162 }
163
164 /*
165  * Return 1 if two futex_keys are equal, 0 otherwise.
166  */
167 static inline int match_futex(union futex_key *key1, union futex_key *key2)
168 {
169         return (key1 && key2
170                 && key1->both.word == key2->both.word
171                 && key1->both.ptr == key2->both.ptr
172                 && key1->both.offset == key2->both.offset);
173 }
174
175 /*
176  * Take a reference to the resource addressed by a key.
177  * Can be called while holding spinlocks.
178  *
179  */
180 static void get_futex_key_refs(union futex_key *key)
181 {
182         if (!key->both.ptr)
183                 return;
184
185         switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
186         case FUT_OFF_INODE:
187                 ihold(key->shared.inode);
188                 break;
189         case FUT_OFF_MMSHARED:
190                 atomic_inc(&key->private.mm->mm_count);
191                 break;
192         }
193 }
194
195 /*
196  * Drop a reference to the resource addressed by a key.
197  * The hash bucket spinlock must not be held.
198  */
199 static void drop_futex_key_refs(union futex_key *key)
200 {
201         if (!key->both.ptr) {
202                 /* If we're here then we tried to put a key we failed to get */
203                 WARN_ON_ONCE(1);
204                 return;
205         }
206
207         switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
208         case FUT_OFF_INODE:
209                 iput(key->shared.inode);
210                 break;
211         case FUT_OFF_MMSHARED:
212                 mmdrop(key->private.mm);
213                 break;
214         }
215 }
216
217 /**
218  * get_futex_key() - Get parameters which are the keys for a futex
219  * @uaddr:      virtual address of the futex
220  * @fshared:    0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
221  * @key:        address where result is stored.
222  * @rw:         mapping needs to be read/write (values: VERIFY_READ,
223  *              VERIFY_WRITE)
224  *
225  * Returns a negative error code or 0
226  * The key words are stored in *key on success.
227  *
228  * For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,
229  * offset_within_page).  For private mappings, it's (uaddr, current->mm).
230  * We can usually work out the index without swapping in the page.
231  *
232  * lock_page() might sleep, the caller should not hold a spinlock.
233  */
234 static int
235 get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
236 {
237         unsigned long address = (unsigned long)uaddr;
238         struct mm_struct *mm = current->mm;
239         struct page *page, *page_head;
240         int err, ro = 0;
241
242         /*
243          * The futex address must be "naturally" aligned.
244          */
245         key->both.offset = address % PAGE_SIZE;
246         if (unlikely((address % sizeof(u32)) != 0))
247                 return -EINVAL;
248         address -= key->both.offset;
249
250         /*
251          * PROCESS_PRIVATE futexes are fast.
252          * As the mm cannot disappear under us and the 'key' only needs
253          * virtual address, we dont even have to find the underlying vma.
254          * Note : We do have to check 'uaddr' is a valid user address,
255          *        but access_ok() should be faster than find_vma()
256          */
257         if (!fshared) {
258                 if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))))
259                         return -EFAULT;
260                 key->private.mm = mm;
261                 key->private.address = address;
262                 get_futex_key_refs(key);
263                 return 0;
264         }
265
266 again:
267         err = get_user_pages_fast(address, 1, 1, &page);
268         /*
269          * If write access is not required (eg. FUTEX_WAIT), try
270          * and get read-only access.
271          */
272         if (err == -EFAULT && rw == VERIFY_READ) {
273                 err = get_user_pages_fast(address, 1, 0, &page);
274                 ro = 1;
275         }
276         if (err < 0)
277                 return err;
278         else
279                 err = 0;
280
281 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
282         page_head = page;
283         if (unlikely(PageTail(page))) {
284                 put_page(page);
285                 /* serialize against __split_huge_page_splitting() */
286                 local_irq_disable();
287                 if (likely(__get_user_pages_fast(address, 1, 1, &page) == 1)) {
288                         page_head = compound_head(page);
289                         /*
290                          * page_head is valid pointer but we must pin
291                          * it before taking the PG_lock and/or
292                          * PG_compound_lock. The moment we re-enable
293                          * irqs __split_huge_page_splitting() can
294                          * return and the head page can be freed from
295                          * under us. We can't take the PG_lock and/or
296                          * PG_compound_lock on a page that could be
297                          * freed from under us.
298                          */
299                         if (page != page_head) {
300                                 get_page(page_head);
301                                 put_page(page);
302                         }
303                         local_irq_enable();
304                 } else {
305                         local_irq_enable();
306                         goto again;
307                 }
308         }
309 #else
310         page_head = compound_head(page);
311         if (page != page_head) {
312                 get_page(page_head);
313                 put_page(page);
314         }
315 #endif
316
317         lock_page(page_head);
318
319         /*
320          * If page_head->mapping is NULL, then it cannot be a PageAnon
321          * page; but it might be the ZERO_PAGE or in the gate area or
322          * in a special mapping (all cases which we are happy to fail);
323          * or it may have been a good file page when get_user_pages_fast
324          * found it, but truncated or holepunched or subjected to
325          * invalidate_complete_page2 before we got the page lock (also
326          * cases which we are happy to fail).  And we hold a reference,
327          * so refcount care in invalidate_complete_page's remove_mapping
328          * prevents drop_caches from setting mapping to NULL beneath us.
329          *
330          * The case we do have to guard against is when memory pressure made
331          * shmem_writepage move it from filecache to swapcache beneath us:
332          * an unlikely race, but we do need to retry for page_head->mapping.
333          */
334         if (!page_head->mapping) {
335                 int shmem_swizzled = PageSwapCache(page_head);
336                 unlock_page(page_head);
337                 put_page(page_head);
338                 if (shmem_swizzled)
339                         goto again;
340                 return -EFAULT;
341         }
342
343         /*
344          * Private mappings are handled in a simple way.
345          *
346          * NOTE: When userspace waits on a MAP_SHARED mapping, even if
347          * it's a read-only handle, it's expected that futexes attach to
348          * the object not the particular process.
349          */
350         if (PageAnon(page_head)) {
351                 /*
352                  * A RO anonymous page will never change and thus doesn't make
353                  * sense for futex operations.
354                  */
355                 if (ro) {
356                         err = -EFAULT;
357                         goto out;
358                 }
359
360                 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
361                 key->private.mm = mm;
362                 key->private.address = address;
363         } else {
364                 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
365                 key->shared.inode = page_head->mapping->host;
366                 key->shared.pgoff = page_head->index;
367         }
368
369         get_futex_key_refs(key);
370
371 out:
372         unlock_page(page_head);
373         put_page(page_head);
374         return err;
375 }
376
377 static inline void put_futex_key(union futex_key *key)
378 {
379         drop_futex_key_refs(key);
380 }
381
382 /**
383  * fault_in_user_writeable() - Fault in user address and verify RW access
384  * @uaddr:      pointer to faulting user space address
385  *
386  * Slow path to fixup the fault we just took in the atomic write
387  * access to @uaddr.
388  *
389  * We have no generic implementation of a non-destructive write to the
390  * user address. We know that we faulted in the atomic pagefault
391  * disabled section so we can as well avoid the #PF overhead by
392  * calling get_user_pages() right away.
393  */
394 static int fault_in_user_writeable(u32 __user *uaddr)
395 {
396         struct mm_struct *mm = current->mm;
397         int ret;
398
399         down_read(&mm->mmap_sem);
400         ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
401                                FAULT_FLAG_WRITE);
402         up_read(&mm->mmap_sem);
403
404         return ret < 0 ? ret : 0;
405 }
406
407 /**
408  * futex_top_waiter() - Return the highest priority waiter on a futex
409  * @hb:         the hash bucket the futex_q's reside in
410  * @key:        the futex key (to distinguish it from other futex futex_q's)
411  *
412  * Must be called with the hb lock held.
413  */
414 static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
415                                         union futex_key *key)
416 {
417         struct futex_q *this;
418
419         plist_for_each_entry(this, &hb->chain, list) {
420                 if (match_futex(&this->key, key))
421                         return this;
422         }
423         return NULL;
424 }
425
426 static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
427                                       u32 uval, u32 newval)
428 {
429         int ret;
430
431         pagefault_disable();
432         ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
433         pagefault_enable();
434
435         return ret;
436 }
437
438 static int get_futex_value_locked(u32 *dest, u32 __user *from)
439 {
440         int ret;
441
442         pagefault_disable();
443         ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
444         pagefault_enable();
445
446         return ret ? -EFAULT : 0;
447 }
448
449
450 /*
451  * PI code:
452  */
453 static int refill_pi_state_cache(void)
454 {
455         struct futex_pi_state *pi_state;
456
457         if (likely(current->pi_state_cache))
458                 return 0;
459
460         pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
461
462         if (!pi_state)
463                 return -ENOMEM;
464
465         INIT_LIST_HEAD(&pi_state->list);
466         /* pi_mutex gets initialized later */
467         pi_state->owner = NULL;
468         atomic_set(&pi_state->refcount, 1);
469         pi_state->key = FUTEX_KEY_INIT;
470
471         current->pi_state_cache = pi_state;
472
473         return 0;
474 }
475
476 static struct futex_pi_state * alloc_pi_state(void)
477 {
478         struct futex_pi_state *pi_state = current->pi_state_cache;
479
480         WARN_ON(!pi_state);
481         current->pi_state_cache = NULL;
482
483         return pi_state;
484 }
485
486 static void free_pi_state(struct futex_pi_state *pi_state)
487 {
488         if (!atomic_dec_and_test(&pi_state->refcount))
489                 return;
490
491         /*
492          * If pi_state->owner is NULL, the owner is most probably dying
493          * and has cleaned up the pi_state already
494          */
495         if (pi_state->owner) {
496                 raw_spin_lock_irq(&pi_state->owner->pi_lock);
497                 list_del_init(&pi_state->list);
498                 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
499
500                 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
501         }
502
503         if (current->pi_state_cache)
504                 kfree(pi_state);
505         else {
506                 /*
507                  * pi_state->list is already empty.
508                  * clear pi_state->owner.
509                  * refcount is at 0 - put it back to 1.
510                  */
511                 pi_state->owner = NULL;
512                 atomic_set(&pi_state->refcount, 1);
513                 current->pi_state_cache = pi_state;
514         }
515 }
516
517 /*
518  * Look up the task based on what TID userspace gave us.
519  * We dont trust it.
520  */
521 static struct task_struct * futex_find_get_task(pid_t pid)
522 {
523         struct task_struct *p;
524
525         rcu_read_lock();
526         p = find_task_by_vpid(pid);
527         if (p)
528                 get_task_struct(p);
529
530         rcu_read_unlock();
531
532         return p;
533 }
534
535 /*
536  * This task is holding PI mutexes at exit time => bad.
537  * Kernel cleans up PI-state, but userspace is likely hosed.
538  * (Robust-futex cleanup is separate and might save the day for userspace.)
539  */
540 void exit_pi_state_list(struct task_struct *curr)
541 {
542         struct list_head *next, *head = &curr->pi_state_list;
543         struct futex_pi_state *pi_state;
544         struct futex_hash_bucket *hb;
545         union futex_key key = FUTEX_KEY_INIT;
546
547         if (!futex_cmpxchg_enabled)
548                 return;
549         /*
550          * We are a ZOMBIE and nobody can enqueue itself on
551          * pi_state_list anymore, but we have to be careful
552          * versus waiters unqueueing themselves:
553          */
554         raw_spin_lock_irq(&curr->pi_lock);
555         while (!list_empty(head)) {
556
557                 next = head->next;
558                 pi_state = list_entry(next, struct futex_pi_state, list);
559                 key = pi_state->key;
560                 hb = hash_futex(&key);
561                 raw_spin_unlock_irq(&curr->pi_lock);
562
563                 spin_lock(&hb->lock);
564
565                 raw_spin_lock_irq(&curr->pi_lock);
566                 /*
567                  * We dropped the pi-lock, so re-check whether this
568                  * task still owns the PI-state:
569                  */
570                 if (head->next != next) {
571                         spin_unlock(&hb->lock);
572                         continue;
573                 }
574
575                 WARN_ON(pi_state->owner != curr);
576                 WARN_ON(list_empty(&pi_state->list));
577                 list_del_init(&pi_state->list);
578                 pi_state->owner = NULL;
579                 raw_spin_unlock_irq(&curr->pi_lock);
580
581                 rt_mutex_unlock(&pi_state->pi_mutex);
582
583                 spin_unlock(&hb->lock);
584
585                 raw_spin_lock_irq(&curr->pi_lock);
586         }
587         raw_spin_unlock_irq(&curr->pi_lock);
588 }
589
590 static int
591 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
592                 union futex_key *key, struct futex_pi_state **ps)
593 {
594         struct futex_pi_state *pi_state = NULL;
595         struct futex_q *this, *next;
596         struct plist_head *head;
597         struct task_struct *p;
598         pid_t pid = uval & FUTEX_TID_MASK;
599
600         head = &hb->chain;
601
602         plist_for_each_entry_safe(this, next, head, list) {
603                 if (match_futex(&this->key, key)) {
604                         /*
605                          * Another waiter already exists - bump up
606                          * the refcount and return its pi_state:
607                          */
608                         pi_state = this->pi_state;
609                         /*
610                          * Userspace might have messed up non-PI and PI futexes
611                          */
612                         if (unlikely(!pi_state))
613                                 return -EINVAL;
614
615                         WARN_ON(!atomic_read(&pi_state->refcount));
616
617                         /*
618                          * When pi_state->owner is NULL then the owner died
619                          * and another waiter is on the fly. pi_state->owner
620                          * is fixed up by the task which acquires
621                          * pi_state->rt_mutex.
622                          *
623                          * We do not check for pid == 0 which can happen when
624                          * the owner died and robust_list_exit() cleared the
625                          * TID.
626                          */
627                         if (pid && pi_state->owner) {
628                                 /*
629                                  * Bail out if user space manipulated the
630                                  * futex value.
631                                  */
632                                 if (pid != task_pid_vnr(pi_state->owner))
633                                         return -EINVAL;
634                         }
635
636                         atomic_inc(&pi_state->refcount);
637                         *ps = pi_state;
638
639                         return 0;
640                 }
641         }
642
643         /*
644          * We are the first waiter - try to look up the real owner and attach
645          * the new pi_state to it, but bail out when TID = 0
646          */
647         if (!pid)
648                 return -ESRCH;
649         p = futex_find_get_task(pid);
650         if (!p)
651                 return -ESRCH;
652
653         /*
654          * We need to look at the task state flags to figure out,
655          * whether the task is exiting. To protect against the do_exit
656          * change of the task flags, we do this protected by
657          * p->pi_lock:
658          */
659         raw_spin_lock_irq(&p->pi_lock);
660         if (unlikely(p->flags & PF_EXITING)) {
661                 /*
662                  * The task is on the way out. When PF_EXITPIDONE is
663                  * set, we know that the task has finished the
664                  * cleanup:
665                  */
666                 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
667
668                 raw_spin_unlock_irq(&p->pi_lock);
669                 put_task_struct(p);
670                 return ret;
671         }
672
673         pi_state = alloc_pi_state();
674
675         /*
676          * Initialize the pi_mutex in locked state and make 'p'
677          * the owner of it:
678          */
679         rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
680
681         /* Store the key for possible exit cleanups: */
682         pi_state->key = *key;
683
684         WARN_ON(!list_empty(&pi_state->list));
685         list_add(&pi_state->list, &p->pi_state_list);
686         pi_state->owner = p;
687         raw_spin_unlock_irq(&p->pi_lock);
688
689         put_task_struct(p);
690
691         *ps = pi_state;
692
693         return 0;
694 }
695
696 /**
697  * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
698  * @uaddr:              the pi futex user address
699  * @hb:                 the pi futex hash bucket
700  * @key:                the futex key associated with uaddr and hb
701  * @ps:                 the pi_state pointer where we store the result of the
702  *                      lookup
703  * @task:               the task to perform the atomic lock work for.  This will
704  *                      be "current" except in the case of requeue pi.
705  * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
706  *
707  * Returns:
708  *  0 - ready to wait
709  *  1 - acquired the lock
710  * <0 - error
711  *
712  * The hb->lock and futex_key refs shall be held by the caller.
713  */
714 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
715                                 union futex_key *key,
716                                 struct futex_pi_state **ps,
717                                 struct task_struct *task, int set_waiters)
718 {
719         int lock_taken, ret, force_take = 0;
720         u32 uval, newval, curval, vpid = task_pid_vnr(task);
721
722 retry:
723         ret = lock_taken = 0;
724
725         /*
726          * To avoid races, we attempt to take the lock here again
727          * (by doing a 0 -> TID atomic cmpxchg), while holding all
728          * the locks. It will most likely not succeed.
729          */
730         newval = vpid;
731         if (set_waiters)
732                 newval |= FUTEX_WAITERS;
733
734         if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval)))
735                 return -EFAULT;
736
737         /*
738          * Detect deadlocks.
739          */
740         if ((unlikely((curval & FUTEX_TID_MASK) == vpid)))
741                 return -EDEADLK;
742
743         /*
744          * Surprise - we got the lock. Just return to userspace:
745          */
746         if (unlikely(!curval))
747                 return 1;
748
749         uval = curval;
750
751         /*
752          * Set the FUTEX_WAITERS flag, so the owner will know it has someone
753          * to wake at the next unlock.
754          */
755         newval = curval | FUTEX_WAITERS;
756
757         /*
758          * Should we force take the futex? See below.
759          */
760         if (unlikely(force_take)) {
761                 /*
762                  * Keep the OWNER_DIED and the WAITERS bit and set the
763                  * new TID value.
764                  */
765                 newval = (curval & ~FUTEX_TID_MASK) | vpid;
766                 force_take = 0;
767                 lock_taken = 1;
768         }
769
770         if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
771                 return -EFAULT;
772         if (unlikely(curval != uval))
773                 goto retry;
774
775         /*
776          * We took the lock due to forced take over.
777          */
778         if (unlikely(lock_taken))
779                 return 1;
780
781         /*
782          * We dont have the lock. Look up the PI state (or create it if
783          * we are the first waiter):
784          */
785         ret = lookup_pi_state(uval, hb, key, ps);
786
787         if (unlikely(ret)) {
788                 switch (ret) {
789                 case -ESRCH:
790                         /*
791                          * We failed to find an owner for this
792                          * futex. So we have no pi_state to block
793                          * on. This can happen in two cases:
794                          *
795                          * 1) The owner died
796                          * 2) A stale FUTEX_WAITERS bit
797                          *
798                          * Re-read the futex value.
799                          */
800                         if (get_futex_value_locked(&curval, uaddr))
801                                 return -EFAULT;
802
803                         /*
804                          * If the owner died or we have a stale
805                          * WAITERS bit the owner TID in the user space
806                          * futex is 0.
807                          */
808                         if (!(curval & FUTEX_TID_MASK)) {
809                                 force_take = 1;
810                                 goto retry;
811                         }
812                 default:
813                         break;
814                 }
815         }
816
817         return ret;
818 }
819
820 /**
821  * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
822  * @q:  The futex_q to unqueue
823  *
824  * The q->lock_ptr must not be NULL and must be held by the caller.
825  */
826 static void __unqueue_futex(struct futex_q *q)
827 {
828         struct futex_hash_bucket *hb;
829
830         if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
831             || WARN_ON(plist_node_empty(&q->list)))
832                 return;
833
834         hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
835         plist_del(&q->list, &hb->chain);
836 }
837
838 /*
839  * The hash bucket lock must be held when this is called.
840  * Afterwards, the futex_q must not be accessed.
841  */
842 static void wake_futex(struct futex_q *q)
843 {
844         struct task_struct *p = q->task;
845
846         if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
847                 return;
848
849         /*
850          * We set q->lock_ptr = NULL _before_ we wake up the task. If
851          * a non-futex wake up happens on another CPU then the task
852          * might exit and p would dereference a non-existing task
853          * struct. Prevent this by holding a reference on p across the
854          * wake up.
855          */
856         get_task_struct(p);
857
858         __unqueue_futex(q);
859         /*
860          * The waiting task can free the futex_q as soon as
861          * q->lock_ptr = NULL is written, without taking any locks. A
862          * memory barrier is required here to prevent the following
863          * store to lock_ptr from getting ahead of the plist_del.
864          */
865         smp_wmb();
866         q->lock_ptr = NULL;
867
868         wake_up_state(p, TASK_NORMAL);
869         put_task_struct(p);
870 }
871
872 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
873 {
874         struct task_struct *new_owner;
875         struct futex_pi_state *pi_state = this->pi_state;
876         u32 uninitialized_var(curval), newval;
877
878         if (!pi_state)
879                 return -EINVAL;
880
881         /*
882          * If current does not own the pi_state then the futex is
883          * inconsistent and user space fiddled with the futex value.
884          */
885         if (pi_state->owner != current)
886                 return -EINVAL;
887
888         raw_spin_lock(&pi_state->pi_mutex.wait_lock);
889         new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
890
891         /*
892          * It is possible that the next waiter (the one that brought
893          * this owner to the kernel) timed out and is no longer
894          * waiting on the lock.
895          */
896         if (!new_owner)
897                 new_owner = this->task;
898
899         /*
900          * We pass it to the next owner. (The WAITERS bit is always
901          * kept enabled while there is PI state around. We must also
902          * preserve the owner died bit.)
903          */
904         if (!(uval & FUTEX_OWNER_DIED)) {
905                 int ret = 0;
906
907                 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
908
909                 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
910                         ret = -EFAULT;
911                 else if (curval != uval)
912                         ret = -EINVAL;
913                 if (ret) {
914                         raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
915                         return ret;
916                 }
917         }
918
919         raw_spin_lock_irq(&pi_state->owner->pi_lock);
920         WARN_ON(list_empty(&pi_state->list));
921         list_del_init(&pi_state->list);
922         raw_spin_unlock_irq(&pi_state->owner->pi_lock);
923
924         raw_spin_lock_irq(&new_owner->pi_lock);
925         WARN_ON(!list_empty(&pi_state->list));
926         list_add(&pi_state->list, &new_owner->pi_state_list);
927         pi_state->owner = new_owner;
928         raw_spin_unlock_irq(&new_owner->pi_lock);
929
930         raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
931         rt_mutex_unlock(&pi_state->pi_mutex);
932
933         return 0;
934 }
935
936 static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
937 {
938         u32 uninitialized_var(oldval);
939
940         /*
941          * There is no waiter, so we unlock the futex. The owner died
942          * bit has not to be preserved here. We are the owner:
943          */
944         if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0))
945                 return -EFAULT;
946         if (oldval != uval)
947                 return -EAGAIN;
948
949         return 0;
950 }
951
952 /*
953  * Express the locking dependencies for lockdep:
954  */
955 static inline void
956 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
957 {
958         if (hb1 <= hb2) {
959                 spin_lock(&hb1->lock);
960                 if (hb1 < hb2)
961                         spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
962         } else { /* hb1 > hb2 */
963                 spin_lock(&hb2->lock);
964                 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
965         }
966 }
967
968 static inline void
969 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
970 {
971         spin_unlock(&hb1->lock);
972         if (hb1 != hb2)
973                 spin_unlock(&hb2->lock);
974 }
975
976 /*
977  * Wake up waiters matching bitset queued on this futex (uaddr).
978  */
979 static int
980 futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
981 {
982         struct futex_hash_bucket *hb;
983         struct futex_q *this, *next;
984         struct plist_head *head;
985         union futex_key key = FUTEX_KEY_INIT;
986         int ret;
987
988         if (!bitset)
989                 return -EINVAL;
990
991         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
992         if (unlikely(ret != 0))
993                 goto out;
994
995         hb = hash_futex(&key);
996         spin_lock(&hb->lock);
997         head = &hb->chain;
998
999         plist_for_each_entry_safe(this, next, head, list) {
1000                 if (match_futex (&this->key, &key)) {
1001                         if (this->pi_state || this->rt_waiter) {
1002                                 ret = -EINVAL;
1003                                 break;
1004                         }
1005
1006                         /* Check if one of the bits is set in both bitsets */
1007                         if (!(this->bitset & bitset))
1008                                 continue;
1009
1010                         wake_futex(this);
1011                         if (++ret >= nr_wake)
1012                                 break;
1013                 }
1014         }
1015
1016         spin_unlock(&hb->lock);
1017         put_futex_key(&key);
1018 out:
1019         return ret;
1020 }
1021
1022 /*
1023  * Wake up all waiters hashed on the physical page that is mapped
1024  * to this virtual address:
1025  */
1026 static int
1027 futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
1028               int nr_wake, int nr_wake2, int op)
1029 {
1030         union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1031         struct futex_hash_bucket *hb1, *hb2;
1032         struct plist_head *head;
1033         struct futex_q *this, *next;
1034         int ret, op_ret;
1035
1036 retry:
1037         ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1038         if (unlikely(ret != 0))
1039                 goto out;
1040         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
1041         if (unlikely(ret != 0))
1042                 goto out_put_key1;
1043
1044         hb1 = hash_futex(&key1);
1045         hb2 = hash_futex(&key2);
1046
1047 retry_private:
1048         double_lock_hb(hb1, hb2);
1049         op_ret = futex_atomic_op_inuser(op, uaddr2);
1050         if (unlikely(op_ret < 0)) {
1051
1052                 double_unlock_hb(hb1, hb2);
1053
1054 #ifndef CONFIG_MMU
1055                 /*
1056                  * we don't get EFAULT from MMU faults if we don't have an MMU,
1057                  * but we might get them from range checking
1058                  */
1059                 ret = op_ret;
1060                 goto out_put_keys;
1061 #endif
1062
1063                 if (unlikely(op_ret != -EFAULT)) {
1064                         ret = op_ret;
1065                         goto out_put_keys;
1066                 }
1067
1068                 ret = fault_in_user_writeable(uaddr2);
1069                 if (ret)
1070                         goto out_put_keys;
1071
1072                 if (!(flags & FLAGS_SHARED))
1073                         goto retry_private;
1074
1075                 put_futex_key(&key2);
1076                 put_futex_key(&key1);
1077                 goto retry;
1078         }
1079
1080         head = &hb1->chain;
1081
1082         plist_for_each_entry_safe(this, next, head, list) {
1083                 if (match_futex (&this->key, &key1)) {
1084                         if (this->pi_state || this->rt_waiter) {
1085                                 ret = -EINVAL;
1086                                 goto out_unlock;
1087                         }
1088                         wake_futex(this);
1089                         if (++ret >= nr_wake)
1090                                 break;
1091                 }
1092         }
1093
1094         if (op_ret > 0) {
1095                 head = &hb2->chain;
1096
1097                 op_ret = 0;
1098                 plist_for_each_entry_safe(this, next, head, list) {
1099                         if (match_futex (&this->key, &key2)) {
1100                                 if (this->pi_state || this->rt_waiter) {
1101                                         ret = -EINVAL;
1102                                         goto out_unlock;
1103                                 }
1104                                 wake_futex(this);
1105                                 if (++op_ret >= nr_wake2)
1106                                         break;
1107                         }
1108                 }
1109                 ret += op_ret;
1110         }
1111
1112 out_unlock:
1113         double_unlock_hb(hb1, hb2);
1114 out_put_keys:
1115         put_futex_key(&key2);
1116 out_put_key1:
1117         put_futex_key(&key1);
1118 out:
1119         return ret;
1120 }
1121
1122 /**
1123  * requeue_futex() - Requeue a futex_q from one hb to another
1124  * @q:          the futex_q to requeue
1125  * @hb1:        the source hash_bucket
1126  * @hb2:        the target hash_bucket
1127  * @key2:       the new key for the requeued futex_q
1128  */
1129 static inline
1130 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1131                    struct futex_hash_bucket *hb2, union futex_key *key2)
1132 {
1133
1134         /*
1135          * If key1 and key2 hash to the same bucket, no need to
1136          * requeue.
1137          */
1138         if (likely(&hb1->chain != &hb2->chain)) {
1139                 plist_del(&q->list, &hb1->chain);
1140                 plist_add(&q->list, &hb2->chain);
1141                 q->lock_ptr = &hb2->lock;
1142         }
1143         get_futex_key_refs(key2);
1144         q->key = *key2;
1145 }
1146
1147 /**
1148  * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1149  * @q:          the futex_q
1150  * @key:        the key of the requeue target futex
1151  * @hb:         the hash_bucket of the requeue target futex
1152  *
1153  * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1154  * target futex if it is uncontended or via a lock steal.  Set the futex_q key
1155  * to the requeue target futex so the waiter can detect the wakeup on the right
1156  * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1157  * atomic lock acquisition.  Set the q->lock_ptr to the requeue target hb->lock
1158  * to protect access to the pi_state to fixup the owner later.  Must be called
1159  * with both q->lock_ptr and hb->lock held.
1160  */
1161 static inline
1162 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1163                            struct futex_hash_bucket *hb)
1164 {
1165         get_futex_key_refs(key);
1166         q->key = *key;
1167
1168         __unqueue_futex(q);
1169
1170         WARN_ON(!q->rt_waiter);
1171         q->rt_waiter = NULL;
1172
1173         q->lock_ptr = &hb->lock;
1174
1175         wake_up_state(q->task, TASK_NORMAL);
1176 }
1177
1178 /**
1179  * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1180  * @pifutex:            the user address of the to futex
1181  * @hb1:                the from futex hash bucket, must be locked by the caller
1182  * @hb2:                the to futex hash bucket, must be locked by the caller
1183  * @key1:               the from futex key
1184  * @key2:               the to futex key
1185  * @ps:                 address to store the pi_state pointer
1186  * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
1187  *
1188  * Try and get the lock on behalf of the top waiter if we can do it atomically.
1189  * Wake the top waiter if we succeed.  If the caller specified set_waiters,
1190  * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1191  * hb1 and hb2 must be held by the caller.
1192  *
1193  * Returns:
1194  *  0 - failed to acquire the lock atomicly
1195  *  1 - acquired the lock
1196  * <0 - error
1197  */
1198 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1199                                  struct futex_hash_bucket *hb1,
1200                                  struct futex_hash_bucket *hb2,
1201                                  union futex_key *key1, union futex_key *key2,
1202                                  struct futex_pi_state **ps, int set_waiters)
1203 {
1204         struct futex_q *top_waiter = NULL;
1205         u32 curval;
1206         int ret;
1207
1208         if (get_futex_value_locked(&curval, pifutex))
1209                 return -EFAULT;
1210
1211         /*
1212          * Find the top_waiter and determine if there are additional waiters.
1213          * If the caller intends to requeue more than 1 waiter to pifutex,
1214          * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1215          * as we have means to handle the possible fault.  If not, don't set
1216          * the bit unecessarily as it will force the subsequent unlock to enter
1217          * the kernel.
1218          */
1219         top_waiter = futex_top_waiter(hb1, key1);
1220
1221         /* There are no waiters, nothing for us to do. */
1222         if (!top_waiter)
1223                 return 0;
1224
1225         /* Ensure we requeue to the expected futex. */
1226         if (!match_futex(top_waiter->requeue_pi_key, key2))
1227                 return -EINVAL;
1228
1229         /*
1230          * Try to take the lock for top_waiter.  Set the FUTEX_WAITERS bit in
1231          * the contended case or if set_waiters is 1.  The pi_state is returned
1232          * in ps in contended cases.
1233          */
1234         ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1235                                    set_waiters);
1236         if (ret == 1)
1237                 requeue_pi_wake_futex(top_waiter, key2, hb2);
1238
1239         return ret;
1240 }
1241
1242 /**
1243  * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1244  * @uaddr1:     source futex user address
1245  * @flags:      futex flags (FLAGS_SHARED, etc.)
1246  * @uaddr2:     target futex user address
1247  * @nr_wake:    number of waiters to wake (must be 1 for requeue_pi)
1248  * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1249  * @cmpval:     @uaddr1 expected value (or %NULL)
1250  * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1251  *              pi futex (pi to pi requeue is not supported)
1252  *
1253  * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1254  * uaddr2 atomically on behalf of the top waiter.
1255  *
1256  * Returns:
1257  * >=0 - on success, the number of tasks requeued or woken
1258  *  <0 - on error
1259  */
1260 static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1261                          u32 __user *uaddr2, int nr_wake, int nr_requeue,
1262                          u32 *cmpval, int requeue_pi)
1263 {
1264         union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1265         int drop_count = 0, task_count = 0, ret;
1266         struct futex_pi_state *pi_state = NULL;
1267         struct futex_hash_bucket *hb1, *hb2;
1268         struct plist_head *head1;
1269         struct futex_q *this, *next;
1270         u32 curval2;
1271
1272         if (requeue_pi) {
1273                 /*
1274                  * requeue_pi requires a pi_state, try to allocate it now
1275                  * without any locks in case it fails.
1276                  */
1277                 if (refill_pi_state_cache())
1278                         return -ENOMEM;
1279                 /*
1280                  * requeue_pi must wake as many tasks as it can, up to nr_wake
1281                  * + nr_requeue, since it acquires the rt_mutex prior to
1282                  * returning to userspace, so as to not leave the rt_mutex with
1283                  * waiters and no owner.  However, second and third wake-ups
1284                  * cannot be predicted as they involve race conditions with the
1285                  * first wake and a fault while looking up the pi_state.  Both
1286                  * pthread_cond_signal() and pthread_cond_broadcast() should
1287                  * use nr_wake=1.
1288                  */
1289                 if (nr_wake != 1)
1290                         return -EINVAL;
1291         }
1292
1293 retry:
1294         if (pi_state != NULL) {
1295                 /*
1296                  * We will have to lookup the pi_state again, so free this one
1297                  * to keep the accounting correct.
1298                  */
1299                 free_pi_state(pi_state);
1300                 pi_state = NULL;
1301         }
1302
1303         ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1304         if (unlikely(ret != 0))
1305                 goto out;
1306         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
1307                             requeue_pi ? VERIFY_WRITE : VERIFY_READ);
1308         if (unlikely(ret != 0))
1309                 goto out_put_key1;
1310
1311         hb1 = hash_futex(&key1);
1312         hb2 = hash_futex(&key2);
1313
1314 retry_private:
1315         double_lock_hb(hb1, hb2);
1316
1317         if (likely(cmpval != NULL)) {
1318                 u32 curval;
1319
1320                 ret = get_futex_value_locked(&curval, uaddr1);
1321
1322                 if (unlikely(ret)) {
1323                         double_unlock_hb(hb1, hb2);
1324
1325                         ret = get_user(curval, uaddr1);
1326                         if (ret)
1327                                 goto out_put_keys;
1328
1329                         if (!(flags & FLAGS_SHARED))
1330                                 goto retry_private;
1331
1332                         put_futex_key(&key2);
1333                         put_futex_key(&key1);
1334                         goto retry;
1335                 }
1336                 if (curval != *cmpval) {
1337                         ret = -EAGAIN;
1338                         goto out_unlock;
1339                 }
1340         }
1341
1342         if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1343                 /*
1344                  * Attempt to acquire uaddr2 and wake the top waiter. If we
1345                  * intend to requeue waiters, force setting the FUTEX_WAITERS
1346                  * bit.  We force this here where we are able to easily handle
1347                  * faults rather in the requeue loop below.
1348                  */
1349                 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1350                                                  &key2, &pi_state, nr_requeue);
1351
1352                 /*
1353                  * At this point the top_waiter has either taken uaddr2 or is
1354                  * waiting on it.  If the former, then the pi_state will not
1355                  * exist yet, look it up one more time to ensure we have a
1356                  * reference to it.
1357                  */
1358                 if (ret == 1) {
1359                         WARN_ON(pi_state);
1360                         drop_count++;
1361                         task_count++;
1362                         ret = get_futex_value_locked(&curval2, uaddr2);
1363                         if (!ret)
1364                                 ret = lookup_pi_state(curval2, hb2, &key2,
1365                                                       &pi_state);
1366                 }
1367
1368                 switch (ret) {
1369                 case 0:
1370                         break;
1371                 case -EFAULT:
1372                         double_unlock_hb(hb1, hb2);
1373                         put_futex_key(&key2);
1374                         put_futex_key(&key1);
1375                         ret = fault_in_user_writeable(uaddr2);
1376                         if (!ret)
1377                                 goto retry;
1378                         goto out;
1379                 case -EAGAIN:
1380                         /* The owner was exiting, try again. */
1381                         double_unlock_hb(hb1, hb2);
1382                         put_futex_key(&key2);
1383                         put_futex_key(&key1);
1384                         cond_resched();
1385                         goto retry;
1386                 default:
1387                         goto out_unlock;
1388                 }
1389         }
1390
1391         head1 = &hb1->chain;
1392         plist_for_each_entry_safe(this, next, head1, list) {
1393                 if (task_count - nr_wake >= nr_requeue)
1394                         break;
1395
1396                 if (!match_futex(&this->key, &key1))
1397                         continue;
1398
1399                 /*
1400                  * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1401                  * be paired with each other and no other futex ops.
1402                  *
1403                  * We should never be requeueing a futex_q with a pi_state,
1404                  * which is awaiting a futex_unlock_pi().
1405                  */
1406                 if ((requeue_pi && !this->rt_waiter) ||
1407                     (!requeue_pi && this->rt_waiter) ||
1408                     this->pi_state) {
1409                         ret = -EINVAL;
1410                         break;
1411                 }
1412
1413                 /*
1414                  * Wake nr_wake waiters.  For requeue_pi, if we acquired the
1415                  * lock, we already woke the top_waiter.  If not, it will be
1416                  * woken by futex_unlock_pi().
1417                  */
1418                 if (++task_count <= nr_wake && !requeue_pi) {
1419                         wake_futex(this);
1420                         continue;
1421                 }
1422
1423                 /* Ensure we requeue to the expected futex for requeue_pi. */
1424                 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1425                         ret = -EINVAL;
1426                         break;
1427                 }
1428
1429                 /*
1430                  * Requeue nr_requeue waiters and possibly one more in the case
1431                  * of requeue_pi if we couldn't acquire the lock atomically.
1432                  */
1433                 if (requeue_pi) {
1434                         /* Prepare the waiter to take the rt_mutex. */
1435                         atomic_inc(&pi_state->refcount);
1436                         this->pi_state = pi_state;
1437                         ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1438                                                         this->rt_waiter,
1439                                                         this->task, 1);
1440                         if (ret == 1) {
1441                                 /* We got the lock. */
1442                                 requeue_pi_wake_futex(this, &key2, hb2);
1443                                 drop_count++;
1444                                 continue;
1445                         } else if (ret) {
1446                                 /* -EDEADLK */
1447                                 this->pi_state = NULL;
1448                                 free_pi_state(pi_state);
1449                                 goto out_unlock;
1450                         }
1451                 }
1452                 requeue_futex(this, hb1, hb2, &key2);
1453                 drop_count++;
1454         }
1455
1456 out_unlock:
1457         double_unlock_hb(hb1, hb2);
1458
1459         /*
1460          * drop_futex_key_refs() must be called outside the spinlocks. During
1461          * the requeue we moved futex_q's from the hash bucket at key1 to the
1462          * one at key2 and updated their key pointer.  We no longer need to
1463          * hold the references to key1.
1464          */
1465         while (--drop_count >= 0)
1466                 drop_futex_key_refs(&key1);
1467
1468 out_put_keys:
1469         put_futex_key(&key2);
1470 out_put_key1:
1471         put_futex_key(&key1);
1472 out:
1473         if (pi_state != NULL)
1474                 free_pi_state(pi_state);
1475         return ret ? ret : task_count;
1476 }
1477
1478 /* The key must be already stored in q->key. */
1479 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
1480         __acquires(&hb->lock)
1481 {
1482         struct futex_hash_bucket *hb;
1483
1484         hb = hash_futex(&q->key);
1485         q->lock_ptr = &hb->lock;
1486
1487         spin_lock(&hb->lock);
1488         return hb;
1489 }
1490
1491 static inline void
1492 queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
1493         __releases(&hb->lock)
1494 {
1495         spin_unlock(&hb->lock);
1496 }
1497
1498 /**
1499  * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1500  * @q:  The futex_q to enqueue
1501  * @hb: The destination hash bucket
1502  *
1503  * The hb->lock must be held by the caller, and is released here. A call to
1504  * queue_me() is typically paired with exactly one call to unqueue_me().  The
1505  * exceptions involve the PI related operations, which may use unqueue_me_pi()
1506  * or nothing if the unqueue is done as part of the wake process and the unqueue
1507  * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1508  * an example).
1509  */
1510 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1511         __releases(&hb->lock)
1512 {
1513         int prio;
1514
1515         /*
1516          * The priority used to register this element is
1517          * - either the real thread-priority for the real-time threads
1518          * (i.e. threads with a priority lower than MAX_RT_PRIO)
1519          * - or MAX_RT_PRIO for non-RT threads.
1520          * Thus, all RT-threads are woken first in priority order, and
1521          * the others are woken last, in FIFO order.
1522          */
1523         prio = min(current->normal_prio, MAX_RT_PRIO);
1524
1525         plist_node_init(&q->list, prio);
1526         plist_add(&q->list, &hb->chain);
1527         q->task = current;
1528         spin_unlock(&hb->lock);
1529 }
1530
1531 /**
1532  * unqueue_me() - Remove the futex_q from its futex_hash_bucket
1533  * @q:  The futex_q to unqueue
1534  *
1535  * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
1536  * be paired with exactly one earlier call to queue_me().
1537  *
1538  * Returns:
1539  *   1 - if the futex_q was still queued (and we removed unqueued it)
1540  *   0 - if the futex_q was already removed by the waking thread
1541  */
1542 static int unqueue_me(struct futex_q *q)
1543 {
1544         spinlock_t *lock_ptr;
1545         int ret = 0;
1546
1547         /* In the common case we don't take the spinlock, which is nice. */
1548 retry:
1549         lock_ptr = q->lock_ptr;
1550         barrier();
1551         if (lock_ptr != NULL) {
1552                 spin_lock(lock_ptr);
1553                 /*
1554                  * q->lock_ptr can change between reading it and
1555                  * spin_lock(), causing us to take the wrong lock.  This
1556                  * corrects the race condition.
1557                  *
1558                  * Reasoning goes like this: if we have the wrong lock,
1559                  * q->lock_ptr must have changed (maybe several times)
1560                  * between reading it and the spin_lock().  It can
1561                  * change again after the spin_lock() but only if it was
1562                  * already changed before the spin_lock().  It cannot,
1563                  * however, change back to the original value.  Therefore
1564                  * we can detect whether we acquired the correct lock.
1565                  */
1566                 if (unlikely(lock_ptr != q->lock_ptr)) {
1567                         spin_unlock(lock_ptr);
1568                         goto retry;
1569                 }
1570                 __unqueue_futex(q);
1571
1572                 BUG_ON(q->pi_state);
1573
1574                 spin_unlock(lock_ptr);
1575                 ret = 1;
1576         }
1577
1578         drop_futex_key_refs(&q->key);
1579         return ret;
1580 }
1581
1582 /*
1583  * PI futexes can not be requeued and must remove themself from the
1584  * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1585  * and dropped here.
1586  */
1587 static void unqueue_me_pi(struct futex_q *q)
1588         __releases(q->lock_ptr)
1589 {
1590         __unqueue_futex(q);
1591
1592         BUG_ON(!q->pi_state);
1593         free_pi_state(q->pi_state);
1594         q->pi_state = NULL;
1595
1596         spin_unlock(q->lock_ptr);
1597 }
1598
1599 /*
1600  * Fixup the pi_state owner with the new owner.
1601  *
1602  * Must be called with hash bucket lock held and mm->sem held for non
1603  * private futexes.
1604  */
1605 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1606                                 struct task_struct *newowner)
1607 {
1608         u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
1609         struct futex_pi_state *pi_state = q->pi_state;
1610         struct task_struct *oldowner = pi_state->owner;
1611         u32 uval, uninitialized_var(curval), newval;
1612         int ret;
1613
1614         /* Owner died? */
1615         if (!pi_state->owner)
1616                 newtid |= FUTEX_OWNER_DIED;
1617
1618         /*
1619          * We are here either because we stole the rtmutex from the
1620          * previous highest priority waiter or we are the highest priority
1621          * waiter but failed to get the rtmutex the first time.
1622          * We have to replace the newowner TID in the user space variable.
1623          * This must be atomic as we have to preserve the owner died bit here.
1624          *
1625          * Note: We write the user space value _before_ changing the pi_state
1626          * because we can fault here. Imagine swapped out pages or a fork
1627          * that marked all the anonymous memory readonly for cow.
1628          *
1629          * Modifying pi_state _before_ the user space value would
1630          * leave the pi_state in an inconsistent state when we fault
1631          * here, because we need to drop the hash bucket lock to
1632          * handle the fault. This might be observed in the PID check
1633          * in lookup_pi_state.
1634          */
1635 retry:
1636         if (get_futex_value_locked(&uval, uaddr))
1637                 goto handle_fault;
1638
1639         while (1) {
1640                 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1641
1642                 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
1643                         goto handle_fault;
1644                 if (curval == uval)
1645                         break;
1646                 uval = curval;
1647         }
1648
1649         /*
1650          * We fixed up user space. Now we need to fix the pi_state
1651          * itself.
1652          */
1653         if (pi_state->owner != NULL) {
1654                 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1655                 WARN_ON(list_empty(&pi_state->list));
1656                 list_del_init(&pi_state->list);
1657                 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1658         }
1659
1660         pi_state->owner = newowner;
1661
1662         raw_spin_lock_irq(&newowner->pi_lock);
1663         WARN_ON(!list_empty(&pi_state->list));
1664         list_add(&pi_state->list, &newowner->pi_state_list);
1665         raw_spin_unlock_irq(&newowner->pi_lock);
1666         return 0;
1667
1668         /*
1669          * To handle the page fault we need to drop the hash bucket
1670          * lock here. That gives the other task (either the highest priority
1671          * waiter itself or the task which stole the rtmutex) the
1672          * chance to try the fixup of the pi_state. So once we are
1673          * back from handling the fault we need to check the pi_state
1674          * after reacquiring the hash bucket lock and before trying to
1675          * do another fixup. When the fixup has been done already we
1676          * simply return.
1677          */
1678 handle_fault:
1679         spin_unlock(q->lock_ptr);
1680
1681         ret = fault_in_user_writeable(uaddr);
1682
1683         spin_lock(q->lock_ptr);
1684
1685         /*
1686          * Check if someone else fixed it for us:
1687          */
1688         if (pi_state->owner != oldowner)
1689                 return 0;
1690
1691         if (ret)
1692                 return ret;
1693
1694         goto retry;
1695 }
1696
1697 static long futex_wait_restart(struct restart_block *restart);
1698
1699 /**
1700  * fixup_owner() - Post lock pi_state and corner case management
1701  * @uaddr:      user address of the futex
1702  * @q:          futex_q (contains pi_state and access to the rt_mutex)
1703  * @locked:     if the attempt to take the rt_mutex succeeded (1) or not (0)
1704  *
1705  * After attempting to lock an rt_mutex, this function is called to cleanup
1706  * the pi_state owner as well as handle race conditions that may allow us to
1707  * acquire the lock. Must be called with the hb lock held.
1708  *
1709  * Returns:
1710  *  1 - success, lock taken
1711  *  0 - success, lock not taken
1712  * <0 - on error (-EFAULT)
1713  */
1714 static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
1715 {
1716         struct task_struct *owner;
1717         int ret = 0;
1718
1719         if (locked) {
1720                 /*
1721                  * Got the lock. We might not be the anticipated owner if we
1722                  * did a lock-steal - fix up the PI-state in that case:
1723                  */
1724                 if (q->pi_state->owner != current)
1725                         ret = fixup_pi_state_owner(uaddr, q, current);
1726                 goto out;
1727         }
1728
1729         /*
1730          * Catch the rare case, where the lock was released when we were on the
1731          * way back before we locked the hash bucket.
1732          */
1733         if (q->pi_state->owner == current) {
1734                 /*
1735                  * Try to get the rt_mutex now. This might fail as some other
1736                  * task acquired the rt_mutex after we removed ourself from the
1737                  * rt_mutex waiters list.
1738                  */
1739                 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
1740                         locked = 1;
1741                         goto out;
1742                 }
1743
1744                 /*
1745                  * pi_state is incorrect, some other task did a lock steal and
1746                  * we returned due to timeout or signal without taking the
1747                  * rt_mutex. Too late.
1748                  */
1749                 raw_spin_lock(&q->pi_state->pi_mutex.wait_lock);
1750                 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
1751                 if (!owner)
1752                         owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
1753                 raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock);
1754                 ret = fixup_pi_state_owner(uaddr, q, owner);
1755                 goto out;
1756         }
1757
1758         /*
1759          * Paranoia check. If we did not take the lock, then we should not be
1760          * the owner of the rt_mutex.
1761          */
1762         if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
1763                 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
1764                                 "pi-state %p\n", ret,
1765                                 q->pi_state->pi_mutex.owner,
1766                                 q->pi_state->owner);
1767
1768 out:
1769         return ret ? ret : locked;
1770 }
1771
1772 /**
1773  * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
1774  * @hb:         the futex hash bucket, must be locked by the caller
1775  * @q:          the futex_q to queue up on
1776  * @timeout:    the prepared hrtimer_sleeper, or null for no timeout
1777  */
1778 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
1779                                 struct hrtimer_sleeper *timeout)
1780 {
1781         /*
1782          * The task state is guaranteed to be set before another task can
1783          * wake it. set_current_state() is implemented using set_mb() and
1784          * queue_me() calls spin_unlock() upon completion, both serializing
1785          * access to the hash list and forcing another memory barrier.
1786          */
1787         set_current_state(TASK_INTERRUPTIBLE);
1788         queue_me(q, hb);
1789
1790         /* Arm the timer */
1791         if (timeout) {
1792                 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1793                 if (!hrtimer_active(&timeout->timer))
1794                         timeout->task = NULL;
1795         }
1796
1797         /*
1798          * If we have been removed from the hash list, then another task
1799          * has tried to wake us, and we can skip the call to schedule().
1800          */
1801         if (likely(!plist_node_empty(&q->list))) {
1802                 /*
1803                  * If the timer has already expired, current will already be
1804                  * flagged for rescheduling. Only call schedule if there
1805                  * is no timeout, or if it has yet to expire.
1806                  */
1807                 if (!timeout || timeout->task)
1808                         schedule();
1809         }
1810         __set_current_state(TASK_RUNNING);
1811 }
1812
1813 /**
1814  * futex_wait_setup() - Prepare to wait on a futex
1815  * @uaddr:      the futex userspace address
1816  * @val:        the expected value
1817  * @flags:      futex flags (FLAGS_SHARED, etc.)
1818  * @q:          the associated futex_q
1819  * @hb:         storage for hash_bucket pointer to be returned to caller
1820  *
1821  * Setup the futex_q and locate the hash_bucket.  Get the futex value and
1822  * compare it with the expected value.  Handle atomic faults internally.
1823  * Return with the hb lock held and a q.key reference on success, and unlocked
1824  * with no q.key reference on failure.
1825  *
1826  * Returns:
1827  *  0 - uaddr contains val and hb has been locked
1828  * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
1829  */
1830 static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
1831                            struct futex_q *q, struct futex_hash_bucket **hb)
1832 {
1833         u32 uval;
1834         int ret;
1835
1836         /*
1837          * Access the page AFTER the hash-bucket is locked.
1838          * Order is important:
1839          *
1840          *   Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1841          *   Userspace waker:  if (cond(var)) { var = new; futex_wake(&var); }
1842          *
1843          * The basic logical guarantee of a futex is that it blocks ONLY
1844          * if cond(var) is known to be true at the time of blocking, for
1845          * any cond.  If we locked the hash-bucket after testing *uaddr, that
1846          * would open a race condition where we could block indefinitely with
1847          * cond(var) false, which would violate the guarantee.
1848          *
1849          * On the other hand, we insert q and release the hash-bucket only
1850          * after testing *uaddr.  This guarantees that futex_wait() will NOT
1851          * absorb a wakeup if *uaddr does not match the desired values
1852          * while the syscall executes.
1853          */
1854 retry:
1855         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
1856         if (unlikely(ret != 0))
1857                 return ret;
1858
1859 retry_private:
1860         *hb = queue_lock(q);
1861
1862         ret = get_futex_value_locked(&uval, uaddr);
1863
1864         if (ret) {
1865                 queue_unlock(q, *hb);
1866
1867                 ret = get_user(uval, uaddr);
1868                 if (ret)
1869                         goto out;
1870
1871                 if (!(flags & FLAGS_SHARED))
1872                         goto retry_private;
1873
1874                 put_futex_key(&q->key);
1875                 goto retry;
1876         }
1877
1878         if (uval != val) {
1879                 queue_unlock(q, *hb);
1880                 ret = -EWOULDBLOCK;
1881         }
1882
1883 out:
1884         if (ret)
1885                 put_futex_key(&q->key);
1886         return ret;
1887 }
1888
1889 static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
1890                       ktime_t *abs_time, u32 bitset)
1891 {
1892         struct hrtimer_sleeper timeout, *to = NULL;
1893         struct restart_block *restart;
1894         struct futex_hash_bucket *hb;
1895         struct futex_q q = futex_q_init;
1896         int ret;
1897
1898         if (!bitset)
1899                 return -EINVAL;
1900         q.bitset = bitset;
1901
1902         if (abs_time) {
1903                 to = &timeout;
1904
1905                 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
1906                                       CLOCK_REALTIME : CLOCK_MONOTONIC,
1907                                       HRTIMER_MODE_ABS);
1908                 hrtimer_init_sleeper(to, current);
1909                 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
1910                                              current->timer_slack_ns);
1911         }
1912
1913 retry:
1914         /*
1915          * Prepare to wait on uaddr. On success, holds hb lock and increments
1916          * q.key refs.
1917          */
1918         ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
1919         if (ret)
1920                 goto out;
1921
1922         /* queue_me and wait for wakeup, timeout, or a signal. */
1923         futex_wait_queue_me(hb, &q, to);
1924
1925         /* If we were woken (and unqueued), we succeeded, whatever. */
1926         ret = 0;
1927         /* unqueue_me() drops q.key ref */
1928         if (!unqueue_me(&q))
1929                 goto out;
1930         ret = -ETIMEDOUT;
1931         if (to && !to->task)
1932                 goto out;
1933
1934         /*
1935          * We expect signal_pending(current), but we might be the
1936          * victim of a spurious wakeup as well.
1937          */
1938         if (!signal_pending(current))
1939                 goto retry;
1940
1941         ret = -ERESTARTSYS;
1942         if (!abs_time)
1943                 goto out;
1944
1945         restart = &current_thread_info()->restart_block;
1946         restart->fn = futex_wait_restart;
1947         restart->futex.uaddr = uaddr;
1948         restart->futex.val = val;
1949         restart->futex.time = abs_time->tv64;
1950         restart->futex.bitset = bitset;
1951         restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
1952
1953         ret = -ERESTART_RESTARTBLOCK;
1954
1955 out:
1956         if (to) {
1957                 hrtimer_cancel(&to->timer);
1958                 destroy_hrtimer_on_stack(&to->timer);
1959         }
1960         return ret;
1961 }
1962
1963
1964 static long futex_wait_restart(struct restart_block *restart)
1965 {
1966         u32 __user *uaddr = restart->futex.uaddr;
1967         ktime_t t, *tp = NULL;
1968
1969         if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
1970                 t.tv64 = restart->futex.time;
1971                 tp = &t;
1972         }
1973         restart->fn = do_no_restart_syscall;
1974
1975         return (long)futex_wait(uaddr, restart->futex.flags,
1976                                 restart->futex.val, tp, restart->futex.bitset);
1977 }
1978
1979
1980 /*
1981  * Userspace tried a 0 -> TID atomic transition of the futex value
1982  * and failed. The kernel side here does the whole locking operation:
1983  * if there are waiters then it will block, it does PI, etc. (Due to
1984  * races the kernel might see a 0 value of the futex too.)
1985  */
1986 static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect,
1987                          ktime_t *time, int trylock)
1988 {
1989         struct hrtimer_sleeper timeout, *to = NULL;
1990         struct futex_hash_bucket *hb;
1991         struct futex_q q = futex_q_init;
1992         int res, ret;
1993
1994         if (refill_pi_state_cache())
1995                 return -ENOMEM;
1996
1997         if (time) {
1998                 to = &timeout;
1999                 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
2000                                       HRTIMER_MODE_ABS);
2001                 hrtimer_init_sleeper(to, current);
2002                 hrtimer_set_expires(&to->timer, *time);
2003         }
2004
2005 retry:
2006         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
2007         if (unlikely(ret != 0))
2008                 goto out;
2009
2010 retry_private:
2011         hb = queue_lock(&q);
2012
2013         ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
2014         if (unlikely(ret)) {
2015                 switch (ret) {
2016                 case 1:
2017                         /* We got the lock. */
2018                         ret = 0;
2019                         goto out_unlock_put_key;
2020                 case -EFAULT:
2021                         goto uaddr_faulted;
2022                 case -EAGAIN:
2023                         /*
2024                          * Task is exiting and we just wait for the
2025                          * exit to complete.
2026                          */
2027                         queue_unlock(&q, hb);
2028                         put_futex_key(&q.key);
2029                         cond_resched();
2030                         goto retry;
2031                 default:
2032                         goto out_unlock_put_key;
2033                 }
2034         }
2035
2036         /*
2037          * Only actually queue now that the atomic ops are done:
2038          */
2039         queue_me(&q, hb);
2040
2041         WARN_ON(!q.pi_state);
2042         /*
2043          * Block on the PI mutex:
2044          */
2045         if (!trylock)
2046                 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
2047         else {
2048                 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
2049                 /* Fixup the trylock return value: */
2050                 ret = ret ? 0 : -EWOULDBLOCK;
2051         }
2052
2053         spin_lock(q.lock_ptr);
2054         /*
2055          * Fixup the pi_state owner and possibly acquire the lock if we
2056          * haven't already.
2057          */
2058         res = fixup_owner(uaddr, &q, !ret);
2059         /*
2060          * If fixup_owner() returned an error, proprogate that.  If it acquired
2061          * the lock, clear our -ETIMEDOUT or -EINTR.
2062          */
2063         if (res)
2064                 ret = (res < 0) ? res : 0;
2065
2066         /*
2067          * If fixup_owner() faulted and was unable to handle the fault, unlock
2068          * it and return the fault to userspace.
2069          */
2070         if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
2071                 rt_mutex_unlock(&q.pi_state->pi_mutex);
2072
2073         /* Unqueue and drop the lock */
2074         unqueue_me_pi(&q);
2075
2076         goto out_put_key;
2077
2078 out_unlock_put_key:
2079         queue_unlock(&q, hb);
2080
2081 out_put_key:
2082         put_futex_key(&q.key);
2083 out:
2084         if (to)
2085                 destroy_hrtimer_on_stack(&to->timer);
2086         return ret != -EINTR ? ret : -ERESTARTNOINTR;
2087
2088 uaddr_faulted:
2089         queue_unlock(&q, hb);
2090
2091         ret = fault_in_user_writeable(uaddr);
2092         if (ret)
2093                 goto out_put_key;
2094
2095         if (!(flags & FLAGS_SHARED))
2096                 goto retry_private;
2097
2098         put_futex_key(&q.key);
2099         goto retry;
2100 }
2101
2102 /*
2103  * Userspace attempted a TID -> 0 atomic transition, and failed.
2104  * This is the in-kernel slowpath: we look up the PI state (if any),
2105  * and do the rt-mutex unlock.
2106  */
2107 static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
2108 {
2109         struct futex_hash_bucket *hb;
2110         struct futex_q *this, *next;
2111         struct plist_head *head;
2112         union futex_key key = FUTEX_KEY_INIT;
2113         u32 uval, vpid = task_pid_vnr(current);
2114         int ret;
2115
2116 retry:
2117         if (get_user(uval, uaddr))
2118                 return -EFAULT;
2119         /*
2120          * We release only a lock we actually own:
2121          */
2122         if ((uval & FUTEX_TID_MASK) != vpid)
2123                 return -EPERM;
2124
2125         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
2126         if (unlikely(ret != 0))
2127                 goto out;
2128
2129         hb = hash_futex(&key);
2130         spin_lock(&hb->lock);
2131
2132         /*
2133          * To avoid races, try to do the TID -> 0 atomic transition
2134          * again. If it succeeds then we can return without waking
2135          * anyone else up:
2136          */
2137         if (!(uval & FUTEX_OWNER_DIED) &&
2138             cmpxchg_futex_value_locked(&uval, uaddr, vpid, 0))
2139                 goto pi_faulted;
2140         /*
2141          * Rare case: we managed to release the lock atomically,
2142          * no need to wake anyone else up:
2143          */
2144         if (unlikely(uval == vpid))
2145                 goto out_unlock;
2146
2147         /*
2148          * Ok, other tasks may need to be woken up - check waiters
2149          * and do the wakeup if necessary:
2150          */
2151         head = &hb->chain;
2152
2153         plist_for_each_entry_safe(this, next, head, list) {
2154                 if (!match_futex (&this->key, &key))
2155                         continue;
2156                 ret = wake_futex_pi(uaddr, uval, this);
2157                 /*
2158                  * The atomic access to the futex value
2159                  * generated a pagefault, so retry the
2160                  * user-access and the wakeup:
2161                  */
2162                 if (ret == -EFAULT)
2163                         goto pi_faulted;
2164                 goto out_unlock;
2165         }
2166         /*
2167          * No waiters - kernel unlocks the futex:
2168          */
2169         if (!(uval & FUTEX_OWNER_DIED)) {
2170                 ret = unlock_futex_pi(uaddr, uval);
2171                 if (ret == -EFAULT)
2172                         goto pi_faulted;
2173         }
2174
2175 out_unlock:
2176         spin_unlock(&hb->lock);
2177         put_futex_key(&key);
2178
2179 out:
2180         return ret;
2181
2182 pi_faulted:
2183         spin_unlock(&hb->lock);
2184         put_futex_key(&key);
2185
2186         ret = fault_in_user_writeable(uaddr);
2187         if (!ret)
2188                 goto retry;
2189
2190         return ret;
2191 }
2192
2193 /**
2194  * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2195  * @hb:         the hash_bucket futex_q was original enqueued on
2196  * @q:          the futex_q woken while waiting to be requeued
2197  * @key2:       the futex_key of the requeue target futex
2198  * @timeout:    the timeout associated with the wait (NULL if none)
2199  *
2200  * Detect if the task was woken on the initial futex as opposed to the requeue
2201  * target futex.  If so, determine if it was a timeout or a signal that caused
2202  * the wakeup and return the appropriate error code to the caller.  Must be
2203  * called with the hb lock held.
2204  *
2205  * Returns
2206  *  0 - no early wakeup detected
2207  * <0 - -ETIMEDOUT or -ERESTARTNOINTR
2208  */
2209 static inline
2210 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2211                                    struct futex_q *q, union futex_key *key2,
2212                                    struct hrtimer_sleeper *timeout)
2213 {
2214         int ret = 0;
2215
2216         /*
2217          * With the hb lock held, we avoid races while we process the wakeup.
2218          * We only need to hold hb (and not hb2) to ensure atomicity as the
2219          * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2220          * It can't be requeued from uaddr2 to something else since we don't
2221          * support a PI aware source futex for requeue.
2222          */
2223         if (!match_futex(&q->key, key2)) {
2224                 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2225                 /*
2226                  * We were woken prior to requeue by a timeout or a signal.
2227                  * Unqueue the futex_q and determine which it was.
2228                  */
2229                 plist_del(&q->list, &hb->chain);
2230
2231                 /* Handle spurious wakeups gracefully */
2232                 ret = -EWOULDBLOCK;
2233                 if (timeout && !timeout->task)
2234                         ret = -ETIMEDOUT;
2235                 else if (signal_pending(current))
2236                         ret = -ERESTARTNOINTR;
2237         }
2238         return ret;
2239 }
2240
2241 /**
2242  * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2243  * @uaddr:      the futex we initially wait on (non-pi)
2244  * @flags:      futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
2245  *              the same type, no requeueing from private to shared, etc.
2246  * @val:        the expected value of uaddr
2247  * @abs_time:   absolute timeout
2248  * @bitset:     32 bit wakeup bitset set by userspace, defaults to all
2249  * @clockrt:    whether to use CLOCK_REALTIME (1) or CLOCK_MONOTONIC (0)
2250  * @uaddr2:     the pi futex we will take prior to returning to user-space
2251  *
2252  * The caller will wait on uaddr and will be requeued by futex_requeue() to
2253  * uaddr2 which must be PI aware and unique from uaddr.  Normal wakeup will wake
2254  * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
2255  * userspace.  This ensures the rt_mutex maintains an owner when it has waiters;
2256  * without one, the pi logic would not know which task to boost/deboost, if
2257  * there was a need to.
2258  *
2259  * We call schedule in futex_wait_queue_me() when we enqueue and return there
2260  * via the following:
2261  * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2262  * 2) wakeup on uaddr2 after a requeue
2263  * 3) signal
2264  * 4) timeout
2265  *
2266  * If 3, cleanup and return -ERESTARTNOINTR.
2267  *
2268  * If 2, we may then block on trying to take the rt_mutex and return via:
2269  * 5) successful lock
2270  * 6) signal
2271  * 7) timeout
2272  * 8) other lock acquisition failure
2273  *
2274  * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2275  *
2276  * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2277  *
2278  * Returns:
2279  *  0 - On success
2280  * <0 - On error
2281  */
2282 static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
2283                                  u32 val, ktime_t *abs_time, u32 bitset,
2284                                  u32 __user *uaddr2)
2285 {
2286         struct hrtimer_sleeper timeout, *to = NULL;
2287         struct rt_mutex_waiter rt_waiter;
2288         struct rt_mutex *pi_mutex = NULL;
2289         struct futex_hash_bucket *hb;
2290         union futex_key key2 = FUTEX_KEY_INIT;
2291         struct futex_q q = futex_q_init;
2292         int res, ret;
2293
2294         if (uaddr == uaddr2)
2295                 return -EINVAL;
2296
2297         if (!bitset)
2298                 return -EINVAL;
2299
2300         if (abs_time) {
2301                 to = &timeout;
2302                 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2303                                       CLOCK_REALTIME : CLOCK_MONOTONIC,
2304                                       HRTIMER_MODE_ABS);
2305                 hrtimer_init_sleeper(to, current);
2306                 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2307                                              current->timer_slack_ns);
2308         }
2309
2310         /*
2311          * The waiter is allocated on our stack, manipulated by the requeue
2312          * code while we sleep on uaddr.
2313          */
2314         debug_rt_mutex_init_waiter(&rt_waiter);
2315         rt_waiter.task = NULL;
2316
2317         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
2318         if (unlikely(ret != 0))
2319                 goto out;
2320
2321         q.bitset = bitset;
2322         q.rt_waiter = &rt_waiter;
2323         q.requeue_pi_key = &key2;
2324
2325         /*
2326          * Prepare to wait on uaddr. On success, increments q.key (key1) ref
2327          * count.
2328          */
2329         ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2330         if (ret)
2331                 goto out_key2;
2332
2333         /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2334         futex_wait_queue_me(hb, &q, to);
2335
2336         spin_lock(&hb->lock);
2337         ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2338         spin_unlock(&hb->lock);
2339         if (ret)
2340                 goto out_put_keys;
2341
2342         /*
2343          * In order for us to be here, we know our q.key == key2, and since
2344          * we took the hb->lock above, we also know that futex_requeue() has
2345          * completed and we no longer have to concern ourselves with a wakeup
2346          * race with the atomic proxy lock acquisition by the requeue code. The
2347          * futex_requeue dropped our key1 reference and incremented our key2
2348          * reference count.
2349          */
2350
2351         /* Check if the requeue code acquired the second futex for us. */
2352         if (!q.rt_waiter) {
2353                 /*
2354                  * Got the lock. We might not be the anticipated owner if we
2355                  * did a lock-steal - fix up the PI-state in that case.
2356                  */
2357                 if (q.pi_state && (q.pi_state->owner != current)) {
2358                         spin_lock(q.lock_ptr);
2359                         ret = fixup_pi_state_owner(uaddr2, &q, current);
2360                         spin_unlock(q.lock_ptr);
2361                 }
2362         } else {
2363                 /*
2364                  * We have been woken up by futex_unlock_pi(), a timeout, or a
2365                  * signal.  futex_unlock_pi() will not destroy the lock_ptr nor
2366                  * the pi_state.
2367                  */
2368                 WARN_ON(!q.pi_state);
2369                 pi_mutex = &q.pi_state->pi_mutex;
2370                 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
2371                 debug_rt_mutex_free_waiter(&rt_waiter);
2372
2373                 spin_lock(q.lock_ptr);
2374                 /*
2375                  * Fixup the pi_state owner and possibly acquire the lock if we
2376                  * haven't already.
2377                  */
2378                 res = fixup_owner(uaddr2, &q, !ret);
2379                 /*
2380                  * If fixup_owner() returned an error, proprogate that.  If it
2381                  * acquired the lock, clear -ETIMEDOUT or -EINTR.
2382                  */
2383                 if (res)
2384                         ret = (res < 0) ? res : 0;
2385
2386                 /* Unqueue and drop the lock. */
2387                 unqueue_me_pi(&q);
2388         }
2389
2390         /*
2391          * If fixup_pi_state_owner() faulted and was unable to handle the
2392          * fault, unlock the rt_mutex and return the fault to userspace.
2393          */
2394         if (ret == -EFAULT) {
2395                 if (pi_mutex && rt_mutex_owner(pi_mutex) == current)
2396                         rt_mutex_unlock(pi_mutex);
2397         } else if (ret == -EINTR) {
2398                 /*
2399                  * We've already been requeued, but cannot restart by calling
2400                  * futex_lock_pi() directly. We could restart this syscall, but
2401                  * it would detect that the user space "val" changed and return
2402                  * -EWOULDBLOCK.  Save the overhead of the restart and return
2403                  * -EWOULDBLOCK directly.
2404                  */
2405                 ret = -EWOULDBLOCK;
2406         }
2407
2408 out_put_keys:
2409         put_futex_key(&q.key);
2410 out_key2:
2411         put_futex_key(&key2);
2412
2413 out:
2414         if (to) {
2415                 hrtimer_cancel(&to->timer);
2416                 destroy_hrtimer_on_stack(&to->timer);
2417         }
2418         return ret;
2419 }
2420
2421 /*
2422  * Support for robust futexes: the kernel cleans up held futexes at
2423  * thread exit time.
2424  *
2425  * Implementation: user-space maintains a per-thread list of locks it
2426  * is holding. Upon do_exit(), the kernel carefully walks this list,
2427  * and marks all locks that are owned by this thread with the
2428  * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2429  * always manipulated with the lock held, so the list is private and
2430  * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2431  * field, to allow the kernel to clean up if the thread dies after
2432  * acquiring the lock, but just before it could have added itself to
2433  * the list. There can only be one such pending lock.
2434  */
2435
2436 /**
2437  * sys_set_robust_list() - Set the robust-futex list head of a task
2438  * @head:       pointer to the list-head
2439  * @len:        length of the list-head, as userspace expects
2440  */
2441 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2442                 size_t, len)
2443 {
2444         if (!futex_cmpxchg_enabled)
2445                 return -ENOSYS;
2446         /*
2447          * The kernel knows only one size for now:
2448          */
2449         if (unlikely(len != sizeof(*head)))
2450                 return -EINVAL;
2451
2452         current->robust_list = head;
2453
2454         return 0;
2455 }
2456
2457 /**
2458  * sys_get_robust_list() - Get the robust-futex list head of a task
2459  * @pid:        pid of the process [zero for current task]
2460  * @head_ptr:   pointer to a list-head pointer, the kernel fills it in
2461  * @len_ptr:    pointer to a length field, the kernel fills in the header size
2462  */
2463 SYSCALL_DEFINE3(get_robust_list, int, pid,
2464                 struct robust_list_head __user * __user *, head_ptr,
2465                 size_t __user *, len_ptr)
2466 {
2467         struct robust_list_head __user *head;
2468         unsigned long ret;
2469         struct task_struct *p;
2470
2471         if (!futex_cmpxchg_enabled)
2472                 return -ENOSYS;
2473
2474         rcu_read_lock();
2475
2476         ret = -ESRCH;
2477         if (!pid)
2478                 p = current;
2479         else {
2480                 p = find_task_by_vpid(pid);
2481                 if (!p)
2482                         goto err_unlock;
2483         }
2484
2485         ret = -EPERM;
2486         if (!ptrace_may_access(p, PTRACE_MODE_READ))
2487                 goto err_unlock;
2488
2489         head = p->robust_list;
2490         rcu_read_unlock();
2491
2492         if (put_user(sizeof(*head), len_ptr))
2493                 return -EFAULT;
2494         return put_user(head, head_ptr);
2495
2496 err_unlock:
2497         rcu_read_unlock();
2498
2499         return ret;
2500 }
2501
2502 /*
2503  * Process a futex-list entry, check whether it's owned by the
2504  * dying task, and do notification if so:
2505  */
2506 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
2507 {
2508         u32 uval, uninitialized_var(nval), mval;
2509
2510 retry:
2511         if (get_user(uval, uaddr))
2512                 return -1;
2513
2514         if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
2515                 /*
2516                  * Ok, this dying thread is truly holding a futex
2517                  * of interest. Set the OWNER_DIED bit atomically
2518                  * via cmpxchg, and if the value had FUTEX_WAITERS
2519                  * set, wake up a waiter (if any). (We have to do a
2520                  * futex_wake() even if OWNER_DIED is already set -
2521                  * to handle the rare but possible case of recursive
2522                  * thread-death.) The rest of the cleanup is done in
2523                  * userspace.
2524                  */
2525                 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
2526                 /*
2527                  * We are not holding a lock here, but we want to have
2528                  * the pagefault_disable/enable() protection because
2529                  * we want to handle the fault gracefully. If the
2530                  * access fails we try to fault in the futex with R/W
2531                  * verification via get_user_pages. get_user() above
2532                  * does not guarantee R/W access. If that fails we
2533                  * give up and leave the futex locked.
2534                  */
2535                 if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
2536                         if (fault_in_user_writeable(uaddr))
2537                                 return -1;
2538                         goto retry;
2539                 }
2540                 if (nval != uval)
2541                         goto retry;
2542
2543                 /*
2544                  * Wake robust non-PI futexes here. The wakeup of
2545                  * PI futexes happens in exit_pi_state():
2546                  */
2547                 if (!pi && (uval & FUTEX_WAITERS))
2548                         futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
2549         }
2550         return 0;
2551 }
2552
2553 /*
2554  * Fetch a robust-list pointer. Bit 0 signals PI futexes:
2555  */
2556 static inline int fetch_robust_entry(struct robust_list __user **entry,
2557                                      struct robust_list __user * __user *head,
2558                                      unsigned int *pi)
2559 {
2560         unsigned long uentry;
2561
2562         if (get_user(uentry, (unsigned long __user *)head))
2563                 return -EFAULT;
2564
2565         *entry = (void __user *)(uentry & ~1UL);
2566         *pi = uentry & 1;
2567
2568         return 0;
2569 }
2570
2571 /*
2572  * Walk curr->robust_list (very carefully, it's a userspace list!)
2573  * and mark any locks found there dead, and notify any waiters.
2574  *
2575  * We silently return on any sign of list-walking problem.
2576  */
2577 void exit_robust_list(struct task_struct *curr)
2578 {
2579         struct robust_list_head __user *head = curr->robust_list;
2580         struct robust_list __user *entry, *next_entry, *pending;
2581         unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
2582         unsigned int uninitialized_var(next_pi);
2583         unsigned long futex_offset;
2584         int rc;
2585
2586         if (!futex_cmpxchg_enabled)
2587                 return;
2588
2589         /*
2590          * Fetch the list head (which was registered earlier, via
2591          * sys_set_robust_list()):
2592          */
2593         if (fetch_robust_entry(&entry, &head->list.next, &pi))
2594                 return;
2595         /*
2596          * Fetch the relative futex offset:
2597          */
2598         if (get_user(futex_offset, &head->futex_offset))
2599                 return;
2600         /*
2601          * Fetch any possibly pending lock-add first, and handle it
2602          * if it exists:
2603          */
2604         if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
2605                 return;
2606
2607         next_entry = NULL;      /* avoid warning with gcc */
2608         while (entry != &head->list) {
2609                 /*
2610                  * Fetch the next entry in the list before calling
2611                  * handle_futex_death:
2612                  */
2613                 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
2614                 /*
2615                  * A pending lock might already be on the list, so
2616                  * don't process it twice:
2617                  */
2618                 if (entry != pending)
2619                         if (handle_futex_death((void __user *)entry + futex_offset,
2620                                                 curr, pi))
2621                                 return;
2622                 if (rc)
2623                         return;
2624                 entry = next_entry;
2625                 pi = next_pi;
2626                 /*
2627                  * Avoid excessively long or circular lists:
2628                  */
2629                 if (!--limit)
2630                         break;
2631
2632                 cond_resched();
2633         }
2634
2635         if (pending)
2636                 handle_futex_death((void __user *)pending + futex_offset,
2637                                    curr, pip);
2638 }
2639
2640 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
2641                 u32 __user *uaddr2, u32 val2, u32 val3)
2642 {
2643         int cmd = op & FUTEX_CMD_MASK;
2644         unsigned int flags = 0;
2645
2646         if (!(op & FUTEX_PRIVATE_FLAG))
2647                 flags |= FLAGS_SHARED;
2648
2649         if (op & FUTEX_CLOCK_REALTIME) {
2650                 flags |= FLAGS_CLOCKRT;
2651                 if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
2652                         return -ENOSYS;
2653         }
2654
2655         switch (cmd) {
2656         case FUTEX_LOCK_PI:
2657         case FUTEX_UNLOCK_PI:
2658         case FUTEX_TRYLOCK_PI:
2659         case FUTEX_WAIT_REQUEUE_PI:
2660         case FUTEX_CMP_REQUEUE_PI:
2661                 if (!futex_cmpxchg_enabled)
2662                         return -ENOSYS;
2663         }
2664
2665         switch (cmd) {
2666         case FUTEX_WAIT:
2667                 val3 = FUTEX_BITSET_MATCH_ANY;
2668         case FUTEX_WAIT_BITSET:
2669                 return futex_wait(uaddr, flags, val, timeout, val3);
2670         case FUTEX_WAKE:
2671                 val3 = FUTEX_BITSET_MATCH_ANY;
2672         case FUTEX_WAKE_BITSET:
2673                 return futex_wake(uaddr, flags, val, val3);
2674         case FUTEX_REQUEUE:
2675                 return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
2676         case FUTEX_CMP_REQUEUE:
2677                 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
2678         case FUTEX_WAKE_OP:
2679                 return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
2680         case FUTEX_LOCK_PI:
2681                 return futex_lock_pi(uaddr, flags, val, timeout, 0);
2682         case FUTEX_UNLOCK_PI:
2683                 return futex_unlock_pi(uaddr, flags);
2684         case FUTEX_TRYLOCK_PI:
2685                 return futex_lock_pi(uaddr, flags, 0, timeout, 1);
2686         case FUTEX_WAIT_REQUEUE_PI:
2687                 val3 = FUTEX_BITSET_MATCH_ANY;
2688                 return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
2689                                              uaddr2);
2690         case FUTEX_CMP_REQUEUE_PI:
2691                 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
2692         }
2693         return -ENOSYS;
2694 }
2695
2696
2697 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
2698                 struct timespec __user *, utime, u32 __user *, uaddr2,
2699                 u32, val3)
2700 {
2701         struct timespec ts;
2702         ktime_t t, *tp = NULL;
2703         u32 val2 = 0;
2704         int cmd = op & FUTEX_CMD_MASK;
2705
2706         if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
2707                       cmd == FUTEX_WAIT_BITSET ||
2708                       cmd == FUTEX_WAIT_REQUEUE_PI)) {
2709                 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
2710                         return -EFAULT;
2711                 if (!timespec_valid(&ts))
2712                         return -EINVAL;
2713
2714                 t = timespec_to_ktime(ts);
2715                 if (cmd == FUTEX_WAIT)
2716                         t = ktime_add_safe(ktime_get(), t);
2717                 tp = &t;
2718         }
2719         /*
2720          * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
2721          * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
2722          */
2723         if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
2724             cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
2725                 val2 = (u32) (unsigned long) utime;
2726
2727         return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
2728 }
2729
2730 static int __init futex_init(void)
2731 {
2732         u32 curval;
2733         int i;
2734
2735         /*
2736          * This will fail and we want it. Some arch implementations do
2737          * runtime detection of the futex_atomic_cmpxchg_inatomic()
2738          * functionality. We want to know that before we call in any
2739          * of the complex code paths. Also we want to prevent
2740          * registration of robust lists in that case. NULL is
2741          * guaranteed to fault and we get -EFAULT on functional
2742          * implementation, the non-functional ones will return
2743          * -ENOSYS.
2744          */
2745         if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
2746                 futex_cmpxchg_enabled = 1;
2747
2748         for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
2749                 plist_head_init(&futex_queues[i].chain);
2750                 spin_lock_init(&futex_queues[i].lock);
2751         }
2752
2753         return 0;
2754 }
2755 __initcall(futex_init);