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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 ihold(key->shared.inode);
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 hb = hash_futex(&q->key);
1371 q->lock_ptr = &hb->lock;
1372
1373 spin_lock(&hb->lock);
1374 return hb;
1375 }
1376
1377 static inline void
1378 queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
1379 __releases(&hb->lock)
1380 {
1381 spin_unlock(&hb->lock);
1382 }
1383
1384 /**
1385 * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1386 * @q: The futex_q to enqueue
1387 * @hb: The destination hash bucket
1388 *
1389 * The hb->lock must be held by the caller, and is released here. A call to
1390 * queue_me() is typically paired with exactly one call to unqueue_me(). The
1391 * exceptions involve the PI related operations, which may use unqueue_me_pi()
1392 * or nothing if the unqueue is done as part of the wake process and the unqueue
1393 * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1394 * an example).
1395 */
1396 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1397 __releases(&hb->lock)
1398 {
1399 int prio;
1400
1401 /*
1402 * The priority used to register this element is
1403 * - either the real thread-priority for the real-time threads
1404 * (i.e. threads with a priority lower than MAX_RT_PRIO)
1405 * - or MAX_RT_PRIO for non-RT threads.
1406 * Thus, all RT-threads are woken first in priority order, and
1407 * the others are woken last, in FIFO order.
1408 */
1409 prio = min(current->normal_prio, MAX_RT_PRIO);
1410
1411 plist_node_init(&q->list, prio);
1412 #ifdef CONFIG_DEBUG_PI_LIST
1413 q->list.plist.spinlock = &hb->lock;
1414 #endif
1415 plist_add(&q->list, &hb->chain);
1416 q->task = current;
1417 spin_unlock(&hb->lock);
1418 }
1419
1420 /**
1421 * unqueue_me() - Remove the futex_q from its futex_hash_bucket
1422 * @q: The futex_q to unqueue
1423 *
1424 * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
1425 * be paired with exactly one earlier call to queue_me().
1426 *
1427 * Returns:
1428 * 1 - if the futex_q was still queued (and we removed unqueued it)
1429 * 0 - if the futex_q was already removed by the waking thread
1430 */
1431 static int unqueue_me(struct futex_q *q)
1432 {
1433 spinlock_t *lock_ptr;
1434 int ret = 0;
1435
1436 /* In the common case we don't take the spinlock, which is nice. */
1437 retry:
1438 lock_ptr = q->lock_ptr;
1439 barrier();
1440 if (lock_ptr != NULL) {
1441 spin_lock(lock_ptr);
1442 /*
1443 * q->lock_ptr can change between reading it and
1444 * spin_lock(), causing us to take the wrong lock. This
1445 * corrects the race condition.
1446 *
1447 * Reasoning goes like this: if we have the wrong lock,
1448 * q->lock_ptr must have changed (maybe several times)
1449 * between reading it and the spin_lock(). It can
1450 * change again after the spin_lock() but only if it was
1451 * already changed before the spin_lock(). It cannot,
1452 * however, change back to the original value. Therefore
1453 * we can detect whether we acquired the correct lock.
1454 */
1455 if (unlikely(lock_ptr != q->lock_ptr)) {
1456 spin_unlock(lock_ptr);
1457 goto retry;
1458 }
1459 WARN_ON(plist_node_empty(&q->list));
1460 plist_del(&q->list, &q->list.plist);
1461
1462 BUG_ON(q->pi_state);
1463
1464 spin_unlock(lock_ptr);
1465 ret = 1;
1466 }
1467
1468 drop_futex_key_refs(&q->key);
1469 return ret;
1470 }
1471
1472 /*
1473 * PI futexes can not be requeued and must remove themself from the
1474 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1475 * and dropped here.
1476 */
1477 static void unqueue_me_pi(struct futex_q *q)
1478 __releases(q->lock_ptr)
1479 {
1480 WARN_ON(plist_node_empty(&q->list));
1481 plist_del(&q->list, &q->list.plist);
1482
1483 BUG_ON(!q->pi_state);
1484 free_pi_state(q->pi_state);
1485 q->pi_state = NULL;
1486
1487 spin_unlock(q->lock_ptr);
1488 }
1489
1490 /*
1491 * Fixup the pi_state owner with the new owner.
1492 *
1493 * Must be called with hash bucket lock held and mm->sem held for non
1494 * private futexes.
1495 */
1496 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1497 struct task_struct *newowner, int fshared)
1498 {
1499 u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
1500 struct futex_pi_state *pi_state = q->pi_state;
1501 struct task_struct *oldowner = pi_state->owner;
1502 u32 uval, curval, newval;
1503 int ret;
1504
1505 /* Owner died? */
1506 if (!pi_state->owner)
1507 newtid |= FUTEX_OWNER_DIED;
1508
1509 /*
1510 * We are here either because we stole the rtmutex from the
1511 * pending owner or we are the pending owner which failed to
1512 * get the rtmutex. We have to replace the pending owner TID
1513 * in the user space variable. This must be atomic as we have
1514 * to preserve the owner died bit here.
1515 *
1516 * Note: We write the user space value _before_ changing the pi_state
1517 * because we can fault here. Imagine swapped out pages or a fork
1518 * that marked all the anonymous memory readonly for cow.
1519 *
1520 * Modifying pi_state _before_ the user space value would
1521 * leave the pi_state in an inconsistent state when we fault
1522 * here, because we need to drop the hash bucket lock to
1523 * handle the fault. This might be observed in the PID check
1524 * in lookup_pi_state.
1525 */
1526 retry:
1527 if (get_futex_value_locked(&uval, uaddr))
1528 goto handle_fault;
1529
1530 while (1) {
1531 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1532
1533 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
1534
1535 if (curval == -EFAULT)
1536 goto handle_fault;
1537 if (curval == uval)
1538 break;
1539 uval = curval;
1540 }
1541
1542 /*
1543 * We fixed up user space. Now we need to fix the pi_state
1544 * itself.
1545 */
1546 if (pi_state->owner != NULL) {
1547 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1548 WARN_ON(list_empty(&pi_state->list));
1549 list_del_init(&pi_state->list);
1550 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1551 }
1552
1553 pi_state->owner = newowner;
1554
1555 raw_spin_lock_irq(&newowner->pi_lock);
1556 WARN_ON(!list_empty(&pi_state->list));
1557 list_add(&pi_state->list, &newowner->pi_state_list);
1558 raw_spin_unlock_irq(&newowner->pi_lock);
1559 return 0;
1560
1561 /*
1562 * To handle the page fault we need to drop the hash bucket
1563 * lock here. That gives the other task (either the pending
1564 * owner itself or the task which stole the rtmutex) the
1565 * chance to try the fixup of the pi_state. So once we are
1566 * back from handling the fault we need to check the pi_state
1567 * after reacquiring the hash bucket lock and before trying to
1568 * do another fixup. When the fixup has been done already we
1569 * simply return.
1570 */
1571 handle_fault:
1572 spin_unlock(q->lock_ptr);
1573
1574 ret = fault_in_user_writeable(uaddr);
1575
1576 spin_lock(q->lock_ptr);
1577
1578 /*
1579 * Check if someone else fixed it for us:
1580 */
1581 if (pi_state->owner != oldowner)
1582 return 0;
1583
1584 if (ret)
1585 return ret;
1586
1587 goto retry;
1588 }
1589
1590 /*
1591 * In case we must use restart_block to restart a futex_wait,
1592 * we encode in the 'flags' shared capability
1593 */
1594 #define FLAGS_SHARED 0x01
1595 #define FLAGS_CLOCKRT 0x02
1596 #define FLAGS_HAS_TIMEOUT 0x04
1597
1598 static long futex_wait_restart(struct restart_block *restart);
1599
1600 /**
1601 * fixup_owner() - Post lock pi_state and corner case management
1602 * @uaddr: user address of the futex
1603 * @fshared: whether the futex is shared (1) or not (0)
1604 * @q: futex_q (contains pi_state and access to the rt_mutex)
1605 * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
1606 *
1607 * After attempting to lock an rt_mutex, this function is called to cleanup
1608 * the pi_state owner as well as handle race conditions that may allow us to
1609 * acquire the lock. Must be called with the hb lock held.
1610 *
1611 * Returns:
1612 * 1 - success, lock taken
1613 * 0 - success, lock not taken
1614 * <0 - on error (-EFAULT)
1615 */
1616 static int fixup_owner(u32 __user *uaddr, int fshared, struct futex_q *q,
1617 int locked)
1618 {
1619 struct task_struct *owner;
1620 int ret = 0;
1621
1622 if (locked) {
1623 /*
1624 * Got the lock. We might not be the anticipated owner if we
1625 * did a lock-steal - fix up the PI-state in that case:
1626 */
1627 if (q->pi_state->owner != current)
1628 ret = fixup_pi_state_owner(uaddr, q, current, fshared);
1629 goto out;
1630 }
1631
1632 /*
1633 * Catch the rare case, where the lock was released when we were on the
1634 * way back before we locked the hash bucket.
1635 */
1636 if (q->pi_state->owner == current) {
1637 /*
1638 * Try to get the rt_mutex now. This might fail as some other
1639 * task acquired the rt_mutex after we removed ourself from the
1640 * rt_mutex waiters list.
1641 */
1642 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
1643 locked = 1;
1644 goto out;
1645 }
1646
1647 /*
1648 * pi_state is incorrect, some other task did a lock steal and
1649 * we returned due to timeout or signal without taking the
1650 * rt_mutex. Too late. We can access the rt_mutex_owner without
1651 * locking, as the other task is now blocked on the hash bucket
1652 * lock. Fix the state up.
1653 */
1654 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
1655 ret = fixup_pi_state_owner(uaddr, q, owner, fshared);
1656 goto out;
1657 }
1658
1659 /*
1660 * Paranoia check. If we did not take the lock, then we should not be
1661 * the owner, nor the pending owner, of the rt_mutex.
1662 */
1663 if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
1664 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
1665 "pi-state %p\n", ret,
1666 q->pi_state->pi_mutex.owner,
1667 q->pi_state->owner);
1668
1669 out:
1670 return ret ? ret : locked;
1671 }
1672
1673 /**
1674 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
1675 * @hb: the futex hash bucket, must be locked by the caller
1676 * @q: the futex_q to queue up on
1677 * @timeout: the prepared hrtimer_sleeper, or null for no timeout
1678 */
1679 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
1680 struct hrtimer_sleeper *timeout)
1681 {
1682 /*
1683 * The task state is guaranteed to be set before another task can
1684 * wake it. set_current_state() is implemented using set_mb() and
1685 * queue_me() calls spin_unlock() upon completion, both serializing
1686 * access to the hash list and forcing another memory barrier.
1687 */
1688 set_current_state(TASK_INTERRUPTIBLE);
1689 queue_me(q, hb);
1690
1691 /* Arm the timer */
1692 if (timeout) {
1693 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1694 if (!hrtimer_active(&timeout->timer))
1695 timeout->task = NULL;
1696 }
1697
1698 /*
1699 * If we have been removed from the hash list, then another task
1700 * has tried to wake us, and we can skip the call to schedule().
1701 */
1702 if (likely(!plist_node_empty(&q->list))) {
1703 /*
1704 * If the timer has already expired, current will already be
1705 * flagged for rescheduling. Only call schedule if there
1706 * is no timeout, or if it has yet to expire.
1707 */
1708 if (!timeout || timeout->task)
1709 schedule();
1710 }
1711 __set_current_state(TASK_RUNNING);
1712 }
1713
1714 /**
1715 * futex_wait_setup() - Prepare to wait on a futex
1716 * @uaddr: the futex userspace address
1717 * @val: the expected value
1718 * @fshared: whether the futex is shared (1) or not (0)
1719 * @q: the associated futex_q
1720 * @hb: storage for hash_bucket pointer to be returned to caller
1721 *
1722 * Setup the futex_q and locate the hash_bucket. Get the futex value and
1723 * compare it with the expected value. Handle atomic faults internally.
1724 * Return with the hb lock held and a q.key reference on success, and unlocked
1725 * with no q.key reference on failure.
1726 *
1727 * Returns:
1728 * 0 - uaddr contains val and hb has been locked
1729 * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlcoked
1730 */
1731 static int futex_wait_setup(u32 __user *uaddr, u32 val, int fshared,
1732 struct futex_q *q, struct futex_hash_bucket **hb)
1733 {
1734 u32 uval;
1735 int ret;
1736
1737 /*
1738 * Access the page AFTER the hash-bucket is locked.
1739 * Order is important:
1740 *
1741 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1742 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
1743 *
1744 * The basic logical guarantee of a futex is that it blocks ONLY
1745 * if cond(var) is known to be true at the time of blocking, for
1746 * any cond. If we queued after testing *uaddr, that would open
1747 * a race condition where we could block indefinitely with
1748 * cond(var) false, which would violate the guarantee.
1749 *
1750 * A consequence is that futex_wait() can return zero and absorb
1751 * a wakeup when *uaddr != val on entry to the syscall. This is
1752 * rare, but normal.
1753 */
1754 retry:
1755 q->key = FUTEX_KEY_INIT;
1756 ret = get_futex_key(uaddr, fshared, &q->key);
1757 if (unlikely(ret != 0))
1758 return ret;
1759
1760 retry_private:
1761 *hb = queue_lock(q);
1762
1763 ret = get_futex_value_locked(&uval, uaddr);
1764
1765 if (ret) {
1766 queue_unlock(q, *hb);
1767
1768 ret = get_user(uval, uaddr);
1769 if (ret)
1770 goto out;
1771
1772 if (!fshared)
1773 goto retry_private;
1774
1775 put_futex_key(fshared, &q->key);
1776 goto retry;
1777 }
1778
1779 if (uval != val) {
1780 queue_unlock(q, *hb);
1781 ret = -EWOULDBLOCK;
1782 }
1783
1784 out:
1785 if (ret)
1786 put_futex_key(fshared, &q->key);
1787 return ret;
1788 }
1789
1790 static int futex_wait(u32 __user *uaddr, int fshared,
1791 u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
1792 {
1793 struct hrtimer_sleeper timeout, *to = NULL;
1794 struct restart_block *restart;
1795 struct futex_hash_bucket *hb;
1796 struct futex_q q;
1797 int ret;
1798
1799 if (!bitset)
1800 return -EINVAL;
1801
1802 q.pi_state = NULL;
1803 q.bitset = bitset;
1804 q.rt_waiter = NULL;
1805 q.requeue_pi_key = NULL;
1806
1807 if (abs_time) {
1808 to = &timeout;
1809
1810 hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
1811 CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1812 hrtimer_init_sleeper(to, current);
1813 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
1814 current->timer_slack_ns);
1815 }
1816
1817 retry:
1818 /*
1819 * Prepare to wait on uaddr. On success, holds hb lock and increments
1820 * q.key refs.
1821 */
1822 ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
1823 if (ret)
1824 goto out;
1825
1826 /* queue_me and wait for wakeup, timeout, or a signal. */
1827 futex_wait_queue_me(hb, &q, to);
1828
1829 /* If we were woken (and unqueued), we succeeded, whatever. */
1830 ret = 0;
1831 /* unqueue_me() drops q.key ref */
1832 if (!unqueue_me(&q))
1833 goto out;
1834 ret = -ETIMEDOUT;
1835 if (to && !to->task)
1836 goto out;
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 goto retry;
1844
1845 ret = -ERESTARTSYS;
1846 if (!abs_time)
1847 goto out;
1848
1849 restart = &current_thread_info()->restart_block;
1850 restart->fn = futex_wait_restart;
1851 restart->futex.uaddr = uaddr;
1852 restart->futex.val = val;
1853 restart->futex.time = abs_time->tv64;
1854 restart->futex.bitset = bitset;
1855 restart->futex.flags = FLAGS_HAS_TIMEOUT;
1856
1857 if (fshared)
1858 restart->futex.flags |= FLAGS_SHARED;
1859 if (clockrt)
1860 restart->futex.flags |= FLAGS_CLOCKRT;
1861
1862 ret = -ERESTART_RESTARTBLOCK;
1863
1864 out:
1865 if (to) {
1866 hrtimer_cancel(&to->timer);
1867 destroy_hrtimer_on_stack(&to->timer);
1868 }
1869 return ret;
1870 }
1871
1872
1873 static long futex_wait_restart(struct restart_block *restart)
1874 {
1875 u32 __user *uaddr = restart->futex.uaddr;
1876 int fshared = 0;
1877 ktime_t t, *tp = NULL;
1878
1879 if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
1880 t.tv64 = restart->futex.time;
1881 tp = &t;
1882 }
1883 restart->fn = do_no_restart_syscall;
1884 if (restart->futex.flags & FLAGS_SHARED)
1885 fshared = 1;
1886 return (long)futex_wait(uaddr, fshared, restart->futex.val, tp,
1887 restart->futex.bitset,
1888 restart->futex.flags & FLAGS_CLOCKRT);
1889 }
1890
1891
1892 /*
1893 * Userspace tried a 0 -> TID atomic transition of the futex value
1894 * and failed. The kernel side here does the whole locking operation:
1895 * if there are waiters then it will block, it does PI, etc. (Due to
1896 * races the kernel might see a 0 value of the futex too.)
1897 */
1898 static int futex_lock_pi(u32 __user *uaddr, int fshared,
1899 int detect, ktime_t *time, int trylock)
1900 {
1901 struct hrtimer_sleeper timeout, *to = NULL;
1902 struct futex_hash_bucket *hb;
1903 struct futex_q q;
1904 int res, ret;
1905
1906 if (refill_pi_state_cache())
1907 return -ENOMEM;
1908
1909 if (time) {
1910 to = &timeout;
1911 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
1912 HRTIMER_MODE_ABS);
1913 hrtimer_init_sleeper(to, current);
1914 hrtimer_set_expires(&to->timer, *time);
1915 }
1916
1917 q.pi_state = NULL;
1918 q.rt_waiter = NULL;
1919 q.requeue_pi_key = NULL;
1920 retry:
1921 q.key = FUTEX_KEY_INIT;
1922 ret = get_futex_key(uaddr, fshared, &q.key);
1923 if (unlikely(ret != 0))
1924 goto out;
1925
1926 retry_private:
1927 hb = queue_lock(&q);
1928
1929 ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
1930 if (unlikely(ret)) {
1931 switch (ret) {
1932 case 1:
1933 /* We got the lock. */
1934 ret = 0;
1935 goto out_unlock_put_key;
1936 case -EFAULT:
1937 goto uaddr_faulted;
1938 case -EAGAIN:
1939 /*
1940 * Task is exiting and we just wait for the
1941 * exit to complete.
1942 */
1943 queue_unlock(&q, hb);
1944 put_futex_key(fshared, &q.key);
1945 cond_resched();
1946 goto retry;
1947 default:
1948 goto out_unlock_put_key;
1949 }
1950 }
1951
1952 /*
1953 * Only actually queue now that the atomic ops are done:
1954 */
1955 queue_me(&q, hb);
1956
1957 WARN_ON(!q.pi_state);
1958 /*
1959 * Block on the PI mutex:
1960 */
1961 if (!trylock)
1962 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
1963 else {
1964 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
1965 /* Fixup the trylock return value: */
1966 ret = ret ? 0 : -EWOULDBLOCK;
1967 }
1968
1969 spin_lock(q.lock_ptr);
1970 /*
1971 * Fixup the pi_state owner and possibly acquire the lock if we
1972 * haven't already.
1973 */
1974 res = fixup_owner(uaddr, fshared, &q, !ret);
1975 /*
1976 * If fixup_owner() returned an error, proprogate that. If it acquired
1977 * the lock, clear our -ETIMEDOUT or -EINTR.
1978 */
1979 if (res)
1980 ret = (res < 0) ? res : 0;
1981
1982 /*
1983 * If fixup_owner() faulted and was unable to handle the fault, unlock
1984 * it and return the fault to userspace.
1985 */
1986 if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
1987 rt_mutex_unlock(&q.pi_state->pi_mutex);
1988
1989 /* Unqueue and drop the lock */
1990 unqueue_me_pi(&q);
1991
1992 goto out_put_key;
1993
1994 out_unlock_put_key:
1995 queue_unlock(&q, hb);
1996
1997 out_put_key:
1998 put_futex_key(fshared, &q.key);
1999 out:
2000 if (to)
2001 destroy_hrtimer_on_stack(&to->timer);
2002 return ret != -EINTR ? ret : -ERESTARTNOINTR;
2003
2004 uaddr_faulted:
2005 queue_unlock(&q, hb);
2006
2007 ret = fault_in_user_writeable(uaddr);
2008 if (ret)
2009 goto out_put_key;
2010
2011 if (!fshared)
2012 goto retry_private;
2013
2014 put_futex_key(fshared, &q.key);
2015 goto retry;
2016 }
2017
2018 /*
2019 * Userspace attempted a TID -> 0 atomic transition, and failed.
2020 * This is the in-kernel slowpath: we look up the PI state (if any),
2021 * and do the rt-mutex unlock.
2022 */
2023 static int futex_unlock_pi(u32 __user *uaddr, int fshared)
2024 {
2025 struct futex_hash_bucket *hb;
2026 struct futex_q *this, *next;
2027 u32 uval;
2028 struct plist_head *head;
2029 union futex_key key = FUTEX_KEY_INIT;
2030 int ret;
2031
2032 retry:
2033 if (get_user(uval, uaddr))
2034 return -EFAULT;
2035 /*
2036 * We release only a lock we actually own:
2037 */
2038 if ((uval & FUTEX_TID_MASK) != task_pid_vnr(current))
2039 return -EPERM;
2040
2041 ret = get_futex_key(uaddr, fshared, &key);
2042 if (unlikely(ret != 0))
2043 goto out;
2044
2045 hb = hash_futex(&key);
2046 spin_lock(&hb->lock);
2047
2048 /*
2049 * To avoid races, try to do the TID -> 0 atomic transition
2050 * again. If it succeeds then we can return without waking
2051 * anyone else up:
2052 */
2053 if (!(uval & FUTEX_OWNER_DIED))
2054 uval = cmpxchg_futex_value_locked(uaddr, task_pid_vnr(current), 0);
2055
2056
2057 if (unlikely(uval == -EFAULT))
2058 goto pi_faulted;
2059 /*
2060 * Rare case: we managed to release the lock atomically,
2061 * no need to wake anyone else up:
2062 */
2063 if (unlikely(uval == task_pid_vnr(current)))
2064 goto out_unlock;
2065
2066 /*
2067 * Ok, other tasks may need to be woken up - check waiters
2068 * and do the wakeup if necessary:
2069 */
2070 head = &hb->chain;
2071
2072 plist_for_each_entry_safe(this, next, head, list) {
2073 if (!match_futex (&this->key, &key))
2074 continue;
2075 ret = wake_futex_pi(uaddr, uval, this);
2076 /*
2077 * The atomic access to the futex value
2078 * generated a pagefault, so retry the
2079 * user-access and the wakeup:
2080 */
2081 if (ret == -EFAULT)
2082 goto pi_faulted;
2083 goto out_unlock;
2084 }
2085 /*
2086 * No waiters - kernel unlocks the futex:
2087 */
2088 if (!(uval & FUTEX_OWNER_DIED)) {
2089 ret = unlock_futex_pi(uaddr, uval);
2090 if (ret == -EFAULT)
2091 goto pi_faulted;
2092 }
2093
2094 out_unlock:
2095 spin_unlock(&hb->lock);
2096 put_futex_key(fshared, &key);
2097
2098 out:
2099 return ret;
2100
2101 pi_faulted:
2102 spin_unlock(&hb->lock);
2103 put_futex_key(fshared, &key);
2104
2105 ret = fault_in_user_writeable(uaddr);
2106 if (!ret)
2107 goto retry;
2108
2109 return ret;
2110 }
2111
2112 /**
2113 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2114 * @hb: the hash_bucket futex_q was original enqueued on
2115 * @q: the futex_q woken while waiting to be requeued
2116 * @key2: the futex_key of the requeue target futex
2117 * @timeout: the timeout associated with the wait (NULL if none)
2118 *
2119 * Detect if the task was woken on the initial futex as opposed to the requeue
2120 * target futex. If so, determine if it was a timeout or a signal that caused
2121 * the wakeup and return the appropriate error code to the caller. Must be
2122 * called with the hb lock held.
2123 *
2124 * Returns
2125 * 0 - no early wakeup detected
2126 * <0 - -ETIMEDOUT or -ERESTARTNOINTR
2127 */
2128 static inline
2129 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2130 struct futex_q *q, union futex_key *key2,
2131 struct hrtimer_sleeper *timeout)
2132 {
2133 int ret = 0;
2134
2135 /*
2136 * With the hb lock held, we avoid races while we process the wakeup.
2137 * We only need to hold hb (and not hb2) to ensure atomicity as the
2138 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2139 * It can't be requeued from uaddr2 to something else since we don't
2140 * support a PI aware source futex for requeue.
2141 */
2142 if (!match_futex(&q->key, key2)) {
2143 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2144 /*
2145 * We were woken prior to requeue by a timeout or a signal.
2146 * Unqueue the futex_q and determine which it was.
2147 */
2148 plist_del(&q->list, &q->list.plist);
2149
2150 /* Handle spurious wakeups gracefully */
2151 ret = -EWOULDBLOCK;
2152 if (timeout && !timeout->task)
2153 ret = -ETIMEDOUT;
2154 else if (signal_pending(current))
2155 ret = -ERESTARTNOINTR;
2156 }
2157 return ret;
2158 }
2159
2160 /**
2161 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2162 * @uaddr: the futex we initially wait on (non-pi)
2163 * @fshared: whether the futexes are shared (1) or not (0). They must be
2164 * the same type, no requeueing from private to shared, etc.
2165 * @val: the expected value of uaddr
2166 * @abs_time: absolute timeout
2167 * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
2168 * @clockrt: whether to use CLOCK_REALTIME (1) or CLOCK_MONOTONIC (0)
2169 * @uaddr2: the pi futex we will take prior to returning to user-space
2170 *
2171 * The caller will wait on uaddr and will be requeued by futex_requeue() to
2172 * uaddr2 which must be PI aware. Normal wakeup will wake on uaddr2 and
2173 * complete the acquisition of the rt_mutex prior to returning to userspace.
2174 * This ensures the rt_mutex maintains an owner when it has waiters; without
2175 * one, the pi logic wouldn't know which task to boost/deboost, if there was a
2176 * need to.
2177 *
2178 * We call schedule in futex_wait_queue_me() when we enqueue and return there
2179 * via the following:
2180 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2181 * 2) wakeup on uaddr2 after a requeue
2182 * 3) signal
2183 * 4) timeout
2184 *
2185 * If 3, cleanup and return -ERESTARTNOINTR.
2186 *
2187 * If 2, we may then block on trying to take the rt_mutex and return via:
2188 * 5) successful lock
2189 * 6) signal
2190 * 7) timeout
2191 * 8) other lock acquisition failure
2192 *
2193 * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2194 *
2195 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2196 *
2197 * Returns:
2198 * 0 - On success
2199 * <0 - On error
2200 */
2201 static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
2202 u32 val, ktime_t *abs_time, u32 bitset,
2203 int clockrt, u32 __user *uaddr2)
2204 {
2205 struct hrtimer_sleeper timeout, *to = NULL;
2206 struct rt_mutex_waiter rt_waiter;
2207 struct rt_mutex *pi_mutex = NULL;
2208 struct futex_hash_bucket *hb;
2209 union futex_key key2;
2210 struct futex_q q;
2211 int res, ret;
2212
2213 if (!bitset)
2214 return -EINVAL;
2215
2216 if (abs_time) {
2217 to = &timeout;
2218 hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
2219 CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
2220 hrtimer_init_sleeper(to, current);
2221 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2222 current->timer_slack_ns);
2223 }
2224
2225 /*
2226 * The waiter is allocated on our stack, manipulated by the requeue
2227 * code while we sleep on uaddr.
2228 */
2229 debug_rt_mutex_init_waiter(&rt_waiter);
2230 rt_waiter.task = NULL;
2231
2232 key2 = FUTEX_KEY_INIT;
2233 ret = get_futex_key(uaddr2, fshared, &key2);
2234 if (unlikely(ret != 0))
2235 goto out;
2236
2237 q.pi_state = NULL;
2238 q.bitset = bitset;
2239 q.rt_waiter = &rt_waiter;
2240 q.requeue_pi_key = &key2;
2241
2242 /*
2243 * Prepare to wait on uaddr. On success, increments q.key (key1) ref
2244 * count.
2245 */
2246 ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
2247 if (ret)
2248 goto out_key2;
2249
2250 /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2251 futex_wait_queue_me(hb, &q, to);
2252
2253 spin_lock(&hb->lock);
2254 ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2255 spin_unlock(&hb->lock);
2256 if (ret)
2257 goto out_put_keys;
2258
2259 /*
2260 * In order for us to be here, we know our q.key == key2, and since
2261 * we took the hb->lock above, we also know that futex_requeue() has
2262 * completed and we no longer have to concern ourselves with a wakeup
2263 * race with the atomic proxy lock acquisition by the requeue code. The
2264 * futex_requeue dropped our key1 reference and incremented our key2
2265 * reference count.
2266 */
2267
2268 /* Check if the requeue code acquired the second futex for us. */
2269 if (!q.rt_waiter) {
2270 /*
2271 * Got the lock. We might not be the anticipated owner if we
2272 * did a lock-steal - fix up the PI-state in that case.
2273 */
2274 if (q.pi_state && (q.pi_state->owner != current)) {
2275 spin_lock(q.lock_ptr);
2276 ret = fixup_pi_state_owner(uaddr2, &q, current,
2277 fshared);
2278 spin_unlock(q.lock_ptr);
2279 }
2280 } else {
2281 /*
2282 * We have been woken up by futex_unlock_pi(), a timeout, or a
2283 * signal. futex_unlock_pi() will not destroy the lock_ptr nor
2284 * the pi_state.
2285 */
2286 WARN_ON(!&q.pi_state);
2287 pi_mutex = &q.pi_state->pi_mutex;
2288 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
2289 debug_rt_mutex_free_waiter(&rt_waiter);
2290
2291 spin_lock(q.lock_ptr);
2292 /*
2293 * Fixup the pi_state owner and possibly acquire the lock if we
2294 * haven't already.
2295 */
2296 res = fixup_owner(uaddr2, fshared, &q, !ret);
2297 /*
2298 * If fixup_owner() returned an error, proprogate that. If it
2299 * acquired the lock, clear -ETIMEDOUT or -EINTR.
2300 */
2301 if (res)
2302 ret = (res < 0) ? res : 0;
2303
2304 /* Unqueue and drop the lock. */
2305 unqueue_me_pi(&q);
2306 }
2307
2308 /*
2309 * If fixup_pi_state_owner() faulted and was unable to handle the
2310 * fault, unlock the rt_mutex and return the fault to userspace.
2311 */
2312 if (ret == -EFAULT) {
2313 if (rt_mutex_owner(pi_mutex) == current)
2314 rt_mutex_unlock(pi_mutex);
2315 } else if (ret == -EINTR) {
2316 /*
2317 * We've already been requeued, but cannot restart by calling
2318 * futex_lock_pi() directly. We could restart this syscall, but
2319 * it would detect that the user space "val" changed and return
2320 * -EWOULDBLOCK. Save the overhead of the restart and return
2321 * -EWOULDBLOCK directly.
2322 */
2323 ret = -EWOULDBLOCK;
2324 }
2325
2326 out_put_keys:
2327 put_futex_key(fshared, &q.key);
2328 out_key2:
2329 put_futex_key(fshared, &key2);
2330
2331 out:
2332 if (to) {
2333 hrtimer_cancel(&to->timer);
2334 destroy_hrtimer_on_stack(&to->timer);
2335 }
2336 return ret;
2337 }
2338
2339 /*
2340 * Support for robust futexes: the kernel cleans up held futexes at
2341 * thread exit time.
2342 *
2343 * Implementation: user-space maintains a per-thread list of locks it
2344 * is holding. Upon do_exit(), the kernel carefully walks this list,
2345 * and marks all locks that are owned by this thread with the
2346 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2347 * always manipulated with the lock held, so the list is private and
2348 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2349 * field, to allow the kernel to clean up if the thread dies after
2350 * acquiring the lock, but just before it could have added itself to
2351 * the list. There can only be one such pending lock.
2352 */
2353
2354 /**
2355 * sys_set_robust_list() - Set the robust-futex list head of a task
2356 * @head: pointer to the list-head
2357 * @len: length of the list-head, as userspace expects
2358 */
2359 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2360 size_t, len)
2361 {
2362 if (!futex_cmpxchg_enabled)
2363 return -ENOSYS;
2364 /*
2365 * The kernel knows only one size for now:
2366 */
2367 if (unlikely(len != sizeof(*head)))
2368 return -EINVAL;
2369
2370 current->robust_list = head;
2371
2372 return 0;
2373 }
2374
2375 /**
2376 * sys_get_robust_list() - Get the robust-futex list head of a task
2377 * @pid: pid of the process [zero for current task]
2378 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
2379 * @len_ptr: pointer to a length field, the kernel fills in the header size
2380 */
2381 SYSCALL_DEFINE3(get_robust_list, int, pid,
2382 struct robust_list_head __user * __user *, head_ptr,
2383 size_t __user *, len_ptr)
2384 {
2385 struct robust_list_head __user *head;
2386 unsigned long ret;
2387 const struct cred *cred = current_cred(), *pcred;
2388
2389 if (!futex_cmpxchg_enabled)
2390 return -ENOSYS;
2391
2392 if (!pid)
2393 head = current->robust_list;
2394 else {
2395 struct task_struct *p;
2396
2397 ret = -ESRCH;
2398 rcu_read_lock();
2399 p = find_task_by_vpid(pid);
2400 if (!p)
2401 goto err_unlock;
2402 ret = -EPERM;
2403 pcred = __task_cred(p);
2404 if (cred->euid != pcred->euid &&
2405 cred->euid != pcred->uid &&
2406 !capable(CAP_SYS_PTRACE))
2407 goto err_unlock;
2408 head = p->robust_list;
2409 rcu_read_unlock();
2410 }
2411
2412 if (put_user(sizeof(*head), len_ptr))
2413 return -EFAULT;
2414 return put_user(head, head_ptr);
2415
2416 err_unlock:
2417 rcu_read_unlock();
2418
2419 return ret;
2420 }
2421
2422 /*
2423 * Process a futex-list entry, check whether it's owned by the
2424 * dying task, and do notification if so:
2425 */
2426 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
2427 {
2428 u32 uval, nval, mval;
2429
2430 retry:
2431 if (get_user(uval, uaddr))
2432 return -1;
2433
2434 if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
2435 /*
2436 * Ok, this dying thread is truly holding a futex
2437 * of interest. Set the OWNER_DIED bit atomically
2438 * via cmpxchg, and if the value had FUTEX_WAITERS
2439 * set, wake up a waiter (if any). (We have to do a
2440 * futex_wake() even if OWNER_DIED is already set -
2441 * to handle the rare but possible case of recursive
2442 * thread-death.) The rest of the cleanup is done in
2443 * userspace.
2444 */
2445 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
2446 nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
2447
2448 if (nval == -EFAULT)
2449 return -1;
2450
2451 if (nval != uval)
2452 goto retry;
2453
2454 /*
2455 * Wake robust non-PI futexes here. The wakeup of
2456 * PI futexes happens in exit_pi_state():
2457 */
2458 if (!pi && (uval & FUTEX_WAITERS))
2459 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
2460 }
2461 return 0;
2462 }
2463
2464 /*
2465 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
2466 */
2467 static inline int fetch_robust_entry(struct robust_list __user **entry,
2468 struct robust_list __user * __user *head,
2469 unsigned int *pi)
2470 {
2471 unsigned long uentry;
2472
2473 if (get_user(uentry, (unsigned long __user *)head))
2474 return -EFAULT;
2475
2476 *entry = (void __user *)(uentry & ~1UL);
2477 *pi = uentry & 1;
2478
2479 return 0;
2480 }
2481
2482 /*
2483 * Walk curr->robust_list (very carefully, it's a userspace list!)
2484 * and mark any locks found there dead, and notify any waiters.
2485 *
2486 * We silently return on any sign of list-walking problem.
2487 */
2488 void exit_robust_list(struct task_struct *curr)
2489 {
2490 struct robust_list_head __user *head = curr->robust_list;
2491 struct robust_list __user *entry, *next_entry, *pending;
2492 unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
2493 unsigned long futex_offset;
2494 int rc;
2495
2496 if (!futex_cmpxchg_enabled)
2497 return;
2498
2499 /*
2500 * Fetch the list head (which was registered earlier, via
2501 * sys_set_robust_list()):
2502 */
2503 if (fetch_robust_entry(&entry, &head->list.next, &pi))
2504 return;
2505 /*
2506 * Fetch the relative futex offset:
2507 */
2508 if (get_user(futex_offset, &head->futex_offset))
2509 return;
2510 /*
2511 * Fetch any possibly pending lock-add first, and handle it
2512 * if it exists:
2513 */
2514 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
2515 return;
2516
2517 next_entry = NULL; /* avoid warning with gcc */
2518 while (entry != &head->list) {
2519 /*
2520 * Fetch the next entry in the list before calling
2521 * handle_futex_death:
2522 */
2523 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
2524 /*
2525 * A pending lock might already be on the list, so
2526 * don't process it twice:
2527 */
2528 if (entry != pending)
2529 if (handle_futex_death((void __user *)entry + futex_offset,
2530 curr, pi))
2531 return;
2532 if (rc)
2533 return;
2534 entry = next_entry;
2535 pi = next_pi;
2536 /*
2537 * Avoid excessively long or circular lists:
2538 */
2539 if (!--limit)
2540 break;
2541
2542 cond_resched();
2543 }
2544
2545 if (pending)
2546 handle_futex_death((void __user *)pending + futex_offset,
2547 curr, pip);
2548 }
2549
2550 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
2551 u32 __user *uaddr2, u32 val2, u32 val3)
2552 {
2553 int clockrt, ret = -ENOSYS;
2554 int cmd = op & FUTEX_CMD_MASK;
2555 int fshared = 0;
2556
2557 if (!(op & FUTEX_PRIVATE_FLAG))
2558 fshared = 1;
2559
2560 clockrt = op & FUTEX_CLOCK_REALTIME;
2561 if (clockrt && cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
2562 return -ENOSYS;
2563
2564 switch (cmd) {
2565 case FUTEX_WAIT:
2566 val3 = FUTEX_BITSET_MATCH_ANY;
2567 case FUTEX_WAIT_BITSET:
2568 ret = futex_wait(uaddr, fshared, val, timeout, val3, clockrt);
2569 break;
2570 case FUTEX_WAKE:
2571 val3 = FUTEX_BITSET_MATCH_ANY;
2572 case FUTEX_WAKE_BITSET:
2573 ret = futex_wake(uaddr, fshared, val, val3);
2574 break;
2575 case FUTEX_REQUEUE:
2576 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL, 0);
2577 break;
2578 case FUTEX_CMP_REQUEUE:
2579 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
2580 0);
2581 break;
2582 case FUTEX_WAKE_OP:
2583 ret = futex_wake_op(uaddr, fshared, uaddr2, val, val2, val3);
2584 break;
2585 case FUTEX_LOCK_PI:
2586 if (futex_cmpxchg_enabled)
2587 ret = futex_lock_pi(uaddr, fshared, val, timeout, 0);
2588 break;
2589 case FUTEX_UNLOCK_PI:
2590 if (futex_cmpxchg_enabled)
2591 ret = futex_unlock_pi(uaddr, fshared);
2592 break;
2593 case FUTEX_TRYLOCK_PI:
2594 if (futex_cmpxchg_enabled)
2595 ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1);
2596 break;
2597 case FUTEX_WAIT_REQUEUE_PI:
2598 val3 = FUTEX_BITSET_MATCH_ANY;
2599 ret = futex_wait_requeue_pi(uaddr, fshared, val, timeout, val3,
2600 clockrt, uaddr2);
2601 break;
2602 case FUTEX_CMP_REQUEUE_PI:
2603 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
2604 1);
2605 break;
2606 default:
2607 ret = -ENOSYS;
2608 }
2609 return ret;
2610 }
2611
2612
2613 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
2614 struct timespec __user *, utime, u32 __user *, uaddr2,
2615 u32, val3)
2616 {
2617 struct timespec ts;
2618 ktime_t t, *tp = NULL;
2619 u32 val2 = 0;
2620 int cmd = op & FUTEX_CMD_MASK;
2621
2622 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
2623 cmd == FUTEX_WAIT_BITSET ||
2624 cmd == FUTEX_WAIT_REQUEUE_PI)) {
2625 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
2626 return -EFAULT;
2627 if (!timespec_valid(&ts))
2628 return -EINVAL;
2629
2630 t = timespec_to_ktime(ts);
2631 if (cmd == FUTEX_WAIT)
2632 t = ktime_add_safe(ktime_get(), t);
2633 tp = &t;
2634 }
2635 /*
2636 * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
2637 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
2638 */
2639 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
2640 cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
2641 val2 = (u32) (unsigned long) utime;
2642
2643 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
2644 }
2645
2646 static int __init futex_init(void)
2647 {
2648 u32 curval;
2649 int i;
2650
2651 /*
2652 * This will fail and we want it. Some arch implementations do
2653 * runtime detection of the futex_atomic_cmpxchg_inatomic()
2654 * functionality. We want to know that before we call in any
2655 * of the complex code paths. Also we want to prevent
2656 * registration of robust lists in that case. NULL is
2657 * guaranteed to fault and we get -EFAULT on functional
2658 * implementation, the non-functional ones will return
2659 * -ENOSYS.
2660 */
2661 curval = cmpxchg_futex_value_locked(NULL, 0, 0);
2662 if (curval == -EFAULT)
2663 futex_cmpxchg_enabled = 1;
2664
2665 for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
2666 plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock);
2667 spin_lock_init(&futex_queues[i].lock);
2668 }
2669
2670 return 0;
2671 }
2672 __initcall(futex_init);