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