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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/export.h>
59#include <linux/magic.h>
60#include <linux/pid.h>
61#include <linux/nsproxy.h>
62#include <linux/ptrace.h>
63#include <linux/sched/rt.h>
64#include <linux/hugetlb.h>
65#include <linux/freezer.h>
66#include <linux/bootmem.h>
67
68#include <asm/futex.h>
69
70#include "locking/rtmutex_common.h"
71
72/*
73 * READ this before attempting to hack on futexes!
74 *
75 * Basic futex operation and ordering guarantees
76 * =============================================
77 *
78 * The waiter reads the futex value in user space and calls
79 * futex_wait(). This function computes the hash bucket and acquires
80 * the hash bucket lock. After that it reads the futex user space value
81 * again and verifies that the data has not changed. If it has not changed
82 * it enqueues itself into the hash bucket, releases the hash bucket lock
83 * and schedules.
84 *
85 * The waker side modifies the user space value of the futex and calls
86 * futex_wake(). This function computes the hash bucket and acquires the
87 * hash bucket lock. Then it looks for waiters on that futex in the hash
88 * bucket and wakes them.
89 *
90 * In futex wake up scenarios where no tasks are blocked on a futex, taking
91 * the hb spinlock can be avoided and simply return. In order for this
92 * optimization to work, ordering guarantees must exist so that the waiter
93 * being added to the list is acknowledged when the list is concurrently being
94 * checked by the waker, avoiding scenarios like the following:
95 *
96 * CPU 0 CPU 1
97 * val = *futex;
98 * sys_futex(WAIT, futex, val);
99 * futex_wait(futex, val);
100 * uval = *futex;
101 * *futex = newval;
102 * sys_futex(WAKE, futex);
103 * futex_wake(futex);
104 * if (queue_empty())
105 * return;
106 * if (uval == val)
107 * lock(hash_bucket(futex));
108 * queue();
109 * unlock(hash_bucket(futex));
110 * schedule();
111 *
112 * This would cause the waiter on CPU 0 to wait forever because it
113 * missed the transition of the user space value from val to newval
114 * and the waker did not find the waiter in the hash bucket queue.
115 *
116 * The correct serialization ensures that a waiter either observes
117 * the changed user space value before blocking or is woken by a
118 * concurrent waker:
119 *
120 * CPU 0 CPU 1
121 * val = *futex;
122 * sys_futex(WAIT, futex, val);
123 * futex_wait(futex, val);
124 *
125 * waiters++; (a)
126 * mb(); (A) <-- paired with -.
127 * |
128 * lock(hash_bucket(futex)); |
129 * |
130 * uval = *futex; |
131 * | *futex = newval;
132 * | sys_futex(WAKE, futex);
133 * | futex_wake(futex);
134 * |
135 * `-------> mb(); (B)
136 * if (uval == val)
137 * queue();
138 * unlock(hash_bucket(futex));
139 * schedule(); if (waiters)
140 * lock(hash_bucket(futex));
141 * else wake_waiters(futex);
142 * waiters--; (b) unlock(hash_bucket(futex));
143 *
144 * Where (A) orders the waiters increment and the futex value read through
145 * atomic operations (see hb_waiters_inc) and where (B) orders the write
146 * to futex and the waiters read -- this is done by the barriers in
147 * get_futex_key_refs(), through either ihold or atomic_inc, depending on the
148 * futex type.
149 *
150 * This yields the following case (where X:=waiters, Y:=futex):
151 *
152 * X = Y = 0
153 *
154 * w[X]=1 w[Y]=1
155 * MB MB
156 * r[Y]=y r[X]=x
157 *
158 * Which guarantees that x==0 && y==0 is impossible; which translates back into
159 * the guarantee that we cannot both miss the futex variable change and the
160 * enqueue.
161 *
162 * Note that a new waiter is accounted for in (a) even when it is possible that
163 * the wait call can return error, in which case we backtrack from it in (b).
164 * Refer to the comment in queue_lock().
165 *
166 * Similarly, in order to account for waiters being requeued on another
167 * address we always increment the waiters for the destination bucket before
168 * acquiring the lock. It then decrements them again after releasing it -
169 * the code that actually moves the futex(es) between hash buckets (requeue_futex)
170 * will do the additional required waiter count housekeeping. This is done for
171 * double_lock_hb() and double_unlock_hb(), respectively.
172 */
173
174#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
175int __read_mostly futex_cmpxchg_enabled;
176#endif
177
178/*
179 * Futex flags used to encode options to functions and preserve them across
180 * restarts.
181 */
182#define FLAGS_SHARED 0x01
183#define FLAGS_CLOCKRT 0x02
184#define FLAGS_HAS_TIMEOUT 0x04
185
186/*
187 * Priority Inheritance state:
188 */
189struct futex_pi_state {
190 /*
191 * list of 'owned' pi_state instances - these have to be
192 * cleaned up in do_exit() if the task exits prematurely:
193 */
194 struct list_head list;
195
196 /*
197 * The PI object:
198 */
199 struct rt_mutex pi_mutex;
200
201 struct task_struct *owner;
202 atomic_t refcount;
203
204 union futex_key key;
205};
206
207/**
208 * struct futex_q - The hashed futex queue entry, one per waiting task
209 * @list: priority-sorted list of tasks waiting on this futex
210 * @task: the task waiting on the futex
211 * @lock_ptr: the hash bucket lock
212 * @key: the key the futex is hashed on
213 * @pi_state: optional priority inheritance state
214 * @rt_waiter: rt_waiter storage for use with requeue_pi
215 * @requeue_pi_key: the requeue_pi target futex key
216 * @bitset: bitset for the optional bitmasked wakeup
217 *
218 * We use this hashed waitqueue, instead of a normal wait_queue_t, so
219 * we can wake only the relevant ones (hashed queues may be shared).
220 *
221 * A futex_q has a woken state, just like tasks have TASK_RUNNING.
222 * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
223 * The order of wakeup is always to make the first condition true, then
224 * the second.
225 *
226 * PI futexes are typically woken before they are removed from the hash list via
227 * the rt_mutex code. See unqueue_me_pi().
228 */
229struct futex_q {
230 struct plist_node list;
231
232 struct task_struct *task;
233 spinlock_t *lock_ptr;
234 union futex_key key;
235 struct futex_pi_state *pi_state;
236 struct rt_mutex_waiter *rt_waiter;
237 union futex_key *requeue_pi_key;
238 u32 bitset;
239};
240
241static const struct futex_q futex_q_init = {
242 /* list gets initialized in queue_me()*/
243 .key = FUTEX_KEY_INIT,
244 .bitset = FUTEX_BITSET_MATCH_ANY
245};
246
247/*
248 * Hash buckets are shared by all the futex_keys that hash to the same
249 * location. Each key may have multiple futex_q structures, one for each task
250 * waiting on a futex.
251 */
252struct futex_hash_bucket {
253 atomic_t waiters;
254 spinlock_t lock;
255 struct plist_head chain;
256} ____cacheline_aligned_in_smp;
257
258static unsigned long __read_mostly futex_hashsize;
259
260static struct futex_hash_bucket *futex_queues;
261
262static inline void futex_get_mm(union futex_key *key)
263{
264 atomic_inc(&key->private.mm->mm_count);
265 /*
266 * Ensure futex_get_mm() implies a full barrier such that
267 * get_futex_key() implies a full barrier. This is relied upon
268 * as full barrier (B), see the ordering comment above.
269 */
270 smp_mb__after_atomic_inc();
271}
272
273/*
274 * Reflects a new waiter being added to the waitqueue.
275 */
276static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
277{
278#ifdef CONFIG_SMP
279 atomic_inc(&hb->waiters);
280 /*
281 * Full barrier (A), see the ordering comment above.
282 */
283 smp_mb__after_atomic_inc();
284#endif
285}
286
287/*
288 * Reflects a waiter being removed from the waitqueue by wakeup
289 * paths.
290 */
291static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
292{
293#ifdef CONFIG_SMP
294 atomic_dec(&hb->waiters);
295#endif
296}
297
298static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
299{
300#ifdef CONFIG_SMP
301 return atomic_read(&hb->waiters);
302#else
303 return 1;
304#endif
305}
306
307/*
308 * We hash on the keys returned from get_futex_key (see below).
309 */
310static struct futex_hash_bucket *hash_futex(union futex_key *key)
311{
312 u32 hash = jhash2((u32*)&key->both.word,
313 (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
314 key->both.offset);
315 return &futex_queues[hash & (futex_hashsize - 1)];
316}
317
318/*
319 * Return 1 if two futex_keys are equal, 0 otherwise.
320 */
321static inline int match_futex(union futex_key *key1, union futex_key *key2)
322{
323 return (key1 && key2
324 && key1->both.word == key2->both.word
325 && key1->both.ptr == key2->both.ptr
326 && key1->both.offset == key2->both.offset);
327}
328
329/*
330 * Take a reference to the resource addressed by a key.
331 * Can be called while holding spinlocks.
332 *
333 */
334static void get_futex_key_refs(union futex_key *key)
335{
336 if (!key->both.ptr)
337 return;
338
339 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
340 case FUT_OFF_INODE:
341 ihold(key->shared.inode); /* implies MB (B) */
342 break;
343 case FUT_OFF_MMSHARED:
344 futex_get_mm(key); /* implies MB (B) */
345 break;
346 }
347}
348
349/*
350 * Drop a reference to the resource addressed by a key.
351 * The hash bucket spinlock must not be held.
352 */
353static void drop_futex_key_refs(union futex_key *key)
354{
355 if (!key->both.ptr) {
356 /* If we're here then we tried to put a key we failed to get */
357 WARN_ON_ONCE(1);
358 return;
359 }
360
361 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
362 case FUT_OFF_INODE:
363 iput(key->shared.inode);
364 break;
365 case FUT_OFF_MMSHARED:
366 mmdrop(key->private.mm);
367 break;
368 }
369}
370
371/**
372 * get_futex_key() - Get parameters which are the keys for a futex
373 * @uaddr: virtual address of the futex
374 * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
375 * @key: address where result is stored.
376 * @rw: mapping needs to be read/write (values: VERIFY_READ,
377 * VERIFY_WRITE)
378 *
379 * Return: a negative error code or 0
380 *
381 * The key words are stored in *key on success.
382 *
383 * For shared mappings, it's (page->index, file_inode(vma->vm_file),
384 * offset_within_page). For private mappings, it's (uaddr, current->mm).
385 * We can usually work out the index without swapping in the page.
386 *
387 * lock_page() might sleep, the caller should not hold a spinlock.
388 */
389static int
390get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
391{
392 unsigned long address = (unsigned long)uaddr;
393 struct mm_struct *mm = current->mm;
394 struct page *page, *page_head;
395 int err, ro = 0;
396
397 /*
398 * The futex address must be "naturally" aligned.
399 */
400 key->both.offset = address % PAGE_SIZE;
401 if (unlikely((address % sizeof(u32)) != 0))
402 return -EINVAL;
403 address -= key->both.offset;
404
405 if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
406 return -EFAULT;
407
408 /*
409 * PROCESS_PRIVATE futexes are fast.
410 * As the mm cannot disappear under us and the 'key' only needs
411 * virtual address, we dont even have to find the underlying vma.
412 * Note : We do have to check 'uaddr' is a valid user address,
413 * but access_ok() should be faster than find_vma()
414 */
415 if (!fshared) {
416 key->private.mm = mm;
417 key->private.address = address;
418 get_futex_key_refs(key); /* implies MB (B) */
419 return 0;
420 }
421
422again:
423 err = get_user_pages_fast(address, 1, 1, &page);
424 /*
425 * If write access is not required (eg. FUTEX_WAIT), try
426 * and get read-only access.
427 */
428 if (err == -EFAULT && rw == VERIFY_READ) {
429 err = get_user_pages_fast(address, 1, 0, &page);
430 ro = 1;
431 }
432 if (err < 0)
433 return err;
434 else
435 err = 0;
436
437#ifdef CONFIG_TRANSPARENT_HUGEPAGE
438 page_head = page;
439 if (unlikely(PageTail(page))) {
440 put_page(page);
441 /* serialize against __split_huge_page_splitting() */
442 local_irq_disable();
443 if (likely(__get_user_pages_fast(address, 1, !ro, &page) == 1)) {
444 page_head = compound_head(page);
445 /*
446 * page_head is valid pointer but we must pin
447 * it before taking the PG_lock and/or
448 * PG_compound_lock. The moment we re-enable
449 * irqs __split_huge_page_splitting() can
450 * return and the head page can be freed from
451 * under us. We can't take the PG_lock and/or
452 * PG_compound_lock on a page that could be
453 * freed from under us.
454 */
455 if (page != page_head) {
456 get_page(page_head);
457 put_page(page);
458 }
459 local_irq_enable();
460 } else {
461 local_irq_enable();
462 goto again;
463 }
464 }
465#else
466 page_head = compound_head(page);
467 if (page != page_head) {
468 get_page(page_head);
469 put_page(page);
470 }
471#endif
472
473 lock_page(page_head);
474
475 /*
476 * If page_head->mapping is NULL, then it cannot be a PageAnon
477 * page; but it might be the ZERO_PAGE or in the gate area or
478 * in a special mapping (all cases which we are happy to fail);
479 * or it may have been a good file page when get_user_pages_fast
480 * found it, but truncated or holepunched or subjected to
481 * invalidate_complete_page2 before we got the page lock (also
482 * cases which we are happy to fail). And we hold a reference,
483 * so refcount care in invalidate_complete_page's remove_mapping
484 * prevents drop_caches from setting mapping to NULL beneath us.
485 *
486 * The case we do have to guard against is when memory pressure made
487 * shmem_writepage move it from filecache to swapcache beneath us:
488 * an unlikely race, but we do need to retry for page_head->mapping.
489 */
490 if (!page_head->mapping) {
491 int shmem_swizzled = PageSwapCache(page_head);
492 unlock_page(page_head);
493 put_page(page_head);
494 if (shmem_swizzled)
495 goto again;
496 return -EFAULT;
497 }
498
499 /*
500 * Private mappings are handled in a simple way.
501 *
502 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
503 * it's a read-only handle, it's expected that futexes attach to
504 * the object not the particular process.
505 */
506 if (PageAnon(page_head)) {
507 /*
508 * A RO anonymous page will never change and thus doesn't make
509 * sense for futex operations.
510 */
511 if (ro) {
512 err = -EFAULT;
513 goto out;
514 }
515
516 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
517 key->private.mm = mm;
518 key->private.address = address;
519 } else {
520 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
521 key->shared.inode = page_head->mapping->host;
522 key->shared.pgoff = basepage_index(page);
523 }
524
525 get_futex_key_refs(key); /* implies MB (B) */
526
527out:
528 unlock_page(page_head);
529 put_page(page_head);
530 return err;
531}
532
533static inline void put_futex_key(union futex_key *key)
534{
535 drop_futex_key_refs(key);
536}
537
538/**
539 * fault_in_user_writeable() - Fault in user address and verify RW access
540 * @uaddr: pointer to faulting user space address
541 *
542 * Slow path to fixup the fault we just took in the atomic write
543 * access to @uaddr.
544 *
545 * We have no generic implementation of a non-destructive write to the
546 * user address. We know that we faulted in the atomic pagefault
547 * disabled section so we can as well avoid the #PF overhead by
548 * calling get_user_pages() right away.
549 */
550static int fault_in_user_writeable(u32 __user *uaddr)
551{
552 struct mm_struct *mm = current->mm;
553 int ret;
554
555 down_read(&mm->mmap_sem);
556 ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
557 FAULT_FLAG_WRITE);
558 up_read(&mm->mmap_sem);
559
560 return ret < 0 ? ret : 0;
561}
562
563/**
564 * futex_top_waiter() - Return the highest priority waiter on a futex
565 * @hb: the hash bucket the futex_q's reside in
566 * @key: the futex key (to distinguish it from other futex futex_q's)
567 *
568 * Must be called with the hb lock held.
569 */
570static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
571 union futex_key *key)
572{
573 struct futex_q *this;
574
575 plist_for_each_entry(this, &hb->chain, list) {
576 if (match_futex(&this->key, key))
577 return this;
578 }
579 return NULL;
580}
581
582static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
583 u32 uval, u32 newval)
584{
585 int ret;
586
587 pagefault_disable();
588 ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
589 pagefault_enable();
590
591 return ret;
592}
593
594static int get_futex_value_locked(u32 *dest, u32 __user *from)
595{
596 int ret;
597
598 pagefault_disable();
599 ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
600 pagefault_enable();
601
602 return ret ? -EFAULT : 0;
603}
604
605
606/*
607 * PI code:
608 */
609static int refill_pi_state_cache(void)
610{
611 struct futex_pi_state *pi_state;
612
613 if (likely(current->pi_state_cache))
614 return 0;
615
616 pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
617
618 if (!pi_state)
619 return -ENOMEM;
620
621 INIT_LIST_HEAD(&pi_state->list);
622 /* pi_mutex gets initialized later */
623 pi_state->owner = NULL;
624 atomic_set(&pi_state->refcount, 1);
625 pi_state->key = FUTEX_KEY_INIT;
626
627 current->pi_state_cache = pi_state;
628
629 return 0;
630}
631
632static struct futex_pi_state * alloc_pi_state(void)
633{
634 struct futex_pi_state *pi_state = current->pi_state_cache;
635
636 WARN_ON(!pi_state);
637 current->pi_state_cache = NULL;
638
639 return pi_state;
640}
641
642static void free_pi_state(struct futex_pi_state *pi_state)
643{
644 if (!atomic_dec_and_test(&pi_state->refcount))
645 return;
646
647 /*
648 * If pi_state->owner is NULL, the owner is most probably dying
649 * and has cleaned up the pi_state already
650 */
651 if (pi_state->owner) {
652 raw_spin_lock_irq(&pi_state->owner->pi_lock);
653 list_del_init(&pi_state->list);
654 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
655
656 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
657 }
658
659 if (current->pi_state_cache)
660 kfree(pi_state);
661 else {
662 /*
663 * pi_state->list is already empty.
664 * clear pi_state->owner.
665 * refcount is at 0 - put it back to 1.
666 */
667 pi_state->owner = NULL;
668 atomic_set(&pi_state->refcount, 1);
669 current->pi_state_cache = pi_state;
670 }
671}
672
673/*
674 * Look up the task based on what TID userspace gave us.
675 * We dont trust it.
676 */
677static struct task_struct * futex_find_get_task(pid_t pid)
678{
679 struct task_struct *p;
680
681 rcu_read_lock();
682 p = find_task_by_vpid(pid);
683 if (p)
684 get_task_struct(p);
685
686 rcu_read_unlock();
687
688 return p;
689}
690
691/*
692 * This task is holding PI mutexes at exit time => bad.
693 * Kernel cleans up PI-state, but userspace is likely hosed.
694 * (Robust-futex cleanup is separate and might save the day for userspace.)
695 */
696void exit_pi_state_list(struct task_struct *curr)
697{
698 struct list_head *next, *head = &curr->pi_state_list;
699 struct futex_pi_state *pi_state;
700 struct futex_hash_bucket *hb;
701 union futex_key key = FUTEX_KEY_INIT;
702
703 if (!futex_cmpxchg_enabled)
704 return;
705 /*
706 * We are a ZOMBIE and nobody can enqueue itself on
707 * pi_state_list anymore, but we have to be careful
708 * versus waiters unqueueing themselves:
709 */
710 raw_spin_lock_irq(&curr->pi_lock);
711 while (!list_empty(head)) {
712
713 next = head->next;
714 pi_state = list_entry(next, struct futex_pi_state, list);
715 key = pi_state->key;
716 hb = hash_futex(&key);
717 raw_spin_unlock_irq(&curr->pi_lock);
718
719 spin_lock(&hb->lock);
720
721 raw_spin_lock_irq(&curr->pi_lock);
722 /*
723 * We dropped the pi-lock, so re-check whether this
724 * task still owns the PI-state:
725 */
726 if (head->next != next) {
727 spin_unlock(&hb->lock);
728 continue;
729 }
730
731 WARN_ON(pi_state->owner != curr);
732 WARN_ON(list_empty(&pi_state->list));
733 list_del_init(&pi_state->list);
734 pi_state->owner = NULL;
735 raw_spin_unlock_irq(&curr->pi_lock);
736
737 rt_mutex_unlock(&pi_state->pi_mutex);
738
739 spin_unlock(&hb->lock);
740
741 raw_spin_lock_irq(&curr->pi_lock);
742 }
743 raw_spin_unlock_irq(&curr->pi_lock);
744}
745
746/*
747 * We need to check the following states:
748 *
749 * Waiter | pi_state | pi->owner | uTID | uODIED | ?
750 *
751 * [1] NULL | --- | --- | 0 | 0/1 | Valid
752 * [2] NULL | --- | --- | >0 | 0/1 | Valid
753 *
754 * [3] Found | NULL | -- | Any | 0/1 | Invalid
755 *
756 * [4] Found | Found | NULL | 0 | 1 | Valid
757 * [5] Found | Found | NULL | >0 | 1 | Invalid
758 *
759 * [6] Found | Found | task | 0 | 1 | Valid
760 *
761 * [7] Found | Found | NULL | Any | 0 | Invalid
762 *
763 * [8] Found | Found | task | ==taskTID | 0/1 | Valid
764 * [9] Found | Found | task | 0 | 0 | Invalid
765 * [10] Found | Found | task | !=taskTID | 0/1 | Invalid
766 *
767 * [1] Indicates that the kernel can acquire the futex atomically. We
768 * came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
769 *
770 * [2] Valid, if TID does not belong to a kernel thread. If no matching
771 * thread is found then it indicates that the owner TID has died.
772 *
773 * [3] Invalid. The waiter is queued on a non PI futex
774 *
775 * [4] Valid state after exit_robust_list(), which sets the user space
776 * value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
777 *
778 * [5] The user space value got manipulated between exit_robust_list()
779 * and exit_pi_state_list()
780 *
781 * [6] Valid state after exit_pi_state_list() which sets the new owner in
782 * the pi_state but cannot access the user space value.
783 *
784 * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
785 *
786 * [8] Owner and user space value match
787 *
788 * [9] There is no transient state which sets the user space TID to 0
789 * except exit_robust_list(), but this is indicated by the
790 * FUTEX_OWNER_DIED bit. See [4]
791 *
792 * [10] There is no transient state which leaves owner and user space
793 * TID out of sync.
794 */
795static int
796lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
797 union futex_key *key, struct futex_pi_state **ps)
798{
799 struct futex_pi_state *pi_state = NULL;
800 struct futex_q *this, *next;
801 struct task_struct *p;
802 pid_t pid = uval & FUTEX_TID_MASK;
803
804 plist_for_each_entry_safe(this, next, &hb->chain, list) {
805 if (match_futex(&this->key, key)) {
806 /*
807 * Sanity check the waiter before increasing
808 * the refcount and attaching to it.
809 */
810 pi_state = this->pi_state;
811 /*
812 * Userspace might have messed up non-PI and
813 * PI futexes [3]
814 */
815 if (unlikely(!pi_state))
816 return -EINVAL;
817
818 WARN_ON(!atomic_read(&pi_state->refcount));
819
820 /*
821 * Handle the owner died case:
822 */
823 if (uval & FUTEX_OWNER_DIED) {
824 /*
825 * exit_pi_state_list sets owner to NULL and
826 * wakes the topmost waiter. The task which
827 * acquires the pi_state->rt_mutex will fixup
828 * owner.
829 */
830 if (!pi_state->owner) {
831 /*
832 * No pi state owner, but the user
833 * space TID is not 0. Inconsistent
834 * state. [5]
835 */
836 if (pid)
837 return -EINVAL;
838 /*
839 * Take a ref on the state and
840 * return. [4]
841 */
842 goto out_state;
843 }
844
845 /*
846 * If TID is 0, then either the dying owner
847 * has not yet executed exit_pi_state_list()
848 * or some waiter acquired the rtmutex in the
849 * pi state, but did not yet fixup the TID in
850 * user space.
851 *
852 * Take a ref on the state and return. [6]
853 */
854 if (!pid)
855 goto out_state;
856 } else {
857 /*
858 * If the owner died bit is not set,
859 * then the pi_state must have an
860 * owner. [7]
861 */
862 if (!pi_state->owner)
863 return -EINVAL;
864 }
865
866 /*
867 * Bail out if user space manipulated the
868 * futex value. If pi state exists then the
869 * owner TID must be the same as the user
870 * space TID. [9/10]
871 */
872 if (pid != task_pid_vnr(pi_state->owner))
873 return -EINVAL;
874
875 out_state:
876 atomic_inc(&pi_state->refcount);
877 *ps = pi_state;
878 return 0;
879 }
880 }
881
882 /*
883 * We are the first waiter - try to look up the real owner and attach
884 * the new pi_state to it, but bail out when TID = 0 [1]
885 */
886 if (!pid)
887 return -ESRCH;
888 p = futex_find_get_task(pid);
889 if (!p)
890 return -ESRCH;
891
892 if (!p->mm) {
893 put_task_struct(p);
894 return -EPERM;
895 }
896
897 /*
898 * We need to look at the task state flags to figure out,
899 * whether the task is exiting. To protect against the do_exit
900 * change of the task flags, we do this protected by
901 * p->pi_lock:
902 */
903 raw_spin_lock_irq(&p->pi_lock);
904 if (unlikely(p->flags & PF_EXITING)) {
905 /*
906 * The task is on the way out. When PF_EXITPIDONE is
907 * set, we know that the task has finished the
908 * cleanup:
909 */
910 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
911
912 raw_spin_unlock_irq(&p->pi_lock);
913 put_task_struct(p);
914 return ret;
915 }
916
917 /*
918 * No existing pi state. First waiter. [2]
919 */
920 pi_state = alloc_pi_state();
921
922 /*
923 * Initialize the pi_mutex in locked state and make 'p'
924 * the owner of it:
925 */
926 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
927
928 /* Store the key for possible exit cleanups: */
929 pi_state->key = *key;
930
931 WARN_ON(!list_empty(&pi_state->list));
932 list_add(&pi_state->list, &p->pi_state_list);
933 pi_state->owner = p;
934 raw_spin_unlock_irq(&p->pi_lock);
935
936 put_task_struct(p);
937
938 *ps = pi_state;
939
940 return 0;
941}
942
943/**
944 * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
945 * @uaddr: the pi futex user address
946 * @hb: the pi futex hash bucket
947 * @key: the futex key associated with uaddr and hb
948 * @ps: the pi_state pointer where we store the result of the
949 * lookup
950 * @task: the task to perform the atomic lock work for. This will
951 * be "current" except in the case of requeue pi.
952 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
953 *
954 * Return:
955 * 0 - ready to wait;
956 * 1 - acquired the lock;
957 * <0 - error
958 *
959 * The hb->lock and futex_key refs shall be held by the caller.
960 */
961static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
962 union futex_key *key,
963 struct futex_pi_state **ps,
964 struct task_struct *task, int set_waiters)
965{
966 int lock_taken, ret, force_take = 0;
967 u32 uval, newval, curval, vpid = task_pid_vnr(task);
968
969retry:
970 ret = lock_taken = 0;
971
972 /*
973 * To avoid races, we attempt to take the lock here again
974 * (by doing a 0 -> TID atomic cmpxchg), while holding all
975 * the locks. It will most likely not succeed.
976 */
977 newval = vpid;
978 if (set_waiters)
979 newval |= FUTEX_WAITERS;
980
981 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval)))
982 return -EFAULT;
983
984 /*
985 * Detect deadlocks.
986 */
987 if ((unlikely((curval & FUTEX_TID_MASK) == vpid)))
988 return -EDEADLK;
989
990 /*
991 * Surprise - we got the lock, but we do not trust user space at all.
992 */
993 if (unlikely(!curval)) {
994 /*
995 * We verify whether there is kernel state for this
996 * futex. If not, we can safely assume, that the 0 ->
997 * TID transition is correct. If state exists, we do
998 * not bother to fixup the user space state as it was
999 * corrupted already.
1000 */
1001 return futex_top_waiter(hb, key) ? -EINVAL : 1;
1002 }
1003
1004 uval = curval;
1005
1006 /*
1007 * Set the FUTEX_WAITERS flag, so the owner will know it has someone
1008 * to wake at the next unlock.
1009 */
1010 newval = curval | FUTEX_WAITERS;
1011
1012 /*
1013 * Should we force take the futex? See below.
1014 */
1015 if (unlikely(force_take)) {
1016 /*
1017 * Keep the OWNER_DIED and the WAITERS bit and set the
1018 * new TID value.
1019 */
1020 newval = (curval & ~FUTEX_TID_MASK) | vpid;
1021 force_take = 0;
1022 lock_taken = 1;
1023 }
1024
1025 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
1026 return -EFAULT;
1027 if (unlikely(curval != uval))
1028 goto retry;
1029
1030 /*
1031 * We took the lock due to forced take over.
1032 */
1033 if (unlikely(lock_taken))
1034 return 1;
1035
1036 /*
1037 * We dont have the lock. Look up the PI state (or create it if
1038 * we are the first waiter):
1039 */
1040 ret = lookup_pi_state(uval, hb, key, ps);
1041
1042 if (unlikely(ret)) {
1043 switch (ret) {
1044 case -ESRCH:
1045 /*
1046 * We failed to find an owner for this
1047 * futex. So we have no pi_state to block
1048 * on. This can happen in two cases:
1049 *
1050 * 1) The owner died
1051 * 2) A stale FUTEX_WAITERS bit
1052 *
1053 * Re-read the futex value.
1054 */
1055 if (get_futex_value_locked(&curval, uaddr))
1056 return -EFAULT;
1057
1058 /*
1059 * If the owner died or we have a stale
1060 * WAITERS bit the owner TID in the user space
1061 * futex is 0.
1062 */
1063 if (!(curval & FUTEX_TID_MASK)) {
1064 force_take = 1;
1065 goto retry;
1066 }
1067 default:
1068 break;
1069 }
1070 }
1071
1072 return ret;
1073}
1074
1075/**
1076 * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
1077 * @q: The futex_q to unqueue
1078 *
1079 * The q->lock_ptr must not be NULL and must be held by the caller.
1080 */
1081static void __unqueue_futex(struct futex_q *q)
1082{
1083 struct futex_hash_bucket *hb;
1084
1085 if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
1086 || WARN_ON(plist_node_empty(&q->list)))
1087 return;
1088
1089 hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
1090 plist_del(&q->list, &hb->chain);
1091 hb_waiters_dec(hb);
1092}
1093
1094/*
1095 * The hash bucket lock must be held when this is called.
1096 * Afterwards, the futex_q must not be accessed.
1097 */
1098static void wake_futex(struct futex_q *q)
1099{
1100 struct task_struct *p = q->task;
1101
1102 if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
1103 return;
1104
1105 /*
1106 * We set q->lock_ptr = NULL _before_ we wake up the task. If
1107 * a non-futex wake up happens on another CPU then the task
1108 * might exit and p would dereference a non-existing task
1109 * struct. Prevent this by holding a reference on p across the
1110 * wake up.
1111 */
1112 get_task_struct(p);
1113
1114 __unqueue_futex(q);
1115 /*
1116 * The waiting task can free the futex_q as soon as
1117 * q->lock_ptr = NULL is written, without taking any locks. A
1118 * memory barrier is required here to prevent the following
1119 * store to lock_ptr from getting ahead of the plist_del.
1120 */
1121 smp_wmb();
1122 q->lock_ptr = NULL;
1123
1124 wake_up_state(p, TASK_NORMAL);
1125 put_task_struct(p);
1126}
1127
1128static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
1129{
1130 struct task_struct *new_owner;
1131 struct futex_pi_state *pi_state = this->pi_state;
1132 u32 uninitialized_var(curval), newval;
1133 int ret = 0;
1134
1135 if (!pi_state)
1136 return -EINVAL;
1137
1138 /*
1139 * If current does not own the pi_state then the futex is
1140 * inconsistent and user space fiddled with the futex value.
1141 */
1142 if (pi_state->owner != current)
1143 return -EINVAL;
1144
1145 raw_spin_lock(&pi_state->pi_mutex.wait_lock);
1146 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
1147
1148 /*
1149 * It is possible that the next waiter (the one that brought
1150 * this owner to the kernel) timed out and is no longer
1151 * waiting on the lock.
1152 */
1153 if (!new_owner)
1154 new_owner = this->task;
1155
1156 /*
1157 * We pass it to the next owner. The WAITERS bit is always
1158 * kept enabled while there is PI state around. We cleanup the
1159 * owner died bit, because we are the owner.
1160 */
1161 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
1162
1163 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
1164 ret = -EFAULT;
1165 else if (curval != uval)
1166 ret = -EINVAL;
1167 if (ret) {
1168 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
1169 return ret;
1170 }
1171
1172 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1173 WARN_ON(list_empty(&pi_state->list));
1174 list_del_init(&pi_state->list);
1175 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1176
1177 raw_spin_lock_irq(&new_owner->pi_lock);
1178 WARN_ON(!list_empty(&pi_state->list));
1179 list_add(&pi_state->list, &new_owner->pi_state_list);
1180 pi_state->owner = new_owner;
1181 raw_spin_unlock_irq(&new_owner->pi_lock);
1182
1183 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
1184 rt_mutex_unlock(&pi_state->pi_mutex);
1185
1186 return 0;
1187}
1188
1189static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
1190{
1191 u32 uninitialized_var(oldval);
1192
1193 /*
1194 * There is no waiter, so we unlock the futex. The owner died
1195 * bit has not to be preserved here. We are the owner:
1196 */
1197 if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0))
1198 return -EFAULT;
1199 if (oldval != uval)
1200 return -EAGAIN;
1201
1202 return 0;
1203}
1204
1205/*
1206 * Express the locking dependencies for lockdep:
1207 */
1208static inline void
1209double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1210{
1211 if (hb1 <= hb2) {
1212 spin_lock(&hb1->lock);
1213 if (hb1 < hb2)
1214 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
1215 } else { /* hb1 > hb2 */
1216 spin_lock(&hb2->lock);
1217 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
1218 }
1219}
1220
1221static inline void
1222double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1223{
1224 spin_unlock(&hb1->lock);
1225 if (hb1 != hb2)
1226 spin_unlock(&hb2->lock);
1227}
1228
1229/*
1230 * Wake up waiters matching bitset queued on this futex (uaddr).
1231 */
1232static int
1233futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
1234{
1235 struct futex_hash_bucket *hb;
1236 struct futex_q *this, *next;
1237 union futex_key key = FUTEX_KEY_INIT;
1238 int ret;
1239
1240 if (!bitset)
1241 return -EINVAL;
1242
1243 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
1244 if (unlikely(ret != 0))
1245 goto out;
1246
1247 hb = hash_futex(&key);
1248
1249 /* Make sure we really have tasks to wakeup */
1250 if (!hb_waiters_pending(hb))
1251 goto out_put_key;
1252
1253 spin_lock(&hb->lock);
1254
1255 plist_for_each_entry_safe(this, next, &hb->chain, list) {
1256 if (match_futex (&this->key, &key)) {
1257 if (this->pi_state || this->rt_waiter) {
1258 ret = -EINVAL;
1259 break;
1260 }
1261
1262 /* Check if one of the bits is set in both bitsets */
1263 if (!(this->bitset & bitset))
1264 continue;
1265
1266 wake_futex(this);
1267 if (++ret >= nr_wake)
1268 break;
1269 }
1270 }
1271
1272 spin_unlock(&hb->lock);
1273out_put_key:
1274 put_futex_key(&key);
1275out:
1276 return ret;
1277}
1278
1279/*
1280 * Wake up all waiters hashed on the physical page that is mapped
1281 * to this virtual address:
1282 */
1283static int
1284futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
1285 int nr_wake, int nr_wake2, int op)
1286{
1287 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1288 struct futex_hash_bucket *hb1, *hb2;
1289 struct futex_q *this, *next;
1290 int ret, op_ret;
1291
1292retry:
1293 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1294 if (unlikely(ret != 0))
1295 goto out;
1296 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
1297 if (unlikely(ret != 0))
1298 goto out_put_key1;
1299
1300 hb1 = hash_futex(&key1);
1301 hb2 = hash_futex(&key2);
1302
1303retry_private:
1304 double_lock_hb(hb1, hb2);
1305 op_ret = futex_atomic_op_inuser(op, uaddr2);
1306 if (unlikely(op_ret < 0)) {
1307
1308 double_unlock_hb(hb1, hb2);
1309
1310#ifndef CONFIG_MMU
1311 /*
1312 * we don't get EFAULT from MMU faults if we don't have an MMU,
1313 * but we might get them from range checking
1314 */
1315 ret = op_ret;
1316 goto out_put_keys;
1317#endif
1318
1319 if (unlikely(op_ret != -EFAULT)) {
1320 ret = op_ret;
1321 goto out_put_keys;
1322 }
1323
1324 ret = fault_in_user_writeable(uaddr2);
1325 if (ret)
1326 goto out_put_keys;
1327
1328 if (!(flags & FLAGS_SHARED))
1329 goto retry_private;
1330
1331 put_futex_key(&key2);
1332 put_futex_key(&key1);
1333 goto retry;
1334 }
1335
1336 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1337 if (match_futex (&this->key, &key1)) {
1338 if (this->pi_state || this->rt_waiter) {
1339 ret = -EINVAL;
1340 goto out_unlock;
1341 }
1342 wake_futex(this);
1343 if (++ret >= nr_wake)
1344 break;
1345 }
1346 }
1347
1348 if (op_ret > 0) {
1349 op_ret = 0;
1350 plist_for_each_entry_safe(this, next, &hb2->chain, list) {
1351 if (match_futex (&this->key, &key2)) {
1352 if (this->pi_state || this->rt_waiter) {
1353 ret = -EINVAL;
1354 goto out_unlock;
1355 }
1356 wake_futex(this);
1357 if (++op_ret >= nr_wake2)
1358 break;
1359 }
1360 }
1361 ret += op_ret;
1362 }
1363
1364out_unlock:
1365 double_unlock_hb(hb1, hb2);
1366out_put_keys:
1367 put_futex_key(&key2);
1368out_put_key1:
1369 put_futex_key(&key1);
1370out:
1371 return ret;
1372}
1373
1374/**
1375 * requeue_futex() - Requeue a futex_q from one hb to another
1376 * @q: the futex_q to requeue
1377 * @hb1: the source hash_bucket
1378 * @hb2: the target hash_bucket
1379 * @key2: the new key for the requeued futex_q
1380 */
1381static inline
1382void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1383 struct futex_hash_bucket *hb2, union futex_key *key2)
1384{
1385
1386 /*
1387 * If key1 and key2 hash to the same bucket, no need to
1388 * requeue.
1389 */
1390 if (likely(&hb1->chain != &hb2->chain)) {
1391 plist_del(&q->list, &hb1->chain);
1392 hb_waiters_dec(hb1);
1393 plist_add(&q->list, &hb2->chain);
1394 hb_waiters_inc(hb2);
1395 q->lock_ptr = &hb2->lock;
1396 }
1397 get_futex_key_refs(key2);
1398 q->key = *key2;
1399}
1400
1401/**
1402 * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1403 * @q: the futex_q
1404 * @key: the key of the requeue target futex
1405 * @hb: the hash_bucket of the requeue target futex
1406 *
1407 * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1408 * target futex if it is uncontended or via a lock steal. Set the futex_q key
1409 * to the requeue target futex so the waiter can detect the wakeup on the right
1410 * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1411 * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
1412 * to protect access to the pi_state to fixup the owner later. Must be called
1413 * with both q->lock_ptr and hb->lock held.
1414 */
1415static inline
1416void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1417 struct futex_hash_bucket *hb)
1418{
1419 get_futex_key_refs(key);
1420 q->key = *key;
1421
1422 __unqueue_futex(q);
1423
1424 WARN_ON(!q->rt_waiter);
1425 q->rt_waiter = NULL;
1426
1427 q->lock_ptr = &hb->lock;
1428
1429 wake_up_state(q->task, TASK_NORMAL);
1430}
1431
1432/**
1433 * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1434 * @pifutex: the user address of the to futex
1435 * @hb1: the from futex hash bucket, must be locked by the caller
1436 * @hb2: the to futex hash bucket, must be locked by the caller
1437 * @key1: the from futex key
1438 * @key2: the to futex key
1439 * @ps: address to store the pi_state pointer
1440 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1441 *
1442 * Try and get the lock on behalf of the top waiter if we can do it atomically.
1443 * Wake the top waiter if we succeed. If the caller specified set_waiters,
1444 * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1445 * hb1 and hb2 must be held by the caller.
1446 *
1447 * Return:
1448 * 0 - failed to acquire the lock atomically;
1449 * >0 - acquired the lock, return value is vpid of the top_waiter
1450 * <0 - error
1451 */
1452static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1453 struct futex_hash_bucket *hb1,
1454 struct futex_hash_bucket *hb2,
1455 union futex_key *key1, union futex_key *key2,
1456 struct futex_pi_state **ps, int set_waiters)
1457{
1458 struct futex_q *top_waiter = NULL;
1459 u32 curval;
1460 int ret, vpid;
1461
1462 if (get_futex_value_locked(&curval, pifutex))
1463 return -EFAULT;
1464
1465 /*
1466 * Find the top_waiter and determine if there are additional waiters.
1467 * If the caller intends to requeue more than 1 waiter to pifutex,
1468 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1469 * as we have means to handle the possible fault. If not, don't set
1470 * the bit unecessarily as it will force the subsequent unlock to enter
1471 * the kernel.
1472 */
1473 top_waiter = futex_top_waiter(hb1, key1);
1474
1475 /* There are no waiters, nothing for us to do. */
1476 if (!top_waiter)
1477 return 0;
1478
1479 /* Ensure we requeue to the expected futex. */
1480 if (!match_futex(top_waiter->requeue_pi_key, key2))
1481 return -EINVAL;
1482
1483 /*
1484 * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
1485 * the contended case or if set_waiters is 1. The pi_state is returned
1486 * in ps in contended cases.
1487 */
1488 vpid = task_pid_vnr(top_waiter->task);
1489 ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1490 set_waiters);
1491 if (ret == 1) {
1492 requeue_pi_wake_futex(top_waiter, key2, hb2);
1493 return vpid;
1494 }
1495 return ret;
1496}
1497
1498/**
1499 * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1500 * @uaddr1: source futex user address
1501 * @flags: futex flags (FLAGS_SHARED, etc.)
1502 * @uaddr2: target futex user address
1503 * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
1504 * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1505 * @cmpval: @uaddr1 expected value (or %NULL)
1506 * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1507 * pi futex (pi to pi requeue is not supported)
1508 *
1509 * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1510 * uaddr2 atomically on behalf of the top waiter.
1511 *
1512 * Return:
1513 * >=0 - on success, the number of tasks requeued or woken;
1514 * <0 - on error
1515 */
1516static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1517 u32 __user *uaddr2, int nr_wake, int nr_requeue,
1518 u32 *cmpval, int requeue_pi)
1519{
1520 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1521 int drop_count = 0, task_count = 0, ret;
1522 struct futex_pi_state *pi_state = NULL;
1523 struct futex_hash_bucket *hb1, *hb2;
1524 struct futex_q *this, *next;
1525
1526 if (requeue_pi) {
1527 /*
1528 * Requeue PI only works on two distinct uaddrs. This
1529 * check is only valid for private futexes. See below.
1530 */
1531 if (uaddr1 == uaddr2)
1532 return -EINVAL;
1533
1534 /*
1535 * requeue_pi requires a pi_state, try to allocate it now
1536 * without any locks in case it fails.
1537 */
1538 if (refill_pi_state_cache())
1539 return -ENOMEM;
1540 /*
1541 * requeue_pi must wake as many tasks as it can, up to nr_wake
1542 * + nr_requeue, since it acquires the rt_mutex prior to
1543 * returning to userspace, so as to not leave the rt_mutex with
1544 * waiters and no owner. However, second and third wake-ups
1545 * cannot be predicted as they involve race conditions with the
1546 * first wake and a fault while looking up the pi_state. Both
1547 * pthread_cond_signal() and pthread_cond_broadcast() should
1548 * use nr_wake=1.
1549 */
1550 if (nr_wake != 1)
1551 return -EINVAL;
1552 }
1553
1554retry:
1555 if (pi_state != NULL) {
1556 /*
1557 * We will have to lookup the pi_state again, so free this one
1558 * to keep the accounting correct.
1559 */
1560 free_pi_state(pi_state);
1561 pi_state = NULL;
1562 }
1563
1564 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1565 if (unlikely(ret != 0))
1566 goto out;
1567 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
1568 requeue_pi ? VERIFY_WRITE : VERIFY_READ);
1569 if (unlikely(ret != 0))
1570 goto out_put_key1;
1571
1572 /*
1573 * The check above which compares uaddrs is not sufficient for
1574 * shared futexes. We need to compare the keys:
1575 */
1576 if (requeue_pi && match_futex(&key1, &key2)) {
1577 ret = -EINVAL;
1578 goto out_put_keys;
1579 }
1580
1581 hb1 = hash_futex(&key1);
1582 hb2 = hash_futex(&key2);
1583
1584retry_private:
1585 hb_waiters_inc(hb2);
1586 double_lock_hb(hb1, hb2);
1587
1588 if (likely(cmpval != NULL)) {
1589 u32 curval;
1590
1591 ret = get_futex_value_locked(&curval, uaddr1);
1592
1593 if (unlikely(ret)) {
1594 double_unlock_hb(hb1, hb2);
1595 hb_waiters_dec(hb2);
1596
1597 ret = get_user(curval, uaddr1);
1598 if (ret)
1599 goto out_put_keys;
1600
1601 if (!(flags & FLAGS_SHARED))
1602 goto retry_private;
1603
1604 put_futex_key(&key2);
1605 put_futex_key(&key1);
1606 goto retry;
1607 }
1608 if (curval != *cmpval) {
1609 ret = -EAGAIN;
1610 goto out_unlock;
1611 }
1612 }
1613
1614 if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1615 /*
1616 * Attempt to acquire uaddr2 and wake the top waiter. If we
1617 * intend to requeue waiters, force setting the FUTEX_WAITERS
1618 * bit. We force this here where we are able to easily handle
1619 * faults rather in the requeue loop below.
1620 */
1621 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1622 &key2, &pi_state, nr_requeue);
1623
1624 /*
1625 * At this point the top_waiter has either taken uaddr2 or is
1626 * waiting on it. If the former, then the pi_state will not
1627 * exist yet, look it up one more time to ensure we have a
1628 * reference to it. If the lock was taken, ret contains the
1629 * vpid of the top waiter task.
1630 */
1631 if (ret > 0) {
1632 WARN_ON(pi_state);
1633 drop_count++;
1634 task_count++;
1635 /*
1636 * If we acquired the lock, then the user
1637 * space value of uaddr2 should be vpid. It
1638 * cannot be changed by the top waiter as it
1639 * is blocked on hb2 lock if it tries to do
1640 * so. If something fiddled with it behind our
1641 * back the pi state lookup might unearth
1642 * it. So we rather use the known value than
1643 * rereading and handing potential crap to
1644 * lookup_pi_state.
1645 */
1646 ret = lookup_pi_state(ret, hb2, &key2, &pi_state);
1647 }
1648
1649 switch (ret) {
1650 case 0:
1651 break;
1652 case -EFAULT:
1653 double_unlock_hb(hb1, hb2);
1654 hb_waiters_dec(hb2);
1655 put_futex_key(&key2);
1656 put_futex_key(&key1);
1657 ret = fault_in_user_writeable(uaddr2);
1658 if (!ret)
1659 goto retry;
1660 goto out;
1661 case -EAGAIN:
1662 /* The owner was exiting, try again. */
1663 double_unlock_hb(hb1, hb2);
1664 hb_waiters_dec(hb2);
1665 put_futex_key(&key2);
1666 put_futex_key(&key1);
1667 cond_resched();
1668 goto retry;
1669 default:
1670 goto out_unlock;
1671 }
1672 }
1673
1674 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1675 if (task_count - nr_wake >= nr_requeue)
1676 break;
1677
1678 if (!match_futex(&this->key, &key1))
1679 continue;
1680
1681 /*
1682 * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1683 * be paired with each other and no other futex ops.
1684 *
1685 * We should never be requeueing a futex_q with a pi_state,
1686 * which is awaiting a futex_unlock_pi().
1687 */
1688 if ((requeue_pi && !this->rt_waiter) ||
1689 (!requeue_pi && this->rt_waiter) ||
1690 this->pi_state) {
1691 ret = -EINVAL;
1692 break;
1693 }
1694
1695 /*
1696 * Wake nr_wake waiters. For requeue_pi, if we acquired the
1697 * lock, we already woke the top_waiter. If not, it will be
1698 * woken by futex_unlock_pi().
1699 */
1700 if (++task_count <= nr_wake && !requeue_pi) {
1701 wake_futex(this);
1702 continue;
1703 }
1704
1705 /* Ensure we requeue to the expected futex for requeue_pi. */
1706 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1707 ret = -EINVAL;
1708 break;
1709 }
1710
1711 /*
1712 * Requeue nr_requeue waiters and possibly one more in the case
1713 * of requeue_pi if we couldn't acquire the lock atomically.
1714 */
1715 if (requeue_pi) {
1716 /* Prepare the waiter to take the rt_mutex. */
1717 atomic_inc(&pi_state->refcount);
1718 this->pi_state = pi_state;
1719 ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1720 this->rt_waiter,
1721 this->task, 1);
1722 if (ret == 1) {
1723 /* We got the lock. */
1724 requeue_pi_wake_futex(this, &key2, hb2);
1725 drop_count++;
1726 continue;
1727 } else if (ret) {
1728 /* -EDEADLK */
1729 this->pi_state = NULL;
1730 free_pi_state(pi_state);
1731 goto out_unlock;
1732 }
1733 }
1734 requeue_futex(this, hb1, hb2, &key2);
1735 drop_count++;
1736 }
1737
1738out_unlock:
1739 double_unlock_hb(hb1, hb2);
1740 hb_waiters_dec(hb2);
1741
1742 /*
1743 * drop_futex_key_refs() must be called outside the spinlocks. During
1744 * the requeue we moved futex_q's from the hash bucket at key1 to the
1745 * one at key2 and updated their key pointer. We no longer need to
1746 * hold the references to key1.
1747 */
1748 while (--drop_count >= 0)
1749 drop_futex_key_refs(&key1);
1750
1751out_put_keys:
1752 put_futex_key(&key2);
1753out_put_key1:
1754 put_futex_key(&key1);
1755out:
1756 if (pi_state != NULL)
1757 free_pi_state(pi_state);
1758 return ret ? ret : task_count;
1759}
1760
1761/* The key must be already stored in q->key. */
1762static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
1763 __acquires(&hb->lock)
1764{
1765 struct futex_hash_bucket *hb;
1766
1767 hb = hash_futex(&q->key);
1768
1769 /*
1770 * Increment the counter before taking the lock so that
1771 * a potential waker won't miss a to-be-slept task that is
1772 * waiting for the spinlock. This is safe as all queue_lock()
1773 * users end up calling queue_me(). Similarly, for housekeeping,
1774 * decrement the counter at queue_unlock() when some error has
1775 * occurred and we don't end up adding the task to the list.
1776 */
1777 hb_waiters_inc(hb);
1778
1779 q->lock_ptr = &hb->lock;
1780
1781 spin_lock(&hb->lock); /* implies MB (A) */
1782 return hb;
1783}
1784
1785static inline void
1786queue_unlock(struct futex_hash_bucket *hb)
1787 __releases(&hb->lock)
1788{
1789 spin_unlock(&hb->lock);
1790 hb_waiters_dec(hb);
1791}
1792
1793/**
1794 * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1795 * @q: The futex_q to enqueue
1796 * @hb: The destination hash bucket
1797 *
1798 * The hb->lock must be held by the caller, and is released here. A call to
1799 * queue_me() is typically paired with exactly one call to unqueue_me(). The
1800 * exceptions involve the PI related operations, which may use unqueue_me_pi()
1801 * or nothing if the unqueue is done as part of the wake process and the unqueue
1802 * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1803 * an example).
1804 */
1805static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1806 __releases(&hb->lock)
1807{
1808 int prio;
1809
1810 /*
1811 * The priority used to register this element is
1812 * - either the real thread-priority for the real-time threads
1813 * (i.e. threads with a priority lower than MAX_RT_PRIO)
1814 * - or MAX_RT_PRIO for non-RT threads.
1815 * Thus, all RT-threads are woken first in priority order, and
1816 * the others are woken last, in FIFO order.
1817 */
1818 prio = min(current->normal_prio, MAX_RT_PRIO);
1819
1820 plist_node_init(&q->list, prio);
1821 plist_add(&q->list, &hb->chain);
1822 q->task = current;
1823 spin_unlock(&hb->lock);
1824}
1825
1826/**
1827 * unqueue_me() - Remove the futex_q from its futex_hash_bucket
1828 * @q: The futex_q to unqueue
1829 *
1830 * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
1831 * be paired with exactly one earlier call to queue_me().
1832 *
1833 * Return:
1834 * 1 - if the futex_q was still queued (and we removed unqueued it);
1835 * 0 - if the futex_q was already removed by the waking thread
1836 */
1837static int unqueue_me(struct futex_q *q)
1838{
1839 spinlock_t *lock_ptr;
1840 int ret = 0;
1841
1842 /* In the common case we don't take the spinlock, which is nice. */
1843retry:
1844 lock_ptr = q->lock_ptr;
1845 barrier();
1846 if (lock_ptr != NULL) {
1847 spin_lock(lock_ptr);
1848 /*
1849 * q->lock_ptr can change between reading it and
1850 * spin_lock(), causing us to take the wrong lock. This
1851 * corrects the race condition.
1852 *
1853 * Reasoning goes like this: if we have the wrong lock,
1854 * q->lock_ptr must have changed (maybe several times)
1855 * between reading it and the spin_lock(). It can
1856 * change again after the spin_lock() but only if it was
1857 * already changed before the spin_lock(). It cannot,
1858 * however, change back to the original value. Therefore
1859 * we can detect whether we acquired the correct lock.
1860 */
1861 if (unlikely(lock_ptr != q->lock_ptr)) {
1862 spin_unlock(lock_ptr);
1863 goto retry;
1864 }
1865 __unqueue_futex(q);
1866
1867 BUG_ON(q->pi_state);
1868
1869 spin_unlock(lock_ptr);
1870 ret = 1;
1871 }
1872
1873 drop_futex_key_refs(&q->key);
1874 return ret;
1875}
1876
1877/*
1878 * PI futexes can not be requeued and must remove themself from the
1879 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1880 * and dropped here.
1881 */
1882static void unqueue_me_pi(struct futex_q *q)
1883 __releases(q->lock_ptr)
1884{
1885 __unqueue_futex(q);
1886
1887 BUG_ON(!q->pi_state);
1888 free_pi_state(q->pi_state);
1889 q->pi_state = NULL;
1890
1891 spin_unlock(q->lock_ptr);
1892}
1893
1894/*
1895 * Fixup the pi_state owner with the new owner.
1896 *
1897 * Must be called with hash bucket lock held and mm->sem held for non
1898 * private futexes.
1899 */
1900static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1901 struct task_struct *newowner)
1902{
1903 u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
1904 struct futex_pi_state *pi_state = q->pi_state;
1905 struct task_struct *oldowner = pi_state->owner;
1906 u32 uval, uninitialized_var(curval), newval;
1907 int ret;
1908
1909 /* Owner died? */
1910 if (!pi_state->owner)
1911 newtid |= FUTEX_OWNER_DIED;
1912
1913 /*
1914 * We are here either because we stole the rtmutex from the
1915 * previous highest priority waiter or we are the highest priority
1916 * waiter but failed to get the rtmutex the first time.
1917 * We have to replace the newowner TID in the user space variable.
1918 * This must be atomic as we have to preserve the owner died bit here.
1919 *
1920 * Note: We write the user space value _before_ changing the pi_state
1921 * because we can fault here. Imagine swapped out pages or a fork
1922 * that marked all the anonymous memory readonly for cow.
1923 *
1924 * Modifying pi_state _before_ the user space value would
1925 * leave the pi_state in an inconsistent state when we fault
1926 * here, because we need to drop the hash bucket lock to
1927 * handle the fault. This might be observed in the PID check
1928 * in lookup_pi_state.
1929 */
1930retry:
1931 if (get_futex_value_locked(&uval, uaddr))
1932 goto handle_fault;
1933
1934 while (1) {
1935 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1936
1937 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
1938 goto handle_fault;
1939 if (curval == uval)
1940 break;
1941 uval = curval;
1942 }
1943
1944 /*
1945 * We fixed up user space. Now we need to fix the pi_state
1946 * itself.
1947 */
1948 if (pi_state->owner != NULL) {
1949 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1950 WARN_ON(list_empty(&pi_state->list));
1951 list_del_init(&pi_state->list);
1952 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1953 }
1954
1955 pi_state->owner = newowner;
1956
1957 raw_spin_lock_irq(&newowner->pi_lock);
1958 WARN_ON(!list_empty(&pi_state->list));
1959 list_add(&pi_state->list, &newowner->pi_state_list);
1960 raw_spin_unlock_irq(&newowner->pi_lock);
1961 return 0;
1962
1963 /*
1964 * To handle the page fault we need to drop the hash bucket
1965 * lock here. That gives the other task (either the highest priority
1966 * waiter itself or the task which stole the rtmutex) the
1967 * chance to try the fixup of the pi_state. So once we are
1968 * back from handling the fault we need to check the pi_state
1969 * after reacquiring the hash bucket lock and before trying to
1970 * do another fixup. When the fixup has been done already we
1971 * simply return.
1972 */
1973handle_fault:
1974 spin_unlock(q->lock_ptr);
1975
1976 ret = fault_in_user_writeable(uaddr);
1977
1978 spin_lock(q->lock_ptr);
1979
1980 /*
1981 * Check if someone else fixed it for us:
1982 */
1983 if (pi_state->owner != oldowner)
1984 return 0;
1985
1986 if (ret)
1987 return ret;
1988
1989 goto retry;
1990}
1991
1992static long futex_wait_restart(struct restart_block *restart);
1993
1994/**
1995 * fixup_owner() - Post lock pi_state and corner case management
1996 * @uaddr: user address of the futex
1997 * @q: futex_q (contains pi_state and access to the rt_mutex)
1998 * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
1999 *
2000 * After attempting to lock an rt_mutex, this function is called to cleanup
2001 * the pi_state owner as well as handle race conditions that may allow us to
2002 * acquire the lock. Must be called with the hb lock held.
2003 *
2004 * Return:
2005 * 1 - success, lock taken;
2006 * 0 - success, lock not taken;
2007 * <0 - on error (-EFAULT)
2008 */
2009static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
2010{
2011 struct task_struct *owner;
2012 int ret = 0;
2013
2014 if (locked) {
2015 /*
2016 * Got the lock. We might not be the anticipated owner if we
2017 * did a lock-steal - fix up the PI-state in that case:
2018 */
2019 if (q->pi_state->owner != current)
2020 ret = fixup_pi_state_owner(uaddr, q, current);
2021 goto out;
2022 }
2023
2024 /*
2025 * Catch the rare case, where the lock was released when we were on the
2026 * way back before we locked the hash bucket.
2027 */
2028 if (q->pi_state->owner == current) {
2029 /*
2030 * Try to get the rt_mutex now. This might fail as some other
2031 * task acquired the rt_mutex after we removed ourself from the
2032 * rt_mutex waiters list.
2033 */
2034 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
2035 locked = 1;
2036 goto out;
2037 }
2038
2039 /*
2040 * pi_state is incorrect, some other task did a lock steal and
2041 * we returned due to timeout or signal without taking the
2042 * rt_mutex. Too late.
2043 */
2044 raw_spin_lock(&q->pi_state->pi_mutex.wait_lock);
2045 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
2046 if (!owner)
2047 owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
2048 raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock);
2049 ret = fixup_pi_state_owner(uaddr, q, owner);
2050 goto out;
2051 }
2052
2053 /*
2054 * Paranoia check. If we did not take the lock, then we should not be
2055 * the owner of the rt_mutex.
2056 */
2057 if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
2058 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
2059 "pi-state %p\n", ret,
2060 q->pi_state->pi_mutex.owner,
2061 q->pi_state->owner);
2062
2063out:
2064 return ret ? ret : locked;
2065}
2066
2067/**
2068 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
2069 * @hb: the futex hash bucket, must be locked by the caller
2070 * @q: the futex_q to queue up on
2071 * @timeout: the prepared hrtimer_sleeper, or null for no timeout
2072 */
2073static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
2074 struct hrtimer_sleeper *timeout)
2075{
2076 /*
2077 * The task state is guaranteed to be set before another task can
2078 * wake it. set_current_state() is implemented using set_mb() and
2079 * queue_me() calls spin_unlock() upon completion, both serializing
2080 * access to the hash list and forcing another memory barrier.
2081 */
2082 set_current_state(TASK_INTERRUPTIBLE);
2083 queue_me(q, hb);
2084
2085 /* Arm the timer */
2086 if (timeout) {
2087 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
2088 if (!hrtimer_active(&timeout->timer))
2089 timeout->task = NULL;
2090 }
2091
2092 /*
2093 * If we have been removed from the hash list, then another task
2094 * has tried to wake us, and we can skip the call to schedule().
2095 */
2096 if (likely(!plist_node_empty(&q->list))) {
2097 /*
2098 * If the timer has already expired, current will already be
2099 * flagged for rescheduling. Only call schedule if there
2100 * is no timeout, or if it has yet to expire.
2101 */
2102 if (!timeout || timeout->task)
2103 freezable_schedule();
2104 }
2105 __set_current_state(TASK_RUNNING);
2106}
2107
2108/**
2109 * futex_wait_setup() - Prepare to wait on a futex
2110 * @uaddr: the futex userspace address
2111 * @val: the expected value
2112 * @flags: futex flags (FLAGS_SHARED, etc.)
2113 * @q: the associated futex_q
2114 * @hb: storage for hash_bucket pointer to be returned to caller
2115 *
2116 * Setup the futex_q and locate the hash_bucket. Get the futex value and
2117 * compare it with the expected value. Handle atomic faults internally.
2118 * Return with the hb lock held and a q.key reference on success, and unlocked
2119 * with no q.key reference on failure.
2120 *
2121 * Return:
2122 * 0 - uaddr contains val and hb has been locked;
2123 * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
2124 */
2125static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
2126 struct futex_q *q, struct futex_hash_bucket **hb)
2127{
2128 u32 uval;
2129 int ret;
2130
2131 /*
2132 * Access the page AFTER the hash-bucket is locked.
2133 * Order is important:
2134 *
2135 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
2136 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
2137 *
2138 * The basic logical guarantee of a futex is that it blocks ONLY
2139 * if cond(var) is known to be true at the time of blocking, for
2140 * any cond. If we locked the hash-bucket after testing *uaddr, that
2141 * would open a race condition where we could block indefinitely with
2142 * cond(var) false, which would violate the guarantee.
2143 *
2144 * On the other hand, we insert q and release the hash-bucket only
2145 * after testing *uaddr. This guarantees that futex_wait() will NOT
2146 * absorb a wakeup if *uaddr does not match the desired values
2147 * while the syscall executes.
2148 */
2149retry:
2150 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
2151 if (unlikely(ret != 0))
2152 return ret;
2153
2154retry_private:
2155 *hb = queue_lock(q);
2156
2157 ret = get_futex_value_locked(&uval, uaddr);
2158
2159 if (ret) {
2160 queue_unlock(*hb);
2161
2162 ret = get_user(uval, uaddr);
2163 if (ret)
2164 goto out;
2165
2166 if (!(flags & FLAGS_SHARED))
2167 goto retry_private;
2168
2169 put_futex_key(&q->key);
2170 goto retry;
2171 }
2172
2173 if (uval != val) {
2174 queue_unlock(*hb);
2175 ret = -EWOULDBLOCK;
2176 }
2177
2178out:
2179 if (ret)
2180 put_futex_key(&q->key);
2181 return ret;
2182}
2183
2184static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
2185 ktime_t *abs_time, u32 bitset)
2186{
2187 struct hrtimer_sleeper timeout, *to = NULL;
2188 struct restart_block *restart;
2189 struct futex_hash_bucket *hb;
2190 struct futex_q q = futex_q_init;
2191 int ret;
2192
2193 if (!bitset)
2194 return -EINVAL;
2195 q.bitset = bitset;
2196
2197 if (abs_time) {
2198 to = &timeout;
2199
2200 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2201 CLOCK_REALTIME : CLOCK_MONOTONIC,
2202 HRTIMER_MODE_ABS);
2203 hrtimer_init_sleeper(to, current);
2204 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2205 current->timer_slack_ns);
2206 }
2207
2208retry:
2209 /*
2210 * Prepare to wait on uaddr. On success, holds hb lock and increments
2211 * q.key refs.
2212 */
2213 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2214 if (ret)
2215 goto out;
2216
2217 /* queue_me and wait for wakeup, timeout, or a signal. */
2218 futex_wait_queue_me(hb, &q, to);
2219
2220 /* If we were woken (and unqueued), we succeeded, whatever. */
2221 ret = 0;
2222 /* unqueue_me() drops q.key ref */
2223 if (!unqueue_me(&q))
2224 goto out;
2225 ret = -ETIMEDOUT;
2226 if (to && !to->task)
2227 goto out;
2228
2229 /*
2230 * We expect signal_pending(current), but we might be the
2231 * victim of a spurious wakeup as well.
2232 */
2233 if (!signal_pending(current))
2234 goto retry;
2235
2236 ret = -ERESTARTSYS;
2237 if (!abs_time)
2238 goto out;
2239
2240 restart = ¤t_thread_info()->restart_block;
2241 restart->fn = futex_wait_restart;
2242 restart->futex.uaddr = uaddr;
2243 restart->futex.val = val;
2244 restart->futex.time = abs_time->tv64;
2245 restart->futex.bitset = bitset;
2246 restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
2247
2248 ret = -ERESTART_RESTARTBLOCK;
2249
2250out:
2251 if (to) {
2252 hrtimer_cancel(&to->timer);
2253 destroy_hrtimer_on_stack(&to->timer);
2254 }
2255 return ret;
2256}
2257
2258
2259static long futex_wait_restart(struct restart_block *restart)
2260{
2261 u32 __user *uaddr = restart->futex.uaddr;
2262 ktime_t t, *tp = NULL;
2263
2264 if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
2265 t.tv64 = restart->futex.time;
2266 tp = &t;
2267 }
2268 restart->fn = do_no_restart_syscall;
2269
2270 return (long)futex_wait(uaddr, restart->futex.flags,
2271 restart->futex.val, tp, restart->futex.bitset);
2272}
2273
2274
2275/*
2276 * Userspace tried a 0 -> TID atomic transition of the futex value
2277 * and failed. The kernel side here does the whole locking operation:
2278 * if there are waiters then it will block, it does PI, etc. (Due to
2279 * races the kernel might see a 0 value of the futex too.)
2280 */
2281static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect,
2282 ktime_t *time, int trylock)
2283{
2284 struct hrtimer_sleeper timeout, *to = NULL;
2285 struct futex_hash_bucket *hb;
2286 struct futex_q q = futex_q_init;
2287 int res, ret;
2288
2289 if (refill_pi_state_cache())
2290 return -ENOMEM;
2291
2292 if (time) {
2293 to = &timeout;
2294 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
2295 HRTIMER_MODE_ABS);
2296 hrtimer_init_sleeper(to, current);
2297 hrtimer_set_expires(&to->timer, *time);
2298 }
2299
2300retry:
2301 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
2302 if (unlikely(ret != 0))
2303 goto out;
2304
2305retry_private:
2306 hb = queue_lock(&q);
2307
2308 ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
2309 if (unlikely(ret)) {
2310 switch (ret) {
2311 case 1:
2312 /* We got the lock. */
2313 ret = 0;
2314 goto out_unlock_put_key;
2315 case -EFAULT:
2316 goto uaddr_faulted;
2317 case -EAGAIN:
2318 /*
2319 * Task is exiting and we just wait for the
2320 * exit to complete.
2321 */
2322 queue_unlock(hb);
2323 put_futex_key(&q.key);
2324 cond_resched();
2325 goto retry;
2326 default:
2327 goto out_unlock_put_key;
2328 }
2329 }
2330
2331 /*
2332 * Only actually queue now that the atomic ops are done:
2333 */
2334 queue_me(&q, hb);
2335
2336 WARN_ON(!q.pi_state);
2337 /*
2338 * Block on the PI mutex:
2339 */
2340 if (!trylock)
2341 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
2342 else {
2343 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
2344 /* Fixup the trylock return value: */
2345 ret = ret ? 0 : -EWOULDBLOCK;
2346 }
2347
2348 spin_lock(q.lock_ptr);
2349 /*
2350 * Fixup the pi_state owner and possibly acquire the lock if we
2351 * haven't already.
2352 */
2353 res = fixup_owner(uaddr, &q, !ret);
2354 /*
2355 * If fixup_owner() returned an error, proprogate that. If it acquired
2356 * the lock, clear our -ETIMEDOUT or -EINTR.
2357 */
2358 if (res)
2359 ret = (res < 0) ? res : 0;
2360
2361 /*
2362 * If fixup_owner() faulted and was unable to handle the fault, unlock
2363 * it and return the fault to userspace.
2364 */
2365 if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
2366 rt_mutex_unlock(&q.pi_state->pi_mutex);
2367
2368 /* Unqueue and drop the lock */
2369 unqueue_me_pi(&q);
2370
2371 goto out_put_key;
2372
2373out_unlock_put_key:
2374 queue_unlock(hb);
2375
2376out_put_key:
2377 put_futex_key(&q.key);
2378out:
2379 if (to)
2380 destroy_hrtimer_on_stack(&to->timer);
2381 return ret != -EINTR ? ret : -ERESTARTNOINTR;
2382
2383uaddr_faulted:
2384 queue_unlock(hb);
2385
2386 ret = fault_in_user_writeable(uaddr);
2387 if (ret)
2388 goto out_put_key;
2389
2390 if (!(flags & FLAGS_SHARED))
2391 goto retry_private;
2392
2393 put_futex_key(&q.key);
2394 goto retry;
2395}
2396
2397/*
2398 * Userspace attempted a TID -> 0 atomic transition, and failed.
2399 * This is the in-kernel slowpath: we look up the PI state (if any),
2400 * and do the rt-mutex unlock.
2401 */
2402static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
2403{
2404 struct futex_hash_bucket *hb;
2405 struct futex_q *this, *next;
2406 union futex_key key = FUTEX_KEY_INIT;
2407 u32 uval, vpid = task_pid_vnr(current);
2408 int ret;
2409
2410retry:
2411 if (get_user(uval, uaddr))
2412 return -EFAULT;
2413 /*
2414 * We release only a lock we actually own:
2415 */
2416 if ((uval & FUTEX_TID_MASK) != vpid)
2417 return -EPERM;
2418
2419 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
2420 if (unlikely(ret != 0))
2421 goto out;
2422
2423 hb = hash_futex(&key);
2424 spin_lock(&hb->lock);
2425
2426 /*
2427 * To avoid races, try to do the TID -> 0 atomic transition
2428 * again. If it succeeds then we can return without waking
2429 * anyone else up. We only try this if neither the waiters nor
2430 * the owner died bit are set.
2431 */
2432 if (!(uval & ~FUTEX_TID_MASK) &&
2433 cmpxchg_futex_value_locked(&uval, uaddr, vpid, 0))
2434 goto pi_faulted;
2435 /*
2436 * Rare case: we managed to release the lock atomically,
2437 * no need to wake anyone else up:
2438 */
2439 if (unlikely(uval == vpid))
2440 goto out_unlock;
2441
2442 /*
2443 * Ok, other tasks may need to be woken up - check waiters
2444 * and do the wakeup if necessary:
2445 */
2446 plist_for_each_entry_safe(this, next, &hb->chain, list) {
2447 if (!match_futex (&this->key, &key))
2448 continue;
2449 ret = wake_futex_pi(uaddr, uval, this);
2450 /*
2451 * The atomic access to the futex value
2452 * generated a pagefault, so retry the
2453 * user-access and the wakeup:
2454 */
2455 if (ret == -EFAULT)
2456 goto pi_faulted;
2457 goto out_unlock;
2458 }
2459 /*
2460 * No waiters - kernel unlocks the futex:
2461 */
2462 ret = unlock_futex_pi(uaddr, uval);
2463 if (ret == -EFAULT)
2464 goto pi_faulted;
2465
2466out_unlock:
2467 spin_unlock(&hb->lock);
2468 put_futex_key(&key);
2469
2470out:
2471 return ret;
2472
2473pi_faulted:
2474 spin_unlock(&hb->lock);
2475 put_futex_key(&key);
2476
2477 ret = fault_in_user_writeable(uaddr);
2478 if (!ret)
2479 goto retry;
2480
2481 return ret;
2482}
2483
2484/**
2485 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2486 * @hb: the hash_bucket futex_q was original enqueued on
2487 * @q: the futex_q woken while waiting to be requeued
2488 * @key2: the futex_key of the requeue target futex
2489 * @timeout: the timeout associated with the wait (NULL if none)
2490 *
2491 * Detect if the task was woken on the initial futex as opposed to the requeue
2492 * target futex. If so, determine if it was a timeout or a signal that caused
2493 * the wakeup and return the appropriate error code to the caller. Must be
2494 * called with the hb lock held.
2495 *
2496 * Return:
2497 * 0 = no early wakeup detected;
2498 * <0 = -ETIMEDOUT or -ERESTARTNOINTR
2499 */
2500static inline
2501int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2502 struct futex_q *q, union futex_key *key2,
2503 struct hrtimer_sleeper *timeout)
2504{
2505 int ret = 0;
2506
2507 /*
2508 * With the hb lock held, we avoid races while we process the wakeup.
2509 * We only need to hold hb (and not hb2) to ensure atomicity as the
2510 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2511 * It can't be requeued from uaddr2 to something else since we don't
2512 * support a PI aware source futex for requeue.
2513 */
2514 if (!match_futex(&q->key, key2)) {
2515 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2516 /*
2517 * We were woken prior to requeue by a timeout or a signal.
2518 * Unqueue the futex_q and determine which it was.
2519 */
2520 plist_del(&q->list, &hb->chain);
2521 hb_waiters_dec(hb);
2522
2523 /* Handle spurious wakeups gracefully */
2524 ret = -EWOULDBLOCK;
2525 if (timeout && !timeout->task)
2526 ret = -ETIMEDOUT;
2527 else if (signal_pending(current))
2528 ret = -ERESTARTNOINTR;
2529 }
2530 return ret;
2531}
2532
2533/**
2534 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2535 * @uaddr: the futex we initially wait on (non-pi)
2536 * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
2537 * the same type, no requeueing from private to shared, etc.
2538 * @val: the expected value of uaddr
2539 * @abs_time: absolute timeout
2540 * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
2541 * @uaddr2: the pi futex we will take prior to returning to user-space
2542 *
2543 * The caller will wait on uaddr and will be requeued by futex_requeue() to
2544 * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
2545 * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
2546 * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
2547 * without one, the pi logic would not know which task to boost/deboost, if
2548 * there was a need to.
2549 *
2550 * We call schedule in futex_wait_queue_me() when we enqueue and return there
2551 * via the following--
2552 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2553 * 2) wakeup on uaddr2 after a requeue
2554 * 3) signal
2555 * 4) timeout
2556 *
2557 * If 3, cleanup and return -ERESTARTNOINTR.
2558 *
2559 * If 2, we may then block on trying to take the rt_mutex and return via:
2560 * 5) successful lock
2561 * 6) signal
2562 * 7) timeout
2563 * 8) other lock acquisition failure
2564 *
2565 * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2566 *
2567 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2568 *
2569 * Return:
2570 * 0 - On success;
2571 * <0 - On error
2572 */
2573static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
2574 u32 val, ktime_t *abs_time, u32 bitset,
2575 u32 __user *uaddr2)
2576{
2577 struct hrtimer_sleeper timeout, *to = NULL;
2578 struct rt_mutex_waiter rt_waiter;
2579 struct rt_mutex *pi_mutex = NULL;
2580 struct futex_hash_bucket *hb;
2581 union futex_key key2 = FUTEX_KEY_INIT;
2582 struct futex_q q = futex_q_init;
2583 int res, ret;
2584
2585 if (uaddr == uaddr2)
2586 return -EINVAL;
2587
2588 if (!bitset)
2589 return -EINVAL;
2590
2591 if (abs_time) {
2592 to = &timeout;
2593 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2594 CLOCK_REALTIME : CLOCK_MONOTONIC,
2595 HRTIMER_MODE_ABS);
2596 hrtimer_init_sleeper(to, current);
2597 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2598 current->timer_slack_ns);
2599 }
2600
2601 /*
2602 * The waiter is allocated on our stack, manipulated by the requeue
2603 * code while we sleep on uaddr.
2604 */
2605 debug_rt_mutex_init_waiter(&rt_waiter);
2606 RB_CLEAR_NODE(&rt_waiter.pi_tree_entry);
2607 RB_CLEAR_NODE(&rt_waiter.tree_entry);
2608 rt_waiter.task = NULL;
2609
2610 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
2611 if (unlikely(ret != 0))
2612 goto out;
2613
2614 q.bitset = bitset;
2615 q.rt_waiter = &rt_waiter;
2616 q.requeue_pi_key = &key2;
2617
2618 /*
2619 * Prepare to wait on uaddr. On success, increments q.key (key1) ref
2620 * count.
2621 */
2622 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2623 if (ret)
2624 goto out_key2;
2625
2626 /*
2627 * The check above which compares uaddrs is not sufficient for
2628 * shared futexes. We need to compare the keys:
2629 */
2630 if (match_futex(&q.key, &key2)) {
2631 ret = -EINVAL;
2632 goto out_put_keys;
2633 }
2634
2635 /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2636 futex_wait_queue_me(hb, &q, to);
2637
2638 spin_lock(&hb->lock);
2639 ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2640 spin_unlock(&hb->lock);
2641 if (ret)
2642 goto out_put_keys;
2643
2644 /*
2645 * In order for us to be here, we know our q.key == key2, and since
2646 * we took the hb->lock above, we also know that futex_requeue() has
2647 * completed and we no longer have to concern ourselves with a wakeup
2648 * race with the atomic proxy lock acquisition by the requeue code. The
2649 * futex_requeue dropped our key1 reference and incremented our key2
2650 * reference count.
2651 */
2652
2653 /* Check if the requeue code acquired the second futex for us. */
2654 if (!q.rt_waiter) {
2655 /*
2656 * Got the lock. We might not be the anticipated owner if we
2657 * did a lock-steal - fix up the PI-state in that case.
2658 */
2659 if (q.pi_state && (q.pi_state->owner != current)) {
2660 spin_lock(q.lock_ptr);
2661 ret = fixup_pi_state_owner(uaddr2, &q, current);
2662 spin_unlock(q.lock_ptr);
2663 }
2664 } else {
2665 /*
2666 * We have been woken up by futex_unlock_pi(), a timeout, or a
2667 * signal. futex_unlock_pi() will not destroy the lock_ptr nor
2668 * the pi_state.
2669 */
2670 WARN_ON(!q.pi_state);
2671 pi_mutex = &q.pi_state->pi_mutex;
2672 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
2673 debug_rt_mutex_free_waiter(&rt_waiter);
2674
2675 spin_lock(q.lock_ptr);
2676 /*
2677 * Fixup the pi_state owner and possibly acquire the lock if we
2678 * haven't already.
2679 */
2680 res = fixup_owner(uaddr2, &q, !ret);
2681 /*
2682 * If fixup_owner() returned an error, proprogate that. If it
2683 * acquired the lock, clear -ETIMEDOUT or -EINTR.
2684 */
2685 if (res)
2686 ret = (res < 0) ? res : 0;
2687
2688 /* Unqueue and drop the lock. */
2689 unqueue_me_pi(&q);
2690 }
2691
2692 /*
2693 * If fixup_pi_state_owner() faulted and was unable to handle the
2694 * fault, unlock the rt_mutex and return the fault to userspace.
2695 */
2696 if (ret == -EFAULT) {
2697 if (pi_mutex && rt_mutex_owner(pi_mutex) == current)
2698 rt_mutex_unlock(pi_mutex);
2699 } else if (ret == -EINTR) {
2700 /*
2701 * We've already been requeued, but cannot restart by calling
2702 * futex_lock_pi() directly. We could restart this syscall, but
2703 * it would detect that the user space "val" changed and return
2704 * -EWOULDBLOCK. Save the overhead of the restart and return
2705 * -EWOULDBLOCK directly.
2706 */
2707 ret = -EWOULDBLOCK;
2708 }
2709
2710out_put_keys:
2711 put_futex_key(&q.key);
2712out_key2:
2713 put_futex_key(&key2);
2714
2715out:
2716 if (to) {
2717 hrtimer_cancel(&to->timer);
2718 destroy_hrtimer_on_stack(&to->timer);
2719 }
2720 return ret;
2721}
2722
2723/*
2724 * Support for robust futexes: the kernel cleans up held futexes at
2725 * thread exit time.
2726 *
2727 * Implementation: user-space maintains a per-thread list of locks it
2728 * is holding. Upon do_exit(), the kernel carefully walks this list,
2729 * and marks all locks that are owned by this thread with the
2730 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2731 * always manipulated with the lock held, so the list is private and
2732 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2733 * field, to allow the kernel to clean up if the thread dies after
2734 * acquiring the lock, but just before it could have added itself to
2735 * the list. There can only be one such pending lock.
2736 */
2737
2738/**
2739 * sys_set_robust_list() - Set the robust-futex list head of a task
2740 * @head: pointer to the list-head
2741 * @len: length of the list-head, as userspace expects
2742 */
2743SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2744 size_t, len)
2745{
2746 if (!futex_cmpxchg_enabled)
2747 return -ENOSYS;
2748 /*
2749 * The kernel knows only one size for now:
2750 */
2751 if (unlikely(len != sizeof(*head)))
2752 return -EINVAL;
2753
2754 current->robust_list = head;
2755
2756 return 0;
2757}
2758
2759/**
2760 * sys_get_robust_list() - Get the robust-futex list head of a task
2761 * @pid: pid of the process [zero for current task]
2762 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
2763 * @len_ptr: pointer to a length field, the kernel fills in the header size
2764 */
2765SYSCALL_DEFINE3(get_robust_list, int, pid,
2766 struct robust_list_head __user * __user *, head_ptr,
2767 size_t __user *, len_ptr)
2768{
2769 struct robust_list_head __user *head;
2770 unsigned long ret;
2771 struct task_struct *p;
2772
2773 if (!futex_cmpxchg_enabled)
2774 return -ENOSYS;
2775
2776 rcu_read_lock();
2777
2778 ret = -ESRCH;
2779 if (!pid)
2780 p = current;
2781 else {
2782 p = find_task_by_vpid(pid);
2783 if (!p)
2784 goto err_unlock;
2785 }
2786
2787 ret = -EPERM;
2788 if (!ptrace_may_access(p, PTRACE_MODE_READ))
2789 goto err_unlock;
2790
2791 head = p->robust_list;
2792 rcu_read_unlock();
2793
2794 if (put_user(sizeof(*head), len_ptr))
2795 return -EFAULT;
2796 return put_user(head, head_ptr);
2797
2798err_unlock:
2799 rcu_read_unlock();
2800
2801 return ret;
2802}
2803
2804/*
2805 * Process a futex-list entry, check whether it's owned by the
2806 * dying task, and do notification if so:
2807 */
2808int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
2809{
2810 u32 uval, uninitialized_var(nval), mval;
2811
2812retry:
2813 if (get_user(uval, uaddr))
2814 return -1;
2815
2816 if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
2817 /*
2818 * Ok, this dying thread is truly holding a futex
2819 * of interest. Set the OWNER_DIED bit atomically
2820 * via cmpxchg, and if the value had FUTEX_WAITERS
2821 * set, wake up a waiter (if any). (We have to do a
2822 * futex_wake() even if OWNER_DIED is already set -
2823 * to handle the rare but possible case of recursive
2824 * thread-death.) The rest of the cleanup is done in
2825 * userspace.
2826 */
2827 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
2828 /*
2829 * We are not holding a lock here, but we want to have
2830 * the pagefault_disable/enable() protection because
2831 * we want to handle the fault gracefully. If the
2832 * access fails we try to fault in the futex with R/W
2833 * verification via get_user_pages. get_user() above
2834 * does not guarantee R/W access. If that fails we
2835 * give up and leave the futex locked.
2836 */
2837 if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
2838 if (fault_in_user_writeable(uaddr))
2839 return -1;
2840 goto retry;
2841 }
2842 if (nval != uval)
2843 goto retry;
2844
2845 /*
2846 * Wake robust non-PI futexes here. The wakeup of
2847 * PI futexes happens in exit_pi_state():
2848 */
2849 if (!pi && (uval & FUTEX_WAITERS))
2850 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
2851 }
2852 return 0;
2853}
2854
2855/*
2856 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
2857 */
2858static inline int fetch_robust_entry(struct robust_list __user **entry,
2859 struct robust_list __user * __user *head,
2860 unsigned int *pi)
2861{
2862 unsigned long uentry;
2863
2864 if (get_user(uentry, (unsigned long __user *)head))
2865 return -EFAULT;
2866
2867 *entry = (void __user *)(uentry & ~1UL);
2868 *pi = uentry & 1;
2869
2870 return 0;
2871}
2872
2873/*
2874 * Walk curr->robust_list (very carefully, it's a userspace list!)
2875 * and mark any locks found there dead, and notify any waiters.
2876 *
2877 * We silently return on any sign of list-walking problem.
2878 */
2879void exit_robust_list(struct task_struct *curr)
2880{
2881 struct robust_list_head __user *head = curr->robust_list;
2882 struct robust_list __user *entry, *next_entry, *pending;
2883 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
2884 unsigned int uninitialized_var(next_pi);
2885 unsigned long futex_offset;
2886 int rc;
2887
2888 if (!futex_cmpxchg_enabled)
2889 return;
2890
2891 /*
2892 * Fetch the list head (which was registered earlier, via
2893 * sys_set_robust_list()):
2894 */
2895 if (fetch_robust_entry(&entry, &head->list.next, &pi))
2896 return;
2897 /*
2898 * Fetch the relative futex offset:
2899 */
2900 if (get_user(futex_offset, &head->futex_offset))
2901 return;
2902 /*
2903 * Fetch any possibly pending lock-add first, and handle it
2904 * if it exists:
2905 */
2906 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
2907 return;
2908
2909 next_entry = NULL; /* avoid warning with gcc */
2910 while (entry != &head->list) {
2911 /*
2912 * Fetch the next entry in the list before calling
2913 * handle_futex_death:
2914 */
2915 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
2916 /*
2917 * A pending lock might already be on the list, so
2918 * don't process it twice:
2919 */
2920 if (entry != pending)
2921 if (handle_futex_death((void __user *)entry + futex_offset,
2922 curr, pi))
2923 return;
2924 if (rc)
2925 return;
2926 entry = next_entry;
2927 pi = next_pi;
2928 /*
2929 * Avoid excessively long or circular lists:
2930 */
2931 if (!--limit)
2932 break;
2933
2934 cond_resched();
2935 }
2936
2937 if (pending)
2938 handle_futex_death((void __user *)pending + futex_offset,
2939 curr, pip);
2940}
2941
2942long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
2943 u32 __user *uaddr2, u32 val2, u32 val3)
2944{
2945 int cmd = op & FUTEX_CMD_MASK;
2946 unsigned int flags = 0;
2947
2948 if (!(op & FUTEX_PRIVATE_FLAG))
2949 flags |= FLAGS_SHARED;
2950
2951 if (op & FUTEX_CLOCK_REALTIME) {
2952 flags |= FLAGS_CLOCKRT;
2953 if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
2954 return -ENOSYS;
2955 }
2956
2957 switch (cmd) {
2958 case FUTEX_LOCK_PI:
2959 case FUTEX_UNLOCK_PI:
2960 case FUTEX_TRYLOCK_PI:
2961 case FUTEX_WAIT_REQUEUE_PI:
2962 case FUTEX_CMP_REQUEUE_PI:
2963 if (!futex_cmpxchg_enabled)
2964 return -ENOSYS;
2965 }
2966
2967 switch (cmd) {
2968 case FUTEX_WAIT:
2969 val3 = FUTEX_BITSET_MATCH_ANY;
2970 case FUTEX_WAIT_BITSET:
2971 return futex_wait(uaddr, flags, val, timeout, val3);
2972 case FUTEX_WAKE:
2973 val3 = FUTEX_BITSET_MATCH_ANY;
2974 case FUTEX_WAKE_BITSET:
2975 return futex_wake(uaddr, flags, val, val3);
2976 case FUTEX_REQUEUE:
2977 return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
2978 case FUTEX_CMP_REQUEUE:
2979 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
2980 case FUTEX_WAKE_OP:
2981 return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
2982 case FUTEX_LOCK_PI:
2983 return futex_lock_pi(uaddr, flags, val, timeout, 0);
2984 case FUTEX_UNLOCK_PI:
2985 return futex_unlock_pi(uaddr, flags);
2986 case FUTEX_TRYLOCK_PI:
2987 return futex_lock_pi(uaddr, flags, 0, timeout, 1);
2988 case FUTEX_WAIT_REQUEUE_PI:
2989 val3 = FUTEX_BITSET_MATCH_ANY;
2990 return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
2991 uaddr2);
2992 case FUTEX_CMP_REQUEUE_PI:
2993 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
2994 }
2995 return -ENOSYS;
2996}
2997
2998
2999SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
3000 struct timespec __user *, utime, u32 __user *, uaddr2,
3001 u32, val3)
3002{
3003 struct timespec ts;
3004 ktime_t t, *tp = NULL;
3005 u32 val2 = 0;
3006 int cmd = op & FUTEX_CMD_MASK;
3007
3008 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
3009 cmd == FUTEX_WAIT_BITSET ||
3010 cmd == FUTEX_WAIT_REQUEUE_PI)) {
3011 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
3012 return -EFAULT;
3013 if (!timespec_valid(&ts))
3014 return -EINVAL;
3015
3016 t = timespec_to_ktime(ts);
3017 if (cmd == FUTEX_WAIT)
3018 t = ktime_add_safe(ktime_get(), t);
3019 tp = &t;
3020 }
3021 /*
3022 * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
3023 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
3024 */
3025 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
3026 cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
3027 val2 = (u32) (unsigned long) utime;
3028
3029 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
3030}
3031
3032static void __init futex_detect_cmpxchg(void)
3033{
3034#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
3035 u32 curval;
3036
3037 /*
3038 * This will fail and we want it. Some arch implementations do
3039 * runtime detection of the futex_atomic_cmpxchg_inatomic()
3040 * functionality. We want to know that before we call in any
3041 * of the complex code paths. Also we want to prevent
3042 * registration of robust lists in that case. NULL is
3043 * guaranteed to fault and we get -EFAULT on functional
3044 * implementation, the non-functional ones will return
3045 * -ENOSYS.
3046 */
3047 if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
3048 futex_cmpxchg_enabled = 1;
3049#endif
3050}
3051
3052static int __init futex_init(void)
3053{
3054 unsigned int futex_shift;
3055 unsigned long i;
3056
3057#if CONFIG_BASE_SMALL
3058 futex_hashsize = 16;
3059#else
3060 futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
3061#endif
3062
3063 futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
3064 futex_hashsize, 0,
3065 futex_hashsize < 256 ? HASH_SMALL : 0,
3066 &futex_shift, NULL,
3067 futex_hashsize, futex_hashsize);
3068 futex_hashsize = 1UL << futex_shift;
3069
3070 futex_detect_cmpxchg();
3071
3072 for (i = 0; i < futex_hashsize; i++) {
3073 atomic_set(&futex_queues[i].waiters, 0);
3074 plist_head_init(&futex_queues[i].chain);
3075 spin_lock_init(&futex_queues[i].lock);
3076 }
3077
3078 return 0;
3079}
3080__initcall(futex_init);