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1 | /* | |
2 | * Fast Userspace Mutexes (which I call "Futexes!"). | |
3 | * (C) Rusty Russell, IBM 2002 | |
4 | * | |
5 | * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar | |
6 | * (C) Copyright 2003 Red Hat Inc, All Rights Reserved | |
7 | * | |
8 | * Removed page pinning, fix privately mapped COW pages and other cleanups | |
9 | * (C) Copyright 2003, 2004 Jamie Lokier | |
10 | * | |
11 | * Robust futex support started by Ingo Molnar | |
12 | * (C) Copyright 2006 Red Hat Inc, All Rights Reserved | |
13 | * Thanks to Thomas Gleixner for suggestions, analysis and fixes. | |
14 | * | |
15 | * PI-futex support started by Ingo Molnar and Thomas Gleixner | |
16 | * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> | |
17 | * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com> | |
18 | * | |
19 | * PRIVATE futexes by Eric Dumazet | |
20 | * Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com> | |
21 | * | |
22 | * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly | |
23 | * enough at me, Linus for the original (flawed) idea, Matthew | |
24 | * Kirkwood for proof-of-concept implementation. | |
25 | * | |
26 | * "The futexes are also cursed." | |
27 | * "But they come in a choice of three flavours!" | |
28 | * | |
29 | * This program is free software; you can redistribute it and/or modify | |
30 | * it under the terms of the GNU General Public License as published by | |
31 | * the Free Software Foundation; either version 2 of the License, or | |
32 | * (at your option) any later version. | |
33 | * | |
34 | * This program is distributed in the hope that it will be useful, | |
35 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
36 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
37 | * GNU General Public License for more details. | |
38 | * | |
39 | * You should have received a copy of the GNU General Public License | |
40 | * along with this program; if not, write to the Free Software | |
41 | * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA | |
42 | */ | |
43 | #include <linux/slab.h> | |
44 | #include <linux/poll.h> | |
45 | #include <linux/fs.h> | |
46 | #include <linux/file.h> | |
47 | #include <linux/jhash.h> | |
48 | #include <linux/init.h> | |
49 | #include <linux/futex.h> | |
50 | #include <linux/mount.h> | |
51 | #include <linux/pagemap.h> | |
52 | #include <linux/syscalls.h> | |
53 | #include <linux/signal.h> | |
54 | #include <linux/module.h> | |
55 | #include <linux/magic.h> | |
56 | #include <asm/futex.h> | |
57 | ||
58 | #include "rtmutex_common.h" | |
59 | ||
60 | #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8) | |
61 | ||
62 | /* | |
63 | * Priority Inheritance state: | |
64 | */ | |
65 | struct futex_pi_state { | |
66 | /* | |
67 | * list of 'owned' pi_state instances - these have to be | |
68 | * cleaned up in do_exit() if the task exits prematurely: | |
69 | */ | |
70 | struct list_head list; | |
71 | ||
72 | /* | |
73 | * The PI object: | |
74 | */ | |
75 | struct rt_mutex pi_mutex; | |
76 | ||
77 | struct task_struct *owner; | |
78 | atomic_t refcount; | |
79 | ||
80 | union futex_key key; | |
81 | }; | |
82 | ||
83 | /* | |
84 | * We use this hashed waitqueue instead of a normal wait_queue_t, so | |
85 | * we can wake only the relevant ones (hashed queues may be shared). | |
86 | * | |
87 | * A futex_q has a woken state, just like tasks have TASK_RUNNING. | |
88 | * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0. | |
89 | * The order of wakup is always to make the first condition true, then | |
90 | * wake up q->waiters, then make the second condition true. | |
91 | */ | |
92 | struct futex_q { | |
93 | struct plist_node list; | |
94 | wait_queue_head_t waiters; | |
95 | ||
96 | /* Which hash list lock to use: */ | |
97 | spinlock_t *lock_ptr; | |
98 | ||
99 | /* Key which the futex is hashed on: */ | |
100 | union futex_key key; | |
101 | ||
102 | /* For fd, sigio sent using these: */ | |
103 | int fd; | |
104 | struct file *filp; | |
105 | ||
106 | /* Optional priority inheritance state: */ | |
107 | struct futex_pi_state *pi_state; | |
108 | struct task_struct *task; | |
109 | }; | |
110 | ||
111 | /* | |
112 | * Split the global futex_lock into every hash list lock. | |
113 | */ | |
114 | struct futex_hash_bucket { | |
115 | spinlock_t lock; | |
116 | struct plist_head chain; | |
117 | }; | |
118 | ||
119 | static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS]; | |
120 | ||
121 | /* Futex-fs vfsmount entry: */ | |
122 | static struct vfsmount *futex_mnt; | |
123 | ||
124 | /* | |
125 | * Take mm->mmap_sem, when futex is shared | |
126 | */ | |
127 | static inline void futex_lock_mm(struct rw_semaphore *fshared) | |
128 | { | |
129 | if (fshared) | |
130 | down_read(fshared); | |
131 | } | |
132 | ||
133 | /* | |
134 | * Release mm->mmap_sem, when the futex is shared | |
135 | */ | |
136 | static inline void futex_unlock_mm(struct rw_semaphore *fshared) | |
137 | { | |
138 | if (fshared) | |
139 | up_read(fshared); | |
140 | } | |
141 | ||
142 | /* | |
143 | * We hash on the keys returned from get_futex_key (see below). | |
144 | */ | |
145 | static struct futex_hash_bucket *hash_futex(union futex_key *key) | |
146 | { | |
147 | u32 hash = jhash2((u32*)&key->both.word, | |
148 | (sizeof(key->both.word)+sizeof(key->both.ptr))/4, | |
149 | key->both.offset); | |
150 | return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)]; | |
151 | } | |
152 | ||
153 | /* | |
154 | * Return 1 if two futex_keys are equal, 0 otherwise. | |
155 | */ | |
156 | static inline int match_futex(union futex_key *key1, union futex_key *key2) | |
157 | { | |
158 | return (key1->both.word == key2->both.word | |
159 | && key1->both.ptr == key2->both.ptr | |
160 | && key1->both.offset == key2->both.offset); | |
161 | } | |
162 | ||
163 | /** | |
164 | * get_futex_key - Get parameters which are the keys for a futex. | |
165 | * @uaddr: virtual address of the futex | |
166 | * @shared: NULL for a PROCESS_PRIVATE futex, | |
167 | * ¤t->mm->mmap_sem for a PROCESS_SHARED futex | |
168 | * @key: address where result is stored. | |
169 | * | |
170 | * Returns a negative error code or 0 | |
171 | * The key words are stored in *key on success. | |
172 | * | |
173 | * For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode, | |
174 | * offset_within_page). For private mappings, it's (uaddr, current->mm). | |
175 | * We can usually work out the index without swapping in the page. | |
176 | * | |
177 | * fshared is NULL for PROCESS_PRIVATE futexes | |
178 | * For other futexes, it points to ¤t->mm->mmap_sem and | |
179 | * caller must have taken the reader lock. but NOT any spinlocks. | |
180 | */ | |
181 | int get_futex_key(u32 __user *uaddr, struct rw_semaphore *fshared, | |
182 | union futex_key *key) | |
183 | { | |
184 | unsigned long address = (unsigned long)uaddr; | |
185 | struct mm_struct *mm = current->mm; | |
186 | struct vm_area_struct *vma; | |
187 | struct page *page; | |
188 | int err; | |
189 | ||
190 | /* | |
191 | * The futex address must be "naturally" aligned. | |
192 | */ | |
193 | key->both.offset = address % PAGE_SIZE; | |
194 | if (unlikely((address % sizeof(u32)) != 0)) | |
195 | return -EINVAL; | |
196 | address -= key->both.offset; | |
197 | ||
198 | /* | |
199 | * PROCESS_PRIVATE futexes are fast. | |
200 | * As the mm cannot disappear under us and the 'key' only needs | |
201 | * virtual address, we dont even have to find the underlying vma. | |
202 | * Note : We do have to check 'uaddr' is a valid user address, | |
203 | * but access_ok() should be faster than find_vma() | |
204 | */ | |
205 | if (!fshared) { | |
206 | if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))) | |
207 | return -EFAULT; | |
208 | key->private.mm = mm; | |
209 | key->private.address = address; | |
210 | return 0; | |
211 | } | |
212 | /* | |
213 | * The futex is hashed differently depending on whether | |
214 | * it's in a shared or private mapping. So check vma first. | |
215 | */ | |
216 | vma = find_extend_vma(mm, address); | |
217 | if (unlikely(!vma)) | |
218 | return -EFAULT; | |
219 | ||
220 | /* | |
221 | * Permissions. | |
222 | */ | |
223 | if (unlikely((vma->vm_flags & (VM_IO|VM_READ)) != VM_READ)) | |
224 | return (vma->vm_flags & VM_IO) ? -EPERM : -EACCES; | |
225 | ||
226 | /* | |
227 | * Private mappings are handled in a simple way. | |
228 | * | |
229 | * NOTE: When userspace waits on a MAP_SHARED mapping, even if | |
230 | * it's a read-only handle, it's expected that futexes attach to | |
231 | * the object not the particular process. Therefore we use | |
232 | * VM_MAYSHARE here, not VM_SHARED which is restricted to shared | |
233 | * mappings of _writable_ handles. | |
234 | */ | |
235 | if (likely(!(vma->vm_flags & VM_MAYSHARE))) { | |
236 | key->both.offset |= FUT_OFF_MMSHARED; /* reference taken on mm */ | |
237 | key->private.mm = mm; | |
238 | key->private.address = address; | |
239 | return 0; | |
240 | } | |
241 | ||
242 | /* | |
243 | * Linear file mappings are also simple. | |
244 | */ | |
245 | key->shared.inode = vma->vm_file->f_path.dentry->d_inode; | |
246 | key->both.offset |= FUT_OFF_INODE; /* inode-based key. */ | |
247 | if (likely(!(vma->vm_flags & VM_NONLINEAR))) { | |
248 | key->shared.pgoff = (((address - vma->vm_start) >> PAGE_SHIFT) | |
249 | + vma->vm_pgoff); | |
250 | return 0; | |
251 | } | |
252 | ||
253 | /* | |
254 | * We could walk the page table to read the non-linear | |
255 | * pte, and get the page index without fetching the page | |
256 | * from swap. But that's a lot of code to duplicate here | |
257 | * for a rare case, so we simply fetch the page. | |
258 | */ | |
259 | err = get_user_pages(current, mm, address, 1, 0, 0, &page, NULL); | |
260 | if (err >= 0) { | |
261 | key->shared.pgoff = | |
262 | page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); | |
263 | put_page(page); | |
264 | return 0; | |
265 | } | |
266 | return err; | |
267 | } | |
268 | EXPORT_SYMBOL_GPL(get_futex_key); | |
269 | ||
270 | /* | |
271 | * Take a reference to the resource addressed by a key. | |
272 | * Can be called while holding spinlocks. | |
273 | * | |
274 | */ | |
275 | inline void get_futex_key_refs(union futex_key *key) | |
276 | { | |
277 | if (key->both.ptr == 0) | |
278 | return; | |
279 | switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) { | |
280 | case FUT_OFF_INODE: | |
281 | atomic_inc(&key->shared.inode->i_count); | |
282 | break; | |
283 | case FUT_OFF_MMSHARED: | |
284 | atomic_inc(&key->private.mm->mm_count); | |
285 | break; | |
286 | } | |
287 | } | |
288 | EXPORT_SYMBOL_GPL(get_futex_key_refs); | |
289 | ||
290 | /* | |
291 | * Drop a reference to the resource addressed by a key. | |
292 | * The hash bucket spinlock must not be held. | |
293 | */ | |
294 | void drop_futex_key_refs(union futex_key *key) | |
295 | { | |
296 | if (!key->both.ptr) | |
297 | return; | |
298 | switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) { | |
299 | case FUT_OFF_INODE: | |
300 | iput(key->shared.inode); | |
301 | break; | |
302 | case FUT_OFF_MMSHARED: | |
303 | mmdrop(key->private.mm); | |
304 | break; | |
305 | } | |
306 | } | |
307 | EXPORT_SYMBOL_GPL(drop_futex_key_refs); | |
308 | ||
309 | static u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval) | |
310 | { | |
311 | u32 curval; | |
312 | ||
313 | pagefault_disable(); | |
314 | curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval); | |
315 | pagefault_enable(); | |
316 | ||
317 | return curval; | |
318 | } | |
319 | ||
320 | static int get_futex_value_locked(u32 *dest, u32 __user *from) | |
321 | { | |
322 | int ret; | |
323 | ||
324 | pagefault_disable(); | |
325 | ret = __copy_from_user_inatomic(dest, from, sizeof(u32)); | |
326 | pagefault_enable(); | |
327 | ||
328 | return ret ? -EFAULT : 0; | |
329 | } | |
330 | ||
331 | /* | |
332 | * Fault handling. | |
333 | * if fshared is non NULL, current->mm->mmap_sem is already held | |
334 | */ | |
335 | static int futex_handle_fault(unsigned long address, | |
336 | struct rw_semaphore *fshared, int attempt) | |
337 | { | |
338 | struct vm_area_struct * vma; | |
339 | struct mm_struct *mm = current->mm; | |
340 | int ret = -EFAULT; | |
341 | ||
342 | if (attempt > 2) | |
343 | return ret; | |
344 | ||
345 | if (!fshared) | |
346 | down_read(&mm->mmap_sem); | |
347 | vma = find_vma(mm, address); | |
348 | if (vma && address >= vma->vm_start && | |
349 | (vma->vm_flags & VM_WRITE)) { | |
350 | int fault; | |
351 | fault = handle_mm_fault(mm, vma, address, 1); | |
352 | if (unlikely((fault & VM_FAULT_ERROR))) { | |
353 | #if 0 | |
354 | /* XXX: let's do this when we verify it is OK */ | |
355 | if (ret & VM_FAULT_OOM) | |
356 | ret = -ENOMEM; | |
357 | #endif | |
358 | } else { | |
359 | ret = 0; | |
360 | if (fault & VM_FAULT_MAJOR) | |
361 | current->maj_flt++; | |
362 | else | |
363 | current->min_flt++; | |
364 | } | |
365 | } | |
366 | if (!fshared) | |
367 | up_read(&mm->mmap_sem); | |
368 | return ret; | |
369 | } | |
370 | ||
371 | /* | |
372 | * PI code: | |
373 | */ | |
374 | static int refill_pi_state_cache(void) | |
375 | { | |
376 | struct futex_pi_state *pi_state; | |
377 | ||
378 | if (likely(current->pi_state_cache)) | |
379 | return 0; | |
380 | ||
381 | pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL); | |
382 | ||
383 | if (!pi_state) | |
384 | return -ENOMEM; | |
385 | ||
386 | INIT_LIST_HEAD(&pi_state->list); | |
387 | /* pi_mutex gets initialized later */ | |
388 | pi_state->owner = NULL; | |
389 | atomic_set(&pi_state->refcount, 1); | |
390 | ||
391 | current->pi_state_cache = pi_state; | |
392 | ||
393 | return 0; | |
394 | } | |
395 | ||
396 | static struct futex_pi_state * alloc_pi_state(void) | |
397 | { | |
398 | struct futex_pi_state *pi_state = current->pi_state_cache; | |
399 | ||
400 | WARN_ON(!pi_state); | |
401 | current->pi_state_cache = NULL; | |
402 | ||
403 | return pi_state; | |
404 | } | |
405 | ||
406 | static void free_pi_state(struct futex_pi_state *pi_state) | |
407 | { | |
408 | if (!atomic_dec_and_test(&pi_state->refcount)) | |
409 | return; | |
410 | ||
411 | /* | |
412 | * If pi_state->owner is NULL, the owner is most probably dying | |
413 | * and has cleaned up the pi_state already | |
414 | */ | |
415 | if (pi_state->owner) { | |
416 | spin_lock_irq(&pi_state->owner->pi_lock); | |
417 | list_del_init(&pi_state->list); | |
418 | spin_unlock_irq(&pi_state->owner->pi_lock); | |
419 | ||
420 | rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner); | |
421 | } | |
422 | ||
423 | if (current->pi_state_cache) | |
424 | kfree(pi_state); | |
425 | else { | |
426 | /* | |
427 | * pi_state->list is already empty. | |
428 | * clear pi_state->owner. | |
429 | * refcount is at 0 - put it back to 1. | |
430 | */ | |
431 | pi_state->owner = NULL; | |
432 | atomic_set(&pi_state->refcount, 1); | |
433 | current->pi_state_cache = pi_state; | |
434 | } | |
435 | } | |
436 | ||
437 | /* | |
438 | * Look up the task based on what TID userspace gave us. | |
439 | * We dont trust it. | |
440 | */ | |
441 | static struct task_struct * futex_find_get_task(pid_t pid) | |
442 | { | |
443 | struct task_struct *p; | |
444 | ||
445 | rcu_read_lock(); | |
446 | p = find_task_by_pid(pid); | |
447 | ||
448 | if (!p || ((current->euid != p->euid) && (current->euid != p->uid))) | |
449 | p = ERR_PTR(-ESRCH); | |
450 | else | |
451 | get_task_struct(p); | |
452 | ||
453 | rcu_read_unlock(); | |
454 | ||
455 | return p; | |
456 | } | |
457 | ||
458 | /* | |
459 | * This task is holding PI mutexes at exit time => bad. | |
460 | * Kernel cleans up PI-state, but userspace is likely hosed. | |
461 | * (Robust-futex cleanup is separate and might save the day for userspace.) | |
462 | */ | |
463 | void exit_pi_state_list(struct task_struct *curr) | |
464 | { | |
465 | struct list_head *next, *head = &curr->pi_state_list; | |
466 | struct futex_pi_state *pi_state; | |
467 | struct futex_hash_bucket *hb; | |
468 | union futex_key key; | |
469 | ||
470 | /* | |
471 | * We are a ZOMBIE and nobody can enqueue itself on | |
472 | * pi_state_list anymore, but we have to be careful | |
473 | * versus waiters unqueueing themselves: | |
474 | */ | |
475 | spin_lock_irq(&curr->pi_lock); | |
476 | while (!list_empty(head)) { | |
477 | ||
478 | next = head->next; | |
479 | pi_state = list_entry(next, struct futex_pi_state, list); | |
480 | key = pi_state->key; | |
481 | hb = hash_futex(&key); | |
482 | spin_unlock_irq(&curr->pi_lock); | |
483 | ||
484 | spin_lock(&hb->lock); | |
485 | ||
486 | spin_lock_irq(&curr->pi_lock); | |
487 | /* | |
488 | * We dropped the pi-lock, so re-check whether this | |
489 | * task still owns the PI-state: | |
490 | */ | |
491 | if (head->next != next) { | |
492 | spin_unlock(&hb->lock); | |
493 | continue; | |
494 | } | |
495 | ||
496 | WARN_ON(pi_state->owner != curr); | |
497 | WARN_ON(list_empty(&pi_state->list)); | |
498 | list_del_init(&pi_state->list); | |
499 | pi_state->owner = NULL; | |
500 | spin_unlock_irq(&curr->pi_lock); | |
501 | ||
502 | rt_mutex_unlock(&pi_state->pi_mutex); | |
503 | ||
504 | spin_unlock(&hb->lock); | |
505 | ||
506 | spin_lock_irq(&curr->pi_lock); | |
507 | } | |
508 | spin_unlock_irq(&curr->pi_lock); | |
509 | } | |
510 | ||
511 | static int | |
512 | lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, | |
513 | union futex_key *key, struct futex_pi_state **ps) | |
514 | { | |
515 | struct futex_pi_state *pi_state = NULL; | |
516 | struct futex_q *this, *next; | |
517 | struct plist_head *head; | |
518 | struct task_struct *p; | |
519 | pid_t pid = uval & FUTEX_TID_MASK; | |
520 | ||
521 | head = &hb->chain; | |
522 | ||
523 | plist_for_each_entry_safe(this, next, head, list) { | |
524 | if (match_futex(&this->key, key)) { | |
525 | /* | |
526 | * Another waiter already exists - bump up | |
527 | * the refcount and return its pi_state: | |
528 | */ | |
529 | pi_state = this->pi_state; | |
530 | /* | |
531 | * Userspace might have messed up non PI and PI futexes | |
532 | */ | |
533 | if (unlikely(!pi_state)) | |
534 | return -EINVAL; | |
535 | ||
536 | WARN_ON(!atomic_read(&pi_state->refcount)); | |
537 | WARN_ON(pid && pi_state->owner && | |
538 | pi_state->owner->pid != pid); | |
539 | ||
540 | atomic_inc(&pi_state->refcount); | |
541 | *ps = pi_state; | |
542 | ||
543 | return 0; | |
544 | } | |
545 | } | |
546 | ||
547 | /* | |
548 | * We are the first waiter - try to look up the real owner and attach | |
549 | * the new pi_state to it, but bail out when TID = 0 | |
550 | */ | |
551 | if (!pid) | |
552 | return -ESRCH; | |
553 | p = futex_find_get_task(pid); | |
554 | if (IS_ERR(p)) | |
555 | return PTR_ERR(p); | |
556 | ||
557 | /* | |
558 | * We need to look at the task state flags to figure out, | |
559 | * whether the task is exiting. To protect against the do_exit | |
560 | * change of the task flags, we do this protected by | |
561 | * p->pi_lock: | |
562 | */ | |
563 | spin_lock_irq(&p->pi_lock); | |
564 | if (unlikely(p->flags & PF_EXITING)) { | |
565 | /* | |
566 | * The task is on the way out. When PF_EXITPIDONE is | |
567 | * set, we know that the task has finished the | |
568 | * cleanup: | |
569 | */ | |
570 | int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN; | |
571 | ||
572 | spin_unlock_irq(&p->pi_lock); | |
573 | put_task_struct(p); | |
574 | return ret; | |
575 | } | |
576 | ||
577 | pi_state = alloc_pi_state(); | |
578 | ||
579 | /* | |
580 | * Initialize the pi_mutex in locked state and make 'p' | |
581 | * the owner of it: | |
582 | */ | |
583 | rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p); | |
584 | ||
585 | /* Store the key for possible exit cleanups: */ | |
586 | pi_state->key = *key; | |
587 | ||
588 | WARN_ON(!list_empty(&pi_state->list)); | |
589 | list_add(&pi_state->list, &p->pi_state_list); | |
590 | pi_state->owner = p; | |
591 | spin_unlock_irq(&p->pi_lock); | |
592 | ||
593 | put_task_struct(p); | |
594 | ||
595 | *ps = pi_state; | |
596 | ||
597 | return 0; | |
598 | } | |
599 | ||
600 | /* | |
601 | * The hash bucket lock must be held when this is called. | |
602 | * Afterwards, the futex_q must not be accessed. | |
603 | */ | |
604 | static void wake_futex(struct futex_q *q) | |
605 | { | |
606 | plist_del(&q->list, &q->list.plist); | |
607 | if (q->filp) | |
608 | send_sigio(&q->filp->f_owner, q->fd, POLL_IN); | |
609 | /* | |
610 | * The lock in wake_up_all() is a crucial memory barrier after the | |
611 | * plist_del() and also before assigning to q->lock_ptr. | |
612 | */ | |
613 | wake_up_all(&q->waiters); | |
614 | /* | |
615 | * The waiting task can free the futex_q as soon as this is written, | |
616 | * without taking any locks. This must come last. | |
617 | * | |
618 | * A memory barrier is required here to prevent the following store | |
619 | * to lock_ptr from getting ahead of the wakeup. Clearing the lock | |
620 | * at the end of wake_up_all() does not prevent this store from | |
621 | * moving. | |
622 | */ | |
623 | smp_wmb(); | |
624 | q->lock_ptr = NULL; | |
625 | } | |
626 | ||
627 | static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this) | |
628 | { | |
629 | struct task_struct *new_owner; | |
630 | struct futex_pi_state *pi_state = this->pi_state; | |
631 | u32 curval, newval; | |
632 | ||
633 | if (!pi_state) | |
634 | return -EINVAL; | |
635 | ||
636 | spin_lock(&pi_state->pi_mutex.wait_lock); | |
637 | new_owner = rt_mutex_next_owner(&pi_state->pi_mutex); | |
638 | ||
639 | /* | |
640 | * This happens when we have stolen the lock and the original | |
641 | * pending owner did not enqueue itself back on the rt_mutex. | |
642 | * Thats not a tragedy. We know that way, that a lock waiter | |
643 | * is on the fly. We make the futex_q waiter the pending owner. | |
644 | */ | |
645 | if (!new_owner) | |
646 | new_owner = this->task; | |
647 | ||
648 | /* | |
649 | * We pass it to the next owner. (The WAITERS bit is always | |
650 | * kept enabled while there is PI state around. We must also | |
651 | * preserve the owner died bit.) | |
652 | */ | |
653 | if (!(uval & FUTEX_OWNER_DIED)) { | |
654 | int ret = 0; | |
655 | ||
656 | newval = FUTEX_WAITERS | new_owner->pid; | |
657 | ||
658 | curval = cmpxchg_futex_value_locked(uaddr, uval, newval); | |
659 | ||
660 | if (curval == -EFAULT) | |
661 | ret = -EFAULT; | |
662 | if (curval != uval) | |
663 | ret = -EINVAL; | |
664 | if (ret) { | |
665 | spin_unlock(&pi_state->pi_mutex.wait_lock); | |
666 | return ret; | |
667 | } | |
668 | } | |
669 | ||
670 | spin_lock_irq(&pi_state->owner->pi_lock); | |
671 | WARN_ON(list_empty(&pi_state->list)); | |
672 | list_del_init(&pi_state->list); | |
673 | spin_unlock_irq(&pi_state->owner->pi_lock); | |
674 | ||
675 | spin_lock_irq(&new_owner->pi_lock); | |
676 | WARN_ON(!list_empty(&pi_state->list)); | |
677 | list_add(&pi_state->list, &new_owner->pi_state_list); | |
678 | pi_state->owner = new_owner; | |
679 | spin_unlock_irq(&new_owner->pi_lock); | |
680 | ||
681 | spin_unlock(&pi_state->pi_mutex.wait_lock); | |
682 | rt_mutex_unlock(&pi_state->pi_mutex); | |
683 | ||
684 | return 0; | |
685 | } | |
686 | ||
687 | static int unlock_futex_pi(u32 __user *uaddr, u32 uval) | |
688 | { | |
689 | u32 oldval; | |
690 | ||
691 | /* | |
692 | * There is no waiter, so we unlock the futex. The owner died | |
693 | * bit has not to be preserved here. We are the owner: | |
694 | */ | |
695 | oldval = cmpxchg_futex_value_locked(uaddr, uval, 0); | |
696 | ||
697 | if (oldval == -EFAULT) | |
698 | return oldval; | |
699 | if (oldval != uval) | |
700 | return -EAGAIN; | |
701 | ||
702 | return 0; | |
703 | } | |
704 | ||
705 | /* | |
706 | * Express the locking dependencies for lockdep: | |
707 | */ | |
708 | static inline void | |
709 | double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) | |
710 | { | |
711 | if (hb1 <= hb2) { | |
712 | spin_lock(&hb1->lock); | |
713 | if (hb1 < hb2) | |
714 | spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING); | |
715 | } else { /* hb1 > hb2 */ | |
716 | spin_lock(&hb2->lock); | |
717 | spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING); | |
718 | } | |
719 | } | |
720 | ||
721 | /* | |
722 | * Wake up all waiters hashed on the physical page that is mapped | |
723 | * to this virtual address: | |
724 | */ | |
725 | static int futex_wake(u32 __user *uaddr, struct rw_semaphore *fshared, | |
726 | int nr_wake) | |
727 | { | |
728 | struct futex_hash_bucket *hb; | |
729 | struct futex_q *this, *next; | |
730 | struct plist_head *head; | |
731 | union futex_key key; | |
732 | int ret; | |
733 | ||
734 | futex_lock_mm(fshared); | |
735 | ||
736 | ret = get_futex_key(uaddr, fshared, &key); | |
737 | if (unlikely(ret != 0)) | |
738 | goto out; | |
739 | ||
740 | hb = hash_futex(&key); | |
741 | spin_lock(&hb->lock); | |
742 | head = &hb->chain; | |
743 | ||
744 | plist_for_each_entry_safe(this, next, head, list) { | |
745 | if (match_futex (&this->key, &key)) { | |
746 | if (this->pi_state) { | |
747 | ret = -EINVAL; | |
748 | break; | |
749 | } | |
750 | wake_futex(this); | |
751 | if (++ret >= nr_wake) | |
752 | break; | |
753 | } | |
754 | } | |
755 | ||
756 | spin_unlock(&hb->lock); | |
757 | out: | |
758 | futex_unlock_mm(fshared); | |
759 | return ret; | |
760 | } | |
761 | ||
762 | /* | |
763 | * Wake up all waiters hashed on the physical page that is mapped | |
764 | * to this virtual address: | |
765 | */ | |
766 | static int | |
767 | futex_wake_op(u32 __user *uaddr1, struct rw_semaphore *fshared, | |
768 | u32 __user *uaddr2, | |
769 | int nr_wake, int nr_wake2, int op) | |
770 | { | |
771 | union futex_key key1, key2; | |
772 | struct futex_hash_bucket *hb1, *hb2; | |
773 | struct plist_head *head; | |
774 | struct futex_q *this, *next; | |
775 | int ret, op_ret, attempt = 0; | |
776 | ||
777 | retryfull: | |
778 | futex_lock_mm(fshared); | |
779 | ||
780 | ret = get_futex_key(uaddr1, fshared, &key1); | |
781 | if (unlikely(ret != 0)) | |
782 | goto out; | |
783 | ret = get_futex_key(uaddr2, fshared, &key2); | |
784 | if (unlikely(ret != 0)) | |
785 | goto out; | |
786 | ||
787 | hb1 = hash_futex(&key1); | |
788 | hb2 = hash_futex(&key2); | |
789 | ||
790 | retry: | |
791 | double_lock_hb(hb1, hb2); | |
792 | ||
793 | op_ret = futex_atomic_op_inuser(op, uaddr2); | |
794 | if (unlikely(op_ret < 0)) { | |
795 | u32 dummy; | |
796 | ||
797 | spin_unlock(&hb1->lock); | |
798 | if (hb1 != hb2) | |
799 | spin_unlock(&hb2->lock); | |
800 | ||
801 | #ifndef CONFIG_MMU | |
802 | /* | |
803 | * we don't get EFAULT from MMU faults if we don't have an MMU, | |
804 | * but we might get them from range checking | |
805 | */ | |
806 | ret = op_ret; | |
807 | goto out; | |
808 | #endif | |
809 | ||
810 | if (unlikely(op_ret != -EFAULT)) { | |
811 | ret = op_ret; | |
812 | goto out; | |
813 | } | |
814 | ||
815 | /* | |
816 | * futex_atomic_op_inuser needs to both read and write | |
817 | * *(int __user *)uaddr2, but we can't modify it | |
818 | * non-atomically. Therefore, if get_user below is not | |
819 | * enough, we need to handle the fault ourselves, while | |
820 | * still holding the mmap_sem. | |
821 | */ | |
822 | if (attempt++) { | |
823 | ret = futex_handle_fault((unsigned long)uaddr2, | |
824 | fshared, attempt); | |
825 | if (ret) | |
826 | goto out; | |
827 | goto retry; | |
828 | } | |
829 | ||
830 | /* | |
831 | * If we would have faulted, release mmap_sem, | |
832 | * fault it in and start all over again. | |
833 | */ | |
834 | futex_unlock_mm(fshared); | |
835 | ||
836 | ret = get_user(dummy, uaddr2); | |
837 | if (ret) | |
838 | return ret; | |
839 | ||
840 | goto retryfull; | |
841 | } | |
842 | ||
843 | head = &hb1->chain; | |
844 | ||
845 | plist_for_each_entry_safe(this, next, head, list) { | |
846 | if (match_futex (&this->key, &key1)) { | |
847 | wake_futex(this); | |
848 | if (++ret >= nr_wake) | |
849 | break; | |
850 | } | |
851 | } | |
852 | ||
853 | if (op_ret > 0) { | |
854 | head = &hb2->chain; | |
855 | ||
856 | op_ret = 0; | |
857 | plist_for_each_entry_safe(this, next, head, list) { | |
858 | if (match_futex (&this->key, &key2)) { | |
859 | wake_futex(this); | |
860 | if (++op_ret >= nr_wake2) | |
861 | break; | |
862 | } | |
863 | } | |
864 | ret += op_ret; | |
865 | } | |
866 | ||
867 | spin_unlock(&hb1->lock); | |
868 | if (hb1 != hb2) | |
869 | spin_unlock(&hb2->lock); | |
870 | out: | |
871 | futex_unlock_mm(fshared); | |
872 | ||
873 | return ret; | |
874 | } | |
875 | ||
876 | /* | |
877 | * Requeue all waiters hashed on one physical page to another | |
878 | * physical page. | |
879 | */ | |
880 | static int futex_requeue(u32 __user *uaddr1, struct rw_semaphore *fshared, | |
881 | u32 __user *uaddr2, | |
882 | int nr_wake, int nr_requeue, u32 *cmpval) | |
883 | { | |
884 | union futex_key key1, key2; | |
885 | struct futex_hash_bucket *hb1, *hb2; | |
886 | struct plist_head *head1; | |
887 | struct futex_q *this, *next; | |
888 | int ret, drop_count = 0; | |
889 | ||
890 | retry: | |
891 | futex_lock_mm(fshared); | |
892 | ||
893 | ret = get_futex_key(uaddr1, fshared, &key1); | |
894 | if (unlikely(ret != 0)) | |
895 | goto out; | |
896 | ret = get_futex_key(uaddr2, fshared, &key2); | |
897 | if (unlikely(ret != 0)) | |
898 | goto out; | |
899 | ||
900 | hb1 = hash_futex(&key1); | |
901 | hb2 = hash_futex(&key2); | |
902 | ||
903 | double_lock_hb(hb1, hb2); | |
904 | ||
905 | if (likely(cmpval != NULL)) { | |
906 | u32 curval; | |
907 | ||
908 | ret = get_futex_value_locked(&curval, uaddr1); | |
909 | ||
910 | if (unlikely(ret)) { | |
911 | spin_unlock(&hb1->lock); | |
912 | if (hb1 != hb2) | |
913 | spin_unlock(&hb2->lock); | |
914 | ||
915 | /* | |
916 | * If we would have faulted, release mmap_sem, fault | |
917 | * it in and start all over again. | |
918 | */ | |
919 | futex_unlock_mm(fshared); | |
920 | ||
921 | ret = get_user(curval, uaddr1); | |
922 | ||
923 | if (!ret) | |
924 | goto retry; | |
925 | ||
926 | return ret; | |
927 | } | |
928 | if (curval != *cmpval) { | |
929 | ret = -EAGAIN; | |
930 | goto out_unlock; | |
931 | } | |
932 | } | |
933 | ||
934 | head1 = &hb1->chain; | |
935 | plist_for_each_entry_safe(this, next, head1, list) { | |
936 | if (!match_futex (&this->key, &key1)) | |
937 | continue; | |
938 | if (++ret <= nr_wake) { | |
939 | wake_futex(this); | |
940 | } else { | |
941 | /* | |
942 | * If key1 and key2 hash to the same bucket, no need to | |
943 | * requeue. | |
944 | */ | |
945 | if (likely(head1 != &hb2->chain)) { | |
946 | plist_del(&this->list, &hb1->chain); | |
947 | plist_add(&this->list, &hb2->chain); | |
948 | this->lock_ptr = &hb2->lock; | |
949 | #ifdef CONFIG_DEBUG_PI_LIST | |
950 | this->list.plist.lock = &hb2->lock; | |
951 | #endif | |
952 | } | |
953 | this->key = key2; | |
954 | get_futex_key_refs(&key2); | |
955 | drop_count++; | |
956 | ||
957 | if (ret - nr_wake >= nr_requeue) | |
958 | break; | |
959 | } | |
960 | } | |
961 | ||
962 | out_unlock: | |
963 | spin_unlock(&hb1->lock); | |
964 | if (hb1 != hb2) | |
965 | spin_unlock(&hb2->lock); | |
966 | ||
967 | /* drop_futex_key_refs() must be called outside the spinlocks. */ | |
968 | while (--drop_count >= 0) | |
969 | drop_futex_key_refs(&key1); | |
970 | ||
971 | out: | |
972 | futex_unlock_mm(fshared); | |
973 | return ret; | |
974 | } | |
975 | ||
976 | /* The key must be already stored in q->key. */ | |
977 | static inline struct futex_hash_bucket * | |
978 | queue_lock(struct futex_q *q, int fd, struct file *filp) | |
979 | { | |
980 | struct futex_hash_bucket *hb; | |
981 | ||
982 | q->fd = fd; | |
983 | q->filp = filp; | |
984 | ||
985 | init_waitqueue_head(&q->waiters); | |
986 | ||
987 | get_futex_key_refs(&q->key); | |
988 | hb = hash_futex(&q->key); | |
989 | q->lock_ptr = &hb->lock; | |
990 | ||
991 | spin_lock(&hb->lock); | |
992 | return hb; | |
993 | } | |
994 | ||
995 | static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb) | |
996 | { | |
997 | int prio; | |
998 | ||
999 | /* | |
1000 | * The priority used to register this element is | |
1001 | * - either the real thread-priority for the real-time threads | |
1002 | * (i.e. threads with a priority lower than MAX_RT_PRIO) | |
1003 | * - or MAX_RT_PRIO for non-RT threads. | |
1004 | * Thus, all RT-threads are woken first in priority order, and | |
1005 | * the others are woken last, in FIFO order. | |
1006 | */ | |
1007 | prio = min(current->normal_prio, MAX_RT_PRIO); | |
1008 | ||
1009 | plist_node_init(&q->list, prio); | |
1010 | #ifdef CONFIG_DEBUG_PI_LIST | |
1011 | q->list.plist.lock = &hb->lock; | |
1012 | #endif | |
1013 | plist_add(&q->list, &hb->chain); | |
1014 | q->task = current; | |
1015 | spin_unlock(&hb->lock); | |
1016 | } | |
1017 | ||
1018 | static inline void | |
1019 | queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb) | |
1020 | { | |
1021 | spin_unlock(&hb->lock); | |
1022 | drop_futex_key_refs(&q->key); | |
1023 | } | |
1024 | ||
1025 | /* | |
1026 | * queue_me and unqueue_me must be called as a pair, each | |
1027 | * exactly once. They are called with the hashed spinlock held. | |
1028 | */ | |
1029 | ||
1030 | /* The key must be already stored in q->key. */ | |
1031 | static void queue_me(struct futex_q *q, int fd, struct file *filp) | |
1032 | { | |
1033 | struct futex_hash_bucket *hb; | |
1034 | ||
1035 | hb = queue_lock(q, fd, filp); | |
1036 | __queue_me(q, hb); | |
1037 | } | |
1038 | ||
1039 | /* Return 1 if we were still queued (ie. 0 means we were woken) */ | |
1040 | static int unqueue_me(struct futex_q *q) | |
1041 | { | |
1042 | spinlock_t *lock_ptr; | |
1043 | int ret = 0; | |
1044 | ||
1045 | /* In the common case we don't take the spinlock, which is nice. */ | |
1046 | retry: | |
1047 | lock_ptr = q->lock_ptr; | |
1048 | barrier(); | |
1049 | if (lock_ptr != NULL) { | |
1050 | spin_lock(lock_ptr); | |
1051 | /* | |
1052 | * q->lock_ptr can change between reading it and | |
1053 | * spin_lock(), causing us to take the wrong lock. This | |
1054 | * corrects the race condition. | |
1055 | * | |
1056 | * Reasoning goes like this: if we have the wrong lock, | |
1057 | * q->lock_ptr must have changed (maybe several times) | |
1058 | * between reading it and the spin_lock(). It can | |
1059 | * change again after the spin_lock() but only if it was | |
1060 | * already changed before the spin_lock(). It cannot, | |
1061 | * however, change back to the original value. Therefore | |
1062 | * we can detect whether we acquired the correct lock. | |
1063 | */ | |
1064 | if (unlikely(lock_ptr != q->lock_ptr)) { | |
1065 | spin_unlock(lock_ptr); | |
1066 | goto retry; | |
1067 | } | |
1068 | WARN_ON(plist_node_empty(&q->list)); | |
1069 | plist_del(&q->list, &q->list.plist); | |
1070 | ||
1071 | BUG_ON(q->pi_state); | |
1072 | ||
1073 | spin_unlock(lock_ptr); | |
1074 | ret = 1; | |
1075 | } | |
1076 | ||
1077 | drop_futex_key_refs(&q->key); | |
1078 | return ret; | |
1079 | } | |
1080 | ||
1081 | /* | |
1082 | * PI futexes can not be requeued and must remove themself from the | |
1083 | * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry | |
1084 | * and dropped here. | |
1085 | */ | |
1086 | static void unqueue_me_pi(struct futex_q *q) | |
1087 | { | |
1088 | WARN_ON(plist_node_empty(&q->list)); | |
1089 | plist_del(&q->list, &q->list.plist); | |
1090 | ||
1091 | BUG_ON(!q->pi_state); | |
1092 | free_pi_state(q->pi_state); | |
1093 | q->pi_state = NULL; | |
1094 | ||
1095 | spin_unlock(q->lock_ptr); | |
1096 | ||
1097 | drop_futex_key_refs(&q->key); | |
1098 | } | |
1099 | ||
1100 | /* | |
1101 | * Fixup the pi_state owner with current. | |
1102 | * | |
1103 | * Must be called with hash bucket lock held and mm->sem held for non | |
1104 | * private futexes. | |
1105 | */ | |
1106 | static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q, | |
1107 | struct task_struct *curr) | |
1108 | { | |
1109 | u32 newtid = curr->pid | FUTEX_WAITERS; | |
1110 | struct futex_pi_state *pi_state = q->pi_state; | |
1111 | u32 uval, curval, newval; | |
1112 | int ret; | |
1113 | ||
1114 | /* Owner died? */ | |
1115 | if (pi_state->owner != NULL) { | |
1116 | spin_lock_irq(&pi_state->owner->pi_lock); | |
1117 | WARN_ON(list_empty(&pi_state->list)); | |
1118 | list_del_init(&pi_state->list); | |
1119 | spin_unlock_irq(&pi_state->owner->pi_lock); | |
1120 | } else | |
1121 | newtid |= FUTEX_OWNER_DIED; | |
1122 | ||
1123 | pi_state->owner = curr; | |
1124 | ||
1125 | spin_lock_irq(&curr->pi_lock); | |
1126 | WARN_ON(!list_empty(&pi_state->list)); | |
1127 | list_add(&pi_state->list, &curr->pi_state_list); | |
1128 | spin_unlock_irq(&curr->pi_lock); | |
1129 | ||
1130 | /* | |
1131 | * We own it, so we have to replace the pending owner | |
1132 | * TID. This must be atomic as we have preserve the | |
1133 | * owner died bit here. | |
1134 | */ | |
1135 | ret = get_futex_value_locked(&uval, uaddr); | |
1136 | ||
1137 | while (!ret) { | |
1138 | newval = (uval & FUTEX_OWNER_DIED) | newtid; | |
1139 | ||
1140 | curval = cmpxchg_futex_value_locked(uaddr, uval, newval); | |
1141 | ||
1142 | if (curval == -EFAULT) | |
1143 | ret = -EFAULT; | |
1144 | if (curval == uval) | |
1145 | break; | |
1146 | uval = curval; | |
1147 | } | |
1148 | return ret; | |
1149 | } | |
1150 | ||
1151 | /* | |
1152 | * In case we must use restart_block to restart a futex_wait, | |
1153 | * we encode in the 'arg3' shared capability | |
1154 | */ | |
1155 | #define ARG3_SHARED 1 | |
1156 | ||
1157 | static long futex_wait_restart(struct restart_block *restart); | |
1158 | ||
1159 | static int futex_wait(u32 __user *uaddr, struct rw_semaphore *fshared, | |
1160 | u32 val, ktime_t *abs_time) | |
1161 | { | |
1162 | struct task_struct *curr = current; | |
1163 | DECLARE_WAITQUEUE(wait, curr); | |
1164 | struct futex_hash_bucket *hb; | |
1165 | struct futex_q q; | |
1166 | u32 uval; | |
1167 | int ret; | |
1168 | struct hrtimer_sleeper t; | |
1169 | int rem = 0; | |
1170 | ||
1171 | q.pi_state = NULL; | |
1172 | retry: | |
1173 | futex_lock_mm(fshared); | |
1174 | ||
1175 | ret = get_futex_key(uaddr, fshared, &q.key); | |
1176 | if (unlikely(ret != 0)) | |
1177 | goto out_release_sem; | |
1178 | ||
1179 | hb = queue_lock(&q, -1, NULL); | |
1180 | ||
1181 | /* | |
1182 | * Access the page AFTER the futex is queued. | |
1183 | * Order is important: | |
1184 | * | |
1185 | * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val); | |
1186 | * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); } | |
1187 | * | |
1188 | * The basic logical guarantee of a futex is that it blocks ONLY | |
1189 | * if cond(var) is known to be true at the time of blocking, for | |
1190 | * any cond. If we queued after testing *uaddr, that would open | |
1191 | * a race condition where we could block indefinitely with | |
1192 | * cond(var) false, which would violate the guarantee. | |
1193 | * | |
1194 | * A consequence is that futex_wait() can return zero and absorb | |
1195 | * a wakeup when *uaddr != val on entry to the syscall. This is | |
1196 | * rare, but normal. | |
1197 | * | |
1198 | * for shared futexes, we hold the mmap semaphore, so the mapping | |
1199 | * cannot have changed since we looked it up in get_futex_key. | |
1200 | */ | |
1201 | ret = get_futex_value_locked(&uval, uaddr); | |
1202 | ||
1203 | if (unlikely(ret)) { | |
1204 | queue_unlock(&q, hb); | |
1205 | ||
1206 | /* | |
1207 | * If we would have faulted, release mmap_sem, fault it in and | |
1208 | * start all over again. | |
1209 | */ | |
1210 | futex_unlock_mm(fshared); | |
1211 | ||
1212 | ret = get_user(uval, uaddr); | |
1213 | ||
1214 | if (!ret) | |
1215 | goto retry; | |
1216 | return ret; | |
1217 | } | |
1218 | ret = -EWOULDBLOCK; | |
1219 | if (uval != val) | |
1220 | goto out_unlock_release_sem; | |
1221 | ||
1222 | /* Only actually queue if *uaddr contained val. */ | |
1223 | __queue_me(&q, hb); | |
1224 | ||
1225 | /* | |
1226 | * Now the futex is queued and we have checked the data, we | |
1227 | * don't want to hold mmap_sem while we sleep. | |
1228 | */ | |
1229 | futex_unlock_mm(fshared); | |
1230 | ||
1231 | /* | |
1232 | * There might have been scheduling since the queue_me(), as we | |
1233 | * cannot hold a spinlock across the get_user() in case it | |
1234 | * faults, and we cannot just set TASK_INTERRUPTIBLE state when | |
1235 | * queueing ourselves into the futex hash. This code thus has to | |
1236 | * rely on the futex_wake() code removing us from hash when it | |
1237 | * wakes us up. | |
1238 | */ | |
1239 | ||
1240 | /* add_wait_queue is the barrier after __set_current_state. */ | |
1241 | __set_current_state(TASK_INTERRUPTIBLE); | |
1242 | add_wait_queue(&q.waiters, &wait); | |
1243 | /* | |
1244 | * !plist_node_empty() is safe here without any lock. | |
1245 | * q.lock_ptr != 0 is not safe, because of ordering against wakeup. | |
1246 | */ | |
1247 | if (likely(!plist_node_empty(&q.list))) { | |
1248 | if (!abs_time) | |
1249 | schedule(); | |
1250 | else { | |
1251 | hrtimer_init(&t.timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); | |
1252 | hrtimer_init_sleeper(&t, current); | |
1253 | t.timer.expires = *abs_time; | |
1254 | ||
1255 | hrtimer_start(&t.timer, t.timer.expires, HRTIMER_MODE_ABS); | |
1256 | ||
1257 | /* | |
1258 | * the timer could have already expired, in which | |
1259 | * case current would be flagged for rescheduling. | |
1260 | * Don't bother calling schedule. | |
1261 | */ | |
1262 | if (likely(t.task)) | |
1263 | schedule(); | |
1264 | ||
1265 | hrtimer_cancel(&t.timer); | |
1266 | ||
1267 | /* Flag if a timeout occured */ | |
1268 | rem = (t.task == NULL); | |
1269 | } | |
1270 | } | |
1271 | __set_current_state(TASK_RUNNING); | |
1272 | ||
1273 | /* | |
1274 | * NOTE: we don't remove ourselves from the waitqueue because | |
1275 | * we are the only user of it. | |
1276 | */ | |
1277 | ||
1278 | /* If we were woken (and unqueued), we succeeded, whatever. */ | |
1279 | if (!unqueue_me(&q)) | |
1280 | return 0; | |
1281 | if (rem) | |
1282 | return -ETIMEDOUT; | |
1283 | ||
1284 | /* | |
1285 | * We expect signal_pending(current), but another thread may | |
1286 | * have handled it for us already. | |
1287 | */ | |
1288 | if (!abs_time) | |
1289 | return -ERESTARTSYS; | |
1290 | else { | |
1291 | struct restart_block *restart; | |
1292 | restart = ¤t_thread_info()->restart_block; | |
1293 | restart->fn = futex_wait_restart; | |
1294 | restart->arg0 = (unsigned long)uaddr; | |
1295 | restart->arg1 = (unsigned long)val; | |
1296 | restart->arg2 = (unsigned long)abs_time; | |
1297 | restart->arg3 = 0; | |
1298 | if (fshared) | |
1299 | restart->arg3 |= ARG3_SHARED; | |
1300 | return -ERESTART_RESTARTBLOCK; | |
1301 | } | |
1302 | ||
1303 | out_unlock_release_sem: | |
1304 | queue_unlock(&q, hb); | |
1305 | ||
1306 | out_release_sem: | |
1307 | futex_unlock_mm(fshared); | |
1308 | return ret; | |
1309 | } | |
1310 | ||
1311 | ||
1312 | static long futex_wait_restart(struct restart_block *restart) | |
1313 | { | |
1314 | u32 __user *uaddr = (u32 __user *)restart->arg0; | |
1315 | u32 val = (u32)restart->arg1; | |
1316 | ktime_t *abs_time = (ktime_t *)restart->arg2; | |
1317 | struct rw_semaphore *fshared = NULL; | |
1318 | ||
1319 | restart->fn = do_no_restart_syscall; | |
1320 | if (restart->arg3 & ARG3_SHARED) | |
1321 | fshared = ¤t->mm->mmap_sem; | |
1322 | return (long)futex_wait(uaddr, fshared, val, abs_time); | |
1323 | } | |
1324 | ||
1325 | ||
1326 | /* | |
1327 | * Userspace tried a 0 -> TID atomic transition of the futex value | |
1328 | * and failed. The kernel side here does the whole locking operation: | |
1329 | * if there are waiters then it will block, it does PI, etc. (Due to | |
1330 | * races the kernel might see a 0 value of the futex too.) | |
1331 | */ | |
1332 | static int futex_lock_pi(u32 __user *uaddr, struct rw_semaphore *fshared, | |
1333 | int detect, ktime_t *time, int trylock) | |
1334 | { | |
1335 | struct hrtimer_sleeper timeout, *to = NULL; | |
1336 | struct task_struct *curr = current; | |
1337 | struct futex_hash_bucket *hb; | |
1338 | u32 uval, newval, curval; | |
1339 | struct futex_q q; | |
1340 | int ret, lock_taken, ownerdied = 0, attempt = 0; | |
1341 | ||
1342 | if (refill_pi_state_cache()) | |
1343 | return -ENOMEM; | |
1344 | ||
1345 | if (time) { | |
1346 | to = &timeout; | |
1347 | hrtimer_init(&to->timer, CLOCK_REALTIME, HRTIMER_MODE_ABS); | |
1348 | hrtimer_init_sleeper(to, current); | |
1349 | to->timer.expires = *time; | |
1350 | } | |
1351 | ||
1352 | q.pi_state = NULL; | |
1353 | retry: | |
1354 | futex_lock_mm(fshared); | |
1355 | ||
1356 | ret = get_futex_key(uaddr, fshared, &q.key); | |
1357 | if (unlikely(ret != 0)) | |
1358 | goto out_release_sem; | |
1359 | ||
1360 | retry_unlocked: | |
1361 | hb = queue_lock(&q, -1, NULL); | |
1362 | ||
1363 | retry_locked: | |
1364 | ret = lock_taken = 0; | |
1365 | ||
1366 | /* | |
1367 | * To avoid races, we attempt to take the lock here again | |
1368 | * (by doing a 0 -> TID atomic cmpxchg), while holding all | |
1369 | * the locks. It will most likely not succeed. | |
1370 | */ | |
1371 | newval = current->pid; | |
1372 | ||
1373 | curval = cmpxchg_futex_value_locked(uaddr, 0, newval); | |
1374 | ||
1375 | if (unlikely(curval == -EFAULT)) | |
1376 | goto uaddr_faulted; | |
1377 | ||
1378 | /* | |
1379 | * Detect deadlocks. In case of REQUEUE_PI this is a valid | |
1380 | * situation and we return success to user space. | |
1381 | */ | |
1382 | if (unlikely((curval & FUTEX_TID_MASK) == current->pid)) { | |
1383 | ret = -EDEADLK; | |
1384 | goto out_unlock_release_sem; | |
1385 | } | |
1386 | ||
1387 | /* | |
1388 | * Surprise - we got the lock. Just return to userspace: | |
1389 | */ | |
1390 | if (unlikely(!curval)) | |
1391 | goto out_unlock_release_sem; | |
1392 | ||
1393 | uval = curval; | |
1394 | ||
1395 | /* | |
1396 | * Set the WAITERS flag, so the owner will know it has someone | |
1397 | * to wake at next unlock | |
1398 | */ | |
1399 | newval = curval | FUTEX_WAITERS; | |
1400 | ||
1401 | /* | |
1402 | * There are two cases, where a futex might have no owner (the | |
1403 | * owner TID is 0): OWNER_DIED. We take over the futex in this | |
1404 | * case. We also do an unconditional take over, when the owner | |
1405 | * of the futex died. | |
1406 | * | |
1407 | * This is safe as we are protected by the hash bucket lock ! | |
1408 | */ | |
1409 | if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) { | |
1410 | /* Keep the OWNER_DIED bit */ | |
1411 | newval = (curval & ~FUTEX_TID_MASK) | current->pid; | |
1412 | ownerdied = 0; | |
1413 | lock_taken = 1; | |
1414 | } | |
1415 | ||
1416 | curval = cmpxchg_futex_value_locked(uaddr, uval, newval); | |
1417 | ||
1418 | if (unlikely(curval == -EFAULT)) | |
1419 | goto uaddr_faulted; | |
1420 | if (unlikely(curval != uval)) | |
1421 | goto retry_locked; | |
1422 | ||
1423 | /* | |
1424 | * We took the lock due to owner died take over. | |
1425 | */ | |
1426 | if (unlikely(lock_taken)) | |
1427 | goto out_unlock_release_sem; | |
1428 | ||
1429 | /* | |
1430 | * We dont have the lock. Look up the PI state (or create it if | |
1431 | * we are the first waiter): | |
1432 | */ | |
1433 | ret = lookup_pi_state(uval, hb, &q.key, &q.pi_state); | |
1434 | ||
1435 | if (unlikely(ret)) { | |
1436 | switch (ret) { | |
1437 | ||
1438 | case -EAGAIN: | |
1439 | /* | |
1440 | * Task is exiting and we just wait for the | |
1441 | * exit to complete. | |
1442 | */ | |
1443 | queue_unlock(&q, hb); | |
1444 | futex_unlock_mm(fshared); | |
1445 | cond_resched(); | |
1446 | goto retry; | |
1447 | ||
1448 | case -ESRCH: | |
1449 | /* | |
1450 | * No owner found for this futex. Check if the | |
1451 | * OWNER_DIED bit is set to figure out whether | |
1452 | * this is a robust futex or not. | |
1453 | */ | |
1454 | if (get_futex_value_locked(&curval, uaddr)) | |
1455 | goto uaddr_faulted; | |
1456 | ||
1457 | /* | |
1458 | * We simply start over in case of a robust | |
1459 | * futex. The code above will take the futex | |
1460 | * and return happy. | |
1461 | */ | |
1462 | if (curval & FUTEX_OWNER_DIED) { | |
1463 | ownerdied = 1; | |
1464 | goto retry_locked; | |
1465 | } | |
1466 | default: | |
1467 | goto out_unlock_release_sem; | |
1468 | } | |
1469 | } | |
1470 | ||
1471 | /* | |
1472 | * Only actually queue now that the atomic ops are done: | |
1473 | */ | |
1474 | __queue_me(&q, hb); | |
1475 | ||
1476 | /* | |
1477 | * Now the futex is queued and we have checked the data, we | |
1478 | * don't want to hold mmap_sem while we sleep. | |
1479 | */ | |
1480 | futex_unlock_mm(fshared); | |
1481 | ||
1482 | WARN_ON(!q.pi_state); | |
1483 | /* | |
1484 | * Block on the PI mutex: | |
1485 | */ | |
1486 | if (!trylock) | |
1487 | ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1); | |
1488 | else { | |
1489 | ret = rt_mutex_trylock(&q.pi_state->pi_mutex); | |
1490 | /* Fixup the trylock return value: */ | |
1491 | ret = ret ? 0 : -EWOULDBLOCK; | |
1492 | } | |
1493 | ||
1494 | futex_lock_mm(fshared); | |
1495 | spin_lock(q.lock_ptr); | |
1496 | ||
1497 | if (!ret) { | |
1498 | /* | |
1499 | * Got the lock. We might not be the anticipated owner | |
1500 | * if we did a lock-steal - fix up the PI-state in | |
1501 | * that case: | |
1502 | */ | |
1503 | if (q.pi_state->owner != curr) | |
1504 | ret = fixup_pi_state_owner(uaddr, &q, curr); | |
1505 | } else { | |
1506 | /* | |
1507 | * Catch the rare case, where the lock was released | |
1508 | * when we were on the way back before we locked the | |
1509 | * hash bucket. | |
1510 | */ | |
1511 | if (q.pi_state->owner == curr && | |
1512 | rt_mutex_trylock(&q.pi_state->pi_mutex)) { | |
1513 | ret = 0; | |
1514 | } else { | |
1515 | /* | |
1516 | * Paranoia check. If we did not take the lock | |
1517 | * in the trylock above, then we should not be | |
1518 | * the owner of the rtmutex, neither the real | |
1519 | * nor the pending one: | |
1520 | */ | |
1521 | if (rt_mutex_owner(&q.pi_state->pi_mutex) == curr) | |
1522 | printk(KERN_ERR "futex_lock_pi: ret = %d " | |
1523 | "pi-mutex: %p pi-state %p\n", ret, | |
1524 | q.pi_state->pi_mutex.owner, | |
1525 | q.pi_state->owner); | |
1526 | } | |
1527 | } | |
1528 | ||
1529 | /* Unqueue and drop the lock */ | |
1530 | unqueue_me_pi(&q); | |
1531 | futex_unlock_mm(fshared); | |
1532 | ||
1533 | return ret != -EINTR ? ret : -ERESTARTNOINTR; | |
1534 | ||
1535 | out_unlock_release_sem: | |
1536 | queue_unlock(&q, hb); | |
1537 | ||
1538 | out_release_sem: | |
1539 | futex_unlock_mm(fshared); | |
1540 | return ret; | |
1541 | ||
1542 | uaddr_faulted: | |
1543 | /* | |
1544 | * We have to r/w *(int __user *)uaddr, but we can't modify it | |
1545 | * non-atomically. Therefore, if get_user below is not | |
1546 | * enough, we need to handle the fault ourselves, while | |
1547 | * still holding the mmap_sem. | |
1548 | * | |
1549 | * ... and hb->lock. :-) --ANK | |
1550 | */ | |
1551 | queue_unlock(&q, hb); | |
1552 | ||
1553 | if (attempt++) { | |
1554 | ret = futex_handle_fault((unsigned long)uaddr, fshared, | |
1555 | attempt); | |
1556 | if (ret) | |
1557 | goto out_release_sem; | |
1558 | goto retry_unlocked; | |
1559 | } | |
1560 | ||
1561 | futex_unlock_mm(fshared); | |
1562 | ||
1563 | ret = get_user(uval, uaddr); | |
1564 | if (!ret && (uval != -EFAULT)) | |
1565 | goto retry; | |
1566 | ||
1567 | return ret; | |
1568 | } | |
1569 | ||
1570 | /* | |
1571 | * Userspace attempted a TID -> 0 atomic transition, and failed. | |
1572 | * This is the in-kernel slowpath: we look up the PI state (if any), | |
1573 | * and do the rt-mutex unlock. | |
1574 | */ | |
1575 | static int futex_unlock_pi(u32 __user *uaddr, struct rw_semaphore *fshared) | |
1576 | { | |
1577 | struct futex_hash_bucket *hb; | |
1578 | struct futex_q *this, *next; | |
1579 | u32 uval; | |
1580 | struct plist_head *head; | |
1581 | union futex_key key; | |
1582 | int ret, attempt = 0; | |
1583 | ||
1584 | retry: | |
1585 | if (get_user(uval, uaddr)) | |
1586 | return -EFAULT; | |
1587 | /* | |
1588 | * We release only a lock we actually own: | |
1589 | */ | |
1590 | if ((uval & FUTEX_TID_MASK) != current->pid) | |
1591 | return -EPERM; | |
1592 | /* | |
1593 | * First take all the futex related locks: | |
1594 | */ | |
1595 | futex_lock_mm(fshared); | |
1596 | ||
1597 | ret = get_futex_key(uaddr, fshared, &key); | |
1598 | if (unlikely(ret != 0)) | |
1599 | goto out; | |
1600 | ||
1601 | hb = hash_futex(&key); | |
1602 | retry_unlocked: | |
1603 | spin_lock(&hb->lock); | |
1604 | ||
1605 | /* | |
1606 | * To avoid races, try to do the TID -> 0 atomic transition | |
1607 | * again. If it succeeds then we can return without waking | |
1608 | * anyone else up: | |
1609 | */ | |
1610 | if (!(uval & FUTEX_OWNER_DIED)) | |
1611 | uval = cmpxchg_futex_value_locked(uaddr, current->pid, 0); | |
1612 | ||
1613 | ||
1614 | if (unlikely(uval == -EFAULT)) | |
1615 | goto pi_faulted; | |
1616 | /* | |
1617 | * Rare case: we managed to release the lock atomically, | |
1618 | * no need to wake anyone else up: | |
1619 | */ | |
1620 | if (unlikely(uval == current->pid)) | |
1621 | goto out_unlock; | |
1622 | ||
1623 | /* | |
1624 | * Ok, other tasks may need to be woken up - check waiters | |
1625 | * and do the wakeup if necessary: | |
1626 | */ | |
1627 | head = &hb->chain; | |
1628 | ||
1629 | plist_for_each_entry_safe(this, next, head, list) { | |
1630 | if (!match_futex (&this->key, &key)) | |
1631 | continue; | |
1632 | ret = wake_futex_pi(uaddr, uval, this); | |
1633 | /* | |
1634 | * The atomic access to the futex value | |
1635 | * generated a pagefault, so retry the | |
1636 | * user-access and the wakeup: | |
1637 | */ | |
1638 | if (ret == -EFAULT) | |
1639 | goto pi_faulted; | |
1640 | goto out_unlock; | |
1641 | } | |
1642 | /* | |
1643 | * No waiters - kernel unlocks the futex: | |
1644 | */ | |
1645 | if (!(uval & FUTEX_OWNER_DIED)) { | |
1646 | ret = unlock_futex_pi(uaddr, uval); | |
1647 | if (ret == -EFAULT) | |
1648 | goto pi_faulted; | |
1649 | } | |
1650 | ||
1651 | out_unlock: | |
1652 | spin_unlock(&hb->lock); | |
1653 | out: | |
1654 | futex_unlock_mm(fshared); | |
1655 | ||
1656 | return ret; | |
1657 | ||
1658 | pi_faulted: | |
1659 | /* | |
1660 | * We have to r/w *(int __user *)uaddr, but we can't modify it | |
1661 | * non-atomically. Therefore, if get_user below is not | |
1662 | * enough, we need to handle the fault ourselves, while | |
1663 | * still holding the mmap_sem. | |
1664 | * | |
1665 | * ... and hb->lock. --ANK | |
1666 | */ | |
1667 | spin_unlock(&hb->lock); | |
1668 | ||
1669 | if (attempt++) { | |
1670 | ret = futex_handle_fault((unsigned long)uaddr, fshared, | |
1671 | attempt); | |
1672 | if (ret) | |
1673 | goto out; | |
1674 | uval = 0; | |
1675 | goto retry_unlocked; | |
1676 | } | |
1677 | ||
1678 | futex_unlock_mm(fshared); | |
1679 | ||
1680 | ret = get_user(uval, uaddr); | |
1681 | if (!ret && (uval != -EFAULT)) | |
1682 | goto retry; | |
1683 | ||
1684 | return ret; | |
1685 | } | |
1686 | ||
1687 | static int futex_close(struct inode *inode, struct file *filp) | |
1688 | { | |
1689 | struct futex_q *q = filp->private_data; | |
1690 | ||
1691 | unqueue_me(q); | |
1692 | kfree(q); | |
1693 | ||
1694 | return 0; | |
1695 | } | |
1696 | ||
1697 | /* This is one-shot: once it's gone off you need a new fd */ | |
1698 | static unsigned int futex_poll(struct file *filp, | |
1699 | struct poll_table_struct *wait) | |
1700 | { | |
1701 | struct futex_q *q = filp->private_data; | |
1702 | int ret = 0; | |
1703 | ||
1704 | poll_wait(filp, &q->waiters, wait); | |
1705 | ||
1706 | /* | |
1707 | * plist_node_empty() is safe here without any lock. | |
1708 | * q->lock_ptr != 0 is not safe, because of ordering against wakeup. | |
1709 | */ | |
1710 | if (plist_node_empty(&q->list)) | |
1711 | ret = POLLIN | POLLRDNORM; | |
1712 | ||
1713 | return ret; | |
1714 | } | |
1715 | ||
1716 | static const struct file_operations futex_fops = { | |
1717 | .release = futex_close, | |
1718 | .poll = futex_poll, | |
1719 | }; | |
1720 | ||
1721 | /* | |
1722 | * Signal allows caller to avoid the race which would occur if they | |
1723 | * set the sigio stuff up afterwards. | |
1724 | */ | |
1725 | static int futex_fd(u32 __user *uaddr, int signal) | |
1726 | { | |
1727 | struct futex_q *q; | |
1728 | struct file *filp; | |
1729 | int ret, err; | |
1730 | struct rw_semaphore *fshared; | |
1731 | static unsigned long printk_interval; | |
1732 | ||
1733 | if (printk_timed_ratelimit(&printk_interval, 60 * 60 * 1000)) { | |
1734 | printk(KERN_WARNING "Process `%s' used FUTEX_FD, which " | |
1735 | "will be removed from the kernel in June 2007\n", | |
1736 | current->comm); | |
1737 | } | |
1738 | ||
1739 | ret = -EINVAL; | |
1740 | if (!valid_signal(signal)) | |
1741 | goto out; | |
1742 | ||
1743 | ret = get_unused_fd(); | |
1744 | if (ret < 0) | |
1745 | goto out; | |
1746 | filp = get_empty_filp(); | |
1747 | if (!filp) { | |
1748 | put_unused_fd(ret); | |
1749 | ret = -ENFILE; | |
1750 | goto out; | |
1751 | } | |
1752 | filp->f_op = &futex_fops; | |
1753 | filp->f_path.mnt = mntget(futex_mnt); | |
1754 | filp->f_path.dentry = dget(futex_mnt->mnt_root); | |
1755 | filp->f_mapping = filp->f_path.dentry->d_inode->i_mapping; | |
1756 | ||
1757 | if (signal) { | |
1758 | err = __f_setown(filp, task_pid(current), PIDTYPE_PID, 1); | |
1759 | if (err < 0) { | |
1760 | goto error; | |
1761 | } | |
1762 | filp->f_owner.signum = signal; | |
1763 | } | |
1764 | ||
1765 | q = kmalloc(sizeof(*q), GFP_KERNEL); | |
1766 | if (!q) { | |
1767 | err = -ENOMEM; | |
1768 | goto error; | |
1769 | } | |
1770 | q->pi_state = NULL; | |
1771 | ||
1772 | fshared = ¤t->mm->mmap_sem; | |
1773 | down_read(fshared); | |
1774 | err = get_futex_key(uaddr, fshared, &q->key); | |
1775 | ||
1776 | if (unlikely(err != 0)) { | |
1777 | up_read(fshared); | |
1778 | kfree(q); | |
1779 | goto error; | |
1780 | } | |
1781 | ||
1782 | /* | |
1783 | * queue_me() must be called before releasing mmap_sem, because | |
1784 | * key->shared.inode needs to be referenced while holding it. | |
1785 | */ | |
1786 | filp->private_data = q; | |
1787 | ||
1788 | queue_me(q, ret, filp); | |
1789 | up_read(fshared); | |
1790 | ||
1791 | /* Now we map fd to filp, so userspace can access it */ | |
1792 | fd_install(ret, filp); | |
1793 | out: | |
1794 | return ret; | |
1795 | error: | |
1796 | put_unused_fd(ret); | |
1797 | put_filp(filp); | |
1798 | ret = err; | |
1799 | goto out; | |
1800 | } | |
1801 | ||
1802 | /* | |
1803 | * Support for robust futexes: the kernel cleans up held futexes at | |
1804 | * thread exit time. | |
1805 | * | |
1806 | * Implementation: user-space maintains a per-thread list of locks it | |
1807 | * is holding. Upon do_exit(), the kernel carefully walks this list, | |
1808 | * and marks all locks that are owned by this thread with the | |
1809 | * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is | |
1810 | * always manipulated with the lock held, so the list is private and | |
1811 | * per-thread. Userspace also maintains a per-thread 'list_op_pending' | |
1812 | * field, to allow the kernel to clean up if the thread dies after | |
1813 | * acquiring the lock, but just before it could have added itself to | |
1814 | * the list. There can only be one such pending lock. | |
1815 | */ | |
1816 | ||
1817 | /** | |
1818 | * sys_set_robust_list - set the robust-futex list head of a task | |
1819 | * @head: pointer to the list-head | |
1820 | * @len: length of the list-head, as userspace expects | |
1821 | */ | |
1822 | asmlinkage long | |
1823 | sys_set_robust_list(struct robust_list_head __user *head, | |
1824 | size_t len) | |
1825 | { | |
1826 | /* | |
1827 | * The kernel knows only one size for now: | |
1828 | */ | |
1829 | if (unlikely(len != sizeof(*head))) | |
1830 | return -EINVAL; | |
1831 | ||
1832 | current->robust_list = head; | |
1833 | ||
1834 | return 0; | |
1835 | } | |
1836 | ||
1837 | /** | |
1838 | * sys_get_robust_list - get the robust-futex list head of a task | |
1839 | * @pid: pid of the process [zero for current task] | |
1840 | * @head_ptr: pointer to a list-head pointer, the kernel fills it in | |
1841 | * @len_ptr: pointer to a length field, the kernel fills in the header size | |
1842 | */ | |
1843 | asmlinkage long | |
1844 | sys_get_robust_list(int pid, struct robust_list_head __user * __user *head_ptr, | |
1845 | size_t __user *len_ptr) | |
1846 | { | |
1847 | struct robust_list_head __user *head; | |
1848 | unsigned long ret; | |
1849 | ||
1850 | if (!pid) | |
1851 | head = current->robust_list; | |
1852 | else { | |
1853 | struct task_struct *p; | |
1854 | ||
1855 | ret = -ESRCH; | |
1856 | rcu_read_lock(); | |
1857 | p = find_task_by_pid(pid); | |
1858 | if (!p) | |
1859 | goto err_unlock; | |
1860 | ret = -EPERM; | |
1861 | if ((current->euid != p->euid) && (current->euid != p->uid) && | |
1862 | !capable(CAP_SYS_PTRACE)) | |
1863 | goto err_unlock; | |
1864 | head = p->robust_list; | |
1865 | rcu_read_unlock(); | |
1866 | } | |
1867 | ||
1868 | if (put_user(sizeof(*head), len_ptr)) | |
1869 | return -EFAULT; | |
1870 | return put_user(head, head_ptr); | |
1871 | ||
1872 | err_unlock: | |
1873 | rcu_read_unlock(); | |
1874 | ||
1875 | return ret; | |
1876 | } | |
1877 | ||
1878 | /* | |
1879 | * Process a futex-list entry, check whether it's owned by the | |
1880 | * dying task, and do notification if so: | |
1881 | */ | |
1882 | int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi) | |
1883 | { | |
1884 | u32 uval, nval, mval; | |
1885 | ||
1886 | retry: | |
1887 | if (get_user(uval, uaddr)) | |
1888 | return -1; | |
1889 | ||
1890 | if ((uval & FUTEX_TID_MASK) == curr->pid) { | |
1891 | /* | |
1892 | * Ok, this dying thread is truly holding a futex | |
1893 | * of interest. Set the OWNER_DIED bit atomically | |
1894 | * via cmpxchg, and if the value had FUTEX_WAITERS | |
1895 | * set, wake up a waiter (if any). (We have to do a | |
1896 | * futex_wake() even if OWNER_DIED is already set - | |
1897 | * to handle the rare but possible case of recursive | |
1898 | * thread-death.) The rest of the cleanup is done in | |
1899 | * userspace. | |
1900 | */ | |
1901 | mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED; | |
1902 | nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval); | |
1903 | ||
1904 | if (nval == -EFAULT) | |
1905 | return -1; | |
1906 | ||
1907 | if (nval != uval) | |
1908 | goto retry; | |
1909 | ||
1910 | /* | |
1911 | * Wake robust non-PI futexes here. The wakeup of | |
1912 | * PI futexes happens in exit_pi_state(): | |
1913 | */ | |
1914 | if (!pi && (uval & FUTEX_WAITERS)) | |
1915 | futex_wake(uaddr, &curr->mm->mmap_sem, 1); | |
1916 | } | |
1917 | return 0; | |
1918 | } | |
1919 | ||
1920 | /* | |
1921 | * Fetch a robust-list pointer. Bit 0 signals PI futexes: | |
1922 | */ | |
1923 | static inline int fetch_robust_entry(struct robust_list __user **entry, | |
1924 | struct robust_list __user * __user *head, | |
1925 | int *pi) | |
1926 | { | |
1927 | unsigned long uentry; | |
1928 | ||
1929 | if (get_user(uentry, (unsigned long __user *)head)) | |
1930 | return -EFAULT; | |
1931 | ||
1932 | *entry = (void __user *)(uentry & ~1UL); | |
1933 | *pi = uentry & 1; | |
1934 | ||
1935 | return 0; | |
1936 | } | |
1937 | ||
1938 | /* | |
1939 | * Walk curr->robust_list (very carefully, it's a userspace list!) | |
1940 | * and mark any locks found there dead, and notify any waiters. | |
1941 | * | |
1942 | * We silently return on any sign of list-walking problem. | |
1943 | */ | |
1944 | void exit_robust_list(struct task_struct *curr) | |
1945 | { | |
1946 | struct robust_list_head __user *head = curr->robust_list; | |
1947 | struct robust_list __user *entry, *next_entry, *pending; | |
1948 | unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip; | |
1949 | unsigned long futex_offset; | |
1950 | int rc; | |
1951 | ||
1952 | /* | |
1953 | * Fetch the list head (which was registered earlier, via | |
1954 | * sys_set_robust_list()): | |
1955 | */ | |
1956 | if (fetch_robust_entry(&entry, &head->list.next, &pi)) | |
1957 | return; | |
1958 | /* | |
1959 | * Fetch the relative futex offset: | |
1960 | */ | |
1961 | if (get_user(futex_offset, &head->futex_offset)) | |
1962 | return; | |
1963 | /* | |
1964 | * Fetch any possibly pending lock-add first, and handle it | |
1965 | * if it exists: | |
1966 | */ | |
1967 | if (fetch_robust_entry(&pending, &head->list_op_pending, &pip)) | |
1968 | return; | |
1969 | ||
1970 | next_entry = NULL; /* avoid warning with gcc */ | |
1971 | while (entry != &head->list) { | |
1972 | /* | |
1973 | * Fetch the next entry in the list before calling | |
1974 | * handle_futex_death: | |
1975 | */ | |
1976 | rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi); | |
1977 | /* | |
1978 | * A pending lock might already be on the list, so | |
1979 | * don't process it twice: | |
1980 | */ | |
1981 | if (entry != pending) | |
1982 | if (handle_futex_death((void __user *)entry + futex_offset, | |
1983 | curr, pi)) | |
1984 | return; | |
1985 | if (rc) | |
1986 | return; | |
1987 | entry = next_entry; | |
1988 | pi = next_pi; | |
1989 | /* | |
1990 | * Avoid excessively long or circular lists: | |
1991 | */ | |
1992 | if (!--limit) | |
1993 | break; | |
1994 | ||
1995 | cond_resched(); | |
1996 | } | |
1997 | ||
1998 | if (pending) | |
1999 | handle_futex_death((void __user *)pending + futex_offset, | |
2000 | curr, pip); | |
2001 | } | |
2002 | ||
2003 | long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, | |
2004 | u32 __user *uaddr2, u32 val2, u32 val3) | |
2005 | { | |
2006 | int ret; | |
2007 | int cmd = op & FUTEX_CMD_MASK; | |
2008 | struct rw_semaphore *fshared = NULL; | |
2009 | ||
2010 | if (!(op & FUTEX_PRIVATE_FLAG)) | |
2011 | fshared = ¤t->mm->mmap_sem; | |
2012 | ||
2013 | switch (cmd) { | |
2014 | case FUTEX_WAIT: | |
2015 | ret = futex_wait(uaddr, fshared, val, timeout); | |
2016 | break; | |
2017 | case FUTEX_WAKE: | |
2018 | ret = futex_wake(uaddr, fshared, val); | |
2019 | break; | |
2020 | case FUTEX_FD: | |
2021 | /* non-zero val means F_SETOWN(getpid()) & F_SETSIG(val) */ | |
2022 | ret = futex_fd(uaddr, val); | |
2023 | break; | |
2024 | case FUTEX_REQUEUE: | |
2025 | ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL); | |
2026 | break; | |
2027 | case FUTEX_CMP_REQUEUE: | |
2028 | ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3); | |
2029 | break; | |
2030 | case FUTEX_WAKE_OP: | |
2031 | ret = futex_wake_op(uaddr, fshared, uaddr2, val, val2, val3); | |
2032 | break; | |
2033 | case FUTEX_LOCK_PI: | |
2034 | ret = futex_lock_pi(uaddr, fshared, val, timeout, 0); | |
2035 | break; | |
2036 | case FUTEX_UNLOCK_PI: | |
2037 | ret = futex_unlock_pi(uaddr, fshared); | |
2038 | break; | |
2039 | case FUTEX_TRYLOCK_PI: | |
2040 | ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1); | |
2041 | break; | |
2042 | default: | |
2043 | ret = -ENOSYS; | |
2044 | } | |
2045 | return ret; | |
2046 | } | |
2047 | ||
2048 | ||
2049 | asmlinkage long sys_futex(u32 __user *uaddr, int op, u32 val, | |
2050 | struct timespec __user *utime, u32 __user *uaddr2, | |
2051 | u32 val3) | |
2052 | { | |
2053 | struct timespec ts; | |
2054 | ktime_t t, *tp = NULL; | |
2055 | u32 val2 = 0; | |
2056 | int cmd = op & FUTEX_CMD_MASK; | |
2057 | ||
2058 | if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI)) { | |
2059 | if (copy_from_user(&ts, utime, sizeof(ts)) != 0) | |
2060 | return -EFAULT; | |
2061 | if (!timespec_valid(&ts)) | |
2062 | return -EINVAL; | |
2063 | ||
2064 | t = timespec_to_ktime(ts); | |
2065 | if (cmd == FUTEX_WAIT) | |
2066 | t = ktime_add(ktime_get(), t); | |
2067 | tp = &t; | |
2068 | } | |
2069 | /* | |
2070 | * requeue parameter in 'utime' if cmd == FUTEX_REQUEUE. | |
2071 | * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP. | |
2072 | */ | |
2073 | if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE || | |
2074 | cmd == FUTEX_WAKE_OP) | |
2075 | val2 = (u32) (unsigned long) utime; | |
2076 | ||
2077 | return do_futex(uaddr, op, val, tp, uaddr2, val2, val3); | |
2078 | } | |
2079 | ||
2080 | static int futexfs_get_sb(struct file_system_type *fs_type, | |
2081 | int flags, const char *dev_name, void *data, | |
2082 | struct vfsmount *mnt) | |
2083 | { | |
2084 | return get_sb_pseudo(fs_type, "futex", NULL, FUTEXFS_SUPER_MAGIC, mnt); | |
2085 | } | |
2086 | ||
2087 | static struct file_system_type futex_fs_type = { | |
2088 | .name = "futexfs", | |
2089 | .get_sb = futexfs_get_sb, | |
2090 | .kill_sb = kill_anon_super, | |
2091 | }; | |
2092 | ||
2093 | static int __init init(void) | |
2094 | { | |
2095 | int i = register_filesystem(&futex_fs_type); | |
2096 | ||
2097 | if (i) | |
2098 | return i; | |
2099 | ||
2100 | futex_mnt = kern_mount(&futex_fs_type); | |
2101 | if (IS_ERR(futex_mnt)) { | |
2102 | unregister_filesystem(&futex_fs_type); | |
2103 | return PTR_ERR(futex_mnt); | |
2104 | } | |
2105 | ||
2106 | for (i = 0; i < ARRAY_SIZE(futex_queues); i++) { | |
2107 | plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock); | |
2108 | spin_lock_init(&futex_queues[i].lock); | |
2109 | } | |
2110 | return 0; | |
2111 | } | |
2112 | __initcall(init); |