projects/linux·blob v3.0 · refs

2706 lines · 69.7 KiB

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 <[email protected]>
17 * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <[email protected]>
18 *
19 * PRIVATE futexes by Eric Dumazet
20 * Copyright (C) 2007 Eric Dumazet <[email protected]>
21 *
22 * Requeue-PI support by Darren Hart <[email protected]>
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
67int __read_mostly futex_cmpxchg_enabled;
68
69#define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
70
71/*
72 * Futex flags used to encode options to functions and preserve them across
73 * restarts.
74 */
75#define FLAGS_SHARED 0x01
76#define FLAGS_CLOCKRT 0x02
77#define FLAGS_HAS_TIMEOUT 0x04
78
79/*
80 * Priority Inheritance state:
81 */
82struct futex_pi_state {
83 /*
84 * list of 'owned' pi_state instances - these have to be
85 * cleaned up in do_exit() if the task exits prematurely:
86 */
87 struct list_head list;
88
89 /*
90 * The PI object:
91 */
92 struct rt_mutex pi_mutex;
93
94 struct task_struct *owner;
95 atomic_t refcount;
96
97 union futex_key key;
98};
99
100/**
101 * struct futex_q - The hashed futex queue entry, one per waiting task
102 * @list: priority-sorted list of tasks waiting on this futex
103 * @task: the task waiting on the futex
104 * @lock_ptr: the hash bucket lock
105 * @key: the key the futex is hashed on
106 * @pi_state: optional priority inheritance state
107 * @rt_waiter: rt_waiter storage for use with requeue_pi
108 * @requeue_pi_key: the requeue_pi target futex key
109 * @bitset: bitset for the optional bitmasked wakeup
110 *
111 * We use this hashed waitqueue, instead of a normal wait_queue_t, so
112 * we can wake only the relevant ones (hashed queues may be shared).
113 *
114 * A futex_q has a woken state, just like tasks have TASK_RUNNING.
115 * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
116 * The order of wakeup is always to make the first condition true, then
117 * the second.
118 *
119 * PI futexes are typically woken before they are removed from the hash list via
120 * the rt_mutex code. See unqueue_me_pi().
121 */
122struct futex_q {
123 struct plist_node list;
124
125 struct task_struct *task;
126 spinlock_t *lock_ptr;
127 union futex_key key;
128 struct futex_pi_state *pi_state;
129 struct rt_mutex_waiter *rt_waiter;
130 union futex_key *requeue_pi_key;
131 u32 bitset;
132};
133
134static const struct futex_q futex_q_init = {
135 /* list gets initialized in queue_me()*/
136 .key = FUTEX_KEY_INIT,
137 .bitset = FUTEX_BITSET_MATCH_ANY
138};
139
140/*
141 * Hash buckets are shared by all the futex_keys that hash to the same
142 * location. Each key may have multiple futex_q structures, one for each task
143 * waiting on a futex.
144 */
145struct futex_hash_bucket {
146 spinlock_t lock;
147 struct plist_head chain;
148};
149
150static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
151
152/*
153 * We hash on the keys returned from get_futex_key (see below).
154 */
155static struct futex_hash_bucket *hash_futex(union futex_key *key)
156{
157 u32 hash = jhash2((u32*)&key->both.word,
158 (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
159 key->both.offset);
160 return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
161}
162
163/*
164 * Return 1 if two futex_keys are equal, 0 otherwise.
165 */
166static inline int match_futex(union futex_key *key1, union futex_key *key2)
167{
168 return (key1 && key2
169 && key1->both.word == key2->both.word
170 && key1->both.ptr == key2->both.ptr
171 && key1->both.offset == key2->both.offset);
172}
173
174/*
175 * Take a reference to the resource addressed by a key.
176 * Can be called while holding spinlocks.
177 *
178 */
179static void get_futex_key_refs(union futex_key *key)
180{
181 if (!key->both.ptr)
182 return;
183
184 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
185 case FUT_OFF_INODE:
186 ihold(key->shared.inode);
187 break;
188 case FUT_OFF_MMSHARED:
189 atomic_inc(&key->private.mm->mm_count);
190 break;
191 }
192}
193
194/*
195 * Drop a reference to the resource addressed by a key.
196 * The hash bucket spinlock must not be held.
197 */
198static void drop_futex_key_refs(union futex_key *key)
199{
200 if (!key->both.ptr) {
201 /* If we're here then we tried to put a key we failed to get */
202 WARN_ON_ONCE(1);
203 return;
204 }
205
206 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
207 case FUT_OFF_INODE:
208 iput(key->shared.inode);
209 break;
210 case FUT_OFF_MMSHARED:
211 mmdrop(key->private.mm);
212 break;
213 }
214}
215
216/**
217 * get_futex_key() - Get parameters which are the keys for a futex
218 * @uaddr: virtual address of the futex
219 * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
220 * @key: address where result is stored.
221 *
222 * Returns a negative error code or 0
223 * The key words are stored in *key on success.
224 *
225 * For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,
226 * offset_within_page). For private mappings, it's (uaddr, current->mm).
227 * We can usually work out the index without swapping in the page.
228 *
229 * lock_page() might sleep, the caller should not hold a spinlock.
230 */
231static int
232get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key)
233{
234 unsigned long address = (unsigned long)uaddr;
235 struct mm_struct *mm = current->mm;
236 struct page *page, *page_head;
237 int err;
238
239 /*
240 * The futex address must be "naturally" aligned.
241 */
242 key->both.offset = address % PAGE_SIZE;
243 if (unlikely((address % sizeof(u32)) != 0))
244 return -EINVAL;
245 address -= key->both.offset;
246
247 /*
248 * PROCESS_PRIVATE futexes are fast.
249 * As the mm cannot disappear under us and the 'key' only needs
250 * virtual address, we dont even have to find the underlying vma.
251 * Note : We do have to check 'uaddr' is a valid user address,
252 * but access_ok() should be faster than find_vma()
253 */
254 if (!fshared) {
255 if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))))
256 return -EFAULT;
257 key->private.mm = mm;
258 key->private.address = address;
259 get_futex_key_refs(key);
260 return 0;
261 }
262
263again:
264 err = get_user_pages_fast(address, 1, 1, &page);
265 if (err < 0)
266 return err;
267
268#ifdef CONFIG_TRANSPARENT_HUGEPAGE
269 page_head = page;
270 if (unlikely(PageTail(page))) {
271 put_page(page);
272 /* serialize against __split_huge_page_splitting() */
273 local_irq_disable();
274 if (likely(__get_user_pages_fast(address, 1, 1, &page) == 1)) {
275 page_head = compound_head(page);
276 /*
277 * page_head is valid pointer but we must pin
278 * it before taking the PG_lock and/or
279 * PG_compound_lock. The moment we re-enable
280 * irqs __split_huge_page_splitting() can
281 * return and the head page can be freed from
282 * under us. We can't take the PG_lock and/or
283 * PG_compound_lock on a page that could be
284 * freed from under us.
285 */
286 if (page != page_head) {
287 get_page(page_head);
288 put_page(page);
289 }
290 local_irq_enable();
291 } else {
292 local_irq_enable();
293 goto again;
294 }
295 }
296#else
297 page_head = compound_head(page);
298 if (page != page_head) {
299 get_page(page_head);
300 put_page(page);
301 }
302#endif
303
304 lock_page(page_head);
305 if (!page_head->mapping) {
306 unlock_page(page_head);
307 put_page(page_head);
308 goto again;
309 }
310
311 /*
312 * Private mappings are handled in a simple way.
313 *
314 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
315 * it's a read-only handle, it's expected that futexes attach to
316 * the object not the particular process.
317 */
318 if (PageAnon(page_head)) {
319 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
320 key->private.mm = mm;
321 key->private.address = address;
322 } else {
323 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
324 key->shared.inode = page_head->mapping->host;
325 key->shared.pgoff = page_head->index;
326 }
327
328 get_futex_key_refs(key);
329
330 unlock_page(page_head);
331 put_page(page_head);
332 return 0;
333}
334
335static inline void put_futex_key(union futex_key *key)
336{
337 drop_futex_key_refs(key);
338}
339
340/**
341 * fault_in_user_writeable() - Fault in user address and verify RW access
342 * @uaddr: pointer to faulting user space address
343 *
344 * Slow path to fixup the fault we just took in the atomic write
345 * access to @uaddr.
346 *
347 * We have no generic implementation of a non-destructive write to the
348 * user address. We know that we faulted in the atomic pagefault
349 * disabled section so we can as well avoid the #PF overhead by
350 * calling get_user_pages() right away.
351 */
352static int fault_in_user_writeable(u32 __user *uaddr)
353{
354 struct mm_struct *mm = current->mm;
355 int ret;
356
357 down_read(&mm->mmap_sem);
358 ret = get_user_pages(current, mm, (unsigned long)uaddr,
359 1, 1, 0, NULL, NULL);
360 up_read(&mm->mmap_sem);
361
362 return ret < 0 ? ret : 0;
363}
364
365/**
366 * futex_top_waiter() - Return the highest priority waiter on a futex
367 * @hb: the hash bucket the futex_q's reside in
368 * @key: the futex key (to distinguish it from other futex futex_q's)
369 *
370 * Must be called with the hb lock held.
371 */
372static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
373 union futex_key *key)
374{
375 struct futex_q *this;
376
377 plist_for_each_entry(this, &hb->chain, list) {
378 if (match_futex(&this->key, key))
379 return this;
380 }
381 return NULL;
382}
383
384static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
385 u32 uval, u32 newval)
386{
387 int ret;
388
389 pagefault_disable();
390 ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
391 pagefault_enable();
392
393 return ret;
394}
395
396static int get_futex_value_locked(u32 *dest, u32 __user *from)
397{
398 int ret;
399
400 pagefault_disable();
401 ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
402 pagefault_enable();
403
404 return ret ? -EFAULT : 0;
405}
406
407
408/*
409 * PI code:
410 */
411static int refill_pi_state_cache(void)
412{
413 struct futex_pi_state *pi_state;
414
415 if (likely(current->pi_state_cache))
416 return 0;
417
418 pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
419
420 if (!pi_state)
421 return -ENOMEM;
422
423 INIT_LIST_HEAD(&pi_state->list);
424 /* pi_mutex gets initialized later */
425 pi_state->owner = NULL;
426 atomic_set(&pi_state->refcount, 1);
427 pi_state->key = FUTEX_KEY_INIT;
428
429 current->pi_state_cache = pi_state;
430
431 return 0;
432}
433
434static struct futex_pi_state * alloc_pi_state(void)
435{
436 struct futex_pi_state *pi_state = current->pi_state_cache;
437
438 WARN_ON(!pi_state);
439 current->pi_state_cache = NULL;
440
441 return pi_state;
442}
443
444static void free_pi_state(struct futex_pi_state *pi_state)
445{
446 if (!atomic_dec_and_test(&pi_state->refcount))
447 return;
448
449 /*
450 * If pi_state->owner is NULL, the owner is most probably dying
451 * and has cleaned up the pi_state already
452 */
453 if (pi_state->owner) {
454 raw_spin_lock_irq(&pi_state->owner->pi_lock);
455 list_del_init(&pi_state->list);
456 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
457
458 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
459 }
460
461 if (current->pi_state_cache)
462 kfree(pi_state);
463 else {
464 /*
465 * pi_state->list is already empty.
466 * clear pi_state->owner.
467 * refcount is at 0 - put it back to 1.
468 */
469 pi_state->owner = NULL;
470 atomic_set(&pi_state->refcount, 1);
471 current->pi_state_cache = pi_state;
472 }
473}
474
475/*
476 * Look up the task based on what TID userspace gave us.
477 * We dont trust it.
478 */
479static struct task_struct * futex_find_get_task(pid_t pid)
480{
481 struct task_struct *p;
482
483 rcu_read_lock();
484 p = find_task_by_vpid(pid);
485 if (p)
486 get_task_struct(p);
487
488 rcu_read_unlock();
489
490 return p;
491}
492
493/*
494 * This task is holding PI mutexes at exit time => bad.
495 * Kernel cleans up PI-state, but userspace is likely hosed.
496 * (Robust-futex cleanup is separate and might save the day for userspace.)
497 */
498void exit_pi_state_list(struct task_struct *curr)
499{
500 struct list_head *next, *head = &curr->pi_state_list;
501 struct futex_pi_state *pi_state;
502 struct futex_hash_bucket *hb;
503 union futex_key key = FUTEX_KEY_INIT;
504
505 if (!futex_cmpxchg_enabled)
506 return;
507 /*
508 * We are a ZOMBIE and nobody can enqueue itself on
509 * pi_state_list anymore, but we have to be careful
510 * versus waiters unqueueing themselves:
511 */
512 raw_spin_lock_irq(&curr->pi_lock);
513 while (!list_empty(head)) {
514
515 next = head->next;
516 pi_state = list_entry(next, struct futex_pi_state, list);
517 key = pi_state->key;
518 hb = hash_futex(&key);
519 raw_spin_unlock_irq(&curr->pi_lock);
520
521 spin_lock(&hb->lock);
522
523 raw_spin_lock_irq(&curr->pi_lock);
524 /*
525 * We dropped the pi-lock, so re-check whether this
526 * task still owns the PI-state:
527 */
528 if (head->next != next) {
529 spin_unlock(&hb->lock);
530 continue;
531 }
532
533 WARN_ON(pi_state->owner != curr);
534 WARN_ON(list_empty(&pi_state->list));
535 list_del_init(&pi_state->list);
536 pi_state->owner = NULL;
537 raw_spin_unlock_irq(&curr->pi_lock);
538
539 rt_mutex_unlock(&pi_state->pi_mutex);
540
541 spin_unlock(&hb->lock);
542
543 raw_spin_lock_irq(&curr->pi_lock);
544 }
545 raw_spin_unlock_irq(&curr->pi_lock);
546}
547
548static int
549lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
550 union futex_key *key, struct futex_pi_state **ps)
551{
552 struct futex_pi_state *pi_state = NULL;
553 struct futex_q *this, *next;
554 struct plist_head *head;
555 struct task_struct *p;
556 pid_t pid = uval & FUTEX_TID_MASK;
557
558 head = &hb->chain;
559
560 plist_for_each_entry_safe(this, next, head, list) {
561 if (match_futex(&this->key, key)) {
562 /*
563 * Another waiter already exists - bump up
564 * the refcount and return its pi_state:
565 */
566 pi_state = this->pi_state;
567 /*
568 * Userspace might have messed up non-PI and PI futexes
569 */
570 if (unlikely(!pi_state))
571 return -EINVAL;
572
573 WARN_ON(!atomic_read(&pi_state->refcount));
574
575 /*
576 * When pi_state->owner is NULL then the owner died
577 * and another waiter is on the fly. pi_state->owner
578 * is fixed up by the task which acquires
579 * pi_state->rt_mutex.
580 *
581 * We do not check for pid == 0 which can happen when
582 * the owner died and robust_list_exit() cleared the
583 * TID.
584 */
585 if (pid && pi_state->owner) {
586 /*
587 * Bail out if user space manipulated the
588 * futex value.
589 */
590 if (pid != task_pid_vnr(pi_state->owner))
591 return -EINVAL;
592 }
593
594 atomic_inc(&pi_state->refcount);
595 *ps = pi_state;
596
597 return 0;
598 }
599 }
600
601 /*
602 * We are the first waiter - try to look up the real owner and attach
603 * the new pi_state to it, but bail out when TID = 0
604 */
605 if (!pid)
606 return -ESRCH;
607 p = futex_find_get_task(pid);
608 if (!p)
609 return -ESRCH;
610
611 /*
612 * We need to look at the task state flags to figure out,
613 * whether the task is exiting. To protect against the do_exit
614 * change of the task flags, we do this protected by
615 * p->pi_lock:
616 */
617 raw_spin_lock_irq(&p->pi_lock);
618 if (unlikely(p->flags & PF_EXITING)) {
619 /*
620 * The task is on the way out. When PF_EXITPIDONE is
621 * set, we know that the task has finished the
622 * cleanup:
623 */
624 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
625
626 raw_spin_unlock_irq(&p->pi_lock);
627 put_task_struct(p);
628 return ret;
629 }
630
631 pi_state = alloc_pi_state();
632
633 /*
634 * Initialize the pi_mutex in locked state and make 'p'
635 * the owner of it:
636 */
637 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
638
639 /* Store the key for possible exit cleanups: */
640 pi_state->key = *key;
641
642 WARN_ON(!list_empty(&pi_state->list));
643 list_add(&pi_state->list, &p->pi_state_list);
644 pi_state->owner = p;
645 raw_spin_unlock_irq(&p->pi_lock);
646
647 put_task_struct(p);
648
649 *ps = pi_state;
650
651 return 0;
652}
653
654/**
655 * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
656 * @uaddr: the pi futex user address
657 * @hb: the pi futex hash bucket
658 * @key: the futex key associated with uaddr and hb
659 * @ps: the pi_state pointer where we store the result of the
660 * lookup
661 * @task: the task to perform the atomic lock work for. This will
662 * be "current" except in the case of requeue pi.
663 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
664 *
665 * Returns:
666 * 0 - ready to wait
667 * 1 - acquired the lock
668 * <0 - error
669 *
670 * The hb->lock and futex_key refs shall be held by the caller.
671 */
672static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
673 union futex_key *key,
674 struct futex_pi_state **ps,
675 struct task_struct *task, int set_waiters)
676{
677 int lock_taken, ret, ownerdied = 0;
678 u32 uval, newval, curval, vpid = task_pid_vnr(task);
679
680retry:
681 ret = lock_taken = 0;
682
683 /*
684 * To avoid races, we attempt to take the lock here again
685 * (by doing a 0 -> TID atomic cmpxchg), while holding all
686 * the locks. It will most likely not succeed.
687 */
688 newval = vpid;
689 if (set_waiters)
690 newval |= FUTEX_WAITERS;
691
692 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval)))
693 return -EFAULT;
694
695 /*
696 * Detect deadlocks.
697 */
698 if ((unlikely((curval & FUTEX_TID_MASK) == vpid)))
699 return -EDEADLK;
700
701 /*
702 * Surprise - we got the lock. Just return to userspace:
703 */
704 if (unlikely(!curval))
705 return 1;
706
707 uval = curval;
708
709 /*
710 * Set the FUTEX_WAITERS flag, so the owner will know it has someone
711 * to wake at the next unlock.
712 */
713 newval = curval | FUTEX_WAITERS;
714
715 /*
716 * There are two cases, where a futex might have no owner (the
717 * owner TID is 0): OWNER_DIED. We take over the futex in this
718 * case. We also do an unconditional take over, when the owner
719 * of the futex died.
720 *
721 * This is safe as we are protected by the hash bucket lock !
722 */
723 if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
724 /* Keep the OWNER_DIED bit */
725 newval = (curval & ~FUTEX_TID_MASK) | vpid;
726 ownerdied = 0;
727 lock_taken = 1;
728 }
729
730 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
731 return -EFAULT;
732 if (unlikely(curval != uval))
733 goto retry;
734
735 /*
736 * We took the lock due to owner died take over.
737 */
738 if (unlikely(lock_taken))
739 return 1;
740
741 /*
742 * We dont have the lock. Look up the PI state (or create it if
743 * we are the first waiter):
744 */
745 ret = lookup_pi_state(uval, hb, key, ps);
746
747 if (unlikely(ret)) {
748 switch (ret) {
749 case -ESRCH:
750 /*
751 * No owner found for this futex. Check if the
752 * OWNER_DIED bit is set to figure out whether
753 * this is a robust futex or not.
754 */
755 if (get_futex_value_locked(&curval, uaddr))
756 return -EFAULT;
757
758 /*
759 * We simply start over in case of a robust
760 * futex. The code above will take the futex
761 * and return happy.
762 */
763 if (curval & FUTEX_OWNER_DIED) {
764 ownerdied = 1;
765 goto retry;
766 }
767 default:
768 break;
769 }
770 }
771
772 return ret;
773}
774
775/**
776 * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
777 * @q: The futex_q to unqueue
778 *
779 * The q->lock_ptr must not be NULL and must be held by the caller.
780 */
781static void __unqueue_futex(struct futex_q *q)
782{
783 struct futex_hash_bucket *hb;
784
785 if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
786 || WARN_ON(plist_node_empty(&q->list)))
787 return;
788
789 hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
790 plist_del(&q->list, &hb->chain);
791}
792
793/*
794 * The hash bucket lock must be held when this is called.
795 * Afterwards, the futex_q must not be accessed.
796 */
797static void wake_futex(struct futex_q *q)
798{
799 struct task_struct *p = q->task;
800
801 /*
802 * We set q->lock_ptr = NULL _before_ we wake up the task. If
803 * a non-futex wake up happens on another CPU then the task
804 * might exit and p would dereference a non-existing task
805 * struct. Prevent this by holding a reference on p across the
806 * wake up.
807 */
808 get_task_struct(p);
809
810 __unqueue_futex(q);
811 /*
812 * The waiting task can free the futex_q as soon as
813 * q->lock_ptr = NULL is written, without taking any locks. A
814 * memory barrier is required here to prevent the following
815 * store to lock_ptr from getting ahead of the plist_del.
816 */
817 smp_wmb();
818 q->lock_ptr = NULL;
819
820 wake_up_state(p, TASK_NORMAL);
821 put_task_struct(p);
822}
823
824static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
825{
826 struct task_struct *new_owner;
827 struct futex_pi_state *pi_state = this->pi_state;
828 u32 curval, newval;
829
830 if (!pi_state)
831 return -EINVAL;
832
833 /*
834 * If current does not own the pi_state then the futex is
835 * inconsistent and user space fiddled with the futex value.
836 */
837 if (pi_state->owner != current)
838 return -EINVAL;
839
840 raw_spin_lock(&pi_state->pi_mutex.wait_lock);
841 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
842
843 /*
844 * It is possible that the next waiter (the one that brought
845 * this owner to the kernel) timed out and is no longer
846 * waiting on the lock.
847 */
848 if (!new_owner)
849 new_owner = this->task;
850
851 /*
852 * We pass it to the next owner. (The WAITERS bit is always
853 * kept enabled while there is PI state around. We must also
854 * preserve the owner died bit.)
855 */
856 if (!(uval & FUTEX_OWNER_DIED)) {
857 int ret = 0;
858
859 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
860
861 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
862 ret = -EFAULT;
863 else if (curval != uval)
864 ret = -EINVAL;
865 if (ret) {
866 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
867 return ret;
868 }
869 }
870
871 raw_spin_lock_irq(&pi_state->owner->pi_lock);
872 WARN_ON(list_empty(&pi_state->list));
873 list_del_init(&pi_state->list);
874 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
875
876 raw_spin_lock_irq(&new_owner->pi_lock);
877 WARN_ON(!list_empty(&pi_state->list));
878 list_add(&pi_state->list, &new_owner->pi_state_list);
879 pi_state->owner = new_owner;
880 raw_spin_unlock_irq(&new_owner->pi_lock);
881
882 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
883 rt_mutex_unlock(&pi_state->pi_mutex);
884
885 return 0;
886}
887
888static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
889{
890 u32 oldval;
891
892 /*
893 * There is no waiter, so we unlock the futex. The owner died
894 * bit has not to be preserved here. We are the owner:
895 */
896 if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0))
897 return -EFAULT;
898 if (oldval != uval)
899 return -EAGAIN;
900
901 return 0;
902}
903
904/*
905 * Express the locking dependencies for lockdep:
906 */
907static inline void
908double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
909{
910 if (hb1 <= hb2) {
911 spin_lock(&hb1->lock);
912 if (hb1 < hb2)
913 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
914 } else { /* hb1 > hb2 */
915 spin_lock(&hb2->lock);
916 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
917 }
918}
919
920static inline void
921double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
922{
923 spin_unlock(&hb1->lock);
924 if (hb1 != hb2)
925 spin_unlock(&hb2->lock);
926}
927
928/*
929 * Wake up waiters matching bitset queued on this futex (uaddr).
930 */
931static int
932futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
933{
934 struct futex_hash_bucket *hb;
935 struct futex_q *this, *next;
936 struct plist_head *head;
937 union futex_key key = FUTEX_KEY_INIT;
938 int ret;
939
940 if (!bitset)
941 return -EINVAL;
942
943 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key);
944 if (unlikely(ret != 0))
945 goto out;
946
947 hb = hash_futex(&key);
948 spin_lock(&hb->lock);
949 head = &hb->chain;
950
951 plist_for_each_entry_safe(this, next, head, list) {
952 if (match_futex (&this->key, &key)) {
953 if (this->pi_state || this->rt_waiter) {
954 ret = -EINVAL;
955 break;
956 }
957
958 /* Check if one of the bits is set in both bitsets */
959 if (!(this->bitset & bitset))
960 continue;
961
962 wake_futex(this);
963 if (++ret >= nr_wake)
964 break;
965 }
966 }
967
968 spin_unlock(&hb->lock);
969 put_futex_key(&key);
970out:
971 return ret;
972}
973
974/*
975 * Wake up all waiters hashed on the physical page that is mapped
976 * to this virtual address:
977 */
978static int
979futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
980 int nr_wake, int nr_wake2, int op)
981{
982 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
983 struct futex_hash_bucket *hb1, *hb2;
984 struct plist_head *head;
985 struct futex_q *this, *next;
986 int ret, op_ret;
987
988retry:
989 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1);
990 if (unlikely(ret != 0))
991 goto out;
992 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2);
993 if (unlikely(ret != 0))
994 goto out_put_key1;
995
996 hb1 = hash_futex(&key1);
997 hb2 = hash_futex(&key2);
998
999retry_private:
1000 double_lock_hb(hb1, hb2);
1001 op_ret = futex_atomic_op_inuser(op, uaddr2);
1002 if (unlikely(op_ret < 0)) {
1003
1004 double_unlock_hb(hb1, hb2);
1005
1006#ifndef CONFIG_MMU
1007 /*
1008 * we don't get EFAULT from MMU faults if we don't have an MMU,
1009 * but we might get them from range checking
1010 */
1011 ret = op_ret;
1012 goto out_put_keys;
1013#endif
1014
1015 if (unlikely(op_ret != -EFAULT)) {
1016 ret = op_ret;
1017 goto out_put_keys;
1018 }
1019
1020 ret = fault_in_user_writeable(uaddr2);
1021 if (ret)
1022 goto out_put_keys;
1023
1024 if (!(flags & FLAGS_SHARED))
1025 goto retry_private;
1026
1027 put_futex_key(&key2);
1028 put_futex_key(&key1);
1029 goto retry;
1030 }
1031
1032 head = &hb1->chain;
1033
1034 plist_for_each_entry_safe(this, next, head, list) {
1035 if (match_futex (&this->key, &key1)) {
1036 wake_futex(this);
1037 if (++ret >= nr_wake)
1038 break;
1039 }
1040 }
1041
1042 if (op_ret > 0) {
1043 head = &hb2->chain;
1044
1045 op_ret = 0;
1046 plist_for_each_entry_safe(this, next, head, list) {
1047 if (match_futex (&this->key, &key2)) {
1048 wake_futex(this);
1049 if (++op_ret >= nr_wake2)
1050 break;
1051 }
1052 }
1053 ret += op_ret;
1054 }
1055
1056 double_unlock_hb(hb1, hb2);
1057out_put_keys:
1058 put_futex_key(&key2);
1059out_put_key1:
1060 put_futex_key(&key1);
1061out:
1062 return ret;
1063}
1064
1065/**
1066 * requeue_futex() - Requeue a futex_q from one hb to another
1067 * @q: the futex_q to requeue
1068 * @hb1: the source hash_bucket
1069 * @hb2: the target hash_bucket
1070 * @key2: the new key for the requeued futex_q
1071 */
1072static inline
1073void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1074 struct futex_hash_bucket *hb2, union futex_key *key2)
1075{
1076
1077 /*
1078 * If key1 and key2 hash to the same bucket, no need to
1079 * requeue.
1080 */
1081 if (likely(&hb1->chain != &hb2->chain)) {
1082 plist_del(&q->list, &hb1->chain);
1083 plist_add(&q->list, &hb2->chain);
1084 q->lock_ptr = &hb2->lock;
1085 }
1086 get_futex_key_refs(key2);
1087 q->key = *key2;
1088}
1089
1090/**
1091 * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1092 * @q: the futex_q
1093 * @key: the key of the requeue target futex
1094 * @hb: the hash_bucket of the requeue target futex
1095 *
1096 * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1097 * target futex if it is uncontended or via a lock steal. Set the futex_q key
1098 * to the requeue target futex so the waiter can detect the wakeup on the right
1099 * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1100 * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
1101 * to protect access to the pi_state to fixup the owner later. Must be called
1102 * with both q->lock_ptr and hb->lock held.
1103 */
1104static inline
1105void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1106 struct futex_hash_bucket *hb)
1107{
1108 get_futex_key_refs(key);
1109 q->key = *key;
1110
1111 __unqueue_futex(q);
1112
1113 WARN_ON(!q->rt_waiter);
1114 q->rt_waiter = NULL;
1115
1116 q->lock_ptr = &hb->lock;
1117
1118 wake_up_state(q->task, TASK_NORMAL);
1119}
1120
1121/**
1122 * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1123 * @pifutex: the user address of the to futex
1124 * @hb1: the from futex hash bucket, must be locked by the caller
1125 * @hb2: the to futex hash bucket, must be locked by the caller
1126 * @key1: the from futex key
1127 * @key2: the to futex key
1128 * @ps: address to store the pi_state pointer
1129 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1130 *
1131 * Try and get the lock on behalf of the top waiter if we can do it atomically.
1132 * Wake the top waiter if we succeed. If the caller specified set_waiters,
1133 * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1134 * hb1 and hb2 must be held by the caller.
1135 *
1136 * Returns:
1137 * 0 - failed to acquire the lock atomicly
1138 * 1 - acquired the lock
1139 * <0 - error
1140 */
1141static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1142 struct futex_hash_bucket *hb1,
1143 struct futex_hash_bucket *hb2,
1144 union futex_key *key1, union futex_key *key2,
1145 struct futex_pi_state **ps, int set_waiters)
1146{
1147 struct futex_q *top_waiter = NULL;
1148 u32 curval;
1149 int ret;
1150
1151 if (get_futex_value_locked(&curval, pifutex))
1152 return -EFAULT;
1153
1154 /*
1155 * Find the top_waiter and determine if there are additional waiters.
1156 * If the caller intends to requeue more than 1 waiter to pifutex,
1157 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1158 * as we have means to handle the possible fault. If not, don't set
1159 * the bit unecessarily as it will force the subsequent unlock to enter
1160 * the kernel.
1161 */
1162 top_waiter = futex_top_waiter(hb1, key1);
1163
1164 /* There are no waiters, nothing for us to do. */
1165 if (!top_waiter)
1166 return 0;
1167
1168 /* Ensure we requeue to the expected futex. */
1169 if (!match_futex(top_waiter->requeue_pi_key, key2))
1170 return -EINVAL;
1171
1172 /*
1173 * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
1174 * the contended case or if set_waiters is 1. The pi_state is returned
1175 * in ps in contended cases.
1176 */
1177 ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1178 set_waiters);
1179 if (ret == 1)
1180 requeue_pi_wake_futex(top_waiter, key2, hb2);
1181
1182 return ret;
1183}
1184
1185/**
1186 * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1187 * @uaddr1: source futex user address
1188 * @flags: futex flags (FLAGS_SHARED, etc.)
1189 * @uaddr2: target futex user address
1190 * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
1191 * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1192 * @cmpval: @uaddr1 expected value (or %NULL)
1193 * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1194 * pi futex (pi to pi requeue is not supported)
1195 *
1196 * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1197 * uaddr2 atomically on behalf of the top waiter.
1198 *
1199 * Returns:
1200 * >=0 - on success, the number of tasks requeued or woken
1201 * <0 - on error
1202 */
1203static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1204 u32 __user *uaddr2, int nr_wake, int nr_requeue,
1205 u32 *cmpval, int requeue_pi)
1206{
1207 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1208 int drop_count = 0, task_count = 0, ret;
1209 struct futex_pi_state *pi_state = NULL;
1210 struct futex_hash_bucket *hb1, *hb2;
1211 struct plist_head *head1;
1212 struct futex_q *this, *next;
1213 u32 curval2;
1214
1215 if (requeue_pi) {
1216 /*
1217 * requeue_pi requires a pi_state, try to allocate it now
1218 * without any locks in case it fails.
1219 */
1220 if (refill_pi_state_cache())
1221 return -ENOMEM;
1222 /*
1223 * requeue_pi must wake as many tasks as it can, up to nr_wake
1224 * + nr_requeue, since it acquires the rt_mutex prior to
1225 * returning to userspace, so as to not leave the rt_mutex with
1226 * waiters and no owner. However, second and third wake-ups
1227 * cannot be predicted as they involve race conditions with the
1228 * first wake and a fault while looking up the pi_state. Both
1229 * pthread_cond_signal() and pthread_cond_broadcast() should
1230 * use nr_wake=1.
1231 */
1232 if (nr_wake != 1)
1233 return -EINVAL;
1234 }
1235
1236retry:
1237 if (pi_state != NULL) {
1238 /*
1239 * We will have to lookup the pi_state again, so free this one
1240 * to keep the accounting correct.
1241 */
1242 free_pi_state(pi_state);
1243 pi_state = NULL;
1244 }
1245
1246 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1);
1247 if (unlikely(ret != 0))
1248 goto out;
1249 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2);
1250 if (unlikely(ret != 0))
1251 goto out_put_key1;
1252
1253 hb1 = hash_futex(&key1);
1254 hb2 = hash_futex(&key2);
1255
1256retry_private:
1257 double_lock_hb(hb1, hb2);
1258
1259 if (likely(cmpval != NULL)) {
1260 u32 curval;
1261
1262 ret = get_futex_value_locked(&curval, uaddr1);
1263
1264 if (unlikely(ret)) {
1265 double_unlock_hb(hb1, hb2);
1266
1267 ret = get_user(curval, uaddr1);
1268 if (ret)
1269 goto out_put_keys;
1270
1271 if (!(flags & FLAGS_SHARED))
1272 goto retry_private;
1273
1274 put_futex_key(&key2);
1275 put_futex_key(&key1);
1276 goto retry;
1277 }
1278 if (curval != *cmpval) {
1279 ret = -EAGAIN;
1280 goto out_unlock;
1281 }
1282 }
1283
1284 if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1285 /*
1286 * Attempt to acquire uaddr2 and wake the top waiter. If we
1287 * intend to requeue waiters, force setting the FUTEX_WAITERS
1288 * bit. We force this here where we are able to easily handle
1289 * faults rather in the requeue loop below.
1290 */
1291 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1292 &key2, &pi_state, nr_requeue);
1293
1294 /*
1295 * At this point the top_waiter has either taken uaddr2 or is
1296 * waiting on it. If the former, then the pi_state will not
1297 * exist yet, look it up one more time to ensure we have a
1298 * reference to it.
1299 */
1300 if (ret == 1) {
1301 WARN_ON(pi_state);
1302 drop_count++;
1303 task_count++;
1304 ret = get_futex_value_locked(&curval2, uaddr2);
1305 if (!ret)
1306 ret = lookup_pi_state(curval2, hb2, &key2,
1307 &pi_state);
1308 }
1309
1310 switch (ret) {
1311 case 0:
1312 break;
1313 case -EFAULT:
1314 double_unlock_hb(hb1, hb2);
1315 put_futex_key(&key2);
1316 put_futex_key(&key1);
1317 ret = fault_in_user_writeable(uaddr2);
1318 if (!ret)
1319 goto retry;
1320 goto out;
1321 case -EAGAIN:
1322 /* The owner was exiting, try again. */
1323 double_unlock_hb(hb1, hb2);
1324 put_futex_key(&key2);
1325 put_futex_key(&key1);
1326 cond_resched();
1327 goto retry;
1328 default:
1329 goto out_unlock;
1330 }
1331 }
1332
1333 head1 = &hb1->chain;
1334 plist_for_each_entry_safe(this, next, head1, list) {
1335 if (task_count - nr_wake >= nr_requeue)
1336 break;
1337
1338 if (!match_futex(&this->key, &key1))
1339 continue;
1340
1341 /*
1342 * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1343 * be paired with each other and no other futex ops.
1344 */
1345 if ((requeue_pi && !this->rt_waiter) ||
1346 (!requeue_pi && this->rt_waiter)) {
1347 ret = -EINVAL;
1348 break;
1349 }
1350
1351 /*
1352 * Wake nr_wake waiters. For requeue_pi, if we acquired the
1353 * lock, we already woke the top_waiter. If not, it will be
1354 * woken by futex_unlock_pi().
1355 */
1356 if (++task_count <= nr_wake && !requeue_pi) {
1357 wake_futex(this);
1358 continue;
1359 }
1360
1361 /* Ensure we requeue to the expected futex for requeue_pi. */
1362 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1363 ret = -EINVAL;
1364 break;
1365 }
1366
1367 /*
1368 * Requeue nr_requeue waiters and possibly one more in the case
1369 * of requeue_pi if we couldn't acquire the lock atomically.
1370 */
1371 if (requeue_pi) {
1372 /* Prepare the waiter to take the rt_mutex. */
1373 atomic_inc(&pi_state->refcount);
1374 this->pi_state = pi_state;
1375 ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1376 this->rt_waiter,
1377 this->task, 1);
1378 if (ret == 1) {
1379 /* We got the lock. */
1380 requeue_pi_wake_futex(this, &key2, hb2);
1381 drop_count++;
1382 continue;
1383 } else if (ret) {
1384 /* -EDEADLK */
1385 this->pi_state = NULL;
1386 free_pi_state(pi_state);
1387 goto out_unlock;
1388 }
1389 }
1390 requeue_futex(this, hb1, hb2, &key2);
1391 drop_count++;
1392 }
1393
1394out_unlock:
1395 double_unlock_hb(hb1, hb2);
1396
1397 /*
1398 * drop_futex_key_refs() must be called outside the spinlocks. During
1399 * the requeue we moved futex_q's from the hash bucket at key1 to the
1400 * one at key2 and updated their key pointer. We no longer need to
1401 * hold the references to key1.
1402 */
1403 while (--drop_count >= 0)
1404 drop_futex_key_refs(&key1);
1405
1406out_put_keys:
1407 put_futex_key(&key2);
1408out_put_key1:
1409 put_futex_key(&key1);
1410out:
1411 if (pi_state != NULL)
1412 free_pi_state(pi_state);
1413 return ret ? ret : task_count;
1414}
1415
1416/* The key must be already stored in q->key. */
1417static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
1418 __acquires(&hb->lock)
1419{
1420 struct futex_hash_bucket *hb;
1421
1422 hb = hash_futex(&q->key);
1423 q->lock_ptr = &hb->lock;
1424
1425 spin_lock(&hb->lock);
1426 return hb;
1427}
1428
1429static inline void
1430queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
1431 __releases(&hb->lock)
1432{
1433 spin_unlock(&hb->lock);
1434}
1435
1436/**
1437 * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1438 * @q: The futex_q to enqueue
1439 * @hb: The destination hash bucket
1440 *
1441 * The hb->lock must be held by the caller, and is released here. A call to
1442 * queue_me() is typically paired with exactly one call to unqueue_me(). The
1443 * exceptions involve the PI related operations, which may use unqueue_me_pi()
1444 * or nothing if the unqueue is done as part of the wake process and the unqueue
1445 * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1446 * an example).
1447 */
1448static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1449 __releases(&hb->lock)
1450{
1451 int prio;
1452
1453 /*
1454 * The priority used to register this element is
1455 * - either the real thread-priority for the real-time threads
1456 * (i.e. threads with a priority lower than MAX_RT_PRIO)
1457 * - or MAX_RT_PRIO for non-RT threads.
1458 * Thus, all RT-threads are woken first in priority order, and
1459 * the others are woken last, in FIFO order.
1460 */
1461 prio = min(current->normal_prio, MAX_RT_PRIO);
1462
1463 plist_node_init(&q->list, prio);
1464 plist_add(&q->list, &hb->chain);
1465 q->task = current;
1466 spin_unlock(&hb->lock);
1467}
1468
1469/**
1470 * unqueue_me() - Remove the futex_q from its futex_hash_bucket
1471 * @q: The futex_q to unqueue
1472 *
1473 * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
1474 * be paired with exactly one earlier call to queue_me().
1475 *
1476 * Returns:
1477 * 1 - if the futex_q was still queued (and we removed unqueued it)
1478 * 0 - if the futex_q was already removed by the waking thread
1479 */
1480static int unqueue_me(struct futex_q *q)
1481{
1482 spinlock_t *lock_ptr;
1483 int ret = 0;
1484
1485 /* In the common case we don't take the spinlock, which is nice. */
1486retry:
1487 lock_ptr = q->lock_ptr;
1488 barrier();
1489 if (lock_ptr != NULL) {
1490 spin_lock(lock_ptr);
1491 /*
1492 * q->lock_ptr can change between reading it and
1493 * spin_lock(), causing us to take the wrong lock. This
1494 * corrects the race condition.
1495 *
1496 * Reasoning goes like this: if we have the wrong lock,
1497 * q->lock_ptr must have changed (maybe several times)
1498 * between reading it and the spin_lock(). It can
1499 * change again after the spin_lock() but only if it was
1500 * already changed before the spin_lock(). It cannot,
1501 * however, change back to the original value. Therefore
1502 * we can detect whether we acquired the correct lock.
1503 */
1504 if (unlikely(lock_ptr != q->lock_ptr)) {
1505 spin_unlock(lock_ptr);
1506 goto retry;
1507 }
1508 __unqueue_futex(q);
1509
1510 BUG_ON(q->pi_state);
1511
1512 spin_unlock(lock_ptr);
1513 ret = 1;
1514 }
1515
1516 drop_futex_key_refs(&q->key);
1517 return ret;
1518}
1519
1520/*
1521 * PI futexes can not be requeued and must remove themself from the
1522 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1523 * and dropped here.
1524 */
1525static void unqueue_me_pi(struct futex_q *q)
1526 __releases(q->lock_ptr)
1527{
1528 __unqueue_futex(q);
1529
1530 BUG_ON(!q->pi_state);
1531 free_pi_state(q->pi_state);
1532 q->pi_state = NULL;
1533
1534 spin_unlock(q->lock_ptr);
1535}
1536
1537/*
1538 * Fixup the pi_state owner with the new owner.
1539 *
1540 * Must be called with hash bucket lock held and mm->sem held for non
1541 * private futexes.
1542 */
1543static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1544 struct task_struct *newowner)
1545{
1546 u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
1547 struct futex_pi_state *pi_state = q->pi_state;
1548 struct task_struct *oldowner = pi_state->owner;
1549 u32 uval, curval, newval;
1550 int ret;
1551
1552 /* Owner died? */
1553 if (!pi_state->owner)
1554 newtid |= FUTEX_OWNER_DIED;
1555
1556 /*
1557 * We are here either because we stole the rtmutex from the
1558 * previous highest priority waiter or we are the highest priority
1559 * waiter but failed to get the rtmutex the first time.
1560 * We have to replace the newowner TID in the user space variable.
1561 * This must be atomic as we have to preserve the owner died bit here.
1562 *
1563 * Note: We write the user space value _before_ changing the pi_state
1564 * because we can fault here. Imagine swapped out pages or a fork
1565 * that marked all the anonymous memory readonly for cow.
1566 *
1567 * Modifying pi_state _before_ the user space value would
1568 * leave the pi_state in an inconsistent state when we fault
1569 * here, because we need to drop the hash bucket lock to
1570 * handle the fault. This might be observed in the PID check
1571 * in lookup_pi_state.
1572 */
1573retry:
1574 if (get_futex_value_locked(&uval, uaddr))
1575 goto handle_fault;
1576
1577 while (1) {
1578 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1579
1580 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
1581 goto handle_fault;
1582 if (curval == uval)
1583 break;
1584 uval = curval;
1585 }
1586
1587 /*
1588 * We fixed up user space. Now we need to fix the pi_state
1589 * itself.
1590 */
1591 if (pi_state->owner != NULL) {
1592 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1593 WARN_ON(list_empty(&pi_state->list));
1594 list_del_init(&pi_state->list);
1595 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1596 }
1597
1598 pi_state->owner = newowner;
1599
1600 raw_spin_lock_irq(&newowner->pi_lock);
1601 WARN_ON(!list_empty(&pi_state->list));
1602 list_add(&pi_state->list, &newowner->pi_state_list);
1603 raw_spin_unlock_irq(&newowner->pi_lock);
1604 return 0;
1605
1606 /*
1607 * To handle the page fault we need to drop the hash bucket
1608 * lock here. That gives the other task (either the highest priority
1609 * waiter itself or the task which stole the rtmutex) the
1610 * chance to try the fixup of the pi_state. So once we are
1611 * back from handling the fault we need to check the pi_state
1612 * after reacquiring the hash bucket lock and before trying to
1613 * do another fixup. When the fixup has been done already we
1614 * simply return.
1615 */
1616handle_fault:
1617 spin_unlock(q->lock_ptr);
1618
1619 ret = fault_in_user_writeable(uaddr);
1620
1621 spin_lock(q->lock_ptr);
1622
1623 /*
1624 * Check if someone else fixed it for us:
1625 */
1626 if (pi_state->owner != oldowner)
1627 return 0;
1628
1629 if (ret)
1630 return ret;
1631
1632 goto retry;
1633}
1634
1635static long futex_wait_restart(struct restart_block *restart);
1636
1637/**
1638 * fixup_owner() - Post lock pi_state and corner case management
1639 * @uaddr: user address of the futex
1640 * @q: futex_q (contains pi_state and access to the rt_mutex)
1641 * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
1642 *
1643 * After attempting to lock an rt_mutex, this function is called to cleanup
1644 * the pi_state owner as well as handle race conditions that may allow us to
1645 * acquire the lock. Must be called with the hb lock held.
1646 *
1647 * Returns:
1648 * 1 - success, lock taken
1649 * 0 - success, lock not taken
1650 * <0 - on error (-EFAULT)
1651 */
1652static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
1653{
1654 struct task_struct *owner;
1655 int ret = 0;
1656
1657 if (locked) {
1658 /*
1659 * Got the lock. We might not be the anticipated owner if we
1660 * did a lock-steal - fix up the PI-state in that case:
1661 */
1662 if (q->pi_state->owner != current)
1663 ret = fixup_pi_state_owner(uaddr, q, current);
1664 goto out;
1665 }
1666
1667 /*
1668 * Catch the rare case, where the lock was released when we were on the
1669 * way back before we locked the hash bucket.
1670 */
1671 if (q->pi_state->owner == current) {
1672 /*
1673 * Try to get the rt_mutex now. This might fail as some other
1674 * task acquired the rt_mutex after we removed ourself from the
1675 * rt_mutex waiters list.
1676 */
1677 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
1678 locked = 1;
1679 goto out;
1680 }
1681
1682 /*
1683 * pi_state is incorrect, some other task did a lock steal and
1684 * we returned due to timeout or signal without taking the
1685 * rt_mutex. Too late.
1686 */
1687 raw_spin_lock(&q->pi_state->pi_mutex.wait_lock);
1688 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
1689 if (!owner)
1690 owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
1691 raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock);
1692 ret = fixup_pi_state_owner(uaddr, q, owner);
1693 goto out;
1694 }
1695
1696 /*
1697 * Paranoia check. If we did not take the lock, then we should not be
1698 * the owner of the rt_mutex.
1699 */
1700 if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
1701 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
1702 "pi-state %p\n", ret,
1703 q->pi_state->pi_mutex.owner,
1704 q->pi_state->owner);
1705
1706out:
1707 return ret ? ret : locked;
1708}
1709
1710/**
1711 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
1712 * @hb: the futex hash bucket, must be locked by the caller
1713 * @q: the futex_q to queue up on
1714 * @timeout: the prepared hrtimer_sleeper, or null for no timeout
1715 */
1716static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
1717 struct hrtimer_sleeper *timeout)
1718{
1719 /*
1720 * The task state is guaranteed to be set before another task can
1721 * wake it. set_current_state() is implemented using set_mb() and
1722 * queue_me() calls spin_unlock() upon completion, both serializing
1723 * access to the hash list and forcing another memory barrier.
1724 */
1725 set_current_state(TASK_INTERRUPTIBLE);
1726 queue_me(q, hb);
1727
1728 /* Arm the timer */
1729 if (timeout) {
1730 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1731 if (!hrtimer_active(&timeout->timer))
1732 timeout->task = NULL;
1733 }
1734
1735 /*
1736 * If we have been removed from the hash list, then another task
1737 * has tried to wake us, and we can skip the call to schedule().
1738 */
1739 if (likely(!plist_node_empty(&q->list))) {
1740 /*
1741 * If the timer has already expired, current will already be
1742 * flagged for rescheduling. Only call schedule if there
1743 * is no timeout, or if it has yet to expire.
1744 */
1745 if (!timeout || timeout->task)
1746 schedule();
1747 }
1748 __set_current_state(TASK_RUNNING);
1749}
1750
1751/**
1752 * futex_wait_setup() - Prepare to wait on a futex
1753 * @uaddr: the futex userspace address
1754 * @val: the expected value
1755 * @flags: futex flags (FLAGS_SHARED, etc.)
1756 * @q: the associated futex_q
1757 * @hb: storage for hash_bucket pointer to be returned to caller
1758 *
1759 * Setup the futex_q and locate the hash_bucket. Get the futex value and
1760 * compare it with the expected value. Handle atomic faults internally.
1761 * Return with the hb lock held and a q.key reference on success, and unlocked
1762 * with no q.key reference on failure.
1763 *
1764 * Returns:
1765 * 0 - uaddr contains val and hb has been locked
1766 * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlcoked
1767 */
1768static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
1769 struct futex_q *q, struct futex_hash_bucket **hb)
1770{
1771 u32 uval;
1772 int ret;
1773
1774 /*
1775 * Access the page AFTER the hash-bucket is locked.
1776 * Order is important:
1777 *
1778 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1779 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
1780 *
1781 * The basic logical guarantee of a futex is that it blocks ONLY
1782 * if cond(var) is known to be true at the time of blocking, for
1783 * any cond. If we locked the hash-bucket after testing *uaddr, that
1784 * would open a race condition where we could block indefinitely with
1785 * cond(var) false, which would violate the guarantee.
1786 *
1787 * On the other hand, we insert q and release the hash-bucket only
1788 * after testing *uaddr. This guarantees that futex_wait() will NOT
1789 * absorb a wakeup if *uaddr does not match the desired values
1790 * while the syscall executes.
1791 */
1792retry:
1793 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key);
1794 if (unlikely(ret != 0))
1795 return ret;
1796
1797retry_private:
1798 *hb = queue_lock(q);
1799
1800 ret = get_futex_value_locked(&uval, uaddr);
1801
1802 if (ret) {
1803 queue_unlock(q, *hb);
1804
1805 ret = get_user(uval, uaddr);
1806 if (ret)
1807 goto out;
1808
1809 if (!(flags & FLAGS_SHARED))
1810 goto retry_private;
1811
1812 put_futex_key(&q->key);
1813 goto retry;
1814 }
1815
1816 if (uval != val) {
1817 queue_unlock(q, *hb);
1818 ret = -EWOULDBLOCK;
1819 }
1820
1821out:
1822 if (ret)
1823 put_futex_key(&q->key);
1824 return ret;
1825}
1826
1827static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
1828 ktime_t *abs_time, u32 bitset)
1829{
1830 struct hrtimer_sleeper timeout, *to = NULL;
1831 struct restart_block *restart;
1832 struct futex_hash_bucket *hb;
1833 struct futex_q q = futex_q_init;
1834 int ret;
1835
1836 if (!bitset)
1837 return -EINVAL;
1838 q.bitset = bitset;
1839
1840 if (abs_time) {
1841 to = &timeout;
1842
1843 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
1844 CLOCK_REALTIME : CLOCK_MONOTONIC,
1845 HRTIMER_MODE_ABS);
1846 hrtimer_init_sleeper(to, current);
1847 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
1848 current->timer_slack_ns);
1849 }
1850
1851retry:
1852 /*
1853 * Prepare to wait on uaddr. On success, holds hb lock and increments
1854 * q.key refs.
1855 */
1856 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
1857 if (ret)
1858 goto out;
1859
1860 /* queue_me and wait for wakeup, timeout, or a signal. */
1861 futex_wait_queue_me(hb, &q, to);
1862
1863 /* If we were woken (and unqueued), we succeeded, whatever. */
1864 ret = 0;
1865 /* unqueue_me() drops q.key ref */
1866 if (!unqueue_me(&q))
1867 goto out;
1868 ret = -ETIMEDOUT;
1869 if (to && !to->task)
1870 goto out;
1871
1872 /*
1873 * We expect signal_pending(current), but we might be the
1874 * victim of a spurious wakeup as well.
1875 */
1876 if (!signal_pending(current))
1877 goto retry;
1878
1879 ret = -ERESTARTSYS;
1880 if (!abs_time)
1881 goto out;
1882
1883 restart = &current_thread_info()->restart_block;
1884 restart->fn = futex_wait_restart;
1885 restart->futex.uaddr = uaddr;
1886 restart->futex.val = val;
1887 restart->futex.time = abs_time->tv64;
1888 restart->futex.bitset = bitset;
1889 restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
1890
1891 ret = -ERESTART_RESTARTBLOCK;
1892
1893out:
1894 if (to) {
1895 hrtimer_cancel(&to->timer);
1896 destroy_hrtimer_on_stack(&to->timer);
1897 }
1898 return ret;
1899}
1900
1901
1902static long futex_wait_restart(struct restart_block *restart)
1903{
1904 u32 __user *uaddr = restart->futex.uaddr;
1905 ktime_t t, *tp = NULL;
1906
1907 if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
1908 t.tv64 = restart->futex.time;
1909 tp = &t;
1910 }
1911 restart->fn = do_no_restart_syscall;
1912
1913 return (long)futex_wait(uaddr, restart->futex.flags,
1914 restart->futex.val, tp, restart->futex.bitset);
1915}
1916
1917
1918/*
1919 * Userspace tried a 0 -> TID atomic transition of the futex value
1920 * and failed. The kernel side here does the whole locking operation:
1921 * if there are waiters then it will block, it does PI, etc. (Due to
1922 * races the kernel might see a 0 value of the futex too.)
1923 */
1924static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect,
1925 ktime_t *time, int trylock)
1926{
1927 struct hrtimer_sleeper timeout, *to = NULL;
1928 struct futex_hash_bucket *hb;
1929 struct futex_q q = futex_q_init;
1930 int res, ret;
1931
1932 if (refill_pi_state_cache())
1933 return -ENOMEM;
1934
1935 if (time) {
1936 to = &timeout;
1937 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
1938 HRTIMER_MODE_ABS);
1939 hrtimer_init_sleeper(to, current);
1940 hrtimer_set_expires(&to->timer, *time);
1941 }
1942
1943retry:
1944 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key);
1945 if (unlikely(ret != 0))
1946 goto out;
1947
1948retry_private:
1949 hb = queue_lock(&q);
1950
1951 ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
1952 if (unlikely(ret)) {
1953 switch (ret) {
1954 case 1:
1955 /* We got the lock. */
1956 ret = 0;
1957 goto out_unlock_put_key;
1958 case -EFAULT:
1959 goto uaddr_faulted;
1960 case -EAGAIN:
1961 /*
1962 * Task is exiting and we just wait for the
1963 * exit to complete.
1964 */
1965 queue_unlock(&q, hb);
1966 put_futex_key(&q.key);
1967 cond_resched();
1968 goto retry;
1969 default:
1970 goto out_unlock_put_key;
1971 }
1972 }
1973
1974 /*
1975 * Only actually queue now that the atomic ops are done:
1976 */
1977 queue_me(&q, hb);
1978
1979 WARN_ON(!q.pi_state);
1980 /*
1981 * Block on the PI mutex:
1982 */
1983 if (!trylock)
1984 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
1985 else {
1986 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
1987 /* Fixup the trylock return value: */
1988 ret = ret ? 0 : -EWOULDBLOCK;
1989 }
1990
1991 spin_lock(q.lock_ptr);
1992 /*
1993 * Fixup the pi_state owner and possibly acquire the lock if we
1994 * haven't already.
1995 */
1996 res = fixup_owner(uaddr, &q, !ret);
1997 /*
1998 * If fixup_owner() returned an error, proprogate that. If it acquired
1999 * the lock, clear our -ETIMEDOUT or -EINTR.
2000 */
2001 if (res)
2002 ret = (res < 0) ? res : 0;
2003
2004 /*
2005 * If fixup_owner() faulted and was unable to handle the fault, unlock
2006 * it and return the fault to userspace.
2007 */
2008 if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
2009 rt_mutex_unlock(&q.pi_state->pi_mutex);
2010
2011 /* Unqueue and drop the lock */
2012 unqueue_me_pi(&q);
2013
2014 goto out_put_key;
2015
2016out_unlock_put_key:
2017 queue_unlock(&q, hb);
2018
2019out_put_key:
2020 put_futex_key(&q.key);
2021out:
2022 if (to)
2023 destroy_hrtimer_on_stack(&to->timer);
2024 return ret != -EINTR ? ret : -ERESTARTNOINTR;
2025
2026uaddr_faulted:
2027 queue_unlock(&q, hb);
2028
2029 ret = fault_in_user_writeable(uaddr);
2030 if (ret)
2031 goto out_put_key;
2032
2033 if (!(flags & FLAGS_SHARED))
2034 goto retry_private;
2035
2036 put_futex_key(&q.key);
2037 goto retry;
2038}
2039
2040/*
2041 * Userspace attempted a TID -> 0 atomic transition, and failed.
2042 * This is the in-kernel slowpath: we look up the PI state (if any),
2043 * and do the rt-mutex unlock.
2044 */
2045static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
2046{
2047 struct futex_hash_bucket *hb;
2048 struct futex_q *this, *next;
2049 struct plist_head *head;
2050 union futex_key key = FUTEX_KEY_INIT;
2051 u32 uval, vpid = task_pid_vnr(current);
2052 int ret;
2053
2054retry:
2055 if (get_user(uval, uaddr))
2056 return -EFAULT;
2057 /*
2058 * We release only a lock we actually own:
2059 */
2060 if ((uval & FUTEX_TID_MASK) != vpid)
2061 return -EPERM;
2062
2063 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key);
2064 if (unlikely(ret != 0))
2065 goto out;
2066
2067 hb = hash_futex(&key);
2068 spin_lock(&hb->lock);
2069
2070 /*
2071 * To avoid races, try to do the TID -> 0 atomic transition
2072 * again. If it succeeds then we can return without waking
2073 * anyone else up:
2074 */
2075 if (!(uval & FUTEX_OWNER_DIED) &&
2076 cmpxchg_futex_value_locked(&uval, uaddr, vpid, 0))
2077 goto pi_faulted;
2078 /*
2079 * Rare case: we managed to release the lock atomically,
2080 * no need to wake anyone else up:
2081 */
2082 if (unlikely(uval == vpid))
2083 goto out_unlock;
2084
2085 /*
2086 * Ok, other tasks may need to be woken up - check waiters
2087 * and do the wakeup if necessary:
2088 */
2089 head = &hb->chain;
2090
2091 plist_for_each_entry_safe(this, next, head, list) {
2092 if (!match_futex (&this->key, &key))
2093 continue;
2094 ret = wake_futex_pi(uaddr, uval, this);
2095 /*
2096 * The atomic access to the futex value
2097 * generated a pagefault, so retry the
2098 * user-access and the wakeup:
2099 */
2100 if (ret == -EFAULT)
2101 goto pi_faulted;
2102 goto out_unlock;
2103 }
2104 /*
2105 * No waiters - kernel unlocks the futex:
2106 */
2107 if (!(uval & FUTEX_OWNER_DIED)) {
2108 ret = unlock_futex_pi(uaddr, uval);
2109 if (ret == -EFAULT)
2110 goto pi_faulted;
2111 }
2112
2113out_unlock:
2114 spin_unlock(&hb->lock);
2115 put_futex_key(&key);
2116
2117out:
2118 return ret;
2119
2120pi_faulted:
2121 spin_unlock(&hb->lock);
2122 put_futex_key(&key);
2123
2124 ret = fault_in_user_writeable(uaddr);
2125 if (!ret)
2126 goto retry;
2127
2128 return ret;
2129}
2130
2131/**
2132 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2133 * @hb: the hash_bucket futex_q was original enqueued on
2134 * @q: the futex_q woken while waiting to be requeued
2135 * @key2: the futex_key of the requeue target futex
2136 * @timeout: the timeout associated with the wait (NULL if none)
2137 *
2138 * Detect if the task was woken on the initial futex as opposed to the requeue
2139 * target futex. If so, determine if it was a timeout or a signal that caused
2140 * the wakeup and return the appropriate error code to the caller. Must be
2141 * called with the hb lock held.
2142 *
2143 * Returns
2144 * 0 - no early wakeup detected
2145 * <0 - -ETIMEDOUT or -ERESTARTNOINTR
2146 */
2147static inline
2148int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2149 struct futex_q *q, union futex_key *key2,
2150 struct hrtimer_sleeper *timeout)
2151{
2152 int ret = 0;
2153
2154 /*
2155 * With the hb lock held, we avoid races while we process the wakeup.
2156 * We only need to hold hb (and not hb2) to ensure atomicity as the
2157 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2158 * It can't be requeued from uaddr2 to something else since we don't
2159 * support a PI aware source futex for requeue.
2160 */
2161 if (!match_futex(&q->key, key2)) {
2162 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2163 /*
2164 * We were woken prior to requeue by a timeout or a signal.
2165 * Unqueue the futex_q and determine which it was.
2166 */
2167 plist_del(&q->list, &hb->chain);
2168
2169 /* Handle spurious wakeups gracefully */
2170 ret = -EWOULDBLOCK;
2171 if (timeout && !timeout->task)
2172 ret = -ETIMEDOUT;
2173 else if (signal_pending(current))
2174 ret = -ERESTARTNOINTR;
2175 }
2176 return ret;
2177}
2178
2179/**
2180 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2181 * @uaddr: the futex we initially wait on (non-pi)
2182 * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
2183 * the same type, no requeueing from private to shared, etc.
2184 * @val: the expected value of uaddr
2185 * @abs_time: absolute timeout
2186 * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
2187 * @clockrt: whether to use CLOCK_REALTIME (1) or CLOCK_MONOTONIC (0)
2188 * @uaddr2: the pi futex we will take prior to returning to user-space
2189 *
2190 * The caller will wait on uaddr and will be requeued by futex_requeue() to
2191 * uaddr2 which must be PI aware. Normal wakeup will wake on uaddr2 and
2192 * complete the acquisition of the rt_mutex prior to returning to userspace.
2193 * This ensures the rt_mutex maintains an owner when it has waiters; without
2194 * one, the pi logic wouldn't know which task to boost/deboost, if there was a
2195 * need to.
2196 *
2197 * We call schedule in futex_wait_queue_me() when we enqueue and return there
2198 * via the following:
2199 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2200 * 2) wakeup on uaddr2 after a requeue
2201 * 3) signal
2202 * 4) timeout
2203 *
2204 * If 3, cleanup and return -ERESTARTNOINTR.
2205 *
2206 * If 2, we may then block on trying to take the rt_mutex and return via:
2207 * 5) successful lock
2208 * 6) signal
2209 * 7) timeout
2210 * 8) other lock acquisition failure
2211 *
2212 * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2213 *
2214 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2215 *
2216 * Returns:
2217 * 0 - On success
2218 * <0 - On error
2219 */
2220static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
2221 u32 val, ktime_t *abs_time, u32 bitset,
2222 u32 __user *uaddr2)
2223{
2224 struct hrtimer_sleeper timeout, *to = NULL;
2225 struct rt_mutex_waiter rt_waiter;
2226 struct rt_mutex *pi_mutex = NULL;
2227 struct futex_hash_bucket *hb;
2228 union futex_key key2 = FUTEX_KEY_INIT;
2229 struct futex_q q = futex_q_init;
2230 int res, ret;
2231
2232 if (!bitset)
2233 return -EINVAL;
2234
2235 if (abs_time) {
2236 to = &timeout;
2237 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2238 CLOCK_REALTIME : CLOCK_MONOTONIC,
2239 HRTIMER_MODE_ABS);
2240 hrtimer_init_sleeper(to, current);
2241 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2242 current->timer_slack_ns);
2243 }
2244
2245 /*
2246 * The waiter is allocated on our stack, manipulated by the requeue
2247 * code while we sleep on uaddr.
2248 */
2249 debug_rt_mutex_init_waiter(&rt_waiter);
2250 rt_waiter.task = NULL;
2251
2252 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2);
2253 if (unlikely(ret != 0))
2254 goto out;
2255
2256 q.bitset = bitset;
2257 q.rt_waiter = &rt_waiter;
2258 q.requeue_pi_key = &key2;
2259
2260 /*
2261 * Prepare to wait on uaddr. On success, increments q.key (key1) ref
2262 * count.
2263 */
2264 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2265 if (ret)
2266 goto out_key2;
2267
2268 /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2269 futex_wait_queue_me(hb, &q, to);
2270
2271 spin_lock(&hb->lock);
2272 ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2273 spin_unlock(&hb->lock);
2274 if (ret)
2275 goto out_put_keys;
2276
2277 /*
2278 * In order for us to be here, we know our q.key == key2, and since
2279 * we took the hb->lock above, we also know that futex_requeue() has
2280 * completed and we no longer have to concern ourselves with a wakeup
2281 * race with the atomic proxy lock acquisition by the requeue code. The
2282 * futex_requeue dropped our key1 reference and incremented our key2
2283 * reference count.
2284 */
2285
2286 /* Check if the requeue code acquired the second futex for us. */
2287 if (!q.rt_waiter) {
2288 /*
2289 * Got the lock. We might not be the anticipated owner if we
2290 * did a lock-steal - fix up the PI-state in that case.
2291 */
2292 if (q.pi_state && (q.pi_state->owner != current)) {
2293 spin_lock(q.lock_ptr);
2294 ret = fixup_pi_state_owner(uaddr2, &q, current);
2295 spin_unlock(q.lock_ptr);
2296 }
2297 } else {
2298 /*
2299 * We have been woken up by futex_unlock_pi(), a timeout, or a
2300 * signal. futex_unlock_pi() will not destroy the lock_ptr nor
2301 * the pi_state.
2302 */
2303 WARN_ON(!&q.pi_state);
2304 pi_mutex = &q.pi_state->pi_mutex;
2305 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
2306 debug_rt_mutex_free_waiter(&rt_waiter);
2307
2308 spin_lock(q.lock_ptr);
2309 /*
2310 * Fixup the pi_state owner and possibly acquire the lock if we
2311 * haven't already.
2312 */
2313 res = fixup_owner(uaddr2, &q, !ret);
2314 /*
2315 * If fixup_owner() returned an error, proprogate that. If it
2316 * acquired the lock, clear -ETIMEDOUT or -EINTR.
2317 */
2318 if (res)
2319 ret = (res < 0) ? res : 0;
2320
2321 /* Unqueue and drop the lock. */
2322 unqueue_me_pi(&q);
2323 }
2324
2325 /*
2326 * If fixup_pi_state_owner() faulted and was unable to handle the
2327 * fault, unlock the rt_mutex and return the fault to userspace.
2328 */
2329 if (ret == -EFAULT) {
2330 if (rt_mutex_owner(pi_mutex) == current)
2331 rt_mutex_unlock(pi_mutex);
2332 } else if (ret == -EINTR) {
2333 /*
2334 * We've already been requeued, but cannot restart by calling
2335 * futex_lock_pi() directly. We could restart this syscall, but
2336 * it would detect that the user space "val" changed and return
2337 * -EWOULDBLOCK. Save the overhead of the restart and return
2338 * -EWOULDBLOCK directly.
2339 */
2340 ret = -EWOULDBLOCK;
2341 }
2342
2343out_put_keys:
2344 put_futex_key(&q.key);
2345out_key2:
2346 put_futex_key(&key2);
2347
2348out:
2349 if (to) {
2350 hrtimer_cancel(&to->timer);
2351 destroy_hrtimer_on_stack(&to->timer);
2352 }
2353 return ret;
2354}
2355
2356/*
2357 * Support for robust futexes: the kernel cleans up held futexes at
2358 * thread exit time.
2359 *
2360 * Implementation: user-space maintains a per-thread list of locks it
2361 * is holding. Upon do_exit(), the kernel carefully walks this list,
2362 * and marks all locks that are owned by this thread with the
2363 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2364 * always manipulated with the lock held, so the list is private and
2365 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2366 * field, to allow the kernel to clean up if the thread dies after
2367 * acquiring the lock, but just before it could have added itself to
2368 * the list. There can only be one such pending lock.
2369 */
2370
2371/**
2372 * sys_set_robust_list() - Set the robust-futex list head of a task
2373 * @head: pointer to the list-head
2374 * @len: length of the list-head, as userspace expects
2375 */
2376SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2377 size_t, len)
2378{
2379 if (!futex_cmpxchg_enabled)
2380 return -ENOSYS;
2381 /*
2382 * The kernel knows only one size for now:
2383 */
2384 if (unlikely(len != sizeof(*head)))
2385 return -EINVAL;
2386
2387 current->robust_list = head;
2388
2389 return 0;
2390}
2391
2392/**
2393 * sys_get_robust_list() - Get the robust-futex list head of a task
2394 * @pid: pid of the process [zero for current task]
2395 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
2396 * @len_ptr: pointer to a length field, the kernel fills in the header size
2397 */
2398SYSCALL_DEFINE3(get_robust_list, int, pid,
2399 struct robust_list_head __user * __user *, head_ptr,
2400 size_t __user *, len_ptr)
2401{
2402 struct robust_list_head __user *head;
2403 unsigned long ret;
2404 const struct cred *cred = current_cred(), *pcred;
2405
2406 if (!futex_cmpxchg_enabled)
2407 return -ENOSYS;
2408
2409 if (!pid)
2410 head = current->robust_list;
2411 else {
2412 struct task_struct *p;
2413
2414 ret = -ESRCH;
2415 rcu_read_lock();
2416 p = find_task_by_vpid(pid);
2417 if (!p)
2418 goto err_unlock;
2419 ret = -EPERM;
2420 pcred = __task_cred(p);
2421 /* If victim is in different user_ns, then uids are not
2422 comparable, so we must have CAP_SYS_PTRACE */
2423 if (cred->user->user_ns != pcred->user->user_ns) {
2424 if (!ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE))
2425 goto err_unlock;
2426 goto ok;
2427 }
2428 /* If victim is in same user_ns, then uids are comparable */
2429 if (cred->euid != pcred->euid &&
2430 cred->euid != pcred->uid &&
2431 !ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE))
2432 goto err_unlock;
2433ok:
2434 head = p->robust_list;
2435 rcu_read_unlock();
2436 }
2437
2438 if (put_user(sizeof(*head), len_ptr))
2439 return -EFAULT;
2440 return put_user(head, head_ptr);
2441
2442err_unlock:
2443 rcu_read_unlock();
2444
2445 return ret;
2446}
2447
2448/*
2449 * Process a futex-list entry, check whether it's owned by the
2450 * dying task, and do notification if so:
2451 */
2452int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
2453{
2454 u32 uval, nval, mval;
2455
2456retry:
2457 if (get_user(uval, uaddr))
2458 return -1;
2459
2460 if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
2461 /*
2462 * Ok, this dying thread is truly holding a futex
2463 * of interest. Set the OWNER_DIED bit atomically
2464 * via cmpxchg, and if the value had FUTEX_WAITERS
2465 * set, wake up a waiter (if any). (We have to do a
2466 * futex_wake() even if OWNER_DIED is already set -
2467 * to handle the rare but possible case of recursive
2468 * thread-death.) The rest of the cleanup is done in
2469 * userspace.
2470 */
2471 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
2472 /*
2473 * We are not holding a lock here, but we want to have
2474 * the pagefault_disable/enable() protection because
2475 * we want to handle the fault gracefully. If the
2476 * access fails we try to fault in the futex with R/W
2477 * verification via get_user_pages. get_user() above
2478 * does not guarantee R/W access. If that fails we
2479 * give up and leave the futex locked.
2480 */
2481 if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
2482 if (fault_in_user_writeable(uaddr))
2483 return -1;
2484 goto retry;
2485 }
2486 if (nval != uval)
2487 goto retry;
2488
2489 /*
2490 * Wake robust non-PI futexes here. The wakeup of
2491 * PI futexes happens in exit_pi_state():
2492 */
2493 if (!pi && (uval & FUTEX_WAITERS))
2494 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
2495 }
2496 return 0;
2497}
2498
2499/*
2500 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
2501 */
2502static inline int fetch_robust_entry(struct robust_list __user **entry,
2503 struct robust_list __user * __user *head,
2504 unsigned int *pi)
2505{
2506 unsigned long uentry;
2507
2508 if (get_user(uentry, (unsigned long __user *)head))
2509 return -EFAULT;
2510
2511 *entry = (void __user *)(uentry & ~1UL);
2512 *pi = uentry & 1;
2513
2514 return 0;
2515}
2516
2517/*
2518 * Walk curr->robust_list (very carefully, it's a userspace list!)
2519 * and mark any locks found there dead, and notify any waiters.
2520 *
2521 * We silently return on any sign of list-walking problem.
2522 */
2523void exit_robust_list(struct task_struct *curr)
2524{
2525 struct robust_list_head __user *head = curr->robust_list;
2526 struct robust_list __user *entry, *next_entry, *pending;
2527 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
2528 unsigned int uninitialized_var(next_pi);
2529 unsigned long futex_offset;
2530 int rc;
2531
2532 if (!futex_cmpxchg_enabled)
2533 return;
2534
2535 /*
2536 * Fetch the list head (which was registered earlier, via
2537 * sys_set_robust_list()):
2538 */
2539 if (fetch_robust_entry(&entry, &head->list.next, &pi))
2540 return;
2541 /*
2542 * Fetch the relative futex offset:
2543 */
2544 if (get_user(futex_offset, &head->futex_offset))
2545 return;
2546 /*
2547 * Fetch any possibly pending lock-add first, and handle it
2548 * if it exists:
2549 */
2550 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
2551 return;
2552
2553 next_entry = NULL; /* avoid warning with gcc */
2554 while (entry != &head->list) {
2555 /*
2556 * Fetch the next entry in the list before calling
2557 * handle_futex_death:
2558 */
2559 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
2560 /*
2561 * A pending lock might already be on the list, so
2562 * don't process it twice:
2563 */
2564 if (entry != pending)
2565 if (handle_futex_death((void __user *)entry + futex_offset,
2566 curr, pi))
2567 return;
2568 if (rc)
2569 return;
2570 entry = next_entry;
2571 pi = next_pi;
2572 /*
2573 * Avoid excessively long or circular lists:
2574 */
2575 if (!--limit)
2576 break;
2577
2578 cond_resched();
2579 }
2580
2581 if (pending)
2582 handle_futex_death((void __user *)pending + futex_offset,
2583 curr, pip);
2584}
2585
2586long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
2587 u32 __user *uaddr2, u32 val2, u32 val3)
2588{
2589 int ret = -ENOSYS, cmd = op & FUTEX_CMD_MASK;
2590 unsigned int flags = 0;
2591
2592 if (!(op & FUTEX_PRIVATE_FLAG))
2593 flags |= FLAGS_SHARED;
2594
2595 if (op & FUTEX_CLOCK_REALTIME) {
2596 flags |= FLAGS_CLOCKRT;
2597 if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
2598 return -ENOSYS;
2599 }
2600
2601 switch (cmd) {
2602 case FUTEX_WAIT:
2603 val3 = FUTEX_BITSET_MATCH_ANY;
2604 case FUTEX_WAIT_BITSET:
2605 ret = futex_wait(uaddr, flags, val, timeout, val3);
2606 break;
2607 case FUTEX_WAKE:
2608 val3 = FUTEX_BITSET_MATCH_ANY;
2609 case FUTEX_WAKE_BITSET:
2610 ret = futex_wake(uaddr, flags, val, val3);
2611 break;
2612 case FUTEX_REQUEUE:
2613 ret = futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
2614 break;
2615 case FUTEX_CMP_REQUEUE:
2616 ret = futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
2617 break;
2618 case FUTEX_WAKE_OP:
2619 ret = futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
2620 break;
2621 case FUTEX_LOCK_PI:
2622 if (futex_cmpxchg_enabled)
2623 ret = futex_lock_pi(uaddr, flags, val, timeout, 0);
2624 break;
2625 case FUTEX_UNLOCK_PI:
2626 if (futex_cmpxchg_enabled)
2627 ret = futex_unlock_pi(uaddr, flags);
2628 break;
2629 case FUTEX_TRYLOCK_PI:
2630 if (futex_cmpxchg_enabled)
2631 ret = futex_lock_pi(uaddr, flags, 0, timeout, 1);
2632 break;
2633 case FUTEX_WAIT_REQUEUE_PI:
2634 val3 = FUTEX_BITSET_MATCH_ANY;
2635 ret = futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
2636 uaddr2);
2637 break;
2638 case FUTEX_CMP_REQUEUE_PI:
2639 ret = futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
2640 break;
2641 default:
2642 ret = -ENOSYS;
2643 }
2644 return ret;
2645}
2646
2647
2648SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
2649 struct timespec __user *, utime, u32 __user *, uaddr2,
2650 u32, val3)
2651{
2652 struct timespec ts;
2653 ktime_t t, *tp = NULL;
2654 u32 val2 = 0;
2655 int cmd = op & FUTEX_CMD_MASK;
2656
2657 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
2658 cmd == FUTEX_WAIT_BITSET ||
2659 cmd == FUTEX_WAIT_REQUEUE_PI)) {
2660 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
2661 return -EFAULT;
2662 if (!timespec_valid(&ts))
2663 return -EINVAL;
2664
2665 t = timespec_to_ktime(ts);
2666 if (cmd == FUTEX_WAIT)
2667 t = ktime_add_safe(ktime_get(), t);
2668 tp = &t;
2669 }
2670 /*
2671 * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
2672 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
2673 */
2674 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
2675 cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
2676 val2 = (u32) (unsigned long) utime;
2677
2678 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
2679}
2680
2681static int __init futex_init(void)
2682{
2683 u32 curval;
2684 int i;
2685
2686 /*
2687 * This will fail and we want it. Some arch implementations do
2688 * runtime detection of the futex_atomic_cmpxchg_inatomic()
2689 * functionality. We want to know that before we call in any
2690 * of the complex code paths. Also we want to prevent
2691 * registration of robust lists in that case. NULL is
2692 * guaranteed to fault and we get -EFAULT on functional
2693 * implementation, the non-functional ones will return
2694 * -ENOSYS.
2695 */
2696 if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
2697 futex_cmpxchg_enabled = 1;
2698
2699 for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
2700 plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock);
2701 spin_lock_init(&futex_queues[i].lock);
2702 }
2703
2704 return 0;
2705}
2706__initcall(futex_init);