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1da177e4 LT |
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 | * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly | |
12 | * enough at me, Linus for the original (flawed) idea, Matthew | |
13 | * Kirkwood for proof-of-concept implementation. | |
14 | * | |
15 | * "The futexes are also cursed." | |
16 | * "But they come in a choice of three flavours!" | |
17 | * | |
18 | * This program is free software; you can redistribute it and/or modify | |
19 | * it under the terms of the GNU General Public License as published by | |
20 | * the Free Software Foundation; either version 2 of the License, or | |
21 | * (at your option) any later version. | |
22 | * | |
23 | * This program is distributed in the hope that it will be useful, | |
24 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
25 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
26 | * GNU General Public License for more details. | |
27 | * | |
28 | * You should have received a copy of the GNU General Public License | |
29 | * along with this program; if not, write to the Free Software | |
30 | * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA | |
31 | */ | |
32 | #include <linux/slab.h> | |
33 | #include <linux/poll.h> | |
34 | #include <linux/fs.h> | |
35 | #include <linux/file.h> | |
36 | #include <linux/jhash.h> | |
37 | #include <linux/init.h> | |
38 | #include <linux/futex.h> | |
39 | #include <linux/mount.h> | |
40 | #include <linux/pagemap.h> | |
41 | #include <linux/syscalls.h> | |
42 | ||
43 | #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8) | |
44 | ||
45 | /* | |
46 | * Futexes are matched on equal values of this key. | |
47 | * The key type depends on whether it's a shared or private mapping. | |
48 | * Don't rearrange members without looking at hash_futex(). | |
49 | * | |
50 | * offset is aligned to a multiple of sizeof(u32) (== 4) by definition. | |
51 | * We set bit 0 to indicate if it's an inode-based key. | |
52 | */ | |
53 | union futex_key { | |
54 | struct { | |
55 | unsigned long pgoff; | |
56 | struct inode *inode; | |
57 | int offset; | |
58 | } shared; | |
59 | struct { | |
60 | unsigned long uaddr; | |
61 | struct mm_struct *mm; | |
62 | int offset; | |
63 | } private; | |
64 | struct { | |
65 | unsigned long word; | |
66 | void *ptr; | |
67 | int offset; | |
68 | } both; | |
69 | }; | |
70 | ||
71 | /* | |
72 | * We use this hashed waitqueue instead of a normal wait_queue_t, so | |
73 | * we can wake only the relevant ones (hashed queues may be shared). | |
74 | * | |
75 | * A futex_q has a woken state, just like tasks have TASK_RUNNING. | |
76 | * It is considered woken when list_empty(&q->list) || q->lock_ptr == 0. | |
77 | * The order of wakup is always to make the first condition true, then | |
78 | * wake up q->waiters, then make the second condition true. | |
79 | */ | |
80 | struct futex_q { | |
81 | struct list_head list; | |
82 | wait_queue_head_t waiters; | |
83 | ||
84 | /* Which hash list lock to use. */ | |
85 | spinlock_t *lock_ptr; | |
86 | ||
87 | /* Key which the futex is hashed on. */ | |
88 | union futex_key key; | |
89 | ||
90 | /* For fd, sigio sent using these. */ | |
91 | int fd; | |
92 | struct file *filp; | |
93 | }; | |
94 | ||
95 | /* | |
96 | * Split the global futex_lock into every hash list lock. | |
97 | */ | |
98 | struct futex_hash_bucket { | |
99 | spinlock_t lock; | |
100 | struct list_head chain; | |
101 | }; | |
102 | ||
103 | static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS]; | |
104 | ||
105 | /* Futex-fs vfsmount entry: */ | |
106 | static struct vfsmount *futex_mnt; | |
107 | ||
108 | /* | |
109 | * We hash on the keys returned from get_futex_key (see below). | |
110 | */ | |
111 | static struct futex_hash_bucket *hash_futex(union futex_key *key) | |
112 | { | |
113 | u32 hash = jhash2((u32*)&key->both.word, | |
114 | (sizeof(key->both.word)+sizeof(key->both.ptr))/4, | |
115 | key->both.offset); | |
116 | return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)]; | |
117 | } | |
118 | ||
119 | /* | |
120 | * Return 1 if two futex_keys are equal, 0 otherwise. | |
121 | */ | |
122 | static inline int match_futex(union futex_key *key1, union futex_key *key2) | |
123 | { | |
124 | return (key1->both.word == key2->both.word | |
125 | && key1->both.ptr == key2->both.ptr | |
126 | && key1->both.offset == key2->both.offset); | |
127 | } | |
128 | ||
129 | /* | |
130 | * Get parameters which are the keys for a futex. | |
131 | * | |
132 | * For shared mappings, it's (page->index, vma->vm_file->f_dentry->d_inode, | |
133 | * offset_within_page). For private mappings, it's (uaddr, current->mm). | |
134 | * We can usually work out the index without swapping in the page. | |
135 | * | |
136 | * Returns: 0, or negative error code. | |
137 | * The key words are stored in *key on success. | |
138 | * | |
139 | * Should be called with ¤t->mm->mmap_sem but NOT any spinlocks. | |
140 | */ | |
141 | static int get_futex_key(unsigned long uaddr, union futex_key *key) | |
142 | { | |
143 | struct mm_struct *mm = current->mm; | |
144 | struct vm_area_struct *vma; | |
145 | struct page *page; | |
146 | int err; | |
147 | ||
148 | /* | |
149 | * The futex address must be "naturally" aligned. | |
150 | */ | |
151 | key->both.offset = uaddr % PAGE_SIZE; | |
152 | if (unlikely((key->both.offset % sizeof(u32)) != 0)) | |
153 | return -EINVAL; | |
154 | uaddr -= key->both.offset; | |
155 | ||
156 | /* | |
157 | * The futex is hashed differently depending on whether | |
158 | * it's in a shared or private mapping. So check vma first. | |
159 | */ | |
160 | vma = find_extend_vma(mm, uaddr); | |
161 | if (unlikely(!vma)) | |
162 | return -EFAULT; | |
163 | ||
164 | /* | |
165 | * Permissions. | |
166 | */ | |
167 | if (unlikely((vma->vm_flags & (VM_IO|VM_READ)) != VM_READ)) | |
168 | return (vma->vm_flags & VM_IO) ? -EPERM : -EACCES; | |
169 | ||
170 | /* | |
171 | * Private mappings are handled in a simple way. | |
172 | * | |
173 | * NOTE: When userspace waits on a MAP_SHARED mapping, even if | |
174 | * it's a read-only handle, it's expected that futexes attach to | |
175 | * the object not the particular process. Therefore we use | |
176 | * VM_MAYSHARE here, not VM_SHARED which is restricted to shared | |
177 | * mappings of _writable_ handles. | |
178 | */ | |
179 | if (likely(!(vma->vm_flags & VM_MAYSHARE))) { | |
180 | key->private.mm = mm; | |
181 | key->private.uaddr = uaddr; | |
182 | return 0; | |
183 | } | |
184 | ||
185 | /* | |
186 | * Linear file mappings are also simple. | |
187 | */ | |
188 | key->shared.inode = vma->vm_file->f_dentry->d_inode; | |
189 | key->both.offset++; /* Bit 0 of offset indicates inode-based key. */ | |
190 | if (likely(!(vma->vm_flags & VM_NONLINEAR))) { | |
191 | key->shared.pgoff = (((uaddr - vma->vm_start) >> PAGE_SHIFT) | |
192 | + vma->vm_pgoff); | |
193 | return 0; | |
194 | } | |
195 | ||
196 | /* | |
197 | * We could walk the page table to read the non-linear | |
198 | * pte, and get the page index without fetching the page | |
199 | * from swap. But that's a lot of code to duplicate here | |
200 | * for a rare case, so we simply fetch the page. | |
201 | */ | |
202 | ||
203 | /* | |
204 | * Do a quick atomic lookup first - this is the fastpath. | |
205 | */ | |
206 | spin_lock(¤t->mm->page_table_lock); | |
207 | page = follow_page(mm, uaddr, 0); | |
208 | if (likely(page != NULL)) { | |
209 | key->shared.pgoff = | |
210 | page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); | |
211 | spin_unlock(¤t->mm->page_table_lock); | |
212 | return 0; | |
213 | } | |
214 | spin_unlock(¤t->mm->page_table_lock); | |
215 | ||
216 | /* | |
217 | * Do it the general way. | |
218 | */ | |
219 | err = get_user_pages(current, mm, uaddr, 1, 0, 0, &page, NULL); | |
220 | if (err >= 0) { | |
221 | key->shared.pgoff = | |
222 | page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); | |
223 | put_page(page); | |
224 | return 0; | |
225 | } | |
226 | return err; | |
227 | } | |
228 | ||
229 | /* | |
230 | * Take a reference to the resource addressed by a key. | |
231 | * Can be called while holding spinlocks. | |
232 | * | |
233 | * NOTE: mmap_sem MUST be held between get_futex_key() and calling this | |
234 | * function, if it is called at all. mmap_sem keeps key->shared.inode valid. | |
235 | */ | |
236 | static inline void get_key_refs(union futex_key *key) | |
237 | { | |
238 | if (key->both.ptr != 0) { | |
239 | if (key->both.offset & 1) | |
240 | atomic_inc(&key->shared.inode->i_count); | |
241 | else | |
242 | atomic_inc(&key->private.mm->mm_count); | |
243 | } | |
244 | } | |
245 | ||
246 | /* | |
247 | * Drop a reference to the resource addressed by a key. | |
248 | * The hash bucket spinlock must not be held. | |
249 | */ | |
250 | static void drop_key_refs(union futex_key *key) | |
251 | { | |
252 | if (key->both.ptr != 0) { | |
253 | if (key->both.offset & 1) | |
254 | iput(key->shared.inode); | |
255 | else | |
256 | mmdrop(key->private.mm); | |
257 | } | |
258 | } | |
259 | ||
260 | static inline int get_futex_value_locked(int *dest, int __user *from) | |
261 | { | |
262 | int ret; | |
263 | ||
264 | inc_preempt_count(); | |
265 | ret = __copy_from_user_inatomic(dest, from, sizeof(int)); | |
266 | dec_preempt_count(); | |
267 | ||
268 | return ret ? -EFAULT : 0; | |
269 | } | |
270 | ||
271 | /* | |
272 | * The hash bucket lock must be held when this is called. | |
273 | * Afterwards, the futex_q must not be accessed. | |
274 | */ | |
275 | static void wake_futex(struct futex_q *q) | |
276 | { | |
277 | list_del_init(&q->list); | |
278 | if (q->filp) | |
279 | send_sigio(&q->filp->f_owner, q->fd, POLL_IN); | |
280 | /* | |
281 | * The lock in wake_up_all() is a crucial memory barrier after the | |
282 | * list_del_init() and also before assigning to q->lock_ptr. | |
283 | */ | |
284 | wake_up_all(&q->waiters); | |
285 | /* | |
286 | * The waiting task can free the futex_q as soon as this is written, | |
287 | * without taking any locks. This must come last. | |
288 | */ | |
289 | q->lock_ptr = NULL; | |
290 | } | |
291 | ||
292 | /* | |
293 | * Wake up all waiters hashed on the physical page that is mapped | |
294 | * to this virtual address: | |
295 | */ | |
296 | static int futex_wake(unsigned long uaddr, int nr_wake) | |
297 | { | |
298 | union futex_key key; | |
299 | struct futex_hash_bucket *bh; | |
300 | struct list_head *head; | |
301 | struct futex_q *this, *next; | |
302 | int ret; | |
303 | ||
304 | down_read(¤t->mm->mmap_sem); | |
305 | ||
306 | ret = get_futex_key(uaddr, &key); | |
307 | if (unlikely(ret != 0)) | |
308 | goto out; | |
309 | ||
310 | bh = hash_futex(&key); | |
311 | spin_lock(&bh->lock); | |
312 | head = &bh->chain; | |
313 | ||
314 | list_for_each_entry_safe(this, next, head, list) { | |
315 | if (match_futex (&this->key, &key)) { | |
316 | wake_futex(this); | |
317 | if (++ret >= nr_wake) | |
318 | break; | |
319 | } | |
320 | } | |
321 | ||
322 | spin_unlock(&bh->lock); | |
323 | out: | |
324 | up_read(¤t->mm->mmap_sem); | |
325 | return ret; | |
326 | } | |
327 | ||
328 | /* | |
329 | * Requeue all waiters hashed on one physical page to another | |
330 | * physical page. | |
331 | */ | |
332 | static int futex_requeue(unsigned long uaddr1, unsigned long uaddr2, | |
333 | int nr_wake, int nr_requeue, int *valp) | |
334 | { | |
335 | union futex_key key1, key2; | |
336 | struct futex_hash_bucket *bh1, *bh2; | |
337 | struct list_head *head1; | |
338 | struct futex_q *this, *next; | |
339 | int ret, drop_count = 0; | |
340 | ||
341 | retry: | |
342 | down_read(¤t->mm->mmap_sem); | |
343 | ||
344 | ret = get_futex_key(uaddr1, &key1); | |
345 | if (unlikely(ret != 0)) | |
346 | goto out; | |
347 | ret = get_futex_key(uaddr2, &key2); | |
348 | if (unlikely(ret != 0)) | |
349 | goto out; | |
350 | ||
351 | bh1 = hash_futex(&key1); | |
352 | bh2 = hash_futex(&key2); | |
353 | ||
354 | if (bh1 < bh2) | |
355 | spin_lock(&bh1->lock); | |
356 | spin_lock(&bh2->lock); | |
357 | if (bh1 > bh2) | |
358 | spin_lock(&bh1->lock); | |
359 | ||
360 | if (likely(valp != NULL)) { | |
361 | int curval; | |
362 | ||
363 | ret = get_futex_value_locked(&curval, (int __user *)uaddr1); | |
364 | ||
365 | if (unlikely(ret)) { | |
366 | spin_unlock(&bh1->lock); | |
367 | if (bh1 != bh2) | |
368 | spin_unlock(&bh2->lock); | |
369 | ||
370 | /* If we would have faulted, release mmap_sem, fault | |
371 | * it in and start all over again. | |
372 | */ | |
373 | up_read(¤t->mm->mmap_sem); | |
374 | ||
375 | ret = get_user(curval, (int __user *)uaddr1); | |
376 | ||
377 | if (!ret) | |
378 | goto retry; | |
379 | ||
380 | return ret; | |
381 | } | |
382 | if (curval != *valp) { | |
383 | ret = -EAGAIN; | |
384 | goto out_unlock; | |
385 | } | |
386 | } | |
387 | ||
388 | head1 = &bh1->chain; | |
389 | list_for_each_entry_safe(this, next, head1, list) { | |
390 | if (!match_futex (&this->key, &key1)) | |
391 | continue; | |
392 | if (++ret <= nr_wake) { | |
393 | wake_futex(this); | |
394 | } else { | |
395 | list_move_tail(&this->list, &bh2->chain); | |
396 | this->lock_ptr = &bh2->lock; | |
397 | this->key = key2; | |
398 | get_key_refs(&key2); | |
399 | drop_count++; | |
400 | ||
401 | if (ret - nr_wake >= nr_requeue) | |
402 | break; | |
403 | /* Make sure to stop if key1 == key2 */ | |
404 | if (head1 == &bh2->chain && head1 != &next->list) | |
405 | head1 = &this->list; | |
406 | } | |
407 | } | |
408 | ||
409 | out_unlock: | |
410 | spin_unlock(&bh1->lock); | |
411 | if (bh1 != bh2) | |
412 | spin_unlock(&bh2->lock); | |
413 | ||
414 | /* drop_key_refs() must be called outside the spinlocks. */ | |
415 | while (--drop_count >= 0) | |
416 | drop_key_refs(&key1); | |
417 | ||
418 | out: | |
419 | up_read(¤t->mm->mmap_sem); | |
420 | return ret; | |
421 | } | |
422 | ||
423 | /* The key must be already stored in q->key. */ | |
424 | static inline struct futex_hash_bucket * | |
425 | queue_lock(struct futex_q *q, int fd, struct file *filp) | |
426 | { | |
427 | struct futex_hash_bucket *bh; | |
428 | ||
429 | q->fd = fd; | |
430 | q->filp = filp; | |
431 | ||
432 | init_waitqueue_head(&q->waiters); | |
433 | ||
434 | get_key_refs(&q->key); | |
435 | bh = hash_futex(&q->key); | |
436 | q->lock_ptr = &bh->lock; | |
437 | ||
438 | spin_lock(&bh->lock); | |
439 | return bh; | |
440 | } | |
441 | ||
442 | static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *bh) | |
443 | { | |
444 | list_add_tail(&q->list, &bh->chain); | |
445 | spin_unlock(&bh->lock); | |
446 | } | |
447 | ||
448 | static inline void | |
449 | queue_unlock(struct futex_q *q, struct futex_hash_bucket *bh) | |
450 | { | |
451 | spin_unlock(&bh->lock); | |
452 | drop_key_refs(&q->key); | |
453 | } | |
454 | ||
455 | /* | |
456 | * queue_me and unqueue_me must be called as a pair, each | |
457 | * exactly once. They are called with the hashed spinlock held. | |
458 | */ | |
459 | ||
460 | /* The key must be already stored in q->key. */ | |
461 | static void queue_me(struct futex_q *q, int fd, struct file *filp) | |
462 | { | |
463 | struct futex_hash_bucket *bh; | |
464 | bh = queue_lock(q, fd, filp); | |
465 | __queue_me(q, bh); | |
466 | } | |
467 | ||
468 | /* Return 1 if we were still queued (ie. 0 means we were woken) */ | |
469 | static int unqueue_me(struct futex_q *q) | |
470 | { | |
471 | int ret = 0; | |
472 | spinlock_t *lock_ptr; | |
473 | ||
474 | /* In the common case we don't take the spinlock, which is nice. */ | |
475 | retry: | |
476 | lock_ptr = q->lock_ptr; | |
477 | if (lock_ptr != 0) { | |
478 | spin_lock(lock_ptr); | |
479 | /* | |
480 | * q->lock_ptr can change between reading it and | |
481 | * spin_lock(), causing us to take the wrong lock. This | |
482 | * corrects the race condition. | |
483 | * | |
484 | * Reasoning goes like this: if we have the wrong lock, | |
485 | * q->lock_ptr must have changed (maybe several times) | |
486 | * between reading it and the spin_lock(). It can | |
487 | * change again after the spin_lock() but only if it was | |
488 | * already changed before the spin_lock(). It cannot, | |
489 | * however, change back to the original value. Therefore | |
490 | * we can detect whether we acquired the correct lock. | |
491 | */ | |
492 | if (unlikely(lock_ptr != q->lock_ptr)) { | |
493 | spin_unlock(lock_ptr); | |
494 | goto retry; | |
495 | } | |
496 | WARN_ON(list_empty(&q->list)); | |
497 | list_del(&q->list); | |
498 | spin_unlock(lock_ptr); | |
499 | ret = 1; | |
500 | } | |
501 | ||
502 | drop_key_refs(&q->key); | |
503 | return ret; | |
504 | } | |
505 | ||
506 | static int futex_wait(unsigned long uaddr, int val, unsigned long time) | |
507 | { | |
508 | DECLARE_WAITQUEUE(wait, current); | |
509 | int ret, curval; | |
510 | struct futex_q q; | |
511 | struct futex_hash_bucket *bh; | |
512 | ||
513 | retry: | |
514 | down_read(¤t->mm->mmap_sem); | |
515 | ||
516 | ret = get_futex_key(uaddr, &q.key); | |
517 | if (unlikely(ret != 0)) | |
518 | goto out_release_sem; | |
519 | ||
520 | bh = queue_lock(&q, -1, NULL); | |
521 | ||
522 | /* | |
523 | * Access the page AFTER the futex is queued. | |
524 | * Order is important: | |
525 | * | |
526 | * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val); | |
527 | * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); } | |
528 | * | |
529 | * The basic logical guarantee of a futex is that it blocks ONLY | |
530 | * if cond(var) is known to be true at the time of blocking, for | |
531 | * any cond. If we queued after testing *uaddr, that would open | |
532 | * a race condition where we could block indefinitely with | |
533 | * cond(var) false, which would violate the guarantee. | |
534 | * | |
535 | * A consequence is that futex_wait() can return zero and absorb | |
536 | * a wakeup when *uaddr != val on entry to the syscall. This is | |
537 | * rare, but normal. | |
538 | * | |
539 | * We hold the mmap semaphore, so the mapping cannot have changed | |
540 | * since we looked it up in get_futex_key. | |
541 | */ | |
542 | ||
543 | ret = get_futex_value_locked(&curval, (int __user *)uaddr); | |
544 | ||
545 | if (unlikely(ret)) { | |
546 | queue_unlock(&q, bh); | |
547 | ||
548 | /* If we would have faulted, release mmap_sem, fault it in and | |
549 | * start all over again. | |
550 | */ | |
551 | up_read(¤t->mm->mmap_sem); | |
552 | ||
553 | ret = get_user(curval, (int __user *)uaddr); | |
554 | ||
555 | if (!ret) | |
556 | goto retry; | |
557 | return ret; | |
558 | } | |
559 | if (curval != val) { | |
560 | ret = -EWOULDBLOCK; | |
561 | queue_unlock(&q, bh); | |
562 | goto out_release_sem; | |
563 | } | |
564 | ||
565 | /* Only actually queue if *uaddr contained val. */ | |
566 | __queue_me(&q, bh); | |
567 | ||
568 | /* | |
569 | * Now the futex is queued and we have checked the data, we | |
570 | * don't want to hold mmap_sem while we sleep. | |
571 | */ | |
572 | up_read(¤t->mm->mmap_sem); | |
573 | ||
574 | /* | |
575 | * There might have been scheduling since the queue_me(), as we | |
576 | * cannot hold a spinlock across the get_user() in case it | |
577 | * faults, and we cannot just set TASK_INTERRUPTIBLE state when | |
578 | * queueing ourselves into the futex hash. This code thus has to | |
579 | * rely on the futex_wake() code removing us from hash when it | |
580 | * wakes us up. | |
581 | */ | |
582 | ||
583 | /* add_wait_queue is the barrier after __set_current_state. */ | |
584 | __set_current_state(TASK_INTERRUPTIBLE); | |
585 | add_wait_queue(&q.waiters, &wait); | |
586 | /* | |
587 | * !list_empty() is safe here without any lock. | |
588 | * q.lock_ptr != 0 is not safe, because of ordering against wakeup. | |
589 | */ | |
590 | if (likely(!list_empty(&q.list))) | |
591 | time = schedule_timeout(time); | |
592 | __set_current_state(TASK_RUNNING); | |
593 | ||
594 | /* | |
595 | * NOTE: we don't remove ourselves from the waitqueue because | |
596 | * we are the only user of it. | |
597 | */ | |
598 | ||
599 | /* If we were woken (and unqueued), we succeeded, whatever. */ | |
600 | if (!unqueue_me(&q)) | |
601 | return 0; | |
602 | if (time == 0) | |
603 | return -ETIMEDOUT; | |
604 | /* We expect signal_pending(current), but another thread may | |
605 | * have handled it for us already. */ | |
606 | return -EINTR; | |
607 | ||
608 | out_release_sem: | |
609 | up_read(¤t->mm->mmap_sem); | |
610 | return ret; | |
611 | } | |
612 | ||
613 | static int futex_close(struct inode *inode, struct file *filp) | |
614 | { | |
615 | struct futex_q *q = filp->private_data; | |
616 | ||
617 | unqueue_me(q); | |
618 | kfree(q); | |
619 | return 0; | |
620 | } | |
621 | ||
622 | /* This is one-shot: once it's gone off you need a new fd */ | |
623 | static unsigned int futex_poll(struct file *filp, | |
624 | struct poll_table_struct *wait) | |
625 | { | |
626 | struct futex_q *q = filp->private_data; | |
627 | int ret = 0; | |
628 | ||
629 | poll_wait(filp, &q->waiters, wait); | |
630 | ||
631 | /* | |
632 | * list_empty() is safe here without any lock. | |
633 | * q->lock_ptr != 0 is not safe, because of ordering against wakeup. | |
634 | */ | |
635 | if (list_empty(&q->list)) | |
636 | ret = POLLIN | POLLRDNORM; | |
637 | ||
638 | return ret; | |
639 | } | |
640 | ||
641 | static struct file_operations futex_fops = { | |
642 | .release = futex_close, | |
643 | .poll = futex_poll, | |
644 | }; | |
645 | ||
646 | /* | |
647 | * Signal allows caller to avoid the race which would occur if they | |
648 | * set the sigio stuff up afterwards. | |
649 | */ | |
650 | static int futex_fd(unsigned long uaddr, int signal) | |
651 | { | |
652 | struct futex_q *q; | |
653 | struct file *filp; | |
654 | int ret, err; | |
655 | ||
656 | ret = -EINVAL; | |
657 | if (signal < 0 || signal > _NSIG) | |
658 | goto out; | |
659 | ||
660 | ret = get_unused_fd(); | |
661 | if (ret < 0) | |
662 | goto out; | |
663 | filp = get_empty_filp(); | |
664 | if (!filp) { | |
665 | put_unused_fd(ret); | |
666 | ret = -ENFILE; | |
667 | goto out; | |
668 | } | |
669 | filp->f_op = &futex_fops; | |
670 | filp->f_vfsmnt = mntget(futex_mnt); | |
671 | filp->f_dentry = dget(futex_mnt->mnt_root); | |
672 | filp->f_mapping = filp->f_dentry->d_inode->i_mapping; | |
673 | ||
674 | if (signal) { | |
675 | int err; | |
676 | err = f_setown(filp, current->pid, 1); | |
677 | if (err < 0) { | |
678 | put_unused_fd(ret); | |
679 | put_filp(filp); | |
680 | ret = err; | |
681 | goto out; | |
682 | } | |
683 | filp->f_owner.signum = signal; | |
684 | } | |
685 | ||
686 | q = kmalloc(sizeof(*q), GFP_KERNEL); | |
687 | if (!q) { | |
688 | put_unused_fd(ret); | |
689 | put_filp(filp); | |
690 | ret = -ENOMEM; | |
691 | goto out; | |
692 | } | |
693 | ||
694 | down_read(¤t->mm->mmap_sem); | |
695 | err = get_futex_key(uaddr, &q->key); | |
696 | ||
697 | if (unlikely(err != 0)) { | |
698 | up_read(¤t->mm->mmap_sem); | |
699 | put_unused_fd(ret); | |
700 | put_filp(filp); | |
701 | kfree(q); | |
702 | return err; | |
703 | } | |
704 | ||
705 | /* | |
706 | * queue_me() must be called before releasing mmap_sem, because | |
707 | * key->shared.inode needs to be referenced while holding it. | |
708 | */ | |
709 | filp->private_data = q; | |
710 | ||
711 | queue_me(q, ret, filp); | |
712 | up_read(¤t->mm->mmap_sem); | |
713 | ||
714 | /* Now we map fd to filp, so userspace can access it */ | |
715 | fd_install(ret, filp); | |
716 | out: | |
717 | return ret; | |
718 | } | |
719 | ||
720 | long do_futex(unsigned long uaddr, int op, int val, unsigned long timeout, | |
721 | unsigned long uaddr2, int val2, int val3) | |
722 | { | |
723 | int ret; | |
724 | ||
725 | switch (op) { | |
726 | case FUTEX_WAIT: | |
727 | ret = futex_wait(uaddr, val, timeout); | |
728 | break; | |
729 | case FUTEX_WAKE: | |
730 | ret = futex_wake(uaddr, val); | |
731 | break; | |
732 | case FUTEX_FD: | |
733 | /* non-zero val means F_SETOWN(getpid()) & F_SETSIG(val) */ | |
734 | ret = futex_fd(uaddr, val); | |
735 | break; | |
736 | case FUTEX_REQUEUE: | |
737 | ret = futex_requeue(uaddr, uaddr2, val, val2, NULL); | |
738 | break; | |
739 | case FUTEX_CMP_REQUEUE: | |
740 | ret = futex_requeue(uaddr, uaddr2, val, val2, &val3); | |
741 | break; | |
742 | default: | |
743 | ret = -ENOSYS; | |
744 | } | |
745 | return ret; | |
746 | } | |
747 | ||
748 | ||
749 | asmlinkage long sys_futex(u32 __user *uaddr, int op, int val, | |
750 | struct timespec __user *utime, u32 __user *uaddr2, | |
751 | int val3) | |
752 | { | |
753 | struct timespec t; | |
754 | unsigned long timeout = MAX_SCHEDULE_TIMEOUT; | |
755 | int val2 = 0; | |
756 | ||
757 | if ((op == FUTEX_WAIT) && utime) { | |
758 | if (copy_from_user(&t, utime, sizeof(t)) != 0) | |
759 | return -EFAULT; | |
760 | timeout = timespec_to_jiffies(&t) + 1; | |
761 | } | |
762 | /* | |
763 | * requeue parameter in 'utime' if op == FUTEX_REQUEUE. | |
764 | */ | |
765 | if (op >= FUTEX_REQUEUE) | |
766 | val2 = (int) (unsigned long) utime; | |
767 | ||
768 | return do_futex((unsigned long)uaddr, op, val, timeout, | |
769 | (unsigned long)uaddr2, val2, val3); | |
770 | } | |
771 | ||
772 | static struct super_block * | |
773 | futexfs_get_sb(struct file_system_type *fs_type, | |
774 | int flags, const char *dev_name, void *data) | |
775 | { | |
776 | return get_sb_pseudo(fs_type, "futex", NULL, 0xBAD1DEA); | |
777 | } | |
778 | ||
779 | static struct file_system_type futex_fs_type = { | |
780 | .name = "futexfs", | |
781 | .get_sb = futexfs_get_sb, | |
782 | .kill_sb = kill_anon_super, | |
783 | }; | |
784 | ||
785 | static int __init init(void) | |
786 | { | |
787 | unsigned int i; | |
788 | ||
789 | register_filesystem(&futex_fs_type); | |
790 | futex_mnt = kern_mount(&futex_fs_type); | |
791 | ||
792 | for (i = 0; i < ARRAY_SIZE(futex_queues); i++) { | |
793 | INIT_LIST_HEAD(&futex_queues[i].chain); | |
794 | spin_lock_init(&futex_queues[i].lock); | |
795 | } | |
796 | return 0; | |
797 | } | |
798 | __initcall(init); |