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