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1 | /* | |
2 | * Fast Userspace Mutexes (which I call "Futexes!"). | |
3 | * (C) Rusty Russell, IBM 2002 | |
4 | * | |
5 | * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar | |
6 | * (C) Copyright 2003 Red Hat Inc, All Rights Reserved | |
7 | * | |
8 | * Removed page pinning, fix privately mapped COW pages and other cleanups | |
9 | * (C) Copyright 2003, 2004 Jamie Lokier | |
10 | * | |
11 | * Robust futex support started by Ingo Molnar | |
12 | * (C) Copyright 2006 Red Hat Inc, All Rights Reserved | |
13 | * Thanks to Thomas Gleixner for suggestions, analysis and fixes. | |
14 | * | |
15 | * PI-futex support started by Ingo Molnar and Thomas Gleixner | |
16 | * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> | |
17 | * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com> | |
18 | * | |
19 | * PRIVATE futexes by Eric Dumazet | |
20 | * Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com> | |
21 | * | |
22 | * Requeue-PI support by Darren Hart <dvhltc@us.ibm.com> | |
23 | * Copyright (C) IBM Corporation, 2009 | |
24 | * Thanks to Thomas Gleixner for conceptual design and careful reviews. | |
25 | * | |
26 | * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly | |
27 | * enough at me, Linus for the original (flawed) idea, Matthew | |
28 | * Kirkwood for proof-of-concept implementation. | |
29 | * | |
30 | * "The futexes are also cursed." | |
31 | * "But they come in a choice of three flavours!" | |
32 | * | |
33 | * This program is free software; you can redistribute it and/or modify | |
34 | * it under the terms of the GNU General Public License as published by | |
35 | * the Free Software Foundation; either version 2 of the License, or | |
36 | * (at your option) any later version. | |
37 | * | |
38 | * This program is distributed in the hope that it will be useful, | |
39 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
40 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
41 | * GNU General Public License for more details. | |
42 | * | |
43 | * You should have received a copy of the GNU General Public License | |
44 | * along with this program; if not, write to the Free Software | |
45 | * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA | |
46 | */ | |
47 | #include <linux/slab.h> | |
48 | #include <linux/poll.h> | |
49 | #include <linux/fs.h> | |
50 | #include <linux/file.h> | |
51 | #include <linux/jhash.h> | |
52 | #include <linux/init.h> | |
53 | #include <linux/futex.h> | |
54 | #include <linux/mount.h> | |
55 | #include <linux/pagemap.h> | |
56 | #include <linux/syscalls.h> | |
57 | #include <linux/signal.h> | |
58 | #include <linux/export.h> | |
59 | #include <linux/magic.h> | |
60 | #include <linux/pid.h> | |
61 | #include <linux/nsproxy.h> | |
62 | #include <linux/ptrace.h> | |
63 | #include <linux/sched/rt.h> | |
64 | #include <linux/hugetlb.h> | |
65 | #include <linux/freezer.h> | |
66 | #include <linux/bootmem.h> | |
67 | #include <linux/fault-inject.h> | |
68 | ||
69 | #include <asm/futex.h> | |
70 | ||
71 | #include "locking/rtmutex_common.h" | |
72 | ||
73 | /* | |
74 | * READ this before attempting to hack on futexes! | |
75 | * | |
76 | * Basic futex operation and ordering guarantees | |
77 | * ============================================= | |
78 | * | |
79 | * The waiter reads the futex value in user space and calls | |
80 | * futex_wait(). This function computes the hash bucket and acquires | |
81 | * the hash bucket lock. After that it reads the futex user space value | |
82 | * again and verifies that the data has not changed. If it has not changed | |
83 | * it enqueues itself into the hash bucket, releases the hash bucket lock | |
84 | * and schedules. | |
85 | * | |
86 | * The waker side modifies the user space value of the futex and calls | |
87 | * futex_wake(). This function computes the hash bucket and acquires the | |
88 | * hash bucket lock. Then it looks for waiters on that futex in the hash | |
89 | * bucket and wakes them. | |
90 | * | |
91 | * In futex wake up scenarios where no tasks are blocked on a futex, taking | |
92 | * the hb spinlock can be avoided and simply return. In order for this | |
93 | * optimization to work, ordering guarantees must exist so that the waiter | |
94 | * being added to the list is acknowledged when the list is concurrently being | |
95 | * checked by the waker, avoiding scenarios like the following: | |
96 | * | |
97 | * CPU 0 CPU 1 | |
98 | * val = *futex; | |
99 | * sys_futex(WAIT, futex, val); | |
100 | * futex_wait(futex, val); | |
101 | * uval = *futex; | |
102 | * *futex = newval; | |
103 | * sys_futex(WAKE, futex); | |
104 | * futex_wake(futex); | |
105 | * if (queue_empty()) | |
106 | * return; | |
107 | * if (uval == val) | |
108 | * lock(hash_bucket(futex)); | |
109 | * queue(); | |
110 | * unlock(hash_bucket(futex)); | |
111 | * schedule(); | |
112 | * | |
113 | * This would cause the waiter on CPU 0 to wait forever because it | |
114 | * missed the transition of the user space value from val to newval | |
115 | * and the waker did not find the waiter in the hash bucket queue. | |
116 | * | |
117 | * The correct serialization ensures that a waiter either observes | |
118 | * the changed user space value before blocking or is woken by a | |
119 | * concurrent waker: | |
120 | * | |
121 | * CPU 0 CPU 1 | |
122 | * val = *futex; | |
123 | * sys_futex(WAIT, futex, val); | |
124 | * futex_wait(futex, val); | |
125 | * | |
126 | * waiters++; (a) | |
127 | * smp_mb(); (A) <-- paired with -. | |
128 | * | | |
129 | * lock(hash_bucket(futex)); | | |
130 | * | | |
131 | * uval = *futex; | | |
132 | * | *futex = newval; | |
133 | * | sys_futex(WAKE, futex); | |
134 | * | futex_wake(futex); | |
135 | * | | |
136 | * `--------> smp_mb(); (B) | |
137 | * if (uval == val) | |
138 | * queue(); | |
139 | * unlock(hash_bucket(futex)); | |
140 | * schedule(); if (waiters) | |
141 | * lock(hash_bucket(futex)); | |
142 | * else wake_waiters(futex); | |
143 | * waiters--; (b) unlock(hash_bucket(futex)); | |
144 | * | |
145 | * Where (A) orders the waiters increment and the futex value read through | |
146 | * atomic operations (see hb_waiters_inc) and where (B) orders the write | |
147 | * to futex and the waiters read -- this is done by the barriers for both | |
148 | * shared and private futexes in get_futex_key_refs(). | |
149 | * | |
150 | * This yields the following case (where X:=waiters, Y:=futex): | |
151 | * | |
152 | * X = Y = 0 | |
153 | * | |
154 | * w[X]=1 w[Y]=1 | |
155 | * MB MB | |
156 | * r[Y]=y r[X]=x | |
157 | * | |
158 | * Which guarantees that x==0 && y==0 is impossible; which translates back into | |
159 | * the guarantee that we cannot both miss the futex variable change and the | |
160 | * enqueue. | |
161 | * | |
162 | * Note that a new waiter is accounted for in (a) even when it is possible that | |
163 | * the wait call can return error, in which case we backtrack from it in (b). | |
164 | * Refer to the comment in queue_lock(). | |
165 | * | |
166 | * Similarly, in order to account for waiters being requeued on another | |
167 | * address we always increment the waiters for the destination bucket before | |
168 | * acquiring the lock. It then decrements them again after releasing it - | |
169 | * the code that actually moves the futex(es) between hash buckets (requeue_futex) | |
170 | * will do the additional required waiter count housekeeping. This is done for | |
171 | * double_lock_hb() and double_unlock_hb(), respectively. | |
172 | */ | |
173 | ||
174 | #ifndef CONFIG_HAVE_FUTEX_CMPXCHG | |
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 | #ifdef CONFIG_MMU | |
183 | # define FLAGS_SHARED 0x01 | |
184 | #else | |
185 | /* | |
186 | * NOMMU does not have per process address space. Let the compiler optimize | |
187 | * code away. | |
188 | */ | |
189 | # define FLAGS_SHARED 0x00 | |
190 | #endif | |
191 | #define FLAGS_CLOCKRT 0x02 | |
192 | #define FLAGS_HAS_TIMEOUT 0x04 | |
193 | ||
194 | /* | |
195 | * Priority Inheritance state: | |
196 | */ | |
197 | struct futex_pi_state { | |
198 | /* | |
199 | * list of 'owned' pi_state instances - these have to be | |
200 | * cleaned up in do_exit() if the task exits prematurely: | |
201 | */ | |
202 | struct list_head list; | |
203 | ||
204 | /* | |
205 | * The PI object: | |
206 | */ | |
207 | struct rt_mutex pi_mutex; | |
208 | ||
209 | struct task_struct *owner; | |
210 | atomic_t refcount; | |
211 | ||
212 | union futex_key key; | |
213 | }; | |
214 | ||
215 | /** | |
216 | * struct futex_q - The hashed futex queue entry, one per waiting task | |
217 | * @list: priority-sorted list of tasks waiting on this futex | |
218 | * @task: the task waiting on the futex | |
219 | * @lock_ptr: the hash bucket lock | |
220 | * @key: the key the futex is hashed on | |
221 | * @pi_state: optional priority inheritance state | |
222 | * @rt_waiter: rt_waiter storage for use with requeue_pi | |
223 | * @requeue_pi_key: the requeue_pi target futex key | |
224 | * @bitset: bitset for the optional bitmasked wakeup | |
225 | * | |
226 | * We use this hashed waitqueue, instead of a normal wait_queue_t, so | |
227 | * we can wake only the relevant ones (hashed queues may be shared). | |
228 | * | |
229 | * A futex_q has a woken state, just like tasks have TASK_RUNNING. | |
230 | * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0. | |
231 | * The order of wakeup is always to make the first condition true, then | |
232 | * the second. | |
233 | * | |
234 | * PI futexes are typically woken before they are removed from the hash list via | |
235 | * the rt_mutex code. See unqueue_me_pi(). | |
236 | */ | |
237 | struct futex_q { | |
238 | struct plist_node list; | |
239 | ||
240 | struct task_struct *task; | |
241 | spinlock_t *lock_ptr; | |
242 | union futex_key key; | |
243 | struct futex_pi_state *pi_state; | |
244 | struct rt_mutex_waiter *rt_waiter; | |
245 | union futex_key *requeue_pi_key; | |
246 | u32 bitset; | |
247 | }; | |
248 | ||
249 | static const struct futex_q futex_q_init = { | |
250 | /* list gets initialized in queue_me()*/ | |
251 | .key = FUTEX_KEY_INIT, | |
252 | .bitset = FUTEX_BITSET_MATCH_ANY | |
253 | }; | |
254 | ||
255 | /* | |
256 | * Hash buckets are shared by all the futex_keys that hash to the same | |
257 | * location. Each key may have multiple futex_q structures, one for each task | |
258 | * waiting on a futex. | |
259 | */ | |
260 | struct futex_hash_bucket { | |
261 | atomic_t waiters; | |
262 | spinlock_t lock; | |
263 | struct plist_head chain; | |
264 | } ____cacheline_aligned_in_smp; | |
265 | ||
266 | /* | |
267 | * The base of the bucket array and its size are always used together | |
268 | * (after initialization only in hash_futex()), so ensure that they | |
269 | * reside in the same cacheline. | |
270 | */ | |
271 | static struct { | |
272 | struct futex_hash_bucket *queues; | |
273 | unsigned long hashsize; | |
274 | } __futex_data __read_mostly __aligned(2*sizeof(long)); | |
275 | #define futex_queues (__futex_data.queues) | |
276 | #define futex_hashsize (__futex_data.hashsize) | |
277 | ||
278 | ||
279 | /* | |
280 | * Fault injections for futexes. | |
281 | */ | |
282 | #ifdef CONFIG_FAIL_FUTEX | |
283 | ||
284 | static struct { | |
285 | struct fault_attr attr; | |
286 | ||
287 | bool ignore_private; | |
288 | } fail_futex = { | |
289 | .attr = FAULT_ATTR_INITIALIZER, | |
290 | .ignore_private = false, | |
291 | }; | |
292 | ||
293 | static int __init setup_fail_futex(char *str) | |
294 | { | |
295 | return setup_fault_attr(&fail_futex.attr, str); | |
296 | } | |
297 | __setup("fail_futex=", setup_fail_futex); | |
298 | ||
299 | static bool should_fail_futex(bool fshared) | |
300 | { | |
301 | if (fail_futex.ignore_private && !fshared) | |
302 | return false; | |
303 | ||
304 | return should_fail(&fail_futex.attr, 1); | |
305 | } | |
306 | ||
307 | #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS | |
308 | ||
309 | static int __init fail_futex_debugfs(void) | |
310 | { | |
311 | umode_t mode = S_IFREG | S_IRUSR | S_IWUSR; | |
312 | struct dentry *dir; | |
313 | ||
314 | dir = fault_create_debugfs_attr("fail_futex", NULL, | |
315 | &fail_futex.attr); | |
316 | if (IS_ERR(dir)) | |
317 | return PTR_ERR(dir); | |
318 | ||
319 | if (!debugfs_create_bool("ignore-private", mode, dir, | |
320 | &fail_futex.ignore_private)) { | |
321 | debugfs_remove_recursive(dir); | |
322 | return -ENOMEM; | |
323 | } | |
324 | ||
325 | return 0; | |
326 | } | |
327 | ||
328 | late_initcall(fail_futex_debugfs); | |
329 | ||
330 | #endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */ | |
331 | ||
332 | #else | |
333 | static inline bool should_fail_futex(bool fshared) | |
334 | { | |
335 | return false; | |
336 | } | |
337 | #endif /* CONFIG_FAIL_FUTEX */ | |
338 | ||
339 | static inline void futex_get_mm(union futex_key *key) | |
340 | { | |
341 | atomic_inc(&key->private.mm->mm_count); | |
342 | /* | |
343 | * Ensure futex_get_mm() implies a full barrier such that | |
344 | * get_futex_key() implies a full barrier. This is relied upon | |
345 | * as smp_mb(); (B), see the ordering comment above. | |
346 | */ | |
347 | smp_mb__after_atomic(); | |
348 | } | |
349 | ||
350 | /* | |
351 | * Reflects a new waiter being added to the waitqueue. | |
352 | */ | |
353 | static inline void hb_waiters_inc(struct futex_hash_bucket *hb) | |
354 | { | |
355 | #ifdef CONFIG_SMP | |
356 | atomic_inc(&hb->waiters); | |
357 | /* | |
358 | * Full barrier (A), see the ordering comment above. | |
359 | */ | |
360 | smp_mb__after_atomic(); | |
361 | #endif | |
362 | } | |
363 | ||
364 | /* | |
365 | * Reflects a waiter being removed from the waitqueue by wakeup | |
366 | * paths. | |
367 | */ | |
368 | static inline void hb_waiters_dec(struct futex_hash_bucket *hb) | |
369 | { | |
370 | #ifdef CONFIG_SMP | |
371 | atomic_dec(&hb->waiters); | |
372 | #endif | |
373 | } | |
374 | ||
375 | static inline int hb_waiters_pending(struct futex_hash_bucket *hb) | |
376 | { | |
377 | #ifdef CONFIG_SMP | |
378 | return atomic_read(&hb->waiters); | |
379 | #else | |
380 | return 1; | |
381 | #endif | |
382 | } | |
383 | ||
384 | /** | |
385 | * hash_futex - Return the hash bucket in the global hash | |
386 | * @key: Pointer to the futex key for which the hash is calculated | |
387 | * | |
388 | * We hash on the keys returned from get_futex_key (see below) and return the | |
389 | * corresponding hash bucket in the global hash. | |
390 | */ | |
391 | static struct futex_hash_bucket *hash_futex(union futex_key *key) | |
392 | { | |
393 | u32 hash = jhash2((u32*)&key->both.word, | |
394 | (sizeof(key->both.word)+sizeof(key->both.ptr))/4, | |
395 | key->both.offset); | |
396 | return &futex_queues[hash & (futex_hashsize - 1)]; | |
397 | } | |
398 | ||
399 | ||
400 | /** | |
401 | * match_futex - Check whether two futex keys are equal | |
402 | * @key1: Pointer to key1 | |
403 | * @key2: Pointer to key2 | |
404 | * | |
405 | * Return 1 if two futex_keys are equal, 0 otherwise. | |
406 | */ | |
407 | static inline int match_futex(union futex_key *key1, union futex_key *key2) | |
408 | { | |
409 | return (key1 && key2 | |
410 | && key1->both.word == key2->both.word | |
411 | && key1->both.ptr == key2->both.ptr | |
412 | && key1->both.offset == key2->both.offset); | |
413 | } | |
414 | ||
415 | /* | |
416 | * Take a reference to the resource addressed by a key. | |
417 | * Can be called while holding spinlocks. | |
418 | * | |
419 | */ | |
420 | static void get_futex_key_refs(union futex_key *key) | |
421 | { | |
422 | if (!key->both.ptr) | |
423 | return; | |
424 | ||
425 | /* | |
426 | * On MMU less systems futexes are always "private" as there is no per | |
427 | * process address space. We need the smp wmb nevertheless - yes, | |
428 | * arch/blackfin has MMU less SMP ... | |
429 | */ | |
430 | if (!IS_ENABLED(CONFIG_MMU)) { | |
431 | smp_mb(); /* explicit smp_mb(); (B) */ | |
432 | return; | |
433 | } | |
434 | ||
435 | switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) { | |
436 | case FUT_OFF_INODE: | |
437 | ihold(key->shared.inode); /* implies smp_mb(); (B) */ | |
438 | break; | |
439 | case FUT_OFF_MMSHARED: | |
440 | futex_get_mm(key); /* implies smp_mb(); (B) */ | |
441 | break; | |
442 | default: | |
443 | /* | |
444 | * Private futexes do not hold reference on an inode or | |
445 | * mm, therefore the only purpose of calling get_futex_key_refs | |
446 | * is because we need the barrier for the lockless waiter check. | |
447 | */ | |
448 | smp_mb(); /* explicit smp_mb(); (B) */ | |
449 | } | |
450 | } | |
451 | ||
452 | /* | |
453 | * Drop a reference to the resource addressed by a key. | |
454 | * The hash bucket spinlock must not be held. This is | |
455 | * a no-op for private futexes, see comment in the get | |
456 | * counterpart. | |
457 | */ | |
458 | static void drop_futex_key_refs(union futex_key *key) | |
459 | { | |
460 | if (!key->both.ptr) { | |
461 | /* If we're here then we tried to put a key we failed to get */ | |
462 | WARN_ON_ONCE(1); | |
463 | return; | |
464 | } | |
465 | ||
466 | if (!IS_ENABLED(CONFIG_MMU)) | |
467 | return; | |
468 | ||
469 | switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) { | |
470 | case FUT_OFF_INODE: | |
471 | iput(key->shared.inode); | |
472 | break; | |
473 | case FUT_OFF_MMSHARED: | |
474 | mmdrop(key->private.mm); | |
475 | break; | |
476 | } | |
477 | } | |
478 | ||
479 | /** | |
480 | * get_futex_key() - Get parameters which are the keys for a futex | |
481 | * @uaddr: virtual address of the futex | |
482 | * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED | |
483 | * @key: address where result is stored. | |
484 | * @rw: mapping needs to be read/write (values: VERIFY_READ, | |
485 | * VERIFY_WRITE) | |
486 | * | |
487 | * Return: a negative error code or 0 | |
488 | * | |
489 | * The key words are stored in *key on success. | |
490 | * | |
491 | * For shared mappings, it's (page->index, file_inode(vma->vm_file), | |
492 | * offset_within_page). For private mappings, it's (uaddr, current->mm). | |
493 | * We can usually work out the index without swapping in the page. | |
494 | * | |
495 | * lock_page() might sleep, the caller should not hold a spinlock. | |
496 | */ | |
497 | static int | |
498 | get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw) | |
499 | { | |
500 | unsigned long address = (unsigned long)uaddr; | |
501 | struct mm_struct *mm = current->mm; | |
502 | struct page *page, *tail; | |
503 | struct address_space *mapping; | |
504 | int err, ro = 0; | |
505 | ||
506 | /* | |
507 | * The futex address must be "naturally" aligned. | |
508 | */ | |
509 | key->both.offset = address % PAGE_SIZE; | |
510 | if (unlikely((address % sizeof(u32)) != 0)) | |
511 | return -EINVAL; | |
512 | address -= key->both.offset; | |
513 | ||
514 | if (unlikely(!access_ok(rw, uaddr, sizeof(u32)))) | |
515 | return -EFAULT; | |
516 | ||
517 | if (unlikely(should_fail_futex(fshared))) | |
518 | return -EFAULT; | |
519 | ||
520 | /* | |
521 | * PROCESS_PRIVATE futexes are fast. | |
522 | * As the mm cannot disappear under us and the 'key' only needs | |
523 | * virtual address, we dont even have to find the underlying vma. | |
524 | * Note : We do have to check 'uaddr' is a valid user address, | |
525 | * but access_ok() should be faster than find_vma() | |
526 | */ | |
527 | if (!fshared) { | |
528 | key->private.mm = mm; | |
529 | key->private.address = address; | |
530 | get_futex_key_refs(key); /* implies smp_mb(); (B) */ | |
531 | return 0; | |
532 | } | |
533 | ||
534 | again: | |
535 | /* Ignore any VERIFY_READ mapping (futex common case) */ | |
536 | if (unlikely(should_fail_futex(fshared))) | |
537 | return -EFAULT; | |
538 | ||
539 | err = get_user_pages_fast(address, 1, 1, &page); | |
540 | /* | |
541 | * If write access is not required (eg. FUTEX_WAIT), try | |
542 | * and get read-only access. | |
543 | */ | |
544 | if (err == -EFAULT && rw == VERIFY_READ) { | |
545 | err = get_user_pages_fast(address, 1, 0, &page); | |
546 | ro = 1; | |
547 | } | |
548 | if (err < 0) | |
549 | return err; | |
550 | else | |
551 | err = 0; | |
552 | ||
553 | /* | |
554 | * The treatment of mapping from this point on is critical. The page | |
555 | * lock protects many things but in this context the page lock | |
556 | * stabilizes mapping, prevents inode freeing in the shared | |
557 | * file-backed region case and guards against movement to swap cache. | |
558 | * | |
559 | * Strictly speaking the page lock is not needed in all cases being | |
560 | * considered here and page lock forces unnecessarily serialization | |
561 | * From this point on, mapping will be re-verified if necessary and | |
562 | * page lock will be acquired only if it is unavoidable | |
563 | * | |
564 | * Mapping checks require the head page for any compound page so the | |
565 | * head page and mapping is looked up now. For anonymous pages, it | |
566 | * does not matter if the page splits in the future as the key is | |
567 | * based on the address. For filesystem-backed pages, the tail is | |
568 | * required as the index of the page determines the key. For | |
569 | * base pages, there is no tail page and tail == page. | |
570 | */ | |
571 | tail = page; | |
572 | page = compound_head(page); | |
573 | mapping = READ_ONCE(page->mapping); | |
574 | ||
575 | /* | |
576 | * If page->mapping is NULL, then it cannot be a PageAnon | |
577 | * page; but it might be the ZERO_PAGE or in the gate area or | |
578 | * in a special mapping (all cases which we are happy to fail); | |
579 | * or it may have been a good file page when get_user_pages_fast | |
580 | * found it, but truncated or holepunched or subjected to | |
581 | * invalidate_complete_page2 before we got the page lock (also | |
582 | * cases which we are happy to fail). And we hold a reference, | |
583 | * so refcount care in invalidate_complete_page's remove_mapping | |
584 | * prevents drop_caches from setting mapping to NULL beneath us. | |
585 | * | |
586 | * The case we do have to guard against is when memory pressure made | |
587 | * shmem_writepage move it from filecache to swapcache beneath us: | |
588 | * an unlikely race, but we do need to retry for page->mapping. | |
589 | */ | |
590 | if (unlikely(!mapping)) { | |
591 | int shmem_swizzled; | |
592 | ||
593 | /* | |
594 | * Page lock is required to identify which special case above | |
595 | * applies. If this is really a shmem page then the page lock | |
596 | * will prevent unexpected transitions. | |
597 | */ | |
598 | lock_page(page); | |
599 | shmem_swizzled = PageSwapCache(page) || page->mapping; | |
600 | unlock_page(page); | |
601 | put_page(page); | |
602 | ||
603 | if (shmem_swizzled) | |
604 | goto again; | |
605 | ||
606 | return -EFAULT; | |
607 | } | |
608 | ||
609 | /* | |
610 | * Private mappings are handled in a simple way. | |
611 | * | |
612 | * If the futex key is stored on an anonymous page, then the associated | |
613 | * object is the mm which is implicitly pinned by the calling process. | |
614 | * | |
615 | * NOTE: When userspace waits on a MAP_SHARED mapping, even if | |
616 | * it's a read-only handle, it's expected that futexes attach to | |
617 | * the object not the particular process. | |
618 | */ | |
619 | if (PageAnon(page)) { | |
620 | /* | |
621 | * A RO anonymous page will never change and thus doesn't make | |
622 | * sense for futex operations. | |
623 | */ | |
624 | if (unlikely(should_fail_futex(fshared)) || ro) { | |
625 | err = -EFAULT; | |
626 | goto out; | |
627 | } | |
628 | ||
629 | key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */ | |
630 | key->private.mm = mm; | |
631 | key->private.address = address; | |
632 | ||
633 | get_futex_key_refs(key); /* implies smp_mb(); (B) */ | |
634 | ||
635 | } else { | |
636 | struct inode *inode; | |
637 | ||
638 | /* | |
639 | * The associated futex object in this case is the inode and | |
640 | * the page->mapping must be traversed. Ordinarily this should | |
641 | * be stabilised under page lock but it's not strictly | |
642 | * necessary in this case as we just want to pin the inode, not | |
643 | * update the radix tree or anything like that. | |
644 | * | |
645 | * The RCU read lock is taken as the inode is finally freed | |
646 | * under RCU. If the mapping still matches expectations then the | |
647 | * mapping->host can be safely accessed as being a valid inode. | |
648 | */ | |
649 | rcu_read_lock(); | |
650 | ||
651 | if (READ_ONCE(page->mapping) != mapping) { | |
652 | rcu_read_unlock(); | |
653 | put_page(page); | |
654 | ||
655 | goto again; | |
656 | } | |
657 | ||
658 | inode = READ_ONCE(mapping->host); | |
659 | if (!inode) { | |
660 | rcu_read_unlock(); | |
661 | put_page(page); | |
662 | ||
663 | goto again; | |
664 | } | |
665 | ||
666 | /* | |
667 | * Take a reference unless it is about to be freed. Previously | |
668 | * this reference was taken by ihold under the page lock | |
669 | * pinning the inode in place so i_lock was unnecessary. The | |
670 | * only way for this check to fail is if the inode was | |
671 | * truncated in parallel so warn for now if this happens. | |
672 | * | |
673 | * We are not calling into get_futex_key_refs() in file-backed | |
674 | * cases, therefore a successful atomic_inc return below will | |
675 | * guarantee that get_futex_key() will still imply smp_mb(); (B). | |
676 | */ | |
677 | if (WARN_ON_ONCE(!atomic_inc_not_zero(&inode->i_count))) { | |
678 | rcu_read_unlock(); | |
679 | put_page(page); | |
680 | ||
681 | goto again; | |
682 | } | |
683 | ||
684 | /* Should be impossible but lets be paranoid for now */ | |
685 | if (WARN_ON_ONCE(inode->i_mapping != mapping)) { | |
686 | err = -EFAULT; | |
687 | rcu_read_unlock(); | |
688 | iput(inode); | |
689 | ||
690 | goto out; | |
691 | } | |
692 | ||
693 | key->both.offset |= FUT_OFF_INODE; /* inode-based key */ | |
694 | key->shared.inode = inode; | |
695 | key->shared.pgoff = basepage_index(tail); | |
696 | rcu_read_unlock(); | |
697 | } | |
698 | ||
699 | out: | |
700 | put_page(page); | |
701 | return err; | |
702 | } | |
703 | ||
704 | static inline void put_futex_key(union futex_key *key) | |
705 | { | |
706 | drop_futex_key_refs(key); | |
707 | } | |
708 | ||
709 | /** | |
710 | * fault_in_user_writeable() - Fault in user address and verify RW access | |
711 | * @uaddr: pointer to faulting user space address | |
712 | * | |
713 | * Slow path to fixup the fault we just took in the atomic write | |
714 | * access to @uaddr. | |
715 | * | |
716 | * We have no generic implementation of a non-destructive write to the | |
717 | * user address. We know that we faulted in the atomic pagefault | |
718 | * disabled section so we can as well avoid the #PF overhead by | |
719 | * calling get_user_pages() right away. | |
720 | */ | |
721 | static int fault_in_user_writeable(u32 __user *uaddr) | |
722 | { | |
723 | struct mm_struct *mm = current->mm; | |
724 | int ret; | |
725 | ||
726 | down_read(&mm->mmap_sem); | |
727 | ret = fixup_user_fault(current, mm, (unsigned long)uaddr, | |
728 | FAULT_FLAG_WRITE, NULL); | |
729 | up_read(&mm->mmap_sem); | |
730 | ||
731 | return ret < 0 ? ret : 0; | |
732 | } | |
733 | ||
734 | /** | |
735 | * futex_top_waiter() - Return the highest priority waiter on a futex | |
736 | * @hb: the hash bucket the futex_q's reside in | |
737 | * @key: the futex key (to distinguish it from other futex futex_q's) | |
738 | * | |
739 | * Must be called with the hb lock held. | |
740 | */ | |
741 | static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb, | |
742 | union futex_key *key) | |
743 | { | |
744 | struct futex_q *this; | |
745 | ||
746 | plist_for_each_entry(this, &hb->chain, list) { | |
747 | if (match_futex(&this->key, key)) | |
748 | return this; | |
749 | } | |
750 | return NULL; | |
751 | } | |
752 | ||
753 | static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr, | |
754 | u32 uval, u32 newval) | |
755 | { | |
756 | int ret; | |
757 | ||
758 | pagefault_disable(); | |
759 | ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval); | |
760 | pagefault_enable(); | |
761 | ||
762 | return ret; | |
763 | } | |
764 | ||
765 | static int get_futex_value_locked(u32 *dest, u32 __user *from) | |
766 | { | |
767 | int ret; | |
768 | ||
769 | pagefault_disable(); | |
770 | ret = __get_user(*dest, from); | |
771 | pagefault_enable(); | |
772 | ||
773 | return ret ? -EFAULT : 0; | |
774 | } | |
775 | ||
776 | ||
777 | /* | |
778 | * PI code: | |
779 | */ | |
780 | static int refill_pi_state_cache(void) | |
781 | { | |
782 | struct futex_pi_state *pi_state; | |
783 | ||
784 | if (likely(current->pi_state_cache)) | |
785 | return 0; | |
786 | ||
787 | pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL); | |
788 | ||
789 | if (!pi_state) | |
790 | return -ENOMEM; | |
791 | ||
792 | INIT_LIST_HEAD(&pi_state->list); | |
793 | /* pi_mutex gets initialized later */ | |
794 | pi_state->owner = NULL; | |
795 | atomic_set(&pi_state->refcount, 1); | |
796 | pi_state->key = FUTEX_KEY_INIT; | |
797 | ||
798 | current->pi_state_cache = pi_state; | |
799 | ||
800 | return 0; | |
801 | } | |
802 | ||
803 | static struct futex_pi_state * alloc_pi_state(void) | |
804 | { | |
805 | struct futex_pi_state *pi_state = current->pi_state_cache; | |
806 | ||
807 | WARN_ON(!pi_state); | |
808 | current->pi_state_cache = NULL; | |
809 | ||
810 | return pi_state; | |
811 | } | |
812 | ||
813 | /* | |
814 | * Drops a reference to the pi_state object and frees or caches it | |
815 | * when the last reference is gone. | |
816 | * | |
817 | * Must be called with the hb lock held. | |
818 | */ | |
819 | static void put_pi_state(struct futex_pi_state *pi_state) | |
820 | { | |
821 | if (!pi_state) | |
822 | return; | |
823 | ||
824 | if (!atomic_dec_and_test(&pi_state->refcount)) | |
825 | return; | |
826 | ||
827 | /* | |
828 | * If pi_state->owner is NULL, the owner is most probably dying | |
829 | * and has cleaned up the pi_state already | |
830 | */ | |
831 | if (pi_state->owner) { | |
832 | raw_spin_lock_irq(&pi_state->owner->pi_lock); | |
833 | list_del_init(&pi_state->list); | |
834 | raw_spin_unlock_irq(&pi_state->owner->pi_lock); | |
835 | ||
836 | rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner); | |
837 | } | |
838 | ||
839 | if (current->pi_state_cache) | |
840 | kfree(pi_state); | |
841 | else { | |
842 | /* | |
843 | * pi_state->list is already empty. | |
844 | * clear pi_state->owner. | |
845 | * refcount is at 0 - put it back to 1. | |
846 | */ | |
847 | pi_state->owner = NULL; | |
848 | atomic_set(&pi_state->refcount, 1); | |
849 | current->pi_state_cache = pi_state; | |
850 | } | |
851 | } | |
852 | ||
853 | /* | |
854 | * Look up the task based on what TID userspace gave us. | |
855 | * We dont trust it. | |
856 | */ | |
857 | static struct task_struct * futex_find_get_task(pid_t pid) | |
858 | { | |
859 | struct task_struct *p; | |
860 | ||
861 | rcu_read_lock(); | |
862 | p = find_task_by_vpid(pid); | |
863 | if (p) | |
864 | get_task_struct(p); | |
865 | ||
866 | rcu_read_unlock(); | |
867 | ||
868 | return p; | |
869 | } | |
870 | ||
871 | /* | |
872 | * This task is holding PI mutexes at exit time => bad. | |
873 | * Kernel cleans up PI-state, but userspace is likely hosed. | |
874 | * (Robust-futex cleanup is separate and might save the day for userspace.) | |
875 | */ | |
876 | void exit_pi_state_list(struct task_struct *curr) | |
877 | { | |
878 | struct list_head *next, *head = &curr->pi_state_list; | |
879 | struct futex_pi_state *pi_state; | |
880 | struct futex_hash_bucket *hb; | |
881 | union futex_key key = FUTEX_KEY_INIT; | |
882 | ||
883 | if (!futex_cmpxchg_enabled) | |
884 | return; | |
885 | /* | |
886 | * We are a ZOMBIE and nobody can enqueue itself on | |
887 | * pi_state_list anymore, but we have to be careful | |
888 | * versus waiters unqueueing themselves: | |
889 | */ | |
890 | raw_spin_lock_irq(&curr->pi_lock); | |
891 | while (!list_empty(head)) { | |
892 | ||
893 | next = head->next; | |
894 | pi_state = list_entry(next, struct futex_pi_state, list); | |
895 | key = pi_state->key; | |
896 | hb = hash_futex(&key); | |
897 | raw_spin_unlock_irq(&curr->pi_lock); | |
898 | ||
899 | spin_lock(&hb->lock); | |
900 | ||
901 | raw_spin_lock_irq(&curr->pi_lock); | |
902 | /* | |
903 | * We dropped the pi-lock, so re-check whether this | |
904 | * task still owns the PI-state: | |
905 | */ | |
906 | if (head->next != next) { | |
907 | spin_unlock(&hb->lock); | |
908 | continue; | |
909 | } | |
910 | ||
911 | WARN_ON(pi_state->owner != curr); | |
912 | WARN_ON(list_empty(&pi_state->list)); | |
913 | list_del_init(&pi_state->list); | |
914 | pi_state->owner = NULL; | |
915 | raw_spin_unlock_irq(&curr->pi_lock); | |
916 | ||
917 | rt_mutex_unlock(&pi_state->pi_mutex); | |
918 | ||
919 | spin_unlock(&hb->lock); | |
920 | ||
921 | raw_spin_lock_irq(&curr->pi_lock); | |
922 | } | |
923 | raw_spin_unlock_irq(&curr->pi_lock); | |
924 | } | |
925 | ||
926 | /* | |
927 | * We need to check the following states: | |
928 | * | |
929 | * Waiter | pi_state | pi->owner | uTID | uODIED | ? | |
930 | * | |
931 | * [1] NULL | --- | --- | 0 | 0/1 | Valid | |
932 | * [2] NULL | --- | --- | >0 | 0/1 | Valid | |
933 | * | |
934 | * [3] Found | NULL | -- | Any | 0/1 | Invalid | |
935 | * | |
936 | * [4] Found | Found | NULL | 0 | 1 | Valid | |
937 | * [5] Found | Found | NULL | >0 | 1 | Invalid | |
938 | * | |
939 | * [6] Found | Found | task | 0 | 1 | Valid | |
940 | * | |
941 | * [7] Found | Found | NULL | Any | 0 | Invalid | |
942 | * | |
943 | * [8] Found | Found | task | ==taskTID | 0/1 | Valid | |
944 | * [9] Found | Found | task | 0 | 0 | Invalid | |
945 | * [10] Found | Found | task | !=taskTID | 0/1 | Invalid | |
946 | * | |
947 | * [1] Indicates that the kernel can acquire the futex atomically. We | |
948 | * came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit. | |
949 | * | |
950 | * [2] Valid, if TID does not belong to a kernel thread. If no matching | |
951 | * thread is found then it indicates that the owner TID has died. | |
952 | * | |
953 | * [3] Invalid. The waiter is queued on a non PI futex | |
954 | * | |
955 | * [4] Valid state after exit_robust_list(), which sets the user space | |
956 | * value to FUTEX_WAITERS | FUTEX_OWNER_DIED. | |
957 | * | |
958 | * [5] The user space value got manipulated between exit_robust_list() | |
959 | * and exit_pi_state_list() | |
960 | * | |
961 | * [6] Valid state after exit_pi_state_list() which sets the new owner in | |
962 | * the pi_state but cannot access the user space value. | |
963 | * | |
964 | * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set. | |
965 | * | |
966 | * [8] Owner and user space value match | |
967 | * | |
968 | * [9] There is no transient state which sets the user space TID to 0 | |
969 | * except exit_robust_list(), but this is indicated by the | |
970 | * FUTEX_OWNER_DIED bit. See [4] | |
971 | * | |
972 | * [10] There is no transient state which leaves owner and user space | |
973 | * TID out of sync. | |
974 | */ | |
975 | ||
976 | /* | |
977 | * Validate that the existing waiter has a pi_state and sanity check | |
978 | * the pi_state against the user space value. If correct, attach to | |
979 | * it. | |
980 | */ | |
981 | static int attach_to_pi_state(u32 uval, struct futex_pi_state *pi_state, | |
982 | struct futex_pi_state **ps) | |
983 | { | |
984 | pid_t pid = uval & FUTEX_TID_MASK; | |
985 | ||
986 | /* | |
987 | * Userspace might have messed up non-PI and PI futexes [3] | |
988 | */ | |
989 | if (unlikely(!pi_state)) | |
990 | return -EINVAL; | |
991 | ||
992 | WARN_ON(!atomic_read(&pi_state->refcount)); | |
993 | ||
994 | /* | |
995 | * Handle the owner died case: | |
996 | */ | |
997 | if (uval & FUTEX_OWNER_DIED) { | |
998 | /* | |
999 | * exit_pi_state_list sets owner to NULL and wakes the | |
1000 | * topmost waiter. The task which acquires the | |
1001 | * pi_state->rt_mutex will fixup owner. | |
1002 | */ | |
1003 | if (!pi_state->owner) { | |
1004 | /* | |
1005 | * No pi state owner, but the user space TID | |
1006 | * is not 0. Inconsistent state. [5] | |
1007 | */ | |
1008 | if (pid) | |
1009 | return -EINVAL; | |
1010 | /* | |
1011 | * Take a ref on the state and return success. [4] | |
1012 | */ | |
1013 | goto out_state; | |
1014 | } | |
1015 | ||
1016 | /* | |
1017 | * If TID is 0, then either the dying owner has not | |
1018 | * yet executed exit_pi_state_list() or some waiter | |
1019 | * acquired the rtmutex in the pi state, but did not | |
1020 | * yet fixup the TID in user space. | |
1021 | * | |
1022 | * Take a ref on the state and return success. [6] | |
1023 | */ | |
1024 | if (!pid) | |
1025 | goto out_state; | |
1026 | } else { | |
1027 | /* | |
1028 | * If the owner died bit is not set, then the pi_state | |
1029 | * must have an owner. [7] | |
1030 | */ | |
1031 | if (!pi_state->owner) | |
1032 | return -EINVAL; | |
1033 | } | |
1034 | ||
1035 | /* | |
1036 | * Bail out if user space manipulated the futex value. If pi | |
1037 | * state exists then the owner TID must be the same as the | |
1038 | * user space TID. [9/10] | |
1039 | */ | |
1040 | if (pid != task_pid_vnr(pi_state->owner)) | |
1041 | return -EINVAL; | |
1042 | out_state: | |
1043 | atomic_inc(&pi_state->refcount); | |
1044 | *ps = pi_state; | |
1045 | return 0; | |
1046 | } | |
1047 | ||
1048 | /* | |
1049 | * Lookup the task for the TID provided from user space and attach to | |
1050 | * it after doing proper sanity checks. | |
1051 | */ | |
1052 | static int attach_to_pi_owner(u32 uval, union futex_key *key, | |
1053 | struct futex_pi_state **ps) | |
1054 | { | |
1055 | pid_t pid = uval & FUTEX_TID_MASK; | |
1056 | struct futex_pi_state *pi_state; | |
1057 | struct task_struct *p; | |
1058 | ||
1059 | /* | |
1060 | * We are the first waiter - try to look up the real owner and attach | |
1061 | * the new pi_state to it, but bail out when TID = 0 [1] | |
1062 | */ | |
1063 | if (!pid) | |
1064 | return -ESRCH; | |
1065 | p = futex_find_get_task(pid); | |
1066 | if (!p) | |
1067 | return -ESRCH; | |
1068 | ||
1069 | if (unlikely(p->flags & PF_KTHREAD)) { | |
1070 | put_task_struct(p); | |
1071 | return -EPERM; | |
1072 | } | |
1073 | ||
1074 | /* | |
1075 | * We need to look at the task state flags to figure out, | |
1076 | * whether the task is exiting. To protect against the do_exit | |
1077 | * change of the task flags, we do this protected by | |
1078 | * p->pi_lock: | |
1079 | */ | |
1080 | raw_spin_lock_irq(&p->pi_lock); | |
1081 | if (unlikely(p->flags & PF_EXITING)) { | |
1082 | /* | |
1083 | * The task is on the way out. When PF_EXITPIDONE is | |
1084 | * set, we know that the task has finished the | |
1085 | * cleanup: | |
1086 | */ | |
1087 | int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN; | |
1088 | ||
1089 | raw_spin_unlock_irq(&p->pi_lock); | |
1090 | put_task_struct(p); | |
1091 | return ret; | |
1092 | } | |
1093 | ||
1094 | /* | |
1095 | * No existing pi state. First waiter. [2] | |
1096 | */ | |
1097 | pi_state = alloc_pi_state(); | |
1098 | ||
1099 | /* | |
1100 | * Initialize the pi_mutex in locked state and make @p | |
1101 | * the owner of it: | |
1102 | */ | |
1103 | rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p); | |
1104 | ||
1105 | /* Store the key for possible exit cleanups: */ | |
1106 | pi_state->key = *key; | |
1107 | ||
1108 | WARN_ON(!list_empty(&pi_state->list)); | |
1109 | list_add(&pi_state->list, &p->pi_state_list); | |
1110 | pi_state->owner = p; | |
1111 | raw_spin_unlock_irq(&p->pi_lock); | |
1112 | ||
1113 | put_task_struct(p); | |
1114 | ||
1115 | *ps = pi_state; | |
1116 | ||
1117 | return 0; | |
1118 | } | |
1119 | ||
1120 | static int lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, | |
1121 | union futex_key *key, struct futex_pi_state **ps) | |
1122 | { | |
1123 | struct futex_q *match = futex_top_waiter(hb, key); | |
1124 | ||
1125 | /* | |
1126 | * If there is a waiter on that futex, validate it and | |
1127 | * attach to the pi_state when the validation succeeds. | |
1128 | */ | |
1129 | if (match) | |
1130 | return attach_to_pi_state(uval, match->pi_state, ps); | |
1131 | ||
1132 | /* | |
1133 | * We are the first waiter - try to look up the owner based on | |
1134 | * @uval and attach to it. | |
1135 | */ | |
1136 | return attach_to_pi_owner(uval, key, ps); | |
1137 | } | |
1138 | ||
1139 | static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval) | |
1140 | { | |
1141 | u32 uninitialized_var(curval); | |
1142 | ||
1143 | if (unlikely(should_fail_futex(true))) | |
1144 | return -EFAULT; | |
1145 | ||
1146 | if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))) | |
1147 | return -EFAULT; | |
1148 | ||
1149 | /*If user space value changed, let the caller retry */ | |
1150 | return curval != uval ? -EAGAIN : 0; | |
1151 | } | |
1152 | ||
1153 | /** | |
1154 | * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex | |
1155 | * @uaddr: the pi futex user address | |
1156 | * @hb: the pi futex hash bucket | |
1157 | * @key: the futex key associated with uaddr and hb | |
1158 | * @ps: the pi_state pointer where we store the result of the | |
1159 | * lookup | |
1160 | * @task: the task to perform the atomic lock work for. This will | |
1161 | * be "current" except in the case of requeue pi. | |
1162 | * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) | |
1163 | * | |
1164 | * Return: | |
1165 | * 0 - ready to wait; | |
1166 | * 1 - acquired the lock; | |
1167 | * <0 - error | |
1168 | * | |
1169 | * The hb->lock and futex_key refs shall be held by the caller. | |
1170 | */ | |
1171 | static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb, | |
1172 | union futex_key *key, | |
1173 | struct futex_pi_state **ps, | |
1174 | struct task_struct *task, int set_waiters) | |
1175 | { | |
1176 | u32 uval, newval, vpid = task_pid_vnr(task); | |
1177 | struct futex_q *match; | |
1178 | int ret; | |
1179 | ||
1180 | /* | |
1181 | * Read the user space value first so we can validate a few | |
1182 | * things before proceeding further. | |
1183 | */ | |
1184 | if (get_futex_value_locked(&uval, uaddr)) | |
1185 | return -EFAULT; | |
1186 | ||
1187 | if (unlikely(should_fail_futex(true))) | |
1188 | return -EFAULT; | |
1189 | ||
1190 | /* | |
1191 | * Detect deadlocks. | |
1192 | */ | |
1193 | if ((unlikely((uval & FUTEX_TID_MASK) == vpid))) | |
1194 | return -EDEADLK; | |
1195 | ||
1196 | if ((unlikely(should_fail_futex(true)))) | |
1197 | return -EDEADLK; | |
1198 | ||
1199 | /* | |
1200 | * Lookup existing state first. If it exists, try to attach to | |
1201 | * its pi_state. | |
1202 | */ | |
1203 | match = futex_top_waiter(hb, key); | |
1204 | if (match) | |
1205 | return attach_to_pi_state(uval, match->pi_state, ps); | |
1206 | ||
1207 | /* | |
1208 | * No waiter and user TID is 0. We are here because the | |
1209 | * waiters or the owner died bit is set or called from | |
1210 | * requeue_cmp_pi or for whatever reason something took the | |
1211 | * syscall. | |
1212 | */ | |
1213 | if (!(uval & FUTEX_TID_MASK)) { | |
1214 | /* | |
1215 | * We take over the futex. No other waiters and the user space | |
1216 | * TID is 0. We preserve the owner died bit. | |
1217 | */ | |
1218 | newval = uval & FUTEX_OWNER_DIED; | |
1219 | newval |= vpid; | |
1220 | ||
1221 | /* The futex requeue_pi code can enforce the waiters bit */ | |
1222 | if (set_waiters) | |
1223 | newval |= FUTEX_WAITERS; | |
1224 | ||
1225 | ret = lock_pi_update_atomic(uaddr, uval, newval); | |
1226 | /* If the take over worked, return 1 */ | |
1227 | return ret < 0 ? ret : 1; | |
1228 | } | |
1229 | ||
1230 | /* | |
1231 | * First waiter. Set the waiters bit before attaching ourself to | |
1232 | * the owner. If owner tries to unlock, it will be forced into | |
1233 | * the kernel and blocked on hb->lock. | |
1234 | */ | |
1235 | newval = uval | FUTEX_WAITERS; | |
1236 | ret = lock_pi_update_atomic(uaddr, uval, newval); | |
1237 | if (ret) | |
1238 | return ret; | |
1239 | /* | |
1240 | * If the update of the user space value succeeded, we try to | |
1241 | * attach to the owner. If that fails, no harm done, we only | |
1242 | * set the FUTEX_WAITERS bit in the user space variable. | |
1243 | */ | |
1244 | return attach_to_pi_owner(uval, key, ps); | |
1245 | } | |
1246 | ||
1247 | /** | |
1248 | * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket | |
1249 | * @q: The futex_q to unqueue | |
1250 | * | |
1251 | * The q->lock_ptr must not be NULL and must be held by the caller. | |
1252 | */ | |
1253 | static void __unqueue_futex(struct futex_q *q) | |
1254 | { | |
1255 | struct futex_hash_bucket *hb; | |
1256 | ||
1257 | if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr)) | |
1258 | || WARN_ON(plist_node_empty(&q->list))) | |
1259 | return; | |
1260 | ||
1261 | hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock); | |
1262 | plist_del(&q->list, &hb->chain); | |
1263 | hb_waiters_dec(hb); | |
1264 | } | |
1265 | ||
1266 | /* | |
1267 | * The hash bucket lock must be held when this is called. | |
1268 | * Afterwards, the futex_q must not be accessed. Callers | |
1269 | * must ensure to later call wake_up_q() for the actual | |
1270 | * wakeups to occur. | |
1271 | */ | |
1272 | static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q) | |
1273 | { | |
1274 | struct task_struct *p = q->task; | |
1275 | ||
1276 | if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n")) | |
1277 | return; | |
1278 | ||
1279 | /* | |
1280 | * Queue the task for later wakeup for after we've released | |
1281 | * the hb->lock. wake_q_add() grabs reference to p. | |
1282 | */ | |
1283 | wake_q_add(wake_q, p); | |
1284 | __unqueue_futex(q); | |
1285 | /* | |
1286 | * The waiting task can free the futex_q as soon as | |
1287 | * q->lock_ptr = NULL is written, without taking any locks. A | |
1288 | * memory barrier is required here to prevent the following | |
1289 | * store to lock_ptr from getting ahead of the plist_del. | |
1290 | */ | |
1291 | smp_wmb(); | |
1292 | q->lock_ptr = NULL; | |
1293 | } | |
1294 | ||
1295 | static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this, | |
1296 | struct futex_hash_bucket *hb) | |
1297 | { | |
1298 | struct task_struct *new_owner; | |
1299 | struct futex_pi_state *pi_state = this->pi_state; | |
1300 | u32 uninitialized_var(curval), newval; | |
1301 | DEFINE_WAKE_Q(wake_q); | |
1302 | bool deboost; | |
1303 | int ret = 0; | |
1304 | ||
1305 | if (!pi_state) | |
1306 | return -EINVAL; | |
1307 | ||
1308 | /* | |
1309 | * If current does not own the pi_state then the futex is | |
1310 | * inconsistent and user space fiddled with the futex value. | |
1311 | */ | |
1312 | if (pi_state->owner != current) | |
1313 | return -EINVAL; | |
1314 | ||
1315 | raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); | |
1316 | new_owner = rt_mutex_next_owner(&pi_state->pi_mutex); | |
1317 | ||
1318 | /* | |
1319 | * It is possible that the next waiter (the one that brought | |
1320 | * this owner to the kernel) timed out and is no longer | |
1321 | * waiting on the lock. | |
1322 | */ | |
1323 | if (!new_owner) | |
1324 | new_owner = this->task; | |
1325 | ||
1326 | /* | |
1327 | * We pass it to the next owner. The WAITERS bit is always | |
1328 | * kept enabled while there is PI state around. We cleanup the | |
1329 | * owner died bit, because we are the owner. | |
1330 | */ | |
1331 | newval = FUTEX_WAITERS | task_pid_vnr(new_owner); | |
1332 | ||
1333 | if (unlikely(should_fail_futex(true))) | |
1334 | ret = -EFAULT; | |
1335 | ||
1336 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) { | |
1337 | ret = -EFAULT; | |
1338 | } else if (curval != uval) { | |
1339 | /* | |
1340 | * If a unconditional UNLOCK_PI operation (user space did not | |
1341 | * try the TID->0 transition) raced with a waiter setting the | |
1342 | * FUTEX_WAITERS flag between get_user() and locking the hash | |
1343 | * bucket lock, retry the operation. | |
1344 | */ | |
1345 | if ((FUTEX_TID_MASK & curval) == uval) | |
1346 | ret = -EAGAIN; | |
1347 | else | |
1348 | ret = -EINVAL; | |
1349 | } | |
1350 | if (ret) { | |
1351 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); | |
1352 | return ret; | |
1353 | } | |
1354 | ||
1355 | raw_spin_lock(&pi_state->owner->pi_lock); | |
1356 | WARN_ON(list_empty(&pi_state->list)); | |
1357 | list_del_init(&pi_state->list); | |
1358 | raw_spin_unlock(&pi_state->owner->pi_lock); | |
1359 | ||
1360 | raw_spin_lock(&new_owner->pi_lock); | |
1361 | WARN_ON(!list_empty(&pi_state->list)); | |
1362 | list_add(&pi_state->list, &new_owner->pi_state_list); | |
1363 | pi_state->owner = new_owner; | |
1364 | raw_spin_unlock(&new_owner->pi_lock); | |
1365 | ||
1366 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); | |
1367 | ||
1368 | deboost = rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q); | |
1369 | ||
1370 | /* | |
1371 | * First unlock HB so the waiter does not spin on it once he got woken | |
1372 | * up. Second wake up the waiter before the priority is adjusted. If we | |
1373 | * deboost first (and lose our higher priority), then the task might get | |
1374 | * scheduled away before the wake up can take place. | |
1375 | */ | |
1376 | spin_unlock(&hb->lock); | |
1377 | wake_up_q(&wake_q); | |
1378 | if (deboost) | |
1379 | rt_mutex_adjust_prio(current); | |
1380 | ||
1381 | return 0; | |
1382 | } | |
1383 | ||
1384 | /* | |
1385 | * Express the locking dependencies for lockdep: | |
1386 | */ | |
1387 | static inline void | |
1388 | double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) | |
1389 | { | |
1390 | if (hb1 <= hb2) { | |
1391 | spin_lock(&hb1->lock); | |
1392 | if (hb1 < hb2) | |
1393 | spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING); | |
1394 | } else { /* hb1 > hb2 */ | |
1395 | spin_lock(&hb2->lock); | |
1396 | spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING); | |
1397 | } | |
1398 | } | |
1399 | ||
1400 | static inline void | |
1401 | double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) | |
1402 | { | |
1403 | spin_unlock(&hb1->lock); | |
1404 | if (hb1 != hb2) | |
1405 | spin_unlock(&hb2->lock); | |
1406 | } | |
1407 | ||
1408 | /* | |
1409 | * Wake up waiters matching bitset queued on this futex (uaddr). | |
1410 | */ | |
1411 | static int | |
1412 | futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset) | |
1413 | { | |
1414 | struct futex_hash_bucket *hb; | |
1415 | struct futex_q *this, *next; | |
1416 | union futex_key key = FUTEX_KEY_INIT; | |
1417 | int ret; | |
1418 | DEFINE_WAKE_Q(wake_q); | |
1419 | ||
1420 | if (!bitset) | |
1421 | return -EINVAL; | |
1422 | ||
1423 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ); | |
1424 | if (unlikely(ret != 0)) | |
1425 | goto out; | |
1426 | ||
1427 | hb = hash_futex(&key); | |
1428 | ||
1429 | /* Make sure we really have tasks to wakeup */ | |
1430 | if (!hb_waiters_pending(hb)) | |
1431 | goto out_put_key; | |
1432 | ||
1433 | spin_lock(&hb->lock); | |
1434 | ||
1435 | plist_for_each_entry_safe(this, next, &hb->chain, list) { | |
1436 | if (match_futex (&this->key, &key)) { | |
1437 | if (this->pi_state || this->rt_waiter) { | |
1438 | ret = -EINVAL; | |
1439 | break; | |
1440 | } | |
1441 | ||
1442 | /* Check if one of the bits is set in both bitsets */ | |
1443 | if (!(this->bitset & bitset)) | |
1444 | continue; | |
1445 | ||
1446 | mark_wake_futex(&wake_q, this); | |
1447 | if (++ret >= nr_wake) | |
1448 | break; | |
1449 | } | |
1450 | } | |
1451 | ||
1452 | spin_unlock(&hb->lock); | |
1453 | wake_up_q(&wake_q); | |
1454 | out_put_key: | |
1455 | put_futex_key(&key); | |
1456 | out: | |
1457 | return ret; | |
1458 | } | |
1459 | ||
1460 | /* | |
1461 | * Wake up all waiters hashed on the physical page that is mapped | |
1462 | * to this virtual address: | |
1463 | */ | |
1464 | static int | |
1465 | futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2, | |
1466 | int nr_wake, int nr_wake2, int op) | |
1467 | { | |
1468 | union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; | |
1469 | struct futex_hash_bucket *hb1, *hb2; | |
1470 | struct futex_q *this, *next; | |
1471 | int ret, op_ret; | |
1472 | DEFINE_WAKE_Q(wake_q); | |
1473 | ||
1474 | retry: | |
1475 | ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ); | |
1476 | if (unlikely(ret != 0)) | |
1477 | goto out; | |
1478 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE); | |
1479 | if (unlikely(ret != 0)) | |
1480 | goto out_put_key1; | |
1481 | ||
1482 | hb1 = hash_futex(&key1); | |
1483 | hb2 = hash_futex(&key2); | |
1484 | ||
1485 | retry_private: | |
1486 | double_lock_hb(hb1, hb2); | |
1487 | op_ret = futex_atomic_op_inuser(op, uaddr2); | |
1488 | if (unlikely(op_ret < 0)) { | |
1489 | ||
1490 | double_unlock_hb(hb1, hb2); | |
1491 | ||
1492 | #ifndef CONFIG_MMU | |
1493 | /* | |
1494 | * we don't get EFAULT from MMU faults if we don't have an MMU, | |
1495 | * but we might get them from range checking | |
1496 | */ | |
1497 | ret = op_ret; | |
1498 | goto out_put_keys; | |
1499 | #endif | |
1500 | ||
1501 | if (unlikely(op_ret != -EFAULT)) { | |
1502 | ret = op_ret; | |
1503 | goto out_put_keys; | |
1504 | } | |
1505 | ||
1506 | ret = fault_in_user_writeable(uaddr2); | |
1507 | if (ret) | |
1508 | goto out_put_keys; | |
1509 | ||
1510 | if (!(flags & FLAGS_SHARED)) | |
1511 | goto retry_private; | |
1512 | ||
1513 | put_futex_key(&key2); | |
1514 | put_futex_key(&key1); | |
1515 | goto retry; | |
1516 | } | |
1517 | ||
1518 | plist_for_each_entry_safe(this, next, &hb1->chain, list) { | |
1519 | if (match_futex (&this->key, &key1)) { | |
1520 | if (this->pi_state || this->rt_waiter) { | |
1521 | ret = -EINVAL; | |
1522 | goto out_unlock; | |
1523 | } | |
1524 | mark_wake_futex(&wake_q, this); | |
1525 | if (++ret >= nr_wake) | |
1526 | break; | |
1527 | } | |
1528 | } | |
1529 | ||
1530 | if (op_ret > 0) { | |
1531 | op_ret = 0; | |
1532 | plist_for_each_entry_safe(this, next, &hb2->chain, list) { | |
1533 | if (match_futex (&this->key, &key2)) { | |
1534 | if (this->pi_state || this->rt_waiter) { | |
1535 | ret = -EINVAL; | |
1536 | goto out_unlock; | |
1537 | } | |
1538 | mark_wake_futex(&wake_q, this); | |
1539 | if (++op_ret >= nr_wake2) | |
1540 | break; | |
1541 | } | |
1542 | } | |
1543 | ret += op_ret; | |
1544 | } | |
1545 | ||
1546 | out_unlock: | |
1547 | double_unlock_hb(hb1, hb2); | |
1548 | wake_up_q(&wake_q); | |
1549 | out_put_keys: | |
1550 | put_futex_key(&key2); | |
1551 | out_put_key1: | |
1552 | put_futex_key(&key1); | |
1553 | out: | |
1554 | return ret; | |
1555 | } | |
1556 | ||
1557 | /** | |
1558 | * requeue_futex() - Requeue a futex_q from one hb to another | |
1559 | * @q: the futex_q to requeue | |
1560 | * @hb1: the source hash_bucket | |
1561 | * @hb2: the target hash_bucket | |
1562 | * @key2: the new key for the requeued futex_q | |
1563 | */ | |
1564 | static inline | |
1565 | void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1, | |
1566 | struct futex_hash_bucket *hb2, union futex_key *key2) | |
1567 | { | |
1568 | ||
1569 | /* | |
1570 | * If key1 and key2 hash to the same bucket, no need to | |
1571 | * requeue. | |
1572 | */ | |
1573 | if (likely(&hb1->chain != &hb2->chain)) { | |
1574 | plist_del(&q->list, &hb1->chain); | |
1575 | hb_waiters_dec(hb1); | |
1576 | hb_waiters_inc(hb2); | |
1577 | plist_add(&q->list, &hb2->chain); | |
1578 | q->lock_ptr = &hb2->lock; | |
1579 | } | |
1580 | get_futex_key_refs(key2); | |
1581 | q->key = *key2; | |
1582 | } | |
1583 | ||
1584 | /** | |
1585 | * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue | |
1586 | * @q: the futex_q | |
1587 | * @key: the key of the requeue target futex | |
1588 | * @hb: the hash_bucket of the requeue target futex | |
1589 | * | |
1590 | * During futex_requeue, with requeue_pi=1, it is possible to acquire the | |
1591 | * target futex if it is uncontended or via a lock steal. Set the futex_q key | |
1592 | * to the requeue target futex so the waiter can detect the wakeup on the right | |
1593 | * futex, but remove it from the hb and NULL the rt_waiter so it can detect | |
1594 | * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock | |
1595 | * to protect access to the pi_state to fixup the owner later. Must be called | |
1596 | * with both q->lock_ptr and hb->lock held. | |
1597 | */ | |
1598 | static inline | |
1599 | void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key, | |
1600 | struct futex_hash_bucket *hb) | |
1601 | { | |
1602 | get_futex_key_refs(key); | |
1603 | q->key = *key; | |
1604 | ||
1605 | __unqueue_futex(q); | |
1606 | ||
1607 | WARN_ON(!q->rt_waiter); | |
1608 | q->rt_waiter = NULL; | |
1609 | ||
1610 | q->lock_ptr = &hb->lock; | |
1611 | ||
1612 | wake_up_state(q->task, TASK_NORMAL); | |
1613 | } | |
1614 | ||
1615 | /** | |
1616 | * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter | |
1617 | * @pifutex: the user address of the to futex | |
1618 | * @hb1: the from futex hash bucket, must be locked by the caller | |
1619 | * @hb2: the to futex hash bucket, must be locked by the caller | |
1620 | * @key1: the from futex key | |
1621 | * @key2: the to futex key | |
1622 | * @ps: address to store the pi_state pointer | |
1623 | * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) | |
1624 | * | |
1625 | * Try and get the lock on behalf of the top waiter if we can do it atomically. | |
1626 | * Wake the top waiter if we succeed. If the caller specified set_waiters, | |
1627 | * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit. | |
1628 | * hb1 and hb2 must be held by the caller. | |
1629 | * | |
1630 | * Return: | |
1631 | * 0 - failed to acquire the lock atomically; | |
1632 | * >0 - acquired the lock, return value is vpid of the top_waiter | |
1633 | * <0 - error | |
1634 | */ | |
1635 | static int futex_proxy_trylock_atomic(u32 __user *pifutex, | |
1636 | struct futex_hash_bucket *hb1, | |
1637 | struct futex_hash_bucket *hb2, | |
1638 | union futex_key *key1, union futex_key *key2, | |
1639 | struct futex_pi_state **ps, int set_waiters) | |
1640 | { | |
1641 | struct futex_q *top_waiter = NULL; | |
1642 | u32 curval; | |
1643 | int ret, vpid; | |
1644 | ||
1645 | if (get_futex_value_locked(&curval, pifutex)) | |
1646 | return -EFAULT; | |
1647 | ||
1648 | if (unlikely(should_fail_futex(true))) | |
1649 | return -EFAULT; | |
1650 | ||
1651 | /* | |
1652 | * Find the top_waiter and determine if there are additional waiters. | |
1653 | * If the caller intends to requeue more than 1 waiter to pifutex, | |
1654 | * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now, | |
1655 | * as we have means to handle the possible fault. If not, don't set | |
1656 | * the bit unecessarily as it will force the subsequent unlock to enter | |
1657 | * the kernel. | |
1658 | */ | |
1659 | top_waiter = futex_top_waiter(hb1, key1); | |
1660 | ||
1661 | /* There are no waiters, nothing for us to do. */ | |
1662 | if (!top_waiter) | |
1663 | return 0; | |
1664 | ||
1665 | /* Ensure we requeue to the expected futex. */ | |
1666 | if (!match_futex(top_waiter->requeue_pi_key, key2)) | |
1667 | return -EINVAL; | |
1668 | ||
1669 | /* | |
1670 | * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in | |
1671 | * the contended case or if set_waiters is 1. The pi_state is returned | |
1672 | * in ps in contended cases. | |
1673 | */ | |
1674 | vpid = task_pid_vnr(top_waiter->task); | |
1675 | ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task, | |
1676 | set_waiters); | |
1677 | if (ret == 1) { | |
1678 | requeue_pi_wake_futex(top_waiter, key2, hb2); | |
1679 | return vpid; | |
1680 | } | |
1681 | return ret; | |
1682 | } | |
1683 | ||
1684 | /** | |
1685 | * futex_requeue() - Requeue waiters from uaddr1 to uaddr2 | |
1686 | * @uaddr1: source futex user address | |
1687 | * @flags: futex flags (FLAGS_SHARED, etc.) | |
1688 | * @uaddr2: target futex user address | |
1689 | * @nr_wake: number of waiters to wake (must be 1 for requeue_pi) | |
1690 | * @nr_requeue: number of waiters to requeue (0-INT_MAX) | |
1691 | * @cmpval: @uaddr1 expected value (or %NULL) | |
1692 | * @requeue_pi: if we are attempting to requeue from a non-pi futex to a | |
1693 | * pi futex (pi to pi requeue is not supported) | |
1694 | * | |
1695 | * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire | |
1696 | * uaddr2 atomically on behalf of the top waiter. | |
1697 | * | |
1698 | * Return: | |
1699 | * >=0 - on success, the number of tasks requeued or woken; | |
1700 | * <0 - on error | |
1701 | */ | |
1702 | static int futex_requeue(u32 __user *uaddr1, unsigned int flags, | |
1703 | u32 __user *uaddr2, int nr_wake, int nr_requeue, | |
1704 | u32 *cmpval, int requeue_pi) | |
1705 | { | |
1706 | union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; | |
1707 | int drop_count = 0, task_count = 0, ret; | |
1708 | struct futex_pi_state *pi_state = NULL; | |
1709 | struct futex_hash_bucket *hb1, *hb2; | |
1710 | struct futex_q *this, *next; | |
1711 | DEFINE_WAKE_Q(wake_q); | |
1712 | ||
1713 | if (requeue_pi) { | |
1714 | /* | |
1715 | * Requeue PI only works on two distinct uaddrs. This | |
1716 | * check is only valid for private futexes. See below. | |
1717 | */ | |
1718 | if (uaddr1 == uaddr2) | |
1719 | return -EINVAL; | |
1720 | ||
1721 | /* | |
1722 | * requeue_pi requires a pi_state, try to allocate it now | |
1723 | * without any locks in case it fails. | |
1724 | */ | |
1725 | if (refill_pi_state_cache()) | |
1726 | return -ENOMEM; | |
1727 | /* | |
1728 | * requeue_pi must wake as many tasks as it can, up to nr_wake | |
1729 | * + nr_requeue, since it acquires the rt_mutex prior to | |
1730 | * returning to userspace, so as to not leave the rt_mutex with | |
1731 | * waiters and no owner. However, second and third wake-ups | |
1732 | * cannot be predicted as they involve race conditions with the | |
1733 | * first wake and a fault while looking up the pi_state. Both | |
1734 | * pthread_cond_signal() and pthread_cond_broadcast() should | |
1735 | * use nr_wake=1. | |
1736 | */ | |
1737 | if (nr_wake != 1) | |
1738 | return -EINVAL; | |
1739 | } | |
1740 | ||
1741 | retry: | |
1742 | ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ); | |
1743 | if (unlikely(ret != 0)) | |
1744 | goto out; | |
1745 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, | |
1746 | requeue_pi ? VERIFY_WRITE : VERIFY_READ); | |
1747 | if (unlikely(ret != 0)) | |
1748 | goto out_put_key1; | |
1749 | ||
1750 | /* | |
1751 | * The check above which compares uaddrs is not sufficient for | |
1752 | * shared futexes. We need to compare the keys: | |
1753 | */ | |
1754 | if (requeue_pi && match_futex(&key1, &key2)) { | |
1755 | ret = -EINVAL; | |
1756 | goto out_put_keys; | |
1757 | } | |
1758 | ||
1759 | hb1 = hash_futex(&key1); | |
1760 | hb2 = hash_futex(&key2); | |
1761 | ||
1762 | retry_private: | |
1763 | hb_waiters_inc(hb2); | |
1764 | double_lock_hb(hb1, hb2); | |
1765 | ||
1766 | if (likely(cmpval != NULL)) { | |
1767 | u32 curval; | |
1768 | ||
1769 | ret = get_futex_value_locked(&curval, uaddr1); | |
1770 | ||
1771 | if (unlikely(ret)) { | |
1772 | double_unlock_hb(hb1, hb2); | |
1773 | hb_waiters_dec(hb2); | |
1774 | ||
1775 | ret = get_user(curval, uaddr1); | |
1776 | if (ret) | |
1777 | goto out_put_keys; | |
1778 | ||
1779 | if (!(flags & FLAGS_SHARED)) | |
1780 | goto retry_private; | |
1781 | ||
1782 | put_futex_key(&key2); | |
1783 | put_futex_key(&key1); | |
1784 | goto retry; | |
1785 | } | |
1786 | if (curval != *cmpval) { | |
1787 | ret = -EAGAIN; | |
1788 | goto out_unlock; | |
1789 | } | |
1790 | } | |
1791 | ||
1792 | if (requeue_pi && (task_count - nr_wake < nr_requeue)) { | |
1793 | /* | |
1794 | * Attempt to acquire uaddr2 and wake the top waiter. If we | |
1795 | * intend to requeue waiters, force setting the FUTEX_WAITERS | |
1796 | * bit. We force this here where we are able to easily handle | |
1797 | * faults rather in the requeue loop below. | |
1798 | */ | |
1799 | ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1, | |
1800 | &key2, &pi_state, nr_requeue); | |
1801 | ||
1802 | /* | |
1803 | * At this point the top_waiter has either taken uaddr2 or is | |
1804 | * waiting on it. If the former, then the pi_state will not | |
1805 | * exist yet, look it up one more time to ensure we have a | |
1806 | * reference to it. If the lock was taken, ret contains the | |
1807 | * vpid of the top waiter task. | |
1808 | * If the lock was not taken, we have pi_state and an initial | |
1809 | * refcount on it. In case of an error we have nothing. | |
1810 | */ | |
1811 | if (ret > 0) { | |
1812 | WARN_ON(pi_state); | |
1813 | drop_count++; | |
1814 | task_count++; | |
1815 | /* | |
1816 | * If we acquired the lock, then the user space value | |
1817 | * of uaddr2 should be vpid. It cannot be changed by | |
1818 | * the top waiter as it is blocked on hb2 lock if it | |
1819 | * tries to do so. If something fiddled with it behind | |
1820 | * our back the pi state lookup might unearth it. So | |
1821 | * we rather use the known value than rereading and | |
1822 | * handing potential crap to lookup_pi_state. | |
1823 | * | |
1824 | * If that call succeeds then we have pi_state and an | |
1825 | * initial refcount on it. | |
1826 | */ | |
1827 | ret = lookup_pi_state(ret, hb2, &key2, &pi_state); | |
1828 | } | |
1829 | ||
1830 | switch (ret) { | |
1831 | case 0: | |
1832 | /* We hold a reference on the pi state. */ | |
1833 | break; | |
1834 | ||
1835 | /* If the above failed, then pi_state is NULL */ | |
1836 | case -EFAULT: | |
1837 | double_unlock_hb(hb1, hb2); | |
1838 | hb_waiters_dec(hb2); | |
1839 | put_futex_key(&key2); | |
1840 | put_futex_key(&key1); | |
1841 | ret = fault_in_user_writeable(uaddr2); | |
1842 | if (!ret) | |
1843 | goto retry; | |
1844 | goto out; | |
1845 | case -EAGAIN: | |
1846 | /* | |
1847 | * Two reasons for this: | |
1848 | * - Owner is exiting and we just wait for the | |
1849 | * exit to complete. | |
1850 | * - The user space value changed. | |
1851 | */ | |
1852 | double_unlock_hb(hb1, hb2); | |
1853 | hb_waiters_dec(hb2); | |
1854 | put_futex_key(&key2); | |
1855 | put_futex_key(&key1); | |
1856 | cond_resched(); | |
1857 | goto retry; | |
1858 | default: | |
1859 | goto out_unlock; | |
1860 | } | |
1861 | } | |
1862 | ||
1863 | plist_for_each_entry_safe(this, next, &hb1->chain, list) { | |
1864 | if (task_count - nr_wake >= nr_requeue) | |
1865 | break; | |
1866 | ||
1867 | if (!match_futex(&this->key, &key1)) | |
1868 | continue; | |
1869 | ||
1870 | /* | |
1871 | * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always | |
1872 | * be paired with each other and no other futex ops. | |
1873 | * | |
1874 | * We should never be requeueing a futex_q with a pi_state, | |
1875 | * which is awaiting a futex_unlock_pi(). | |
1876 | */ | |
1877 | if ((requeue_pi && !this->rt_waiter) || | |
1878 | (!requeue_pi && this->rt_waiter) || | |
1879 | this->pi_state) { | |
1880 | ret = -EINVAL; | |
1881 | break; | |
1882 | } | |
1883 | ||
1884 | /* | |
1885 | * Wake nr_wake waiters. For requeue_pi, if we acquired the | |
1886 | * lock, we already woke the top_waiter. If not, it will be | |
1887 | * woken by futex_unlock_pi(). | |
1888 | */ | |
1889 | if (++task_count <= nr_wake && !requeue_pi) { | |
1890 | mark_wake_futex(&wake_q, this); | |
1891 | continue; | |
1892 | } | |
1893 | ||
1894 | /* Ensure we requeue to the expected futex for requeue_pi. */ | |
1895 | if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) { | |
1896 | ret = -EINVAL; | |
1897 | break; | |
1898 | } | |
1899 | ||
1900 | /* | |
1901 | * Requeue nr_requeue waiters and possibly one more in the case | |
1902 | * of requeue_pi if we couldn't acquire the lock atomically. | |
1903 | */ | |
1904 | if (requeue_pi) { | |
1905 | /* | |
1906 | * Prepare the waiter to take the rt_mutex. Take a | |
1907 | * refcount on the pi_state and store the pointer in | |
1908 | * the futex_q object of the waiter. | |
1909 | */ | |
1910 | atomic_inc(&pi_state->refcount); | |
1911 | this->pi_state = pi_state; | |
1912 | ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex, | |
1913 | this->rt_waiter, | |
1914 | this->task); | |
1915 | if (ret == 1) { | |
1916 | /* | |
1917 | * We got the lock. We do neither drop the | |
1918 | * refcount on pi_state nor clear | |
1919 | * this->pi_state because the waiter needs the | |
1920 | * pi_state for cleaning up the user space | |
1921 | * value. It will drop the refcount after | |
1922 | * doing so. | |
1923 | */ | |
1924 | requeue_pi_wake_futex(this, &key2, hb2); | |
1925 | drop_count++; | |
1926 | continue; | |
1927 | } else if (ret) { | |
1928 | /* | |
1929 | * rt_mutex_start_proxy_lock() detected a | |
1930 | * potential deadlock when we tried to queue | |
1931 | * that waiter. Drop the pi_state reference | |
1932 | * which we took above and remove the pointer | |
1933 | * to the state from the waiters futex_q | |
1934 | * object. | |
1935 | */ | |
1936 | this->pi_state = NULL; | |
1937 | put_pi_state(pi_state); | |
1938 | /* | |
1939 | * We stop queueing more waiters and let user | |
1940 | * space deal with the mess. | |
1941 | */ | |
1942 | break; | |
1943 | } | |
1944 | } | |
1945 | requeue_futex(this, hb1, hb2, &key2); | |
1946 | drop_count++; | |
1947 | } | |
1948 | ||
1949 | /* | |
1950 | * We took an extra initial reference to the pi_state either | |
1951 | * in futex_proxy_trylock_atomic() or in lookup_pi_state(). We | |
1952 | * need to drop it here again. | |
1953 | */ | |
1954 | put_pi_state(pi_state); | |
1955 | ||
1956 | out_unlock: | |
1957 | double_unlock_hb(hb1, hb2); | |
1958 | wake_up_q(&wake_q); | |
1959 | hb_waiters_dec(hb2); | |
1960 | ||
1961 | /* | |
1962 | * drop_futex_key_refs() must be called outside the spinlocks. During | |
1963 | * the requeue we moved futex_q's from the hash bucket at key1 to the | |
1964 | * one at key2 and updated their key pointer. We no longer need to | |
1965 | * hold the references to key1. | |
1966 | */ | |
1967 | while (--drop_count >= 0) | |
1968 | drop_futex_key_refs(&key1); | |
1969 | ||
1970 | out_put_keys: | |
1971 | put_futex_key(&key2); | |
1972 | out_put_key1: | |
1973 | put_futex_key(&key1); | |
1974 | out: | |
1975 | return ret ? ret : task_count; | |
1976 | } | |
1977 | ||
1978 | /* The key must be already stored in q->key. */ | |
1979 | static inline struct futex_hash_bucket *queue_lock(struct futex_q *q) | |
1980 | __acquires(&hb->lock) | |
1981 | { | |
1982 | struct futex_hash_bucket *hb; | |
1983 | ||
1984 | hb = hash_futex(&q->key); | |
1985 | ||
1986 | /* | |
1987 | * Increment the counter before taking the lock so that | |
1988 | * a potential waker won't miss a to-be-slept task that is | |
1989 | * waiting for the spinlock. This is safe as all queue_lock() | |
1990 | * users end up calling queue_me(). Similarly, for housekeeping, | |
1991 | * decrement the counter at queue_unlock() when some error has | |
1992 | * occurred and we don't end up adding the task to the list. | |
1993 | */ | |
1994 | hb_waiters_inc(hb); | |
1995 | ||
1996 | q->lock_ptr = &hb->lock; | |
1997 | ||
1998 | spin_lock(&hb->lock); /* implies smp_mb(); (A) */ | |
1999 | return hb; | |
2000 | } | |
2001 | ||
2002 | static inline void | |
2003 | queue_unlock(struct futex_hash_bucket *hb) | |
2004 | __releases(&hb->lock) | |
2005 | { | |
2006 | spin_unlock(&hb->lock); | |
2007 | hb_waiters_dec(hb); | |
2008 | } | |
2009 | ||
2010 | /** | |
2011 | * queue_me() - Enqueue the futex_q on the futex_hash_bucket | |
2012 | * @q: The futex_q to enqueue | |
2013 | * @hb: The destination hash bucket | |
2014 | * | |
2015 | * The hb->lock must be held by the caller, and is released here. A call to | |
2016 | * queue_me() is typically paired with exactly one call to unqueue_me(). The | |
2017 | * exceptions involve the PI related operations, which may use unqueue_me_pi() | |
2018 | * or nothing if the unqueue is done as part of the wake process and the unqueue | |
2019 | * state is implicit in the state of woken task (see futex_wait_requeue_pi() for | |
2020 | * an example). | |
2021 | */ | |
2022 | static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb) | |
2023 | __releases(&hb->lock) | |
2024 | { | |
2025 | int prio; | |
2026 | ||
2027 | /* | |
2028 | * The priority used to register this element is | |
2029 | * - either the real thread-priority for the real-time threads | |
2030 | * (i.e. threads with a priority lower than MAX_RT_PRIO) | |
2031 | * - or MAX_RT_PRIO for non-RT threads. | |
2032 | * Thus, all RT-threads are woken first in priority order, and | |
2033 | * the others are woken last, in FIFO order. | |
2034 | */ | |
2035 | prio = min(current->normal_prio, MAX_RT_PRIO); | |
2036 | ||
2037 | plist_node_init(&q->list, prio); | |
2038 | plist_add(&q->list, &hb->chain); | |
2039 | q->task = current; | |
2040 | spin_unlock(&hb->lock); | |
2041 | } | |
2042 | ||
2043 | /** | |
2044 | * unqueue_me() - Remove the futex_q from its futex_hash_bucket | |
2045 | * @q: The futex_q to unqueue | |
2046 | * | |
2047 | * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must | |
2048 | * be paired with exactly one earlier call to queue_me(). | |
2049 | * | |
2050 | * Return: | |
2051 | * 1 - if the futex_q was still queued (and we removed unqueued it); | |
2052 | * 0 - if the futex_q was already removed by the waking thread | |
2053 | */ | |
2054 | static int unqueue_me(struct futex_q *q) | |
2055 | { | |
2056 | spinlock_t *lock_ptr; | |
2057 | int ret = 0; | |
2058 | ||
2059 | /* In the common case we don't take the spinlock, which is nice. */ | |
2060 | retry: | |
2061 | /* | |
2062 | * q->lock_ptr can change between this read and the following spin_lock. | |
2063 | * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and | |
2064 | * optimizing lock_ptr out of the logic below. | |
2065 | */ | |
2066 | lock_ptr = READ_ONCE(q->lock_ptr); | |
2067 | if (lock_ptr != NULL) { | |
2068 | spin_lock(lock_ptr); | |
2069 | /* | |
2070 | * q->lock_ptr can change between reading it and | |
2071 | * spin_lock(), causing us to take the wrong lock. This | |
2072 | * corrects the race condition. | |
2073 | * | |
2074 | * Reasoning goes like this: if we have the wrong lock, | |
2075 | * q->lock_ptr must have changed (maybe several times) | |
2076 | * between reading it and the spin_lock(). It can | |
2077 | * change again after the spin_lock() but only if it was | |
2078 | * already changed before the spin_lock(). It cannot, | |
2079 | * however, change back to the original value. Therefore | |
2080 | * we can detect whether we acquired the correct lock. | |
2081 | */ | |
2082 | if (unlikely(lock_ptr != q->lock_ptr)) { | |
2083 | spin_unlock(lock_ptr); | |
2084 | goto retry; | |
2085 | } | |
2086 | __unqueue_futex(q); | |
2087 | ||
2088 | BUG_ON(q->pi_state); | |
2089 | ||
2090 | spin_unlock(lock_ptr); | |
2091 | ret = 1; | |
2092 | } | |
2093 | ||
2094 | drop_futex_key_refs(&q->key); | |
2095 | return ret; | |
2096 | } | |
2097 | ||
2098 | /* | |
2099 | * PI futexes can not be requeued and must remove themself from the | |
2100 | * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry | |
2101 | * and dropped here. | |
2102 | */ | |
2103 | static void unqueue_me_pi(struct futex_q *q) | |
2104 | __releases(q->lock_ptr) | |
2105 | { | |
2106 | __unqueue_futex(q); | |
2107 | ||
2108 | BUG_ON(!q->pi_state); | |
2109 | put_pi_state(q->pi_state); | |
2110 | q->pi_state = NULL; | |
2111 | ||
2112 | spin_unlock(q->lock_ptr); | |
2113 | } | |
2114 | ||
2115 | /* | |
2116 | * Fixup the pi_state owner with the new owner. | |
2117 | * | |
2118 | * Must be called with hash bucket lock held and mm->sem held for non | |
2119 | * private futexes. | |
2120 | */ | |
2121 | static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q, | |
2122 | struct task_struct *newowner) | |
2123 | { | |
2124 | u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS; | |
2125 | struct futex_pi_state *pi_state = q->pi_state; | |
2126 | struct task_struct *oldowner = pi_state->owner; | |
2127 | u32 uval, uninitialized_var(curval), newval; | |
2128 | int ret; | |
2129 | ||
2130 | /* Owner died? */ | |
2131 | if (!pi_state->owner) | |
2132 | newtid |= FUTEX_OWNER_DIED; | |
2133 | ||
2134 | /* | |
2135 | * We are here either because we stole the rtmutex from the | |
2136 | * previous highest priority waiter or we are the highest priority | |
2137 | * waiter but failed to get the rtmutex the first time. | |
2138 | * We have to replace the newowner TID in the user space variable. | |
2139 | * This must be atomic as we have to preserve the owner died bit here. | |
2140 | * | |
2141 | * Note: We write the user space value _before_ changing the pi_state | |
2142 | * because we can fault here. Imagine swapped out pages or a fork | |
2143 | * that marked all the anonymous memory readonly for cow. | |
2144 | * | |
2145 | * Modifying pi_state _before_ the user space value would | |
2146 | * leave the pi_state in an inconsistent state when we fault | |
2147 | * here, because we need to drop the hash bucket lock to | |
2148 | * handle the fault. This might be observed in the PID check | |
2149 | * in lookup_pi_state. | |
2150 | */ | |
2151 | retry: | |
2152 | if (get_futex_value_locked(&uval, uaddr)) | |
2153 | goto handle_fault; | |
2154 | ||
2155 | while (1) { | |
2156 | newval = (uval & FUTEX_OWNER_DIED) | newtid; | |
2157 | ||
2158 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) | |
2159 | goto handle_fault; | |
2160 | if (curval == uval) | |
2161 | break; | |
2162 | uval = curval; | |
2163 | } | |
2164 | ||
2165 | /* | |
2166 | * We fixed up user space. Now we need to fix the pi_state | |
2167 | * itself. | |
2168 | */ | |
2169 | if (pi_state->owner != NULL) { | |
2170 | raw_spin_lock_irq(&pi_state->owner->pi_lock); | |
2171 | WARN_ON(list_empty(&pi_state->list)); | |
2172 | list_del_init(&pi_state->list); | |
2173 | raw_spin_unlock_irq(&pi_state->owner->pi_lock); | |
2174 | } | |
2175 | ||
2176 | pi_state->owner = newowner; | |
2177 | ||
2178 | raw_spin_lock_irq(&newowner->pi_lock); | |
2179 | WARN_ON(!list_empty(&pi_state->list)); | |
2180 | list_add(&pi_state->list, &newowner->pi_state_list); | |
2181 | raw_spin_unlock_irq(&newowner->pi_lock); | |
2182 | return 0; | |
2183 | ||
2184 | /* | |
2185 | * To handle the page fault we need to drop the hash bucket | |
2186 | * lock here. That gives the other task (either the highest priority | |
2187 | * waiter itself or the task which stole the rtmutex) the | |
2188 | * chance to try the fixup of the pi_state. So once we are | |
2189 | * back from handling the fault we need to check the pi_state | |
2190 | * after reacquiring the hash bucket lock and before trying to | |
2191 | * do another fixup. When the fixup has been done already we | |
2192 | * simply return. | |
2193 | */ | |
2194 | handle_fault: | |
2195 | spin_unlock(q->lock_ptr); | |
2196 | ||
2197 | ret = fault_in_user_writeable(uaddr); | |
2198 | ||
2199 | spin_lock(q->lock_ptr); | |
2200 | ||
2201 | /* | |
2202 | * Check if someone else fixed it for us: | |
2203 | */ | |
2204 | if (pi_state->owner != oldowner) | |
2205 | return 0; | |
2206 | ||
2207 | if (ret) | |
2208 | return ret; | |
2209 | ||
2210 | goto retry; | |
2211 | } | |
2212 | ||
2213 | static long futex_wait_restart(struct restart_block *restart); | |
2214 | ||
2215 | /** | |
2216 | * fixup_owner() - Post lock pi_state and corner case management | |
2217 | * @uaddr: user address of the futex | |
2218 | * @q: futex_q (contains pi_state and access to the rt_mutex) | |
2219 | * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0) | |
2220 | * | |
2221 | * After attempting to lock an rt_mutex, this function is called to cleanup | |
2222 | * the pi_state owner as well as handle race conditions that may allow us to | |
2223 | * acquire the lock. Must be called with the hb lock held. | |
2224 | * | |
2225 | * Return: | |
2226 | * 1 - success, lock taken; | |
2227 | * 0 - success, lock not taken; | |
2228 | * <0 - on error (-EFAULT) | |
2229 | */ | |
2230 | static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked) | |
2231 | { | |
2232 | struct task_struct *owner; | |
2233 | int ret = 0; | |
2234 | ||
2235 | if (locked) { | |
2236 | /* | |
2237 | * Got the lock. We might not be the anticipated owner if we | |
2238 | * did a lock-steal - fix up the PI-state in that case: | |
2239 | */ | |
2240 | if (q->pi_state->owner != current) | |
2241 | ret = fixup_pi_state_owner(uaddr, q, current); | |
2242 | goto out; | |
2243 | } | |
2244 | ||
2245 | /* | |
2246 | * Catch the rare case, where the lock was released when we were on the | |
2247 | * way back before we locked the hash bucket. | |
2248 | */ | |
2249 | if (q->pi_state->owner == current) { | |
2250 | /* | |
2251 | * Try to get the rt_mutex now. This might fail as some other | |
2252 | * task acquired the rt_mutex after we removed ourself from the | |
2253 | * rt_mutex waiters list. | |
2254 | */ | |
2255 | if (rt_mutex_trylock(&q->pi_state->pi_mutex)) { | |
2256 | locked = 1; | |
2257 | goto out; | |
2258 | } | |
2259 | ||
2260 | /* | |
2261 | * pi_state is incorrect, some other task did a lock steal and | |
2262 | * we returned due to timeout or signal without taking the | |
2263 | * rt_mutex. Too late. | |
2264 | */ | |
2265 | raw_spin_lock_irq(&q->pi_state->pi_mutex.wait_lock); | |
2266 | owner = rt_mutex_owner(&q->pi_state->pi_mutex); | |
2267 | if (!owner) | |
2268 | owner = rt_mutex_next_owner(&q->pi_state->pi_mutex); | |
2269 | raw_spin_unlock_irq(&q->pi_state->pi_mutex.wait_lock); | |
2270 | ret = fixup_pi_state_owner(uaddr, q, owner); | |
2271 | goto out; | |
2272 | } | |
2273 | ||
2274 | /* | |
2275 | * Paranoia check. If we did not take the lock, then we should not be | |
2276 | * the owner of the rt_mutex. | |
2277 | */ | |
2278 | if (rt_mutex_owner(&q->pi_state->pi_mutex) == current) | |
2279 | printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p " | |
2280 | "pi-state %p\n", ret, | |
2281 | q->pi_state->pi_mutex.owner, | |
2282 | q->pi_state->owner); | |
2283 | ||
2284 | out: | |
2285 | return ret ? ret : locked; | |
2286 | } | |
2287 | ||
2288 | /** | |
2289 | * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal | |
2290 | * @hb: the futex hash bucket, must be locked by the caller | |
2291 | * @q: the futex_q to queue up on | |
2292 | * @timeout: the prepared hrtimer_sleeper, or null for no timeout | |
2293 | */ | |
2294 | static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q, | |
2295 | struct hrtimer_sleeper *timeout) | |
2296 | { | |
2297 | /* | |
2298 | * The task state is guaranteed to be set before another task can | |
2299 | * wake it. set_current_state() is implemented using smp_store_mb() and | |
2300 | * queue_me() calls spin_unlock() upon completion, both serializing | |
2301 | * access to the hash list and forcing another memory barrier. | |
2302 | */ | |
2303 | set_current_state(TASK_INTERRUPTIBLE); | |
2304 | queue_me(q, hb); | |
2305 | ||
2306 | /* Arm the timer */ | |
2307 | if (timeout) | |
2308 | hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS); | |
2309 | ||
2310 | /* | |
2311 | * If we have been removed from the hash list, then another task | |
2312 | * has tried to wake us, and we can skip the call to schedule(). | |
2313 | */ | |
2314 | if (likely(!plist_node_empty(&q->list))) { | |
2315 | /* | |
2316 | * If the timer has already expired, current will already be | |
2317 | * flagged for rescheduling. Only call schedule if there | |
2318 | * is no timeout, or if it has yet to expire. | |
2319 | */ | |
2320 | if (!timeout || timeout->task) | |
2321 | freezable_schedule(); | |
2322 | } | |
2323 | __set_current_state(TASK_RUNNING); | |
2324 | } | |
2325 | ||
2326 | /** | |
2327 | * futex_wait_setup() - Prepare to wait on a futex | |
2328 | * @uaddr: the futex userspace address | |
2329 | * @val: the expected value | |
2330 | * @flags: futex flags (FLAGS_SHARED, etc.) | |
2331 | * @q: the associated futex_q | |
2332 | * @hb: storage for hash_bucket pointer to be returned to caller | |
2333 | * | |
2334 | * Setup the futex_q and locate the hash_bucket. Get the futex value and | |
2335 | * compare it with the expected value. Handle atomic faults internally. | |
2336 | * Return with the hb lock held and a q.key reference on success, and unlocked | |
2337 | * with no q.key reference on failure. | |
2338 | * | |
2339 | * Return: | |
2340 | * 0 - uaddr contains val and hb has been locked; | |
2341 | * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked | |
2342 | */ | |
2343 | static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags, | |
2344 | struct futex_q *q, struct futex_hash_bucket **hb) | |
2345 | { | |
2346 | u32 uval; | |
2347 | int ret; | |
2348 | ||
2349 | /* | |
2350 | * Access the page AFTER the hash-bucket is locked. | |
2351 | * Order is important: | |
2352 | * | |
2353 | * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val); | |
2354 | * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); } | |
2355 | * | |
2356 | * The basic logical guarantee of a futex is that it blocks ONLY | |
2357 | * if cond(var) is known to be true at the time of blocking, for | |
2358 | * any cond. If we locked the hash-bucket after testing *uaddr, that | |
2359 | * would open a race condition where we could block indefinitely with | |
2360 | * cond(var) false, which would violate the guarantee. | |
2361 | * | |
2362 | * On the other hand, we insert q and release the hash-bucket only | |
2363 | * after testing *uaddr. This guarantees that futex_wait() will NOT | |
2364 | * absorb a wakeup if *uaddr does not match the desired values | |
2365 | * while the syscall executes. | |
2366 | */ | |
2367 | retry: | |
2368 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ); | |
2369 | if (unlikely(ret != 0)) | |
2370 | return ret; | |
2371 | ||
2372 | retry_private: | |
2373 | *hb = queue_lock(q); | |
2374 | ||
2375 | ret = get_futex_value_locked(&uval, uaddr); | |
2376 | ||
2377 | if (ret) { | |
2378 | queue_unlock(*hb); | |
2379 | ||
2380 | ret = get_user(uval, uaddr); | |
2381 | if (ret) | |
2382 | goto out; | |
2383 | ||
2384 | if (!(flags & FLAGS_SHARED)) | |
2385 | goto retry_private; | |
2386 | ||
2387 | put_futex_key(&q->key); | |
2388 | goto retry; | |
2389 | } | |
2390 | ||
2391 | if (uval != val) { | |
2392 | queue_unlock(*hb); | |
2393 | ret = -EWOULDBLOCK; | |
2394 | } | |
2395 | ||
2396 | out: | |
2397 | if (ret) | |
2398 | put_futex_key(&q->key); | |
2399 | return ret; | |
2400 | } | |
2401 | ||
2402 | static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val, | |
2403 | ktime_t *abs_time, u32 bitset) | |
2404 | { | |
2405 | struct hrtimer_sleeper timeout, *to = NULL; | |
2406 | struct restart_block *restart; | |
2407 | struct futex_hash_bucket *hb; | |
2408 | struct futex_q q = futex_q_init; | |
2409 | int ret; | |
2410 | ||
2411 | if (!bitset) | |
2412 | return -EINVAL; | |
2413 | q.bitset = bitset; | |
2414 | ||
2415 | if (abs_time) { | |
2416 | to = &timeout; | |
2417 | ||
2418 | hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ? | |
2419 | CLOCK_REALTIME : CLOCK_MONOTONIC, | |
2420 | HRTIMER_MODE_ABS); | |
2421 | hrtimer_init_sleeper(to, current); | |
2422 | hrtimer_set_expires_range_ns(&to->timer, *abs_time, | |
2423 | current->timer_slack_ns); | |
2424 | } | |
2425 | ||
2426 | retry: | |
2427 | /* | |
2428 | * Prepare to wait on uaddr. On success, holds hb lock and increments | |
2429 | * q.key refs. | |
2430 | */ | |
2431 | ret = futex_wait_setup(uaddr, val, flags, &q, &hb); | |
2432 | if (ret) | |
2433 | goto out; | |
2434 | ||
2435 | /* queue_me and wait for wakeup, timeout, or a signal. */ | |
2436 | futex_wait_queue_me(hb, &q, to); | |
2437 | ||
2438 | /* If we were woken (and unqueued), we succeeded, whatever. */ | |
2439 | ret = 0; | |
2440 | /* unqueue_me() drops q.key ref */ | |
2441 | if (!unqueue_me(&q)) | |
2442 | goto out; | |
2443 | ret = -ETIMEDOUT; | |
2444 | if (to && !to->task) | |
2445 | goto out; | |
2446 | ||
2447 | /* | |
2448 | * We expect signal_pending(current), but we might be the | |
2449 | * victim of a spurious wakeup as well. | |
2450 | */ | |
2451 | if (!signal_pending(current)) | |
2452 | goto retry; | |
2453 | ||
2454 | ret = -ERESTARTSYS; | |
2455 | if (!abs_time) | |
2456 | goto out; | |
2457 | ||
2458 | restart = ¤t->restart_block; | |
2459 | restart->fn = futex_wait_restart; | |
2460 | restart->futex.uaddr = uaddr; | |
2461 | restart->futex.val = val; | |
2462 | restart->futex.time = *abs_time; | |
2463 | restart->futex.bitset = bitset; | |
2464 | restart->futex.flags = flags | FLAGS_HAS_TIMEOUT; | |
2465 | ||
2466 | ret = -ERESTART_RESTARTBLOCK; | |
2467 | ||
2468 | out: | |
2469 | if (to) { | |
2470 | hrtimer_cancel(&to->timer); | |
2471 | destroy_hrtimer_on_stack(&to->timer); | |
2472 | } | |
2473 | return ret; | |
2474 | } | |
2475 | ||
2476 | ||
2477 | static long futex_wait_restart(struct restart_block *restart) | |
2478 | { | |
2479 | u32 __user *uaddr = restart->futex.uaddr; | |
2480 | ktime_t t, *tp = NULL; | |
2481 | ||
2482 | if (restart->futex.flags & FLAGS_HAS_TIMEOUT) { | |
2483 | t = restart->futex.time; | |
2484 | tp = &t; | |
2485 | } | |
2486 | restart->fn = do_no_restart_syscall; | |
2487 | ||
2488 | return (long)futex_wait(uaddr, restart->futex.flags, | |
2489 | restart->futex.val, tp, restart->futex.bitset); | |
2490 | } | |
2491 | ||
2492 | ||
2493 | /* | |
2494 | * Userspace tried a 0 -> TID atomic transition of the futex value | |
2495 | * and failed. The kernel side here does the whole locking operation: | |
2496 | * if there are waiters then it will block as a consequence of relying | |
2497 | * on rt-mutexes, it does PI, etc. (Due to races the kernel might see | |
2498 | * a 0 value of the futex too.). | |
2499 | * | |
2500 | * Also serves as futex trylock_pi()'ing, and due semantics. | |
2501 | */ | |
2502 | static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, | |
2503 | ktime_t *time, int trylock) | |
2504 | { | |
2505 | struct hrtimer_sleeper timeout, *to = NULL; | |
2506 | struct futex_hash_bucket *hb; | |
2507 | struct futex_q q = futex_q_init; | |
2508 | int res, ret; | |
2509 | ||
2510 | if (refill_pi_state_cache()) | |
2511 | return -ENOMEM; | |
2512 | ||
2513 | if (time) { | |
2514 | to = &timeout; | |
2515 | hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME, | |
2516 | HRTIMER_MODE_ABS); | |
2517 | hrtimer_init_sleeper(to, current); | |
2518 | hrtimer_set_expires(&to->timer, *time); | |
2519 | } | |
2520 | ||
2521 | retry: | |
2522 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE); | |
2523 | if (unlikely(ret != 0)) | |
2524 | goto out; | |
2525 | ||
2526 | retry_private: | |
2527 | hb = queue_lock(&q); | |
2528 | ||
2529 | ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0); | |
2530 | if (unlikely(ret)) { | |
2531 | /* | |
2532 | * Atomic work succeeded and we got the lock, | |
2533 | * or failed. Either way, we do _not_ block. | |
2534 | */ | |
2535 | switch (ret) { | |
2536 | case 1: | |
2537 | /* We got the lock. */ | |
2538 | ret = 0; | |
2539 | goto out_unlock_put_key; | |
2540 | case -EFAULT: | |
2541 | goto uaddr_faulted; | |
2542 | case -EAGAIN: | |
2543 | /* | |
2544 | * Two reasons for this: | |
2545 | * - Task is exiting and we just wait for the | |
2546 | * exit to complete. | |
2547 | * - The user space value changed. | |
2548 | */ | |
2549 | queue_unlock(hb); | |
2550 | put_futex_key(&q.key); | |
2551 | cond_resched(); | |
2552 | goto retry; | |
2553 | default: | |
2554 | goto out_unlock_put_key; | |
2555 | } | |
2556 | } | |
2557 | ||
2558 | /* | |
2559 | * Only actually queue now that the atomic ops are done: | |
2560 | */ | |
2561 | queue_me(&q, hb); | |
2562 | ||
2563 | WARN_ON(!q.pi_state); | |
2564 | /* | |
2565 | * Block on the PI mutex: | |
2566 | */ | |
2567 | if (!trylock) { | |
2568 | ret = rt_mutex_timed_futex_lock(&q.pi_state->pi_mutex, to); | |
2569 | } else { | |
2570 | ret = rt_mutex_trylock(&q.pi_state->pi_mutex); | |
2571 | /* Fixup the trylock return value: */ | |
2572 | ret = ret ? 0 : -EWOULDBLOCK; | |
2573 | } | |
2574 | ||
2575 | spin_lock(q.lock_ptr); | |
2576 | /* | |
2577 | * Fixup the pi_state owner and possibly acquire the lock if we | |
2578 | * haven't already. | |
2579 | */ | |
2580 | res = fixup_owner(uaddr, &q, !ret); | |
2581 | /* | |
2582 | * If fixup_owner() returned an error, proprogate that. If it acquired | |
2583 | * the lock, clear our -ETIMEDOUT or -EINTR. | |
2584 | */ | |
2585 | if (res) | |
2586 | ret = (res < 0) ? res : 0; | |
2587 | ||
2588 | /* | |
2589 | * If fixup_owner() faulted and was unable to handle the fault, unlock | |
2590 | * it and return the fault to userspace. | |
2591 | */ | |
2592 | if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) | |
2593 | rt_mutex_unlock(&q.pi_state->pi_mutex); | |
2594 | ||
2595 | /* Unqueue and drop the lock */ | |
2596 | unqueue_me_pi(&q); | |
2597 | ||
2598 | goto out_put_key; | |
2599 | ||
2600 | out_unlock_put_key: | |
2601 | queue_unlock(hb); | |
2602 | ||
2603 | out_put_key: | |
2604 | put_futex_key(&q.key); | |
2605 | out: | |
2606 | if (to) | |
2607 | destroy_hrtimer_on_stack(&to->timer); | |
2608 | return ret != -EINTR ? ret : -ERESTARTNOINTR; | |
2609 | ||
2610 | uaddr_faulted: | |
2611 | queue_unlock(hb); | |
2612 | ||
2613 | ret = fault_in_user_writeable(uaddr); | |
2614 | if (ret) | |
2615 | goto out_put_key; | |
2616 | ||
2617 | if (!(flags & FLAGS_SHARED)) | |
2618 | goto retry_private; | |
2619 | ||
2620 | put_futex_key(&q.key); | |
2621 | goto retry; | |
2622 | } | |
2623 | ||
2624 | /* | |
2625 | * Userspace attempted a TID -> 0 atomic transition, and failed. | |
2626 | * This is the in-kernel slowpath: we look up the PI state (if any), | |
2627 | * and do the rt-mutex unlock. | |
2628 | */ | |
2629 | static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags) | |
2630 | { | |
2631 | u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current); | |
2632 | union futex_key key = FUTEX_KEY_INIT; | |
2633 | struct futex_hash_bucket *hb; | |
2634 | struct futex_q *match; | |
2635 | int ret; | |
2636 | ||
2637 | retry: | |
2638 | if (get_user(uval, uaddr)) | |
2639 | return -EFAULT; | |
2640 | /* | |
2641 | * We release only a lock we actually own: | |
2642 | */ | |
2643 | if ((uval & FUTEX_TID_MASK) != vpid) | |
2644 | return -EPERM; | |
2645 | ||
2646 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE); | |
2647 | if (ret) | |
2648 | return ret; | |
2649 | ||
2650 | hb = hash_futex(&key); | |
2651 | spin_lock(&hb->lock); | |
2652 | ||
2653 | /* | |
2654 | * Check waiters first. We do not trust user space values at | |
2655 | * all and we at least want to know if user space fiddled | |
2656 | * with the futex value instead of blindly unlocking. | |
2657 | */ | |
2658 | match = futex_top_waiter(hb, &key); | |
2659 | if (match) { | |
2660 | ret = wake_futex_pi(uaddr, uval, match, hb); | |
2661 | /* | |
2662 | * In case of success wake_futex_pi dropped the hash | |
2663 | * bucket lock. | |
2664 | */ | |
2665 | if (!ret) | |
2666 | goto out_putkey; | |
2667 | /* | |
2668 | * The atomic access to the futex value generated a | |
2669 | * pagefault, so retry the user-access and the wakeup: | |
2670 | */ | |
2671 | if (ret == -EFAULT) | |
2672 | goto pi_faulted; | |
2673 | /* | |
2674 | * A unconditional UNLOCK_PI op raced against a waiter | |
2675 | * setting the FUTEX_WAITERS bit. Try again. | |
2676 | */ | |
2677 | if (ret == -EAGAIN) { | |
2678 | spin_unlock(&hb->lock); | |
2679 | put_futex_key(&key); | |
2680 | goto retry; | |
2681 | } | |
2682 | /* | |
2683 | * wake_futex_pi has detected invalid state. Tell user | |
2684 | * space. | |
2685 | */ | |
2686 | goto out_unlock; | |
2687 | } | |
2688 | ||
2689 | /* | |
2690 | * We have no kernel internal state, i.e. no waiters in the | |
2691 | * kernel. Waiters which are about to queue themselves are stuck | |
2692 | * on hb->lock. So we can safely ignore them. We do neither | |
2693 | * preserve the WAITERS bit not the OWNER_DIED one. We are the | |
2694 | * owner. | |
2695 | */ | |
2696 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0)) | |
2697 | goto pi_faulted; | |
2698 | ||
2699 | /* | |
2700 | * If uval has changed, let user space handle it. | |
2701 | */ | |
2702 | ret = (curval == uval) ? 0 : -EAGAIN; | |
2703 | ||
2704 | out_unlock: | |
2705 | spin_unlock(&hb->lock); | |
2706 | out_putkey: | |
2707 | put_futex_key(&key); | |
2708 | return ret; | |
2709 | ||
2710 | pi_faulted: | |
2711 | spin_unlock(&hb->lock); | |
2712 | put_futex_key(&key); | |
2713 | ||
2714 | ret = fault_in_user_writeable(uaddr); | |
2715 | if (!ret) | |
2716 | goto retry; | |
2717 | ||
2718 | return ret; | |
2719 | } | |
2720 | ||
2721 | /** | |
2722 | * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex | |
2723 | * @hb: the hash_bucket futex_q was original enqueued on | |
2724 | * @q: the futex_q woken while waiting to be requeued | |
2725 | * @key2: the futex_key of the requeue target futex | |
2726 | * @timeout: the timeout associated with the wait (NULL if none) | |
2727 | * | |
2728 | * Detect if the task was woken on the initial futex as opposed to the requeue | |
2729 | * target futex. If so, determine if it was a timeout or a signal that caused | |
2730 | * the wakeup and return the appropriate error code to the caller. Must be | |
2731 | * called with the hb lock held. | |
2732 | * | |
2733 | * Return: | |
2734 | * 0 = no early wakeup detected; | |
2735 | * <0 = -ETIMEDOUT or -ERESTARTNOINTR | |
2736 | */ | |
2737 | static inline | |
2738 | int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb, | |
2739 | struct futex_q *q, union futex_key *key2, | |
2740 | struct hrtimer_sleeper *timeout) | |
2741 | { | |
2742 | int ret = 0; | |
2743 | ||
2744 | /* | |
2745 | * With the hb lock held, we avoid races while we process the wakeup. | |
2746 | * We only need to hold hb (and not hb2) to ensure atomicity as the | |
2747 | * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb. | |
2748 | * It can't be requeued from uaddr2 to something else since we don't | |
2749 | * support a PI aware source futex for requeue. | |
2750 | */ | |
2751 | if (!match_futex(&q->key, key2)) { | |
2752 | WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr)); | |
2753 | /* | |
2754 | * We were woken prior to requeue by a timeout or a signal. | |
2755 | * Unqueue the futex_q and determine which it was. | |
2756 | */ | |
2757 | plist_del(&q->list, &hb->chain); | |
2758 | hb_waiters_dec(hb); | |
2759 | ||
2760 | /* Handle spurious wakeups gracefully */ | |
2761 | ret = -EWOULDBLOCK; | |
2762 | if (timeout && !timeout->task) | |
2763 | ret = -ETIMEDOUT; | |
2764 | else if (signal_pending(current)) | |
2765 | ret = -ERESTARTNOINTR; | |
2766 | } | |
2767 | return ret; | |
2768 | } | |
2769 | ||
2770 | /** | |
2771 | * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2 | |
2772 | * @uaddr: the futex we initially wait on (non-pi) | |
2773 | * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be | |
2774 | * the same type, no requeueing from private to shared, etc. | |
2775 | * @val: the expected value of uaddr | |
2776 | * @abs_time: absolute timeout | |
2777 | * @bitset: 32 bit wakeup bitset set by userspace, defaults to all | |
2778 | * @uaddr2: the pi futex we will take prior to returning to user-space | |
2779 | * | |
2780 | * The caller will wait on uaddr and will be requeued by futex_requeue() to | |
2781 | * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake | |
2782 | * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to | |
2783 | * userspace. This ensures the rt_mutex maintains an owner when it has waiters; | |
2784 | * without one, the pi logic would not know which task to boost/deboost, if | |
2785 | * there was a need to. | |
2786 | * | |
2787 | * We call schedule in futex_wait_queue_me() when we enqueue and return there | |
2788 | * via the following-- | |
2789 | * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue() | |
2790 | * 2) wakeup on uaddr2 after a requeue | |
2791 | * 3) signal | |
2792 | * 4) timeout | |
2793 | * | |
2794 | * If 3, cleanup and return -ERESTARTNOINTR. | |
2795 | * | |
2796 | * If 2, we may then block on trying to take the rt_mutex and return via: | |
2797 | * 5) successful lock | |
2798 | * 6) signal | |
2799 | * 7) timeout | |
2800 | * 8) other lock acquisition failure | |
2801 | * | |
2802 | * If 6, return -EWOULDBLOCK (restarting the syscall would do the same). | |
2803 | * | |
2804 | * If 4 or 7, we cleanup and return with -ETIMEDOUT. | |
2805 | * | |
2806 | * Return: | |
2807 | * 0 - On success; | |
2808 | * <0 - On error | |
2809 | */ | |
2810 | static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, | |
2811 | u32 val, ktime_t *abs_time, u32 bitset, | |
2812 | u32 __user *uaddr2) | |
2813 | { | |
2814 | struct hrtimer_sleeper timeout, *to = NULL; | |
2815 | struct rt_mutex_waiter rt_waiter; | |
2816 | struct futex_hash_bucket *hb; | |
2817 | union futex_key key2 = FUTEX_KEY_INIT; | |
2818 | struct futex_q q = futex_q_init; | |
2819 | int res, ret; | |
2820 | ||
2821 | if (uaddr == uaddr2) | |
2822 | return -EINVAL; | |
2823 | ||
2824 | if (!bitset) | |
2825 | return -EINVAL; | |
2826 | ||
2827 | if (abs_time) { | |
2828 | to = &timeout; | |
2829 | hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ? | |
2830 | CLOCK_REALTIME : CLOCK_MONOTONIC, | |
2831 | HRTIMER_MODE_ABS); | |
2832 | hrtimer_init_sleeper(to, current); | |
2833 | hrtimer_set_expires_range_ns(&to->timer, *abs_time, | |
2834 | current->timer_slack_ns); | |
2835 | } | |
2836 | ||
2837 | /* | |
2838 | * The waiter is allocated on our stack, manipulated by the requeue | |
2839 | * code while we sleep on uaddr. | |
2840 | */ | |
2841 | debug_rt_mutex_init_waiter(&rt_waiter); | |
2842 | RB_CLEAR_NODE(&rt_waiter.pi_tree_entry); | |
2843 | RB_CLEAR_NODE(&rt_waiter.tree_entry); | |
2844 | rt_waiter.task = NULL; | |
2845 | ||
2846 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE); | |
2847 | if (unlikely(ret != 0)) | |
2848 | goto out; | |
2849 | ||
2850 | q.bitset = bitset; | |
2851 | q.rt_waiter = &rt_waiter; | |
2852 | q.requeue_pi_key = &key2; | |
2853 | ||
2854 | /* | |
2855 | * Prepare to wait on uaddr. On success, increments q.key (key1) ref | |
2856 | * count. | |
2857 | */ | |
2858 | ret = futex_wait_setup(uaddr, val, flags, &q, &hb); | |
2859 | if (ret) | |
2860 | goto out_key2; | |
2861 | ||
2862 | /* | |
2863 | * The check above which compares uaddrs is not sufficient for | |
2864 | * shared futexes. We need to compare the keys: | |
2865 | */ | |
2866 | if (match_futex(&q.key, &key2)) { | |
2867 | queue_unlock(hb); | |
2868 | ret = -EINVAL; | |
2869 | goto out_put_keys; | |
2870 | } | |
2871 | ||
2872 | /* Queue the futex_q, drop the hb lock, wait for wakeup. */ | |
2873 | futex_wait_queue_me(hb, &q, to); | |
2874 | ||
2875 | spin_lock(&hb->lock); | |
2876 | ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to); | |
2877 | spin_unlock(&hb->lock); | |
2878 | if (ret) | |
2879 | goto out_put_keys; | |
2880 | ||
2881 | /* | |
2882 | * In order for us to be here, we know our q.key == key2, and since | |
2883 | * we took the hb->lock above, we also know that futex_requeue() has | |
2884 | * completed and we no longer have to concern ourselves with a wakeup | |
2885 | * race with the atomic proxy lock acquisition by the requeue code. The | |
2886 | * futex_requeue dropped our key1 reference and incremented our key2 | |
2887 | * reference count. | |
2888 | */ | |
2889 | ||
2890 | /* Check if the requeue code acquired the second futex for us. */ | |
2891 | if (!q.rt_waiter) { | |
2892 | /* | |
2893 | * Got the lock. We might not be the anticipated owner if we | |
2894 | * did a lock-steal - fix up the PI-state in that case. | |
2895 | */ | |
2896 | if (q.pi_state && (q.pi_state->owner != current)) { | |
2897 | spin_lock(q.lock_ptr); | |
2898 | ret = fixup_pi_state_owner(uaddr2, &q, current); | |
2899 | if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) | |
2900 | rt_mutex_unlock(&q.pi_state->pi_mutex); | |
2901 | /* | |
2902 | * Drop the reference to the pi state which | |
2903 | * the requeue_pi() code acquired for us. | |
2904 | */ | |
2905 | put_pi_state(q.pi_state); | |
2906 | spin_unlock(q.lock_ptr); | |
2907 | } | |
2908 | } else { | |
2909 | struct rt_mutex *pi_mutex; | |
2910 | ||
2911 | /* | |
2912 | * We have been woken up by futex_unlock_pi(), a timeout, or a | |
2913 | * signal. futex_unlock_pi() will not destroy the lock_ptr nor | |
2914 | * the pi_state. | |
2915 | */ | |
2916 | WARN_ON(!q.pi_state); | |
2917 | pi_mutex = &q.pi_state->pi_mutex; | |
2918 | ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter); | |
2919 | debug_rt_mutex_free_waiter(&rt_waiter); | |
2920 | ||
2921 | spin_lock(q.lock_ptr); | |
2922 | /* | |
2923 | * Fixup the pi_state owner and possibly acquire the lock if we | |
2924 | * haven't already. | |
2925 | */ | |
2926 | res = fixup_owner(uaddr2, &q, !ret); | |
2927 | /* | |
2928 | * If fixup_owner() returned an error, proprogate that. If it | |
2929 | * acquired the lock, clear -ETIMEDOUT or -EINTR. | |
2930 | */ | |
2931 | if (res) | |
2932 | ret = (res < 0) ? res : 0; | |
2933 | ||
2934 | /* | |
2935 | * If fixup_pi_state_owner() faulted and was unable to handle | |
2936 | * the fault, unlock the rt_mutex and return the fault to | |
2937 | * userspace. | |
2938 | */ | |
2939 | if (ret && rt_mutex_owner(pi_mutex) == current) | |
2940 | rt_mutex_unlock(pi_mutex); | |
2941 | ||
2942 | /* Unqueue and drop the lock. */ | |
2943 | unqueue_me_pi(&q); | |
2944 | } | |
2945 | ||
2946 | if (ret == -EINTR) { | |
2947 | /* | |
2948 | * We've already been requeued, but cannot restart by calling | |
2949 | * futex_lock_pi() directly. We could restart this syscall, but | |
2950 | * it would detect that the user space "val" changed and return | |
2951 | * -EWOULDBLOCK. Save the overhead of the restart and return | |
2952 | * -EWOULDBLOCK directly. | |
2953 | */ | |
2954 | ret = -EWOULDBLOCK; | |
2955 | } | |
2956 | ||
2957 | out_put_keys: | |
2958 | put_futex_key(&q.key); | |
2959 | out_key2: | |
2960 | put_futex_key(&key2); | |
2961 | ||
2962 | out: | |
2963 | if (to) { | |
2964 | hrtimer_cancel(&to->timer); | |
2965 | destroy_hrtimer_on_stack(&to->timer); | |
2966 | } | |
2967 | return ret; | |
2968 | } | |
2969 | ||
2970 | /* | |
2971 | * Support for robust futexes: the kernel cleans up held futexes at | |
2972 | * thread exit time. | |
2973 | * | |
2974 | * Implementation: user-space maintains a per-thread list of locks it | |
2975 | * is holding. Upon do_exit(), the kernel carefully walks this list, | |
2976 | * and marks all locks that are owned by this thread with the | |
2977 | * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is | |
2978 | * always manipulated with the lock held, so the list is private and | |
2979 | * per-thread. Userspace also maintains a per-thread 'list_op_pending' | |
2980 | * field, to allow the kernel to clean up if the thread dies after | |
2981 | * acquiring the lock, but just before it could have added itself to | |
2982 | * the list. There can only be one such pending lock. | |
2983 | */ | |
2984 | ||
2985 | /** | |
2986 | * sys_set_robust_list() - Set the robust-futex list head of a task | |
2987 | * @head: pointer to the list-head | |
2988 | * @len: length of the list-head, as userspace expects | |
2989 | */ | |
2990 | SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head, | |
2991 | size_t, len) | |
2992 | { | |
2993 | if (!futex_cmpxchg_enabled) | |
2994 | return -ENOSYS; | |
2995 | /* | |
2996 | * The kernel knows only one size for now: | |
2997 | */ | |
2998 | if (unlikely(len != sizeof(*head))) | |
2999 | return -EINVAL; | |
3000 | ||
3001 | current->robust_list = head; | |
3002 | ||
3003 | return 0; | |
3004 | } | |
3005 | ||
3006 | /** | |
3007 | * sys_get_robust_list() - Get the robust-futex list head of a task | |
3008 | * @pid: pid of the process [zero for current task] | |
3009 | * @head_ptr: pointer to a list-head pointer, the kernel fills it in | |
3010 | * @len_ptr: pointer to a length field, the kernel fills in the header size | |
3011 | */ | |
3012 | SYSCALL_DEFINE3(get_robust_list, int, pid, | |
3013 | struct robust_list_head __user * __user *, head_ptr, | |
3014 | size_t __user *, len_ptr) | |
3015 | { | |
3016 | struct robust_list_head __user *head; | |
3017 | unsigned long ret; | |
3018 | struct task_struct *p; | |
3019 | ||
3020 | if (!futex_cmpxchg_enabled) | |
3021 | return -ENOSYS; | |
3022 | ||
3023 | rcu_read_lock(); | |
3024 | ||
3025 | ret = -ESRCH; | |
3026 | if (!pid) | |
3027 | p = current; | |
3028 | else { | |
3029 | p = find_task_by_vpid(pid); | |
3030 | if (!p) | |
3031 | goto err_unlock; | |
3032 | } | |
3033 | ||
3034 | ret = -EPERM; | |
3035 | if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS)) | |
3036 | goto err_unlock; | |
3037 | ||
3038 | head = p->robust_list; | |
3039 | rcu_read_unlock(); | |
3040 | ||
3041 | if (put_user(sizeof(*head), len_ptr)) | |
3042 | return -EFAULT; | |
3043 | return put_user(head, head_ptr); | |
3044 | ||
3045 | err_unlock: | |
3046 | rcu_read_unlock(); | |
3047 | ||
3048 | return ret; | |
3049 | } | |
3050 | ||
3051 | /* | |
3052 | * Process a futex-list entry, check whether it's owned by the | |
3053 | * dying task, and do notification if so: | |
3054 | */ | |
3055 | int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi) | |
3056 | { | |
3057 | u32 uval, uninitialized_var(nval), mval; | |
3058 | ||
3059 | retry: | |
3060 | if (get_user(uval, uaddr)) | |
3061 | return -1; | |
3062 | ||
3063 | if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) { | |
3064 | /* | |
3065 | * Ok, this dying thread is truly holding a futex | |
3066 | * of interest. Set the OWNER_DIED bit atomically | |
3067 | * via cmpxchg, and if the value had FUTEX_WAITERS | |
3068 | * set, wake up a waiter (if any). (We have to do a | |
3069 | * futex_wake() even if OWNER_DIED is already set - | |
3070 | * to handle the rare but possible case of recursive | |
3071 | * thread-death.) The rest of the cleanup is done in | |
3072 | * userspace. | |
3073 | */ | |
3074 | mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED; | |
3075 | /* | |
3076 | * We are not holding a lock here, but we want to have | |
3077 | * the pagefault_disable/enable() protection because | |
3078 | * we want to handle the fault gracefully. If the | |
3079 | * access fails we try to fault in the futex with R/W | |
3080 | * verification via get_user_pages. get_user() above | |
3081 | * does not guarantee R/W access. If that fails we | |
3082 | * give up and leave the futex locked. | |
3083 | */ | |
3084 | if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) { | |
3085 | if (fault_in_user_writeable(uaddr)) | |
3086 | return -1; | |
3087 | goto retry; | |
3088 | } | |
3089 | if (nval != uval) | |
3090 | goto retry; | |
3091 | ||
3092 | /* | |
3093 | * Wake robust non-PI futexes here. The wakeup of | |
3094 | * PI futexes happens in exit_pi_state(): | |
3095 | */ | |
3096 | if (!pi && (uval & FUTEX_WAITERS)) | |
3097 | futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY); | |
3098 | } | |
3099 | return 0; | |
3100 | } | |
3101 | ||
3102 | /* | |
3103 | * Fetch a robust-list pointer. Bit 0 signals PI futexes: | |
3104 | */ | |
3105 | static inline int fetch_robust_entry(struct robust_list __user **entry, | |
3106 | struct robust_list __user * __user *head, | |
3107 | unsigned int *pi) | |
3108 | { | |
3109 | unsigned long uentry; | |
3110 | ||
3111 | if (get_user(uentry, (unsigned long __user *)head)) | |
3112 | return -EFAULT; | |
3113 | ||
3114 | *entry = (void __user *)(uentry & ~1UL); | |
3115 | *pi = uentry & 1; | |
3116 | ||
3117 | return 0; | |
3118 | } | |
3119 | ||
3120 | /* | |
3121 | * Walk curr->robust_list (very carefully, it's a userspace list!) | |
3122 | * and mark any locks found there dead, and notify any waiters. | |
3123 | * | |
3124 | * We silently return on any sign of list-walking problem. | |
3125 | */ | |
3126 | void exit_robust_list(struct task_struct *curr) | |
3127 | { | |
3128 | struct robust_list_head __user *head = curr->robust_list; | |
3129 | struct robust_list __user *entry, *next_entry, *pending; | |
3130 | unsigned int limit = ROBUST_LIST_LIMIT, pi, pip; | |
3131 | unsigned int uninitialized_var(next_pi); | |
3132 | unsigned long futex_offset; | |
3133 | int rc; | |
3134 | ||
3135 | if (!futex_cmpxchg_enabled) | |
3136 | return; | |
3137 | ||
3138 | /* | |
3139 | * Fetch the list head (which was registered earlier, via | |
3140 | * sys_set_robust_list()): | |
3141 | */ | |
3142 | if (fetch_robust_entry(&entry, &head->list.next, &pi)) | |
3143 | return; | |
3144 | /* | |
3145 | * Fetch the relative futex offset: | |
3146 | */ | |
3147 | if (get_user(futex_offset, &head->futex_offset)) | |
3148 | return; | |
3149 | /* | |
3150 | * Fetch any possibly pending lock-add first, and handle it | |
3151 | * if it exists: | |
3152 | */ | |
3153 | if (fetch_robust_entry(&pending, &head->list_op_pending, &pip)) | |
3154 | return; | |
3155 | ||
3156 | next_entry = NULL; /* avoid warning with gcc */ | |
3157 | while (entry != &head->list) { | |
3158 | /* | |
3159 | * Fetch the next entry in the list before calling | |
3160 | * handle_futex_death: | |
3161 | */ | |
3162 | rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi); | |
3163 | /* | |
3164 | * A pending lock might already be on the list, so | |
3165 | * don't process it twice: | |
3166 | */ | |
3167 | if (entry != pending) | |
3168 | if (handle_futex_death((void __user *)entry + futex_offset, | |
3169 | curr, pi)) | |
3170 | return; | |
3171 | if (rc) | |
3172 | return; | |
3173 | entry = next_entry; | |
3174 | pi = next_pi; | |
3175 | /* | |
3176 | * Avoid excessively long or circular lists: | |
3177 | */ | |
3178 | if (!--limit) | |
3179 | break; | |
3180 | ||
3181 | cond_resched(); | |
3182 | } | |
3183 | ||
3184 | if (pending) | |
3185 | handle_futex_death((void __user *)pending + futex_offset, | |
3186 | curr, pip); | |
3187 | } | |
3188 | ||
3189 | long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, | |
3190 | u32 __user *uaddr2, u32 val2, u32 val3) | |
3191 | { | |
3192 | int cmd = op & FUTEX_CMD_MASK; | |
3193 | unsigned int flags = 0; | |
3194 | ||
3195 | if (!(op & FUTEX_PRIVATE_FLAG)) | |
3196 | flags |= FLAGS_SHARED; | |
3197 | ||
3198 | if (op & FUTEX_CLOCK_REALTIME) { | |
3199 | flags |= FLAGS_CLOCKRT; | |
3200 | if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \ | |
3201 | cmd != FUTEX_WAIT_REQUEUE_PI) | |
3202 | return -ENOSYS; | |
3203 | } | |
3204 | ||
3205 | switch (cmd) { | |
3206 | case FUTEX_LOCK_PI: | |
3207 | case FUTEX_UNLOCK_PI: | |
3208 | case FUTEX_TRYLOCK_PI: | |
3209 | case FUTEX_WAIT_REQUEUE_PI: | |
3210 | case FUTEX_CMP_REQUEUE_PI: | |
3211 | if (!futex_cmpxchg_enabled) | |
3212 | return -ENOSYS; | |
3213 | } | |
3214 | ||
3215 | switch (cmd) { | |
3216 | case FUTEX_WAIT: | |
3217 | val3 = FUTEX_BITSET_MATCH_ANY; | |
3218 | case FUTEX_WAIT_BITSET: | |
3219 | return futex_wait(uaddr, flags, val, timeout, val3); | |
3220 | case FUTEX_WAKE: | |
3221 | val3 = FUTEX_BITSET_MATCH_ANY; | |
3222 | case FUTEX_WAKE_BITSET: | |
3223 | return futex_wake(uaddr, flags, val, val3); | |
3224 | case FUTEX_REQUEUE: | |
3225 | return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0); | |
3226 | case FUTEX_CMP_REQUEUE: | |
3227 | return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0); | |
3228 | case FUTEX_WAKE_OP: | |
3229 | return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3); | |
3230 | case FUTEX_LOCK_PI: | |
3231 | return futex_lock_pi(uaddr, flags, timeout, 0); | |
3232 | case FUTEX_UNLOCK_PI: | |
3233 | return futex_unlock_pi(uaddr, flags); | |
3234 | case FUTEX_TRYLOCK_PI: | |
3235 | return futex_lock_pi(uaddr, flags, NULL, 1); | |
3236 | case FUTEX_WAIT_REQUEUE_PI: | |
3237 | val3 = FUTEX_BITSET_MATCH_ANY; | |
3238 | return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3, | |
3239 | uaddr2); | |
3240 | case FUTEX_CMP_REQUEUE_PI: | |
3241 | return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1); | |
3242 | } | |
3243 | return -ENOSYS; | |
3244 | } | |
3245 | ||
3246 | ||
3247 | SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, | |
3248 | struct timespec __user *, utime, u32 __user *, uaddr2, | |
3249 | u32, val3) | |
3250 | { | |
3251 | struct timespec ts; | |
3252 | ktime_t t, *tp = NULL; | |
3253 | u32 val2 = 0; | |
3254 | int cmd = op & FUTEX_CMD_MASK; | |
3255 | ||
3256 | if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI || | |
3257 | cmd == FUTEX_WAIT_BITSET || | |
3258 | cmd == FUTEX_WAIT_REQUEUE_PI)) { | |
3259 | if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG)))) | |
3260 | return -EFAULT; | |
3261 | if (copy_from_user(&ts, utime, sizeof(ts)) != 0) | |
3262 | return -EFAULT; | |
3263 | if (!timespec_valid(&ts)) | |
3264 | return -EINVAL; | |
3265 | ||
3266 | t = timespec_to_ktime(ts); | |
3267 | if (cmd == FUTEX_WAIT) | |
3268 | t = ktime_add_safe(ktime_get(), t); | |
3269 | tp = &t; | |
3270 | } | |
3271 | /* | |
3272 | * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*. | |
3273 | * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP. | |
3274 | */ | |
3275 | if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE || | |
3276 | cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP) | |
3277 | val2 = (u32) (unsigned long) utime; | |
3278 | ||
3279 | return do_futex(uaddr, op, val, tp, uaddr2, val2, val3); | |
3280 | } | |
3281 | ||
3282 | static void __init futex_detect_cmpxchg(void) | |
3283 | { | |
3284 | #ifndef CONFIG_HAVE_FUTEX_CMPXCHG | |
3285 | u32 curval; | |
3286 | ||
3287 | /* | |
3288 | * This will fail and we want it. Some arch implementations do | |
3289 | * runtime detection of the futex_atomic_cmpxchg_inatomic() | |
3290 | * functionality. We want to know that before we call in any | |
3291 | * of the complex code paths. Also we want to prevent | |
3292 | * registration of robust lists in that case. NULL is | |
3293 | * guaranteed to fault and we get -EFAULT on functional | |
3294 | * implementation, the non-functional ones will return | |
3295 | * -ENOSYS. | |
3296 | */ | |
3297 | if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT) | |
3298 | futex_cmpxchg_enabled = 1; | |
3299 | #endif | |
3300 | } | |
3301 | ||
3302 | static int __init futex_init(void) | |
3303 | { | |
3304 | unsigned int futex_shift; | |
3305 | unsigned long i; | |
3306 | ||
3307 | #if CONFIG_BASE_SMALL | |
3308 | futex_hashsize = 16; | |
3309 | #else | |
3310 | futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus()); | |
3311 | #endif | |
3312 | ||
3313 | futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues), | |
3314 | futex_hashsize, 0, | |
3315 | futex_hashsize < 256 ? HASH_SMALL : 0, | |
3316 | &futex_shift, NULL, | |
3317 | futex_hashsize, futex_hashsize); | |
3318 | futex_hashsize = 1UL << futex_shift; | |
3319 | ||
3320 | futex_detect_cmpxchg(); | |
3321 | ||
3322 | for (i = 0; i < futex_hashsize; i++) { | |
3323 | atomic_set(&futex_queues[i].waiters, 0); | |
3324 | plist_head_init(&futex_queues[i].chain); | |
3325 | spin_lock_init(&futex_queues[i].lock); | |
3326 | } | |
3327 | ||
3328 | return 0; | |
3329 | } | |
3330 | core_initcall(futex_init); |