Root/
1 | /* |
2 | * Fast Userspace Mutexes (which I call "Futexes!"). |
3 | * (C) Rusty Russell, IBM 2002 |
4 | * |
5 | * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar |
6 | * (C) Copyright 2003 Red Hat Inc, All Rights Reserved |
7 | * |
8 | * Removed page pinning, fix privately mapped COW pages and other cleanups |
9 | * (C) Copyright 2003, 2004 Jamie Lokier |
10 | * |
11 | * Robust futex support started by Ingo Molnar |
12 | * (C) Copyright 2006 Red Hat Inc, All Rights Reserved |
13 | * Thanks to Thomas Gleixner for suggestions, analysis and fixes. |
14 | * |
15 | * PI-futex support started by Ingo Molnar and Thomas Gleixner |
16 | * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> |
17 | * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com> |
18 | * |
19 | * PRIVATE futexes by Eric Dumazet |
20 | * Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com> |
21 | * |
22 | * Requeue-PI support by Darren Hart <dvhltc@us.ibm.com> |
23 | * Copyright (C) IBM Corporation, 2009 |
24 | * Thanks to Thomas Gleixner for conceptual design and careful reviews. |
25 | * |
26 | * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly |
27 | * enough at me, Linus for the original (flawed) idea, Matthew |
28 | * Kirkwood for proof-of-concept implementation. |
29 | * |
30 | * "The futexes are also cursed." |
31 | * "But they come in a choice of three flavours!" |
32 | * |
33 | * This program is free software; you can redistribute it and/or modify |
34 | * it under the terms of the GNU General Public License as published by |
35 | * the Free Software Foundation; either version 2 of the License, or |
36 | * (at your option) any later version. |
37 | * |
38 | * This program is distributed in the hope that it will be useful, |
39 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
40 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
41 | * GNU General Public License for more details. |
42 | * |
43 | * You should have received a copy of the GNU General Public License |
44 | * along with this program; if not, write to the Free Software |
45 | * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA |
46 | */ |
47 | #include <linux/slab.h> |
48 | #include <linux/poll.h> |
49 | #include <linux/fs.h> |
50 | #include <linux/file.h> |
51 | #include <linux/jhash.h> |
52 | #include <linux/init.h> |
53 | #include <linux/futex.h> |
54 | #include <linux/mount.h> |
55 | #include <linux/pagemap.h> |
56 | #include <linux/syscalls.h> |
57 | #include <linux/signal.h> |
58 | #include <linux/export.h> |
59 | #include <linux/magic.h> |
60 | #include <linux/pid.h> |
61 | #include <linux/nsproxy.h> |
62 | #include <linux/ptrace.h> |
63 | #include <linux/sched/rt.h> |
64 | #include <linux/hugetlb.h> |
65 | #include <linux/freezer.h> |
66 | #include <linux/bootmem.h> |
67 | |
68 | #include <asm/futex.h> |
69 | |
70 | #include "locking/rtmutex_common.h" |
71 | |
72 | /* |
73 | * READ this before attempting to hack on futexes! |
74 | * |
75 | * Basic futex operation and ordering guarantees |
76 | * ============================================= |
77 | * |
78 | * The waiter reads the futex value in user space and calls |
79 | * futex_wait(). This function computes the hash bucket and acquires |
80 | * the hash bucket lock. After that it reads the futex user space value |
81 | * again and verifies that the data has not changed. If it has not changed |
82 | * it enqueues itself into the hash bucket, releases the hash bucket lock |
83 | * and schedules. |
84 | * |
85 | * The waker side modifies the user space value of the futex and calls |
86 | * futex_wake(). This function computes the hash bucket and acquires the |
87 | * hash bucket lock. Then it looks for waiters on that futex in the hash |
88 | * bucket and wakes them. |
89 | * |
90 | * In futex wake up scenarios where no tasks are blocked on a futex, taking |
91 | * the hb spinlock can be avoided and simply return. In order for this |
92 | * optimization to work, ordering guarantees must exist so that the waiter |
93 | * being added to the list is acknowledged when the list is concurrently being |
94 | * checked by the waker, avoiding scenarios like the following: |
95 | * |
96 | * CPU 0 CPU 1 |
97 | * val = *futex; |
98 | * sys_futex(WAIT, futex, val); |
99 | * futex_wait(futex, val); |
100 | * uval = *futex; |
101 | * *futex = newval; |
102 | * sys_futex(WAKE, futex); |
103 | * futex_wake(futex); |
104 | * if (queue_empty()) |
105 | * return; |
106 | * if (uval == val) |
107 | * lock(hash_bucket(futex)); |
108 | * queue(); |
109 | * unlock(hash_bucket(futex)); |
110 | * schedule(); |
111 | * |
112 | * This would cause the waiter on CPU 0 to wait forever because it |
113 | * missed the transition of the user space value from val to newval |
114 | * and the waker did not find the waiter in the hash bucket queue. |
115 | * |
116 | * The correct serialization ensures that a waiter either observes |
117 | * the changed user space value before blocking or is woken by a |
118 | * concurrent waker: |
119 | * |
120 | * CPU 0 CPU 1 |
121 | * val = *futex; |
122 | * sys_futex(WAIT, futex, val); |
123 | * futex_wait(futex, val); |
124 | * |
125 | * waiters++; (a) |
126 | * mb(); (A) <-- paired with -. |
127 | * | |
128 | * lock(hash_bucket(futex)); | |
129 | * | |
130 | * uval = *futex; | |
131 | * | *futex = newval; |
132 | * | sys_futex(WAKE, futex); |
133 | * | futex_wake(futex); |
134 | * | |
135 | * `-------> mb(); (B) |
136 | * if (uval == val) |
137 | * queue(); |
138 | * unlock(hash_bucket(futex)); |
139 | * schedule(); if (waiters) |
140 | * lock(hash_bucket(futex)); |
141 | * else wake_waiters(futex); |
142 | * waiters--; (b) unlock(hash_bucket(futex)); |
143 | * |
144 | * Where (A) orders the waiters increment and the futex value read through |
145 | * atomic operations (see hb_waiters_inc) and where (B) orders the write |
146 | * to futex and the waiters read -- this is done by the barriers in |
147 | * get_futex_key_refs(), through either ihold or atomic_inc, depending on the |
148 | * futex type. |
149 | * |
150 | * This yields the following case (where X:=waiters, Y:=futex): |
151 | * |
152 | * X = Y = 0 |
153 | * |
154 | * w[X]=1 w[Y]=1 |
155 | * MB MB |
156 | * r[Y]=y r[X]=x |
157 | * |
158 | * Which guarantees that x==0 && y==0 is impossible; which translates back into |
159 | * the guarantee that we cannot both miss the futex variable change and the |
160 | * enqueue. |
161 | * |
162 | * Note that a new waiter is accounted for in (a) even when it is possible that |
163 | * the wait call can return error, in which case we backtrack from it in (b). |
164 | * Refer to the comment in queue_lock(). |
165 | * |
166 | * Similarly, in order to account for waiters being requeued on another |
167 | * address we always increment the waiters for the destination bucket before |
168 | * acquiring the lock. It then decrements them again after releasing it - |
169 | * the code that actually moves the futex(es) between hash buckets (requeue_futex) |
170 | * will do the additional required waiter count housekeeping. This is done for |
171 | * double_lock_hb() and double_unlock_hb(), respectively. |
172 | */ |
173 | |
174 | #ifndef CONFIG_HAVE_FUTEX_CMPXCHG |
175 | int __read_mostly futex_cmpxchg_enabled; |
176 | #endif |
177 | |
178 | /* |
179 | * Futex flags used to encode options to functions and preserve them across |
180 | * restarts. |
181 | */ |
182 | #define FLAGS_SHARED 0x01 |
183 | #define FLAGS_CLOCKRT 0x02 |
184 | #define FLAGS_HAS_TIMEOUT 0x04 |
185 | |
186 | /* |
187 | * Priority Inheritance state: |
188 | */ |
189 | struct futex_pi_state { |
190 | /* |
191 | * list of 'owned' pi_state instances - these have to be |
192 | * cleaned up in do_exit() if the task exits prematurely: |
193 | */ |
194 | struct list_head list; |
195 | |
196 | /* |
197 | * The PI object: |
198 | */ |
199 | struct rt_mutex pi_mutex; |
200 | |
201 | struct task_struct *owner; |
202 | atomic_t refcount; |
203 | |
204 | union futex_key key; |
205 | }; |
206 | |
207 | /** |
208 | * struct futex_q - The hashed futex queue entry, one per waiting task |
209 | * @list: priority-sorted list of tasks waiting on this futex |
210 | * @task: the task waiting on the futex |
211 | * @lock_ptr: the hash bucket lock |
212 | * @key: the key the futex is hashed on |
213 | * @pi_state: optional priority inheritance state |
214 | * @rt_waiter: rt_waiter storage for use with requeue_pi |
215 | * @requeue_pi_key: the requeue_pi target futex key |
216 | * @bitset: bitset for the optional bitmasked wakeup |
217 | * |
218 | * We use this hashed waitqueue, instead of a normal wait_queue_t, so |
219 | * we can wake only the relevant ones (hashed queues may be shared). |
220 | * |
221 | * A futex_q has a woken state, just like tasks have TASK_RUNNING. |
222 | * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0. |
223 | * The order of wakeup is always to make the first condition true, then |
224 | * the second. |
225 | * |
226 | * PI futexes are typically woken before they are removed from the hash list via |
227 | * the rt_mutex code. See unqueue_me_pi(). |
228 | */ |
229 | struct futex_q { |
230 | struct plist_node list; |
231 | |
232 | struct task_struct *task; |
233 | spinlock_t *lock_ptr; |
234 | union futex_key key; |
235 | struct futex_pi_state *pi_state; |
236 | struct rt_mutex_waiter *rt_waiter; |
237 | union futex_key *requeue_pi_key; |
238 | u32 bitset; |
239 | }; |
240 | |
241 | static const struct futex_q futex_q_init = { |
242 | /* list gets initialized in queue_me()*/ |
243 | .key = FUTEX_KEY_INIT, |
244 | .bitset = FUTEX_BITSET_MATCH_ANY |
245 | }; |
246 | |
247 | /* |
248 | * Hash buckets are shared by all the futex_keys that hash to the same |
249 | * location. Each key may have multiple futex_q structures, one for each task |
250 | * waiting on a futex. |
251 | */ |
252 | struct futex_hash_bucket { |
253 | atomic_t waiters; |
254 | spinlock_t lock; |
255 | struct plist_head chain; |
256 | } ____cacheline_aligned_in_smp; |
257 | |
258 | static unsigned long __read_mostly futex_hashsize; |
259 | |
260 | static struct futex_hash_bucket *futex_queues; |
261 | |
262 | static inline void futex_get_mm(union futex_key *key) |
263 | { |
264 | atomic_inc(&key->private.mm->mm_count); |
265 | /* |
266 | * Ensure futex_get_mm() implies a full barrier such that |
267 | * get_futex_key() implies a full barrier. This is relied upon |
268 | * as full barrier (B), see the ordering comment above. |
269 | */ |
270 | smp_mb__after_atomic_inc(); |
271 | } |
272 | |
273 | /* |
274 | * Reflects a new waiter being added to the waitqueue. |
275 | */ |
276 | static inline void hb_waiters_inc(struct futex_hash_bucket *hb) |
277 | { |
278 | #ifdef CONFIG_SMP |
279 | atomic_inc(&hb->waiters); |
280 | /* |
281 | * Full barrier (A), see the ordering comment above. |
282 | */ |
283 | smp_mb__after_atomic_inc(); |
284 | #endif |
285 | } |
286 | |
287 | /* |
288 | * Reflects a waiter being removed from the waitqueue by wakeup |
289 | * paths. |
290 | */ |
291 | static inline void hb_waiters_dec(struct futex_hash_bucket *hb) |
292 | { |
293 | #ifdef CONFIG_SMP |
294 | atomic_dec(&hb->waiters); |
295 | #endif |
296 | } |
297 | |
298 | static inline int hb_waiters_pending(struct futex_hash_bucket *hb) |
299 | { |
300 | #ifdef CONFIG_SMP |
301 | return atomic_read(&hb->waiters); |
302 | #else |
303 | return 1; |
304 | #endif |
305 | } |
306 | |
307 | /* |
308 | * We hash on the keys returned from get_futex_key (see below). |
309 | */ |
310 | static struct futex_hash_bucket *hash_futex(union futex_key *key) |
311 | { |
312 | u32 hash = jhash2((u32*)&key->both.word, |
313 | (sizeof(key->both.word)+sizeof(key->both.ptr))/4, |
314 | key->both.offset); |
315 | return &futex_queues[hash & (futex_hashsize - 1)]; |
316 | } |
317 | |
318 | /* |
319 | * Return 1 if two futex_keys are equal, 0 otherwise. |
320 | */ |
321 | static inline int match_futex(union futex_key *key1, union futex_key *key2) |
322 | { |
323 | return (key1 && key2 |
324 | && key1->both.word == key2->both.word |
325 | && key1->both.ptr == key2->both.ptr |
326 | && key1->both.offset == key2->both.offset); |
327 | } |
328 | |
329 | /* |
330 | * Take a reference to the resource addressed by a key. |
331 | * Can be called while holding spinlocks. |
332 | * |
333 | */ |
334 | static void get_futex_key_refs(union futex_key *key) |
335 | { |
336 | if (!key->both.ptr) |
337 | return; |
338 | |
339 | switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) { |
340 | case FUT_OFF_INODE: |
341 | ihold(key->shared.inode); /* implies MB (B) */ |
342 | break; |
343 | case FUT_OFF_MMSHARED: |
344 | futex_get_mm(key); /* implies MB (B) */ |
345 | break; |
346 | } |
347 | } |
348 | |
349 | /* |
350 | * Drop a reference to the resource addressed by a key. |
351 | * The hash bucket spinlock must not be held. |
352 | */ |
353 | static void drop_futex_key_refs(union futex_key *key) |
354 | { |
355 | if (!key->both.ptr) { |
356 | /* If we're here then we tried to put a key we failed to get */ |
357 | WARN_ON_ONCE(1); |
358 | return; |
359 | } |
360 | |
361 | switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) { |
362 | case FUT_OFF_INODE: |
363 | iput(key->shared.inode); |
364 | break; |
365 | case FUT_OFF_MMSHARED: |
366 | mmdrop(key->private.mm); |
367 | break; |
368 | } |
369 | } |
370 | |
371 | /** |
372 | * get_futex_key() - Get parameters which are the keys for a futex |
373 | * @uaddr: virtual address of the futex |
374 | * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED |
375 | * @key: address where result is stored. |
376 | * @rw: mapping needs to be read/write (values: VERIFY_READ, |
377 | * VERIFY_WRITE) |
378 | * |
379 | * Return: a negative error code or 0 |
380 | * |
381 | * The key words are stored in *key on success. |
382 | * |
383 | * For shared mappings, it's (page->index, file_inode(vma->vm_file), |
384 | * offset_within_page). For private mappings, it's (uaddr, current->mm). |
385 | * We can usually work out the index without swapping in the page. |
386 | * |
387 | * lock_page() might sleep, the caller should not hold a spinlock. |
388 | */ |
389 | static int |
390 | get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw) |
391 | { |
392 | unsigned long address = (unsigned long)uaddr; |
393 | struct mm_struct *mm = current->mm; |
394 | struct page *page, *page_head; |
395 | int err, ro = 0; |
396 | |
397 | /* |
398 | * The futex address must be "naturally" aligned. |
399 | */ |
400 | key->both.offset = address % PAGE_SIZE; |
401 | if (unlikely((address % sizeof(u32)) != 0)) |
402 | return -EINVAL; |
403 | address -= key->both.offset; |
404 | |
405 | if (unlikely(!access_ok(rw, uaddr, sizeof(u32)))) |
406 | return -EFAULT; |
407 | |
408 | /* |
409 | * PROCESS_PRIVATE futexes are fast. |
410 | * As the mm cannot disappear under us and the 'key' only needs |
411 | * virtual address, we dont even have to find the underlying vma. |
412 | * Note : We do have to check 'uaddr' is a valid user address, |
413 | * but access_ok() should be faster than find_vma() |
414 | */ |
415 | if (!fshared) { |
416 | key->private.mm = mm; |
417 | key->private.address = address; |
418 | get_futex_key_refs(key); /* implies MB (B) */ |
419 | return 0; |
420 | } |
421 | |
422 | again: |
423 | err = get_user_pages_fast(address, 1, 1, &page); |
424 | /* |
425 | * If write access is not required (eg. FUTEX_WAIT), try |
426 | * and get read-only access. |
427 | */ |
428 | if (err == -EFAULT && rw == VERIFY_READ) { |
429 | err = get_user_pages_fast(address, 1, 0, &page); |
430 | ro = 1; |
431 | } |
432 | if (err < 0) |
433 | return err; |
434 | else |
435 | err = 0; |
436 | |
437 | #ifdef CONFIG_TRANSPARENT_HUGEPAGE |
438 | page_head = page; |
439 | if (unlikely(PageTail(page))) { |
440 | put_page(page); |
441 | /* serialize against __split_huge_page_splitting() */ |
442 | local_irq_disable(); |
443 | if (likely(__get_user_pages_fast(address, 1, !ro, &page) == 1)) { |
444 | page_head = compound_head(page); |
445 | /* |
446 | * page_head is valid pointer but we must pin |
447 | * it before taking the PG_lock and/or |
448 | * PG_compound_lock. The moment we re-enable |
449 | * irqs __split_huge_page_splitting() can |
450 | * return and the head page can be freed from |
451 | * under us. We can't take the PG_lock and/or |
452 | * PG_compound_lock on a page that could be |
453 | * freed from under us. |
454 | */ |
455 | if (page != page_head) { |
456 | get_page(page_head); |
457 | put_page(page); |
458 | } |
459 | local_irq_enable(); |
460 | } else { |
461 | local_irq_enable(); |
462 | goto again; |
463 | } |
464 | } |
465 | #else |
466 | page_head = compound_head(page); |
467 | if (page != page_head) { |
468 | get_page(page_head); |
469 | put_page(page); |
470 | } |
471 | #endif |
472 | |
473 | lock_page(page_head); |
474 | |
475 | /* |
476 | * If page_head->mapping is NULL, then it cannot be a PageAnon |
477 | * page; but it might be the ZERO_PAGE or in the gate area or |
478 | * in a special mapping (all cases which we are happy to fail); |
479 | * or it may have been a good file page when get_user_pages_fast |
480 | * found it, but truncated or holepunched or subjected to |
481 | * invalidate_complete_page2 before we got the page lock (also |
482 | * cases which we are happy to fail). And we hold a reference, |
483 | * so refcount care in invalidate_complete_page's remove_mapping |
484 | * prevents drop_caches from setting mapping to NULL beneath us. |
485 | * |
486 | * The case we do have to guard against is when memory pressure made |
487 | * shmem_writepage move it from filecache to swapcache beneath us: |
488 | * an unlikely race, but we do need to retry for page_head->mapping. |
489 | */ |
490 | if (!page_head->mapping) { |
491 | int shmem_swizzled = PageSwapCache(page_head); |
492 | unlock_page(page_head); |
493 | put_page(page_head); |
494 | if (shmem_swizzled) |
495 | goto again; |
496 | return -EFAULT; |
497 | } |
498 | |
499 | /* |
500 | * Private mappings are handled in a simple way. |
501 | * |
502 | * NOTE: When userspace waits on a MAP_SHARED mapping, even if |
503 | * it's a read-only handle, it's expected that futexes attach to |
504 | * the object not the particular process. |
505 | */ |
506 | if (PageAnon(page_head)) { |
507 | /* |
508 | * A RO anonymous page will never change and thus doesn't make |
509 | * sense for futex operations. |
510 | */ |
511 | if (ro) { |
512 | err = -EFAULT; |
513 | goto out; |
514 | } |
515 | |
516 | key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */ |
517 | key->private.mm = mm; |
518 | key->private.address = address; |
519 | } else { |
520 | key->both.offset |= FUT_OFF_INODE; /* inode-based key */ |
521 | key->shared.inode = page_head->mapping->host; |
522 | key->shared.pgoff = basepage_index(page); |
523 | } |
524 | |
525 | get_futex_key_refs(key); /* implies MB (B) */ |
526 | |
527 | out: |
528 | unlock_page(page_head); |
529 | put_page(page_head); |
530 | return err; |
531 | } |
532 | |
533 | static inline void put_futex_key(union futex_key *key) |
534 | { |
535 | drop_futex_key_refs(key); |
536 | } |
537 | |
538 | /** |
539 | * fault_in_user_writeable() - Fault in user address and verify RW access |
540 | * @uaddr: pointer to faulting user space address |
541 | * |
542 | * Slow path to fixup the fault we just took in the atomic write |
543 | * access to @uaddr. |
544 | * |
545 | * We have no generic implementation of a non-destructive write to the |
546 | * user address. We know that we faulted in the atomic pagefault |
547 | * disabled section so we can as well avoid the #PF overhead by |
548 | * calling get_user_pages() right away. |
549 | */ |
550 | static int fault_in_user_writeable(u32 __user *uaddr) |
551 | { |
552 | struct mm_struct *mm = current->mm; |
553 | int ret; |
554 | |
555 | down_read(&mm->mmap_sem); |
556 | ret = fixup_user_fault(current, mm, (unsigned long)uaddr, |
557 | FAULT_FLAG_WRITE); |
558 | up_read(&mm->mmap_sem); |
559 | |
560 | return ret < 0 ? ret : 0; |
561 | } |
562 | |
563 | /** |
564 | * futex_top_waiter() - Return the highest priority waiter on a futex |
565 | * @hb: the hash bucket the futex_q's reside in |
566 | * @key: the futex key (to distinguish it from other futex futex_q's) |
567 | * |
568 | * Must be called with the hb lock held. |
569 | */ |
570 | static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb, |
571 | union futex_key *key) |
572 | { |
573 | struct futex_q *this; |
574 | |
575 | plist_for_each_entry(this, &hb->chain, list) { |
576 | if (match_futex(&this->key, key)) |
577 | return this; |
578 | } |
579 | return NULL; |
580 | } |
581 | |
582 | static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr, |
583 | u32 uval, u32 newval) |
584 | { |
585 | int ret; |
586 | |
587 | pagefault_disable(); |
588 | ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval); |
589 | pagefault_enable(); |
590 | |
591 | return ret; |
592 | } |
593 | |
594 | static int get_futex_value_locked(u32 *dest, u32 __user *from) |
595 | { |
596 | int ret; |
597 | |
598 | pagefault_disable(); |
599 | ret = __copy_from_user_inatomic(dest, from, sizeof(u32)); |
600 | pagefault_enable(); |
601 | |
602 | return ret ? -EFAULT : 0; |
603 | } |
604 | |
605 | |
606 | /* |
607 | * PI code: |
608 | */ |
609 | static int refill_pi_state_cache(void) |
610 | { |
611 | struct futex_pi_state *pi_state; |
612 | |
613 | if (likely(current->pi_state_cache)) |
614 | return 0; |
615 | |
616 | pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL); |
617 | |
618 | if (!pi_state) |
619 | return -ENOMEM; |
620 | |
621 | INIT_LIST_HEAD(&pi_state->list); |
622 | /* pi_mutex gets initialized later */ |
623 | pi_state->owner = NULL; |
624 | atomic_set(&pi_state->refcount, 1); |
625 | pi_state->key = FUTEX_KEY_INIT; |
626 | |
627 | current->pi_state_cache = pi_state; |
628 | |
629 | return 0; |
630 | } |
631 | |
632 | static struct futex_pi_state * alloc_pi_state(void) |
633 | { |
634 | struct futex_pi_state *pi_state = current->pi_state_cache; |
635 | |
636 | WARN_ON(!pi_state); |
637 | current->pi_state_cache = NULL; |
638 | |
639 | return pi_state; |
640 | } |
641 | |
642 | static void free_pi_state(struct futex_pi_state *pi_state) |
643 | { |
644 | if (!atomic_dec_and_test(&pi_state->refcount)) |
645 | return; |
646 | |
647 | /* |
648 | * If pi_state->owner is NULL, the owner is most probably dying |
649 | * and has cleaned up the pi_state already |
650 | */ |
651 | if (pi_state->owner) { |
652 | raw_spin_lock_irq(&pi_state->owner->pi_lock); |
653 | list_del_init(&pi_state->list); |
654 | raw_spin_unlock_irq(&pi_state->owner->pi_lock); |
655 | |
656 | rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner); |
657 | } |
658 | |
659 | if (current->pi_state_cache) |
660 | kfree(pi_state); |
661 | else { |
662 | /* |
663 | * pi_state->list is already empty. |
664 | * clear pi_state->owner. |
665 | * refcount is at 0 - put it back to 1. |
666 | */ |
667 | pi_state->owner = NULL; |
668 | atomic_set(&pi_state->refcount, 1); |
669 | current->pi_state_cache = pi_state; |
670 | } |
671 | } |
672 | |
673 | /* |
674 | * Look up the task based on what TID userspace gave us. |
675 | * We dont trust it. |
676 | */ |
677 | static struct task_struct * futex_find_get_task(pid_t pid) |
678 | { |
679 | struct task_struct *p; |
680 | |
681 | rcu_read_lock(); |
682 | p = find_task_by_vpid(pid); |
683 | if (p) |
684 | get_task_struct(p); |
685 | |
686 | rcu_read_unlock(); |
687 | |
688 | return p; |
689 | } |
690 | |
691 | /* |
692 | * This task is holding PI mutexes at exit time => bad. |
693 | * Kernel cleans up PI-state, but userspace is likely hosed. |
694 | * (Robust-futex cleanup is separate and might save the day for userspace.) |
695 | */ |
696 | void exit_pi_state_list(struct task_struct *curr) |
697 | { |
698 | struct list_head *next, *head = &curr->pi_state_list; |
699 | struct futex_pi_state *pi_state; |
700 | struct futex_hash_bucket *hb; |
701 | union futex_key key = FUTEX_KEY_INIT; |
702 | |
703 | if (!futex_cmpxchg_enabled) |
704 | return; |
705 | /* |
706 | * We are a ZOMBIE and nobody can enqueue itself on |
707 | * pi_state_list anymore, but we have to be careful |
708 | * versus waiters unqueueing themselves: |
709 | */ |
710 | raw_spin_lock_irq(&curr->pi_lock); |
711 | while (!list_empty(head)) { |
712 | |
713 | next = head->next; |
714 | pi_state = list_entry(next, struct futex_pi_state, list); |
715 | key = pi_state->key; |
716 | hb = hash_futex(&key); |
717 | raw_spin_unlock_irq(&curr->pi_lock); |
718 | |
719 | spin_lock(&hb->lock); |
720 | |
721 | raw_spin_lock_irq(&curr->pi_lock); |
722 | /* |
723 | * We dropped the pi-lock, so re-check whether this |
724 | * task still owns the PI-state: |
725 | */ |
726 | if (head->next != next) { |
727 | spin_unlock(&hb->lock); |
728 | continue; |
729 | } |
730 | |
731 | WARN_ON(pi_state->owner != curr); |
732 | WARN_ON(list_empty(&pi_state->list)); |
733 | list_del_init(&pi_state->list); |
734 | pi_state->owner = NULL; |
735 | raw_spin_unlock_irq(&curr->pi_lock); |
736 | |
737 | rt_mutex_unlock(&pi_state->pi_mutex); |
738 | |
739 | spin_unlock(&hb->lock); |
740 | |
741 | raw_spin_lock_irq(&curr->pi_lock); |
742 | } |
743 | raw_spin_unlock_irq(&curr->pi_lock); |
744 | } |
745 | |
746 | /* |
747 | * We need to check the following states: |
748 | * |
749 | * Waiter | pi_state | pi->owner | uTID | uODIED | ? |
750 | * |
751 | * [1] NULL | --- | --- | 0 | 0/1 | Valid |
752 | * [2] NULL | --- | --- | >0 | 0/1 | Valid |
753 | * |
754 | * [3] Found | NULL | -- | Any | 0/1 | Invalid |
755 | * |
756 | * [4] Found | Found | NULL | 0 | 1 | Valid |
757 | * [5] Found | Found | NULL | >0 | 1 | Invalid |
758 | * |
759 | * [6] Found | Found | task | 0 | 1 | Valid |
760 | * |
761 | * [7] Found | Found | NULL | Any | 0 | Invalid |
762 | * |
763 | * [8] Found | Found | task | ==taskTID | 0/1 | Valid |
764 | * [9] Found | Found | task | 0 | 0 | Invalid |
765 | * [10] Found | Found | task | !=taskTID | 0/1 | Invalid |
766 | * |
767 | * [1] Indicates that the kernel can acquire the futex atomically. We |
768 | * came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit. |
769 | * |
770 | * [2] Valid, if TID does not belong to a kernel thread. If no matching |
771 | * thread is found then it indicates that the owner TID has died. |
772 | * |
773 | * [3] Invalid. The waiter is queued on a non PI futex |
774 | * |
775 | * [4] Valid state after exit_robust_list(), which sets the user space |
776 | * value to FUTEX_WAITERS | FUTEX_OWNER_DIED. |
777 | * |
778 | * [5] The user space value got manipulated between exit_robust_list() |
779 | * and exit_pi_state_list() |
780 | * |
781 | * [6] Valid state after exit_pi_state_list() which sets the new owner in |
782 | * the pi_state but cannot access the user space value. |
783 | * |
784 | * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set. |
785 | * |
786 | * [8] Owner and user space value match |
787 | * |
788 | * [9] There is no transient state which sets the user space TID to 0 |
789 | * except exit_robust_list(), but this is indicated by the |
790 | * FUTEX_OWNER_DIED bit. See [4] |
791 | * |
792 | * [10] There is no transient state which leaves owner and user space |
793 | * TID out of sync. |
794 | */ |
795 | static int |
796 | lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, |
797 | union futex_key *key, struct futex_pi_state **ps) |
798 | { |
799 | struct futex_pi_state *pi_state = NULL; |
800 | struct futex_q *this, *next; |
801 | struct task_struct *p; |
802 | pid_t pid = uval & FUTEX_TID_MASK; |
803 | |
804 | plist_for_each_entry_safe(this, next, &hb->chain, list) { |
805 | if (match_futex(&this->key, key)) { |
806 | /* |
807 | * Sanity check the waiter before increasing |
808 | * the refcount and attaching to it. |
809 | */ |
810 | pi_state = this->pi_state; |
811 | /* |
812 | * Userspace might have messed up non-PI and |
813 | * PI futexes [3] |
814 | */ |
815 | if (unlikely(!pi_state)) |
816 | return -EINVAL; |
817 | |
818 | WARN_ON(!atomic_read(&pi_state->refcount)); |
819 | |
820 | /* |
821 | * Handle the owner died case: |
822 | */ |
823 | if (uval & FUTEX_OWNER_DIED) { |
824 | /* |
825 | * exit_pi_state_list sets owner to NULL and |
826 | * wakes the topmost waiter. The task which |
827 | * acquires the pi_state->rt_mutex will fixup |
828 | * owner. |
829 | */ |
830 | if (!pi_state->owner) { |
831 | /* |
832 | * No pi state owner, but the user |
833 | * space TID is not 0. Inconsistent |
834 | * state. [5] |
835 | */ |
836 | if (pid) |
837 | return -EINVAL; |
838 | /* |
839 | * Take a ref on the state and |
840 | * return. [4] |
841 | */ |
842 | goto out_state; |
843 | } |
844 | |
845 | /* |
846 | * If TID is 0, then either the dying owner |
847 | * has not yet executed exit_pi_state_list() |
848 | * or some waiter acquired the rtmutex in the |
849 | * pi state, but did not yet fixup the TID in |
850 | * user space. |
851 | * |
852 | * Take a ref on the state and return. [6] |
853 | */ |
854 | if (!pid) |
855 | goto out_state; |
856 | } else { |
857 | /* |
858 | * If the owner died bit is not set, |
859 | * then the pi_state must have an |
860 | * owner. [7] |
861 | */ |
862 | if (!pi_state->owner) |
863 | return -EINVAL; |
864 | } |
865 | |
866 | /* |
867 | * Bail out if user space manipulated the |
868 | * futex value. If pi state exists then the |
869 | * owner TID must be the same as the user |
870 | * space TID. [9/10] |
871 | */ |
872 | if (pid != task_pid_vnr(pi_state->owner)) |
873 | return -EINVAL; |
874 | |
875 | out_state: |
876 | atomic_inc(&pi_state->refcount); |
877 | *ps = pi_state; |
878 | return 0; |
879 | } |
880 | } |
881 | |
882 | /* |
883 | * We are the first waiter - try to look up the real owner and attach |
884 | * the new pi_state to it, but bail out when TID = 0 [1] |
885 | */ |
886 | if (!pid) |
887 | return -ESRCH; |
888 | p = futex_find_get_task(pid); |
889 | if (!p) |
890 | return -ESRCH; |
891 | |
892 | if (!p->mm) { |
893 | put_task_struct(p); |
894 | return -EPERM; |
895 | } |
896 | |
897 | /* |
898 | * We need to look at the task state flags to figure out, |
899 | * whether the task is exiting. To protect against the do_exit |
900 | * change of the task flags, we do this protected by |
901 | * p->pi_lock: |
902 | */ |
903 | raw_spin_lock_irq(&p->pi_lock); |
904 | if (unlikely(p->flags & PF_EXITING)) { |
905 | /* |
906 | * The task is on the way out. When PF_EXITPIDONE is |
907 | * set, we know that the task has finished the |
908 | * cleanup: |
909 | */ |
910 | int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN; |
911 | |
912 | raw_spin_unlock_irq(&p->pi_lock); |
913 | put_task_struct(p); |
914 | return ret; |
915 | } |
916 | |
917 | /* |
918 | * No existing pi state. First waiter. [2] |
919 | */ |
920 | pi_state = alloc_pi_state(); |
921 | |
922 | /* |
923 | * Initialize the pi_mutex in locked state and make 'p' |
924 | * the owner of it: |
925 | */ |
926 | rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p); |
927 | |
928 | /* Store the key for possible exit cleanups: */ |
929 | pi_state->key = *key; |
930 | |
931 | WARN_ON(!list_empty(&pi_state->list)); |
932 | list_add(&pi_state->list, &p->pi_state_list); |
933 | pi_state->owner = p; |
934 | raw_spin_unlock_irq(&p->pi_lock); |
935 | |
936 | put_task_struct(p); |
937 | |
938 | *ps = pi_state; |
939 | |
940 | return 0; |
941 | } |
942 | |
943 | /** |
944 | * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex |
945 | * @uaddr: the pi futex user address |
946 | * @hb: the pi futex hash bucket |
947 | * @key: the futex key associated with uaddr and hb |
948 | * @ps: the pi_state pointer where we store the result of the |
949 | * lookup |
950 | * @task: the task to perform the atomic lock work for. This will |
951 | * be "current" except in the case of requeue pi. |
952 | * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) |
953 | * |
954 | * Return: |
955 | * 0 - ready to wait; |
956 | * 1 - acquired the lock; |
957 | * <0 - error |
958 | * |
959 | * The hb->lock and futex_key refs shall be held by the caller. |
960 | */ |
961 | static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb, |
962 | union futex_key *key, |
963 | struct futex_pi_state **ps, |
964 | struct task_struct *task, int set_waiters) |
965 | { |
966 | int lock_taken, ret, force_take = 0; |
967 | u32 uval, newval, curval, vpid = task_pid_vnr(task); |
968 | |
969 | retry: |
970 | ret = lock_taken = 0; |
971 | |
972 | /* |
973 | * To avoid races, we attempt to take the lock here again |
974 | * (by doing a 0 -> TID atomic cmpxchg), while holding all |
975 | * the locks. It will most likely not succeed. |
976 | */ |
977 | newval = vpid; |
978 | if (set_waiters) |
979 | newval |= FUTEX_WAITERS; |
980 | |
981 | if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval))) |
982 | return -EFAULT; |
983 | |
984 | /* |
985 | * Detect deadlocks. |
986 | */ |
987 | if ((unlikely((curval & FUTEX_TID_MASK) == vpid))) |
988 | return -EDEADLK; |
989 | |
990 | /* |
991 | * Surprise - we got the lock, but we do not trust user space at all. |
992 | */ |
993 | if (unlikely(!curval)) { |
994 | /* |
995 | * We verify whether there is kernel state for this |
996 | * futex. If not, we can safely assume, that the 0 -> |
997 | * TID transition is correct. If state exists, we do |
998 | * not bother to fixup the user space state as it was |
999 | * corrupted already. |
1000 | */ |
1001 | return futex_top_waiter(hb, key) ? -EINVAL : 1; |
1002 | } |
1003 | |
1004 | uval = curval; |
1005 | |
1006 | /* |
1007 | * Set the FUTEX_WAITERS flag, so the owner will know it has someone |
1008 | * to wake at the next unlock. |
1009 | */ |
1010 | newval = curval | FUTEX_WAITERS; |
1011 | |
1012 | /* |
1013 | * Should we force take the futex? See below. |
1014 | */ |
1015 | if (unlikely(force_take)) { |
1016 | /* |
1017 | * Keep the OWNER_DIED and the WAITERS bit and set the |
1018 | * new TID value. |
1019 | */ |
1020 | newval = (curval & ~FUTEX_TID_MASK) | vpid; |
1021 | force_take = 0; |
1022 | lock_taken = 1; |
1023 | } |
1024 | |
1025 | if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))) |
1026 | return -EFAULT; |
1027 | if (unlikely(curval != uval)) |
1028 | goto retry; |
1029 | |
1030 | /* |
1031 | * We took the lock due to forced take over. |
1032 | */ |
1033 | if (unlikely(lock_taken)) |
1034 | return 1; |
1035 | |
1036 | /* |
1037 | * We dont have the lock. Look up the PI state (or create it if |
1038 | * we are the first waiter): |
1039 | */ |
1040 | ret = lookup_pi_state(uval, hb, key, ps); |
1041 | |
1042 | if (unlikely(ret)) { |
1043 | switch (ret) { |
1044 | case -ESRCH: |
1045 | /* |
1046 | * We failed to find an owner for this |
1047 | * futex. So we have no pi_state to block |
1048 | * on. This can happen in two cases: |
1049 | * |
1050 | * 1) The owner died |
1051 | * 2) A stale FUTEX_WAITERS bit |
1052 | * |
1053 | * Re-read the futex value. |
1054 | */ |
1055 | if (get_futex_value_locked(&curval, uaddr)) |
1056 | return -EFAULT; |
1057 | |
1058 | /* |
1059 | * If the owner died or we have a stale |
1060 | * WAITERS bit the owner TID in the user space |
1061 | * futex is 0. |
1062 | */ |
1063 | if (!(curval & FUTEX_TID_MASK)) { |
1064 | force_take = 1; |
1065 | goto retry; |
1066 | } |
1067 | default: |
1068 | break; |
1069 | } |
1070 | } |
1071 | |
1072 | return ret; |
1073 | } |
1074 | |
1075 | /** |
1076 | * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket |
1077 | * @q: The futex_q to unqueue |
1078 | * |
1079 | * The q->lock_ptr must not be NULL and must be held by the caller. |
1080 | */ |
1081 | static void __unqueue_futex(struct futex_q *q) |
1082 | { |
1083 | struct futex_hash_bucket *hb; |
1084 | |
1085 | if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr)) |
1086 | || WARN_ON(plist_node_empty(&q->list))) |
1087 | return; |
1088 | |
1089 | hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock); |
1090 | plist_del(&q->list, &hb->chain); |
1091 | hb_waiters_dec(hb); |
1092 | } |
1093 | |
1094 | /* |
1095 | * The hash bucket lock must be held when this is called. |
1096 | * Afterwards, the futex_q must not be accessed. |
1097 | */ |
1098 | static void wake_futex(struct futex_q *q) |
1099 | { |
1100 | struct task_struct *p = q->task; |
1101 | |
1102 | if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n")) |
1103 | return; |
1104 | |
1105 | /* |
1106 | * We set q->lock_ptr = NULL _before_ we wake up the task. If |
1107 | * a non-futex wake up happens on another CPU then the task |
1108 | * might exit and p would dereference a non-existing task |
1109 | * struct. Prevent this by holding a reference on p across the |
1110 | * wake up. |
1111 | */ |
1112 | get_task_struct(p); |
1113 | |
1114 | __unqueue_futex(q); |
1115 | /* |
1116 | * The waiting task can free the futex_q as soon as |
1117 | * q->lock_ptr = NULL is written, without taking any locks. A |
1118 | * memory barrier is required here to prevent the following |
1119 | * store to lock_ptr from getting ahead of the plist_del. |
1120 | */ |
1121 | smp_wmb(); |
1122 | q->lock_ptr = NULL; |
1123 | |
1124 | wake_up_state(p, TASK_NORMAL); |
1125 | put_task_struct(p); |
1126 | } |
1127 | |
1128 | static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this) |
1129 | { |
1130 | struct task_struct *new_owner; |
1131 | struct futex_pi_state *pi_state = this->pi_state; |
1132 | u32 uninitialized_var(curval), newval; |
1133 | int ret = 0; |
1134 | |
1135 | if (!pi_state) |
1136 | return -EINVAL; |
1137 | |
1138 | /* |
1139 | * If current does not own the pi_state then the futex is |
1140 | * inconsistent and user space fiddled with the futex value. |
1141 | */ |
1142 | if (pi_state->owner != current) |
1143 | return -EINVAL; |
1144 | |
1145 | raw_spin_lock(&pi_state->pi_mutex.wait_lock); |
1146 | new_owner = rt_mutex_next_owner(&pi_state->pi_mutex); |
1147 | |
1148 | /* |
1149 | * It is possible that the next waiter (the one that brought |
1150 | * this owner to the kernel) timed out and is no longer |
1151 | * waiting on the lock. |
1152 | */ |
1153 | if (!new_owner) |
1154 | new_owner = this->task; |
1155 | |
1156 | /* |
1157 | * We pass it to the next owner. The WAITERS bit is always |
1158 | * kept enabled while there is PI state around. We cleanup the |
1159 | * owner died bit, because we are the owner. |
1160 | */ |
1161 | newval = FUTEX_WAITERS | task_pid_vnr(new_owner); |
1162 | |
1163 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) |
1164 | ret = -EFAULT; |
1165 | else if (curval != uval) |
1166 | ret = -EINVAL; |
1167 | if (ret) { |
1168 | raw_spin_unlock(&pi_state->pi_mutex.wait_lock); |
1169 | return ret; |
1170 | } |
1171 | |
1172 | raw_spin_lock_irq(&pi_state->owner->pi_lock); |
1173 | WARN_ON(list_empty(&pi_state->list)); |
1174 | list_del_init(&pi_state->list); |
1175 | raw_spin_unlock_irq(&pi_state->owner->pi_lock); |
1176 | |
1177 | raw_spin_lock_irq(&new_owner->pi_lock); |
1178 | WARN_ON(!list_empty(&pi_state->list)); |
1179 | list_add(&pi_state->list, &new_owner->pi_state_list); |
1180 | pi_state->owner = new_owner; |
1181 | raw_spin_unlock_irq(&new_owner->pi_lock); |
1182 | |
1183 | raw_spin_unlock(&pi_state->pi_mutex.wait_lock); |
1184 | rt_mutex_unlock(&pi_state->pi_mutex); |
1185 | |
1186 | return 0; |
1187 | } |
1188 | |
1189 | static int unlock_futex_pi(u32 __user *uaddr, u32 uval) |
1190 | { |
1191 | u32 uninitialized_var(oldval); |
1192 | |
1193 | /* |
1194 | * There is no waiter, so we unlock the futex. The owner died |
1195 | * bit has not to be preserved here. We are the owner: |
1196 | */ |
1197 | if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0)) |
1198 | return -EFAULT; |
1199 | if (oldval != uval) |
1200 | return -EAGAIN; |
1201 | |
1202 | return 0; |
1203 | } |
1204 | |
1205 | /* |
1206 | * Express the locking dependencies for lockdep: |
1207 | */ |
1208 | static inline void |
1209 | double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) |
1210 | { |
1211 | if (hb1 <= hb2) { |
1212 | spin_lock(&hb1->lock); |
1213 | if (hb1 < hb2) |
1214 | spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING); |
1215 | } else { /* hb1 > hb2 */ |
1216 | spin_lock(&hb2->lock); |
1217 | spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING); |
1218 | } |
1219 | } |
1220 | |
1221 | static inline void |
1222 | double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) |
1223 | { |
1224 | spin_unlock(&hb1->lock); |
1225 | if (hb1 != hb2) |
1226 | spin_unlock(&hb2->lock); |
1227 | } |
1228 | |
1229 | /* |
1230 | * Wake up waiters matching bitset queued on this futex (uaddr). |
1231 | */ |
1232 | static int |
1233 | futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset) |
1234 | { |
1235 | struct futex_hash_bucket *hb; |
1236 | struct futex_q *this, *next; |
1237 | union futex_key key = FUTEX_KEY_INIT; |
1238 | int ret; |
1239 | |
1240 | if (!bitset) |
1241 | return -EINVAL; |
1242 | |
1243 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ); |
1244 | if (unlikely(ret != 0)) |
1245 | goto out; |
1246 | |
1247 | hb = hash_futex(&key); |
1248 | |
1249 | /* Make sure we really have tasks to wakeup */ |
1250 | if (!hb_waiters_pending(hb)) |
1251 | goto out_put_key; |
1252 | |
1253 | spin_lock(&hb->lock); |
1254 | |
1255 | plist_for_each_entry_safe(this, next, &hb->chain, list) { |
1256 | if (match_futex (&this->key, &key)) { |
1257 | if (this->pi_state || this->rt_waiter) { |
1258 | ret = -EINVAL; |
1259 | break; |
1260 | } |
1261 | |
1262 | /* Check if one of the bits is set in both bitsets */ |
1263 | if (!(this->bitset & bitset)) |
1264 | continue; |
1265 | |
1266 | wake_futex(this); |
1267 | if (++ret >= nr_wake) |
1268 | break; |
1269 | } |
1270 | } |
1271 | |
1272 | spin_unlock(&hb->lock); |
1273 | out_put_key: |
1274 | put_futex_key(&key); |
1275 | out: |
1276 | return ret; |
1277 | } |
1278 | |
1279 | /* |
1280 | * Wake up all waiters hashed on the physical page that is mapped |
1281 | * to this virtual address: |
1282 | */ |
1283 | static int |
1284 | futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2, |
1285 | int nr_wake, int nr_wake2, int op) |
1286 | { |
1287 | union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; |
1288 | struct futex_hash_bucket *hb1, *hb2; |
1289 | struct futex_q *this, *next; |
1290 | int ret, op_ret; |
1291 | |
1292 | retry: |
1293 | ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ); |
1294 | if (unlikely(ret != 0)) |
1295 | goto out; |
1296 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE); |
1297 | if (unlikely(ret != 0)) |
1298 | goto out_put_key1; |
1299 | |
1300 | hb1 = hash_futex(&key1); |
1301 | hb2 = hash_futex(&key2); |
1302 | |
1303 | retry_private: |
1304 | double_lock_hb(hb1, hb2); |
1305 | op_ret = futex_atomic_op_inuser(op, uaddr2); |
1306 | if (unlikely(op_ret < 0)) { |
1307 | |
1308 | double_unlock_hb(hb1, hb2); |
1309 | |
1310 | #ifndef CONFIG_MMU |
1311 | /* |
1312 | * we don't get EFAULT from MMU faults if we don't have an MMU, |
1313 | * but we might get them from range checking |
1314 | */ |
1315 | ret = op_ret; |
1316 | goto out_put_keys; |
1317 | #endif |
1318 | |
1319 | if (unlikely(op_ret != -EFAULT)) { |
1320 | ret = op_ret; |
1321 | goto out_put_keys; |
1322 | } |
1323 | |
1324 | ret = fault_in_user_writeable(uaddr2); |
1325 | if (ret) |
1326 | goto out_put_keys; |
1327 | |
1328 | if (!(flags & FLAGS_SHARED)) |
1329 | goto retry_private; |
1330 | |
1331 | put_futex_key(&key2); |
1332 | put_futex_key(&key1); |
1333 | goto retry; |
1334 | } |
1335 | |
1336 | plist_for_each_entry_safe(this, next, &hb1->chain, list) { |
1337 | if (match_futex (&this->key, &key1)) { |
1338 | if (this->pi_state || this->rt_waiter) { |
1339 | ret = -EINVAL; |
1340 | goto out_unlock; |
1341 | } |
1342 | wake_futex(this); |
1343 | if (++ret >= nr_wake) |
1344 | break; |
1345 | } |
1346 | } |
1347 | |
1348 | if (op_ret > 0) { |
1349 | op_ret = 0; |
1350 | plist_for_each_entry_safe(this, next, &hb2->chain, list) { |
1351 | if (match_futex (&this->key, &key2)) { |
1352 | if (this->pi_state || this->rt_waiter) { |
1353 | ret = -EINVAL; |
1354 | goto out_unlock; |
1355 | } |
1356 | wake_futex(this); |
1357 | if (++op_ret >= nr_wake2) |
1358 | break; |
1359 | } |
1360 | } |
1361 | ret += op_ret; |
1362 | } |
1363 | |
1364 | out_unlock: |
1365 | double_unlock_hb(hb1, hb2); |
1366 | out_put_keys: |
1367 | put_futex_key(&key2); |
1368 | out_put_key1: |
1369 | put_futex_key(&key1); |
1370 | out: |
1371 | return ret; |
1372 | } |
1373 | |
1374 | /** |
1375 | * requeue_futex() - Requeue a futex_q from one hb to another |
1376 | * @q: the futex_q to requeue |
1377 | * @hb1: the source hash_bucket |
1378 | * @hb2: the target hash_bucket |
1379 | * @key2: the new key for the requeued futex_q |
1380 | */ |
1381 | static inline |
1382 | void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1, |
1383 | struct futex_hash_bucket *hb2, union futex_key *key2) |
1384 | { |
1385 | |
1386 | /* |
1387 | * If key1 and key2 hash to the same bucket, no need to |
1388 | * requeue. |
1389 | */ |
1390 | if (likely(&hb1->chain != &hb2->chain)) { |
1391 | plist_del(&q->list, &hb1->chain); |
1392 | hb_waiters_dec(hb1); |
1393 | plist_add(&q->list, &hb2->chain); |
1394 | hb_waiters_inc(hb2); |
1395 | q->lock_ptr = &hb2->lock; |
1396 | } |
1397 | get_futex_key_refs(key2); |
1398 | q->key = *key2; |
1399 | } |
1400 | |
1401 | /** |
1402 | * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue |
1403 | * @q: the futex_q |
1404 | * @key: the key of the requeue target futex |
1405 | * @hb: the hash_bucket of the requeue target futex |
1406 | * |
1407 | * During futex_requeue, with requeue_pi=1, it is possible to acquire the |
1408 | * target futex if it is uncontended or via a lock steal. Set the futex_q key |
1409 | * to the requeue target futex so the waiter can detect the wakeup on the right |
1410 | * futex, but remove it from the hb and NULL the rt_waiter so it can detect |
1411 | * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock |
1412 | * to protect access to the pi_state to fixup the owner later. Must be called |
1413 | * with both q->lock_ptr and hb->lock held. |
1414 | */ |
1415 | static inline |
1416 | void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key, |
1417 | struct futex_hash_bucket *hb) |
1418 | { |
1419 | get_futex_key_refs(key); |
1420 | q->key = *key; |
1421 | |
1422 | __unqueue_futex(q); |
1423 | |
1424 | WARN_ON(!q->rt_waiter); |
1425 | q->rt_waiter = NULL; |
1426 | |
1427 | q->lock_ptr = &hb->lock; |
1428 | |
1429 | wake_up_state(q->task, TASK_NORMAL); |
1430 | } |
1431 | |
1432 | /** |
1433 | * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter |
1434 | * @pifutex: the user address of the to futex |
1435 | * @hb1: the from futex hash bucket, must be locked by the caller |
1436 | * @hb2: the to futex hash bucket, must be locked by the caller |
1437 | * @key1: the from futex key |
1438 | * @key2: the to futex key |
1439 | * @ps: address to store the pi_state pointer |
1440 | * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) |
1441 | * |
1442 | * Try and get the lock on behalf of the top waiter if we can do it atomically. |
1443 | * Wake the top waiter if we succeed. If the caller specified set_waiters, |
1444 | * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit. |
1445 | * hb1 and hb2 must be held by the caller. |
1446 | * |
1447 | * Return: |
1448 | * 0 - failed to acquire the lock atomically; |
1449 | * >0 - acquired the lock, return value is vpid of the top_waiter |
1450 | * <0 - error |
1451 | */ |
1452 | static int futex_proxy_trylock_atomic(u32 __user *pifutex, |
1453 | struct futex_hash_bucket *hb1, |
1454 | struct futex_hash_bucket *hb2, |
1455 | union futex_key *key1, union futex_key *key2, |
1456 | struct futex_pi_state **ps, int set_waiters) |
1457 | { |
1458 | struct futex_q *top_waiter = NULL; |
1459 | u32 curval; |
1460 | int ret, vpid; |
1461 | |
1462 | if (get_futex_value_locked(&curval, pifutex)) |
1463 | return -EFAULT; |
1464 | |
1465 | /* |
1466 | * Find the top_waiter and determine if there are additional waiters. |
1467 | * If the caller intends to requeue more than 1 waiter to pifutex, |
1468 | * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now, |
1469 | * as we have means to handle the possible fault. If not, don't set |
1470 | * the bit unecessarily as it will force the subsequent unlock to enter |
1471 | * the kernel. |
1472 | */ |
1473 | top_waiter = futex_top_waiter(hb1, key1); |
1474 | |
1475 | /* There are no waiters, nothing for us to do. */ |
1476 | if (!top_waiter) |
1477 | return 0; |
1478 | |
1479 | /* Ensure we requeue to the expected futex. */ |
1480 | if (!match_futex(top_waiter->requeue_pi_key, key2)) |
1481 | return -EINVAL; |
1482 | |
1483 | /* |
1484 | * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in |
1485 | * the contended case or if set_waiters is 1. The pi_state is returned |
1486 | * in ps in contended cases. |
1487 | */ |
1488 | vpid = task_pid_vnr(top_waiter->task); |
1489 | ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task, |
1490 | set_waiters); |
1491 | if (ret == 1) { |
1492 | requeue_pi_wake_futex(top_waiter, key2, hb2); |
1493 | return vpid; |
1494 | } |
1495 | return ret; |
1496 | } |
1497 | |
1498 | /** |
1499 | * futex_requeue() - Requeue waiters from uaddr1 to uaddr2 |
1500 | * @uaddr1: source futex user address |
1501 | * @flags: futex flags (FLAGS_SHARED, etc.) |
1502 | * @uaddr2: target futex user address |
1503 | * @nr_wake: number of waiters to wake (must be 1 for requeue_pi) |
1504 | * @nr_requeue: number of waiters to requeue (0-INT_MAX) |
1505 | * @cmpval: @uaddr1 expected value (or %NULL) |
1506 | * @requeue_pi: if we are attempting to requeue from a non-pi futex to a |
1507 | * pi futex (pi to pi requeue is not supported) |
1508 | * |
1509 | * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire |
1510 | * uaddr2 atomically on behalf of the top waiter. |
1511 | * |
1512 | * Return: |
1513 | * >=0 - on success, the number of tasks requeued or woken; |
1514 | * <0 - on error |
1515 | */ |
1516 | static int futex_requeue(u32 __user *uaddr1, unsigned int flags, |
1517 | u32 __user *uaddr2, int nr_wake, int nr_requeue, |
1518 | u32 *cmpval, int requeue_pi) |
1519 | { |
1520 | union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; |
1521 | int drop_count = 0, task_count = 0, ret; |
1522 | struct futex_pi_state *pi_state = NULL; |
1523 | struct futex_hash_bucket *hb1, *hb2; |
1524 | struct futex_q *this, *next; |
1525 | |
1526 | if (requeue_pi) { |
1527 | /* |
1528 | * Requeue PI only works on two distinct uaddrs. This |
1529 | * check is only valid for private futexes. See below. |
1530 | */ |
1531 | if (uaddr1 == uaddr2) |
1532 | return -EINVAL; |
1533 | |
1534 | /* |
1535 | * requeue_pi requires a pi_state, try to allocate it now |
1536 | * without any locks in case it fails. |
1537 | */ |
1538 | if (refill_pi_state_cache()) |
1539 | return -ENOMEM; |
1540 | /* |
1541 | * requeue_pi must wake as many tasks as it can, up to nr_wake |
1542 | * + nr_requeue, since it acquires the rt_mutex prior to |
1543 | * returning to userspace, so as to not leave the rt_mutex with |
1544 | * waiters and no owner. However, second and third wake-ups |
1545 | * cannot be predicted as they involve race conditions with the |
1546 | * first wake and a fault while looking up the pi_state. Both |
1547 | * pthread_cond_signal() and pthread_cond_broadcast() should |
1548 | * use nr_wake=1. |
1549 | */ |
1550 | if (nr_wake != 1) |
1551 | return -EINVAL; |
1552 | } |
1553 | |
1554 | retry: |
1555 | if (pi_state != NULL) { |
1556 | /* |
1557 | * We will have to lookup the pi_state again, so free this one |
1558 | * to keep the accounting correct. |
1559 | */ |
1560 | free_pi_state(pi_state); |
1561 | pi_state = NULL; |
1562 | } |
1563 | |
1564 | ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ); |
1565 | if (unlikely(ret != 0)) |
1566 | goto out; |
1567 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, |
1568 | requeue_pi ? VERIFY_WRITE : VERIFY_READ); |
1569 | if (unlikely(ret != 0)) |
1570 | goto out_put_key1; |
1571 | |
1572 | /* |
1573 | * The check above which compares uaddrs is not sufficient for |
1574 | * shared futexes. We need to compare the keys: |
1575 | */ |
1576 | if (requeue_pi && match_futex(&key1, &key2)) { |
1577 | ret = -EINVAL; |
1578 | goto out_put_keys; |
1579 | } |
1580 | |
1581 | hb1 = hash_futex(&key1); |
1582 | hb2 = hash_futex(&key2); |
1583 | |
1584 | retry_private: |
1585 | hb_waiters_inc(hb2); |
1586 | double_lock_hb(hb1, hb2); |
1587 | |
1588 | if (likely(cmpval != NULL)) { |
1589 | u32 curval; |
1590 | |
1591 | ret = get_futex_value_locked(&curval, uaddr1); |
1592 | |
1593 | if (unlikely(ret)) { |
1594 | double_unlock_hb(hb1, hb2); |
1595 | hb_waiters_dec(hb2); |
1596 | |
1597 | ret = get_user(curval, uaddr1); |
1598 | if (ret) |
1599 | goto out_put_keys; |
1600 | |
1601 | if (!(flags & FLAGS_SHARED)) |
1602 | goto retry_private; |
1603 | |
1604 | put_futex_key(&key2); |
1605 | put_futex_key(&key1); |
1606 | goto retry; |
1607 | } |
1608 | if (curval != *cmpval) { |
1609 | ret = -EAGAIN; |
1610 | goto out_unlock; |
1611 | } |
1612 | } |
1613 | |
1614 | if (requeue_pi && (task_count - nr_wake < nr_requeue)) { |
1615 | /* |
1616 | * Attempt to acquire uaddr2 and wake the top waiter. If we |
1617 | * intend to requeue waiters, force setting the FUTEX_WAITERS |
1618 | * bit. We force this here where we are able to easily handle |
1619 | * faults rather in the requeue loop below. |
1620 | */ |
1621 | ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1, |
1622 | &key2, &pi_state, nr_requeue); |
1623 | |
1624 | /* |
1625 | * At this point the top_waiter has either taken uaddr2 or is |
1626 | * waiting on it. If the former, then the pi_state will not |
1627 | * exist yet, look it up one more time to ensure we have a |
1628 | * reference to it. If the lock was taken, ret contains the |
1629 | * vpid of the top waiter task. |
1630 | */ |
1631 | if (ret > 0) { |
1632 | WARN_ON(pi_state); |
1633 | drop_count++; |
1634 | task_count++; |
1635 | /* |
1636 | * If we acquired the lock, then the user |
1637 | * space value of uaddr2 should be vpid. It |
1638 | * cannot be changed by the top waiter as it |
1639 | * is blocked on hb2 lock if it tries to do |
1640 | * so. If something fiddled with it behind our |
1641 | * back the pi state lookup might unearth |
1642 | * it. So we rather use the known value than |
1643 | * rereading and handing potential crap to |
1644 | * lookup_pi_state. |
1645 | */ |
1646 | ret = lookup_pi_state(ret, hb2, &key2, &pi_state); |
1647 | } |
1648 | |
1649 | switch (ret) { |
1650 | case 0: |
1651 | break; |
1652 | case -EFAULT: |
1653 | double_unlock_hb(hb1, hb2); |
1654 | hb_waiters_dec(hb2); |
1655 | put_futex_key(&key2); |
1656 | put_futex_key(&key1); |
1657 | ret = fault_in_user_writeable(uaddr2); |
1658 | if (!ret) |
1659 | goto retry; |
1660 | goto out; |
1661 | case -EAGAIN: |
1662 | /* The owner was exiting, try again. */ |
1663 | double_unlock_hb(hb1, hb2); |
1664 | hb_waiters_dec(hb2); |
1665 | put_futex_key(&key2); |
1666 | put_futex_key(&key1); |
1667 | cond_resched(); |
1668 | goto retry; |
1669 | default: |
1670 | goto out_unlock; |
1671 | } |
1672 | } |
1673 | |
1674 | plist_for_each_entry_safe(this, next, &hb1->chain, list) { |
1675 | if (task_count - nr_wake >= nr_requeue) |
1676 | break; |
1677 | |
1678 | if (!match_futex(&this->key, &key1)) |
1679 | continue; |
1680 | |
1681 | /* |
1682 | * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always |
1683 | * be paired with each other and no other futex ops. |
1684 | * |
1685 | * We should never be requeueing a futex_q with a pi_state, |
1686 | * which is awaiting a futex_unlock_pi(). |
1687 | */ |
1688 | if ((requeue_pi && !this->rt_waiter) || |
1689 | (!requeue_pi && this->rt_waiter) || |
1690 | this->pi_state) { |
1691 | ret = -EINVAL; |
1692 | break; |
1693 | } |
1694 | |
1695 | /* |
1696 | * Wake nr_wake waiters. For requeue_pi, if we acquired the |
1697 | * lock, we already woke the top_waiter. If not, it will be |
1698 | * woken by futex_unlock_pi(). |
1699 | */ |
1700 | if (++task_count <= nr_wake && !requeue_pi) { |
1701 | wake_futex(this); |
1702 | continue; |
1703 | } |
1704 | |
1705 | /* Ensure we requeue to the expected futex for requeue_pi. */ |
1706 | if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) { |
1707 | ret = -EINVAL; |
1708 | break; |
1709 | } |
1710 | |
1711 | /* |
1712 | * Requeue nr_requeue waiters and possibly one more in the case |
1713 | * of requeue_pi if we couldn't acquire the lock atomically. |
1714 | */ |
1715 | if (requeue_pi) { |
1716 | /* Prepare the waiter to take the rt_mutex. */ |
1717 | atomic_inc(&pi_state->refcount); |
1718 | this->pi_state = pi_state; |
1719 | ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex, |
1720 | this->rt_waiter, |
1721 | this->task, 1); |
1722 | if (ret == 1) { |
1723 | /* We got the lock. */ |
1724 | requeue_pi_wake_futex(this, &key2, hb2); |
1725 | drop_count++; |
1726 | continue; |
1727 | } else if (ret) { |
1728 | /* -EDEADLK */ |
1729 | this->pi_state = NULL; |
1730 | free_pi_state(pi_state); |
1731 | goto out_unlock; |
1732 | } |
1733 | } |
1734 | requeue_futex(this, hb1, hb2, &key2); |
1735 | drop_count++; |
1736 | } |
1737 | |
1738 | out_unlock: |
1739 | double_unlock_hb(hb1, hb2); |
1740 | hb_waiters_dec(hb2); |
1741 | |
1742 | /* |
1743 | * drop_futex_key_refs() must be called outside the spinlocks. During |
1744 | * the requeue we moved futex_q's from the hash bucket at key1 to the |
1745 | * one at key2 and updated their key pointer. We no longer need to |
1746 | * hold the references to key1. |
1747 | */ |
1748 | while (--drop_count >= 0) |
1749 | drop_futex_key_refs(&key1); |
1750 | |
1751 | out_put_keys: |
1752 | put_futex_key(&key2); |
1753 | out_put_key1: |
1754 | put_futex_key(&key1); |
1755 | out: |
1756 | if (pi_state != NULL) |
1757 | free_pi_state(pi_state); |
1758 | return ret ? ret : task_count; |
1759 | } |
1760 | |
1761 | /* The key must be already stored in q->key. */ |
1762 | static inline struct futex_hash_bucket *queue_lock(struct futex_q *q) |
1763 | __acquires(&hb->lock) |
1764 | { |
1765 | struct futex_hash_bucket *hb; |
1766 | |
1767 | hb = hash_futex(&q->key); |
1768 | |
1769 | /* |
1770 | * Increment the counter before taking the lock so that |
1771 | * a potential waker won't miss a to-be-slept task that is |
1772 | * waiting for the spinlock. This is safe as all queue_lock() |
1773 | * users end up calling queue_me(). Similarly, for housekeeping, |
1774 | * decrement the counter at queue_unlock() when some error has |
1775 | * occurred and we don't end up adding the task to the list. |
1776 | */ |
1777 | hb_waiters_inc(hb); |
1778 | |
1779 | q->lock_ptr = &hb->lock; |
1780 | |
1781 | spin_lock(&hb->lock); /* implies MB (A) */ |
1782 | return hb; |
1783 | } |
1784 | |
1785 | static inline void |
1786 | queue_unlock(struct futex_hash_bucket *hb) |
1787 | __releases(&hb->lock) |
1788 | { |
1789 | spin_unlock(&hb->lock); |
1790 | hb_waiters_dec(hb); |
1791 | } |
1792 | |
1793 | /** |
1794 | * queue_me() - Enqueue the futex_q on the futex_hash_bucket |
1795 | * @q: The futex_q to enqueue |
1796 | * @hb: The destination hash bucket |
1797 | * |
1798 | * The hb->lock must be held by the caller, and is released here. A call to |
1799 | * queue_me() is typically paired with exactly one call to unqueue_me(). The |
1800 | * exceptions involve the PI related operations, which may use unqueue_me_pi() |
1801 | * or nothing if the unqueue is done as part of the wake process and the unqueue |
1802 | * state is implicit in the state of woken task (see futex_wait_requeue_pi() for |
1803 | * an example). |
1804 | */ |
1805 | static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb) |
1806 | __releases(&hb->lock) |
1807 | { |
1808 | int prio; |
1809 | |
1810 | /* |
1811 | * The priority used to register this element is |
1812 | * - either the real thread-priority for the real-time threads |
1813 | * (i.e. threads with a priority lower than MAX_RT_PRIO) |
1814 | * - or MAX_RT_PRIO for non-RT threads. |
1815 | * Thus, all RT-threads are woken first in priority order, and |
1816 | * the others are woken last, in FIFO order. |
1817 | */ |
1818 | prio = min(current->normal_prio, MAX_RT_PRIO); |
1819 | |
1820 | plist_node_init(&q->list, prio); |
1821 | plist_add(&q->list, &hb->chain); |
1822 | q->task = current; |
1823 | spin_unlock(&hb->lock); |
1824 | } |
1825 | |
1826 | /** |
1827 | * unqueue_me() - Remove the futex_q from its futex_hash_bucket |
1828 | * @q: The futex_q to unqueue |
1829 | * |
1830 | * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must |
1831 | * be paired with exactly one earlier call to queue_me(). |
1832 | * |
1833 | * Return: |
1834 | * 1 - if the futex_q was still queued (and we removed unqueued it); |
1835 | * 0 - if the futex_q was already removed by the waking thread |
1836 | */ |
1837 | static int unqueue_me(struct futex_q *q) |
1838 | { |
1839 | spinlock_t *lock_ptr; |
1840 | int ret = 0; |
1841 | |
1842 | /* In the common case we don't take the spinlock, which is nice. */ |
1843 | retry: |
1844 | lock_ptr = q->lock_ptr; |
1845 | barrier(); |
1846 | if (lock_ptr != NULL) { |
1847 | spin_lock(lock_ptr); |
1848 | /* |
1849 | * q->lock_ptr can change between reading it and |
1850 | * spin_lock(), causing us to take the wrong lock. This |
1851 | * corrects the race condition. |
1852 | * |
1853 | * Reasoning goes like this: if we have the wrong lock, |
1854 | * q->lock_ptr must have changed (maybe several times) |
1855 | * between reading it and the spin_lock(). It can |
1856 | * change again after the spin_lock() but only if it was |
1857 | * already changed before the spin_lock(). It cannot, |
1858 | * however, change back to the original value. Therefore |
1859 | * we can detect whether we acquired the correct lock. |
1860 | */ |
1861 | if (unlikely(lock_ptr != q->lock_ptr)) { |
1862 | spin_unlock(lock_ptr); |
1863 | goto retry; |
1864 | } |
1865 | __unqueue_futex(q); |
1866 | |
1867 | BUG_ON(q->pi_state); |
1868 | |
1869 | spin_unlock(lock_ptr); |
1870 | ret = 1; |
1871 | } |
1872 | |
1873 | drop_futex_key_refs(&q->key); |
1874 | return ret; |
1875 | } |
1876 | |
1877 | /* |
1878 | * PI futexes can not be requeued and must remove themself from the |
1879 | * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry |
1880 | * and dropped here. |
1881 | */ |
1882 | static void unqueue_me_pi(struct futex_q *q) |
1883 | __releases(q->lock_ptr) |
1884 | { |
1885 | __unqueue_futex(q); |
1886 | |
1887 | BUG_ON(!q->pi_state); |
1888 | free_pi_state(q->pi_state); |
1889 | q->pi_state = NULL; |
1890 | |
1891 | spin_unlock(q->lock_ptr); |
1892 | } |
1893 | |
1894 | /* |
1895 | * Fixup the pi_state owner with the new owner. |
1896 | * |
1897 | * Must be called with hash bucket lock held and mm->sem held for non |
1898 | * private futexes. |
1899 | */ |
1900 | static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q, |
1901 | struct task_struct *newowner) |
1902 | { |
1903 | u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS; |
1904 | struct futex_pi_state *pi_state = q->pi_state; |
1905 | struct task_struct *oldowner = pi_state->owner; |
1906 | u32 uval, uninitialized_var(curval), newval; |
1907 | int ret; |
1908 | |
1909 | /* Owner died? */ |
1910 | if (!pi_state->owner) |
1911 | newtid |= FUTEX_OWNER_DIED; |
1912 | |
1913 | /* |
1914 | * We are here either because we stole the rtmutex from the |
1915 | * previous highest priority waiter or we are the highest priority |
1916 | * waiter but failed to get the rtmutex the first time. |
1917 | * We have to replace the newowner TID in the user space variable. |
1918 | * This must be atomic as we have to preserve the owner died bit here. |
1919 | * |
1920 | * Note: We write the user space value _before_ changing the pi_state |
1921 | * because we can fault here. Imagine swapped out pages or a fork |
1922 | * that marked all the anonymous memory readonly for cow. |
1923 | * |
1924 | * Modifying pi_state _before_ the user space value would |
1925 | * leave the pi_state in an inconsistent state when we fault |
1926 | * here, because we need to drop the hash bucket lock to |
1927 | * handle the fault. This might be observed in the PID check |
1928 | * in lookup_pi_state. |
1929 | */ |
1930 | retry: |
1931 | if (get_futex_value_locked(&uval, uaddr)) |
1932 | goto handle_fault; |
1933 | |
1934 | while (1) { |
1935 | newval = (uval & FUTEX_OWNER_DIED) | newtid; |
1936 | |
1937 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) |
1938 | goto handle_fault; |
1939 | if (curval == uval) |
1940 | break; |
1941 | uval = curval; |
1942 | } |
1943 | |
1944 | /* |
1945 | * We fixed up user space. Now we need to fix the pi_state |
1946 | * itself. |
1947 | */ |
1948 | if (pi_state->owner != NULL) { |
1949 | raw_spin_lock_irq(&pi_state->owner->pi_lock); |
1950 | WARN_ON(list_empty(&pi_state->list)); |
1951 | list_del_init(&pi_state->list); |
1952 | raw_spin_unlock_irq(&pi_state->owner->pi_lock); |
1953 | } |
1954 | |
1955 | pi_state->owner = newowner; |
1956 | |
1957 | raw_spin_lock_irq(&newowner->pi_lock); |
1958 | WARN_ON(!list_empty(&pi_state->list)); |
1959 | list_add(&pi_state->list, &newowner->pi_state_list); |
1960 | raw_spin_unlock_irq(&newowner->pi_lock); |
1961 | return 0; |
1962 | |
1963 | /* |
1964 | * To handle the page fault we need to drop the hash bucket |
1965 | * lock here. That gives the other task (either the highest priority |
1966 | * waiter itself or the task which stole the rtmutex) the |
1967 | * chance to try the fixup of the pi_state. So once we are |
1968 | * back from handling the fault we need to check the pi_state |
1969 | * after reacquiring the hash bucket lock and before trying to |
1970 | * do another fixup. When the fixup has been done already we |
1971 | * simply return. |
1972 | */ |
1973 | handle_fault: |
1974 | spin_unlock(q->lock_ptr); |
1975 | |
1976 | ret = fault_in_user_writeable(uaddr); |
1977 | |
1978 | spin_lock(q->lock_ptr); |
1979 | |
1980 | /* |
1981 | * Check if someone else fixed it for us: |
1982 | */ |
1983 | if (pi_state->owner != oldowner) |
1984 | return 0; |
1985 | |
1986 | if (ret) |
1987 | return ret; |
1988 | |
1989 | goto retry; |
1990 | } |
1991 | |
1992 | static long futex_wait_restart(struct restart_block *restart); |
1993 | |
1994 | /** |
1995 | * fixup_owner() - Post lock pi_state and corner case management |
1996 | * @uaddr: user address of the futex |
1997 | * @q: futex_q (contains pi_state and access to the rt_mutex) |
1998 | * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0) |
1999 | * |
2000 | * After attempting to lock an rt_mutex, this function is called to cleanup |
2001 | * the pi_state owner as well as handle race conditions that may allow us to |
2002 | * acquire the lock. Must be called with the hb lock held. |
2003 | * |
2004 | * Return: |
2005 | * 1 - success, lock taken; |
2006 | * 0 - success, lock not taken; |
2007 | * <0 - on error (-EFAULT) |
2008 | */ |
2009 | static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked) |
2010 | { |
2011 | struct task_struct *owner; |
2012 | int ret = 0; |
2013 | |
2014 | if (locked) { |
2015 | /* |
2016 | * Got the lock. We might not be the anticipated owner if we |
2017 | * did a lock-steal - fix up the PI-state in that case: |
2018 | */ |
2019 | if (q->pi_state->owner != current) |
2020 | ret = fixup_pi_state_owner(uaddr, q, current); |
2021 | goto out; |
2022 | } |
2023 | |
2024 | /* |
2025 | * Catch the rare case, where the lock was released when we were on the |
2026 | * way back before we locked the hash bucket. |
2027 | */ |
2028 | if (q->pi_state->owner == current) { |
2029 | /* |
2030 | * Try to get the rt_mutex now. This might fail as some other |
2031 | * task acquired the rt_mutex after we removed ourself from the |
2032 | * rt_mutex waiters list. |
2033 | */ |
2034 | if (rt_mutex_trylock(&q->pi_state->pi_mutex)) { |
2035 | locked = 1; |
2036 | goto out; |
2037 | } |
2038 | |
2039 | /* |
2040 | * pi_state is incorrect, some other task did a lock steal and |
2041 | * we returned due to timeout or signal without taking the |
2042 | * rt_mutex. Too late. |
2043 | */ |
2044 | raw_spin_lock(&q->pi_state->pi_mutex.wait_lock); |
2045 | owner = rt_mutex_owner(&q->pi_state->pi_mutex); |
2046 | if (!owner) |
2047 | owner = rt_mutex_next_owner(&q->pi_state->pi_mutex); |
2048 | raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock); |
2049 | ret = fixup_pi_state_owner(uaddr, q, owner); |
2050 | goto out; |
2051 | } |
2052 | |
2053 | /* |
2054 | * Paranoia check. If we did not take the lock, then we should not be |
2055 | * the owner of the rt_mutex. |
2056 | */ |
2057 | if (rt_mutex_owner(&q->pi_state->pi_mutex) == current) |
2058 | printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p " |
2059 | "pi-state %p\n", ret, |
2060 | q->pi_state->pi_mutex.owner, |
2061 | q->pi_state->owner); |
2062 | |
2063 | out: |
2064 | return ret ? ret : locked; |
2065 | } |
2066 | |
2067 | /** |
2068 | * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal |
2069 | * @hb: the futex hash bucket, must be locked by the caller |
2070 | * @q: the futex_q to queue up on |
2071 | * @timeout: the prepared hrtimer_sleeper, or null for no timeout |
2072 | */ |
2073 | static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q, |
2074 | struct hrtimer_sleeper *timeout) |
2075 | { |
2076 | /* |
2077 | * The task state is guaranteed to be set before another task can |
2078 | * wake it. set_current_state() is implemented using set_mb() and |
2079 | * queue_me() calls spin_unlock() upon completion, both serializing |
2080 | * access to the hash list and forcing another memory barrier. |
2081 | */ |
2082 | set_current_state(TASK_INTERRUPTIBLE); |
2083 | queue_me(q, hb); |
2084 | |
2085 | /* Arm the timer */ |
2086 | if (timeout) { |
2087 | hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS); |
2088 | if (!hrtimer_active(&timeout->timer)) |
2089 | timeout->task = NULL; |
2090 | } |
2091 | |
2092 | /* |
2093 | * If we have been removed from the hash list, then another task |
2094 | * has tried to wake us, and we can skip the call to schedule(). |
2095 | */ |
2096 | if (likely(!plist_node_empty(&q->list))) { |
2097 | /* |
2098 | * If the timer has already expired, current will already be |
2099 | * flagged for rescheduling. Only call schedule if there |
2100 | * is no timeout, or if it has yet to expire. |
2101 | */ |
2102 | if (!timeout || timeout->task) |
2103 | freezable_schedule(); |
2104 | } |
2105 | __set_current_state(TASK_RUNNING); |
2106 | } |
2107 | |
2108 | /** |
2109 | * futex_wait_setup() - Prepare to wait on a futex |
2110 | * @uaddr: the futex userspace address |
2111 | * @val: the expected value |
2112 | * @flags: futex flags (FLAGS_SHARED, etc.) |
2113 | * @q: the associated futex_q |
2114 | * @hb: storage for hash_bucket pointer to be returned to caller |
2115 | * |
2116 | * Setup the futex_q and locate the hash_bucket. Get the futex value and |
2117 | * compare it with the expected value. Handle atomic faults internally. |
2118 | * Return with the hb lock held and a q.key reference on success, and unlocked |
2119 | * with no q.key reference on failure. |
2120 | * |
2121 | * Return: |
2122 | * 0 - uaddr contains val and hb has been locked; |
2123 | * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked |
2124 | */ |
2125 | static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags, |
2126 | struct futex_q *q, struct futex_hash_bucket **hb) |
2127 | { |
2128 | u32 uval; |
2129 | int ret; |
2130 | |
2131 | /* |
2132 | * Access the page AFTER the hash-bucket is locked. |
2133 | * Order is important: |
2134 | * |
2135 | * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val); |
2136 | * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); } |
2137 | * |
2138 | * The basic logical guarantee of a futex is that it blocks ONLY |
2139 | * if cond(var) is known to be true at the time of blocking, for |
2140 | * any cond. If we locked the hash-bucket after testing *uaddr, that |
2141 | * would open a race condition where we could block indefinitely with |
2142 | * cond(var) false, which would violate the guarantee. |
2143 | * |
2144 | * On the other hand, we insert q and release the hash-bucket only |
2145 | * after testing *uaddr. This guarantees that futex_wait() will NOT |
2146 | * absorb a wakeup if *uaddr does not match the desired values |
2147 | * while the syscall executes. |
2148 | */ |
2149 | retry: |
2150 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ); |
2151 | if (unlikely(ret != 0)) |
2152 | return ret; |
2153 | |
2154 | retry_private: |
2155 | *hb = queue_lock(q); |
2156 | |
2157 | ret = get_futex_value_locked(&uval, uaddr); |
2158 | |
2159 | if (ret) { |
2160 | queue_unlock(*hb); |
2161 | |
2162 | ret = get_user(uval, uaddr); |
2163 | if (ret) |
2164 | goto out; |
2165 | |
2166 | if (!(flags & FLAGS_SHARED)) |
2167 | goto retry_private; |
2168 | |
2169 | put_futex_key(&q->key); |
2170 | goto retry; |
2171 | } |
2172 | |
2173 | if (uval != val) { |
2174 | queue_unlock(*hb); |
2175 | ret = -EWOULDBLOCK; |
2176 | } |
2177 | |
2178 | out: |
2179 | if (ret) |
2180 | put_futex_key(&q->key); |
2181 | return ret; |
2182 | } |
2183 | |
2184 | static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val, |
2185 | ktime_t *abs_time, u32 bitset) |
2186 | { |
2187 | struct hrtimer_sleeper timeout, *to = NULL; |
2188 | struct restart_block *restart; |
2189 | struct futex_hash_bucket *hb; |
2190 | struct futex_q q = futex_q_init; |
2191 | int ret; |
2192 | |
2193 | if (!bitset) |
2194 | return -EINVAL; |
2195 | q.bitset = bitset; |
2196 | |
2197 | if (abs_time) { |
2198 | to = &timeout; |
2199 | |
2200 | hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ? |
2201 | CLOCK_REALTIME : CLOCK_MONOTONIC, |
2202 | HRTIMER_MODE_ABS); |
2203 | hrtimer_init_sleeper(to, current); |
2204 | hrtimer_set_expires_range_ns(&to->timer, *abs_time, |
2205 | current->timer_slack_ns); |
2206 | } |
2207 | |
2208 | retry: |
2209 | /* |
2210 | * Prepare to wait on uaddr. On success, holds hb lock and increments |
2211 | * q.key refs. |
2212 | */ |
2213 | ret = futex_wait_setup(uaddr, val, flags, &q, &hb); |
2214 | if (ret) |
2215 | goto out; |
2216 | |
2217 | /* queue_me and wait for wakeup, timeout, or a signal. */ |
2218 | futex_wait_queue_me(hb, &q, to); |
2219 | |
2220 | /* If we were woken (and unqueued), we succeeded, whatever. */ |
2221 | ret = 0; |
2222 | /* unqueue_me() drops q.key ref */ |
2223 | if (!unqueue_me(&q)) |
2224 | goto out; |
2225 | ret = -ETIMEDOUT; |
2226 | if (to && !to->task) |
2227 | goto out; |
2228 | |
2229 | /* |
2230 | * We expect signal_pending(current), but we might be the |
2231 | * victim of a spurious wakeup as well. |
2232 | */ |
2233 | if (!signal_pending(current)) |
2234 | goto retry; |
2235 | |
2236 | ret = -ERESTARTSYS; |
2237 | if (!abs_time) |
2238 | goto out; |
2239 | |
2240 | restart = ¤t_thread_info()->restart_block; |
2241 | restart->fn = futex_wait_restart; |
2242 | restart->futex.uaddr = uaddr; |
2243 | restart->futex.val = val; |
2244 | restart->futex.time = abs_time->tv64; |
2245 | restart->futex.bitset = bitset; |
2246 | restart->futex.flags = flags | FLAGS_HAS_TIMEOUT; |
2247 | |
2248 | ret = -ERESTART_RESTARTBLOCK; |
2249 | |
2250 | out: |
2251 | if (to) { |
2252 | hrtimer_cancel(&to->timer); |
2253 | destroy_hrtimer_on_stack(&to->timer); |
2254 | } |
2255 | return ret; |
2256 | } |
2257 | |
2258 | |
2259 | static long futex_wait_restart(struct restart_block *restart) |
2260 | { |
2261 | u32 __user *uaddr = restart->futex.uaddr; |
2262 | ktime_t t, *tp = NULL; |
2263 | |
2264 | if (restart->futex.flags & FLAGS_HAS_TIMEOUT) { |
2265 | t.tv64 = restart->futex.time; |
2266 | tp = &t; |
2267 | } |
2268 | restart->fn = do_no_restart_syscall; |
2269 | |
2270 | return (long)futex_wait(uaddr, restart->futex.flags, |
2271 | restart->futex.val, tp, restart->futex.bitset); |
2272 | } |
2273 | |
2274 | |
2275 | /* |
2276 | * Userspace tried a 0 -> TID atomic transition of the futex value |
2277 | * and failed. The kernel side here does the whole locking operation: |
2278 | * if there are waiters then it will block, it does PI, etc. (Due to |
2279 | * races the kernel might see a 0 value of the futex too.) |
2280 | */ |
2281 | static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect, |
2282 | ktime_t *time, int trylock) |
2283 | { |
2284 | struct hrtimer_sleeper timeout, *to = NULL; |
2285 | struct futex_hash_bucket *hb; |
2286 | struct futex_q q = futex_q_init; |
2287 | int res, ret; |
2288 | |
2289 | if (refill_pi_state_cache()) |
2290 | return -ENOMEM; |
2291 | |
2292 | if (time) { |
2293 | to = &timeout; |
2294 | hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME, |
2295 | HRTIMER_MODE_ABS); |
2296 | hrtimer_init_sleeper(to, current); |
2297 | hrtimer_set_expires(&to->timer, *time); |
2298 | } |
2299 | |
2300 | retry: |
2301 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE); |
2302 | if (unlikely(ret != 0)) |
2303 | goto out; |
2304 | |
2305 | retry_private: |
2306 | hb = queue_lock(&q); |
2307 | |
2308 | ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0); |
2309 | if (unlikely(ret)) { |
2310 | switch (ret) { |
2311 | case 1: |
2312 | /* We got the lock. */ |
2313 | ret = 0; |
2314 | goto out_unlock_put_key; |
2315 | case -EFAULT: |
2316 | goto uaddr_faulted; |
2317 | case -EAGAIN: |
2318 | /* |
2319 | * Task is exiting and we just wait for the |
2320 | * exit to complete. |
2321 | */ |
2322 | queue_unlock(hb); |
2323 | put_futex_key(&q.key); |
2324 | cond_resched(); |
2325 | goto retry; |
2326 | default: |
2327 | goto out_unlock_put_key; |
2328 | } |
2329 | } |
2330 | |
2331 | /* |
2332 | * Only actually queue now that the atomic ops are done: |
2333 | */ |
2334 | queue_me(&q, hb); |
2335 | |
2336 | WARN_ON(!q.pi_state); |
2337 | /* |
2338 | * Block on the PI mutex: |
2339 | */ |
2340 | if (!trylock) |
2341 | ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1); |
2342 | else { |
2343 | ret = rt_mutex_trylock(&q.pi_state->pi_mutex); |
2344 | /* Fixup the trylock return value: */ |
2345 | ret = ret ? 0 : -EWOULDBLOCK; |
2346 | } |
2347 | |
2348 | spin_lock(q.lock_ptr); |
2349 | /* |
2350 | * Fixup the pi_state owner and possibly acquire the lock if we |
2351 | * haven't already. |
2352 | */ |
2353 | res = fixup_owner(uaddr, &q, !ret); |
2354 | /* |
2355 | * If fixup_owner() returned an error, proprogate that. If it acquired |
2356 | * the lock, clear our -ETIMEDOUT or -EINTR. |
2357 | */ |
2358 | if (res) |
2359 | ret = (res < 0) ? res : 0; |
2360 | |
2361 | /* |
2362 | * If fixup_owner() faulted and was unable to handle the fault, unlock |
2363 | * it and return the fault to userspace. |
2364 | */ |
2365 | if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) |
2366 | rt_mutex_unlock(&q.pi_state->pi_mutex); |
2367 | |
2368 | /* Unqueue and drop the lock */ |
2369 | unqueue_me_pi(&q); |
2370 | |
2371 | goto out_put_key; |
2372 | |
2373 | out_unlock_put_key: |
2374 | queue_unlock(hb); |
2375 | |
2376 | out_put_key: |
2377 | put_futex_key(&q.key); |
2378 | out: |
2379 | if (to) |
2380 | destroy_hrtimer_on_stack(&to->timer); |
2381 | return ret != -EINTR ? ret : -ERESTARTNOINTR; |
2382 | |
2383 | uaddr_faulted: |
2384 | queue_unlock(hb); |
2385 | |
2386 | ret = fault_in_user_writeable(uaddr); |
2387 | if (ret) |
2388 | goto out_put_key; |
2389 | |
2390 | if (!(flags & FLAGS_SHARED)) |
2391 | goto retry_private; |
2392 | |
2393 | put_futex_key(&q.key); |
2394 | goto retry; |
2395 | } |
2396 | |
2397 | /* |
2398 | * Userspace attempted a TID -> 0 atomic transition, and failed. |
2399 | * This is the in-kernel slowpath: we look up the PI state (if any), |
2400 | * and do the rt-mutex unlock. |
2401 | */ |
2402 | static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags) |
2403 | { |
2404 | struct futex_hash_bucket *hb; |
2405 | struct futex_q *this, *next; |
2406 | union futex_key key = FUTEX_KEY_INIT; |
2407 | u32 uval, vpid = task_pid_vnr(current); |
2408 | int ret; |
2409 | |
2410 | retry: |
2411 | if (get_user(uval, uaddr)) |
2412 | return -EFAULT; |
2413 | /* |
2414 | * We release only a lock we actually own: |
2415 | */ |
2416 | if ((uval & FUTEX_TID_MASK) != vpid) |
2417 | return -EPERM; |
2418 | |
2419 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE); |
2420 | if (unlikely(ret != 0)) |
2421 | goto out; |
2422 | |
2423 | hb = hash_futex(&key); |
2424 | spin_lock(&hb->lock); |
2425 | |
2426 | /* |
2427 | * To avoid races, try to do the TID -> 0 atomic transition |
2428 | * again. If it succeeds then we can return without waking |
2429 | * anyone else up. We only try this if neither the waiters nor |
2430 | * the owner died bit are set. |
2431 | */ |
2432 | if (!(uval & ~FUTEX_TID_MASK) && |
2433 | cmpxchg_futex_value_locked(&uval, uaddr, vpid, 0)) |
2434 | goto pi_faulted; |
2435 | /* |
2436 | * Rare case: we managed to release the lock atomically, |
2437 | * no need to wake anyone else up: |
2438 | */ |
2439 | if (unlikely(uval == vpid)) |
2440 | goto out_unlock; |
2441 | |
2442 | /* |
2443 | * Ok, other tasks may need to be woken up - check waiters |
2444 | * and do the wakeup if necessary: |
2445 | */ |
2446 | plist_for_each_entry_safe(this, next, &hb->chain, list) { |
2447 | if (!match_futex (&this->key, &key)) |
2448 | continue; |
2449 | ret = wake_futex_pi(uaddr, uval, this); |
2450 | /* |
2451 | * The atomic access to the futex value |
2452 | * generated a pagefault, so retry the |
2453 | * user-access and the wakeup: |
2454 | */ |
2455 | if (ret == -EFAULT) |
2456 | goto pi_faulted; |
2457 | goto out_unlock; |
2458 | } |
2459 | /* |
2460 | * No waiters - kernel unlocks the futex: |
2461 | */ |
2462 | ret = unlock_futex_pi(uaddr, uval); |
2463 | if (ret == -EFAULT) |
2464 | goto pi_faulted; |
2465 | |
2466 | out_unlock: |
2467 | spin_unlock(&hb->lock); |
2468 | put_futex_key(&key); |
2469 | |
2470 | out: |
2471 | return ret; |
2472 | |
2473 | pi_faulted: |
2474 | spin_unlock(&hb->lock); |
2475 | put_futex_key(&key); |
2476 | |
2477 | ret = fault_in_user_writeable(uaddr); |
2478 | if (!ret) |
2479 | goto retry; |
2480 | |
2481 | return ret; |
2482 | } |
2483 | |
2484 | /** |
2485 | * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex |
2486 | * @hb: the hash_bucket futex_q was original enqueued on |
2487 | * @q: the futex_q woken while waiting to be requeued |
2488 | * @key2: the futex_key of the requeue target futex |
2489 | * @timeout: the timeout associated with the wait (NULL if none) |
2490 | * |
2491 | * Detect if the task was woken on the initial futex as opposed to the requeue |
2492 | * target futex. If so, determine if it was a timeout or a signal that caused |
2493 | * the wakeup and return the appropriate error code to the caller. Must be |
2494 | * called with the hb lock held. |
2495 | * |
2496 | * Return: |
2497 | * 0 = no early wakeup detected; |
2498 | * <0 = -ETIMEDOUT or -ERESTARTNOINTR |
2499 | */ |
2500 | static inline |
2501 | int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb, |
2502 | struct futex_q *q, union futex_key *key2, |
2503 | struct hrtimer_sleeper *timeout) |
2504 | { |
2505 | int ret = 0; |
2506 | |
2507 | /* |
2508 | * With the hb lock held, we avoid races while we process the wakeup. |
2509 | * We only need to hold hb (and not hb2) to ensure atomicity as the |
2510 | * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb. |
2511 | * It can't be requeued from uaddr2 to something else since we don't |
2512 | * support a PI aware source futex for requeue. |
2513 | */ |
2514 | if (!match_futex(&q->key, key2)) { |
2515 | WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr)); |
2516 | /* |
2517 | * We were woken prior to requeue by a timeout or a signal. |
2518 | * Unqueue the futex_q and determine which it was. |
2519 | */ |
2520 | plist_del(&q->list, &hb->chain); |
2521 | hb_waiters_dec(hb); |
2522 | |
2523 | /* Handle spurious wakeups gracefully */ |
2524 | ret = -EWOULDBLOCK; |
2525 | if (timeout && !timeout->task) |
2526 | ret = -ETIMEDOUT; |
2527 | else if (signal_pending(current)) |
2528 | ret = -ERESTARTNOINTR; |
2529 | } |
2530 | return ret; |
2531 | } |
2532 | |
2533 | /** |
2534 | * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2 |
2535 | * @uaddr: the futex we initially wait on (non-pi) |
2536 | * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be |
2537 | * the same type, no requeueing from private to shared, etc. |
2538 | * @val: the expected value of uaddr |
2539 | * @abs_time: absolute timeout |
2540 | * @bitset: 32 bit wakeup bitset set by userspace, defaults to all |
2541 | * @uaddr2: the pi futex we will take prior to returning to user-space |
2542 | * |
2543 | * The caller will wait on uaddr and will be requeued by futex_requeue() to |
2544 | * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake |
2545 | * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to |
2546 | * userspace. This ensures the rt_mutex maintains an owner when it has waiters; |
2547 | * without one, the pi logic would not know which task to boost/deboost, if |
2548 | * there was a need to. |
2549 | * |
2550 | * We call schedule in futex_wait_queue_me() when we enqueue and return there |
2551 | * via the following-- |
2552 | * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue() |
2553 | * 2) wakeup on uaddr2 after a requeue |
2554 | * 3) signal |
2555 | * 4) timeout |
2556 | * |
2557 | * If 3, cleanup and return -ERESTARTNOINTR. |
2558 | * |
2559 | * If 2, we may then block on trying to take the rt_mutex and return via: |
2560 | * 5) successful lock |
2561 | * 6) signal |
2562 | * 7) timeout |
2563 | * 8) other lock acquisition failure |
2564 | * |
2565 | * If 6, return -EWOULDBLOCK (restarting the syscall would do the same). |
2566 | * |
2567 | * If 4 or 7, we cleanup and return with -ETIMEDOUT. |
2568 | * |
2569 | * Return: |
2570 | * 0 - On success; |
2571 | * <0 - On error |
2572 | */ |
2573 | static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, |
2574 | u32 val, ktime_t *abs_time, u32 bitset, |
2575 | u32 __user *uaddr2) |
2576 | { |
2577 | struct hrtimer_sleeper timeout, *to = NULL; |
2578 | struct rt_mutex_waiter rt_waiter; |
2579 | struct rt_mutex *pi_mutex = NULL; |
2580 | struct futex_hash_bucket *hb; |
2581 | union futex_key key2 = FUTEX_KEY_INIT; |
2582 | struct futex_q q = futex_q_init; |
2583 | int res, ret; |
2584 | |
2585 | if (uaddr == uaddr2) |
2586 | return -EINVAL; |
2587 | |
2588 | if (!bitset) |
2589 | return -EINVAL; |
2590 | |
2591 | if (abs_time) { |
2592 | to = &timeout; |
2593 | hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ? |
2594 | CLOCK_REALTIME : CLOCK_MONOTONIC, |
2595 | HRTIMER_MODE_ABS); |
2596 | hrtimer_init_sleeper(to, current); |
2597 | hrtimer_set_expires_range_ns(&to->timer, *abs_time, |
2598 | current->timer_slack_ns); |
2599 | } |
2600 | |
2601 | /* |
2602 | * The waiter is allocated on our stack, manipulated by the requeue |
2603 | * code while we sleep on uaddr. |
2604 | */ |
2605 | debug_rt_mutex_init_waiter(&rt_waiter); |
2606 | RB_CLEAR_NODE(&rt_waiter.pi_tree_entry); |
2607 | RB_CLEAR_NODE(&rt_waiter.tree_entry); |
2608 | rt_waiter.task = NULL; |
2609 | |
2610 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE); |
2611 | if (unlikely(ret != 0)) |
2612 | goto out; |
2613 | |
2614 | q.bitset = bitset; |
2615 | q.rt_waiter = &rt_waiter; |
2616 | q.requeue_pi_key = &key2; |
2617 | |
2618 | /* |
2619 | * Prepare to wait on uaddr. On success, increments q.key (key1) ref |
2620 | * count. |
2621 | */ |
2622 | ret = futex_wait_setup(uaddr, val, flags, &q, &hb); |
2623 | if (ret) |
2624 | goto out_key2; |
2625 | |
2626 | /* |
2627 | * The check above which compares uaddrs is not sufficient for |
2628 | * shared futexes. We need to compare the keys: |
2629 | */ |
2630 | if (match_futex(&q.key, &key2)) { |
2631 | ret = -EINVAL; |
2632 | goto out_put_keys; |
2633 | } |
2634 | |
2635 | /* Queue the futex_q, drop the hb lock, wait for wakeup. */ |
2636 | futex_wait_queue_me(hb, &q, to); |
2637 | |
2638 | spin_lock(&hb->lock); |
2639 | ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to); |
2640 | spin_unlock(&hb->lock); |
2641 | if (ret) |
2642 | goto out_put_keys; |
2643 | |
2644 | /* |
2645 | * In order for us to be here, we know our q.key == key2, and since |
2646 | * we took the hb->lock above, we also know that futex_requeue() has |
2647 | * completed and we no longer have to concern ourselves with a wakeup |
2648 | * race with the atomic proxy lock acquisition by the requeue code. The |
2649 | * futex_requeue dropped our key1 reference and incremented our key2 |
2650 | * reference count. |
2651 | */ |
2652 | |
2653 | /* Check if the requeue code acquired the second futex for us. */ |
2654 | if (!q.rt_waiter) { |
2655 | /* |
2656 | * Got the lock. We might not be the anticipated owner if we |
2657 | * did a lock-steal - fix up the PI-state in that case. |
2658 | */ |
2659 | if (q.pi_state && (q.pi_state->owner != current)) { |
2660 | spin_lock(q.lock_ptr); |
2661 | ret = fixup_pi_state_owner(uaddr2, &q, current); |
2662 | spin_unlock(q.lock_ptr); |
2663 | } |
2664 | } else { |
2665 | /* |
2666 | * We have been woken up by futex_unlock_pi(), a timeout, or a |
2667 | * signal. futex_unlock_pi() will not destroy the lock_ptr nor |
2668 | * the pi_state. |
2669 | */ |
2670 | WARN_ON(!q.pi_state); |
2671 | pi_mutex = &q.pi_state->pi_mutex; |
2672 | ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1); |
2673 | debug_rt_mutex_free_waiter(&rt_waiter); |
2674 | |
2675 | spin_lock(q.lock_ptr); |
2676 | /* |
2677 | * Fixup the pi_state owner and possibly acquire the lock if we |
2678 | * haven't already. |
2679 | */ |
2680 | res = fixup_owner(uaddr2, &q, !ret); |
2681 | /* |
2682 | * If fixup_owner() returned an error, proprogate that. If it |
2683 | * acquired the lock, clear -ETIMEDOUT or -EINTR. |
2684 | */ |
2685 | if (res) |
2686 | ret = (res < 0) ? res : 0; |
2687 | |
2688 | /* Unqueue and drop the lock. */ |
2689 | unqueue_me_pi(&q); |
2690 | } |
2691 | |
2692 | /* |
2693 | * If fixup_pi_state_owner() faulted and was unable to handle the |
2694 | * fault, unlock the rt_mutex and return the fault to userspace. |
2695 | */ |
2696 | if (ret == -EFAULT) { |
2697 | if (pi_mutex && rt_mutex_owner(pi_mutex) == current) |
2698 | rt_mutex_unlock(pi_mutex); |
2699 | } else if (ret == -EINTR) { |
2700 | /* |
2701 | * We've already been requeued, but cannot restart by calling |
2702 | * futex_lock_pi() directly. We could restart this syscall, but |
2703 | * it would detect that the user space "val" changed and return |
2704 | * -EWOULDBLOCK. Save the overhead of the restart and return |
2705 | * -EWOULDBLOCK directly. |
2706 | */ |
2707 | ret = -EWOULDBLOCK; |
2708 | } |
2709 | |
2710 | out_put_keys: |
2711 | put_futex_key(&q.key); |
2712 | out_key2: |
2713 | put_futex_key(&key2); |
2714 | |
2715 | out: |
2716 | if (to) { |
2717 | hrtimer_cancel(&to->timer); |
2718 | destroy_hrtimer_on_stack(&to->timer); |
2719 | } |
2720 | return ret; |
2721 | } |
2722 | |
2723 | /* |
2724 | * Support for robust futexes: the kernel cleans up held futexes at |
2725 | * thread exit time. |
2726 | * |
2727 | * Implementation: user-space maintains a per-thread list of locks it |
2728 | * is holding. Upon do_exit(), the kernel carefully walks this list, |
2729 | * and marks all locks that are owned by this thread with the |
2730 | * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is |
2731 | * always manipulated with the lock held, so the list is private and |
2732 | * per-thread. Userspace also maintains a per-thread 'list_op_pending' |
2733 | * field, to allow the kernel to clean up if the thread dies after |
2734 | * acquiring the lock, but just before it could have added itself to |
2735 | * the list. There can only be one such pending lock. |
2736 | */ |
2737 | |
2738 | /** |
2739 | * sys_set_robust_list() - Set the robust-futex list head of a task |
2740 | * @head: pointer to the list-head |
2741 | * @len: length of the list-head, as userspace expects |
2742 | */ |
2743 | SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head, |
2744 | size_t, len) |
2745 | { |
2746 | if (!futex_cmpxchg_enabled) |
2747 | return -ENOSYS; |
2748 | /* |
2749 | * The kernel knows only one size for now: |
2750 | */ |
2751 | if (unlikely(len != sizeof(*head))) |
2752 | return -EINVAL; |
2753 | |
2754 | current->robust_list = head; |
2755 | |
2756 | return 0; |
2757 | } |
2758 | |
2759 | /** |
2760 | * sys_get_robust_list() - Get the robust-futex list head of a task |
2761 | * @pid: pid of the process [zero for current task] |
2762 | * @head_ptr: pointer to a list-head pointer, the kernel fills it in |
2763 | * @len_ptr: pointer to a length field, the kernel fills in the header size |
2764 | */ |
2765 | SYSCALL_DEFINE3(get_robust_list, int, pid, |
2766 | struct robust_list_head __user * __user *, head_ptr, |
2767 | size_t __user *, len_ptr) |
2768 | { |
2769 | struct robust_list_head __user *head; |
2770 | unsigned long ret; |
2771 | struct task_struct *p; |
2772 | |
2773 | if (!futex_cmpxchg_enabled) |
2774 | return -ENOSYS; |
2775 | |
2776 | rcu_read_lock(); |
2777 | |
2778 | ret = -ESRCH; |
2779 | if (!pid) |
2780 | p = current; |
2781 | else { |
2782 | p = find_task_by_vpid(pid); |
2783 | if (!p) |
2784 | goto err_unlock; |
2785 | } |
2786 | |
2787 | ret = -EPERM; |
2788 | if (!ptrace_may_access(p, PTRACE_MODE_READ)) |
2789 | goto err_unlock; |
2790 | |
2791 | head = p->robust_list; |
2792 | rcu_read_unlock(); |
2793 | |
2794 | if (put_user(sizeof(*head), len_ptr)) |
2795 | return -EFAULT; |
2796 | return put_user(head, head_ptr); |
2797 | |
2798 | err_unlock: |
2799 | rcu_read_unlock(); |
2800 | |
2801 | return ret; |
2802 | } |
2803 | |
2804 | /* |
2805 | * Process a futex-list entry, check whether it's owned by the |
2806 | * dying task, and do notification if so: |
2807 | */ |
2808 | int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi) |
2809 | { |
2810 | u32 uval, uninitialized_var(nval), mval; |
2811 | |
2812 | retry: |
2813 | if (get_user(uval, uaddr)) |
2814 | return -1; |
2815 | |
2816 | if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) { |
2817 | /* |
2818 | * Ok, this dying thread is truly holding a futex |
2819 | * of interest. Set the OWNER_DIED bit atomically |
2820 | * via cmpxchg, and if the value had FUTEX_WAITERS |
2821 | * set, wake up a waiter (if any). (We have to do a |
2822 | * futex_wake() even if OWNER_DIED is already set - |
2823 | * to handle the rare but possible case of recursive |
2824 | * thread-death.) The rest of the cleanup is done in |
2825 | * userspace. |
2826 | */ |
2827 | mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED; |
2828 | /* |
2829 | * We are not holding a lock here, but we want to have |
2830 | * the pagefault_disable/enable() protection because |
2831 | * we want to handle the fault gracefully. If the |
2832 | * access fails we try to fault in the futex with R/W |
2833 | * verification via get_user_pages. get_user() above |
2834 | * does not guarantee R/W access. If that fails we |
2835 | * give up and leave the futex locked. |
2836 | */ |
2837 | if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) { |
2838 | if (fault_in_user_writeable(uaddr)) |
2839 | return -1; |
2840 | goto retry; |
2841 | } |
2842 | if (nval != uval) |
2843 | goto retry; |
2844 | |
2845 | /* |
2846 | * Wake robust non-PI futexes here. The wakeup of |
2847 | * PI futexes happens in exit_pi_state(): |
2848 | */ |
2849 | if (!pi && (uval & FUTEX_WAITERS)) |
2850 | futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY); |
2851 | } |
2852 | return 0; |
2853 | } |
2854 | |
2855 | /* |
2856 | * Fetch a robust-list pointer. Bit 0 signals PI futexes: |
2857 | */ |
2858 | static inline int fetch_robust_entry(struct robust_list __user **entry, |
2859 | struct robust_list __user * __user *head, |
2860 | unsigned int *pi) |
2861 | { |
2862 | unsigned long uentry; |
2863 | |
2864 | if (get_user(uentry, (unsigned long __user *)head)) |
2865 | return -EFAULT; |
2866 | |
2867 | *entry = (void __user *)(uentry & ~1UL); |
2868 | *pi = uentry & 1; |
2869 | |
2870 | return 0; |
2871 | } |
2872 | |
2873 | /* |
2874 | * Walk curr->robust_list (very carefully, it's a userspace list!) |
2875 | * and mark any locks found there dead, and notify any waiters. |
2876 | * |
2877 | * We silently return on any sign of list-walking problem. |
2878 | */ |
2879 | void exit_robust_list(struct task_struct *curr) |
2880 | { |
2881 | struct robust_list_head __user *head = curr->robust_list; |
2882 | struct robust_list __user *entry, *next_entry, *pending; |
2883 | unsigned int limit = ROBUST_LIST_LIMIT, pi, pip; |
2884 | unsigned int uninitialized_var(next_pi); |
2885 | unsigned long futex_offset; |
2886 | int rc; |
2887 | |
2888 | if (!futex_cmpxchg_enabled) |
2889 | return; |
2890 | |
2891 | /* |
2892 | * Fetch the list head (which was registered earlier, via |
2893 | * sys_set_robust_list()): |
2894 | */ |
2895 | if (fetch_robust_entry(&entry, &head->list.next, &pi)) |
2896 | return; |
2897 | /* |
2898 | * Fetch the relative futex offset: |
2899 | */ |
2900 | if (get_user(futex_offset, &head->futex_offset)) |
2901 | return; |
2902 | /* |
2903 | * Fetch any possibly pending lock-add first, and handle it |
2904 | * if it exists: |
2905 | */ |
2906 | if (fetch_robust_entry(&pending, &head->list_op_pending, &pip)) |
2907 | return; |
2908 | |
2909 | next_entry = NULL; /* avoid warning with gcc */ |
2910 | while (entry != &head->list) { |
2911 | /* |
2912 | * Fetch the next entry in the list before calling |
2913 | * handle_futex_death: |
2914 | */ |
2915 | rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi); |
2916 | /* |
2917 | * A pending lock might already be on the list, so |
2918 | * don't process it twice: |
2919 | */ |
2920 | if (entry != pending) |
2921 | if (handle_futex_death((void __user *)entry + futex_offset, |
2922 | curr, pi)) |
2923 | return; |
2924 | if (rc) |
2925 | return; |
2926 | entry = next_entry; |
2927 | pi = next_pi; |
2928 | /* |
2929 | * Avoid excessively long or circular lists: |
2930 | */ |
2931 | if (!--limit) |
2932 | break; |
2933 | |
2934 | cond_resched(); |
2935 | } |
2936 | |
2937 | if (pending) |
2938 | handle_futex_death((void __user *)pending + futex_offset, |
2939 | curr, pip); |
2940 | } |
2941 | |
2942 | long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, |
2943 | u32 __user *uaddr2, u32 val2, u32 val3) |
2944 | { |
2945 | int cmd = op & FUTEX_CMD_MASK; |
2946 | unsigned int flags = 0; |
2947 | |
2948 | if (!(op & FUTEX_PRIVATE_FLAG)) |
2949 | flags |= FLAGS_SHARED; |
2950 | |
2951 | if (op & FUTEX_CLOCK_REALTIME) { |
2952 | flags |= FLAGS_CLOCKRT; |
2953 | if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI) |
2954 | return -ENOSYS; |
2955 | } |
2956 | |
2957 | switch (cmd) { |
2958 | case FUTEX_LOCK_PI: |
2959 | case FUTEX_UNLOCK_PI: |
2960 | case FUTEX_TRYLOCK_PI: |
2961 | case FUTEX_WAIT_REQUEUE_PI: |
2962 | case FUTEX_CMP_REQUEUE_PI: |
2963 | if (!futex_cmpxchg_enabled) |
2964 | return -ENOSYS; |
2965 | } |
2966 | |
2967 | switch (cmd) { |
2968 | case FUTEX_WAIT: |
2969 | val3 = FUTEX_BITSET_MATCH_ANY; |
2970 | case FUTEX_WAIT_BITSET: |
2971 | return futex_wait(uaddr, flags, val, timeout, val3); |
2972 | case FUTEX_WAKE: |
2973 | val3 = FUTEX_BITSET_MATCH_ANY; |
2974 | case FUTEX_WAKE_BITSET: |
2975 | return futex_wake(uaddr, flags, val, val3); |
2976 | case FUTEX_REQUEUE: |
2977 | return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0); |
2978 | case FUTEX_CMP_REQUEUE: |
2979 | return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0); |
2980 | case FUTEX_WAKE_OP: |
2981 | return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3); |
2982 | case FUTEX_LOCK_PI: |
2983 | return futex_lock_pi(uaddr, flags, val, timeout, 0); |
2984 | case FUTEX_UNLOCK_PI: |
2985 | return futex_unlock_pi(uaddr, flags); |
2986 | case FUTEX_TRYLOCK_PI: |
2987 | return futex_lock_pi(uaddr, flags, 0, timeout, 1); |
2988 | case FUTEX_WAIT_REQUEUE_PI: |
2989 | val3 = FUTEX_BITSET_MATCH_ANY; |
2990 | return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3, |
2991 | uaddr2); |
2992 | case FUTEX_CMP_REQUEUE_PI: |
2993 | return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1); |
2994 | } |
2995 | return -ENOSYS; |
2996 | } |
2997 | |
2998 | |
2999 | SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, |
3000 | struct timespec __user *, utime, u32 __user *, uaddr2, |
3001 | u32, val3) |
3002 | { |
3003 | struct timespec ts; |
3004 | ktime_t t, *tp = NULL; |
3005 | u32 val2 = 0; |
3006 | int cmd = op & FUTEX_CMD_MASK; |
3007 | |
3008 | if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI || |
3009 | cmd == FUTEX_WAIT_BITSET || |
3010 | cmd == FUTEX_WAIT_REQUEUE_PI)) { |
3011 | if (copy_from_user(&ts, utime, sizeof(ts)) != 0) |
3012 | return -EFAULT; |
3013 | if (!timespec_valid(&ts)) |
3014 | return -EINVAL; |
3015 | |
3016 | t = timespec_to_ktime(ts); |
3017 | if (cmd == FUTEX_WAIT) |
3018 | t = ktime_add_safe(ktime_get(), t); |
3019 | tp = &t; |
3020 | } |
3021 | /* |
3022 | * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*. |
3023 | * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP. |
3024 | */ |
3025 | if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE || |
3026 | cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP) |
3027 | val2 = (u32) (unsigned long) utime; |
3028 | |
3029 | return do_futex(uaddr, op, val, tp, uaddr2, val2, val3); |
3030 | } |
3031 | |
3032 | static void __init futex_detect_cmpxchg(void) |
3033 | { |
3034 | #ifndef CONFIG_HAVE_FUTEX_CMPXCHG |
3035 | u32 curval; |
3036 | |
3037 | /* |
3038 | * This will fail and we want it. Some arch implementations do |
3039 | * runtime detection of the futex_atomic_cmpxchg_inatomic() |
3040 | * functionality. We want to know that before we call in any |
3041 | * of the complex code paths. Also we want to prevent |
3042 | * registration of robust lists in that case. NULL is |
3043 | * guaranteed to fault and we get -EFAULT on functional |
3044 | * implementation, the non-functional ones will return |
3045 | * -ENOSYS. |
3046 | */ |
3047 | if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT) |
3048 | futex_cmpxchg_enabled = 1; |
3049 | #endif |
3050 | } |
3051 | |
3052 | static int __init futex_init(void) |
3053 | { |
3054 | unsigned int futex_shift; |
3055 | unsigned long i; |
3056 | |
3057 | #if CONFIG_BASE_SMALL |
3058 | futex_hashsize = 16; |
3059 | #else |
3060 | futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus()); |
3061 | #endif |
3062 | |
3063 | futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues), |
3064 | futex_hashsize, 0, |
3065 | futex_hashsize < 256 ? HASH_SMALL : 0, |
3066 | &futex_shift, NULL, |
3067 | futex_hashsize, futex_hashsize); |
3068 | futex_hashsize = 1UL << futex_shift; |
3069 | |
3070 | futex_detect_cmpxchg(); |
3071 | |
3072 | for (i = 0; i < futex_hashsize; i++) { |
3073 | atomic_set(&futex_queues[i].waiters, 0); |
3074 | plist_head_init(&futex_queues[i].chain); |
3075 | spin_lock_init(&futex_queues[i].lock); |
3076 | } |
3077 | |
3078 | return 0; |
3079 | } |
3080 | __initcall(futex_init); |
3081 |
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