futex: Fix kernel-doc notation & typos
[linux-2.6.git] / kernel / futex.c
1 /*
2  *  Fast Userspace Mutexes (which I call "Futexes!").
3  *  (C) Rusty Russell, IBM 2002
4  *
5  *  Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
6  *  (C) Copyright 2003 Red Hat Inc, All Rights Reserved
7  *
8  *  Removed page pinning, fix privately mapped COW pages and other cleanups
9  *  (C) Copyright 2003, 2004 Jamie Lokier
10  *
11  *  Robust futex support started by Ingo Molnar
12  *  (C) Copyright 2006 Red Hat Inc, All Rights Reserved
13  *  Thanks to Thomas Gleixner for suggestions, analysis and fixes.
14  *
15  *  PI-futex support started by Ingo Molnar and Thomas Gleixner
16  *  Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
17  *  Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
18  *
19  *  PRIVATE futexes by Eric Dumazet
20  *  Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
21  *
22  *  Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
23  *  Copyright (C) IBM Corporation, 2009
24  *  Thanks to Thomas Gleixner for conceptual design and careful reviews.
25  *
26  *  Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
27  *  enough at me, Linus for the original (flawed) idea, Matthew
28  *  Kirkwood for proof-of-concept implementation.
29  *
30  *  "The futexes are also cursed."
31  *  "But they come in a choice of three flavours!"
32  *
33  *  This program is free software; you can redistribute it and/or modify
34  *  it under the terms of the GNU General Public License as published by
35  *  the Free Software Foundation; either version 2 of the License, or
36  *  (at your option) any later version.
37  *
38  *  This program is distributed in the hope that it will be useful,
39  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
40  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
41  *  GNU General Public License for more details.
42  *
43  *  You should have received a copy of the GNU General Public License
44  *  along with this program; if not, write to the Free Software
45  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
46  */
47 #include <linux/slab.h>
48 #include <linux/poll.h>
49 #include <linux/fs.h>
50 #include <linux/file.h>
51 #include <linux/jhash.h>
52 #include <linux/init.h>
53 #include <linux/futex.h>
54 #include <linux/mount.h>
55 #include <linux/pagemap.h>
56 #include <linux/syscalls.h>
57 #include <linux/signal.h>
58 #include <linux/module.h>
59 #include <linux/magic.h>
60 #include <linux/pid.h>
61 #include <linux/nsproxy.h>
62
63 #include <asm/futex.h>
64
65 #include "rtmutex_common.h"
66
67 int __read_mostly futex_cmpxchg_enabled;
68
69 #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
70
71 /*
72  * Priority Inheritance state:
73  */
74 struct futex_pi_state {
75         /*
76          * list of 'owned' pi_state instances - these have to be
77          * cleaned up in do_exit() if the task exits prematurely:
78          */
79         struct list_head list;
80
81         /*
82          * The PI object:
83          */
84         struct rt_mutex pi_mutex;
85
86         struct task_struct *owner;
87         atomic_t refcount;
88
89         union futex_key key;
90 };
91
92 /**
93  * struct futex_q - The hashed futex queue entry, one per waiting task
94  * @list:               priority-sorted list of tasks waiting on this futex
95  * @task:               the task waiting on the futex
96  * @lock_ptr:           the hash bucket lock
97  * @key:                the key the futex is hashed on
98  * @pi_state:           optional priority inheritance state
99  * @rt_waiter:          rt_waiter storage for use with requeue_pi
100  * @requeue_pi_key:     the requeue_pi target futex key
101  * @bitset:             bitset for the optional bitmasked wakeup
102  *
103  * We use this hashed waitqueue, instead of a normal wait_queue_t, so
104  * we can wake only the relevant ones (hashed queues may be shared).
105  *
106  * A futex_q has a woken state, just like tasks have TASK_RUNNING.
107  * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
108  * The order of wakeup is always to make the first condition true, then
109  * the second.
110  *
111  * PI futexes are typically woken before they are removed from the hash list via
112  * the rt_mutex code. See unqueue_me_pi().
113  */
114 struct futex_q {
115         struct plist_node list;
116
117         struct task_struct *task;
118         spinlock_t *lock_ptr;
119         union futex_key key;
120         struct futex_pi_state *pi_state;
121         struct rt_mutex_waiter *rt_waiter;
122         union futex_key *requeue_pi_key;
123         u32 bitset;
124 };
125
126 /*
127  * Hash buckets are shared by all the futex_keys that hash to the same
128  * location.  Each key may have multiple futex_q structures, one for each task
129  * waiting on a futex.
130  */
131 struct futex_hash_bucket {
132         spinlock_t lock;
133         struct plist_head chain;
134 };
135
136 static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
137
138 /*
139  * We hash on the keys returned from get_futex_key (see below).
140  */
141 static struct futex_hash_bucket *hash_futex(union futex_key *key)
142 {
143         u32 hash = jhash2((u32*)&key->both.word,
144                           (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
145                           key->both.offset);
146         return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
147 }
148
149 /*
150  * Return 1 if two futex_keys are equal, 0 otherwise.
151  */
152 static inline int match_futex(union futex_key *key1, union futex_key *key2)
153 {
154         return (key1 && key2
155                 && key1->both.word == key2->both.word
156                 && key1->both.ptr == key2->both.ptr
157                 && key1->both.offset == key2->both.offset);
158 }
159
160 /*
161  * Take a reference to the resource addressed by a key.
162  * Can be called while holding spinlocks.
163  *
164  */
165 static void get_futex_key_refs(union futex_key *key)
166 {
167         if (!key->both.ptr)
168                 return;
169
170         switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
171         case FUT_OFF_INODE:
172                 atomic_inc(&key->shared.inode->i_count);
173                 break;
174         case FUT_OFF_MMSHARED:
175                 atomic_inc(&key->private.mm->mm_count);
176                 break;
177         }
178 }
179
180 /*
181  * Drop a reference to the resource addressed by a key.
182  * The hash bucket spinlock must not be held.
183  */
184 static void drop_futex_key_refs(union futex_key *key)
185 {
186         if (!key->both.ptr) {
187                 /* If we're here then we tried to put a key we failed to get */
188                 WARN_ON_ONCE(1);
189                 return;
190         }
191
192         switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
193         case FUT_OFF_INODE:
194                 iput(key->shared.inode);
195                 break;
196         case FUT_OFF_MMSHARED:
197                 mmdrop(key->private.mm);
198                 break;
199         }
200 }
201
202 /**
203  * get_futex_key() - Get parameters which are the keys for a futex
204  * @uaddr:      virtual address of the futex
205  * @fshared:    0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
206  * @key:        address where result is stored.
207  *
208  * Returns a negative error code or 0
209  * The key words are stored in *key on success.
210  *
211  * For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,
212  * offset_within_page).  For private mappings, it's (uaddr, current->mm).
213  * We can usually work out the index without swapping in the page.
214  *
215  * lock_page() might sleep, the caller should not hold a spinlock.
216  */
217 static int
218 get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key)
219 {
220         unsigned long address = (unsigned long)uaddr;
221         struct mm_struct *mm = current->mm;
222         struct page *page;
223         int err;
224
225         /*
226          * The futex address must be "naturally" aligned.
227          */
228         key->both.offset = address % PAGE_SIZE;
229         if (unlikely((address % sizeof(u32)) != 0))
230                 return -EINVAL;
231         address -= key->both.offset;
232
233         /*
234          * PROCESS_PRIVATE futexes are fast.
235          * As the mm cannot disappear under us and the 'key' only needs
236          * virtual address, we dont even have to find the underlying vma.
237          * Note : We do have to check 'uaddr' is a valid user address,
238          *        but access_ok() should be faster than find_vma()
239          */
240         if (!fshared) {
241                 if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))))
242                         return -EFAULT;
243                 key->private.mm = mm;
244                 key->private.address = address;
245                 get_futex_key_refs(key);
246                 return 0;
247         }
248
249 again:
250         err = get_user_pages_fast(address, 1, 1, &page);
251         if (err < 0)
252                 return err;
253
254         page = compound_head(page);
255         lock_page(page);
256         if (!page->mapping) {
257                 unlock_page(page);
258                 put_page(page);
259                 goto again;
260         }
261
262         /*
263          * Private mappings are handled in a simple way.
264          *
265          * NOTE: When userspace waits on a MAP_SHARED mapping, even if
266          * it's a read-only handle, it's expected that futexes attach to
267          * the object not the particular process.
268          */
269         if (PageAnon(page)) {
270                 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
271                 key->private.mm = mm;
272                 key->private.address = address;
273         } else {
274                 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
275                 key->shared.inode = page->mapping->host;
276                 key->shared.pgoff = page->index;
277         }
278
279         get_futex_key_refs(key);
280
281         unlock_page(page);
282         put_page(page);
283         return 0;
284 }
285
286 static inline
287 void put_futex_key(int fshared, union futex_key *key)
288 {
289         drop_futex_key_refs(key);
290 }
291
292 /**
293  * fault_in_user_writeable() - Fault in user address and verify RW access
294  * @uaddr:      pointer to faulting user space address
295  *
296  * Slow path to fixup the fault we just took in the atomic write
297  * access to @uaddr.
298  *
299  * We have no generic implementation of a non-destructive write to the
300  * user address. We know that we faulted in the atomic pagefault
301  * disabled section so we can as well avoid the #PF overhead by
302  * calling get_user_pages() right away.
303  */
304 static int fault_in_user_writeable(u32 __user *uaddr)
305 {
306         struct mm_struct *mm = current->mm;
307         int ret;
308
309         down_read(&mm->mmap_sem);
310         ret = get_user_pages(current, mm, (unsigned long)uaddr,
311                              1, 1, 0, NULL, NULL);
312         up_read(&mm->mmap_sem);
313
314         return ret < 0 ? ret : 0;
315 }
316
317 /**
318  * futex_top_waiter() - Return the highest priority waiter on a futex
319  * @hb:         the hash bucket the futex_q's reside in
320  * @key:        the futex key (to distinguish it from other futex futex_q's)
321  *
322  * Must be called with the hb lock held.
323  */
324 static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
325                                         union futex_key *key)
326 {
327         struct futex_q *this;
328
329         plist_for_each_entry(this, &hb->chain, list) {
330                 if (match_futex(&this->key, key))
331                         return this;
332         }
333         return NULL;
334 }
335
336 static u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval)
337 {
338         u32 curval;
339
340         pagefault_disable();
341         curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
342         pagefault_enable();
343
344         return curval;
345 }
346
347 static int get_futex_value_locked(u32 *dest, u32 __user *from)
348 {
349         int ret;
350
351         pagefault_disable();
352         ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
353         pagefault_enable();
354
355         return ret ? -EFAULT : 0;
356 }
357
358
359 /*
360  * PI code:
361  */
362 static int refill_pi_state_cache(void)
363 {
364         struct futex_pi_state *pi_state;
365
366         if (likely(current->pi_state_cache))
367                 return 0;
368
369         pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
370
371         if (!pi_state)
372                 return -ENOMEM;
373
374         INIT_LIST_HEAD(&pi_state->list);
375         /* pi_mutex gets initialized later */
376         pi_state->owner = NULL;
377         atomic_set(&pi_state->refcount, 1);
378         pi_state->key = FUTEX_KEY_INIT;
379
380         current->pi_state_cache = pi_state;
381
382         return 0;
383 }
384
385 static struct futex_pi_state * alloc_pi_state(void)
386 {
387         struct futex_pi_state *pi_state = current->pi_state_cache;
388
389         WARN_ON(!pi_state);
390         current->pi_state_cache = NULL;
391
392         return pi_state;
393 }
394
395 static void free_pi_state(struct futex_pi_state *pi_state)
396 {
397         if (!atomic_dec_and_test(&pi_state->refcount))
398                 return;
399
400         /*
401          * If pi_state->owner is NULL, the owner is most probably dying
402          * and has cleaned up the pi_state already
403          */
404         if (pi_state->owner) {
405                 raw_spin_lock_irq(&pi_state->owner->pi_lock);
406                 list_del_init(&pi_state->list);
407                 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
408
409                 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
410         }
411
412         if (current->pi_state_cache)
413                 kfree(pi_state);
414         else {
415                 /*
416                  * pi_state->list is already empty.
417                  * clear pi_state->owner.
418                  * refcount is at 0 - put it back to 1.
419                  */
420                 pi_state->owner = NULL;
421                 atomic_set(&pi_state->refcount, 1);
422                 current->pi_state_cache = pi_state;
423         }
424 }
425
426 /*
427  * Look up the task based on what TID userspace gave us.
428  * We dont trust it.
429  */
430 static struct task_struct * futex_find_get_task(pid_t pid)
431 {
432         struct task_struct *p;
433
434         rcu_read_lock();
435         p = find_task_by_vpid(pid);
436         if (p)
437                 get_task_struct(p);
438
439         rcu_read_unlock();
440
441         return p;
442 }
443
444 /*
445  * This task is holding PI mutexes at exit time => bad.
446  * Kernel cleans up PI-state, but userspace is likely hosed.
447  * (Robust-futex cleanup is separate and might save the day for userspace.)
448  */
449 void exit_pi_state_list(struct task_struct *curr)
450 {
451         struct list_head *next, *head = &curr->pi_state_list;
452         struct futex_pi_state *pi_state;
453         struct futex_hash_bucket *hb;
454         union futex_key key = FUTEX_KEY_INIT;
455
456         if (!futex_cmpxchg_enabled)
457                 return;
458         /*
459          * We are a ZOMBIE and nobody can enqueue itself on
460          * pi_state_list anymore, but we have to be careful
461          * versus waiters unqueueing themselves:
462          */
463         raw_spin_lock_irq(&curr->pi_lock);
464         while (!list_empty(head)) {
465
466                 next = head->next;
467                 pi_state = list_entry(next, struct futex_pi_state, list);
468                 key = pi_state->key;
469                 hb = hash_futex(&key);
470                 raw_spin_unlock_irq(&curr->pi_lock);
471
472                 spin_lock(&hb->lock);
473
474                 raw_spin_lock_irq(&curr->pi_lock);
475                 /*
476                  * We dropped the pi-lock, so re-check whether this
477                  * task still owns the PI-state:
478                  */
479                 if (head->next != next) {
480                         spin_unlock(&hb->lock);
481                         continue;
482                 }
483
484                 WARN_ON(pi_state->owner != curr);
485                 WARN_ON(list_empty(&pi_state->list));
486                 list_del_init(&pi_state->list);
487                 pi_state->owner = NULL;
488                 raw_spin_unlock_irq(&curr->pi_lock);
489
490                 rt_mutex_unlock(&pi_state->pi_mutex);
491
492                 spin_unlock(&hb->lock);
493
494                 raw_spin_lock_irq(&curr->pi_lock);
495         }
496         raw_spin_unlock_irq(&curr->pi_lock);
497 }
498
499 static int
500 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
501                 union futex_key *key, struct futex_pi_state **ps)
502 {
503         struct futex_pi_state *pi_state = NULL;
504         struct futex_q *this, *next;
505         struct plist_head *head;
506         struct task_struct *p;
507         pid_t pid = uval & FUTEX_TID_MASK;
508
509         head = &hb->chain;
510
511         plist_for_each_entry_safe(this, next, head, list) {
512                 if (match_futex(&this->key, key)) {
513                         /*
514                          * Another waiter already exists - bump up
515                          * the refcount and return its pi_state:
516                          */
517                         pi_state = this->pi_state;
518                         /*
519                          * Userspace might have messed up non-PI and PI futexes
520                          */
521                         if (unlikely(!pi_state))
522                                 return -EINVAL;
523
524                         WARN_ON(!atomic_read(&pi_state->refcount));
525
526                         /*
527                          * When pi_state->owner is NULL then the owner died
528                          * and another waiter is on the fly. pi_state->owner
529                          * is fixed up by the task which acquires
530                          * pi_state->rt_mutex.
531                          *
532                          * We do not check for pid == 0 which can happen when
533                          * the owner died and robust_list_exit() cleared the
534                          * TID.
535                          */
536                         if (pid && pi_state->owner) {
537                                 /*
538                                  * Bail out if user space manipulated the
539                                  * futex value.
540                                  */
541                                 if (pid != task_pid_vnr(pi_state->owner))
542                                         return -EINVAL;
543                         }
544
545                         atomic_inc(&pi_state->refcount);
546                         *ps = pi_state;
547
548                         return 0;
549                 }
550         }
551
552         /*
553          * We are the first waiter - try to look up the real owner and attach
554          * the new pi_state to it, but bail out when TID = 0
555          */
556         if (!pid)
557                 return -ESRCH;
558         p = futex_find_get_task(pid);
559         if (!p)
560                 return -ESRCH;
561
562         /*
563          * We need to look at the task state flags to figure out,
564          * whether the task is exiting. To protect against the do_exit
565          * change of the task flags, we do this protected by
566          * p->pi_lock:
567          */
568         raw_spin_lock_irq(&p->pi_lock);
569         if (unlikely(p->flags & PF_EXITING)) {
570                 /*
571                  * The task is on the way out. When PF_EXITPIDONE is
572                  * set, we know that the task has finished the
573                  * cleanup:
574                  */
575                 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
576
577                 raw_spin_unlock_irq(&p->pi_lock);
578                 put_task_struct(p);
579                 return ret;
580         }
581
582         pi_state = alloc_pi_state();
583
584         /*
585          * Initialize the pi_mutex in locked state and make 'p'
586          * the owner of it:
587          */
588         rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
589
590         /* Store the key for possible exit cleanups: */
591         pi_state->key = *key;
592
593         WARN_ON(!list_empty(&pi_state->list));
594         list_add(&pi_state->list, &p->pi_state_list);
595         pi_state->owner = p;
596         raw_spin_unlock_irq(&p->pi_lock);
597
598         put_task_struct(p);
599
600         *ps = pi_state;
601
602         return 0;
603 }
604
605 /**
606  * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
607  * @uaddr:              the pi futex user address
608  * @hb:                 the pi futex hash bucket
609  * @key:                the futex key associated with uaddr and hb
610  * @ps:                 the pi_state pointer where we store the result of the
611  *                      lookup
612  * @task:               the task to perform the atomic lock work for.  This will
613  *                      be "current" except in the case of requeue pi.
614  * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
615  *
616  * Returns:
617  *  0 - ready to wait
618  *  1 - acquired the lock
619  * <0 - error
620  *
621  * The hb->lock and futex_key refs shall be held by the caller.
622  */
623 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
624                                 union futex_key *key,
625                                 struct futex_pi_state **ps,
626                                 struct task_struct *task, int set_waiters)
627 {
628         int lock_taken, ret, ownerdied = 0;
629         u32 uval, newval, curval;
630
631 retry:
632         ret = lock_taken = 0;
633
634         /*
635          * To avoid races, we attempt to take the lock here again
636          * (by doing a 0 -> TID atomic cmpxchg), while holding all
637          * the locks. It will most likely not succeed.
638          */
639         newval = task_pid_vnr(task);
640         if (set_waiters)
641                 newval |= FUTEX_WAITERS;
642
643         curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
644
645         if (unlikely(curval == -EFAULT))
646                 return -EFAULT;
647
648         /*
649          * Detect deadlocks.
650          */
651         if ((unlikely((curval & FUTEX_TID_MASK) == task_pid_vnr(task))))
652                 return -EDEADLK;
653
654         /*
655          * Surprise - we got the lock. Just return to userspace:
656          */
657         if (unlikely(!curval))
658                 return 1;
659
660         uval = curval;
661
662         /*
663          * Set the FUTEX_WAITERS flag, so the owner will know it has someone
664          * to wake at the next unlock.
665          */
666         newval = curval | FUTEX_WAITERS;
667
668         /*
669          * There are two cases, where a futex might have no owner (the
670          * owner TID is 0): OWNER_DIED. We take over the futex in this
671          * case. We also do an unconditional take over, when the owner
672          * of the futex died.
673          *
674          * This is safe as we are protected by the hash bucket lock !
675          */
676         if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
677                 /* Keep the OWNER_DIED bit */
678                 newval = (curval & ~FUTEX_TID_MASK) | task_pid_vnr(task);
679                 ownerdied = 0;
680                 lock_taken = 1;
681         }
682
683         curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
684
685         if (unlikely(curval == -EFAULT))
686                 return -EFAULT;
687         if (unlikely(curval != uval))
688                 goto retry;
689
690         /*
691          * We took the lock due to owner died take over.
692          */
693         if (unlikely(lock_taken))
694                 return 1;
695
696         /*
697          * We dont have the lock. Look up the PI state (or create it if
698          * we are the first waiter):
699          */
700         ret = lookup_pi_state(uval, hb, key, ps);
701
702         if (unlikely(ret)) {
703                 switch (ret) {
704                 case -ESRCH:
705                         /*
706                          * No owner found for this futex. Check if the
707                          * OWNER_DIED bit is set to figure out whether
708                          * this is a robust futex or not.
709                          */
710                         if (get_futex_value_locked(&curval, uaddr))
711                                 return -EFAULT;
712
713                         /*
714                          * We simply start over in case of a robust
715                          * futex. The code above will take the futex
716                          * and return happy.
717                          */
718                         if (curval & FUTEX_OWNER_DIED) {
719                                 ownerdied = 1;
720                                 goto retry;
721                         }
722                 default:
723                         break;
724                 }
725         }
726
727         return ret;
728 }
729
730 /*
731  * The hash bucket lock must be held when this is called.
732  * Afterwards, the futex_q must not be accessed.
733  */
734 static void wake_futex(struct futex_q *q)
735 {
736         struct task_struct *p = q->task;
737
738         /*
739          * We set q->lock_ptr = NULL _before_ we wake up the task. If
740          * a non-futex wake up happens on another CPU then the task
741          * might exit and p would dereference a non-existing task
742          * struct. Prevent this by holding a reference on p across the
743          * wake up.
744          */
745         get_task_struct(p);
746
747         plist_del(&q->list, &q->list.plist);
748         /*
749          * The waiting task can free the futex_q as soon as
750          * q->lock_ptr = NULL is written, without taking any locks. A
751          * memory barrier is required here to prevent the following
752          * store to lock_ptr from getting ahead of the plist_del.
753          */
754         smp_wmb();
755         q->lock_ptr = NULL;
756
757         wake_up_state(p, TASK_NORMAL);
758         put_task_struct(p);
759 }
760
761 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
762 {
763         struct task_struct *new_owner;
764         struct futex_pi_state *pi_state = this->pi_state;
765         u32 curval, newval;
766
767         if (!pi_state)
768                 return -EINVAL;
769
770         /*
771          * If current does not own the pi_state then the futex is
772          * inconsistent and user space fiddled with the futex value.
773          */
774         if (pi_state->owner != current)
775                 return -EINVAL;
776
777         raw_spin_lock(&pi_state->pi_mutex.wait_lock);
778         new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
779
780         /*
781          * This happens when we have stolen the lock and the original
782          * pending owner did not enqueue itself back on the rt_mutex.
783          * Thats not a tragedy. We know that way, that a lock waiter
784          * is on the fly. We make the futex_q waiter the pending owner.
785          */
786         if (!new_owner)
787                 new_owner = this->task;
788
789         /*
790          * We pass it to the next owner. (The WAITERS bit is always
791          * kept enabled while there is PI state around. We must also
792          * preserve the owner died bit.)
793          */
794         if (!(uval & FUTEX_OWNER_DIED)) {
795                 int ret = 0;
796
797                 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
798
799                 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
800
801                 if (curval == -EFAULT)
802                         ret = -EFAULT;
803                 else if (curval != uval)
804                         ret = -EINVAL;
805                 if (ret) {
806                         raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
807                         return ret;
808                 }
809         }
810
811         raw_spin_lock_irq(&pi_state->owner->pi_lock);
812         WARN_ON(list_empty(&pi_state->list));
813         list_del_init(&pi_state->list);
814         raw_spin_unlock_irq(&pi_state->owner->pi_lock);
815
816         raw_spin_lock_irq(&new_owner->pi_lock);
817         WARN_ON(!list_empty(&pi_state->list));
818         list_add(&pi_state->list, &new_owner->pi_state_list);
819         pi_state->owner = new_owner;
820         raw_spin_unlock_irq(&new_owner->pi_lock);
821
822         raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
823         rt_mutex_unlock(&pi_state->pi_mutex);
824
825         return 0;
826 }
827
828 static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
829 {
830         u32 oldval;
831
832         /*
833          * There is no waiter, so we unlock the futex. The owner died
834          * bit has not to be preserved here. We are the owner:
835          */
836         oldval = cmpxchg_futex_value_locked(uaddr, uval, 0);
837
838         if (oldval == -EFAULT)
839                 return oldval;
840         if (oldval != uval)
841                 return -EAGAIN;
842
843         return 0;
844 }
845
846 /*
847  * Express the locking dependencies for lockdep:
848  */
849 static inline void
850 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
851 {
852         if (hb1 <= hb2) {
853                 spin_lock(&hb1->lock);
854                 if (hb1 < hb2)
855                         spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
856         } else { /* hb1 > hb2 */
857                 spin_lock(&hb2->lock);
858                 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
859         }
860 }
861
862 static inline void
863 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
864 {
865         spin_unlock(&hb1->lock);
866         if (hb1 != hb2)
867                 spin_unlock(&hb2->lock);
868 }
869
870 /*
871  * Wake up waiters matching bitset queued on this futex (uaddr).
872  */
873 static int futex_wake(u32 __user *uaddr, int fshared, int nr_wake, u32 bitset)
874 {
875         struct futex_hash_bucket *hb;
876         struct futex_q *this, *next;
877         struct plist_head *head;
878         union futex_key key = FUTEX_KEY_INIT;
879         int ret;
880
881         if (!bitset)
882                 return -EINVAL;
883
884         ret = get_futex_key(uaddr, fshared, &key);
885         if (unlikely(ret != 0))
886                 goto out;
887
888         hb = hash_futex(&key);
889         spin_lock(&hb->lock);
890         head = &hb->chain;
891
892         plist_for_each_entry_safe(this, next, head, list) {
893                 if (match_futex (&this->key, &key)) {
894                         if (this->pi_state || this->rt_waiter) {
895                                 ret = -EINVAL;
896                                 break;
897                         }
898
899                         /* Check if one of the bits is set in both bitsets */
900                         if (!(this->bitset & bitset))
901                                 continue;
902
903                         wake_futex(this);
904                         if (++ret >= nr_wake)
905                                 break;
906                 }
907         }
908
909         spin_unlock(&hb->lock);
910         put_futex_key(fshared, &key);
911 out:
912         return ret;
913 }
914
915 /*
916  * Wake up all waiters hashed on the physical page that is mapped
917  * to this virtual address:
918  */
919 static int
920 futex_wake_op(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
921               int nr_wake, int nr_wake2, int op)
922 {
923         union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
924         struct futex_hash_bucket *hb1, *hb2;
925         struct plist_head *head;
926         struct futex_q *this, *next;
927         int ret, op_ret;
928
929 retry:
930         ret = get_futex_key(uaddr1, fshared, &key1);
931         if (unlikely(ret != 0))
932                 goto out;
933         ret = get_futex_key(uaddr2, fshared, &key2);
934         if (unlikely(ret != 0))
935                 goto out_put_key1;
936
937         hb1 = hash_futex(&key1);
938         hb2 = hash_futex(&key2);
939
940 retry_private:
941         double_lock_hb(hb1, hb2);
942         op_ret = futex_atomic_op_inuser(op, uaddr2);
943         if (unlikely(op_ret < 0)) {
944
945                 double_unlock_hb(hb1, hb2);
946
947 #ifndef CONFIG_MMU
948                 /*
949                  * we don't get EFAULT from MMU faults if we don't have an MMU,
950                  * but we might get them from range checking
951                  */
952                 ret = op_ret;
953                 goto out_put_keys;
954 #endif
955
956                 if (unlikely(op_ret != -EFAULT)) {
957                         ret = op_ret;
958                         goto out_put_keys;
959                 }
960
961                 ret = fault_in_user_writeable(uaddr2);
962                 if (ret)
963                         goto out_put_keys;
964
965                 if (!fshared)
966                         goto retry_private;
967
968                 put_futex_key(fshared, &key2);
969                 put_futex_key(fshared, &key1);
970                 goto retry;
971         }
972
973         head = &hb1->chain;
974
975         plist_for_each_entry_safe(this, next, head, list) {
976                 if (match_futex (&this->key, &key1)) {
977                         wake_futex(this);
978                         if (++ret >= nr_wake)
979                                 break;
980                 }
981         }
982
983         if (op_ret > 0) {
984                 head = &hb2->chain;
985
986                 op_ret = 0;
987                 plist_for_each_entry_safe(this, next, head, list) {
988                         if (match_futex (&this->key, &key2)) {
989                                 wake_futex(this);
990                                 if (++op_ret >= nr_wake2)
991                                         break;
992                         }
993                 }
994                 ret += op_ret;
995         }
996
997         double_unlock_hb(hb1, hb2);
998 out_put_keys:
999         put_futex_key(fshared, &key2);
1000 out_put_key1:
1001         put_futex_key(fshared, &key1);
1002 out:
1003         return ret;
1004 }
1005
1006 /**
1007  * requeue_futex() - Requeue a futex_q from one hb to another
1008  * @q:          the futex_q to requeue
1009  * @hb1:        the source hash_bucket
1010  * @hb2:        the target hash_bucket
1011  * @key2:       the new key for the requeued futex_q
1012  */
1013 static inline
1014 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1015                    struct futex_hash_bucket *hb2, union futex_key *key2)
1016 {
1017
1018         /*
1019          * If key1 and key2 hash to the same bucket, no need to
1020          * requeue.
1021          */
1022         if (likely(&hb1->chain != &hb2->chain)) {
1023                 plist_del(&q->list, &hb1->chain);
1024                 plist_add(&q->list, &hb2->chain);
1025                 q->lock_ptr = &hb2->lock;
1026 #ifdef CONFIG_DEBUG_PI_LIST
1027                 q->list.plist.spinlock = &hb2->lock;
1028 #endif
1029         }
1030         get_futex_key_refs(key2);
1031         q->key = *key2;
1032 }
1033
1034 /**
1035  * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1036  * @q:          the futex_q
1037  * @key:        the key of the requeue target futex
1038  * @hb:         the hash_bucket of the requeue target futex
1039  *
1040  * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1041  * target futex if it is uncontended or via a lock steal.  Set the futex_q key
1042  * to the requeue target futex so the waiter can detect the wakeup on the right
1043  * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1044  * atomic lock acquisition.  Set the q->lock_ptr to the requeue target hb->lock
1045  * to protect access to the pi_state to fixup the owner later.  Must be called
1046  * with both q->lock_ptr and hb->lock held.
1047  */
1048 static inline
1049 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1050                            struct futex_hash_bucket *hb)
1051 {
1052         get_futex_key_refs(key);
1053         q->key = *key;
1054
1055         WARN_ON(plist_node_empty(&q->list));
1056         plist_del(&q->list, &q->list.plist);
1057
1058         WARN_ON(!q->rt_waiter);
1059         q->rt_waiter = NULL;
1060
1061         q->lock_ptr = &hb->lock;
1062 #ifdef CONFIG_DEBUG_PI_LIST
1063         q->list.plist.spinlock = &hb->lock;
1064 #endif
1065
1066         wake_up_state(q->task, TASK_NORMAL);
1067 }
1068
1069 /**
1070  * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1071  * @pifutex:            the user address of the to futex
1072  * @hb1:                the from futex hash bucket, must be locked by the caller
1073  * @hb2:                the to futex hash bucket, must be locked by the caller
1074  * @key1:               the from futex key
1075  * @key2:               the to futex key
1076  * @ps:                 address to store the pi_state pointer
1077  * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
1078  *
1079  * Try and get the lock on behalf of the top waiter if we can do it atomically.
1080  * Wake the top waiter if we succeed.  If the caller specified set_waiters,
1081  * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1082  * hb1 and hb2 must be held by the caller.
1083  *
1084  * Returns:
1085  *  0 - failed to acquire the lock atomicly
1086  *  1 - acquired the lock
1087  * <0 - error
1088  */
1089 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1090                                  struct futex_hash_bucket *hb1,
1091                                  struct futex_hash_bucket *hb2,
1092                                  union futex_key *key1, union futex_key *key2,
1093                                  struct futex_pi_state **ps, int set_waiters)
1094 {
1095         struct futex_q *top_waiter = NULL;
1096         u32 curval;
1097         int ret;
1098
1099         if (get_futex_value_locked(&curval, pifutex))
1100                 return -EFAULT;
1101
1102         /*
1103          * Find the top_waiter and determine if there are additional waiters.
1104          * If the caller intends to requeue more than 1 waiter to pifutex,
1105          * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1106          * as we have means to handle the possible fault.  If not, don't set
1107          * the bit unecessarily as it will force the subsequent unlock to enter
1108          * the kernel.
1109          */
1110         top_waiter = futex_top_waiter(hb1, key1);
1111
1112         /* There are no waiters, nothing for us to do. */
1113         if (!top_waiter)
1114                 return 0;
1115
1116         /* Ensure we requeue to the expected futex. */
1117         if (!match_futex(top_waiter->requeue_pi_key, key2))
1118                 return -EINVAL;
1119
1120         /*
1121          * Try to take the lock for top_waiter.  Set the FUTEX_WAITERS bit in
1122          * the contended case or if set_waiters is 1.  The pi_state is returned
1123          * in ps in contended cases.
1124          */
1125         ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1126                                    set_waiters);
1127         if (ret == 1)
1128                 requeue_pi_wake_futex(top_waiter, key2, hb2);
1129
1130         return ret;
1131 }
1132
1133 /**
1134  * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1135  * @uaddr1:     source futex user address
1136  * @fshared:    0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
1137  * @uaddr2:     target futex user address
1138  * @nr_wake:    number of waiters to wake (must be 1 for requeue_pi)
1139  * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1140  * @cmpval:     @uaddr1 expected value (or %NULL)
1141  * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1142  *              pi futex (pi to pi requeue is not supported)
1143  *
1144  * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1145  * uaddr2 atomically on behalf of the top waiter.
1146  *
1147  * Returns:
1148  * >=0 - on success, the number of tasks requeued or woken
1149  *  <0 - on error
1150  */
1151 static int futex_requeue(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
1152                          int nr_wake, int nr_requeue, u32 *cmpval,
1153                          int requeue_pi)
1154 {
1155         union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1156         int drop_count = 0, task_count = 0, ret;
1157         struct futex_pi_state *pi_state = NULL;
1158         struct futex_hash_bucket *hb1, *hb2;
1159         struct plist_head *head1;
1160         struct futex_q *this, *next;
1161         u32 curval2;
1162
1163         if (requeue_pi) {
1164                 /*
1165                  * requeue_pi requires a pi_state, try to allocate it now
1166                  * without any locks in case it fails.
1167                  */
1168                 if (refill_pi_state_cache())
1169                         return -ENOMEM;
1170                 /*
1171                  * requeue_pi must wake as many tasks as it can, up to nr_wake
1172                  * + nr_requeue, since it acquires the rt_mutex prior to
1173                  * returning to userspace, so as to not leave the rt_mutex with
1174                  * waiters and no owner.  However, second and third wake-ups
1175                  * cannot be predicted as they involve race conditions with the
1176                  * first wake and a fault while looking up the pi_state.  Both
1177                  * pthread_cond_signal() and pthread_cond_broadcast() should
1178                  * use nr_wake=1.
1179                  */
1180                 if (nr_wake != 1)
1181                         return -EINVAL;
1182         }
1183
1184 retry:
1185         if (pi_state != NULL) {
1186                 /*
1187                  * We will have to lookup the pi_state again, so free this one
1188                  * to keep the accounting correct.
1189                  */
1190                 free_pi_state(pi_state);
1191                 pi_state = NULL;
1192         }
1193
1194         ret = get_futex_key(uaddr1, fshared, &key1);
1195         if (unlikely(ret != 0))
1196                 goto out;
1197         ret = get_futex_key(uaddr2, fshared, &key2);
1198         if (unlikely(ret != 0))
1199                 goto out_put_key1;
1200
1201         hb1 = hash_futex(&key1);
1202         hb2 = hash_futex(&key2);
1203
1204 retry_private:
1205         double_lock_hb(hb1, hb2);
1206
1207         if (likely(cmpval != NULL)) {
1208                 u32 curval;
1209
1210                 ret = get_futex_value_locked(&curval, uaddr1);
1211
1212                 if (unlikely(ret)) {
1213                         double_unlock_hb(hb1, hb2);
1214
1215                         ret = get_user(curval, uaddr1);
1216                         if (ret)
1217                                 goto out_put_keys;
1218
1219                         if (!fshared)
1220                                 goto retry_private;
1221
1222                         put_futex_key(fshared, &key2);
1223                         put_futex_key(fshared, &key1);
1224                         goto retry;
1225                 }
1226                 if (curval != *cmpval) {
1227                         ret = -EAGAIN;
1228                         goto out_unlock;
1229                 }
1230         }
1231
1232         if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1233                 /*
1234                  * Attempt to acquire uaddr2 and wake the top waiter. If we
1235                  * intend to requeue waiters, force setting the FUTEX_WAITERS
1236                  * bit.  We force this here where we are able to easily handle
1237                  * faults rather in the requeue loop below.
1238                  */
1239                 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1240                                                  &key2, &pi_state, nr_requeue);
1241
1242                 /*
1243                  * At this point the top_waiter has either taken uaddr2 or is
1244                  * waiting on it.  If the former, then the pi_state will not
1245                  * exist yet, look it up one more time to ensure we have a
1246                  * reference to it.
1247                  */
1248                 if (ret == 1) {
1249                         WARN_ON(pi_state);
1250                         drop_count++;
1251                         task_count++;
1252                         ret = get_futex_value_locked(&curval2, uaddr2);
1253                         if (!ret)
1254                                 ret = lookup_pi_state(curval2, hb2, &key2,
1255                                                       &pi_state);
1256                 }
1257
1258                 switch (ret) {
1259                 case 0:
1260                         break;
1261                 case -EFAULT:
1262                         double_unlock_hb(hb1, hb2);
1263                         put_futex_key(fshared, &key2);
1264                         put_futex_key(fshared, &key1);
1265                         ret = fault_in_user_writeable(uaddr2);
1266                         if (!ret)
1267                                 goto retry;
1268                         goto out;
1269                 case -EAGAIN:
1270                         /* The owner was exiting, try again. */
1271                         double_unlock_hb(hb1, hb2);
1272                         put_futex_key(fshared, &key2);
1273                         put_futex_key(fshared, &key1);
1274                         cond_resched();
1275                         goto retry;
1276                 default:
1277                         goto out_unlock;
1278                 }
1279         }
1280
1281         head1 = &hb1->chain;
1282         plist_for_each_entry_safe(this, next, head1, list) {
1283                 if (task_count - nr_wake >= nr_requeue)
1284                         break;
1285
1286                 if (!match_futex(&this->key, &key1))
1287                         continue;
1288
1289                 /*
1290                  * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1291                  * be paired with each other and no other futex ops.
1292                  */
1293                 if ((requeue_pi && !this->rt_waiter) ||
1294                     (!requeue_pi && this->rt_waiter)) {
1295                         ret = -EINVAL;
1296                         break;
1297                 }
1298
1299                 /*
1300                  * Wake nr_wake waiters.  For requeue_pi, if we acquired the
1301                  * lock, we already woke the top_waiter.  If not, it will be
1302                  * woken by futex_unlock_pi().
1303                  */
1304                 if (++task_count <= nr_wake && !requeue_pi) {
1305                         wake_futex(this);
1306                         continue;
1307                 }
1308
1309                 /* Ensure we requeue to the expected futex for requeue_pi. */
1310                 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1311                         ret = -EINVAL;
1312                         break;
1313                 }
1314
1315                 /*
1316                  * Requeue nr_requeue waiters and possibly one more in the case
1317                  * of requeue_pi if we couldn't acquire the lock atomically.
1318                  */
1319                 if (requeue_pi) {
1320                         /* Prepare the waiter to take the rt_mutex. */
1321                         atomic_inc(&pi_state->refcount);
1322                         this->pi_state = pi_state;
1323                         ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1324                                                         this->rt_waiter,
1325                                                         this->task, 1);
1326                         if (ret == 1) {
1327                                 /* We got the lock. */
1328                                 requeue_pi_wake_futex(this, &key2, hb2);
1329                                 drop_count++;
1330                                 continue;
1331                         } else if (ret) {
1332                                 /* -EDEADLK */
1333                                 this->pi_state = NULL;
1334                                 free_pi_state(pi_state);
1335                                 goto out_unlock;
1336                         }
1337                 }
1338                 requeue_futex(this, hb1, hb2, &key2);
1339                 drop_count++;
1340         }
1341
1342 out_unlock:
1343         double_unlock_hb(hb1, hb2);
1344
1345         /*
1346          * drop_futex_key_refs() must be called outside the spinlocks. During
1347          * the requeue we moved futex_q's from the hash bucket at key1 to the
1348          * one at key2 and updated their key pointer.  We no longer need to
1349          * hold the references to key1.
1350          */
1351         while (--drop_count >= 0)
1352                 drop_futex_key_refs(&key1);
1353
1354 out_put_keys:
1355         put_futex_key(fshared, &key2);
1356 out_put_key1:
1357         put_futex_key(fshared, &key1);
1358 out:
1359         if (pi_state != NULL)
1360                 free_pi_state(pi_state);
1361         return ret ? ret : task_count;
1362 }
1363
1364 /* The key must be already stored in q->key. */
1365 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
1366         __acquires(&hb->lock)
1367 {
1368         struct futex_hash_bucket *hb;
1369
1370         get_futex_key_refs(&q->key);
1371         hb = hash_futex(&q->key);
1372         q->lock_ptr = &hb->lock;
1373
1374         spin_lock(&hb->lock);
1375         return hb;
1376 }
1377
1378 static inline void
1379 queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
1380         __releases(&hb->lock)
1381 {
1382         spin_unlock(&hb->lock);
1383         drop_futex_key_refs(&q->key);
1384 }
1385
1386 /**
1387  * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1388  * @q:  The futex_q to enqueue
1389  * @hb: The destination hash bucket
1390  *
1391  * The hb->lock must be held by the caller, and is released here. A call to
1392  * queue_me() is typically paired with exactly one call to unqueue_me().  The
1393  * exceptions involve the PI related operations, which may use unqueue_me_pi()
1394  * or nothing if the unqueue is done as part of the wake process and the unqueue
1395  * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1396  * an example).
1397  */
1398 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1399         __releases(&hb->lock)
1400 {
1401         int prio;
1402
1403         /*
1404          * The priority used to register this element is
1405          * - either the real thread-priority for the real-time threads
1406          * (i.e. threads with a priority lower than MAX_RT_PRIO)
1407          * - or MAX_RT_PRIO for non-RT threads.
1408          * Thus, all RT-threads are woken first in priority order, and
1409          * the others are woken last, in FIFO order.
1410          */
1411         prio = min(current->normal_prio, MAX_RT_PRIO);
1412
1413         plist_node_init(&q->list, prio);
1414 #ifdef CONFIG_DEBUG_PI_LIST
1415         q->list.plist.spinlock = &hb->lock;
1416 #endif
1417         plist_add(&q->list, &hb->chain);
1418         q->task = current;
1419         spin_unlock(&hb->lock);
1420 }
1421
1422 /**
1423  * unqueue_me() - Remove the futex_q from its futex_hash_bucket
1424  * @q:  The futex_q to unqueue
1425  *
1426  * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
1427  * be paired with exactly one earlier call to queue_me().
1428  *
1429  * Returns:
1430  *   1 - if the futex_q was still queued (and we removed unqueued it)
1431  *   0 - if the futex_q was already removed by the waking thread
1432  */
1433 static int unqueue_me(struct futex_q *q)
1434 {
1435         spinlock_t *lock_ptr;
1436         int ret = 0;
1437
1438         /* In the common case we don't take the spinlock, which is nice. */
1439 retry:
1440         lock_ptr = q->lock_ptr;
1441         barrier();
1442         if (lock_ptr != NULL) {
1443                 spin_lock(lock_ptr);
1444                 /*
1445                  * q->lock_ptr can change between reading it and
1446                  * spin_lock(), causing us to take the wrong lock.  This
1447                  * corrects the race condition.
1448                  *
1449                  * Reasoning goes like this: if we have the wrong lock,
1450                  * q->lock_ptr must have changed (maybe several times)
1451                  * between reading it and the spin_lock().  It can
1452                  * change again after the spin_lock() but only if it was
1453                  * already changed before the spin_lock().  It cannot,
1454                  * however, change back to the original value.  Therefore
1455                  * we can detect whether we acquired the correct lock.
1456                  */
1457                 if (unlikely(lock_ptr != q->lock_ptr)) {
1458                         spin_unlock(lock_ptr);
1459                         goto retry;
1460                 }
1461                 WARN_ON(plist_node_empty(&q->list));
1462                 plist_del(&q->list, &q->list.plist);
1463
1464                 BUG_ON(q->pi_state);
1465
1466                 spin_unlock(lock_ptr);
1467                 ret = 1;
1468         }
1469
1470         drop_futex_key_refs(&q->key);
1471         return ret;
1472 }
1473
1474 /*
1475  * PI futexes can not be requeued and must remove themself from the
1476  * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1477  * and dropped here.
1478  */
1479 static void unqueue_me_pi(struct futex_q *q)
1480         __releases(q->lock_ptr)
1481 {
1482         WARN_ON(plist_node_empty(&q->list));
1483         plist_del(&q->list, &q->list.plist);
1484
1485         BUG_ON(!q->pi_state);
1486         free_pi_state(q->pi_state);
1487         q->pi_state = NULL;
1488
1489         spin_unlock(q->lock_ptr);
1490
1491         drop_futex_key_refs(&q->key);
1492 }
1493
1494 /*
1495  * Fixup the pi_state owner with the new owner.
1496  *
1497  * Must be called with hash bucket lock held and mm->sem held for non
1498  * private futexes.
1499  */
1500 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1501                                 struct task_struct *newowner, int fshared)
1502 {
1503         u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
1504         struct futex_pi_state *pi_state = q->pi_state;
1505         struct task_struct *oldowner = pi_state->owner;
1506         u32 uval, curval, newval;
1507         int ret;
1508
1509         /* Owner died? */
1510         if (!pi_state->owner)
1511                 newtid |= FUTEX_OWNER_DIED;
1512
1513         /*
1514          * We are here either because we stole the rtmutex from the
1515          * pending owner or we are the pending owner which failed to
1516          * get the rtmutex. We have to replace the pending owner TID
1517          * in the user space variable. This must be atomic as we have
1518          * to preserve the owner died bit here.
1519          *
1520          * Note: We write the user space value _before_ changing the pi_state
1521          * because we can fault here. Imagine swapped out pages or a fork
1522          * that marked all the anonymous memory readonly for cow.
1523          *
1524          * Modifying pi_state _before_ the user space value would
1525          * leave the pi_state in an inconsistent state when we fault
1526          * here, because we need to drop the hash bucket lock to
1527          * handle the fault. This might be observed in the PID check
1528          * in lookup_pi_state.
1529          */
1530 retry:
1531         if (get_futex_value_locked(&uval, uaddr))
1532                 goto handle_fault;
1533
1534         while (1) {
1535                 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1536
1537                 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
1538
1539                 if (curval == -EFAULT)
1540                         goto handle_fault;
1541                 if (curval == uval)
1542                         break;
1543                 uval = curval;
1544         }
1545
1546         /*
1547          * We fixed up user space. Now we need to fix the pi_state
1548          * itself.
1549          */
1550         if (pi_state->owner != NULL) {
1551                 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1552                 WARN_ON(list_empty(&pi_state->list));
1553                 list_del_init(&pi_state->list);
1554                 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1555         }
1556
1557         pi_state->owner = newowner;
1558
1559         raw_spin_lock_irq(&newowner->pi_lock);
1560         WARN_ON(!list_empty(&pi_state->list));
1561         list_add(&pi_state->list, &newowner->pi_state_list);
1562         raw_spin_unlock_irq(&newowner->pi_lock);
1563         return 0;
1564
1565         /*
1566          * To handle the page fault we need to drop the hash bucket
1567          * lock here. That gives the other task (either the pending
1568          * owner itself or the task which stole the rtmutex) the
1569          * chance to try the fixup of the pi_state. So once we are
1570          * back from handling the fault we need to check the pi_state
1571          * after reacquiring the hash bucket lock and before trying to
1572          * do another fixup. When the fixup has been done already we
1573          * simply return.
1574          */
1575 handle_fault:
1576         spin_unlock(q->lock_ptr);
1577
1578         ret = fault_in_user_writeable(uaddr);
1579
1580         spin_lock(q->lock_ptr);
1581
1582         /*
1583          * Check if someone else fixed it for us:
1584          */
1585         if (pi_state->owner != oldowner)
1586                 return 0;
1587
1588         if (ret)
1589                 return ret;
1590
1591         goto retry;
1592 }
1593
1594 /*
1595  * In case we must use restart_block to restart a futex_wait,
1596  * we encode in the 'flags' shared capability
1597  */
1598 #define FLAGS_SHARED            0x01
1599 #define FLAGS_CLOCKRT           0x02
1600 #define FLAGS_HAS_TIMEOUT       0x04
1601
1602 static long futex_wait_restart(struct restart_block *restart);
1603
1604 /**
1605  * fixup_owner() - Post lock pi_state and corner case management
1606  * @uaddr:      user address of the futex
1607  * @fshared:    whether the futex is shared (1) or not (0)
1608  * @q:          futex_q (contains pi_state and access to the rt_mutex)
1609  * @locked:     if the attempt to take the rt_mutex succeeded (1) or not (0)
1610  *
1611  * After attempting to lock an rt_mutex, this function is called to cleanup
1612  * the pi_state owner as well as handle race conditions that may allow us to
1613  * acquire the lock. Must be called with the hb lock held.
1614  *
1615  * Returns:
1616  *  1 - success, lock taken
1617  *  0 - success, lock not taken
1618  * <0 - on error (-EFAULT)
1619  */
1620 static int fixup_owner(u32 __user *uaddr, int fshared, struct futex_q *q,
1621                        int locked)
1622 {
1623         struct task_struct *owner;
1624         int ret = 0;
1625
1626         if (locked) {
1627                 /*
1628                  * Got the lock. We might not be the anticipated owner if we
1629                  * did a lock-steal - fix up the PI-state in that case:
1630                  */
1631                 if (q->pi_state->owner != current)
1632                         ret = fixup_pi_state_owner(uaddr, q, current, fshared);
1633                 goto out;
1634         }
1635
1636         /*
1637          * Catch the rare case, where the lock was released when we were on the
1638          * way back before we locked the hash bucket.
1639          */
1640         if (q->pi_state->owner == current) {
1641                 /*
1642                  * Try to get the rt_mutex now. This might fail as some other
1643                  * task acquired the rt_mutex after we removed ourself from the
1644                  * rt_mutex waiters list.
1645                  */
1646                 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
1647                         locked = 1;
1648                         goto out;
1649                 }
1650
1651                 /*
1652                  * pi_state is incorrect, some other task did a lock steal and
1653                  * we returned due to timeout or signal without taking the
1654                  * rt_mutex. Too late. We can access the rt_mutex_owner without
1655                  * locking, as the other task is now blocked on the hash bucket
1656                  * lock. Fix the state up.
1657                  */
1658                 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
1659                 ret = fixup_pi_state_owner(uaddr, q, owner, fshared);
1660                 goto out;
1661         }
1662
1663         /*
1664          * Paranoia check. If we did not take the lock, then we should not be
1665          * the owner, nor the pending owner, of the rt_mutex.
1666          */
1667         if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
1668                 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
1669                                 "pi-state %p\n", ret,
1670                                 q->pi_state->pi_mutex.owner,
1671                                 q->pi_state->owner);
1672
1673 out:
1674         return ret ? ret : locked;
1675 }
1676
1677 /**
1678  * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
1679  * @hb:         the futex hash bucket, must be locked by the caller
1680  * @q:          the futex_q to queue up on
1681  * @timeout:    the prepared hrtimer_sleeper, or null for no timeout
1682  */
1683 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
1684                                 struct hrtimer_sleeper *timeout)
1685 {
1686         /*
1687          * The task state is guaranteed to be set before another task can
1688          * wake it. set_current_state() is implemented using set_mb() and
1689          * queue_me() calls spin_unlock() upon completion, both serializing
1690          * access to the hash list and forcing another memory barrier.
1691          */
1692         set_current_state(TASK_INTERRUPTIBLE);
1693         queue_me(q, hb);
1694
1695         /* Arm the timer */
1696         if (timeout) {
1697                 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1698                 if (!hrtimer_active(&timeout->timer))
1699                         timeout->task = NULL;
1700         }
1701
1702         /*
1703          * If we have been removed from the hash list, then another task
1704          * has tried to wake us, and we can skip the call to schedule().
1705          */
1706         if (likely(!plist_node_empty(&q->list))) {
1707                 /*
1708                  * If the timer has already expired, current will already be
1709                  * flagged for rescheduling. Only call schedule if there
1710                  * is no timeout, or if it has yet to expire.
1711                  */
1712                 if (!timeout || timeout->task)
1713                         schedule();
1714         }
1715         __set_current_state(TASK_RUNNING);
1716 }
1717
1718 /**
1719  * futex_wait_setup() - Prepare to wait on a futex
1720  * @uaddr:      the futex userspace address
1721  * @val:        the expected value
1722  * @fshared:    whether the futex is shared (1) or not (0)
1723  * @q:          the associated futex_q
1724  * @hb:         storage for hash_bucket pointer to be returned to caller
1725  *
1726  * Setup the futex_q and locate the hash_bucket.  Get the futex value and
1727  * compare it with the expected value.  Handle atomic faults internally.
1728  * Return with the hb lock held and a q.key reference on success, and unlocked
1729  * with no q.key reference on failure.
1730  *
1731  * Returns:
1732  *  0 - uaddr contains val and hb has been locked
1733  * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlcoked
1734  */
1735 static int futex_wait_setup(u32 __user *uaddr, u32 val, int fshared,
1736                            struct futex_q *q, struct futex_hash_bucket **hb)
1737 {
1738         u32 uval;
1739         int ret;
1740
1741         /*
1742          * Access the page AFTER the hash-bucket is locked.
1743          * Order is important:
1744          *
1745          *   Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1746          *   Userspace waker:  if (cond(var)) { var = new; futex_wake(&var); }
1747          *
1748          * The basic logical guarantee of a futex is that it blocks ONLY
1749          * if cond(var) is known to be true at the time of blocking, for
1750          * any cond.  If we queued after testing *uaddr, that would open
1751          * a race condition where we could block indefinitely with
1752          * cond(var) false, which would violate the guarantee.
1753          *
1754          * A consequence is that futex_wait() can return zero and absorb
1755          * a wakeup when *uaddr != val on entry to the syscall.  This is
1756          * rare, but normal.
1757          */
1758 retry:
1759         q->key = FUTEX_KEY_INIT;
1760         ret = get_futex_key(uaddr, fshared, &q->key);
1761         if (unlikely(ret != 0))
1762                 return ret;
1763
1764 retry_private:
1765         *hb = queue_lock(q);
1766
1767         ret = get_futex_value_locked(&uval, uaddr);
1768
1769         if (ret) {
1770                 queue_unlock(q, *hb);
1771
1772                 ret = get_user(uval, uaddr);
1773                 if (ret)
1774                         goto out;
1775
1776                 if (!fshared)
1777                         goto retry_private;
1778
1779                 put_futex_key(fshared, &q->key);
1780                 goto retry;
1781         }
1782
1783         if (uval != val) {
1784                 queue_unlock(q, *hb);
1785                 ret = -EWOULDBLOCK;
1786         }
1787
1788 out:
1789         if (ret)
1790                 put_futex_key(fshared, &q->key);
1791         return ret;
1792 }
1793
1794 static int futex_wait(u32 __user *uaddr, int fshared,
1795                       u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
1796 {
1797         struct hrtimer_sleeper timeout, *to = NULL;
1798         struct restart_block *restart;
1799         struct futex_hash_bucket *hb;
1800         struct futex_q q;
1801         int ret;
1802
1803         if (!bitset)
1804                 return -EINVAL;
1805
1806         q.pi_state = NULL;
1807         q.bitset = bitset;
1808         q.rt_waiter = NULL;
1809         q.requeue_pi_key = NULL;
1810
1811         if (abs_time) {
1812                 to = &timeout;
1813
1814                 hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
1815                                       CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1816                 hrtimer_init_sleeper(to, current);
1817                 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
1818                                              current->timer_slack_ns);
1819         }
1820
1821 retry:
1822         /* Prepare to wait on uaddr. */
1823         ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
1824         if (ret)
1825                 goto out;
1826
1827         /* queue_me and wait for wakeup, timeout, or a signal. */
1828         futex_wait_queue_me(hb, &q, to);
1829
1830         /* If we were woken (and unqueued), we succeeded, whatever. */
1831         ret = 0;
1832         if (!unqueue_me(&q))
1833                 goto out_put_key;
1834         ret = -ETIMEDOUT;
1835         if (to && !to->task)
1836                 goto out_put_key;
1837
1838         /*
1839          * We expect signal_pending(current), but we might be the
1840          * victim of a spurious wakeup as well.
1841          */
1842         if (!signal_pending(current)) {
1843                 put_futex_key(fshared, &q.key);
1844                 goto retry;
1845         }
1846
1847         ret = -ERESTARTSYS;
1848         if (!abs_time)
1849                 goto out_put_key;
1850
1851         restart = &current_thread_info()->restart_block;
1852         restart->fn = futex_wait_restart;
1853         restart->futex.uaddr = uaddr;
1854         restart->futex.val = val;
1855         restart->futex.time = abs_time->tv64;
1856         restart->futex.bitset = bitset;
1857         restart->futex.flags = FLAGS_HAS_TIMEOUT;
1858
1859         if (fshared)
1860                 restart->futex.flags |= FLAGS_SHARED;
1861         if (clockrt)
1862                 restart->futex.flags |= FLAGS_CLOCKRT;
1863
1864         ret = -ERESTART_RESTARTBLOCK;
1865
1866 out_put_key:
1867         put_futex_key(fshared, &q.key);
1868 out:
1869         if (to) {
1870                 hrtimer_cancel(&to->timer);
1871                 destroy_hrtimer_on_stack(&to->timer);
1872         }
1873         return ret;
1874 }
1875
1876
1877 static long futex_wait_restart(struct restart_block *restart)
1878 {
1879         u32 __user *uaddr = restart->futex.uaddr;
1880         int fshared = 0;
1881         ktime_t t, *tp = NULL;
1882
1883         if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
1884                 t.tv64 = restart->futex.time;
1885                 tp = &t;
1886         }
1887         restart->fn = do_no_restart_syscall;
1888         if (restart->futex.flags & FLAGS_SHARED)
1889                 fshared = 1;
1890         return (long)futex_wait(uaddr, fshared, restart->futex.val, tp,
1891                                 restart->futex.bitset,
1892                                 restart->futex.flags & FLAGS_CLOCKRT);
1893 }
1894
1895
1896 /*
1897  * Userspace tried a 0 -> TID atomic transition of the futex value
1898  * and failed. The kernel side here does the whole locking operation:
1899  * if there are waiters then it will block, it does PI, etc. (Due to
1900  * races the kernel might see a 0 value of the futex too.)
1901  */
1902 static int futex_lock_pi(u32 __user *uaddr, int fshared,
1903                          int detect, ktime_t *time, int trylock)
1904 {
1905         struct hrtimer_sleeper timeout, *to = NULL;
1906         struct futex_hash_bucket *hb;
1907         struct futex_q q;
1908         int res, ret;
1909
1910         if (refill_pi_state_cache())
1911                 return -ENOMEM;
1912
1913         if (time) {
1914                 to = &timeout;
1915                 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
1916                                       HRTIMER_MODE_ABS);
1917                 hrtimer_init_sleeper(to, current);
1918                 hrtimer_set_expires(&to->timer, *time);
1919         }
1920
1921         q.pi_state = NULL;
1922         q.rt_waiter = NULL;
1923         q.requeue_pi_key = NULL;
1924 retry:
1925         q.key = FUTEX_KEY_INIT;
1926         ret = get_futex_key(uaddr, fshared, &q.key);
1927         if (unlikely(ret != 0))
1928                 goto out;
1929
1930 retry_private:
1931         hb = queue_lock(&q);
1932
1933         ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
1934         if (unlikely(ret)) {
1935                 switch (ret) {
1936                 case 1:
1937                         /* We got the lock. */
1938                         ret = 0;
1939                         goto out_unlock_put_key;
1940                 case -EFAULT:
1941                         goto uaddr_faulted;
1942                 case -EAGAIN:
1943                         /*
1944                          * Task is exiting and we just wait for the
1945                          * exit to complete.
1946                          */
1947                         queue_unlock(&q, hb);
1948                         put_futex_key(fshared, &q.key);
1949                         cond_resched();
1950                         goto retry;
1951                 default:
1952                         goto out_unlock_put_key;
1953                 }
1954         }
1955
1956         /*
1957          * Only actually queue now that the atomic ops are done:
1958          */
1959         queue_me(&q, hb);
1960
1961         WARN_ON(!q.pi_state);
1962         /*
1963          * Block on the PI mutex:
1964          */
1965         if (!trylock)
1966                 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
1967         else {
1968                 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
1969                 /* Fixup the trylock return value: */
1970                 ret = ret ? 0 : -EWOULDBLOCK;
1971         }
1972
1973         spin_lock(q.lock_ptr);
1974         /*
1975          * Fixup the pi_state owner and possibly acquire the lock if we
1976          * haven't already.
1977          */
1978         res = fixup_owner(uaddr, fshared, &q, !ret);
1979         /*
1980          * If fixup_owner() returned an error, proprogate that.  If it acquired
1981          * the lock, clear our -ETIMEDOUT or -EINTR.
1982          */
1983         if (res)
1984                 ret = (res < 0) ? res : 0;
1985
1986         /*
1987          * If fixup_owner() faulted and was unable to handle the fault, unlock
1988          * it and return the fault to userspace.
1989          */
1990         if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
1991                 rt_mutex_unlock(&q.pi_state->pi_mutex);
1992
1993         /* Unqueue and drop the lock */
1994         unqueue_me_pi(&q);
1995
1996         goto out_put_key;
1997
1998 out_unlock_put_key:
1999         queue_unlock(&q, hb);
2000
2001 out_put_key:
2002         put_futex_key(fshared, &q.key);
2003 out:
2004         if (to)
2005                 destroy_hrtimer_on_stack(&to->timer);
2006         return ret != -EINTR ? ret : -ERESTARTNOINTR;
2007
2008 uaddr_faulted:
2009         queue_unlock(&q, hb);
2010
2011         ret = fault_in_user_writeable(uaddr);
2012         if (ret)
2013                 goto out_put_key;
2014
2015         if (!fshared)
2016                 goto retry_private;
2017
2018         put_futex_key(fshared, &q.key);
2019         goto retry;
2020 }
2021
2022 /*
2023  * Userspace attempted a TID -> 0 atomic transition, and failed.
2024  * This is the in-kernel slowpath: we look up the PI state (if any),
2025  * and do the rt-mutex unlock.
2026  */
2027 static int futex_unlock_pi(u32 __user *uaddr, int fshared)
2028 {
2029         struct futex_hash_bucket *hb;
2030         struct futex_q *this, *next;
2031         u32 uval;
2032         struct plist_head *head;
2033         union futex_key key = FUTEX_KEY_INIT;
2034         int ret;
2035
2036 retry:
2037         if (get_user(uval, uaddr))
2038                 return -EFAULT;
2039         /*
2040          * We release only a lock we actually own:
2041          */
2042         if ((uval & FUTEX_TID_MASK) != task_pid_vnr(current))
2043                 return -EPERM;
2044
2045         ret = get_futex_key(uaddr, fshared, &key);
2046         if (unlikely(ret != 0))
2047                 goto out;
2048
2049         hb = hash_futex(&key);
2050         spin_lock(&hb->lock);
2051
2052         /*
2053          * To avoid races, try to do the TID -> 0 atomic transition
2054          * again. If it succeeds then we can return without waking
2055          * anyone else up:
2056          */
2057         if (!(uval & FUTEX_OWNER_DIED))
2058                 uval = cmpxchg_futex_value_locked(uaddr, task_pid_vnr(current), 0);
2059
2060
2061         if (unlikely(uval == -EFAULT))
2062                 goto pi_faulted;
2063         /*
2064          * Rare case: we managed to release the lock atomically,
2065          * no need to wake anyone else up:
2066          */
2067         if (unlikely(uval == task_pid_vnr(current)))
2068                 goto out_unlock;
2069
2070         /*
2071          * Ok, other tasks may need to be woken up - check waiters
2072          * and do the wakeup if necessary:
2073          */
2074         head = &hb->chain;
2075
2076         plist_for_each_entry_safe(this, next, head, list) {
2077                 if (!match_futex (&this->key, &key))
2078                         continue;
2079                 ret = wake_futex_pi(uaddr, uval, this);
2080                 /*
2081                  * The atomic access to the futex value
2082                  * generated a pagefault, so retry the
2083                  * user-access and the wakeup:
2084                  */
2085                 if (ret == -EFAULT)
2086                         goto pi_faulted;
2087                 goto out_unlock;
2088         }
2089         /*
2090          * No waiters - kernel unlocks the futex:
2091          */
2092         if (!(uval & FUTEX_OWNER_DIED)) {
2093                 ret = unlock_futex_pi(uaddr, uval);
2094                 if (ret == -EFAULT)
2095                         goto pi_faulted;
2096         }
2097
2098 out_unlock:
2099         spin_unlock(&hb->lock);
2100         put_futex_key(fshared, &key);
2101
2102 out:
2103         return ret;
2104
2105 pi_faulted:
2106         spin_unlock(&hb->lock);
2107         put_futex_key(fshared, &key);
2108
2109         ret = fault_in_user_writeable(uaddr);
2110         if (!ret)
2111                 goto retry;
2112
2113         return ret;
2114 }
2115
2116 /**
2117  * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2118  * @hb:         the hash_bucket futex_q was original enqueued on
2119  * @q:          the futex_q woken while waiting to be requeued
2120  * @key2:       the futex_key of the requeue target futex
2121  * @timeout:    the timeout associated with the wait (NULL if none)
2122  *
2123  * Detect if the task was woken on the initial futex as opposed to the requeue
2124  * target futex.  If so, determine if it was a timeout or a signal that caused
2125  * the wakeup and return the appropriate error code to the caller.  Must be
2126  * called with the hb lock held.
2127  *
2128  * Returns
2129  *  0 - no early wakeup detected
2130  * <0 - -ETIMEDOUT or -ERESTARTNOINTR
2131  */
2132 static inline
2133 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2134                                    struct futex_q *q, union futex_key *key2,
2135                                    struct hrtimer_sleeper *timeout)
2136 {
2137         int ret = 0;
2138
2139         /*
2140          * With the hb lock held, we avoid races while we process the wakeup.
2141          * We only need to hold hb (and not hb2) to ensure atomicity as the
2142          * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2143          * It can't be requeued from uaddr2 to something else since we don't
2144          * support a PI aware source futex for requeue.
2145          */
2146         if (!match_futex(&q->key, key2)) {
2147                 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2148                 /*
2149                  * We were woken prior to requeue by a timeout or a signal.
2150                  * Unqueue the futex_q and determine which it was.
2151                  */
2152                 plist_del(&q->list, &q->list.plist);
2153
2154                 /* Handle spurious wakeups gracefully */
2155                 ret = -EWOULDBLOCK;
2156                 if (timeout && !timeout->task)
2157                         ret = -ETIMEDOUT;
2158                 else if (signal_pending(current))
2159                         ret = -ERESTARTNOINTR;
2160         }
2161         return ret;
2162 }
2163
2164 /**
2165  * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2166  * @uaddr:      the futex we initially wait on (non-pi)
2167  * @fshared:    whether the futexes are shared (1) or not (0).  They must be
2168  *              the same type, no requeueing from private to shared, etc.
2169  * @val:        the expected value of uaddr
2170  * @abs_time:   absolute timeout
2171  * @bitset:     32 bit wakeup bitset set by userspace, defaults to all
2172  * @clockrt:    whether to use CLOCK_REALTIME (1) or CLOCK_MONOTONIC (0)
2173  * @uaddr2:     the pi futex we will take prior to returning to user-space
2174  *
2175  * The caller will wait on uaddr and will be requeued by futex_requeue() to
2176  * uaddr2 which must be PI aware.  Normal wakeup will wake on uaddr2 and
2177  * complete the acquisition of the rt_mutex prior to returning to userspace.
2178  * This ensures the rt_mutex maintains an owner when it has waiters; without
2179  * one, the pi logic wouldn't know which task to boost/deboost, if there was a
2180  * need to.
2181  *
2182  * We call schedule in futex_wait_queue_me() when we enqueue and return there
2183  * via the following:
2184  * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2185  * 2) wakeup on uaddr2 after a requeue
2186  * 3) signal
2187  * 4) timeout
2188  *
2189  * If 3, cleanup and return -ERESTARTNOINTR.
2190  *
2191  * If 2, we may then block on trying to take the rt_mutex and return via:
2192  * 5) successful lock
2193  * 6) signal
2194  * 7) timeout
2195  * 8) other lock acquisition failure
2196  *
2197  * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2198  *
2199  * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2200  *
2201  * Returns:
2202  *  0 - On success
2203  * <0 - On error
2204  */
2205 static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
2206                                  u32 val, ktime_t *abs_time, u32 bitset,
2207                                  int clockrt, u32 __user *uaddr2)
2208 {
2209         struct hrtimer_sleeper timeout, *to = NULL;
2210         struct rt_mutex_waiter rt_waiter;
2211         struct rt_mutex *pi_mutex = NULL;
2212         struct futex_hash_bucket *hb;
2213         union futex_key key2;
2214         struct futex_q q;
2215         int res, ret;
2216
2217         if (!bitset)
2218                 return -EINVAL;
2219
2220         if (abs_time) {
2221                 to = &timeout;
2222                 hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
2223                                       CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
2224                 hrtimer_init_sleeper(to, current);
2225                 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2226                                              current->timer_slack_ns);
2227         }
2228
2229         /*
2230          * The waiter is allocated on our stack, manipulated by the requeue
2231          * code while we sleep on uaddr.
2232          */
2233         debug_rt_mutex_init_waiter(&rt_waiter);
2234         rt_waiter.task = NULL;
2235
2236         key2 = FUTEX_KEY_INIT;
2237         ret = get_futex_key(uaddr2, fshared, &key2);
2238         if (unlikely(ret != 0))
2239                 goto out;
2240
2241         q.pi_state = NULL;
2242         q.bitset = bitset;
2243         q.rt_waiter = &rt_waiter;
2244         q.requeue_pi_key = &key2;
2245
2246         /* Prepare to wait on uaddr. */
2247         ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
2248         if (ret)
2249                 goto out_key2;
2250
2251         /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2252         futex_wait_queue_me(hb, &q, to);
2253
2254         spin_lock(&hb->lock);
2255         ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2256         spin_unlock(&hb->lock);
2257         if (ret)
2258                 goto out_put_keys;
2259
2260         /*
2261          * In order for us to be here, we know our q.key == key2, and since
2262          * we took the hb->lock above, we also know that futex_requeue() has
2263          * completed and we no longer have to concern ourselves with a wakeup
2264          * race with the atomic proxy lock acquition by the requeue code.
2265          */
2266
2267         /* Check if the requeue code acquired the second futex for us. */
2268         if (!q.rt_waiter) {
2269                 /*
2270                  * Got the lock. We might not be the anticipated owner if we
2271                  * did a lock-steal - fix up the PI-state in that case.
2272                  */
2273                 if (q.pi_state && (q.pi_state->owner != current)) {
2274                         spin_lock(q.lock_ptr);
2275                         ret = fixup_pi_state_owner(uaddr2, &q, current,
2276                                                    fshared);
2277                         spin_unlock(q.lock_ptr);
2278                 }
2279         } else {
2280                 /*
2281                  * We have been woken up by futex_unlock_pi(), a timeout, or a
2282                  * signal.  futex_unlock_pi() will not destroy the lock_ptr nor
2283                  * the pi_state.
2284                  */
2285                 WARN_ON(!&q.pi_state);
2286                 pi_mutex = &q.pi_state->pi_mutex;
2287                 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
2288                 debug_rt_mutex_free_waiter(&rt_waiter);
2289
2290                 spin_lock(q.lock_ptr);
2291                 /*
2292                  * Fixup the pi_state owner and possibly acquire the lock if we
2293                  * haven't already.
2294                  */
2295                 res = fixup_owner(uaddr2, fshared, &q, !ret);
2296                 /*
2297                  * If fixup_owner() returned an error, proprogate that.  If it
2298                  * acquired the lock, clear -ETIMEDOUT or -EINTR.
2299                  */
2300                 if (res)
2301                         ret = (res < 0) ? res : 0;
2302
2303                 /* Unqueue and drop the lock. */
2304                 unqueue_me_pi(&q);
2305         }
2306
2307         /*
2308          * If fixup_pi_state_owner() faulted and was unable to handle the
2309          * fault, unlock the rt_mutex and return the fault to userspace.
2310          */
2311         if (ret == -EFAULT) {
2312                 if (rt_mutex_owner(pi_mutex) == current)
2313                         rt_mutex_unlock(pi_mutex);
2314         } else if (ret == -EINTR) {
2315                 /*
2316                  * We've already been requeued, but cannot restart by calling
2317                  * futex_lock_pi() directly. We could restart this syscall, but
2318                  * it would detect that the user space "val" changed and return
2319                  * -EWOULDBLOCK.  Save the overhead of the restart and return
2320                  * -EWOULDBLOCK directly.
2321                  */
2322                 ret = -EWOULDBLOCK;
2323         }
2324
2325 out_put_keys:
2326         put_futex_key(fshared, &q.key);
2327 out_key2:
2328         put_futex_key(fshared, &key2);
2329
2330 out:
2331         if (to) {
2332                 hrtimer_cancel(&to->timer);
2333                 destroy_hrtimer_on_stack(&to->timer);
2334         }
2335         return ret;
2336 }
2337
2338 /*
2339  * Support for robust futexes: the kernel cleans up held futexes at
2340  * thread exit time.
2341  *
2342  * Implementation: user-space maintains a per-thread list of locks it
2343  * is holding. Upon do_exit(), the kernel carefully walks this list,
2344  * and marks all locks that are owned by this thread with the
2345  * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2346  * always manipulated with the lock held, so the list is private and
2347  * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2348  * field, to allow the kernel to clean up if the thread dies after
2349  * acquiring the lock, but just before it could have added itself to
2350  * the list. There can only be one such pending lock.
2351  */
2352
2353 /**
2354  * sys_set_robust_list() - Set the robust-futex list head of a task
2355  * @head:       pointer to the list-head
2356  * @len:        length of the list-head, as userspace expects
2357  */
2358 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2359                 size_t, len)
2360 {
2361         if (!futex_cmpxchg_enabled)
2362                 return -ENOSYS;
2363         /*
2364          * The kernel knows only one size for now:
2365          */
2366         if (unlikely(len != sizeof(*head)))
2367                 return -EINVAL;
2368
2369         current->robust_list = head;
2370
2371         return 0;
2372 }
2373
2374 /**
2375  * sys_get_robust_list() - Get the robust-futex list head of a task
2376  * @pid:        pid of the process [zero for current task]
2377  * @head_ptr:   pointer to a list-head pointer, the kernel fills it in
2378  * @len_ptr:    pointer to a length field, the kernel fills in the header size
2379  */
2380 SYSCALL_DEFINE3(get_robust_list, int, pid,
2381                 struct robust_list_head __user * __user *, head_ptr,
2382                 size_t __user *, len_ptr)
2383 {
2384         struct robust_list_head __user *head;
2385         unsigned long ret;
2386         const struct cred *cred = current_cred(), *pcred;
2387
2388         if (!futex_cmpxchg_enabled)
2389                 return -ENOSYS;
2390
2391         if (!pid)
2392                 head = current->robust_list;
2393         else {
2394                 struct task_struct *p;
2395
2396                 ret = -ESRCH;
2397                 rcu_read_lock();
2398                 p = find_task_by_vpid(pid);
2399                 if (!p)
2400                         goto err_unlock;
2401                 ret = -EPERM;
2402                 pcred = __task_cred(p);
2403                 if (cred->euid != pcred->euid &&
2404                     cred->euid != pcred->uid &&
2405                     !capable(CAP_SYS_PTRACE))
2406                         goto err_unlock;
2407                 head = p->robust_list;
2408                 rcu_read_unlock();
2409         }
2410
2411         if (put_user(sizeof(*head), len_ptr))
2412                 return -EFAULT;
2413         return put_user(head, head_ptr);
2414
2415 err_unlock:
2416         rcu_read_unlock();
2417
2418         return ret;
2419 }
2420
2421 /*
2422  * Process a futex-list entry, check whether it's owned by the
2423  * dying task, and do notification if so:
2424  */
2425 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
2426 {
2427         u32 uval, nval, mval;
2428
2429 retry:
2430         if (get_user(uval, uaddr))
2431                 return -1;
2432
2433         if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
2434                 /*
2435                  * Ok, this dying thread is truly holding a futex
2436                  * of interest. Set the OWNER_DIED bit atomically
2437                  * via cmpxchg, and if the value had FUTEX_WAITERS
2438                  * set, wake up a waiter (if any). (We have to do a
2439                  * futex_wake() even if OWNER_DIED is already set -
2440                  * to handle the rare but possible case of recursive
2441                  * thread-death.) The rest of the cleanup is done in
2442                  * userspace.
2443                  */
2444                 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
2445                 nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
2446
2447                 if (nval == -EFAULT)
2448                         return -1;
2449
2450                 if (nval != uval)
2451                         goto retry;
2452
2453                 /*
2454                  * Wake robust non-PI futexes here. The wakeup of
2455                  * PI futexes happens in exit_pi_state():
2456                  */
2457                 if (!pi && (uval & FUTEX_WAITERS))
2458                         futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
2459         }
2460         return 0;
2461 }
2462
2463 /*
2464  * Fetch a robust-list pointer. Bit 0 signals PI futexes:
2465  */
2466 static inline int fetch_robust_entry(struct robust_list __user **entry,
2467                                      struct robust_list __user * __user *head,
2468                                      unsigned int *pi)
2469 {
2470         unsigned long uentry;
2471
2472         if (get_user(uentry, (unsigned long __user *)head))
2473                 return -EFAULT;
2474
2475         *entry = (void __user *)(uentry & ~1UL);
2476         *pi = uentry & 1;
2477
2478         return 0;
2479 }
2480
2481 /*
2482  * Walk curr->robust_list (very carefully, it's a userspace list!)
2483  * and mark any locks found there dead, and notify any waiters.
2484  *
2485  * We silently return on any sign of list-walking problem.
2486  */
2487 void exit_robust_list(struct task_struct *curr)
2488 {
2489         struct robust_list_head __user *head = curr->robust_list;
2490         struct robust_list __user *entry, *next_entry, *pending;
2491         unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
2492         unsigned long futex_offset;
2493         int rc;
2494
2495         if (!futex_cmpxchg_enabled)
2496                 return;
2497
2498         /*
2499          * Fetch the list head (which was registered earlier, via
2500          * sys_set_robust_list()):
2501          */
2502         if (fetch_robust_entry(&entry, &head->list.next, &pi))
2503                 return;
2504         /*
2505          * Fetch the relative futex offset:
2506          */
2507         if (get_user(futex_offset, &head->futex_offset))
2508                 return;
2509         /*
2510          * Fetch any possibly pending lock-add first, and handle it
2511          * if it exists:
2512          */
2513         if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
2514                 return;
2515
2516         next_entry = NULL;      /* avoid warning with gcc */
2517         while (entry != &head->list) {
2518                 /*
2519                  * Fetch the next entry in the list before calling
2520                  * handle_futex_death:
2521                  */
2522                 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
2523                 /*
2524                  * A pending lock might already be on the list, so
2525                  * don't process it twice:
2526                  */
2527                 if (entry != pending)
2528                         if (handle_futex_death((void __user *)entry + futex_offset,
2529                                                 curr, pi))
2530                                 return;
2531                 if (rc)
2532                         return;
2533                 entry = next_entry;
2534                 pi = next_pi;
2535                 /*
2536                  * Avoid excessively long or circular lists:
2537                  */
2538                 if (!--limit)
2539                         break;
2540
2541                 cond_resched();
2542         }
2543
2544         if (pending)
2545                 handle_futex_death((void __user *)pending + futex_offset,
2546                                    curr, pip);
2547 }
2548
2549 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
2550                 u32 __user *uaddr2, u32 val2, u32 val3)
2551 {
2552         int clockrt, ret = -ENOSYS;
2553         int cmd = op & FUTEX_CMD_MASK;
2554         int fshared = 0;
2555
2556         if (!(op & FUTEX_PRIVATE_FLAG))
2557                 fshared = 1;
2558
2559         clockrt = op & FUTEX_CLOCK_REALTIME;
2560         if (clockrt && cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
2561                 return -ENOSYS;
2562
2563         switch (cmd) {
2564         case FUTEX_WAIT:
2565                 val3 = FUTEX_BITSET_MATCH_ANY;
2566         case FUTEX_WAIT_BITSET:
2567                 ret = futex_wait(uaddr, fshared, val, timeout, val3, clockrt);
2568                 break;
2569         case FUTEX_WAKE:
2570                 val3 = FUTEX_BITSET_MATCH_ANY;
2571         case FUTEX_WAKE_BITSET:
2572                 ret = futex_wake(uaddr, fshared, val, val3);
2573                 break;
2574         case FUTEX_REQUEUE:
2575                 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL, 0);
2576                 break;
2577         case FUTEX_CMP_REQUEUE:
2578                 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
2579                                     0);
2580                 break;
2581         case FUTEX_WAKE_OP:
2582                 ret = futex_wake_op(uaddr, fshared, uaddr2, val, val2, val3);
2583                 break;
2584         case FUTEX_LOCK_PI:
2585                 if (futex_cmpxchg_enabled)
2586                         ret = futex_lock_pi(uaddr, fshared, val, timeout, 0);
2587                 break;
2588         case FUTEX_UNLOCK_PI:
2589                 if (futex_cmpxchg_enabled)
2590                         ret = futex_unlock_pi(uaddr, fshared);
2591                 break;
2592         case FUTEX_TRYLOCK_PI:
2593                 if (futex_cmpxchg_enabled)
2594                         ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1);
2595                 break;
2596         case FUTEX_WAIT_REQUEUE_PI:
2597                 val3 = FUTEX_BITSET_MATCH_ANY;
2598                 ret = futex_wait_requeue_pi(uaddr, fshared, val, timeout, val3,
2599                                             clockrt, uaddr2);
2600                 break;
2601         case FUTEX_CMP_REQUEUE_PI:
2602                 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
2603                                     1);
2604                 break;
2605         default:
2606                 ret = -ENOSYS;
2607         }
2608         return ret;
2609 }
2610
2611
2612 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
2613                 struct timespec __user *, utime, u32 __user *, uaddr2,
2614                 u32, val3)
2615 {
2616         struct timespec ts;
2617         ktime_t t, *tp = NULL;
2618         u32 val2 = 0;
2619         int cmd = op & FUTEX_CMD_MASK;
2620
2621         if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
2622                       cmd == FUTEX_WAIT_BITSET ||
2623                       cmd == FUTEX_WAIT_REQUEUE_PI)) {
2624                 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
2625                         return -EFAULT;
2626                 if (!timespec_valid(&ts))
2627                         return -EINVAL;
2628
2629                 t = timespec_to_ktime(ts);
2630                 if (cmd == FUTEX_WAIT)
2631                         t = ktime_add_safe(ktime_get(), t);
2632                 tp = &t;
2633         }
2634         /*
2635          * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
2636          * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
2637          */
2638         if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
2639             cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
2640                 val2 = (u32) (unsigned long) utime;
2641
2642         return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
2643 }
2644
2645 static int __init futex_init(void)
2646 {
2647         u32 curval;
2648         int i;
2649
2650         /*
2651          * This will fail and we want it. Some arch implementations do
2652          * runtime detection of the futex_atomic_cmpxchg_inatomic()
2653          * functionality. We want to know that before we call in any
2654          * of the complex code paths. Also we want to prevent
2655          * registration of robust lists in that case. NULL is
2656          * guaranteed to fault and we get -EFAULT on functional
2657          * implementation, the non-functional ones will return
2658          * -ENOSYS.
2659          */
2660         curval = cmpxchg_futex_value_locked(NULL, 0, 0);
2661         if (curval == -EFAULT)
2662                 futex_cmpxchg_enabled = 1;
2663
2664         for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
2665                 plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock);
2666                 spin_lock_init(&futex_queues[i].lock);
2667         }
2668
2669         return 0;
2670 }
2671 __initcall(futex_init);