Loading...
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#include <linux/fault-inject.h>
68
69#include <asm/futex.h>
70
71#include "locking/rtmutex_common.h"
72
73/*
74 * READ this before attempting to hack on futexes!
75 *
76 * Basic futex operation and ordering guarantees
77 * =============================================
78 *
79 * The waiter reads the futex value in user space and calls
80 * futex_wait(). This function computes the hash bucket and acquires
81 * the hash bucket lock. After that it reads the futex user space value
82 * again and verifies that the data has not changed. If it has not changed
83 * it enqueues itself into the hash bucket, releases the hash bucket lock
84 * and schedules.
85 *
86 * The waker side modifies the user space value of the futex and calls
87 * futex_wake(). This function computes the hash bucket and acquires the
88 * hash bucket lock. Then it looks for waiters on that futex in the hash
89 * bucket and wakes them.
90 *
91 * In futex wake up scenarios where no tasks are blocked on a futex, taking
92 * the hb spinlock can be avoided and simply return. In order for this
93 * optimization to work, ordering guarantees must exist so that the waiter
94 * being added to the list is acknowledged when the list is concurrently being
95 * checked by the waker, avoiding scenarios like the following:
96 *
97 * CPU 0 CPU 1
98 * val = *futex;
99 * sys_futex(WAIT, futex, val);
100 * futex_wait(futex, val);
101 * uval = *futex;
102 * *futex = newval;
103 * sys_futex(WAKE, futex);
104 * futex_wake(futex);
105 * if (queue_empty())
106 * return;
107 * if (uval == val)
108 * lock(hash_bucket(futex));
109 * queue();
110 * unlock(hash_bucket(futex));
111 * schedule();
112 *
113 * This would cause the waiter on CPU 0 to wait forever because it
114 * missed the transition of the user space value from val to newval
115 * and the waker did not find the waiter in the hash bucket queue.
116 *
117 * The correct serialization ensures that a waiter either observes
118 * the changed user space value before blocking or is woken by a
119 * concurrent waker:
120 *
121 * CPU 0 CPU 1
122 * val = *futex;
123 * sys_futex(WAIT, futex, val);
124 * futex_wait(futex, val);
125 *
126 * waiters++; (a)
127 * smp_mb(); (A) <-- paired with -.
128 * |
129 * lock(hash_bucket(futex)); |
130 * |
131 * uval = *futex; |
132 * | *futex = newval;
133 * | sys_futex(WAKE, futex);
134 * | futex_wake(futex);
135 * |
136 * `--------> smp_mb(); (B)
137 * if (uval == val)
138 * queue();
139 * unlock(hash_bucket(futex));
140 * schedule(); if (waiters)
141 * lock(hash_bucket(futex));
142 * else wake_waiters(futex);
143 * waiters--; (b) unlock(hash_bucket(futex));
144 *
145 * Where (A) orders the waiters increment and the futex value read through
146 * atomic operations (see hb_waiters_inc) and where (B) orders the write
147 * to futex and the waiters read -- this is done by the barriers for both
148 * shared and private futexes in get_futex_key_refs().
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
258/*
259 * The base of the bucket array and its size are always used together
260 * (after initialization only in hash_futex()), so ensure that they
261 * reside in the same cacheline.
262 */
263static struct {
264 struct futex_hash_bucket *queues;
265 unsigned long hashsize;
266} __futex_data __read_mostly __aligned(2*sizeof(long));
267#define futex_queues (__futex_data.queues)
268#define futex_hashsize (__futex_data.hashsize)
269
270
271/*
272 * Fault injections for futexes.
273 */
274#ifdef CONFIG_FAIL_FUTEX
275
276static struct {
277 struct fault_attr attr;
278
279 bool ignore_private;
280} fail_futex = {
281 .attr = FAULT_ATTR_INITIALIZER,
282 .ignore_private = false,
283};
284
285static int __init setup_fail_futex(char *str)
286{
287 return setup_fault_attr(&fail_futex.attr, str);
288}
289__setup("fail_futex=", setup_fail_futex);
290
291static bool should_fail_futex(bool fshared)
292{
293 if (fail_futex.ignore_private && !fshared)
294 return false;
295
296 return should_fail(&fail_futex.attr, 1);
297}
298
299#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
300
301static int __init fail_futex_debugfs(void)
302{
303 umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
304 struct dentry *dir;
305
306 dir = fault_create_debugfs_attr("fail_futex", NULL,
307 &fail_futex.attr);
308 if (IS_ERR(dir))
309 return PTR_ERR(dir);
310
311 if (!debugfs_create_bool("ignore-private", mode, dir,
312 &fail_futex.ignore_private)) {
313 debugfs_remove_recursive(dir);
314 return -ENOMEM;
315 }
316
317 return 0;
318}
319
320late_initcall(fail_futex_debugfs);
321
322#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
323
324#else
325static inline bool should_fail_futex(bool fshared)
326{
327 return false;
328}
329#endif /* CONFIG_FAIL_FUTEX */
330
331static inline void futex_get_mm(union futex_key *key)
332{
333 atomic_inc(&key->private.mm->mm_count);
334 /*
335 * Ensure futex_get_mm() implies a full barrier such that
336 * get_futex_key() implies a full barrier. This is relied upon
337 * as smp_mb(); (B), see the ordering comment above.
338 */
339 smp_mb__after_atomic();
340}
341
342/*
343 * Reflects a new waiter being added to the waitqueue.
344 */
345static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
346{
347#ifdef CONFIG_SMP
348 atomic_inc(&hb->waiters);
349 /*
350 * Full barrier (A), see the ordering comment above.
351 */
352 smp_mb__after_atomic();
353#endif
354}
355
356/*
357 * Reflects a waiter being removed from the waitqueue by wakeup
358 * paths.
359 */
360static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
361{
362#ifdef CONFIG_SMP
363 atomic_dec(&hb->waiters);
364#endif
365}
366
367static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
368{
369#ifdef CONFIG_SMP
370 return atomic_read(&hb->waiters);
371#else
372 return 1;
373#endif
374}
375
376/*
377 * We hash on the keys returned from get_futex_key (see below).
378 */
379static struct futex_hash_bucket *hash_futex(union futex_key *key)
380{
381 u32 hash = jhash2((u32*)&key->both.word,
382 (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
383 key->both.offset);
384 return &futex_queues[hash & (futex_hashsize - 1)];
385}
386
387/*
388 * Return 1 if two futex_keys are equal, 0 otherwise.
389 */
390static inline int match_futex(union futex_key *key1, union futex_key *key2)
391{
392 return (key1 && key2
393 && key1->both.word == key2->both.word
394 && key1->both.ptr == key2->both.ptr
395 && key1->both.offset == key2->both.offset);
396}
397
398/*
399 * Take a reference to the resource addressed by a key.
400 * Can be called while holding spinlocks.
401 *
402 */
403static void get_futex_key_refs(union futex_key *key)
404{
405 if (!key->both.ptr)
406 return;
407
408 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
409 case FUT_OFF_INODE:
410 ihold(key->shared.inode); /* implies smp_mb(); (B) */
411 break;
412 case FUT_OFF_MMSHARED:
413 futex_get_mm(key); /* implies smp_mb(); (B) */
414 break;
415 default:
416 /*
417 * Private futexes do not hold reference on an inode or
418 * mm, therefore the only purpose of calling get_futex_key_refs
419 * is because we need the barrier for the lockless waiter check.
420 */
421 smp_mb(); /* explicit smp_mb(); (B) */
422 }
423}
424
425/*
426 * Drop a reference to the resource addressed by a key.
427 * The hash bucket spinlock must not be held. This is
428 * a no-op for private futexes, see comment in the get
429 * counterpart.
430 */
431static void drop_futex_key_refs(union futex_key *key)
432{
433 if (!key->both.ptr) {
434 /* If we're here then we tried to put a key we failed to get */
435 WARN_ON_ONCE(1);
436 return;
437 }
438
439 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
440 case FUT_OFF_INODE:
441 iput(key->shared.inode);
442 break;
443 case FUT_OFF_MMSHARED:
444 mmdrop(key->private.mm);
445 break;
446 }
447}
448
449/**
450 * get_futex_key() - Get parameters which are the keys for a futex
451 * @uaddr: virtual address of the futex
452 * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
453 * @key: address where result is stored.
454 * @rw: mapping needs to be read/write (values: VERIFY_READ,
455 * VERIFY_WRITE)
456 *
457 * Return: a negative error code or 0
458 *
459 * The key words are stored in *key on success.
460 *
461 * For shared mappings, it's (page->index, file_inode(vma->vm_file),
462 * offset_within_page). For private mappings, it's (uaddr, current->mm).
463 * We can usually work out the index without swapping in the page.
464 *
465 * lock_page() might sleep, the caller should not hold a spinlock.
466 */
467static int
468get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
469{
470 unsigned long address = (unsigned long)uaddr;
471 struct mm_struct *mm = current->mm;
472 struct page *page;
473 struct address_space *mapping;
474 int err, ro = 0;
475
476 /*
477 * The futex address must be "naturally" aligned.
478 */
479 key->both.offset = address % PAGE_SIZE;
480 if (unlikely((address % sizeof(u32)) != 0))
481 return -EINVAL;
482 address -= key->both.offset;
483
484 if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
485 return -EFAULT;
486
487 if (unlikely(should_fail_futex(fshared)))
488 return -EFAULT;
489
490 /*
491 * PROCESS_PRIVATE futexes are fast.
492 * As the mm cannot disappear under us and the 'key' only needs
493 * virtual address, we dont even have to find the underlying vma.
494 * Note : We do have to check 'uaddr' is a valid user address,
495 * but access_ok() should be faster than find_vma()
496 */
497 if (!fshared) {
498 key->private.mm = mm;
499 key->private.address = address;
500 get_futex_key_refs(key); /* implies smp_mb(); (B) */
501 return 0;
502 }
503
504again:
505 /* Ignore any VERIFY_READ mapping (futex common case) */
506 if (unlikely(should_fail_futex(fshared)))
507 return -EFAULT;
508
509 err = get_user_pages_fast(address, 1, 1, &page);
510 /*
511 * If write access is not required (eg. FUTEX_WAIT), try
512 * and get read-only access.
513 */
514 if (err == -EFAULT && rw == VERIFY_READ) {
515 err = get_user_pages_fast(address, 1, 0, &page);
516 ro = 1;
517 }
518 if (err < 0)
519 return err;
520 else
521 err = 0;
522
523 /*
524 * The treatment of mapping from this point on is critical. The page
525 * lock protects many things but in this context the page lock
526 * stabilizes mapping, prevents inode freeing in the shared
527 * file-backed region case and guards against movement to swap cache.
528 *
529 * Strictly speaking the page lock is not needed in all cases being
530 * considered here and page lock forces unnecessarily serialization
531 * From this point on, mapping will be re-verified if necessary and
532 * page lock will be acquired only if it is unavoidable
533 */
534 page = compound_head(page);
535 mapping = READ_ONCE(page->mapping);
536
537 /*
538 * If page->mapping is NULL, then it cannot be a PageAnon
539 * page; but it might be the ZERO_PAGE or in the gate area or
540 * in a special mapping (all cases which we are happy to fail);
541 * or it may have been a good file page when get_user_pages_fast
542 * found it, but truncated or holepunched or subjected to
543 * invalidate_complete_page2 before we got the page lock (also
544 * cases which we are happy to fail). And we hold a reference,
545 * so refcount care in invalidate_complete_page's remove_mapping
546 * prevents drop_caches from setting mapping to NULL beneath us.
547 *
548 * The case we do have to guard against is when memory pressure made
549 * shmem_writepage move it from filecache to swapcache beneath us:
550 * an unlikely race, but we do need to retry for page->mapping.
551 */
552 if (unlikely(!mapping)) {
553 int shmem_swizzled;
554
555 /*
556 * Page lock is required to identify which special case above
557 * applies. If this is really a shmem page then the page lock
558 * will prevent unexpected transitions.
559 */
560 lock_page(page);
561 shmem_swizzled = PageSwapCache(page) || page->mapping;
562 unlock_page(page);
563 put_page(page);
564
565 if (shmem_swizzled)
566 goto again;
567
568 return -EFAULT;
569 }
570
571 /*
572 * Private mappings are handled in a simple way.
573 *
574 * If the futex key is stored on an anonymous page, then the associated
575 * object is the mm which is implicitly pinned by the calling process.
576 *
577 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
578 * it's a read-only handle, it's expected that futexes attach to
579 * the object not the particular process.
580 */
581 if (PageAnon(page)) {
582 /*
583 * A RO anonymous page will never change and thus doesn't make
584 * sense for futex operations.
585 */
586 if (unlikely(should_fail_futex(fshared)) || ro) {
587 err = -EFAULT;
588 goto out;
589 }
590
591 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
592 key->private.mm = mm;
593 key->private.address = address;
594
595 get_futex_key_refs(key); /* implies smp_mb(); (B) */
596
597 } else {
598 struct inode *inode;
599
600 /*
601 * The associated futex object in this case is the inode and
602 * the page->mapping must be traversed. Ordinarily this should
603 * be stabilised under page lock but it's not strictly
604 * necessary in this case as we just want to pin the inode, not
605 * update the radix tree or anything like that.
606 *
607 * The RCU read lock is taken as the inode is finally freed
608 * under RCU. If the mapping still matches expectations then the
609 * mapping->host can be safely accessed as being a valid inode.
610 */
611 rcu_read_lock();
612
613 if (READ_ONCE(page->mapping) != mapping) {
614 rcu_read_unlock();
615 put_page(page);
616
617 goto again;
618 }
619
620 inode = READ_ONCE(mapping->host);
621 if (!inode) {
622 rcu_read_unlock();
623 put_page(page);
624
625 goto again;
626 }
627
628 /*
629 * Take a reference unless it is about to be freed. Previously
630 * this reference was taken by ihold under the page lock
631 * pinning the inode in place so i_lock was unnecessary. The
632 * only way for this check to fail is if the inode was
633 * truncated in parallel so warn for now if this happens.
634 *
635 * We are not calling into get_futex_key_refs() in file-backed
636 * cases, therefore a successful atomic_inc return below will
637 * guarantee that get_futex_key() will still imply smp_mb(); (B).
638 */
639 if (WARN_ON_ONCE(!atomic_inc_not_zero(&inode->i_count))) {
640 rcu_read_unlock();
641 put_page(page);
642
643 goto again;
644 }
645
646 /* Should be impossible but lets be paranoid for now */
647 if (WARN_ON_ONCE(inode->i_mapping != mapping)) {
648 err = -EFAULT;
649 rcu_read_unlock();
650 iput(inode);
651
652 goto out;
653 }
654
655 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
656 key->shared.inode = inode;
657 key->shared.pgoff = basepage_index(page);
658 rcu_read_unlock();
659 }
660
661out:
662 put_page(page);
663 return err;
664}
665
666static inline void put_futex_key(union futex_key *key)
667{
668 drop_futex_key_refs(key);
669}
670
671/**
672 * fault_in_user_writeable() - Fault in user address and verify RW access
673 * @uaddr: pointer to faulting user space address
674 *
675 * Slow path to fixup the fault we just took in the atomic write
676 * access to @uaddr.
677 *
678 * We have no generic implementation of a non-destructive write to the
679 * user address. We know that we faulted in the atomic pagefault
680 * disabled section so we can as well avoid the #PF overhead by
681 * calling get_user_pages() right away.
682 */
683static int fault_in_user_writeable(u32 __user *uaddr)
684{
685 struct mm_struct *mm = current->mm;
686 int ret;
687
688 down_read(&mm->mmap_sem);
689 ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
690 FAULT_FLAG_WRITE, NULL);
691 up_read(&mm->mmap_sem);
692
693 return ret < 0 ? ret : 0;
694}
695
696/**
697 * futex_top_waiter() - Return the highest priority waiter on a futex
698 * @hb: the hash bucket the futex_q's reside in
699 * @key: the futex key (to distinguish it from other futex futex_q's)
700 *
701 * Must be called with the hb lock held.
702 */
703static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
704 union futex_key *key)
705{
706 struct futex_q *this;
707
708 plist_for_each_entry(this, &hb->chain, list) {
709 if (match_futex(&this->key, key))
710 return this;
711 }
712 return NULL;
713}
714
715static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
716 u32 uval, u32 newval)
717{
718 int ret;
719
720 pagefault_disable();
721 ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
722 pagefault_enable();
723
724 return ret;
725}
726
727static int get_futex_value_locked(u32 *dest, u32 __user *from)
728{
729 int ret;
730
731 pagefault_disable();
732 ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
733 pagefault_enable();
734
735 return ret ? -EFAULT : 0;
736}
737
738
739/*
740 * PI code:
741 */
742static int refill_pi_state_cache(void)
743{
744 struct futex_pi_state *pi_state;
745
746 if (likely(current->pi_state_cache))
747 return 0;
748
749 pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
750
751 if (!pi_state)
752 return -ENOMEM;
753
754 INIT_LIST_HEAD(&pi_state->list);
755 /* pi_mutex gets initialized later */
756 pi_state->owner = NULL;
757 atomic_set(&pi_state->refcount, 1);
758 pi_state->key = FUTEX_KEY_INIT;
759
760 current->pi_state_cache = pi_state;
761
762 return 0;
763}
764
765static struct futex_pi_state * alloc_pi_state(void)
766{
767 struct futex_pi_state *pi_state = current->pi_state_cache;
768
769 WARN_ON(!pi_state);
770 current->pi_state_cache = NULL;
771
772 return pi_state;
773}
774
775/*
776 * Drops a reference to the pi_state object and frees or caches it
777 * when the last reference is gone.
778 *
779 * Must be called with the hb lock held.
780 */
781static void put_pi_state(struct futex_pi_state *pi_state)
782{
783 if (!pi_state)
784 return;
785
786 if (!atomic_dec_and_test(&pi_state->refcount))
787 return;
788
789 /*
790 * If pi_state->owner is NULL, the owner is most probably dying
791 * and has cleaned up the pi_state already
792 */
793 if (pi_state->owner) {
794 raw_spin_lock_irq(&pi_state->owner->pi_lock);
795 list_del_init(&pi_state->list);
796 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
797
798 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
799 }
800
801 if (current->pi_state_cache)
802 kfree(pi_state);
803 else {
804 /*
805 * pi_state->list is already empty.
806 * clear pi_state->owner.
807 * refcount is at 0 - put it back to 1.
808 */
809 pi_state->owner = NULL;
810 atomic_set(&pi_state->refcount, 1);
811 current->pi_state_cache = pi_state;
812 }
813}
814
815/*
816 * Look up the task based on what TID userspace gave us.
817 * We dont trust it.
818 */
819static struct task_struct * futex_find_get_task(pid_t pid)
820{
821 struct task_struct *p;
822
823 rcu_read_lock();
824 p = find_task_by_vpid(pid);
825 if (p)
826 get_task_struct(p);
827
828 rcu_read_unlock();
829
830 return p;
831}
832
833/*
834 * This task is holding PI mutexes at exit time => bad.
835 * Kernel cleans up PI-state, but userspace is likely hosed.
836 * (Robust-futex cleanup is separate and might save the day for userspace.)
837 */
838void exit_pi_state_list(struct task_struct *curr)
839{
840 struct list_head *next, *head = &curr->pi_state_list;
841 struct futex_pi_state *pi_state;
842 struct futex_hash_bucket *hb;
843 union futex_key key = FUTEX_KEY_INIT;
844
845 if (!futex_cmpxchg_enabled)
846 return;
847 /*
848 * We are a ZOMBIE and nobody can enqueue itself on
849 * pi_state_list anymore, but we have to be careful
850 * versus waiters unqueueing themselves:
851 */
852 raw_spin_lock_irq(&curr->pi_lock);
853 while (!list_empty(head)) {
854
855 next = head->next;
856 pi_state = list_entry(next, struct futex_pi_state, list);
857 key = pi_state->key;
858 hb = hash_futex(&key);
859 raw_spin_unlock_irq(&curr->pi_lock);
860
861 spin_lock(&hb->lock);
862
863 raw_spin_lock_irq(&curr->pi_lock);
864 /*
865 * We dropped the pi-lock, so re-check whether this
866 * task still owns the PI-state:
867 */
868 if (head->next != next) {
869 spin_unlock(&hb->lock);
870 continue;
871 }
872
873 WARN_ON(pi_state->owner != curr);
874 WARN_ON(list_empty(&pi_state->list));
875 list_del_init(&pi_state->list);
876 pi_state->owner = NULL;
877 raw_spin_unlock_irq(&curr->pi_lock);
878
879 rt_mutex_unlock(&pi_state->pi_mutex);
880
881 spin_unlock(&hb->lock);
882
883 raw_spin_lock_irq(&curr->pi_lock);
884 }
885 raw_spin_unlock_irq(&curr->pi_lock);
886}
887
888/*
889 * We need to check the following states:
890 *
891 * Waiter | pi_state | pi->owner | uTID | uODIED | ?
892 *
893 * [1] NULL | --- | --- | 0 | 0/1 | Valid
894 * [2] NULL | --- | --- | >0 | 0/1 | Valid
895 *
896 * [3] Found | NULL | -- | Any | 0/1 | Invalid
897 *
898 * [4] Found | Found | NULL | 0 | 1 | Valid
899 * [5] Found | Found | NULL | >0 | 1 | Invalid
900 *
901 * [6] Found | Found | task | 0 | 1 | Valid
902 *
903 * [7] Found | Found | NULL | Any | 0 | Invalid
904 *
905 * [8] Found | Found | task | ==taskTID | 0/1 | Valid
906 * [9] Found | Found | task | 0 | 0 | Invalid
907 * [10] Found | Found | task | !=taskTID | 0/1 | Invalid
908 *
909 * [1] Indicates that the kernel can acquire the futex atomically. We
910 * came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
911 *
912 * [2] Valid, if TID does not belong to a kernel thread. If no matching
913 * thread is found then it indicates that the owner TID has died.
914 *
915 * [3] Invalid. The waiter is queued on a non PI futex
916 *
917 * [4] Valid state after exit_robust_list(), which sets the user space
918 * value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
919 *
920 * [5] The user space value got manipulated between exit_robust_list()
921 * and exit_pi_state_list()
922 *
923 * [6] Valid state after exit_pi_state_list() which sets the new owner in
924 * the pi_state but cannot access the user space value.
925 *
926 * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
927 *
928 * [8] Owner and user space value match
929 *
930 * [9] There is no transient state which sets the user space TID to 0
931 * except exit_robust_list(), but this is indicated by the
932 * FUTEX_OWNER_DIED bit. See [4]
933 *
934 * [10] There is no transient state which leaves owner and user space
935 * TID out of sync.
936 */
937
938/*
939 * Validate that the existing waiter has a pi_state and sanity check
940 * the pi_state against the user space value. If correct, attach to
941 * it.
942 */
943static int attach_to_pi_state(u32 uval, struct futex_pi_state *pi_state,
944 struct futex_pi_state **ps)
945{
946 pid_t pid = uval & FUTEX_TID_MASK;
947
948 /*
949 * Userspace might have messed up non-PI and PI futexes [3]
950 */
951 if (unlikely(!pi_state))
952 return -EINVAL;
953
954 WARN_ON(!atomic_read(&pi_state->refcount));
955
956 /*
957 * Handle the owner died case:
958 */
959 if (uval & FUTEX_OWNER_DIED) {
960 /*
961 * exit_pi_state_list sets owner to NULL and wakes the
962 * topmost waiter. The task which acquires the
963 * pi_state->rt_mutex will fixup owner.
964 */
965 if (!pi_state->owner) {
966 /*
967 * No pi state owner, but the user space TID
968 * is not 0. Inconsistent state. [5]
969 */
970 if (pid)
971 return -EINVAL;
972 /*
973 * Take a ref on the state and return success. [4]
974 */
975 goto out_state;
976 }
977
978 /*
979 * If TID is 0, then either the dying owner has not
980 * yet executed exit_pi_state_list() or some waiter
981 * acquired the rtmutex in the pi state, but did not
982 * yet fixup the TID in user space.
983 *
984 * Take a ref on the state and return success. [6]
985 */
986 if (!pid)
987 goto out_state;
988 } else {
989 /*
990 * If the owner died bit is not set, then the pi_state
991 * must have an owner. [7]
992 */
993 if (!pi_state->owner)
994 return -EINVAL;
995 }
996
997 /*
998 * Bail out if user space manipulated the futex value. If pi
999 * state exists then the owner TID must be the same as the
1000 * user space TID. [9/10]
1001 */
1002 if (pid != task_pid_vnr(pi_state->owner))
1003 return -EINVAL;
1004out_state:
1005 atomic_inc(&pi_state->refcount);
1006 *ps = pi_state;
1007 return 0;
1008}
1009
1010/*
1011 * Lookup the task for the TID provided from user space and attach to
1012 * it after doing proper sanity checks.
1013 */
1014static int attach_to_pi_owner(u32 uval, union futex_key *key,
1015 struct futex_pi_state **ps)
1016{
1017 pid_t pid = uval & FUTEX_TID_MASK;
1018 struct futex_pi_state *pi_state;
1019 struct task_struct *p;
1020
1021 /*
1022 * We are the first waiter - try to look up the real owner and attach
1023 * the new pi_state to it, but bail out when TID = 0 [1]
1024 */
1025 if (!pid)
1026 return -ESRCH;
1027 p = futex_find_get_task(pid);
1028 if (!p)
1029 return -ESRCH;
1030
1031 if (unlikely(p->flags & PF_KTHREAD)) {
1032 put_task_struct(p);
1033 return -EPERM;
1034 }
1035
1036 /*
1037 * We need to look at the task state flags to figure out,
1038 * whether the task is exiting. To protect against the do_exit
1039 * change of the task flags, we do this protected by
1040 * p->pi_lock:
1041 */
1042 raw_spin_lock_irq(&p->pi_lock);
1043 if (unlikely(p->flags & PF_EXITING)) {
1044 /*
1045 * The task is on the way out. When PF_EXITPIDONE is
1046 * set, we know that the task has finished the
1047 * cleanup:
1048 */
1049 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
1050
1051 raw_spin_unlock_irq(&p->pi_lock);
1052 put_task_struct(p);
1053 return ret;
1054 }
1055
1056 /*
1057 * No existing pi state. First waiter. [2]
1058 */
1059 pi_state = alloc_pi_state();
1060
1061 /*
1062 * Initialize the pi_mutex in locked state and make @p
1063 * the owner of it:
1064 */
1065 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
1066
1067 /* Store the key for possible exit cleanups: */
1068 pi_state->key = *key;
1069
1070 WARN_ON(!list_empty(&pi_state->list));
1071 list_add(&pi_state->list, &p->pi_state_list);
1072 pi_state->owner = p;
1073 raw_spin_unlock_irq(&p->pi_lock);
1074
1075 put_task_struct(p);
1076
1077 *ps = pi_state;
1078
1079 return 0;
1080}
1081
1082static int lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
1083 union futex_key *key, struct futex_pi_state **ps)
1084{
1085 struct futex_q *match = futex_top_waiter(hb, key);
1086
1087 /*
1088 * If there is a waiter on that futex, validate it and
1089 * attach to the pi_state when the validation succeeds.
1090 */
1091 if (match)
1092 return attach_to_pi_state(uval, match->pi_state, ps);
1093
1094 /*
1095 * We are the first waiter - try to look up the owner based on
1096 * @uval and attach to it.
1097 */
1098 return attach_to_pi_owner(uval, key, ps);
1099}
1100
1101static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
1102{
1103 u32 uninitialized_var(curval);
1104
1105 if (unlikely(should_fail_futex(true)))
1106 return -EFAULT;
1107
1108 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
1109 return -EFAULT;
1110
1111 /*If user space value changed, let the caller retry */
1112 return curval != uval ? -EAGAIN : 0;
1113}
1114
1115/**
1116 * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
1117 * @uaddr: the pi futex user address
1118 * @hb: the pi futex hash bucket
1119 * @key: the futex key associated with uaddr and hb
1120 * @ps: the pi_state pointer where we store the result of the
1121 * lookup
1122 * @task: the task to perform the atomic lock work for. This will
1123 * be "current" except in the case of requeue pi.
1124 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1125 *
1126 * Return:
1127 * 0 - ready to wait;
1128 * 1 - acquired the lock;
1129 * <0 - error
1130 *
1131 * The hb->lock and futex_key refs shall be held by the caller.
1132 */
1133static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
1134 union futex_key *key,
1135 struct futex_pi_state **ps,
1136 struct task_struct *task, int set_waiters)
1137{
1138 u32 uval, newval, vpid = task_pid_vnr(task);
1139 struct futex_q *match;
1140 int ret;
1141
1142 /*
1143 * Read the user space value first so we can validate a few
1144 * things before proceeding further.
1145 */
1146 if (get_futex_value_locked(&uval, uaddr))
1147 return -EFAULT;
1148
1149 if (unlikely(should_fail_futex(true)))
1150 return -EFAULT;
1151
1152 /*
1153 * Detect deadlocks.
1154 */
1155 if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
1156 return -EDEADLK;
1157
1158 if ((unlikely(should_fail_futex(true))))
1159 return -EDEADLK;
1160
1161 /*
1162 * Lookup existing state first. If it exists, try to attach to
1163 * its pi_state.
1164 */
1165 match = futex_top_waiter(hb, key);
1166 if (match)
1167 return attach_to_pi_state(uval, match->pi_state, ps);
1168
1169 /*
1170 * No waiter and user TID is 0. We are here because the
1171 * waiters or the owner died bit is set or called from
1172 * requeue_cmp_pi or for whatever reason something took the
1173 * syscall.
1174 */
1175 if (!(uval & FUTEX_TID_MASK)) {
1176 /*
1177 * We take over the futex. No other waiters and the user space
1178 * TID is 0. We preserve the owner died bit.
1179 */
1180 newval = uval & FUTEX_OWNER_DIED;
1181 newval |= vpid;
1182
1183 /* The futex requeue_pi code can enforce the waiters bit */
1184 if (set_waiters)
1185 newval |= FUTEX_WAITERS;
1186
1187 ret = lock_pi_update_atomic(uaddr, uval, newval);
1188 /* If the take over worked, return 1 */
1189 return ret < 0 ? ret : 1;
1190 }
1191
1192 /*
1193 * First waiter. Set the waiters bit before attaching ourself to
1194 * the owner. If owner tries to unlock, it will be forced into
1195 * the kernel and blocked on hb->lock.
1196 */
1197 newval = uval | FUTEX_WAITERS;
1198 ret = lock_pi_update_atomic(uaddr, uval, newval);
1199 if (ret)
1200 return ret;
1201 /*
1202 * If the update of the user space value succeeded, we try to
1203 * attach to the owner. If that fails, no harm done, we only
1204 * set the FUTEX_WAITERS bit in the user space variable.
1205 */
1206 return attach_to_pi_owner(uval, key, ps);
1207}
1208
1209/**
1210 * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
1211 * @q: The futex_q to unqueue
1212 *
1213 * The q->lock_ptr must not be NULL and must be held by the caller.
1214 */
1215static void __unqueue_futex(struct futex_q *q)
1216{
1217 struct futex_hash_bucket *hb;
1218
1219 if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
1220 || WARN_ON(plist_node_empty(&q->list)))
1221 return;
1222
1223 hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
1224 plist_del(&q->list, &hb->chain);
1225 hb_waiters_dec(hb);
1226}
1227
1228/*
1229 * The hash bucket lock must be held when this is called.
1230 * Afterwards, the futex_q must not be accessed. Callers
1231 * must ensure to later call wake_up_q() for the actual
1232 * wakeups to occur.
1233 */
1234static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
1235{
1236 struct task_struct *p = q->task;
1237
1238 if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
1239 return;
1240
1241 /*
1242 * Queue the task for later wakeup for after we've released
1243 * the hb->lock. wake_q_add() grabs reference to p.
1244 */
1245 wake_q_add(wake_q, p);
1246 __unqueue_futex(q);
1247 /*
1248 * The waiting task can free the futex_q as soon as
1249 * q->lock_ptr = NULL is written, without taking any locks. A
1250 * memory barrier is required here to prevent the following
1251 * store to lock_ptr from getting ahead of the plist_del.
1252 */
1253 smp_wmb();
1254 q->lock_ptr = NULL;
1255}
1256
1257static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this,
1258 struct futex_hash_bucket *hb)
1259{
1260 struct task_struct *new_owner;
1261 struct futex_pi_state *pi_state = this->pi_state;
1262 u32 uninitialized_var(curval), newval;
1263 WAKE_Q(wake_q);
1264 bool deboost;
1265 int ret = 0;
1266
1267 if (!pi_state)
1268 return -EINVAL;
1269
1270 /*
1271 * If current does not own the pi_state then the futex is
1272 * inconsistent and user space fiddled with the futex value.
1273 */
1274 if (pi_state->owner != current)
1275 return -EINVAL;
1276
1277 raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
1278 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
1279
1280 /*
1281 * It is possible that the next waiter (the one that brought
1282 * this owner to the kernel) timed out and is no longer
1283 * waiting on the lock.
1284 */
1285 if (!new_owner)
1286 new_owner = this->task;
1287
1288 /*
1289 * We pass it to the next owner. The WAITERS bit is always
1290 * kept enabled while there is PI state around. We cleanup the
1291 * owner died bit, because we are the owner.
1292 */
1293 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
1294
1295 if (unlikely(should_fail_futex(true)))
1296 ret = -EFAULT;
1297
1298 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) {
1299 ret = -EFAULT;
1300 } else if (curval != uval) {
1301 /*
1302 * If a unconditional UNLOCK_PI operation (user space did not
1303 * try the TID->0 transition) raced with a waiter setting the
1304 * FUTEX_WAITERS flag between get_user() and locking the hash
1305 * bucket lock, retry the operation.
1306 */
1307 if ((FUTEX_TID_MASK & curval) == uval)
1308 ret = -EAGAIN;
1309 else
1310 ret = -EINVAL;
1311 }
1312 if (ret) {
1313 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1314 return ret;
1315 }
1316
1317 raw_spin_lock(&pi_state->owner->pi_lock);
1318 WARN_ON(list_empty(&pi_state->list));
1319 list_del_init(&pi_state->list);
1320 raw_spin_unlock(&pi_state->owner->pi_lock);
1321
1322 raw_spin_lock(&new_owner->pi_lock);
1323 WARN_ON(!list_empty(&pi_state->list));
1324 list_add(&pi_state->list, &new_owner->pi_state_list);
1325 pi_state->owner = new_owner;
1326 raw_spin_unlock(&new_owner->pi_lock);
1327
1328 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1329
1330 deboost = rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
1331
1332 /*
1333 * First unlock HB so the waiter does not spin on it once he got woken
1334 * up. Second wake up the waiter before the priority is adjusted. If we
1335 * deboost first (and lose our higher priority), then the task might get
1336 * scheduled away before the wake up can take place.
1337 */
1338 spin_unlock(&hb->lock);
1339 wake_up_q(&wake_q);
1340 if (deboost)
1341 rt_mutex_adjust_prio(current);
1342
1343 return 0;
1344}
1345
1346/*
1347 * Express the locking dependencies for lockdep:
1348 */
1349static inline void
1350double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1351{
1352 if (hb1 <= hb2) {
1353 spin_lock(&hb1->lock);
1354 if (hb1 < hb2)
1355 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
1356 } else { /* hb1 > hb2 */
1357 spin_lock(&hb2->lock);
1358 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
1359 }
1360}
1361
1362static inline void
1363double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1364{
1365 spin_unlock(&hb1->lock);
1366 if (hb1 != hb2)
1367 spin_unlock(&hb2->lock);
1368}
1369
1370/*
1371 * Wake up waiters matching bitset queued on this futex (uaddr).
1372 */
1373static int
1374futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
1375{
1376 struct futex_hash_bucket *hb;
1377 struct futex_q *this, *next;
1378 union futex_key key = FUTEX_KEY_INIT;
1379 int ret;
1380 WAKE_Q(wake_q);
1381
1382 if (!bitset)
1383 return -EINVAL;
1384
1385 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
1386 if (unlikely(ret != 0))
1387 goto out;
1388
1389 hb = hash_futex(&key);
1390
1391 /* Make sure we really have tasks to wakeup */
1392 if (!hb_waiters_pending(hb))
1393 goto out_put_key;
1394
1395 spin_lock(&hb->lock);
1396
1397 plist_for_each_entry_safe(this, next, &hb->chain, list) {
1398 if (match_futex (&this->key, &key)) {
1399 if (this->pi_state || this->rt_waiter) {
1400 ret = -EINVAL;
1401 break;
1402 }
1403
1404 /* Check if one of the bits is set in both bitsets */
1405 if (!(this->bitset & bitset))
1406 continue;
1407
1408 mark_wake_futex(&wake_q, this);
1409 if (++ret >= nr_wake)
1410 break;
1411 }
1412 }
1413
1414 spin_unlock(&hb->lock);
1415 wake_up_q(&wake_q);
1416out_put_key:
1417 put_futex_key(&key);
1418out:
1419 return ret;
1420}
1421
1422/*
1423 * Wake up all waiters hashed on the physical page that is mapped
1424 * to this virtual address:
1425 */
1426static int
1427futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
1428 int nr_wake, int nr_wake2, int op)
1429{
1430 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1431 struct futex_hash_bucket *hb1, *hb2;
1432 struct futex_q *this, *next;
1433 int ret, op_ret;
1434 WAKE_Q(wake_q);
1435
1436retry:
1437 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1438 if (unlikely(ret != 0))
1439 goto out;
1440 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
1441 if (unlikely(ret != 0))
1442 goto out_put_key1;
1443
1444 hb1 = hash_futex(&key1);
1445 hb2 = hash_futex(&key2);
1446
1447retry_private:
1448 double_lock_hb(hb1, hb2);
1449 op_ret = futex_atomic_op_inuser(op, uaddr2);
1450 if (unlikely(op_ret < 0)) {
1451
1452 double_unlock_hb(hb1, hb2);
1453
1454#ifndef CONFIG_MMU
1455 /*
1456 * we don't get EFAULT from MMU faults if we don't have an MMU,
1457 * but we might get them from range checking
1458 */
1459 ret = op_ret;
1460 goto out_put_keys;
1461#endif
1462
1463 if (unlikely(op_ret != -EFAULT)) {
1464 ret = op_ret;
1465 goto out_put_keys;
1466 }
1467
1468 ret = fault_in_user_writeable(uaddr2);
1469 if (ret)
1470 goto out_put_keys;
1471
1472 if (!(flags & FLAGS_SHARED))
1473 goto retry_private;
1474
1475 put_futex_key(&key2);
1476 put_futex_key(&key1);
1477 goto retry;
1478 }
1479
1480 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1481 if (match_futex (&this->key, &key1)) {
1482 if (this->pi_state || this->rt_waiter) {
1483 ret = -EINVAL;
1484 goto out_unlock;
1485 }
1486 mark_wake_futex(&wake_q, this);
1487 if (++ret >= nr_wake)
1488 break;
1489 }
1490 }
1491
1492 if (op_ret > 0) {
1493 op_ret = 0;
1494 plist_for_each_entry_safe(this, next, &hb2->chain, list) {
1495 if (match_futex (&this->key, &key2)) {
1496 if (this->pi_state || this->rt_waiter) {
1497 ret = -EINVAL;
1498 goto out_unlock;
1499 }
1500 mark_wake_futex(&wake_q, this);
1501 if (++op_ret >= nr_wake2)
1502 break;
1503 }
1504 }
1505 ret += op_ret;
1506 }
1507
1508out_unlock:
1509 double_unlock_hb(hb1, hb2);
1510 wake_up_q(&wake_q);
1511out_put_keys:
1512 put_futex_key(&key2);
1513out_put_key1:
1514 put_futex_key(&key1);
1515out:
1516 return ret;
1517}
1518
1519/**
1520 * requeue_futex() - Requeue a futex_q from one hb to another
1521 * @q: the futex_q to requeue
1522 * @hb1: the source hash_bucket
1523 * @hb2: the target hash_bucket
1524 * @key2: the new key for the requeued futex_q
1525 */
1526static inline
1527void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1528 struct futex_hash_bucket *hb2, union futex_key *key2)
1529{
1530
1531 /*
1532 * If key1 and key2 hash to the same bucket, no need to
1533 * requeue.
1534 */
1535 if (likely(&hb1->chain != &hb2->chain)) {
1536 plist_del(&q->list, &hb1->chain);
1537 hb_waiters_dec(hb1);
1538 hb_waiters_inc(hb2);
1539 plist_add(&q->list, &hb2->chain);
1540 q->lock_ptr = &hb2->lock;
1541 }
1542 get_futex_key_refs(key2);
1543 q->key = *key2;
1544}
1545
1546/**
1547 * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1548 * @q: the futex_q
1549 * @key: the key of the requeue target futex
1550 * @hb: the hash_bucket of the requeue target futex
1551 *
1552 * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1553 * target futex if it is uncontended or via a lock steal. Set the futex_q key
1554 * to the requeue target futex so the waiter can detect the wakeup on the right
1555 * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1556 * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
1557 * to protect access to the pi_state to fixup the owner later. Must be called
1558 * with both q->lock_ptr and hb->lock held.
1559 */
1560static inline
1561void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1562 struct futex_hash_bucket *hb)
1563{
1564 get_futex_key_refs(key);
1565 q->key = *key;
1566
1567 __unqueue_futex(q);
1568
1569 WARN_ON(!q->rt_waiter);
1570 q->rt_waiter = NULL;
1571
1572 q->lock_ptr = &hb->lock;
1573
1574 wake_up_state(q->task, TASK_NORMAL);
1575}
1576
1577/**
1578 * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1579 * @pifutex: the user address of the to futex
1580 * @hb1: the from futex hash bucket, must be locked by the caller
1581 * @hb2: the to futex hash bucket, must be locked by the caller
1582 * @key1: the from futex key
1583 * @key2: the to futex key
1584 * @ps: address to store the pi_state pointer
1585 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1586 *
1587 * Try and get the lock on behalf of the top waiter if we can do it atomically.
1588 * Wake the top waiter if we succeed. If the caller specified set_waiters,
1589 * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1590 * hb1 and hb2 must be held by the caller.
1591 *
1592 * Return:
1593 * 0 - failed to acquire the lock atomically;
1594 * >0 - acquired the lock, return value is vpid of the top_waiter
1595 * <0 - error
1596 */
1597static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1598 struct futex_hash_bucket *hb1,
1599 struct futex_hash_bucket *hb2,
1600 union futex_key *key1, union futex_key *key2,
1601 struct futex_pi_state **ps, int set_waiters)
1602{
1603 struct futex_q *top_waiter = NULL;
1604 u32 curval;
1605 int ret, vpid;
1606
1607 if (get_futex_value_locked(&curval, pifutex))
1608 return -EFAULT;
1609
1610 if (unlikely(should_fail_futex(true)))
1611 return -EFAULT;
1612
1613 /*
1614 * Find the top_waiter and determine if there are additional waiters.
1615 * If the caller intends to requeue more than 1 waiter to pifutex,
1616 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1617 * as we have means to handle the possible fault. If not, don't set
1618 * the bit unecessarily as it will force the subsequent unlock to enter
1619 * the kernel.
1620 */
1621 top_waiter = futex_top_waiter(hb1, key1);
1622
1623 /* There are no waiters, nothing for us to do. */
1624 if (!top_waiter)
1625 return 0;
1626
1627 /* Ensure we requeue to the expected futex. */
1628 if (!match_futex(top_waiter->requeue_pi_key, key2))
1629 return -EINVAL;
1630
1631 /*
1632 * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
1633 * the contended case or if set_waiters is 1. The pi_state is returned
1634 * in ps in contended cases.
1635 */
1636 vpid = task_pid_vnr(top_waiter->task);
1637 ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1638 set_waiters);
1639 if (ret == 1) {
1640 requeue_pi_wake_futex(top_waiter, key2, hb2);
1641 return vpid;
1642 }
1643 return ret;
1644}
1645
1646/**
1647 * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1648 * @uaddr1: source futex user address
1649 * @flags: futex flags (FLAGS_SHARED, etc.)
1650 * @uaddr2: target futex user address
1651 * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
1652 * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1653 * @cmpval: @uaddr1 expected value (or %NULL)
1654 * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1655 * pi futex (pi to pi requeue is not supported)
1656 *
1657 * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1658 * uaddr2 atomically on behalf of the top waiter.
1659 *
1660 * Return:
1661 * >=0 - on success, the number of tasks requeued or woken;
1662 * <0 - on error
1663 */
1664static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1665 u32 __user *uaddr2, int nr_wake, int nr_requeue,
1666 u32 *cmpval, int requeue_pi)
1667{
1668 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1669 int drop_count = 0, task_count = 0, ret;
1670 struct futex_pi_state *pi_state = NULL;
1671 struct futex_hash_bucket *hb1, *hb2;
1672 struct futex_q *this, *next;
1673 WAKE_Q(wake_q);
1674
1675 if (requeue_pi) {
1676 /*
1677 * Requeue PI only works on two distinct uaddrs. This
1678 * check is only valid for private futexes. See below.
1679 */
1680 if (uaddr1 == uaddr2)
1681 return -EINVAL;
1682
1683 /*
1684 * requeue_pi requires a pi_state, try to allocate it now
1685 * without any locks in case it fails.
1686 */
1687 if (refill_pi_state_cache())
1688 return -ENOMEM;
1689 /*
1690 * requeue_pi must wake as many tasks as it can, up to nr_wake
1691 * + nr_requeue, since it acquires the rt_mutex prior to
1692 * returning to userspace, so as to not leave the rt_mutex with
1693 * waiters and no owner. However, second and third wake-ups
1694 * cannot be predicted as they involve race conditions with the
1695 * first wake and a fault while looking up the pi_state. Both
1696 * pthread_cond_signal() and pthread_cond_broadcast() should
1697 * use nr_wake=1.
1698 */
1699 if (nr_wake != 1)
1700 return -EINVAL;
1701 }
1702
1703retry:
1704 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1705 if (unlikely(ret != 0))
1706 goto out;
1707 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
1708 requeue_pi ? VERIFY_WRITE : VERIFY_READ);
1709 if (unlikely(ret != 0))
1710 goto out_put_key1;
1711
1712 /*
1713 * The check above which compares uaddrs is not sufficient for
1714 * shared futexes. We need to compare the keys:
1715 */
1716 if (requeue_pi && match_futex(&key1, &key2)) {
1717 ret = -EINVAL;
1718 goto out_put_keys;
1719 }
1720
1721 hb1 = hash_futex(&key1);
1722 hb2 = hash_futex(&key2);
1723
1724retry_private:
1725 hb_waiters_inc(hb2);
1726 double_lock_hb(hb1, hb2);
1727
1728 if (likely(cmpval != NULL)) {
1729 u32 curval;
1730
1731 ret = get_futex_value_locked(&curval, uaddr1);
1732
1733 if (unlikely(ret)) {
1734 double_unlock_hb(hb1, hb2);
1735 hb_waiters_dec(hb2);
1736
1737 ret = get_user(curval, uaddr1);
1738 if (ret)
1739 goto out_put_keys;
1740
1741 if (!(flags & FLAGS_SHARED))
1742 goto retry_private;
1743
1744 put_futex_key(&key2);
1745 put_futex_key(&key1);
1746 goto retry;
1747 }
1748 if (curval != *cmpval) {
1749 ret = -EAGAIN;
1750 goto out_unlock;
1751 }
1752 }
1753
1754 if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1755 /*
1756 * Attempt to acquire uaddr2 and wake the top waiter. If we
1757 * intend to requeue waiters, force setting the FUTEX_WAITERS
1758 * bit. We force this here where we are able to easily handle
1759 * faults rather in the requeue loop below.
1760 */
1761 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1762 &key2, &pi_state, nr_requeue);
1763
1764 /*
1765 * At this point the top_waiter has either taken uaddr2 or is
1766 * waiting on it. If the former, then the pi_state will not
1767 * exist yet, look it up one more time to ensure we have a
1768 * reference to it. If the lock was taken, ret contains the
1769 * vpid of the top waiter task.
1770 * If the lock was not taken, we have pi_state and an initial
1771 * refcount on it. In case of an error we have nothing.
1772 */
1773 if (ret > 0) {
1774 WARN_ON(pi_state);
1775 drop_count++;
1776 task_count++;
1777 /*
1778 * If we acquired the lock, then the user space value
1779 * of uaddr2 should be vpid. It cannot be changed by
1780 * the top waiter as it is blocked on hb2 lock if it
1781 * tries to do so. If something fiddled with it behind
1782 * our back the pi state lookup might unearth it. So
1783 * we rather use the known value than rereading and
1784 * handing potential crap to lookup_pi_state.
1785 *
1786 * If that call succeeds then we have pi_state and an
1787 * initial refcount on it.
1788 */
1789 ret = lookup_pi_state(ret, hb2, &key2, &pi_state);
1790 }
1791
1792 switch (ret) {
1793 case 0:
1794 /* We hold a reference on the pi state. */
1795 break;
1796
1797 /* If the above failed, then pi_state is NULL */
1798 case -EFAULT:
1799 double_unlock_hb(hb1, hb2);
1800 hb_waiters_dec(hb2);
1801 put_futex_key(&key2);
1802 put_futex_key(&key1);
1803 ret = fault_in_user_writeable(uaddr2);
1804 if (!ret)
1805 goto retry;
1806 goto out;
1807 case -EAGAIN:
1808 /*
1809 * Two reasons for this:
1810 * - Owner is exiting and we just wait for the
1811 * exit to complete.
1812 * - The user space value changed.
1813 */
1814 double_unlock_hb(hb1, hb2);
1815 hb_waiters_dec(hb2);
1816 put_futex_key(&key2);
1817 put_futex_key(&key1);
1818 cond_resched();
1819 goto retry;
1820 default:
1821 goto out_unlock;
1822 }
1823 }
1824
1825 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1826 if (task_count - nr_wake >= nr_requeue)
1827 break;
1828
1829 if (!match_futex(&this->key, &key1))
1830 continue;
1831
1832 /*
1833 * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1834 * be paired with each other and no other futex ops.
1835 *
1836 * We should never be requeueing a futex_q with a pi_state,
1837 * which is awaiting a futex_unlock_pi().
1838 */
1839 if ((requeue_pi && !this->rt_waiter) ||
1840 (!requeue_pi && this->rt_waiter) ||
1841 this->pi_state) {
1842 ret = -EINVAL;
1843 break;
1844 }
1845
1846 /*
1847 * Wake nr_wake waiters. For requeue_pi, if we acquired the
1848 * lock, we already woke the top_waiter. If not, it will be
1849 * woken by futex_unlock_pi().
1850 */
1851 if (++task_count <= nr_wake && !requeue_pi) {
1852 mark_wake_futex(&wake_q, this);
1853 continue;
1854 }
1855
1856 /* Ensure we requeue to the expected futex for requeue_pi. */
1857 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1858 ret = -EINVAL;
1859 break;
1860 }
1861
1862 /*
1863 * Requeue nr_requeue waiters and possibly one more in the case
1864 * of requeue_pi if we couldn't acquire the lock atomically.
1865 */
1866 if (requeue_pi) {
1867 /*
1868 * Prepare the waiter to take the rt_mutex. Take a
1869 * refcount on the pi_state and store the pointer in
1870 * the futex_q object of the waiter.
1871 */
1872 atomic_inc(&pi_state->refcount);
1873 this->pi_state = pi_state;
1874 ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1875 this->rt_waiter,
1876 this->task);
1877 if (ret == 1) {
1878 /*
1879 * We got the lock. We do neither drop the
1880 * refcount on pi_state nor clear
1881 * this->pi_state because the waiter needs the
1882 * pi_state for cleaning up the user space
1883 * value. It will drop the refcount after
1884 * doing so.
1885 */
1886 requeue_pi_wake_futex(this, &key2, hb2);
1887 drop_count++;
1888 continue;
1889 } else if (ret) {
1890 /*
1891 * rt_mutex_start_proxy_lock() detected a
1892 * potential deadlock when we tried to queue
1893 * that waiter. Drop the pi_state reference
1894 * which we took above and remove the pointer
1895 * to the state from the waiters futex_q
1896 * object.
1897 */
1898 this->pi_state = NULL;
1899 put_pi_state(pi_state);
1900 /*
1901 * We stop queueing more waiters and let user
1902 * space deal with the mess.
1903 */
1904 break;
1905 }
1906 }
1907 requeue_futex(this, hb1, hb2, &key2);
1908 drop_count++;
1909 }
1910
1911 /*
1912 * We took an extra initial reference to the pi_state either
1913 * in futex_proxy_trylock_atomic() or in lookup_pi_state(). We
1914 * need to drop it here again.
1915 */
1916 put_pi_state(pi_state);
1917
1918out_unlock:
1919 double_unlock_hb(hb1, hb2);
1920 wake_up_q(&wake_q);
1921 hb_waiters_dec(hb2);
1922
1923 /*
1924 * drop_futex_key_refs() must be called outside the spinlocks. During
1925 * the requeue we moved futex_q's from the hash bucket at key1 to the
1926 * one at key2 and updated their key pointer. We no longer need to
1927 * hold the references to key1.
1928 */
1929 while (--drop_count >= 0)
1930 drop_futex_key_refs(&key1);
1931
1932out_put_keys:
1933 put_futex_key(&key2);
1934out_put_key1:
1935 put_futex_key(&key1);
1936out:
1937 return ret ? ret : task_count;
1938}
1939
1940/* The key must be already stored in q->key. */
1941static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
1942 __acquires(&hb->lock)
1943{
1944 struct futex_hash_bucket *hb;
1945
1946 hb = hash_futex(&q->key);
1947
1948 /*
1949 * Increment the counter before taking the lock so that
1950 * a potential waker won't miss a to-be-slept task that is
1951 * waiting for the spinlock. This is safe as all queue_lock()
1952 * users end up calling queue_me(). Similarly, for housekeeping,
1953 * decrement the counter at queue_unlock() when some error has
1954 * occurred and we don't end up adding the task to the list.
1955 */
1956 hb_waiters_inc(hb);
1957
1958 q->lock_ptr = &hb->lock;
1959
1960 spin_lock(&hb->lock); /* implies smp_mb(); (A) */
1961 return hb;
1962}
1963
1964static inline void
1965queue_unlock(struct futex_hash_bucket *hb)
1966 __releases(&hb->lock)
1967{
1968 spin_unlock(&hb->lock);
1969 hb_waiters_dec(hb);
1970}
1971
1972/**
1973 * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1974 * @q: The futex_q to enqueue
1975 * @hb: The destination hash bucket
1976 *
1977 * The hb->lock must be held by the caller, and is released here. A call to
1978 * queue_me() is typically paired with exactly one call to unqueue_me(). The
1979 * exceptions involve the PI related operations, which may use unqueue_me_pi()
1980 * or nothing if the unqueue is done as part of the wake process and the unqueue
1981 * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1982 * an example).
1983 */
1984static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1985 __releases(&hb->lock)
1986{
1987 int prio;
1988
1989 /*
1990 * The priority used to register this element is
1991 * - either the real thread-priority for the real-time threads
1992 * (i.e. threads with a priority lower than MAX_RT_PRIO)
1993 * - or MAX_RT_PRIO for non-RT threads.
1994 * Thus, all RT-threads are woken first in priority order, and
1995 * the others are woken last, in FIFO order.
1996 */
1997 prio = min(current->normal_prio, MAX_RT_PRIO);
1998
1999 plist_node_init(&q->list, prio);
2000 plist_add(&q->list, &hb->chain);
2001 q->task = current;
2002 spin_unlock(&hb->lock);
2003}
2004
2005/**
2006 * unqueue_me() - Remove the futex_q from its futex_hash_bucket
2007 * @q: The futex_q to unqueue
2008 *
2009 * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
2010 * be paired with exactly one earlier call to queue_me().
2011 *
2012 * Return:
2013 * 1 - if the futex_q was still queued (and we removed unqueued it);
2014 * 0 - if the futex_q was already removed by the waking thread
2015 */
2016static int unqueue_me(struct futex_q *q)
2017{
2018 spinlock_t *lock_ptr;
2019 int ret = 0;
2020
2021 /* In the common case we don't take the spinlock, which is nice. */
2022retry:
2023 /*
2024 * q->lock_ptr can change between this read and the following spin_lock.
2025 * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
2026 * optimizing lock_ptr out of the logic below.
2027 */
2028 lock_ptr = READ_ONCE(q->lock_ptr);
2029 if (lock_ptr != NULL) {
2030 spin_lock(lock_ptr);
2031 /*
2032 * q->lock_ptr can change between reading it and
2033 * spin_lock(), causing us to take the wrong lock. This
2034 * corrects the race condition.
2035 *
2036 * Reasoning goes like this: if we have the wrong lock,
2037 * q->lock_ptr must have changed (maybe several times)
2038 * between reading it and the spin_lock(). It can
2039 * change again after the spin_lock() but only if it was
2040 * already changed before the spin_lock(). It cannot,
2041 * however, change back to the original value. Therefore
2042 * we can detect whether we acquired the correct lock.
2043 */
2044 if (unlikely(lock_ptr != q->lock_ptr)) {
2045 spin_unlock(lock_ptr);
2046 goto retry;
2047 }
2048 __unqueue_futex(q);
2049
2050 BUG_ON(q->pi_state);
2051
2052 spin_unlock(lock_ptr);
2053 ret = 1;
2054 }
2055
2056 drop_futex_key_refs(&q->key);
2057 return ret;
2058}
2059
2060/*
2061 * PI futexes can not be requeued and must remove themself from the
2062 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
2063 * and dropped here.
2064 */
2065static void unqueue_me_pi(struct futex_q *q)
2066 __releases(q->lock_ptr)
2067{
2068 __unqueue_futex(q);
2069
2070 BUG_ON(!q->pi_state);
2071 put_pi_state(q->pi_state);
2072 q->pi_state = NULL;
2073
2074 spin_unlock(q->lock_ptr);
2075}
2076
2077/*
2078 * Fixup the pi_state owner with the new owner.
2079 *
2080 * Must be called with hash bucket lock held and mm->sem held for non
2081 * private futexes.
2082 */
2083static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
2084 struct task_struct *newowner)
2085{
2086 u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
2087 struct futex_pi_state *pi_state = q->pi_state;
2088 struct task_struct *oldowner = pi_state->owner;
2089 u32 uval, uninitialized_var(curval), newval;
2090 int ret;
2091
2092 /* Owner died? */
2093 if (!pi_state->owner)
2094 newtid |= FUTEX_OWNER_DIED;
2095
2096 /*
2097 * We are here either because we stole the rtmutex from the
2098 * previous highest priority waiter or we are the highest priority
2099 * waiter but failed to get the rtmutex the first time.
2100 * We have to replace the newowner TID in the user space variable.
2101 * This must be atomic as we have to preserve the owner died bit here.
2102 *
2103 * Note: We write the user space value _before_ changing the pi_state
2104 * because we can fault here. Imagine swapped out pages or a fork
2105 * that marked all the anonymous memory readonly for cow.
2106 *
2107 * Modifying pi_state _before_ the user space value would
2108 * leave the pi_state in an inconsistent state when we fault
2109 * here, because we need to drop the hash bucket lock to
2110 * handle the fault. This might be observed in the PID check
2111 * in lookup_pi_state.
2112 */
2113retry:
2114 if (get_futex_value_locked(&uval, uaddr))
2115 goto handle_fault;
2116
2117 while (1) {
2118 newval = (uval & FUTEX_OWNER_DIED) | newtid;
2119
2120 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
2121 goto handle_fault;
2122 if (curval == uval)
2123 break;
2124 uval = curval;
2125 }
2126
2127 /*
2128 * We fixed up user space. Now we need to fix the pi_state
2129 * itself.
2130 */
2131 if (pi_state->owner != NULL) {
2132 raw_spin_lock_irq(&pi_state->owner->pi_lock);
2133 WARN_ON(list_empty(&pi_state->list));
2134 list_del_init(&pi_state->list);
2135 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
2136 }
2137
2138 pi_state->owner = newowner;
2139
2140 raw_spin_lock_irq(&newowner->pi_lock);
2141 WARN_ON(!list_empty(&pi_state->list));
2142 list_add(&pi_state->list, &newowner->pi_state_list);
2143 raw_spin_unlock_irq(&newowner->pi_lock);
2144 return 0;
2145
2146 /*
2147 * To handle the page fault we need to drop the hash bucket
2148 * lock here. That gives the other task (either the highest priority
2149 * waiter itself or the task which stole the rtmutex) the
2150 * chance to try the fixup of the pi_state. So once we are
2151 * back from handling the fault we need to check the pi_state
2152 * after reacquiring the hash bucket lock and before trying to
2153 * do another fixup. When the fixup has been done already we
2154 * simply return.
2155 */
2156handle_fault:
2157 spin_unlock(q->lock_ptr);
2158
2159 ret = fault_in_user_writeable(uaddr);
2160
2161 spin_lock(q->lock_ptr);
2162
2163 /*
2164 * Check if someone else fixed it for us:
2165 */
2166 if (pi_state->owner != oldowner)
2167 return 0;
2168
2169 if (ret)
2170 return ret;
2171
2172 goto retry;
2173}
2174
2175static long futex_wait_restart(struct restart_block *restart);
2176
2177/**
2178 * fixup_owner() - Post lock pi_state and corner case management
2179 * @uaddr: user address of the futex
2180 * @q: futex_q (contains pi_state and access to the rt_mutex)
2181 * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
2182 *
2183 * After attempting to lock an rt_mutex, this function is called to cleanup
2184 * the pi_state owner as well as handle race conditions that may allow us to
2185 * acquire the lock. Must be called with the hb lock held.
2186 *
2187 * Return:
2188 * 1 - success, lock taken;
2189 * 0 - success, lock not taken;
2190 * <0 - on error (-EFAULT)
2191 */
2192static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
2193{
2194 struct task_struct *owner;
2195 int ret = 0;
2196
2197 if (locked) {
2198 /*
2199 * Got the lock. We might not be the anticipated owner if we
2200 * did a lock-steal - fix up the PI-state in that case:
2201 */
2202 if (q->pi_state->owner != current)
2203 ret = fixup_pi_state_owner(uaddr, q, current);
2204 goto out;
2205 }
2206
2207 /*
2208 * Catch the rare case, where the lock was released when we were on the
2209 * way back before we locked the hash bucket.
2210 */
2211 if (q->pi_state->owner == current) {
2212 /*
2213 * Try to get the rt_mutex now. This might fail as some other
2214 * task acquired the rt_mutex after we removed ourself from the
2215 * rt_mutex waiters list.
2216 */
2217 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
2218 locked = 1;
2219 goto out;
2220 }
2221
2222 /*
2223 * pi_state is incorrect, some other task did a lock steal and
2224 * we returned due to timeout or signal without taking the
2225 * rt_mutex. Too late.
2226 */
2227 raw_spin_lock_irq(&q->pi_state->pi_mutex.wait_lock);
2228 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
2229 if (!owner)
2230 owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
2231 raw_spin_unlock_irq(&q->pi_state->pi_mutex.wait_lock);
2232 ret = fixup_pi_state_owner(uaddr, q, owner);
2233 goto out;
2234 }
2235
2236 /*
2237 * Paranoia check. If we did not take the lock, then we should not be
2238 * the owner of the rt_mutex.
2239 */
2240 if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
2241 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
2242 "pi-state %p\n", ret,
2243 q->pi_state->pi_mutex.owner,
2244 q->pi_state->owner);
2245
2246out:
2247 return ret ? ret : locked;
2248}
2249
2250/**
2251 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
2252 * @hb: the futex hash bucket, must be locked by the caller
2253 * @q: the futex_q to queue up on
2254 * @timeout: the prepared hrtimer_sleeper, or null for no timeout
2255 */
2256static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
2257 struct hrtimer_sleeper *timeout)
2258{
2259 /*
2260 * The task state is guaranteed to be set before another task can
2261 * wake it. set_current_state() is implemented using smp_store_mb() and
2262 * queue_me() calls spin_unlock() upon completion, both serializing
2263 * access to the hash list and forcing another memory barrier.
2264 */
2265 set_current_state(TASK_INTERRUPTIBLE);
2266 queue_me(q, hb);
2267
2268 /* Arm the timer */
2269 if (timeout)
2270 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
2271
2272 /*
2273 * If we have been removed from the hash list, then another task
2274 * has tried to wake us, and we can skip the call to schedule().
2275 */
2276 if (likely(!plist_node_empty(&q->list))) {
2277 /*
2278 * If the timer has already expired, current will already be
2279 * flagged for rescheduling. Only call schedule if there
2280 * is no timeout, or if it has yet to expire.
2281 */
2282 if (!timeout || timeout->task)
2283 freezable_schedule();
2284 }
2285 __set_current_state(TASK_RUNNING);
2286}
2287
2288/**
2289 * futex_wait_setup() - Prepare to wait on a futex
2290 * @uaddr: the futex userspace address
2291 * @val: the expected value
2292 * @flags: futex flags (FLAGS_SHARED, etc.)
2293 * @q: the associated futex_q
2294 * @hb: storage for hash_bucket pointer to be returned to caller
2295 *
2296 * Setup the futex_q and locate the hash_bucket. Get the futex value and
2297 * compare it with the expected value. Handle atomic faults internally.
2298 * Return with the hb lock held and a q.key reference on success, and unlocked
2299 * with no q.key reference on failure.
2300 *
2301 * Return:
2302 * 0 - uaddr contains val and hb has been locked;
2303 * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
2304 */
2305static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
2306 struct futex_q *q, struct futex_hash_bucket **hb)
2307{
2308 u32 uval;
2309 int ret;
2310
2311 /*
2312 * Access the page AFTER the hash-bucket is locked.
2313 * Order is important:
2314 *
2315 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
2316 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
2317 *
2318 * The basic logical guarantee of a futex is that it blocks ONLY
2319 * if cond(var) is known to be true at the time of blocking, for
2320 * any cond. If we locked the hash-bucket after testing *uaddr, that
2321 * would open a race condition where we could block indefinitely with
2322 * cond(var) false, which would violate the guarantee.
2323 *
2324 * On the other hand, we insert q and release the hash-bucket only
2325 * after testing *uaddr. This guarantees that futex_wait() will NOT
2326 * absorb a wakeup if *uaddr does not match the desired values
2327 * while the syscall executes.
2328 */
2329retry:
2330 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
2331 if (unlikely(ret != 0))
2332 return ret;
2333
2334retry_private:
2335 *hb = queue_lock(q);
2336
2337 ret = get_futex_value_locked(&uval, uaddr);
2338
2339 if (ret) {
2340 queue_unlock(*hb);
2341
2342 ret = get_user(uval, uaddr);
2343 if (ret)
2344 goto out;
2345
2346 if (!(flags & FLAGS_SHARED))
2347 goto retry_private;
2348
2349 put_futex_key(&q->key);
2350 goto retry;
2351 }
2352
2353 if (uval != val) {
2354 queue_unlock(*hb);
2355 ret = -EWOULDBLOCK;
2356 }
2357
2358out:
2359 if (ret)
2360 put_futex_key(&q->key);
2361 return ret;
2362}
2363
2364static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
2365 ktime_t *abs_time, u32 bitset)
2366{
2367 struct hrtimer_sleeper timeout, *to = NULL;
2368 struct restart_block *restart;
2369 struct futex_hash_bucket *hb;
2370 struct futex_q q = futex_q_init;
2371 int ret;
2372
2373 if (!bitset)
2374 return -EINVAL;
2375 q.bitset = bitset;
2376
2377 if (abs_time) {
2378 to = &timeout;
2379
2380 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2381 CLOCK_REALTIME : CLOCK_MONOTONIC,
2382 HRTIMER_MODE_ABS);
2383 hrtimer_init_sleeper(to, current);
2384 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2385 current->timer_slack_ns);
2386 }
2387
2388retry:
2389 /*
2390 * Prepare to wait on uaddr. On success, holds hb lock and increments
2391 * q.key refs.
2392 */
2393 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2394 if (ret)
2395 goto out;
2396
2397 /* queue_me and wait for wakeup, timeout, or a signal. */
2398 futex_wait_queue_me(hb, &q, to);
2399
2400 /* If we were woken (and unqueued), we succeeded, whatever. */
2401 ret = 0;
2402 /* unqueue_me() drops q.key ref */
2403 if (!unqueue_me(&q))
2404 goto out;
2405 ret = -ETIMEDOUT;
2406 if (to && !to->task)
2407 goto out;
2408
2409 /*
2410 * We expect signal_pending(current), but we might be the
2411 * victim of a spurious wakeup as well.
2412 */
2413 if (!signal_pending(current))
2414 goto retry;
2415
2416 ret = -ERESTARTSYS;
2417 if (!abs_time)
2418 goto out;
2419
2420 restart = ¤t->restart_block;
2421 restart->fn = futex_wait_restart;
2422 restart->futex.uaddr = uaddr;
2423 restart->futex.val = val;
2424 restart->futex.time = abs_time->tv64;
2425 restart->futex.bitset = bitset;
2426 restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
2427
2428 ret = -ERESTART_RESTARTBLOCK;
2429
2430out:
2431 if (to) {
2432 hrtimer_cancel(&to->timer);
2433 destroy_hrtimer_on_stack(&to->timer);
2434 }
2435 return ret;
2436}
2437
2438
2439static long futex_wait_restart(struct restart_block *restart)
2440{
2441 u32 __user *uaddr = restart->futex.uaddr;
2442 ktime_t t, *tp = NULL;
2443
2444 if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
2445 t.tv64 = restart->futex.time;
2446 tp = &t;
2447 }
2448 restart->fn = do_no_restart_syscall;
2449
2450 return (long)futex_wait(uaddr, restart->futex.flags,
2451 restart->futex.val, tp, restart->futex.bitset);
2452}
2453
2454
2455/*
2456 * Userspace tried a 0 -> TID atomic transition of the futex value
2457 * and failed. The kernel side here does the whole locking operation:
2458 * if there are waiters then it will block as a consequence of relying
2459 * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
2460 * a 0 value of the futex too.).
2461 *
2462 * Also serves as futex trylock_pi()'ing, and due semantics.
2463 */
2464static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
2465 ktime_t *time, int trylock)
2466{
2467 struct hrtimer_sleeper timeout, *to = NULL;
2468 struct futex_hash_bucket *hb;
2469 struct futex_q q = futex_q_init;
2470 int res, ret;
2471
2472 if (refill_pi_state_cache())
2473 return -ENOMEM;
2474
2475 if (time) {
2476 to = &timeout;
2477 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
2478 HRTIMER_MODE_ABS);
2479 hrtimer_init_sleeper(to, current);
2480 hrtimer_set_expires(&to->timer, *time);
2481 }
2482
2483retry:
2484 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
2485 if (unlikely(ret != 0))
2486 goto out;
2487
2488retry_private:
2489 hb = queue_lock(&q);
2490
2491 ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
2492 if (unlikely(ret)) {
2493 /*
2494 * Atomic work succeeded and we got the lock,
2495 * or failed. Either way, we do _not_ block.
2496 */
2497 switch (ret) {
2498 case 1:
2499 /* We got the lock. */
2500 ret = 0;
2501 goto out_unlock_put_key;
2502 case -EFAULT:
2503 goto uaddr_faulted;
2504 case -EAGAIN:
2505 /*
2506 * Two reasons for this:
2507 * - Task is exiting and we just wait for the
2508 * exit to complete.
2509 * - The user space value changed.
2510 */
2511 queue_unlock(hb);
2512 put_futex_key(&q.key);
2513 cond_resched();
2514 goto retry;
2515 default:
2516 goto out_unlock_put_key;
2517 }
2518 }
2519
2520 /*
2521 * Only actually queue now that the atomic ops are done:
2522 */
2523 queue_me(&q, hb);
2524
2525 WARN_ON(!q.pi_state);
2526 /*
2527 * Block on the PI mutex:
2528 */
2529 if (!trylock) {
2530 ret = rt_mutex_timed_futex_lock(&q.pi_state->pi_mutex, to);
2531 } else {
2532 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
2533 /* Fixup the trylock return value: */
2534 ret = ret ? 0 : -EWOULDBLOCK;
2535 }
2536
2537 spin_lock(q.lock_ptr);
2538 /*
2539 * Fixup the pi_state owner and possibly acquire the lock if we
2540 * haven't already.
2541 */
2542 res = fixup_owner(uaddr, &q, !ret);
2543 /*
2544 * If fixup_owner() returned an error, proprogate that. If it acquired
2545 * the lock, clear our -ETIMEDOUT or -EINTR.
2546 */
2547 if (res)
2548 ret = (res < 0) ? res : 0;
2549
2550 /*
2551 * If fixup_owner() faulted and was unable to handle the fault, unlock
2552 * it and return the fault to userspace.
2553 */
2554 if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
2555 rt_mutex_unlock(&q.pi_state->pi_mutex);
2556
2557 /* Unqueue and drop the lock */
2558 unqueue_me_pi(&q);
2559
2560 goto out_put_key;
2561
2562out_unlock_put_key:
2563 queue_unlock(hb);
2564
2565out_put_key:
2566 put_futex_key(&q.key);
2567out:
2568 if (to)
2569 destroy_hrtimer_on_stack(&to->timer);
2570 return ret != -EINTR ? ret : -ERESTARTNOINTR;
2571
2572uaddr_faulted:
2573 queue_unlock(hb);
2574
2575 ret = fault_in_user_writeable(uaddr);
2576 if (ret)
2577 goto out_put_key;
2578
2579 if (!(flags & FLAGS_SHARED))
2580 goto retry_private;
2581
2582 put_futex_key(&q.key);
2583 goto retry;
2584}
2585
2586/*
2587 * Userspace attempted a TID -> 0 atomic transition, and failed.
2588 * This is the in-kernel slowpath: we look up the PI state (if any),
2589 * and do the rt-mutex unlock.
2590 */
2591static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
2592{
2593 u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current);
2594 union futex_key key = FUTEX_KEY_INIT;
2595 struct futex_hash_bucket *hb;
2596 struct futex_q *match;
2597 int ret;
2598
2599retry:
2600 if (get_user(uval, uaddr))
2601 return -EFAULT;
2602 /*
2603 * We release only a lock we actually own:
2604 */
2605 if ((uval & FUTEX_TID_MASK) != vpid)
2606 return -EPERM;
2607
2608 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
2609 if (ret)
2610 return ret;
2611
2612 hb = hash_futex(&key);
2613 spin_lock(&hb->lock);
2614
2615 /*
2616 * Check waiters first. We do not trust user space values at
2617 * all and we at least want to know if user space fiddled
2618 * with the futex value instead of blindly unlocking.
2619 */
2620 match = futex_top_waiter(hb, &key);
2621 if (match) {
2622 ret = wake_futex_pi(uaddr, uval, match, hb);
2623 /*
2624 * In case of success wake_futex_pi dropped the hash
2625 * bucket lock.
2626 */
2627 if (!ret)
2628 goto out_putkey;
2629 /*
2630 * The atomic access to the futex value generated a
2631 * pagefault, so retry the user-access and the wakeup:
2632 */
2633 if (ret == -EFAULT)
2634 goto pi_faulted;
2635 /*
2636 * A unconditional UNLOCK_PI op raced against a waiter
2637 * setting the FUTEX_WAITERS bit. Try again.
2638 */
2639 if (ret == -EAGAIN) {
2640 spin_unlock(&hb->lock);
2641 put_futex_key(&key);
2642 goto retry;
2643 }
2644 /*
2645 * wake_futex_pi has detected invalid state. Tell user
2646 * space.
2647 */
2648 goto out_unlock;
2649 }
2650
2651 /*
2652 * We have no kernel internal state, i.e. no waiters in the
2653 * kernel. Waiters which are about to queue themselves are stuck
2654 * on hb->lock. So we can safely ignore them. We do neither
2655 * preserve the WAITERS bit not the OWNER_DIED one. We are the
2656 * owner.
2657 */
2658 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))
2659 goto pi_faulted;
2660
2661 /*
2662 * If uval has changed, let user space handle it.
2663 */
2664 ret = (curval == uval) ? 0 : -EAGAIN;
2665
2666out_unlock:
2667 spin_unlock(&hb->lock);
2668out_putkey:
2669 put_futex_key(&key);
2670 return ret;
2671
2672pi_faulted:
2673 spin_unlock(&hb->lock);
2674 put_futex_key(&key);
2675
2676 ret = fault_in_user_writeable(uaddr);
2677 if (!ret)
2678 goto retry;
2679
2680 return ret;
2681}
2682
2683/**
2684 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2685 * @hb: the hash_bucket futex_q was original enqueued on
2686 * @q: the futex_q woken while waiting to be requeued
2687 * @key2: the futex_key of the requeue target futex
2688 * @timeout: the timeout associated with the wait (NULL if none)
2689 *
2690 * Detect if the task was woken on the initial futex as opposed to the requeue
2691 * target futex. If so, determine if it was a timeout or a signal that caused
2692 * the wakeup and return the appropriate error code to the caller. Must be
2693 * called with the hb lock held.
2694 *
2695 * Return:
2696 * 0 = no early wakeup detected;
2697 * <0 = -ETIMEDOUT or -ERESTARTNOINTR
2698 */
2699static inline
2700int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2701 struct futex_q *q, union futex_key *key2,
2702 struct hrtimer_sleeper *timeout)
2703{
2704 int ret = 0;
2705
2706 /*
2707 * With the hb lock held, we avoid races while we process the wakeup.
2708 * We only need to hold hb (and not hb2) to ensure atomicity as the
2709 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2710 * It can't be requeued from uaddr2 to something else since we don't
2711 * support a PI aware source futex for requeue.
2712 */
2713 if (!match_futex(&q->key, key2)) {
2714 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2715 /*
2716 * We were woken prior to requeue by a timeout or a signal.
2717 * Unqueue the futex_q and determine which it was.
2718 */
2719 plist_del(&q->list, &hb->chain);
2720 hb_waiters_dec(hb);
2721
2722 /* Handle spurious wakeups gracefully */
2723 ret = -EWOULDBLOCK;
2724 if (timeout && !timeout->task)
2725 ret = -ETIMEDOUT;
2726 else if (signal_pending(current))
2727 ret = -ERESTARTNOINTR;
2728 }
2729 return ret;
2730}
2731
2732/**
2733 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2734 * @uaddr: the futex we initially wait on (non-pi)
2735 * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
2736 * the same type, no requeueing from private to shared, etc.
2737 * @val: the expected value of uaddr
2738 * @abs_time: absolute timeout
2739 * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
2740 * @uaddr2: the pi futex we will take prior to returning to user-space
2741 *
2742 * The caller will wait on uaddr and will be requeued by futex_requeue() to
2743 * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
2744 * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
2745 * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
2746 * without one, the pi logic would not know which task to boost/deboost, if
2747 * there was a need to.
2748 *
2749 * We call schedule in futex_wait_queue_me() when we enqueue and return there
2750 * via the following--
2751 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2752 * 2) wakeup on uaddr2 after a requeue
2753 * 3) signal
2754 * 4) timeout
2755 *
2756 * If 3, cleanup and return -ERESTARTNOINTR.
2757 *
2758 * If 2, we may then block on trying to take the rt_mutex and return via:
2759 * 5) successful lock
2760 * 6) signal
2761 * 7) timeout
2762 * 8) other lock acquisition failure
2763 *
2764 * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2765 *
2766 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2767 *
2768 * Return:
2769 * 0 - On success;
2770 * <0 - On error
2771 */
2772static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
2773 u32 val, ktime_t *abs_time, u32 bitset,
2774 u32 __user *uaddr2)
2775{
2776 struct hrtimer_sleeper timeout, *to = NULL;
2777 struct rt_mutex_waiter rt_waiter;
2778 struct rt_mutex *pi_mutex = NULL;
2779 struct futex_hash_bucket *hb;
2780 union futex_key key2 = FUTEX_KEY_INIT;
2781 struct futex_q q = futex_q_init;
2782 int res, ret;
2783
2784 if (uaddr == uaddr2)
2785 return -EINVAL;
2786
2787 if (!bitset)
2788 return -EINVAL;
2789
2790 if (abs_time) {
2791 to = &timeout;
2792 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2793 CLOCK_REALTIME : CLOCK_MONOTONIC,
2794 HRTIMER_MODE_ABS);
2795 hrtimer_init_sleeper(to, current);
2796 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2797 current->timer_slack_ns);
2798 }
2799
2800 /*
2801 * The waiter is allocated on our stack, manipulated by the requeue
2802 * code while we sleep on uaddr.
2803 */
2804 debug_rt_mutex_init_waiter(&rt_waiter);
2805 RB_CLEAR_NODE(&rt_waiter.pi_tree_entry);
2806 RB_CLEAR_NODE(&rt_waiter.tree_entry);
2807 rt_waiter.task = NULL;
2808
2809 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
2810 if (unlikely(ret != 0))
2811 goto out;
2812
2813 q.bitset = bitset;
2814 q.rt_waiter = &rt_waiter;
2815 q.requeue_pi_key = &key2;
2816
2817 /*
2818 * Prepare to wait on uaddr. On success, increments q.key (key1) ref
2819 * count.
2820 */
2821 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2822 if (ret)
2823 goto out_key2;
2824
2825 /*
2826 * The check above which compares uaddrs is not sufficient for
2827 * shared futexes. We need to compare the keys:
2828 */
2829 if (match_futex(&q.key, &key2)) {
2830 queue_unlock(hb);
2831 ret = -EINVAL;
2832 goto out_put_keys;
2833 }
2834
2835 /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2836 futex_wait_queue_me(hb, &q, to);
2837
2838 spin_lock(&hb->lock);
2839 ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2840 spin_unlock(&hb->lock);
2841 if (ret)
2842 goto out_put_keys;
2843
2844 /*
2845 * In order for us to be here, we know our q.key == key2, and since
2846 * we took the hb->lock above, we also know that futex_requeue() has
2847 * completed and we no longer have to concern ourselves with a wakeup
2848 * race with the atomic proxy lock acquisition by the requeue code. The
2849 * futex_requeue dropped our key1 reference and incremented our key2
2850 * reference count.
2851 */
2852
2853 /* Check if the requeue code acquired the second futex for us. */
2854 if (!q.rt_waiter) {
2855 /*
2856 * Got the lock. We might not be the anticipated owner if we
2857 * did a lock-steal - fix up the PI-state in that case.
2858 */
2859 if (q.pi_state && (q.pi_state->owner != current)) {
2860 spin_lock(q.lock_ptr);
2861 ret = fixup_pi_state_owner(uaddr2, &q, current);
2862 /*
2863 * Drop the reference to the pi state which
2864 * the requeue_pi() code acquired for us.
2865 */
2866 put_pi_state(q.pi_state);
2867 spin_unlock(q.lock_ptr);
2868 }
2869 } else {
2870 /*
2871 * We have been woken up by futex_unlock_pi(), a timeout, or a
2872 * signal. futex_unlock_pi() will not destroy the lock_ptr nor
2873 * the pi_state.
2874 */
2875 WARN_ON(!q.pi_state);
2876 pi_mutex = &q.pi_state->pi_mutex;
2877 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter);
2878 debug_rt_mutex_free_waiter(&rt_waiter);
2879
2880 spin_lock(q.lock_ptr);
2881 /*
2882 * Fixup the pi_state owner and possibly acquire the lock if we
2883 * haven't already.
2884 */
2885 res = fixup_owner(uaddr2, &q, !ret);
2886 /*
2887 * If fixup_owner() returned an error, proprogate that. If it
2888 * acquired the lock, clear -ETIMEDOUT or -EINTR.
2889 */
2890 if (res)
2891 ret = (res < 0) ? res : 0;
2892
2893 /* Unqueue and drop the lock. */
2894 unqueue_me_pi(&q);
2895 }
2896
2897 /*
2898 * If fixup_pi_state_owner() faulted and was unable to handle the
2899 * fault, unlock the rt_mutex and return the fault to userspace.
2900 */
2901 if (ret == -EFAULT) {
2902 if (pi_mutex && rt_mutex_owner(pi_mutex) == current)
2903 rt_mutex_unlock(pi_mutex);
2904 } else if (ret == -EINTR) {
2905 /*
2906 * We've already been requeued, but cannot restart by calling
2907 * futex_lock_pi() directly. We could restart this syscall, but
2908 * it would detect that the user space "val" changed and return
2909 * -EWOULDBLOCK. Save the overhead of the restart and return
2910 * -EWOULDBLOCK directly.
2911 */
2912 ret = -EWOULDBLOCK;
2913 }
2914
2915out_put_keys:
2916 put_futex_key(&q.key);
2917out_key2:
2918 put_futex_key(&key2);
2919
2920out:
2921 if (to) {
2922 hrtimer_cancel(&to->timer);
2923 destroy_hrtimer_on_stack(&to->timer);
2924 }
2925 return ret;
2926}
2927
2928/*
2929 * Support for robust futexes: the kernel cleans up held futexes at
2930 * thread exit time.
2931 *
2932 * Implementation: user-space maintains a per-thread list of locks it
2933 * is holding. Upon do_exit(), the kernel carefully walks this list,
2934 * and marks all locks that are owned by this thread with the
2935 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2936 * always manipulated with the lock held, so the list is private and
2937 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2938 * field, to allow the kernel to clean up if the thread dies after
2939 * acquiring the lock, but just before it could have added itself to
2940 * the list. There can only be one such pending lock.
2941 */
2942
2943/**
2944 * sys_set_robust_list() - Set the robust-futex list head of a task
2945 * @head: pointer to the list-head
2946 * @len: length of the list-head, as userspace expects
2947 */
2948SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2949 size_t, len)
2950{
2951 if (!futex_cmpxchg_enabled)
2952 return -ENOSYS;
2953 /*
2954 * The kernel knows only one size for now:
2955 */
2956 if (unlikely(len != sizeof(*head)))
2957 return -EINVAL;
2958
2959 current->robust_list = head;
2960
2961 return 0;
2962}
2963
2964/**
2965 * sys_get_robust_list() - Get the robust-futex list head of a task
2966 * @pid: pid of the process [zero for current task]
2967 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
2968 * @len_ptr: pointer to a length field, the kernel fills in the header size
2969 */
2970SYSCALL_DEFINE3(get_robust_list, int, pid,
2971 struct robust_list_head __user * __user *, head_ptr,
2972 size_t __user *, len_ptr)
2973{
2974 struct robust_list_head __user *head;
2975 unsigned long ret;
2976 struct task_struct *p;
2977
2978 if (!futex_cmpxchg_enabled)
2979 return -ENOSYS;
2980
2981 rcu_read_lock();
2982
2983 ret = -ESRCH;
2984 if (!pid)
2985 p = current;
2986 else {
2987 p = find_task_by_vpid(pid);
2988 if (!p)
2989 goto err_unlock;
2990 }
2991
2992 ret = -EPERM;
2993 if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
2994 goto err_unlock;
2995
2996 head = p->robust_list;
2997 rcu_read_unlock();
2998
2999 if (put_user(sizeof(*head), len_ptr))
3000 return -EFAULT;
3001 return put_user(head, head_ptr);
3002
3003err_unlock:
3004 rcu_read_unlock();
3005
3006 return ret;
3007}
3008
3009/*
3010 * Process a futex-list entry, check whether it's owned by the
3011 * dying task, and do notification if so:
3012 */
3013int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
3014{
3015 u32 uval, uninitialized_var(nval), mval;
3016
3017retry:
3018 if (get_user(uval, uaddr))
3019 return -1;
3020
3021 if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
3022 /*
3023 * Ok, this dying thread is truly holding a futex
3024 * of interest. Set the OWNER_DIED bit atomically
3025 * via cmpxchg, and if the value had FUTEX_WAITERS
3026 * set, wake up a waiter (if any). (We have to do a
3027 * futex_wake() even if OWNER_DIED is already set -
3028 * to handle the rare but possible case of recursive
3029 * thread-death.) The rest of the cleanup is done in
3030 * userspace.
3031 */
3032 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
3033 /*
3034 * We are not holding a lock here, but we want to have
3035 * the pagefault_disable/enable() protection because
3036 * we want to handle the fault gracefully. If the
3037 * access fails we try to fault in the futex with R/W
3038 * verification via get_user_pages. get_user() above
3039 * does not guarantee R/W access. If that fails we
3040 * give up and leave the futex locked.
3041 */
3042 if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
3043 if (fault_in_user_writeable(uaddr))
3044 return -1;
3045 goto retry;
3046 }
3047 if (nval != uval)
3048 goto retry;
3049
3050 /*
3051 * Wake robust non-PI futexes here. The wakeup of
3052 * PI futexes happens in exit_pi_state():
3053 */
3054 if (!pi && (uval & FUTEX_WAITERS))
3055 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
3056 }
3057 return 0;
3058}
3059
3060/*
3061 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
3062 */
3063static inline int fetch_robust_entry(struct robust_list __user **entry,
3064 struct robust_list __user * __user *head,
3065 unsigned int *pi)
3066{
3067 unsigned long uentry;
3068
3069 if (get_user(uentry, (unsigned long __user *)head))
3070 return -EFAULT;
3071
3072 *entry = (void __user *)(uentry & ~1UL);
3073 *pi = uentry & 1;
3074
3075 return 0;
3076}
3077
3078/*
3079 * Walk curr->robust_list (very carefully, it's a userspace list!)
3080 * and mark any locks found there dead, and notify any waiters.
3081 *
3082 * We silently return on any sign of list-walking problem.
3083 */
3084void exit_robust_list(struct task_struct *curr)
3085{
3086 struct robust_list_head __user *head = curr->robust_list;
3087 struct robust_list __user *entry, *next_entry, *pending;
3088 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
3089 unsigned int uninitialized_var(next_pi);
3090 unsigned long futex_offset;
3091 int rc;
3092
3093 if (!futex_cmpxchg_enabled)
3094 return;
3095
3096 /*
3097 * Fetch the list head (which was registered earlier, via
3098 * sys_set_robust_list()):
3099 */
3100 if (fetch_robust_entry(&entry, &head->list.next, &pi))
3101 return;
3102 /*
3103 * Fetch the relative futex offset:
3104 */
3105 if (get_user(futex_offset, &head->futex_offset))
3106 return;
3107 /*
3108 * Fetch any possibly pending lock-add first, and handle it
3109 * if it exists:
3110 */
3111 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
3112 return;
3113
3114 next_entry = NULL; /* avoid warning with gcc */
3115 while (entry != &head->list) {
3116 /*
3117 * Fetch the next entry in the list before calling
3118 * handle_futex_death:
3119 */
3120 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
3121 /*
3122 * A pending lock might already be on the list, so
3123 * don't process it twice:
3124 */
3125 if (entry != pending)
3126 if (handle_futex_death((void __user *)entry + futex_offset,
3127 curr, pi))
3128 return;
3129 if (rc)
3130 return;
3131 entry = next_entry;
3132 pi = next_pi;
3133 /*
3134 * Avoid excessively long or circular lists:
3135 */
3136 if (!--limit)
3137 break;
3138
3139 cond_resched();
3140 }
3141
3142 if (pending)
3143 handle_futex_death((void __user *)pending + futex_offset,
3144 curr, pip);
3145}
3146
3147long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
3148 u32 __user *uaddr2, u32 val2, u32 val3)
3149{
3150 int cmd = op & FUTEX_CMD_MASK;
3151 unsigned int flags = 0;
3152
3153 if (!(op & FUTEX_PRIVATE_FLAG))
3154 flags |= FLAGS_SHARED;
3155
3156 if (op & FUTEX_CLOCK_REALTIME) {
3157 flags |= FLAGS_CLOCKRT;
3158 if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \
3159 cmd != FUTEX_WAIT_REQUEUE_PI)
3160 return -ENOSYS;
3161 }
3162
3163 switch (cmd) {
3164 case FUTEX_LOCK_PI:
3165 case FUTEX_UNLOCK_PI:
3166 case FUTEX_TRYLOCK_PI:
3167 case FUTEX_WAIT_REQUEUE_PI:
3168 case FUTEX_CMP_REQUEUE_PI:
3169 if (!futex_cmpxchg_enabled)
3170 return -ENOSYS;
3171 }
3172
3173 switch (cmd) {
3174 case FUTEX_WAIT:
3175 val3 = FUTEX_BITSET_MATCH_ANY;
3176 case FUTEX_WAIT_BITSET:
3177 return futex_wait(uaddr, flags, val, timeout, val3);
3178 case FUTEX_WAKE:
3179 val3 = FUTEX_BITSET_MATCH_ANY;
3180 case FUTEX_WAKE_BITSET:
3181 return futex_wake(uaddr, flags, val, val3);
3182 case FUTEX_REQUEUE:
3183 return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
3184 case FUTEX_CMP_REQUEUE:
3185 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
3186 case FUTEX_WAKE_OP:
3187 return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
3188 case FUTEX_LOCK_PI:
3189 return futex_lock_pi(uaddr, flags, timeout, 0);
3190 case FUTEX_UNLOCK_PI:
3191 return futex_unlock_pi(uaddr, flags);
3192 case FUTEX_TRYLOCK_PI:
3193 return futex_lock_pi(uaddr, flags, NULL, 1);
3194 case FUTEX_WAIT_REQUEUE_PI:
3195 val3 = FUTEX_BITSET_MATCH_ANY;
3196 return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
3197 uaddr2);
3198 case FUTEX_CMP_REQUEUE_PI:
3199 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
3200 }
3201 return -ENOSYS;
3202}
3203
3204
3205SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
3206 struct timespec __user *, utime, u32 __user *, uaddr2,
3207 u32, val3)
3208{
3209 struct timespec ts;
3210 ktime_t t, *tp = NULL;
3211 u32 val2 = 0;
3212 int cmd = op & FUTEX_CMD_MASK;
3213
3214 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
3215 cmd == FUTEX_WAIT_BITSET ||
3216 cmd == FUTEX_WAIT_REQUEUE_PI)) {
3217 if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
3218 return -EFAULT;
3219 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
3220 return -EFAULT;
3221 if (!timespec_valid(&ts))
3222 return -EINVAL;
3223
3224 t = timespec_to_ktime(ts);
3225 if (cmd == FUTEX_WAIT)
3226 t = ktime_add_safe(ktime_get(), t);
3227 tp = &t;
3228 }
3229 /*
3230 * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
3231 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
3232 */
3233 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
3234 cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
3235 val2 = (u32) (unsigned long) utime;
3236
3237 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
3238}
3239
3240static void __init futex_detect_cmpxchg(void)
3241{
3242#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
3243 u32 curval;
3244
3245 /*
3246 * This will fail and we want it. Some arch implementations do
3247 * runtime detection of the futex_atomic_cmpxchg_inatomic()
3248 * functionality. We want to know that before we call in any
3249 * of the complex code paths. Also we want to prevent
3250 * registration of robust lists in that case. NULL is
3251 * guaranteed to fault and we get -EFAULT on functional
3252 * implementation, the non-functional ones will return
3253 * -ENOSYS.
3254 */
3255 if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
3256 futex_cmpxchg_enabled = 1;
3257#endif
3258}
3259
3260static int __init futex_init(void)
3261{
3262 unsigned int futex_shift;
3263 unsigned long i;
3264
3265#if CONFIG_BASE_SMALL
3266 futex_hashsize = 16;
3267#else
3268 futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
3269#endif
3270
3271 futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
3272 futex_hashsize, 0,
3273 futex_hashsize < 256 ? HASH_SMALL : 0,
3274 &futex_shift, NULL,
3275 futex_hashsize, futex_hashsize);
3276 futex_hashsize = 1UL << futex_shift;
3277
3278 futex_detect_cmpxchg();
3279
3280 for (i = 0; i < futex_hashsize; i++) {
3281 atomic_set(&futex_queues[i].waiters, 0);
3282 plist_head_init(&futex_queues[i].chain);
3283 spin_lock_init(&futex_queues[i].lock);
3284 }
3285
3286 return 0;
3287}
3288__initcall(futex_init);
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);