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/compat.h> |
48 | #include <linux/slab.h> |
49 | #include <linux/poll.h> |
50 | #include <linux/fs.h> |
51 | #include <linux/file.h> |
52 | #include <linux/jhash.h> |
53 | #include <linux/init.h> |
54 | #include <linux/futex.h> |
55 | #include <linux/mount.h> |
56 | #include <linux/pagemap.h> |
57 | #include <linux/syscalls.h> |
58 | #include <linux/signal.h> |
59 | #include <linux/export.h> |
60 | #include <linux/magic.h> |
61 | #include <linux/pid.h> |
62 | #include <linux/nsproxy.h> |
63 | #include <linux/ptrace.h> |
64 | #include <linux/sched/rt.h> |
65 | #include <linux/sched/wake_q.h> |
66 | #include <linux/sched/mm.h> |
67 | #include <linux/hugetlb.h> |
68 | #include <linux/freezer.h> |
69 | #include <linux/memblock.h> |
70 | #include <linux/fault-inject.h> |
71 | #include <linux/refcount.h> |
72 | |
73 | #include <asm/futex.h> |
74 | |
75 | #include "locking/rtmutex_common.h" |
76 | |
77 | /* |
78 | * READ this before attempting to hack on futexes! |
79 | * |
80 | * Basic futex operation and ordering guarantees |
81 | * ============================================= |
82 | * |
83 | * The waiter reads the futex value in user space and calls |
84 | * futex_wait(). This function computes the hash bucket and acquires |
85 | * the hash bucket lock. After that it reads the futex user space value |
86 | * again and verifies that the data has not changed. If it has not changed |
87 | * it enqueues itself into the hash bucket, releases the hash bucket lock |
88 | * and schedules. |
89 | * |
90 | * The waker side modifies the user space value of the futex and calls |
91 | * futex_wake(). This function computes the hash bucket and acquires the |
92 | * hash bucket lock. Then it looks for waiters on that futex in the hash |
93 | * bucket and wakes them. |
94 | * |
95 | * In futex wake up scenarios where no tasks are blocked on a futex, taking |
96 | * the hb spinlock can be avoided and simply return. In order for this |
97 | * optimization to work, ordering guarantees must exist so that the waiter |
98 | * being added to the list is acknowledged when the list is concurrently being |
99 | * checked by the waker, avoiding scenarios like the following: |
100 | * |
101 | * CPU 0 CPU 1 |
102 | * val = *futex; |
103 | * sys_futex(WAIT, futex, val); |
104 | * futex_wait(futex, val); |
105 | * uval = *futex; |
106 | * *futex = newval; |
107 | * sys_futex(WAKE, futex); |
108 | * futex_wake(futex); |
109 | * if (queue_empty()) |
110 | * return; |
111 | * if (uval == val) |
112 | * lock(hash_bucket(futex)); |
113 | * queue(); |
114 | * unlock(hash_bucket(futex)); |
115 | * schedule(); |
116 | * |
117 | * This would cause the waiter on CPU 0 to wait forever because it |
118 | * missed the transition of the user space value from val to newval |
119 | * and the waker did not find the waiter in the hash bucket queue. |
120 | * |
121 | * The correct serialization ensures that a waiter either observes |
122 | * the changed user space value before blocking or is woken by a |
123 | * concurrent waker: |
124 | * |
125 | * CPU 0 CPU 1 |
126 | * val = *futex; |
127 | * sys_futex(WAIT, futex, val); |
128 | * futex_wait(futex, val); |
129 | * |
130 | * waiters++; (a) |
131 | * smp_mb(); (A) <-- paired with -. |
132 | * | |
133 | * lock(hash_bucket(futex)); | |
134 | * | |
135 | * uval = *futex; | |
136 | * | *futex = newval; |
137 | * | sys_futex(WAKE, futex); |
138 | * | futex_wake(futex); |
139 | * | |
140 | * `--------> smp_mb(); (B) |
141 | * if (uval == val) |
142 | * queue(); |
143 | * unlock(hash_bucket(futex)); |
144 | * schedule(); if (waiters) |
145 | * lock(hash_bucket(futex)); |
146 | * else wake_waiters(futex); |
147 | * waiters--; (b) unlock(hash_bucket(futex)); |
148 | * |
149 | * Where (A) orders the waiters increment and the futex value read through |
150 | * atomic operations (see hb_waiters_inc) and where (B) orders the write |
151 | * to futex and the waiters read -- this is done by the barriers for both |
152 | * shared and private futexes in get_futex_key_refs(). |
153 | * |
154 | * This yields the following case (where X:=waiters, Y:=futex): |
155 | * |
156 | * X = Y = 0 |
157 | * |
158 | * w[X]=1 w[Y]=1 |
159 | * MB MB |
160 | * r[Y]=y r[X]=x |
161 | * |
162 | * Which guarantees that x==0 && y==0 is impossible; which translates back into |
163 | * the guarantee that we cannot both miss the futex variable change and the |
164 | * enqueue. |
165 | * |
166 | * Note that a new waiter is accounted for in (a) even when it is possible that |
167 | * the wait call can return error, in which case we backtrack from it in (b). |
168 | * Refer to the comment in queue_lock(). |
169 | * |
170 | * Similarly, in order to account for waiters being requeued on another |
171 | * address we always increment the waiters for the destination bucket before |
172 | * acquiring the lock. It then decrements them again after releasing it - |
173 | * the code that actually moves the futex(es) between hash buckets (requeue_futex) |
174 | * will do the additional required waiter count housekeeping. This is done for |
175 | * double_lock_hb() and double_unlock_hb(), respectively. |
176 | */ |
177 | |
178 | #ifdef CONFIG_HAVE_FUTEX_CMPXCHG |
179 | #define futex_cmpxchg_enabled 1 |
180 | #else |
181 | static int __read_mostly futex_cmpxchg_enabled; |
182 | #endif |
183 | |
184 | /* |
185 | * Futex flags used to encode options to functions and preserve them across |
186 | * restarts. |
187 | */ |
188 | #ifdef CONFIG_MMU |
189 | # define FLAGS_SHARED 0x01 |
190 | #else |
191 | /* |
192 | * NOMMU does not have per process address space. Let the compiler optimize |
193 | * code away. |
194 | */ |
195 | # define FLAGS_SHARED 0x00 |
196 | #endif |
197 | #define FLAGS_CLOCKRT 0x02 |
198 | #define FLAGS_HAS_TIMEOUT 0x04 |
199 | |
200 | /* |
201 | * Priority Inheritance state: |
202 | */ |
203 | struct futex_pi_state { |
204 | /* |
205 | * list of 'owned' pi_state instances - these have to be |
206 | * cleaned up in do_exit() if the task exits prematurely: |
207 | */ |
208 | struct list_head list; |
209 | |
210 | /* |
211 | * The PI object: |
212 | */ |
213 | struct rt_mutex pi_mutex; |
214 | |
215 | struct task_struct *owner; |
216 | refcount_t refcount; |
217 | |
218 | union futex_key key; |
219 | } __randomize_layout; |
220 | |
221 | /** |
222 | * struct futex_q - The hashed futex queue entry, one per waiting task |
223 | * @list: priority-sorted list of tasks waiting on this futex |
224 | * @task: the task waiting on the futex |
225 | * @lock_ptr: the hash bucket lock |
226 | * @key: the key the futex is hashed on |
227 | * @pi_state: optional priority inheritance state |
228 | * @rt_waiter: rt_waiter storage for use with requeue_pi |
229 | * @requeue_pi_key: the requeue_pi target futex key |
230 | * @bitset: bitset for the optional bitmasked wakeup |
231 | * |
232 | * We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so |
233 | * we can wake only the relevant ones (hashed queues may be shared). |
234 | * |
235 | * A futex_q has a woken state, just like tasks have TASK_RUNNING. |
236 | * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0. |
237 | * The order of wakeup is always to make the first condition true, then |
238 | * the second. |
239 | * |
240 | * PI futexes are typically woken before they are removed from the hash list via |
241 | * the rt_mutex code. See unqueue_me_pi(). |
242 | */ |
243 | struct futex_q { |
244 | struct plist_node list; |
245 | |
246 | struct task_struct *task; |
247 | spinlock_t *lock_ptr; |
248 | union futex_key key; |
249 | struct futex_pi_state *pi_state; |
250 | struct rt_mutex_waiter *rt_waiter; |
251 | union futex_key *requeue_pi_key; |
252 | u32 bitset; |
253 | } __randomize_layout; |
254 | |
255 | static const struct futex_q futex_q_init = { |
256 | /* list gets initialized in queue_me()*/ |
257 | .key = FUTEX_KEY_INIT, |
258 | .bitset = FUTEX_BITSET_MATCH_ANY |
259 | }; |
260 | |
261 | /* |
262 | * Hash buckets are shared by all the futex_keys that hash to the same |
263 | * location. Each key may have multiple futex_q structures, one for each task |
264 | * waiting on a futex. |
265 | */ |
266 | struct futex_hash_bucket { |
267 | atomic_t waiters; |
268 | spinlock_t lock; |
269 | struct plist_head chain; |
270 | } ____cacheline_aligned_in_smp; |
271 | |
272 | /* |
273 | * The base of the bucket array and its size are always used together |
274 | * (after initialization only in hash_futex()), so ensure that they |
275 | * reside in the same cacheline. |
276 | */ |
277 | static struct { |
278 | struct futex_hash_bucket *queues; |
279 | unsigned long hashsize; |
280 | } __futex_data __read_mostly __aligned(2*sizeof(long)); |
281 | #define futex_queues (__futex_data.queues) |
282 | #define futex_hashsize (__futex_data.hashsize) |
283 | |
284 | |
285 | /* |
286 | * Fault injections for futexes. |
287 | */ |
288 | #ifdef CONFIG_FAIL_FUTEX |
289 | |
290 | static struct { |
291 | struct fault_attr attr; |
292 | |
293 | bool ignore_private; |
294 | } fail_futex = { |
295 | .attr = FAULT_ATTR_INITIALIZER, |
296 | .ignore_private = false, |
297 | }; |
298 | |
299 | static int __init setup_fail_futex(char *str) |
300 | { |
301 | return setup_fault_attr(&fail_futex.attr, str); |
302 | } |
303 | __setup("fail_futex=" , setup_fail_futex); |
304 | |
305 | static bool should_fail_futex(bool fshared) |
306 | { |
307 | if (fail_futex.ignore_private && !fshared) |
308 | return false; |
309 | |
310 | return should_fail(&fail_futex.attr, 1); |
311 | } |
312 | |
313 | #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS |
314 | |
315 | static int __init fail_futex_debugfs(void) |
316 | { |
317 | umode_t mode = S_IFREG | S_IRUSR | S_IWUSR; |
318 | struct dentry *dir; |
319 | |
320 | dir = fault_create_debugfs_attr("fail_futex" , NULL, |
321 | &fail_futex.attr); |
322 | if (IS_ERR(dir)) |
323 | return PTR_ERR(dir); |
324 | |
325 | debugfs_create_bool("ignore-private" , mode, dir, |
326 | &fail_futex.ignore_private); |
327 | return 0; |
328 | } |
329 | |
330 | late_initcall(fail_futex_debugfs); |
331 | |
332 | #endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */ |
333 | |
334 | #else |
335 | static inline bool should_fail_futex(bool fshared) |
336 | { |
337 | return false; |
338 | } |
339 | #endif /* CONFIG_FAIL_FUTEX */ |
340 | |
341 | static inline void futex_get_mm(union futex_key *key) |
342 | { |
343 | mmgrab(key->private.mm); |
344 | /* |
345 | * Ensure futex_get_mm() implies a full barrier such that |
346 | * get_futex_key() implies a full barrier. This is relied upon |
347 | * as smp_mb(); (B), see the ordering comment above. |
348 | */ |
349 | smp_mb__after_atomic(); |
350 | } |
351 | |
352 | /* |
353 | * Reflects a new waiter being added to the waitqueue. |
354 | */ |
355 | static inline void hb_waiters_inc(struct futex_hash_bucket *hb) |
356 | { |
357 | #ifdef CONFIG_SMP |
358 | atomic_inc(&hb->waiters); |
359 | /* |
360 | * Full barrier (A), see the ordering comment above. |
361 | */ |
362 | smp_mb__after_atomic(); |
363 | #endif |
364 | } |
365 | |
366 | /* |
367 | * Reflects a waiter being removed from the waitqueue by wakeup |
368 | * paths. |
369 | */ |
370 | static inline void hb_waiters_dec(struct futex_hash_bucket *hb) |
371 | { |
372 | #ifdef CONFIG_SMP |
373 | atomic_dec(&hb->waiters); |
374 | #endif |
375 | } |
376 | |
377 | static inline int hb_waiters_pending(struct futex_hash_bucket *hb) |
378 | { |
379 | #ifdef CONFIG_SMP |
380 | return atomic_read(&hb->waiters); |
381 | #else |
382 | return 1; |
383 | #endif |
384 | } |
385 | |
386 | /** |
387 | * hash_futex - Return the hash bucket in the global hash |
388 | * @key: Pointer to the futex key for which the hash is calculated |
389 | * |
390 | * We hash on the keys returned from get_futex_key (see below) and return the |
391 | * corresponding hash bucket in the global hash. |
392 | */ |
393 | static struct futex_hash_bucket *hash_futex(union futex_key *key) |
394 | { |
395 | u32 hash = jhash2((u32*)&key->both.word, |
396 | (sizeof(key->both.word)+sizeof(key->both.ptr))/4, |
397 | key->both.offset); |
398 | return &futex_queues[hash & (futex_hashsize - 1)]; |
399 | } |
400 | |
401 | |
402 | /** |
403 | * match_futex - Check whether two futex keys are equal |
404 | * @key1: Pointer to key1 |
405 | * @key2: Pointer to key2 |
406 | * |
407 | * Return 1 if two futex_keys are equal, 0 otherwise. |
408 | */ |
409 | static inline int match_futex(union futex_key *key1, union futex_key *key2) |
410 | { |
411 | return (key1 && key2 |
412 | && key1->both.word == key2->both.word |
413 | && key1->both.ptr == key2->both.ptr |
414 | && key1->both.offset == key2->both.offset); |
415 | } |
416 | |
417 | /* |
418 | * Take a reference to the resource addressed by a key. |
419 | * Can be called while holding spinlocks. |
420 | * |
421 | */ |
422 | static void get_futex_key_refs(union futex_key *key) |
423 | { |
424 | if (!key->both.ptr) |
425 | return; |
426 | |
427 | /* |
428 | * On MMU less systems futexes are always "private" as there is no per |
429 | * process address space. We need the smp wmb nevertheless - yes, |
430 | * arch/blackfin has MMU less SMP ... |
431 | */ |
432 | if (!IS_ENABLED(CONFIG_MMU)) { |
433 | smp_mb(); /* explicit smp_mb(); (B) */ |
434 | return; |
435 | } |
436 | |
437 | switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) { |
438 | case FUT_OFF_INODE: |
439 | ihold(key->shared.inode); /* implies smp_mb(); (B) */ |
440 | break; |
441 | case FUT_OFF_MMSHARED: |
442 | futex_get_mm(key); /* implies smp_mb(); (B) */ |
443 | break; |
444 | default: |
445 | /* |
446 | * Private futexes do not hold reference on an inode or |
447 | * mm, therefore the only purpose of calling get_futex_key_refs |
448 | * is because we need the barrier for the lockless waiter check. |
449 | */ |
450 | smp_mb(); /* explicit smp_mb(); (B) */ |
451 | } |
452 | } |
453 | |
454 | /* |
455 | * Drop a reference to the resource addressed by a key. |
456 | * The hash bucket spinlock must not be held. This is |
457 | * a no-op for private futexes, see comment in the get |
458 | * counterpart. |
459 | */ |
460 | static void drop_futex_key_refs(union futex_key *key) |
461 | { |
462 | if (!key->both.ptr) { |
463 | /* If we're here then we tried to put a key we failed to get */ |
464 | WARN_ON_ONCE(1); |
465 | return; |
466 | } |
467 | |
468 | if (!IS_ENABLED(CONFIG_MMU)) |
469 | return; |
470 | |
471 | switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) { |
472 | case FUT_OFF_INODE: |
473 | iput(key->shared.inode); |
474 | break; |
475 | case FUT_OFF_MMSHARED: |
476 | mmdrop(key->private.mm); |
477 | break; |
478 | } |
479 | } |
480 | |
481 | enum futex_access { |
482 | FUTEX_READ, |
483 | FUTEX_WRITE |
484 | }; |
485 | |
486 | /** |
487 | * get_futex_key() - Get parameters which are the keys for a futex |
488 | * @uaddr: virtual address of the futex |
489 | * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED |
490 | * @key: address where result is stored. |
491 | * @rw: mapping needs to be read/write (values: FUTEX_READ, |
492 | * FUTEX_WRITE) |
493 | * |
494 | * Return: a negative error code or 0 |
495 | * |
496 | * The key words are stored in @key on success. |
497 | * |
498 | * For shared mappings, it's (page->index, file_inode(vma->vm_file), |
499 | * offset_within_page). For private mappings, it's (uaddr, current->mm). |
500 | * We can usually work out the index without swapping in the page. |
501 | * |
502 | * lock_page() might sleep, the caller should not hold a spinlock. |
503 | */ |
504 | static int |
505 | get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, enum futex_access rw) |
506 | { |
507 | unsigned long address = (unsigned long)uaddr; |
508 | struct mm_struct *mm = current->mm; |
509 | struct page *page, *tail; |
510 | struct address_space *mapping; |
511 | int err, ro = 0; |
512 | |
513 | /* |
514 | * The futex address must be "naturally" aligned. |
515 | */ |
516 | key->both.offset = address % PAGE_SIZE; |
517 | if (unlikely((address % sizeof(u32)) != 0)) |
518 | return -EINVAL; |
519 | address -= key->both.offset; |
520 | |
521 | if (unlikely(!access_ok(uaddr, sizeof(u32)))) |
522 | return -EFAULT; |
523 | |
524 | if (unlikely(should_fail_futex(fshared))) |
525 | return -EFAULT; |
526 | |
527 | /* |
528 | * PROCESS_PRIVATE futexes are fast. |
529 | * As the mm cannot disappear under us and the 'key' only needs |
530 | * virtual address, we dont even have to find the underlying vma. |
531 | * Note : We do have to check 'uaddr' is a valid user address, |
532 | * but access_ok() should be faster than find_vma() |
533 | */ |
534 | if (!fshared) { |
535 | key->private.mm = mm; |
536 | key->private.address = address; |
537 | get_futex_key_refs(key); /* implies smp_mb(); (B) */ |
538 | return 0; |
539 | } |
540 | |
541 | again: |
542 | /* Ignore any VERIFY_READ mapping (futex common case) */ |
543 | if (unlikely(should_fail_futex(fshared))) |
544 | return -EFAULT; |
545 | |
546 | err = get_user_pages_fast(address, 1, 1, &page); |
547 | /* |
548 | * If write access is not required (eg. FUTEX_WAIT), try |
549 | * and get read-only access. |
550 | */ |
551 | if (err == -EFAULT && rw == FUTEX_READ) { |
552 | err = get_user_pages_fast(address, 1, 0, &page); |
553 | ro = 1; |
554 | } |
555 | if (err < 0) |
556 | return err; |
557 | else |
558 | err = 0; |
559 | |
560 | /* |
561 | * The treatment of mapping from this point on is critical. The page |
562 | * lock protects many things but in this context the page lock |
563 | * stabilizes mapping, prevents inode freeing in the shared |
564 | * file-backed region case and guards against movement to swap cache. |
565 | * |
566 | * Strictly speaking the page lock is not needed in all cases being |
567 | * considered here and page lock forces unnecessarily serialization |
568 | * From this point on, mapping will be re-verified if necessary and |
569 | * page lock will be acquired only if it is unavoidable |
570 | * |
571 | * Mapping checks require the head page for any compound page so the |
572 | * head page and mapping is looked up now. For anonymous pages, it |
573 | * does not matter if the page splits in the future as the key is |
574 | * based on the address. For filesystem-backed pages, the tail is |
575 | * required as the index of the page determines the key. For |
576 | * base pages, there is no tail page and tail == page. |
577 | */ |
578 | tail = page; |
579 | page = compound_head(page); |
580 | mapping = READ_ONCE(page->mapping); |
581 | |
582 | /* |
583 | * If page->mapping is NULL, then it cannot be a PageAnon |
584 | * page; but it might be the ZERO_PAGE or in the gate area or |
585 | * in a special mapping (all cases which we are happy to fail); |
586 | * or it may have been a good file page when get_user_pages_fast |
587 | * found it, but truncated or holepunched or subjected to |
588 | * invalidate_complete_page2 before we got the page lock (also |
589 | * cases which we are happy to fail). And we hold a reference, |
590 | * so refcount care in invalidate_complete_page's remove_mapping |
591 | * prevents drop_caches from setting mapping to NULL beneath us. |
592 | * |
593 | * The case we do have to guard against is when memory pressure made |
594 | * shmem_writepage move it from filecache to swapcache beneath us: |
595 | * an unlikely race, but we do need to retry for page->mapping. |
596 | */ |
597 | if (unlikely(!mapping)) { |
598 | int shmem_swizzled; |
599 | |
600 | /* |
601 | * Page lock is required to identify which special case above |
602 | * applies. If this is really a shmem page then the page lock |
603 | * will prevent unexpected transitions. |
604 | */ |
605 | lock_page(page); |
606 | shmem_swizzled = PageSwapCache(page) || page->mapping; |
607 | unlock_page(page); |
608 | put_page(page); |
609 | |
610 | if (shmem_swizzled) |
611 | goto again; |
612 | |
613 | return -EFAULT; |
614 | } |
615 | |
616 | /* |
617 | * Private mappings are handled in a simple way. |
618 | * |
619 | * If the futex key is stored on an anonymous page, then the associated |
620 | * object is the mm which is implicitly pinned by the calling process. |
621 | * |
622 | * NOTE: When userspace waits on a MAP_SHARED mapping, even if |
623 | * it's a read-only handle, it's expected that futexes attach to |
624 | * the object not the particular process. |
625 | */ |
626 | if (PageAnon(page)) { |
627 | /* |
628 | * A RO anonymous page will never change and thus doesn't make |
629 | * sense for futex operations. |
630 | */ |
631 | if (unlikely(should_fail_futex(fshared)) || ro) { |
632 | err = -EFAULT; |
633 | goto out; |
634 | } |
635 | |
636 | key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */ |
637 | key->private.mm = mm; |
638 | key->private.address = address; |
639 | |
640 | get_futex_key_refs(key); /* implies smp_mb(); (B) */ |
641 | |
642 | } else { |
643 | struct inode *inode; |
644 | |
645 | /* |
646 | * The associated futex object in this case is the inode and |
647 | * the page->mapping must be traversed. Ordinarily this should |
648 | * be stabilised under page lock but it's not strictly |
649 | * necessary in this case as we just want to pin the inode, not |
650 | * update the radix tree or anything like that. |
651 | * |
652 | * The RCU read lock is taken as the inode is finally freed |
653 | * under RCU. If the mapping still matches expectations then the |
654 | * mapping->host can be safely accessed as being a valid inode. |
655 | */ |
656 | rcu_read_lock(); |
657 | |
658 | if (READ_ONCE(page->mapping) != mapping) { |
659 | rcu_read_unlock(); |
660 | put_page(page); |
661 | |
662 | goto again; |
663 | } |
664 | |
665 | inode = READ_ONCE(mapping->host); |
666 | if (!inode) { |
667 | rcu_read_unlock(); |
668 | put_page(page); |
669 | |
670 | goto again; |
671 | } |
672 | |
673 | /* |
674 | * Take a reference unless it is about to be freed. Previously |
675 | * this reference was taken by ihold under the page lock |
676 | * pinning the inode in place so i_lock was unnecessary. The |
677 | * only way for this check to fail is if the inode was |
678 | * truncated in parallel which is almost certainly an |
679 | * application bug. In such a case, just retry. |
680 | * |
681 | * We are not calling into get_futex_key_refs() in file-backed |
682 | * cases, therefore a successful atomic_inc return below will |
683 | * guarantee that get_futex_key() will still imply smp_mb(); (B). |
684 | */ |
685 | if (!atomic_inc_not_zero(&inode->i_count)) { |
686 | rcu_read_unlock(); |
687 | put_page(page); |
688 | |
689 | goto again; |
690 | } |
691 | |
692 | /* Should be impossible but lets be paranoid for now */ |
693 | if (WARN_ON_ONCE(inode->i_mapping != mapping)) { |
694 | err = -EFAULT; |
695 | rcu_read_unlock(); |
696 | iput(inode); |
697 | |
698 | goto out; |
699 | } |
700 | |
701 | key->both.offset |= FUT_OFF_INODE; /* inode-based key */ |
702 | key->shared.inode = inode; |
703 | key->shared.pgoff = basepage_index(tail); |
704 | rcu_read_unlock(); |
705 | } |
706 | |
707 | out: |
708 | put_page(page); |
709 | return err; |
710 | } |
711 | |
712 | static inline void put_futex_key(union futex_key *key) |
713 | { |
714 | drop_futex_key_refs(key); |
715 | } |
716 | |
717 | /** |
718 | * fault_in_user_writeable() - Fault in user address and verify RW access |
719 | * @uaddr: pointer to faulting user space address |
720 | * |
721 | * Slow path to fixup the fault we just took in the atomic write |
722 | * access to @uaddr. |
723 | * |
724 | * We have no generic implementation of a non-destructive write to the |
725 | * user address. We know that we faulted in the atomic pagefault |
726 | * disabled section so we can as well avoid the #PF overhead by |
727 | * calling get_user_pages() right away. |
728 | */ |
729 | static int fault_in_user_writeable(u32 __user *uaddr) |
730 | { |
731 | struct mm_struct *mm = current->mm; |
732 | int ret; |
733 | |
734 | down_read(&mm->mmap_sem); |
735 | ret = fixup_user_fault(current, mm, (unsigned long)uaddr, |
736 | FAULT_FLAG_WRITE, NULL); |
737 | up_read(&mm->mmap_sem); |
738 | |
739 | return ret < 0 ? ret : 0; |
740 | } |
741 | |
742 | /** |
743 | * futex_top_waiter() - Return the highest priority waiter on a futex |
744 | * @hb: the hash bucket the futex_q's reside in |
745 | * @key: the futex key (to distinguish it from other futex futex_q's) |
746 | * |
747 | * Must be called with the hb lock held. |
748 | */ |
749 | static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb, |
750 | union futex_key *key) |
751 | { |
752 | struct futex_q *this; |
753 | |
754 | plist_for_each_entry(this, &hb->chain, list) { |
755 | if (match_futex(&this->key, key)) |
756 | return this; |
757 | } |
758 | return NULL; |
759 | } |
760 | |
761 | static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr, |
762 | u32 uval, u32 newval) |
763 | { |
764 | int ret; |
765 | |
766 | pagefault_disable(); |
767 | ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval); |
768 | pagefault_enable(); |
769 | |
770 | return ret; |
771 | } |
772 | |
773 | static int get_futex_value_locked(u32 *dest, u32 __user *from) |
774 | { |
775 | int ret; |
776 | |
777 | pagefault_disable(); |
778 | ret = __get_user(*dest, from); |
779 | pagefault_enable(); |
780 | |
781 | return ret ? -EFAULT : 0; |
782 | } |
783 | |
784 | |
785 | /* |
786 | * PI code: |
787 | */ |
788 | static int refill_pi_state_cache(void) |
789 | { |
790 | struct futex_pi_state *pi_state; |
791 | |
792 | if (likely(current->pi_state_cache)) |
793 | return 0; |
794 | |
795 | pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL); |
796 | |
797 | if (!pi_state) |
798 | return -ENOMEM; |
799 | |
800 | INIT_LIST_HEAD(&pi_state->list); |
801 | /* pi_mutex gets initialized later */ |
802 | pi_state->owner = NULL; |
803 | refcount_set(&pi_state->refcount, 1); |
804 | pi_state->key = FUTEX_KEY_INIT; |
805 | |
806 | current->pi_state_cache = pi_state; |
807 | |
808 | return 0; |
809 | } |
810 | |
811 | static struct futex_pi_state *alloc_pi_state(void) |
812 | { |
813 | struct futex_pi_state *pi_state = current->pi_state_cache; |
814 | |
815 | WARN_ON(!pi_state); |
816 | current->pi_state_cache = NULL; |
817 | |
818 | return pi_state; |
819 | } |
820 | |
821 | static void get_pi_state(struct futex_pi_state *pi_state) |
822 | { |
823 | WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount)); |
824 | } |
825 | |
826 | /* |
827 | * Drops a reference to the pi_state object and frees or caches it |
828 | * when the last reference is gone. |
829 | */ |
830 | static void put_pi_state(struct futex_pi_state *pi_state) |
831 | { |
832 | if (!pi_state) |
833 | return; |
834 | |
835 | if (!refcount_dec_and_test(&pi_state->refcount)) |
836 | return; |
837 | |
838 | /* |
839 | * If pi_state->owner is NULL, the owner is most probably dying |
840 | * and has cleaned up the pi_state already |
841 | */ |
842 | if (pi_state->owner) { |
843 | struct task_struct *owner; |
844 | |
845 | raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); |
846 | owner = pi_state->owner; |
847 | if (owner) { |
848 | raw_spin_lock(&owner->pi_lock); |
849 | list_del_init(&pi_state->list); |
850 | raw_spin_unlock(&owner->pi_lock); |
851 | } |
852 | rt_mutex_proxy_unlock(&pi_state->pi_mutex, owner); |
853 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); |
854 | } |
855 | |
856 | if (current->pi_state_cache) { |
857 | kfree(pi_state); |
858 | } else { |
859 | /* |
860 | * pi_state->list is already empty. |
861 | * clear pi_state->owner. |
862 | * refcount is at 0 - put it back to 1. |
863 | */ |
864 | pi_state->owner = NULL; |
865 | refcount_set(&pi_state->refcount, 1); |
866 | current->pi_state_cache = pi_state; |
867 | } |
868 | } |
869 | |
870 | #ifdef CONFIG_FUTEX_PI |
871 | |
872 | /* |
873 | * This task is holding PI mutexes at exit time => bad. |
874 | * Kernel cleans up PI-state, but userspace is likely hosed. |
875 | * (Robust-futex cleanup is separate and might save the day for userspace.) |
876 | */ |
877 | void exit_pi_state_list(struct task_struct *curr) |
878 | { |
879 | struct list_head *next, *head = &curr->pi_state_list; |
880 | struct futex_pi_state *pi_state; |
881 | struct futex_hash_bucket *hb; |
882 | union futex_key key = FUTEX_KEY_INIT; |
883 | |
884 | if (!futex_cmpxchg_enabled) |
885 | return; |
886 | /* |
887 | * We are a ZOMBIE and nobody can enqueue itself on |
888 | * pi_state_list anymore, but we have to be careful |
889 | * versus waiters unqueueing themselves: |
890 | */ |
891 | raw_spin_lock_irq(&curr->pi_lock); |
892 | while (!list_empty(head)) { |
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 | |
898 | /* |
899 | * We can race against put_pi_state() removing itself from the |
900 | * list (a waiter going away). put_pi_state() will first |
901 | * decrement the reference count and then modify the list, so |
902 | * its possible to see the list entry but fail this reference |
903 | * acquire. |
904 | * |
905 | * In that case; drop the locks to let put_pi_state() make |
906 | * progress and retry the loop. |
907 | */ |
908 | if (!refcount_inc_not_zero(&pi_state->refcount)) { |
909 | raw_spin_unlock_irq(&curr->pi_lock); |
910 | cpu_relax(); |
911 | raw_spin_lock_irq(&curr->pi_lock); |
912 | continue; |
913 | } |
914 | raw_spin_unlock_irq(&curr->pi_lock); |
915 | |
916 | spin_lock(&hb->lock); |
917 | raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); |
918 | raw_spin_lock(&curr->pi_lock); |
919 | /* |
920 | * We dropped the pi-lock, so re-check whether this |
921 | * task still owns the PI-state: |
922 | */ |
923 | if (head->next != next) { |
924 | /* retain curr->pi_lock for the loop invariant */ |
925 | raw_spin_unlock(&pi_state->pi_mutex.wait_lock); |
926 | spin_unlock(&hb->lock); |
927 | put_pi_state(pi_state); |
928 | continue; |
929 | } |
930 | |
931 | WARN_ON(pi_state->owner != curr); |
932 | WARN_ON(list_empty(&pi_state->list)); |
933 | list_del_init(&pi_state->list); |
934 | pi_state->owner = NULL; |
935 | |
936 | raw_spin_unlock(&curr->pi_lock); |
937 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); |
938 | spin_unlock(&hb->lock); |
939 | |
940 | rt_mutex_futex_unlock(&pi_state->pi_mutex); |
941 | put_pi_state(pi_state); |
942 | |
943 | raw_spin_lock_irq(&curr->pi_lock); |
944 | } |
945 | raw_spin_unlock_irq(&curr->pi_lock); |
946 | } |
947 | |
948 | #endif |
949 | |
950 | /* |
951 | * We need to check the following states: |
952 | * |
953 | * Waiter | pi_state | pi->owner | uTID | uODIED | ? |
954 | * |
955 | * [1] NULL | --- | --- | 0 | 0/1 | Valid |
956 | * [2] NULL | --- | --- | >0 | 0/1 | Valid |
957 | * |
958 | * [3] Found | NULL | -- | Any | 0/1 | Invalid |
959 | * |
960 | * [4] Found | Found | NULL | 0 | 1 | Valid |
961 | * [5] Found | Found | NULL | >0 | 1 | Invalid |
962 | * |
963 | * [6] Found | Found | task | 0 | 1 | Valid |
964 | * |
965 | * [7] Found | Found | NULL | Any | 0 | Invalid |
966 | * |
967 | * [8] Found | Found | task | ==taskTID | 0/1 | Valid |
968 | * [9] Found | Found | task | 0 | 0 | Invalid |
969 | * [10] Found | Found | task | !=taskTID | 0/1 | Invalid |
970 | * |
971 | * [1] Indicates that the kernel can acquire the futex atomically. We |
972 | * came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit. |
973 | * |
974 | * [2] Valid, if TID does not belong to a kernel thread. If no matching |
975 | * thread is found then it indicates that the owner TID has died. |
976 | * |
977 | * [3] Invalid. The waiter is queued on a non PI futex |
978 | * |
979 | * [4] Valid state after exit_robust_list(), which sets the user space |
980 | * value to FUTEX_WAITERS | FUTEX_OWNER_DIED. |
981 | * |
982 | * [5] The user space value got manipulated between exit_robust_list() |
983 | * and exit_pi_state_list() |
984 | * |
985 | * [6] Valid state after exit_pi_state_list() which sets the new owner in |
986 | * the pi_state but cannot access the user space value. |
987 | * |
988 | * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set. |
989 | * |
990 | * [8] Owner and user space value match |
991 | * |
992 | * [9] There is no transient state which sets the user space TID to 0 |
993 | * except exit_robust_list(), but this is indicated by the |
994 | * FUTEX_OWNER_DIED bit. See [4] |
995 | * |
996 | * [10] There is no transient state which leaves owner and user space |
997 | * TID out of sync. |
998 | * |
999 | * |
1000 | * Serialization and lifetime rules: |
1001 | * |
1002 | * hb->lock: |
1003 | * |
1004 | * hb -> futex_q, relation |
1005 | * futex_q -> pi_state, relation |
1006 | * |
1007 | * (cannot be raw because hb can contain arbitrary amount |
1008 | * of futex_q's) |
1009 | * |
1010 | * pi_mutex->wait_lock: |
1011 | * |
1012 | * {uval, pi_state} |
1013 | * |
1014 | * (and pi_mutex 'obviously') |
1015 | * |
1016 | * p->pi_lock: |
1017 | * |
1018 | * p->pi_state_list -> pi_state->list, relation |
1019 | * |
1020 | * pi_state->refcount: |
1021 | * |
1022 | * pi_state lifetime |
1023 | * |
1024 | * |
1025 | * Lock order: |
1026 | * |
1027 | * hb->lock |
1028 | * pi_mutex->wait_lock |
1029 | * p->pi_lock |
1030 | * |
1031 | */ |
1032 | |
1033 | /* |
1034 | * Validate that the existing waiter has a pi_state and sanity check |
1035 | * the pi_state against the user space value. If correct, attach to |
1036 | * it. |
1037 | */ |
1038 | static int attach_to_pi_state(u32 __user *uaddr, u32 uval, |
1039 | struct futex_pi_state *pi_state, |
1040 | struct futex_pi_state **ps) |
1041 | { |
1042 | pid_t pid = uval & FUTEX_TID_MASK; |
1043 | u32 uval2; |
1044 | int ret; |
1045 | |
1046 | /* |
1047 | * Userspace might have messed up non-PI and PI futexes [3] |
1048 | */ |
1049 | if (unlikely(!pi_state)) |
1050 | return -EINVAL; |
1051 | |
1052 | /* |
1053 | * We get here with hb->lock held, and having found a |
1054 | * futex_top_waiter(). This means that futex_lock_pi() of said futex_q |
1055 | * has dropped the hb->lock in between queue_me() and unqueue_me_pi(), |
1056 | * which in turn means that futex_lock_pi() still has a reference on |
1057 | * our pi_state. |
1058 | * |
1059 | * The waiter holding a reference on @pi_state also protects against |
1060 | * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi() |
1061 | * and futex_wait_requeue_pi() as it cannot go to 0 and consequently |
1062 | * free pi_state before we can take a reference ourselves. |
1063 | */ |
1064 | WARN_ON(!refcount_read(&pi_state->refcount)); |
1065 | |
1066 | /* |
1067 | * Now that we have a pi_state, we can acquire wait_lock |
1068 | * and do the state validation. |
1069 | */ |
1070 | raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); |
1071 | |
1072 | /* |
1073 | * Since {uval, pi_state} is serialized by wait_lock, and our current |
1074 | * uval was read without holding it, it can have changed. Verify it |
1075 | * still is what we expect it to be, otherwise retry the entire |
1076 | * operation. |
1077 | */ |
1078 | if (get_futex_value_locked(&uval2, uaddr)) |
1079 | goto out_efault; |
1080 | |
1081 | if (uval != uval2) |
1082 | goto out_eagain; |
1083 | |
1084 | /* |
1085 | * Handle the owner died case: |
1086 | */ |
1087 | if (uval & FUTEX_OWNER_DIED) { |
1088 | /* |
1089 | * exit_pi_state_list sets owner to NULL and wakes the |
1090 | * topmost waiter. The task which acquires the |
1091 | * pi_state->rt_mutex will fixup owner. |
1092 | */ |
1093 | if (!pi_state->owner) { |
1094 | /* |
1095 | * No pi state owner, but the user space TID |
1096 | * is not 0. Inconsistent state. [5] |
1097 | */ |
1098 | if (pid) |
1099 | goto out_einval; |
1100 | /* |
1101 | * Take a ref on the state and return success. [4] |
1102 | */ |
1103 | goto out_attach; |
1104 | } |
1105 | |
1106 | /* |
1107 | * If TID is 0, then either the dying owner has not |
1108 | * yet executed exit_pi_state_list() or some waiter |
1109 | * acquired the rtmutex in the pi state, but did not |
1110 | * yet fixup the TID in user space. |
1111 | * |
1112 | * Take a ref on the state and return success. [6] |
1113 | */ |
1114 | if (!pid) |
1115 | goto out_attach; |
1116 | } else { |
1117 | /* |
1118 | * If the owner died bit is not set, then the pi_state |
1119 | * must have an owner. [7] |
1120 | */ |
1121 | if (!pi_state->owner) |
1122 | goto out_einval; |
1123 | } |
1124 | |
1125 | /* |
1126 | * Bail out if user space manipulated the futex value. If pi |
1127 | * state exists then the owner TID must be the same as the |
1128 | * user space TID. [9/10] |
1129 | */ |
1130 | if (pid != task_pid_vnr(pi_state->owner)) |
1131 | goto out_einval; |
1132 | |
1133 | out_attach: |
1134 | get_pi_state(pi_state); |
1135 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); |
1136 | *ps = pi_state; |
1137 | return 0; |
1138 | |
1139 | out_einval: |
1140 | ret = -EINVAL; |
1141 | goto out_error; |
1142 | |
1143 | out_eagain: |
1144 | ret = -EAGAIN; |
1145 | goto out_error; |
1146 | |
1147 | out_efault: |
1148 | ret = -EFAULT; |
1149 | goto out_error; |
1150 | |
1151 | out_error: |
1152 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); |
1153 | return ret; |
1154 | } |
1155 | |
1156 | static int handle_exit_race(u32 __user *uaddr, u32 uval, |
1157 | struct task_struct *tsk) |
1158 | { |
1159 | u32 uval2; |
1160 | |
1161 | /* |
1162 | * If PF_EXITPIDONE is not yet set, then try again. |
1163 | */ |
1164 | if (tsk && !(tsk->flags & PF_EXITPIDONE)) |
1165 | return -EAGAIN; |
1166 | |
1167 | /* |
1168 | * Reread the user space value to handle the following situation: |
1169 | * |
1170 | * CPU0 CPU1 |
1171 | * |
1172 | * sys_exit() sys_futex() |
1173 | * do_exit() futex_lock_pi() |
1174 | * futex_lock_pi_atomic() |
1175 | * exit_signals(tsk) No waiters: |
1176 | * tsk->flags |= PF_EXITING; *uaddr == 0x00000PID |
1177 | * mm_release(tsk) Set waiter bit |
1178 | * exit_robust_list(tsk) { *uaddr = 0x80000PID; |
1179 | * Set owner died attach_to_pi_owner() { |
1180 | * *uaddr = 0xC0000000; tsk = get_task(PID); |
1181 | * } if (!tsk->flags & PF_EXITING) { |
1182 | * ... attach(); |
1183 | * tsk->flags |= PF_EXITPIDONE; } else { |
1184 | * if (!(tsk->flags & PF_EXITPIDONE)) |
1185 | * return -EAGAIN; |
1186 | * return -ESRCH; <--- FAIL |
1187 | * } |
1188 | * |
1189 | * Returning ESRCH unconditionally is wrong here because the |
1190 | * user space value has been changed by the exiting task. |
1191 | * |
1192 | * The same logic applies to the case where the exiting task is |
1193 | * already gone. |
1194 | */ |
1195 | if (get_futex_value_locked(&uval2, uaddr)) |
1196 | return -EFAULT; |
1197 | |
1198 | /* If the user space value has changed, try again. */ |
1199 | if (uval2 != uval) |
1200 | return -EAGAIN; |
1201 | |
1202 | /* |
1203 | * The exiting task did not have a robust list, the robust list was |
1204 | * corrupted or the user space value in *uaddr is simply bogus. |
1205 | * Give up and tell user space. |
1206 | */ |
1207 | return -ESRCH; |
1208 | } |
1209 | |
1210 | /* |
1211 | * Lookup the task for the TID provided from user space and attach to |
1212 | * it after doing proper sanity checks. |
1213 | */ |
1214 | static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key, |
1215 | struct futex_pi_state **ps) |
1216 | { |
1217 | pid_t pid = uval & FUTEX_TID_MASK; |
1218 | struct futex_pi_state *pi_state; |
1219 | struct task_struct *p; |
1220 | |
1221 | /* |
1222 | * We are the first waiter - try to look up the real owner and attach |
1223 | * the new pi_state to it, but bail out when TID = 0 [1] |
1224 | * |
1225 | * The !pid check is paranoid. None of the call sites should end up |
1226 | * with pid == 0, but better safe than sorry. Let the caller retry |
1227 | */ |
1228 | if (!pid) |
1229 | return -EAGAIN; |
1230 | p = find_get_task_by_vpid(pid); |
1231 | if (!p) |
1232 | return handle_exit_race(uaddr, uval, NULL); |
1233 | |
1234 | if (unlikely(p->flags & PF_KTHREAD)) { |
1235 | put_task_struct(p); |
1236 | return -EPERM; |
1237 | } |
1238 | |
1239 | /* |
1240 | * We need to look at the task state flags to figure out, |
1241 | * whether the task is exiting. To protect against the do_exit |
1242 | * change of the task flags, we do this protected by |
1243 | * p->pi_lock: |
1244 | */ |
1245 | raw_spin_lock_irq(&p->pi_lock); |
1246 | if (unlikely(p->flags & PF_EXITING)) { |
1247 | /* |
1248 | * The task is on the way out. When PF_EXITPIDONE is |
1249 | * set, we know that the task has finished the |
1250 | * cleanup: |
1251 | */ |
1252 | int ret = handle_exit_race(uaddr, uval, p); |
1253 | |
1254 | raw_spin_unlock_irq(&p->pi_lock); |
1255 | put_task_struct(p); |
1256 | return ret; |
1257 | } |
1258 | |
1259 | /* |
1260 | * No existing pi state. First waiter. [2] |
1261 | * |
1262 | * This creates pi_state, we have hb->lock held, this means nothing can |
1263 | * observe this state, wait_lock is irrelevant. |
1264 | */ |
1265 | pi_state = alloc_pi_state(); |
1266 | |
1267 | /* |
1268 | * Initialize the pi_mutex in locked state and make @p |
1269 | * the owner of it: |
1270 | */ |
1271 | rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p); |
1272 | |
1273 | /* Store the key for possible exit cleanups: */ |
1274 | pi_state->key = *key; |
1275 | |
1276 | WARN_ON(!list_empty(&pi_state->list)); |
1277 | list_add(&pi_state->list, &p->pi_state_list); |
1278 | /* |
1279 | * Assignment without holding pi_state->pi_mutex.wait_lock is safe |
1280 | * because there is no concurrency as the object is not published yet. |
1281 | */ |
1282 | pi_state->owner = p; |
1283 | raw_spin_unlock_irq(&p->pi_lock); |
1284 | |
1285 | put_task_struct(p); |
1286 | |
1287 | *ps = pi_state; |
1288 | |
1289 | return 0; |
1290 | } |
1291 | |
1292 | static int lookup_pi_state(u32 __user *uaddr, u32 uval, |
1293 | struct futex_hash_bucket *hb, |
1294 | union futex_key *key, struct futex_pi_state **ps) |
1295 | { |
1296 | struct futex_q *top_waiter = futex_top_waiter(hb, key); |
1297 | |
1298 | /* |
1299 | * If there is a waiter on that futex, validate it and |
1300 | * attach to the pi_state when the validation succeeds. |
1301 | */ |
1302 | if (top_waiter) |
1303 | return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps); |
1304 | |
1305 | /* |
1306 | * We are the first waiter - try to look up the owner based on |
1307 | * @uval and attach to it. |
1308 | */ |
1309 | return attach_to_pi_owner(uaddr, uval, key, ps); |
1310 | } |
1311 | |
1312 | static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval) |
1313 | { |
1314 | u32 uninitialized_var(curval); |
1315 | |
1316 | if (unlikely(should_fail_futex(true))) |
1317 | return -EFAULT; |
1318 | |
1319 | if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))) |
1320 | return -EFAULT; |
1321 | |
1322 | /* If user space value changed, let the caller retry */ |
1323 | return curval != uval ? -EAGAIN : 0; |
1324 | } |
1325 | |
1326 | /** |
1327 | * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex |
1328 | * @uaddr: the pi futex user address |
1329 | * @hb: the pi futex hash bucket |
1330 | * @key: the futex key associated with uaddr and hb |
1331 | * @ps: the pi_state pointer where we store the result of the |
1332 | * lookup |
1333 | * @task: the task to perform the atomic lock work for. This will |
1334 | * be "current" except in the case of requeue pi. |
1335 | * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) |
1336 | * |
1337 | * Return: |
1338 | * - 0 - ready to wait; |
1339 | * - 1 - acquired the lock; |
1340 | * - <0 - error |
1341 | * |
1342 | * The hb->lock and futex_key refs shall be held by the caller. |
1343 | */ |
1344 | static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb, |
1345 | union futex_key *key, |
1346 | struct futex_pi_state **ps, |
1347 | struct task_struct *task, int set_waiters) |
1348 | { |
1349 | u32 uval, newval, vpid = task_pid_vnr(task); |
1350 | struct futex_q *top_waiter; |
1351 | int ret; |
1352 | |
1353 | /* |
1354 | * Read the user space value first so we can validate a few |
1355 | * things before proceeding further. |
1356 | */ |
1357 | if (get_futex_value_locked(&uval, uaddr)) |
1358 | return -EFAULT; |
1359 | |
1360 | if (unlikely(should_fail_futex(true))) |
1361 | return -EFAULT; |
1362 | |
1363 | /* |
1364 | * Detect deadlocks. |
1365 | */ |
1366 | if ((unlikely((uval & FUTEX_TID_MASK) == vpid))) |
1367 | return -EDEADLK; |
1368 | |
1369 | if ((unlikely(should_fail_futex(true)))) |
1370 | return -EDEADLK; |
1371 | |
1372 | /* |
1373 | * Lookup existing state first. If it exists, try to attach to |
1374 | * its pi_state. |
1375 | */ |
1376 | top_waiter = futex_top_waiter(hb, key); |
1377 | if (top_waiter) |
1378 | return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps); |
1379 | |
1380 | /* |
1381 | * No waiter and user TID is 0. We are here because the |
1382 | * waiters or the owner died bit is set or called from |
1383 | * requeue_cmp_pi or for whatever reason something took the |
1384 | * syscall. |
1385 | */ |
1386 | if (!(uval & FUTEX_TID_MASK)) { |
1387 | /* |
1388 | * We take over the futex. No other waiters and the user space |
1389 | * TID is 0. We preserve the owner died bit. |
1390 | */ |
1391 | newval = uval & FUTEX_OWNER_DIED; |
1392 | newval |= vpid; |
1393 | |
1394 | /* The futex requeue_pi code can enforce the waiters bit */ |
1395 | if (set_waiters) |
1396 | newval |= FUTEX_WAITERS; |
1397 | |
1398 | ret = lock_pi_update_atomic(uaddr, uval, newval); |
1399 | /* If the take over worked, return 1 */ |
1400 | return ret < 0 ? ret : 1; |
1401 | } |
1402 | |
1403 | /* |
1404 | * First waiter. Set the waiters bit before attaching ourself to |
1405 | * the owner. If owner tries to unlock, it will be forced into |
1406 | * the kernel and blocked on hb->lock. |
1407 | */ |
1408 | newval = uval | FUTEX_WAITERS; |
1409 | ret = lock_pi_update_atomic(uaddr, uval, newval); |
1410 | if (ret) |
1411 | return ret; |
1412 | /* |
1413 | * If the update of the user space value succeeded, we try to |
1414 | * attach to the owner. If that fails, no harm done, we only |
1415 | * set the FUTEX_WAITERS bit in the user space variable. |
1416 | */ |
1417 | return attach_to_pi_owner(uaddr, newval, key, ps); |
1418 | } |
1419 | |
1420 | /** |
1421 | * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket |
1422 | * @q: The futex_q to unqueue |
1423 | * |
1424 | * The q->lock_ptr must not be NULL and must be held by the caller. |
1425 | */ |
1426 | static void __unqueue_futex(struct futex_q *q) |
1427 | { |
1428 | struct futex_hash_bucket *hb; |
1429 | |
1430 | if (WARN_ON_SMP(!q->lock_ptr) || WARN_ON(plist_node_empty(&q->list))) |
1431 | return; |
1432 | lockdep_assert_held(q->lock_ptr); |
1433 | |
1434 | hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock); |
1435 | plist_del(&q->list, &hb->chain); |
1436 | hb_waiters_dec(hb); |
1437 | } |
1438 | |
1439 | /* |
1440 | * The hash bucket lock must be held when this is called. |
1441 | * Afterwards, the futex_q must not be accessed. Callers |
1442 | * must ensure to later call wake_up_q() for the actual |
1443 | * wakeups to occur. |
1444 | */ |
1445 | static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q) |
1446 | { |
1447 | struct task_struct *p = q->task; |
1448 | |
1449 | if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n" )) |
1450 | return; |
1451 | |
1452 | get_task_struct(p); |
1453 | __unqueue_futex(q); |
1454 | /* |
1455 | * The waiting task can free the futex_q as soon as q->lock_ptr = NULL |
1456 | * is written, without taking any locks. This is possible in the event |
1457 | * of a spurious wakeup, for example. A memory barrier is required here |
1458 | * to prevent the following store to lock_ptr from getting ahead of the |
1459 | * plist_del in __unqueue_futex(). |
1460 | */ |
1461 | smp_store_release(&q->lock_ptr, NULL); |
1462 | |
1463 | /* |
1464 | * Queue the task for later wakeup for after we've released |
1465 | * the hb->lock. wake_q_add() grabs reference to p. |
1466 | */ |
1467 | wake_q_add_safe(wake_q, p); |
1468 | } |
1469 | |
1470 | /* |
1471 | * Caller must hold a reference on @pi_state. |
1472 | */ |
1473 | static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state) |
1474 | { |
1475 | u32 uninitialized_var(curval), newval; |
1476 | struct task_struct *new_owner; |
1477 | bool postunlock = false; |
1478 | DEFINE_WAKE_Q(wake_q); |
1479 | int ret = 0; |
1480 | |
1481 | new_owner = rt_mutex_next_owner(&pi_state->pi_mutex); |
1482 | if (WARN_ON_ONCE(!new_owner)) { |
1483 | /* |
1484 | * As per the comment in futex_unlock_pi() this should not happen. |
1485 | * |
1486 | * When this happens, give up our locks and try again, giving |
1487 | * the futex_lock_pi() instance time to complete, either by |
1488 | * waiting on the rtmutex or removing itself from the futex |
1489 | * queue. |
1490 | */ |
1491 | ret = -EAGAIN; |
1492 | goto out_unlock; |
1493 | } |
1494 | |
1495 | /* |
1496 | * We pass it to the next owner. The WAITERS bit is always kept |
1497 | * enabled while there is PI state around. We cleanup the owner |
1498 | * died bit, because we are the owner. |
1499 | */ |
1500 | newval = FUTEX_WAITERS | task_pid_vnr(new_owner); |
1501 | |
1502 | if (unlikely(should_fail_futex(true))) |
1503 | ret = -EFAULT; |
1504 | |
1505 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) { |
1506 | ret = -EFAULT; |
1507 | |
1508 | } else if (curval != uval) { |
1509 | /* |
1510 | * If a unconditional UNLOCK_PI operation (user space did not |
1511 | * try the TID->0 transition) raced with a waiter setting the |
1512 | * FUTEX_WAITERS flag between get_user() and locking the hash |
1513 | * bucket lock, retry the operation. |
1514 | */ |
1515 | if ((FUTEX_TID_MASK & curval) == uval) |
1516 | ret = -EAGAIN; |
1517 | else |
1518 | ret = -EINVAL; |
1519 | } |
1520 | |
1521 | if (ret) |
1522 | goto out_unlock; |
1523 | |
1524 | /* |
1525 | * This is a point of no return; once we modify the uval there is no |
1526 | * going back and subsequent operations must not fail. |
1527 | */ |
1528 | |
1529 | raw_spin_lock(&pi_state->owner->pi_lock); |
1530 | WARN_ON(list_empty(&pi_state->list)); |
1531 | list_del_init(&pi_state->list); |
1532 | raw_spin_unlock(&pi_state->owner->pi_lock); |
1533 | |
1534 | raw_spin_lock(&new_owner->pi_lock); |
1535 | WARN_ON(!list_empty(&pi_state->list)); |
1536 | list_add(&pi_state->list, &new_owner->pi_state_list); |
1537 | pi_state->owner = new_owner; |
1538 | raw_spin_unlock(&new_owner->pi_lock); |
1539 | |
1540 | postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q); |
1541 | |
1542 | out_unlock: |
1543 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); |
1544 | |
1545 | if (postunlock) |
1546 | rt_mutex_postunlock(&wake_q); |
1547 | |
1548 | return ret; |
1549 | } |
1550 | |
1551 | /* |
1552 | * Express the locking dependencies for lockdep: |
1553 | */ |
1554 | static inline void |
1555 | double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) |
1556 | { |
1557 | if (hb1 <= hb2) { |
1558 | spin_lock(&hb1->lock); |
1559 | if (hb1 < hb2) |
1560 | spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING); |
1561 | } else { /* hb1 > hb2 */ |
1562 | spin_lock(&hb2->lock); |
1563 | spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING); |
1564 | } |
1565 | } |
1566 | |
1567 | static inline void |
1568 | double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) |
1569 | { |
1570 | spin_unlock(&hb1->lock); |
1571 | if (hb1 != hb2) |
1572 | spin_unlock(&hb2->lock); |
1573 | } |
1574 | |
1575 | /* |
1576 | * Wake up waiters matching bitset queued on this futex (uaddr). |
1577 | */ |
1578 | static int |
1579 | futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset) |
1580 | { |
1581 | struct futex_hash_bucket *hb; |
1582 | struct futex_q *this, *next; |
1583 | union futex_key key = FUTEX_KEY_INIT; |
1584 | int ret; |
1585 | DEFINE_WAKE_Q(wake_q); |
1586 | |
1587 | if (!bitset) |
1588 | return -EINVAL; |
1589 | |
1590 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_READ); |
1591 | if (unlikely(ret != 0)) |
1592 | goto out; |
1593 | |
1594 | hb = hash_futex(&key); |
1595 | |
1596 | /* Make sure we really have tasks to wakeup */ |
1597 | if (!hb_waiters_pending(hb)) |
1598 | goto out_put_key; |
1599 | |
1600 | spin_lock(&hb->lock); |
1601 | |
1602 | plist_for_each_entry_safe(this, next, &hb->chain, list) { |
1603 | if (match_futex (&this->key, &key)) { |
1604 | if (this->pi_state || this->rt_waiter) { |
1605 | ret = -EINVAL; |
1606 | break; |
1607 | } |
1608 | |
1609 | /* Check if one of the bits is set in both bitsets */ |
1610 | if (!(this->bitset & bitset)) |
1611 | continue; |
1612 | |
1613 | mark_wake_futex(&wake_q, this); |
1614 | if (++ret >= nr_wake) |
1615 | break; |
1616 | } |
1617 | } |
1618 | |
1619 | spin_unlock(&hb->lock); |
1620 | wake_up_q(&wake_q); |
1621 | out_put_key: |
1622 | put_futex_key(&key); |
1623 | out: |
1624 | return ret; |
1625 | } |
1626 | |
1627 | static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr) |
1628 | { |
1629 | unsigned int op = (encoded_op & 0x70000000) >> 28; |
1630 | unsigned int cmp = (encoded_op & 0x0f000000) >> 24; |
1631 | int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11); |
1632 | int cmparg = sign_extend32(encoded_op & 0x00000fff, 11); |
1633 | int oldval, ret; |
1634 | |
1635 | if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) { |
1636 | if (oparg < 0 || oparg > 31) { |
1637 | char comm[sizeof(current->comm)]; |
1638 | /* |
1639 | * kill this print and return -EINVAL when userspace |
1640 | * is sane again |
1641 | */ |
1642 | pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n" , |
1643 | get_task_comm(comm, current), oparg); |
1644 | oparg &= 31; |
1645 | } |
1646 | oparg = 1 << oparg; |
1647 | } |
1648 | |
1649 | if (!access_ok(uaddr, sizeof(u32))) |
1650 | return -EFAULT; |
1651 | |
1652 | ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr); |
1653 | if (ret) |
1654 | return ret; |
1655 | |
1656 | switch (cmp) { |
1657 | case FUTEX_OP_CMP_EQ: |
1658 | return oldval == cmparg; |
1659 | case FUTEX_OP_CMP_NE: |
1660 | return oldval != cmparg; |
1661 | case FUTEX_OP_CMP_LT: |
1662 | return oldval < cmparg; |
1663 | case FUTEX_OP_CMP_GE: |
1664 | return oldval >= cmparg; |
1665 | case FUTEX_OP_CMP_LE: |
1666 | return oldval <= cmparg; |
1667 | case FUTEX_OP_CMP_GT: |
1668 | return oldval > cmparg; |
1669 | default: |
1670 | return -ENOSYS; |
1671 | } |
1672 | } |
1673 | |
1674 | /* |
1675 | * Wake up all waiters hashed on the physical page that is mapped |
1676 | * to this virtual address: |
1677 | */ |
1678 | static int |
1679 | futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2, |
1680 | int nr_wake, int nr_wake2, int op) |
1681 | { |
1682 | union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; |
1683 | struct futex_hash_bucket *hb1, *hb2; |
1684 | struct futex_q *this, *next; |
1685 | int ret, op_ret; |
1686 | DEFINE_WAKE_Q(wake_q); |
1687 | |
1688 | retry: |
1689 | ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ); |
1690 | if (unlikely(ret != 0)) |
1691 | goto out; |
1692 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE); |
1693 | if (unlikely(ret != 0)) |
1694 | goto out_put_key1; |
1695 | |
1696 | hb1 = hash_futex(&key1); |
1697 | hb2 = hash_futex(&key2); |
1698 | |
1699 | retry_private: |
1700 | double_lock_hb(hb1, hb2); |
1701 | op_ret = futex_atomic_op_inuser(op, uaddr2); |
1702 | if (unlikely(op_ret < 0)) { |
1703 | |
1704 | double_unlock_hb(hb1, hb2); |
1705 | |
1706 | #ifndef CONFIG_MMU |
1707 | /* |
1708 | * we don't get EFAULT from MMU faults if we don't have an MMU, |
1709 | * but we might get them from range checking |
1710 | */ |
1711 | ret = op_ret; |
1712 | goto out_put_keys; |
1713 | #endif |
1714 | |
1715 | if (unlikely(op_ret != -EFAULT)) { |
1716 | ret = op_ret; |
1717 | goto out_put_keys; |
1718 | } |
1719 | |
1720 | ret = fault_in_user_writeable(uaddr2); |
1721 | if (ret) |
1722 | goto out_put_keys; |
1723 | |
1724 | if (!(flags & FLAGS_SHARED)) |
1725 | goto retry_private; |
1726 | |
1727 | put_futex_key(&key2); |
1728 | put_futex_key(&key1); |
1729 | goto retry; |
1730 | } |
1731 | |
1732 | plist_for_each_entry_safe(this, next, &hb1->chain, list) { |
1733 | if (match_futex (&this->key, &key1)) { |
1734 | if (this->pi_state || this->rt_waiter) { |
1735 | ret = -EINVAL; |
1736 | goto out_unlock; |
1737 | } |
1738 | mark_wake_futex(&wake_q, this); |
1739 | if (++ret >= nr_wake) |
1740 | break; |
1741 | } |
1742 | } |
1743 | |
1744 | if (op_ret > 0) { |
1745 | op_ret = 0; |
1746 | plist_for_each_entry_safe(this, next, &hb2->chain, list) { |
1747 | if (match_futex (&this->key, &key2)) { |
1748 | if (this->pi_state || this->rt_waiter) { |
1749 | ret = -EINVAL; |
1750 | goto out_unlock; |
1751 | } |
1752 | mark_wake_futex(&wake_q, this); |
1753 | if (++op_ret >= nr_wake2) |
1754 | break; |
1755 | } |
1756 | } |
1757 | ret += op_ret; |
1758 | } |
1759 | |
1760 | out_unlock: |
1761 | double_unlock_hb(hb1, hb2); |
1762 | wake_up_q(&wake_q); |
1763 | out_put_keys: |
1764 | put_futex_key(&key2); |
1765 | out_put_key1: |
1766 | put_futex_key(&key1); |
1767 | out: |
1768 | return ret; |
1769 | } |
1770 | |
1771 | /** |
1772 | * requeue_futex() - Requeue a futex_q from one hb to another |
1773 | * @q: the futex_q to requeue |
1774 | * @hb1: the source hash_bucket |
1775 | * @hb2: the target hash_bucket |
1776 | * @key2: the new key for the requeued futex_q |
1777 | */ |
1778 | static inline |
1779 | void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1, |
1780 | struct futex_hash_bucket *hb2, union futex_key *key2) |
1781 | { |
1782 | |
1783 | /* |
1784 | * If key1 and key2 hash to the same bucket, no need to |
1785 | * requeue. |
1786 | */ |
1787 | if (likely(&hb1->chain != &hb2->chain)) { |
1788 | plist_del(&q->list, &hb1->chain); |
1789 | hb_waiters_dec(hb1); |
1790 | hb_waiters_inc(hb2); |
1791 | plist_add(&q->list, &hb2->chain); |
1792 | q->lock_ptr = &hb2->lock; |
1793 | } |
1794 | get_futex_key_refs(key2); |
1795 | q->key = *key2; |
1796 | } |
1797 | |
1798 | /** |
1799 | * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue |
1800 | * @q: the futex_q |
1801 | * @key: the key of the requeue target futex |
1802 | * @hb: the hash_bucket of the requeue target futex |
1803 | * |
1804 | * During futex_requeue, with requeue_pi=1, it is possible to acquire the |
1805 | * target futex if it is uncontended or via a lock steal. Set the futex_q key |
1806 | * to the requeue target futex so the waiter can detect the wakeup on the right |
1807 | * futex, but remove it from the hb and NULL the rt_waiter so it can detect |
1808 | * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock |
1809 | * to protect access to the pi_state to fixup the owner later. Must be called |
1810 | * with both q->lock_ptr and hb->lock held. |
1811 | */ |
1812 | static inline |
1813 | void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key, |
1814 | struct futex_hash_bucket *hb) |
1815 | { |
1816 | get_futex_key_refs(key); |
1817 | q->key = *key; |
1818 | |
1819 | __unqueue_futex(q); |
1820 | |
1821 | WARN_ON(!q->rt_waiter); |
1822 | q->rt_waiter = NULL; |
1823 | |
1824 | q->lock_ptr = &hb->lock; |
1825 | |
1826 | wake_up_state(q->task, TASK_NORMAL); |
1827 | } |
1828 | |
1829 | /** |
1830 | * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter |
1831 | * @pifutex: the user address of the to futex |
1832 | * @hb1: the from futex hash bucket, must be locked by the caller |
1833 | * @hb2: the to futex hash bucket, must be locked by the caller |
1834 | * @key1: the from futex key |
1835 | * @key2: the to futex key |
1836 | * @ps: address to store the pi_state pointer |
1837 | * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) |
1838 | * |
1839 | * Try and get the lock on behalf of the top waiter if we can do it atomically. |
1840 | * Wake the top waiter if we succeed. If the caller specified set_waiters, |
1841 | * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit. |
1842 | * hb1 and hb2 must be held by the caller. |
1843 | * |
1844 | * Return: |
1845 | * - 0 - failed to acquire the lock atomically; |
1846 | * - >0 - acquired the lock, return value is vpid of the top_waiter |
1847 | * - <0 - error |
1848 | */ |
1849 | static int futex_proxy_trylock_atomic(u32 __user *pifutex, |
1850 | struct futex_hash_bucket *hb1, |
1851 | struct futex_hash_bucket *hb2, |
1852 | union futex_key *key1, union futex_key *key2, |
1853 | struct futex_pi_state **ps, int set_waiters) |
1854 | { |
1855 | struct futex_q *top_waiter = NULL; |
1856 | u32 curval; |
1857 | int ret, vpid; |
1858 | |
1859 | if (get_futex_value_locked(&curval, pifutex)) |
1860 | return -EFAULT; |
1861 | |
1862 | if (unlikely(should_fail_futex(true))) |
1863 | return -EFAULT; |
1864 | |
1865 | /* |
1866 | * Find the top_waiter and determine if there are additional waiters. |
1867 | * If the caller intends to requeue more than 1 waiter to pifutex, |
1868 | * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now, |
1869 | * as we have means to handle the possible fault. If not, don't set |
1870 | * the bit unecessarily as it will force the subsequent unlock to enter |
1871 | * the kernel. |
1872 | */ |
1873 | top_waiter = futex_top_waiter(hb1, key1); |
1874 | |
1875 | /* There are no waiters, nothing for us to do. */ |
1876 | if (!top_waiter) |
1877 | return 0; |
1878 | |
1879 | /* Ensure we requeue to the expected futex. */ |
1880 | if (!match_futex(top_waiter->requeue_pi_key, key2)) |
1881 | return -EINVAL; |
1882 | |
1883 | /* |
1884 | * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in |
1885 | * the contended case or if set_waiters is 1. The pi_state is returned |
1886 | * in ps in contended cases. |
1887 | */ |
1888 | vpid = task_pid_vnr(top_waiter->task); |
1889 | ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task, |
1890 | set_waiters); |
1891 | if (ret == 1) { |
1892 | requeue_pi_wake_futex(top_waiter, key2, hb2); |
1893 | return vpid; |
1894 | } |
1895 | return ret; |
1896 | } |
1897 | |
1898 | /** |
1899 | * futex_requeue() - Requeue waiters from uaddr1 to uaddr2 |
1900 | * @uaddr1: source futex user address |
1901 | * @flags: futex flags (FLAGS_SHARED, etc.) |
1902 | * @uaddr2: target futex user address |
1903 | * @nr_wake: number of waiters to wake (must be 1 for requeue_pi) |
1904 | * @nr_requeue: number of waiters to requeue (0-INT_MAX) |
1905 | * @cmpval: @uaddr1 expected value (or %NULL) |
1906 | * @requeue_pi: if we are attempting to requeue from a non-pi futex to a |
1907 | * pi futex (pi to pi requeue is not supported) |
1908 | * |
1909 | * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire |
1910 | * uaddr2 atomically on behalf of the top waiter. |
1911 | * |
1912 | * Return: |
1913 | * - >=0 - on success, the number of tasks requeued or woken; |
1914 | * - <0 - on error |
1915 | */ |
1916 | static int futex_requeue(u32 __user *uaddr1, unsigned int flags, |
1917 | u32 __user *uaddr2, int nr_wake, int nr_requeue, |
1918 | u32 *cmpval, int requeue_pi) |
1919 | { |
1920 | union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; |
1921 | int drop_count = 0, task_count = 0, ret; |
1922 | struct futex_pi_state *pi_state = NULL; |
1923 | struct futex_hash_bucket *hb1, *hb2; |
1924 | struct futex_q *this, *next; |
1925 | DEFINE_WAKE_Q(wake_q); |
1926 | |
1927 | if (nr_wake < 0 || nr_requeue < 0) |
1928 | return -EINVAL; |
1929 | |
1930 | /* |
1931 | * When PI not supported: return -ENOSYS if requeue_pi is true, |
1932 | * consequently the compiler knows requeue_pi is always false past |
1933 | * this point which will optimize away all the conditional code |
1934 | * further down. |
1935 | */ |
1936 | if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi) |
1937 | return -ENOSYS; |
1938 | |
1939 | if (requeue_pi) { |
1940 | /* |
1941 | * Requeue PI only works on two distinct uaddrs. This |
1942 | * check is only valid for private futexes. See below. |
1943 | */ |
1944 | if (uaddr1 == uaddr2) |
1945 | return -EINVAL; |
1946 | |
1947 | /* |
1948 | * requeue_pi requires a pi_state, try to allocate it now |
1949 | * without any locks in case it fails. |
1950 | */ |
1951 | if (refill_pi_state_cache()) |
1952 | return -ENOMEM; |
1953 | /* |
1954 | * requeue_pi must wake as many tasks as it can, up to nr_wake |
1955 | * + nr_requeue, since it acquires the rt_mutex prior to |
1956 | * returning to userspace, so as to not leave the rt_mutex with |
1957 | * waiters and no owner. However, second and third wake-ups |
1958 | * cannot be predicted as they involve race conditions with the |
1959 | * first wake and a fault while looking up the pi_state. Both |
1960 | * pthread_cond_signal() and pthread_cond_broadcast() should |
1961 | * use nr_wake=1. |
1962 | */ |
1963 | if (nr_wake != 1) |
1964 | return -EINVAL; |
1965 | } |
1966 | |
1967 | retry: |
1968 | ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ); |
1969 | if (unlikely(ret != 0)) |
1970 | goto out; |
1971 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, |
1972 | requeue_pi ? FUTEX_WRITE : FUTEX_READ); |
1973 | if (unlikely(ret != 0)) |
1974 | goto out_put_key1; |
1975 | |
1976 | /* |
1977 | * The check above which compares uaddrs is not sufficient for |
1978 | * shared futexes. We need to compare the keys: |
1979 | */ |
1980 | if (requeue_pi && match_futex(&key1, &key2)) { |
1981 | ret = -EINVAL; |
1982 | goto out_put_keys; |
1983 | } |
1984 | |
1985 | hb1 = hash_futex(&key1); |
1986 | hb2 = hash_futex(&key2); |
1987 | |
1988 | retry_private: |
1989 | hb_waiters_inc(hb2); |
1990 | double_lock_hb(hb1, hb2); |
1991 | |
1992 | if (likely(cmpval != NULL)) { |
1993 | u32 curval; |
1994 | |
1995 | ret = get_futex_value_locked(&curval, uaddr1); |
1996 | |
1997 | if (unlikely(ret)) { |
1998 | double_unlock_hb(hb1, hb2); |
1999 | hb_waiters_dec(hb2); |
2000 | |
2001 | ret = get_user(curval, uaddr1); |
2002 | if (ret) |
2003 | goto out_put_keys; |
2004 | |
2005 | if (!(flags & FLAGS_SHARED)) |
2006 | goto retry_private; |
2007 | |
2008 | put_futex_key(&key2); |
2009 | put_futex_key(&key1); |
2010 | goto retry; |
2011 | } |
2012 | if (curval != *cmpval) { |
2013 | ret = -EAGAIN; |
2014 | goto out_unlock; |
2015 | } |
2016 | } |
2017 | |
2018 | if (requeue_pi && (task_count - nr_wake < nr_requeue)) { |
2019 | /* |
2020 | * Attempt to acquire uaddr2 and wake the top waiter. If we |
2021 | * intend to requeue waiters, force setting the FUTEX_WAITERS |
2022 | * bit. We force this here where we are able to easily handle |
2023 | * faults rather in the requeue loop below. |
2024 | */ |
2025 | ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1, |
2026 | &key2, &pi_state, nr_requeue); |
2027 | |
2028 | /* |
2029 | * At this point the top_waiter has either taken uaddr2 or is |
2030 | * waiting on it. If the former, then the pi_state will not |
2031 | * exist yet, look it up one more time to ensure we have a |
2032 | * reference to it. If the lock was taken, ret contains the |
2033 | * vpid of the top waiter task. |
2034 | * If the lock was not taken, we have pi_state and an initial |
2035 | * refcount on it. In case of an error we have nothing. |
2036 | */ |
2037 | if (ret > 0) { |
2038 | WARN_ON(pi_state); |
2039 | drop_count++; |
2040 | task_count++; |
2041 | /* |
2042 | * If we acquired the lock, then the user space value |
2043 | * of uaddr2 should be vpid. It cannot be changed by |
2044 | * the top waiter as it is blocked on hb2 lock if it |
2045 | * tries to do so. If something fiddled with it behind |
2046 | * our back the pi state lookup might unearth it. So |
2047 | * we rather use the known value than rereading and |
2048 | * handing potential crap to lookup_pi_state. |
2049 | * |
2050 | * If that call succeeds then we have pi_state and an |
2051 | * initial refcount on it. |
2052 | */ |
2053 | ret = lookup_pi_state(uaddr2, ret, hb2, &key2, &pi_state); |
2054 | } |
2055 | |
2056 | switch (ret) { |
2057 | case 0: |
2058 | /* We hold a reference on the pi state. */ |
2059 | break; |
2060 | |
2061 | /* If the above failed, then pi_state is NULL */ |
2062 | case -EFAULT: |
2063 | double_unlock_hb(hb1, hb2); |
2064 | hb_waiters_dec(hb2); |
2065 | put_futex_key(&key2); |
2066 | put_futex_key(&key1); |
2067 | ret = fault_in_user_writeable(uaddr2); |
2068 | if (!ret) |
2069 | goto retry; |
2070 | goto out; |
2071 | case -EAGAIN: |
2072 | /* |
2073 | * Two reasons for this: |
2074 | * - Owner is exiting and we just wait for the |
2075 | * exit to complete. |
2076 | * - The user space value changed. |
2077 | */ |
2078 | double_unlock_hb(hb1, hb2); |
2079 | hb_waiters_dec(hb2); |
2080 | put_futex_key(&key2); |
2081 | put_futex_key(&key1); |
2082 | cond_resched(); |
2083 | goto retry; |
2084 | default: |
2085 | goto out_unlock; |
2086 | } |
2087 | } |
2088 | |
2089 | plist_for_each_entry_safe(this, next, &hb1->chain, list) { |
2090 | if (task_count - nr_wake >= nr_requeue) |
2091 | break; |
2092 | |
2093 | if (!match_futex(&this->key, &key1)) |
2094 | continue; |
2095 | |
2096 | /* |
2097 | * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always |
2098 | * be paired with each other and no other futex ops. |
2099 | * |
2100 | * We should never be requeueing a futex_q with a pi_state, |
2101 | * which is awaiting a futex_unlock_pi(). |
2102 | */ |
2103 | if ((requeue_pi && !this->rt_waiter) || |
2104 | (!requeue_pi && this->rt_waiter) || |
2105 | this->pi_state) { |
2106 | ret = -EINVAL; |
2107 | break; |
2108 | } |
2109 | |
2110 | /* |
2111 | * Wake nr_wake waiters. For requeue_pi, if we acquired the |
2112 | * lock, we already woke the top_waiter. If not, it will be |
2113 | * woken by futex_unlock_pi(). |
2114 | */ |
2115 | if (++task_count <= nr_wake && !requeue_pi) { |
2116 | mark_wake_futex(&wake_q, this); |
2117 | continue; |
2118 | } |
2119 | |
2120 | /* Ensure we requeue to the expected futex for requeue_pi. */ |
2121 | if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) { |
2122 | ret = -EINVAL; |
2123 | break; |
2124 | } |
2125 | |
2126 | /* |
2127 | * Requeue nr_requeue waiters and possibly one more in the case |
2128 | * of requeue_pi if we couldn't acquire the lock atomically. |
2129 | */ |
2130 | if (requeue_pi) { |
2131 | /* |
2132 | * Prepare the waiter to take the rt_mutex. Take a |
2133 | * refcount on the pi_state and store the pointer in |
2134 | * the futex_q object of the waiter. |
2135 | */ |
2136 | get_pi_state(pi_state); |
2137 | this->pi_state = pi_state; |
2138 | ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex, |
2139 | this->rt_waiter, |
2140 | this->task); |
2141 | if (ret == 1) { |
2142 | /* |
2143 | * We got the lock. We do neither drop the |
2144 | * refcount on pi_state nor clear |
2145 | * this->pi_state because the waiter needs the |
2146 | * pi_state for cleaning up the user space |
2147 | * value. It will drop the refcount after |
2148 | * doing so. |
2149 | */ |
2150 | requeue_pi_wake_futex(this, &key2, hb2); |
2151 | drop_count++; |
2152 | continue; |
2153 | } else if (ret) { |
2154 | /* |
2155 | * rt_mutex_start_proxy_lock() detected a |
2156 | * potential deadlock when we tried to queue |
2157 | * that waiter. Drop the pi_state reference |
2158 | * which we took above and remove the pointer |
2159 | * to the state from the waiters futex_q |
2160 | * object. |
2161 | */ |
2162 | this->pi_state = NULL; |
2163 | put_pi_state(pi_state); |
2164 | /* |
2165 | * We stop queueing more waiters and let user |
2166 | * space deal with the mess. |
2167 | */ |
2168 | break; |
2169 | } |
2170 | } |
2171 | requeue_futex(this, hb1, hb2, &key2); |
2172 | drop_count++; |
2173 | } |
2174 | |
2175 | /* |
2176 | * We took an extra initial reference to the pi_state either |
2177 | * in futex_proxy_trylock_atomic() or in lookup_pi_state(). We |
2178 | * need to drop it here again. |
2179 | */ |
2180 | put_pi_state(pi_state); |
2181 | |
2182 | out_unlock: |
2183 | double_unlock_hb(hb1, hb2); |
2184 | wake_up_q(&wake_q); |
2185 | hb_waiters_dec(hb2); |
2186 | |
2187 | /* |
2188 | * drop_futex_key_refs() must be called outside the spinlocks. During |
2189 | * the requeue we moved futex_q's from the hash bucket at key1 to the |
2190 | * one at key2 and updated their key pointer. We no longer need to |
2191 | * hold the references to key1. |
2192 | */ |
2193 | while (--drop_count >= 0) |
2194 | drop_futex_key_refs(&key1); |
2195 | |
2196 | out_put_keys: |
2197 | put_futex_key(&key2); |
2198 | out_put_key1: |
2199 | put_futex_key(&key1); |
2200 | out: |
2201 | return ret ? ret : task_count; |
2202 | } |
2203 | |
2204 | /* The key must be already stored in q->key. */ |
2205 | static inline struct futex_hash_bucket *queue_lock(struct futex_q *q) |
2206 | __acquires(&hb->lock) |
2207 | { |
2208 | struct futex_hash_bucket *hb; |
2209 | |
2210 | hb = hash_futex(&q->key); |
2211 | |
2212 | /* |
2213 | * Increment the counter before taking the lock so that |
2214 | * a potential waker won't miss a to-be-slept task that is |
2215 | * waiting for the spinlock. This is safe as all queue_lock() |
2216 | * users end up calling queue_me(). Similarly, for housekeeping, |
2217 | * decrement the counter at queue_unlock() when some error has |
2218 | * occurred and we don't end up adding the task to the list. |
2219 | */ |
2220 | hb_waiters_inc(hb); /* implies smp_mb(); (A) */ |
2221 | |
2222 | q->lock_ptr = &hb->lock; |
2223 | |
2224 | spin_lock(&hb->lock); |
2225 | return hb; |
2226 | } |
2227 | |
2228 | static inline void |
2229 | queue_unlock(struct futex_hash_bucket *hb) |
2230 | __releases(&hb->lock) |
2231 | { |
2232 | spin_unlock(&hb->lock); |
2233 | hb_waiters_dec(hb); |
2234 | } |
2235 | |
2236 | static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb) |
2237 | { |
2238 | int prio; |
2239 | |
2240 | /* |
2241 | * The priority used to register this element is |
2242 | * - either the real thread-priority for the real-time threads |
2243 | * (i.e. threads with a priority lower than MAX_RT_PRIO) |
2244 | * - or MAX_RT_PRIO for non-RT threads. |
2245 | * Thus, all RT-threads are woken first in priority order, and |
2246 | * the others are woken last, in FIFO order. |
2247 | */ |
2248 | prio = min(current->normal_prio, MAX_RT_PRIO); |
2249 | |
2250 | plist_node_init(&q->list, prio); |
2251 | plist_add(&q->list, &hb->chain); |
2252 | q->task = current; |
2253 | } |
2254 | |
2255 | /** |
2256 | * queue_me() - Enqueue the futex_q on the futex_hash_bucket |
2257 | * @q: The futex_q to enqueue |
2258 | * @hb: The destination hash bucket |
2259 | * |
2260 | * The hb->lock must be held by the caller, and is released here. A call to |
2261 | * queue_me() is typically paired with exactly one call to unqueue_me(). The |
2262 | * exceptions involve the PI related operations, which may use unqueue_me_pi() |
2263 | * or nothing if the unqueue is done as part of the wake process and the unqueue |
2264 | * state is implicit in the state of woken task (see futex_wait_requeue_pi() for |
2265 | * an example). |
2266 | */ |
2267 | static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb) |
2268 | __releases(&hb->lock) |
2269 | { |
2270 | __queue_me(q, hb); |
2271 | spin_unlock(&hb->lock); |
2272 | } |
2273 | |
2274 | /** |
2275 | * unqueue_me() - Remove the futex_q from its futex_hash_bucket |
2276 | * @q: The futex_q to unqueue |
2277 | * |
2278 | * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must |
2279 | * be paired with exactly one earlier call to queue_me(). |
2280 | * |
2281 | * Return: |
2282 | * - 1 - if the futex_q was still queued (and we removed unqueued it); |
2283 | * - 0 - if the futex_q was already removed by the waking thread |
2284 | */ |
2285 | static int unqueue_me(struct futex_q *q) |
2286 | { |
2287 | spinlock_t *lock_ptr; |
2288 | int ret = 0; |
2289 | |
2290 | /* In the common case we don't take the spinlock, which is nice. */ |
2291 | retry: |
2292 | /* |
2293 | * q->lock_ptr can change between this read and the following spin_lock. |
2294 | * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and |
2295 | * optimizing lock_ptr out of the logic below. |
2296 | */ |
2297 | lock_ptr = READ_ONCE(q->lock_ptr); |
2298 | if (lock_ptr != NULL) { |
2299 | spin_lock(lock_ptr); |
2300 | /* |
2301 | * q->lock_ptr can change between reading it and |
2302 | * spin_lock(), causing us to take the wrong lock. This |
2303 | * corrects the race condition. |
2304 | * |
2305 | * Reasoning goes like this: if we have the wrong lock, |
2306 | * q->lock_ptr must have changed (maybe several times) |
2307 | * between reading it and the spin_lock(). It can |
2308 | * change again after the spin_lock() but only if it was |
2309 | * already changed before the spin_lock(). It cannot, |
2310 | * however, change back to the original value. Therefore |
2311 | * we can detect whether we acquired the correct lock. |
2312 | */ |
2313 | if (unlikely(lock_ptr != q->lock_ptr)) { |
2314 | spin_unlock(lock_ptr); |
2315 | goto retry; |
2316 | } |
2317 | __unqueue_futex(q); |
2318 | |
2319 | BUG_ON(q->pi_state); |
2320 | |
2321 | spin_unlock(lock_ptr); |
2322 | ret = 1; |
2323 | } |
2324 | |
2325 | drop_futex_key_refs(&q->key); |
2326 | return ret; |
2327 | } |
2328 | |
2329 | /* |
2330 | * PI futexes can not be requeued and must remove themself from the |
2331 | * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry |
2332 | * and dropped here. |
2333 | */ |
2334 | static void unqueue_me_pi(struct futex_q *q) |
2335 | __releases(q->lock_ptr) |
2336 | { |
2337 | __unqueue_futex(q); |
2338 | |
2339 | BUG_ON(!q->pi_state); |
2340 | put_pi_state(q->pi_state); |
2341 | q->pi_state = NULL; |
2342 | |
2343 | spin_unlock(q->lock_ptr); |
2344 | } |
2345 | |
2346 | static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q, |
2347 | struct task_struct *argowner) |
2348 | { |
2349 | struct futex_pi_state *pi_state = q->pi_state; |
2350 | u32 uval, uninitialized_var(curval), newval; |
2351 | struct task_struct *oldowner, *newowner; |
2352 | u32 newtid; |
2353 | int ret; |
2354 | |
2355 | lockdep_assert_held(q->lock_ptr); |
2356 | |
2357 | raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); |
2358 | |
2359 | oldowner = pi_state->owner; |
2360 | |
2361 | /* |
2362 | * We are here because either: |
2363 | * |
2364 | * - we stole the lock and pi_state->owner needs updating to reflect |
2365 | * that (@argowner == current), |
2366 | * |
2367 | * or: |
2368 | * |
2369 | * - someone stole our lock and we need to fix things to point to the |
2370 | * new owner (@argowner == NULL). |
2371 | * |
2372 | * Either way, we have to replace the TID in the user space variable. |
2373 | * This must be atomic as we have to preserve the owner died bit here. |
2374 | * |
2375 | * Note: We write the user space value _before_ changing the pi_state |
2376 | * because we can fault here. Imagine swapped out pages or a fork |
2377 | * that marked all the anonymous memory readonly for cow. |
2378 | * |
2379 | * Modifying pi_state _before_ the user space value would leave the |
2380 | * pi_state in an inconsistent state when we fault here, because we |
2381 | * need to drop the locks to handle the fault. This might be observed |
2382 | * in the PID check in lookup_pi_state. |
2383 | */ |
2384 | retry: |
2385 | if (!argowner) { |
2386 | if (oldowner != current) { |
2387 | /* |
2388 | * We raced against a concurrent self; things are |
2389 | * already fixed up. Nothing to do. |
2390 | */ |
2391 | ret = 0; |
2392 | goto out_unlock; |
2393 | } |
2394 | |
2395 | if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) { |
2396 | /* We got the lock after all, nothing to fix. */ |
2397 | ret = 0; |
2398 | goto out_unlock; |
2399 | } |
2400 | |
2401 | /* |
2402 | * Since we just failed the trylock; there must be an owner. |
2403 | */ |
2404 | newowner = rt_mutex_owner(&pi_state->pi_mutex); |
2405 | BUG_ON(!newowner); |
2406 | } else { |
2407 | WARN_ON_ONCE(argowner != current); |
2408 | if (oldowner == current) { |
2409 | /* |
2410 | * We raced against a concurrent self; things are |
2411 | * already fixed up. Nothing to do. |
2412 | */ |
2413 | ret = 0; |
2414 | goto out_unlock; |
2415 | } |
2416 | newowner = argowner; |
2417 | } |
2418 | |
2419 | newtid = task_pid_vnr(newowner) | FUTEX_WAITERS; |
2420 | /* Owner died? */ |
2421 | if (!pi_state->owner) |
2422 | newtid |= FUTEX_OWNER_DIED; |
2423 | |
2424 | if (get_futex_value_locked(&uval, uaddr)) |
2425 | goto handle_fault; |
2426 | |
2427 | for (;;) { |
2428 | newval = (uval & FUTEX_OWNER_DIED) | newtid; |
2429 | |
2430 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) |
2431 | goto handle_fault; |
2432 | if (curval == uval) |
2433 | break; |
2434 | uval = curval; |
2435 | } |
2436 | |
2437 | /* |
2438 | * We fixed up user space. Now we need to fix the pi_state |
2439 | * itself. |
2440 | */ |
2441 | if (pi_state->owner != NULL) { |
2442 | raw_spin_lock(&pi_state->owner->pi_lock); |
2443 | WARN_ON(list_empty(&pi_state->list)); |
2444 | list_del_init(&pi_state->list); |
2445 | raw_spin_unlock(&pi_state->owner->pi_lock); |
2446 | } |
2447 | |
2448 | pi_state->owner = newowner; |
2449 | |
2450 | raw_spin_lock(&newowner->pi_lock); |
2451 | WARN_ON(!list_empty(&pi_state->list)); |
2452 | list_add(&pi_state->list, &newowner->pi_state_list); |
2453 | raw_spin_unlock(&newowner->pi_lock); |
2454 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); |
2455 | |
2456 | return 0; |
2457 | |
2458 | /* |
2459 | * To handle the page fault we need to drop the locks here. That gives |
2460 | * the other task (either the highest priority waiter itself or the |
2461 | * task which stole the rtmutex) the chance to try the fixup of the |
2462 | * pi_state. So once we are back from handling the fault we need to |
2463 | * check the pi_state after reacquiring the locks and before trying to |
2464 | * do another fixup. When the fixup has been done already we simply |
2465 | * return. |
2466 | * |
2467 | * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely |
2468 | * drop hb->lock since the caller owns the hb -> futex_q relation. |
2469 | * Dropping the pi_mutex->wait_lock requires the state revalidate. |
2470 | */ |
2471 | handle_fault: |
2472 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); |
2473 | spin_unlock(q->lock_ptr); |
2474 | |
2475 | ret = fault_in_user_writeable(uaddr); |
2476 | |
2477 | spin_lock(q->lock_ptr); |
2478 | raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); |
2479 | |
2480 | /* |
2481 | * Check if someone else fixed it for us: |
2482 | */ |
2483 | if (pi_state->owner != oldowner) { |
2484 | ret = 0; |
2485 | goto out_unlock; |
2486 | } |
2487 | |
2488 | if (ret) |
2489 | goto out_unlock; |
2490 | |
2491 | goto retry; |
2492 | |
2493 | out_unlock: |
2494 | raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); |
2495 | return ret; |
2496 | } |
2497 | |
2498 | static long futex_wait_restart(struct restart_block *restart); |
2499 | |
2500 | /** |
2501 | * fixup_owner() - Post lock pi_state and corner case management |
2502 | * @uaddr: user address of the futex |
2503 | * @q: futex_q (contains pi_state and access to the rt_mutex) |
2504 | * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0) |
2505 | * |
2506 | * After attempting to lock an rt_mutex, this function is called to cleanup |
2507 | * the pi_state owner as well as handle race conditions that may allow us to |
2508 | * acquire the lock. Must be called with the hb lock held. |
2509 | * |
2510 | * Return: |
2511 | * - 1 - success, lock taken; |
2512 | * - 0 - success, lock not taken; |
2513 | * - <0 - on error (-EFAULT) |
2514 | */ |
2515 | static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked) |
2516 | { |
2517 | int ret = 0; |
2518 | |
2519 | if (locked) { |
2520 | /* |
2521 | * Got the lock. We might not be the anticipated owner if we |
2522 | * did a lock-steal - fix up the PI-state in that case: |
2523 | * |
2524 | * Speculative pi_state->owner read (we don't hold wait_lock); |
2525 | * since we own the lock pi_state->owner == current is the |
2526 | * stable state, anything else needs more attention. |
2527 | */ |
2528 | if (q->pi_state->owner != current) |
2529 | ret = fixup_pi_state_owner(uaddr, q, current); |
2530 | goto out; |
2531 | } |
2532 | |
2533 | /* |
2534 | * If we didn't get the lock; check if anybody stole it from us. In |
2535 | * that case, we need to fix up the uval to point to them instead of |
2536 | * us, otherwise bad things happen. [10] |
2537 | * |
2538 | * Another speculative read; pi_state->owner == current is unstable |
2539 | * but needs our attention. |
2540 | */ |
2541 | if (q->pi_state->owner == current) { |
2542 | ret = fixup_pi_state_owner(uaddr, q, NULL); |
2543 | goto out; |
2544 | } |
2545 | |
2546 | /* |
2547 | * Paranoia check. If we did not take the lock, then we should not be |
2548 | * the owner of the rt_mutex. |
2549 | */ |
2550 | if (rt_mutex_owner(&q->pi_state->pi_mutex) == current) { |
2551 | printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p " |
2552 | "pi-state %p\n" , ret, |
2553 | q->pi_state->pi_mutex.owner, |
2554 | q->pi_state->owner); |
2555 | } |
2556 | |
2557 | out: |
2558 | return ret ? ret : locked; |
2559 | } |
2560 | |
2561 | /** |
2562 | * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal |
2563 | * @hb: the futex hash bucket, must be locked by the caller |
2564 | * @q: the futex_q to queue up on |
2565 | * @timeout: the prepared hrtimer_sleeper, or null for no timeout |
2566 | */ |
2567 | static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q, |
2568 | struct hrtimer_sleeper *timeout) |
2569 | { |
2570 | /* |
2571 | * The task state is guaranteed to be set before another task can |
2572 | * wake it. set_current_state() is implemented using smp_store_mb() and |
2573 | * queue_me() calls spin_unlock() upon completion, both serializing |
2574 | * access to the hash list and forcing another memory barrier. |
2575 | */ |
2576 | set_current_state(TASK_INTERRUPTIBLE); |
2577 | queue_me(q, hb); |
2578 | |
2579 | /* Arm the timer */ |
2580 | if (timeout) |
2581 | hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS); |
2582 | |
2583 | /* |
2584 | * If we have been removed from the hash list, then another task |
2585 | * has tried to wake us, and we can skip the call to schedule(). |
2586 | */ |
2587 | if (likely(!plist_node_empty(&q->list))) { |
2588 | /* |
2589 | * If the timer has already expired, current will already be |
2590 | * flagged for rescheduling. Only call schedule if there |
2591 | * is no timeout, or if it has yet to expire. |
2592 | */ |
2593 | if (!timeout || timeout->task) |
2594 | freezable_schedule(); |
2595 | } |
2596 | __set_current_state(TASK_RUNNING); |
2597 | } |
2598 | |
2599 | /** |
2600 | * futex_wait_setup() - Prepare to wait on a futex |
2601 | * @uaddr: the futex userspace address |
2602 | * @val: the expected value |
2603 | * @flags: futex flags (FLAGS_SHARED, etc.) |
2604 | * @q: the associated futex_q |
2605 | * @hb: storage for hash_bucket pointer to be returned to caller |
2606 | * |
2607 | * Setup the futex_q and locate the hash_bucket. Get the futex value and |
2608 | * compare it with the expected value. Handle atomic faults internally. |
2609 | * Return with the hb lock held and a q.key reference on success, and unlocked |
2610 | * with no q.key reference on failure. |
2611 | * |
2612 | * Return: |
2613 | * - 0 - uaddr contains val and hb has been locked; |
2614 | * - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked |
2615 | */ |
2616 | static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags, |
2617 | struct futex_q *q, struct futex_hash_bucket **hb) |
2618 | { |
2619 | u32 uval; |
2620 | int ret; |
2621 | |
2622 | /* |
2623 | * Access the page AFTER the hash-bucket is locked. |
2624 | * Order is important: |
2625 | * |
2626 | * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val); |
2627 | * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); } |
2628 | * |
2629 | * The basic logical guarantee of a futex is that it blocks ONLY |
2630 | * if cond(var) is known to be true at the time of blocking, for |
2631 | * any cond. If we locked the hash-bucket after testing *uaddr, that |
2632 | * would open a race condition where we could block indefinitely with |
2633 | * cond(var) false, which would violate the guarantee. |
2634 | * |
2635 | * On the other hand, we insert q and release the hash-bucket only |
2636 | * after testing *uaddr. This guarantees that futex_wait() will NOT |
2637 | * absorb a wakeup if *uaddr does not match the desired values |
2638 | * while the syscall executes. |
2639 | */ |
2640 | retry: |
2641 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, FUTEX_READ); |
2642 | if (unlikely(ret != 0)) |
2643 | return ret; |
2644 | |
2645 | retry_private: |
2646 | *hb = queue_lock(q); |
2647 | |
2648 | ret = get_futex_value_locked(&uval, uaddr); |
2649 | |
2650 | if (ret) { |
2651 | queue_unlock(*hb); |
2652 | |
2653 | ret = get_user(uval, uaddr); |
2654 | if (ret) |
2655 | goto out; |
2656 | |
2657 | if (!(flags & FLAGS_SHARED)) |
2658 | goto retry_private; |
2659 | |
2660 | put_futex_key(&q->key); |
2661 | goto retry; |
2662 | } |
2663 | |
2664 | if (uval != val) { |
2665 | queue_unlock(*hb); |
2666 | ret = -EWOULDBLOCK; |
2667 | } |
2668 | |
2669 | out: |
2670 | if (ret) |
2671 | put_futex_key(&q->key); |
2672 | return ret; |
2673 | } |
2674 | |
2675 | static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val, |
2676 | ktime_t *abs_time, u32 bitset) |
2677 | { |
2678 | struct hrtimer_sleeper timeout, *to = NULL; |
2679 | struct restart_block *restart; |
2680 | struct futex_hash_bucket *hb; |
2681 | struct futex_q q = futex_q_init; |
2682 | int ret; |
2683 | |
2684 | if (!bitset) |
2685 | return -EINVAL; |
2686 | q.bitset = bitset; |
2687 | |
2688 | if (abs_time) { |
2689 | to = &timeout; |
2690 | |
2691 | hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ? |
2692 | CLOCK_REALTIME : CLOCK_MONOTONIC, |
2693 | HRTIMER_MODE_ABS); |
2694 | hrtimer_init_sleeper(to, current); |
2695 | hrtimer_set_expires_range_ns(&to->timer, *abs_time, |
2696 | current->timer_slack_ns); |
2697 | } |
2698 | |
2699 | retry: |
2700 | /* |
2701 | * Prepare to wait on uaddr. On success, holds hb lock and increments |
2702 | * q.key refs. |
2703 | */ |
2704 | ret = futex_wait_setup(uaddr, val, flags, &q, &hb); |
2705 | if (ret) |
2706 | goto out; |
2707 | |
2708 | /* queue_me and wait for wakeup, timeout, or a signal. */ |
2709 | futex_wait_queue_me(hb, &q, to); |
2710 | |
2711 | /* If we were woken (and unqueued), we succeeded, whatever. */ |
2712 | ret = 0; |
2713 | /* unqueue_me() drops q.key ref */ |
2714 | if (!unqueue_me(&q)) |
2715 | goto out; |
2716 | ret = -ETIMEDOUT; |
2717 | if (to && !to->task) |
2718 | goto out; |
2719 | |
2720 | /* |
2721 | * We expect signal_pending(current), but we might be the |
2722 | * victim of a spurious wakeup as well. |
2723 | */ |
2724 | if (!signal_pending(current)) |
2725 | goto retry; |
2726 | |
2727 | ret = -ERESTARTSYS; |
2728 | if (!abs_time) |
2729 | goto out; |
2730 | |
2731 | restart = ¤t->restart_block; |
2732 | restart->fn = futex_wait_restart; |
2733 | restart->futex.uaddr = uaddr; |
2734 | restart->futex.val = val; |
2735 | restart->futex.time = *abs_time; |
2736 | restart->futex.bitset = bitset; |
2737 | restart->futex.flags = flags | FLAGS_HAS_TIMEOUT; |
2738 | |
2739 | ret = -ERESTART_RESTARTBLOCK; |
2740 | |
2741 | out: |
2742 | if (to) { |
2743 | hrtimer_cancel(&to->timer); |
2744 | destroy_hrtimer_on_stack(&to->timer); |
2745 | } |
2746 | return ret; |
2747 | } |
2748 | |
2749 | |
2750 | static long futex_wait_restart(struct restart_block *restart) |
2751 | { |
2752 | u32 __user *uaddr = restart->futex.uaddr; |
2753 | ktime_t t, *tp = NULL; |
2754 | |
2755 | if (restart->futex.flags & FLAGS_HAS_TIMEOUT) { |
2756 | t = restart->futex.time; |
2757 | tp = &t; |
2758 | } |
2759 | restart->fn = do_no_restart_syscall; |
2760 | |
2761 | return (long)futex_wait(uaddr, restart->futex.flags, |
2762 | restart->futex.val, tp, restart->futex.bitset); |
2763 | } |
2764 | |
2765 | |
2766 | /* |
2767 | * Userspace tried a 0 -> TID atomic transition of the futex value |
2768 | * and failed. The kernel side here does the whole locking operation: |
2769 | * if there are waiters then it will block as a consequence of relying |
2770 | * on rt-mutexes, it does PI, etc. (Due to races the kernel might see |
2771 | * a 0 value of the futex too.). |
2772 | * |
2773 | * Also serves as futex trylock_pi()'ing, and due semantics. |
2774 | */ |
2775 | static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, |
2776 | ktime_t *time, int trylock) |
2777 | { |
2778 | struct hrtimer_sleeper timeout, *to = NULL; |
2779 | struct futex_pi_state *pi_state = NULL; |
2780 | struct rt_mutex_waiter rt_waiter; |
2781 | struct futex_hash_bucket *hb; |
2782 | struct futex_q q = futex_q_init; |
2783 | int res, ret; |
2784 | |
2785 | if (!IS_ENABLED(CONFIG_FUTEX_PI)) |
2786 | return -ENOSYS; |
2787 | |
2788 | if (refill_pi_state_cache()) |
2789 | return -ENOMEM; |
2790 | |
2791 | if (time) { |
2792 | to = &timeout; |
2793 | hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME, |
2794 | HRTIMER_MODE_ABS); |
2795 | hrtimer_init_sleeper(to, current); |
2796 | hrtimer_set_expires(&to->timer, *time); |
2797 | } |
2798 | |
2799 | retry: |
2800 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE); |
2801 | if (unlikely(ret != 0)) |
2802 | goto out; |
2803 | |
2804 | retry_private: |
2805 | hb = queue_lock(&q); |
2806 | |
2807 | ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0); |
2808 | if (unlikely(ret)) { |
2809 | /* |
2810 | * Atomic work succeeded and we got the lock, |
2811 | * or failed. Either way, we do _not_ block. |
2812 | */ |
2813 | switch (ret) { |
2814 | case 1: |
2815 | /* We got the lock. */ |
2816 | ret = 0; |
2817 | goto out_unlock_put_key; |
2818 | case -EFAULT: |
2819 | goto uaddr_faulted; |
2820 | case -EAGAIN: |
2821 | /* |
2822 | * Two reasons for this: |
2823 | * - Task is exiting and we just wait for the |
2824 | * exit to complete. |
2825 | * - The user space value changed. |
2826 | */ |
2827 | queue_unlock(hb); |
2828 | put_futex_key(&q.key); |
2829 | cond_resched(); |
2830 | goto retry; |
2831 | default: |
2832 | goto out_unlock_put_key; |
2833 | } |
2834 | } |
2835 | |
2836 | WARN_ON(!q.pi_state); |
2837 | |
2838 | /* |
2839 | * Only actually queue now that the atomic ops are done: |
2840 | */ |
2841 | __queue_me(&q, hb); |
2842 | |
2843 | if (trylock) { |
2844 | ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex); |
2845 | /* Fixup the trylock return value: */ |
2846 | ret = ret ? 0 : -EWOULDBLOCK; |
2847 | goto no_block; |
2848 | } |
2849 | |
2850 | rt_mutex_init_waiter(&rt_waiter); |
2851 | |
2852 | /* |
2853 | * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not |
2854 | * hold it while doing rt_mutex_start_proxy(), because then it will |
2855 | * include hb->lock in the blocking chain, even through we'll not in |
2856 | * fact hold it while blocking. This will lead it to report -EDEADLK |
2857 | * and BUG when futex_unlock_pi() interleaves with this. |
2858 | * |
2859 | * Therefore acquire wait_lock while holding hb->lock, but drop the |
2860 | * latter before calling __rt_mutex_start_proxy_lock(). This |
2861 | * interleaves with futex_unlock_pi() -- which does a similar lock |
2862 | * handoff -- such that the latter can observe the futex_q::pi_state |
2863 | * before __rt_mutex_start_proxy_lock() is done. |
2864 | */ |
2865 | raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock); |
2866 | spin_unlock(q.lock_ptr); |
2867 | /* |
2868 | * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter |
2869 | * such that futex_unlock_pi() is guaranteed to observe the waiter when |
2870 | * it sees the futex_q::pi_state. |
2871 | */ |
2872 | ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current); |
2873 | raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock); |
2874 | |
2875 | if (ret) { |
2876 | if (ret == 1) |
2877 | ret = 0; |
2878 | goto cleanup; |
2879 | } |
2880 | |
2881 | if (unlikely(to)) |
2882 | hrtimer_start_expires(&to->timer, HRTIMER_MODE_ABS); |
2883 | |
2884 | ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter); |
2885 | |
2886 | cleanup: |
2887 | spin_lock(q.lock_ptr); |
2888 | /* |
2889 | * If we failed to acquire the lock (deadlock/signal/timeout), we must |
2890 | * first acquire the hb->lock before removing the lock from the |
2891 | * rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait |
2892 | * lists consistent. |
2893 | * |
2894 | * In particular; it is important that futex_unlock_pi() can not |
2895 | * observe this inconsistency. |
2896 | */ |
2897 | if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter)) |
2898 | ret = 0; |
2899 | |
2900 | no_block: |
2901 | /* |
2902 | * Fixup the pi_state owner and possibly acquire the lock if we |
2903 | * haven't already. |
2904 | */ |
2905 | res = fixup_owner(uaddr, &q, !ret); |
2906 | /* |
2907 | * If fixup_owner() returned an error, proprogate that. If it acquired |
2908 | * the lock, clear our -ETIMEDOUT or -EINTR. |
2909 | */ |
2910 | if (res) |
2911 | ret = (res < 0) ? res : 0; |
2912 | |
2913 | /* |
2914 | * If fixup_owner() faulted and was unable to handle the fault, unlock |
2915 | * it and return the fault to userspace. |
2916 | */ |
2917 | if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) { |
2918 | pi_state = q.pi_state; |
2919 | get_pi_state(pi_state); |
2920 | } |
2921 | |
2922 | /* Unqueue and drop the lock */ |
2923 | unqueue_me_pi(&q); |
2924 | |
2925 | if (pi_state) { |
2926 | rt_mutex_futex_unlock(&pi_state->pi_mutex); |
2927 | put_pi_state(pi_state); |
2928 | } |
2929 | |
2930 | goto out_put_key; |
2931 | |
2932 | out_unlock_put_key: |
2933 | queue_unlock(hb); |
2934 | |
2935 | out_put_key: |
2936 | put_futex_key(&q.key); |
2937 | out: |
2938 | if (to) { |
2939 | hrtimer_cancel(&to->timer); |
2940 | destroy_hrtimer_on_stack(&to->timer); |
2941 | } |
2942 | return ret != -EINTR ? ret : -ERESTARTNOINTR; |
2943 | |
2944 | uaddr_faulted: |
2945 | queue_unlock(hb); |
2946 | |
2947 | ret = fault_in_user_writeable(uaddr); |
2948 | if (ret) |
2949 | goto out_put_key; |
2950 | |
2951 | if (!(flags & FLAGS_SHARED)) |
2952 | goto retry_private; |
2953 | |
2954 | put_futex_key(&q.key); |
2955 | goto retry; |
2956 | } |
2957 | |
2958 | /* |
2959 | * Userspace attempted a TID -> 0 atomic transition, and failed. |
2960 | * This is the in-kernel slowpath: we look up the PI state (if any), |
2961 | * and do the rt-mutex unlock. |
2962 | */ |
2963 | static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags) |
2964 | { |
2965 | u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current); |
2966 | union futex_key key = FUTEX_KEY_INIT; |
2967 | struct futex_hash_bucket *hb; |
2968 | struct futex_q *top_waiter; |
2969 | int ret; |
2970 | |
2971 | if (!IS_ENABLED(CONFIG_FUTEX_PI)) |
2972 | return -ENOSYS; |
2973 | |
2974 | retry: |
2975 | if (get_user(uval, uaddr)) |
2976 | return -EFAULT; |
2977 | /* |
2978 | * We release only a lock we actually own: |
2979 | */ |
2980 | if ((uval & FUTEX_TID_MASK) != vpid) |
2981 | return -EPERM; |
2982 | |
2983 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_WRITE); |
2984 | if (ret) |
2985 | return ret; |
2986 | |
2987 | hb = hash_futex(&key); |
2988 | spin_lock(&hb->lock); |
2989 | |
2990 | /* |
2991 | * Check waiters first. We do not trust user space values at |
2992 | * all and we at least want to know if user space fiddled |
2993 | * with the futex value instead of blindly unlocking. |
2994 | */ |
2995 | top_waiter = futex_top_waiter(hb, &key); |
2996 | if (top_waiter) { |
2997 | struct futex_pi_state *pi_state = top_waiter->pi_state; |
2998 | |
2999 | ret = -EINVAL; |
3000 | if (!pi_state) |
3001 | goto out_unlock; |
3002 | |
3003 | /* |
3004 | * If current does not own the pi_state then the futex is |
3005 | * inconsistent and user space fiddled with the futex value. |
3006 | */ |
3007 | if (pi_state->owner != current) |
3008 | goto out_unlock; |
3009 | |
3010 | get_pi_state(pi_state); |
3011 | /* |
3012 | * By taking wait_lock while still holding hb->lock, we ensure |
3013 | * there is no point where we hold neither; and therefore |
3014 | * wake_futex_pi() must observe a state consistent with what we |
3015 | * observed. |
3016 | * |
3017 | * In particular; this forces __rt_mutex_start_proxy() to |
3018 | * complete such that we're guaranteed to observe the |
3019 | * rt_waiter. Also see the WARN in wake_futex_pi(). |
3020 | */ |
3021 | raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); |
3022 | spin_unlock(&hb->lock); |
3023 | |
3024 | /* drops pi_state->pi_mutex.wait_lock */ |
3025 | ret = wake_futex_pi(uaddr, uval, pi_state); |
3026 | |
3027 | put_pi_state(pi_state); |
3028 | |
3029 | /* |
3030 | * Success, we're done! No tricky corner cases. |
3031 | */ |
3032 | if (!ret) |
3033 | goto out_putkey; |
3034 | /* |
3035 | * The atomic access to the futex value generated a |
3036 | * pagefault, so retry the user-access and the wakeup: |
3037 | */ |
3038 | if (ret == -EFAULT) |
3039 | goto pi_faulted; |
3040 | /* |
3041 | * A unconditional UNLOCK_PI op raced against a waiter |
3042 | * setting the FUTEX_WAITERS bit. Try again. |
3043 | */ |
3044 | if (ret == -EAGAIN) { |
3045 | put_futex_key(&key); |
3046 | goto retry; |
3047 | } |
3048 | /* |
3049 | * wake_futex_pi has detected invalid state. Tell user |
3050 | * space. |
3051 | */ |
3052 | goto out_putkey; |
3053 | } |
3054 | |
3055 | /* |
3056 | * We have no kernel internal state, i.e. no waiters in the |
3057 | * kernel. Waiters which are about to queue themselves are stuck |
3058 | * on hb->lock. So we can safely ignore them. We do neither |
3059 | * preserve the WAITERS bit not the OWNER_DIED one. We are the |
3060 | * owner. |
3061 | */ |
3062 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0)) { |
3063 | spin_unlock(&hb->lock); |
3064 | goto pi_faulted; |
3065 | } |
3066 | |
3067 | /* |
3068 | * If uval has changed, let user space handle it. |
3069 | */ |
3070 | ret = (curval == uval) ? 0 : -EAGAIN; |
3071 | |
3072 | out_unlock: |
3073 | spin_unlock(&hb->lock); |
3074 | out_putkey: |
3075 | put_futex_key(&key); |
3076 | return ret; |
3077 | |
3078 | pi_faulted: |
3079 | put_futex_key(&key); |
3080 | |
3081 | ret = fault_in_user_writeable(uaddr); |
3082 | if (!ret) |
3083 | goto retry; |
3084 | |
3085 | return ret; |
3086 | } |
3087 | |
3088 | /** |
3089 | * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex |
3090 | * @hb: the hash_bucket futex_q was original enqueued on |
3091 | * @q: the futex_q woken while waiting to be requeued |
3092 | * @key2: the futex_key of the requeue target futex |
3093 | * @timeout: the timeout associated with the wait (NULL if none) |
3094 | * |
3095 | * Detect if the task was woken on the initial futex as opposed to the requeue |
3096 | * target futex. If so, determine if it was a timeout or a signal that caused |
3097 | * the wakeup and return the appropriate error code to the caller. Must be |
3098 | * called with the hb lock held. |
3099 | * |
3100 | * Return: |
3101 | * - 0 = no early wakeup detected; |
3102 | * - <0 = -ETIMEDOUT or -ERESTARTNOINTR |
3103 | */ |
3104 | static inline |
3105 | int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb, |
3106 | struct futex_q *q, union futex_key *key2, |
3107 | struct hrtimer_sleeper *timeout) |
3108 | { |
3109 | int ret = 0; |
3110 | |
3111 | /* |
3112 | * With the hb lock held, we avoid races while we process the wakeup. |
3113 | * We only need to hold hb (and not hb2) to ensure atomicity as the |
3114 | * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb. |
3115 | * It can't be requeued from uaddr2 to something else since we don't |
3116 | * support a PI aware source futex for requeue. |
3117 | */ |
3118 | if (!match_futex(&q->key, key2)) { |
3119 | WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr)); |
3120 | /* |
3121 | * We were woken prior to requeue by a timeout or a signal. |
3122 | * Unqueue the futex_q and determine which it was. |
3123 | */ |
3124 | plist_del(&q->list, &hb->chain); |
3125 | hb_waiters_dec(hb); |
3126 | |
3127 | /* Handle spurious wakeups gracefully */ |
3128 | ret = -EWOULDBLOCK; |
3129 | if (timeout && !timeout->task) |
3130 | ret = -ETIMEDOUT; |
3131 | else if (signal_pending(current)) |
3132 | ret = -ERESTARTNOINTR; |
3133 | } |
3134 | return ret; |
3135 | } |
3136 | |
3137 | /** |
3138 | * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2 |
3139 | * @uaddr: the futex we initially wait on (non-pi) |
3140 | * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be |
3141 | * the same type, no requeueing from private to shared, etc. |
3142 | * @val: the expected value of uaddr |
3143 | * @abs_time: absolute timeout |
3144 | * @bitset: 32 bit wakeup bitset set by userspace, defaults to all |
3145 | * @uaddr2: the pi futex we will take prior to returning to user-space |
3146 | * |
3147 | * The caller will wait on uaddr and will be requeued by futex_requeue() to |
3148 | * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake |
3149 | * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to |
3150 | * userspace. This ensures the rt_mutex maintains an owner when it has waiters; |
3151 | * without one, the pi logic would not know which task to boost/deboost, if |
3152 | * there was a need to. |
3153 | * |
3154 | * We call schedule in futex_wait_queue_me() when we enqueue and return there |
3155 | * via the following-- |
3156 | * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue() |
3157 | * 2) wakeup on uaddr2 after a requeue |
3158 | * 3) signal |
3159 | * 4) timeout |
3160 | * |
3161 | * If 3, cleanup and return -ERESTARTNOINTR. |
3162 | * |
3163 | * If 2, we may then block on trying to take the rt_mutex and return via: |
3164 | * 5) successful lock |
3165 | * 6) signal |
3166 | * 7) timeout |
3167 | * 8) other lock acquisition failure |
3168 | * |
3169 | * If 6, return -EWOULDBLOCK (restarting the syscall would do the same). |
3170 | * |
3171 | * If 4 or 7, we cleanup and return with -ETIMEDOUT. |
3172 | * |
3173 | * Return: |
3174 | * - 0 - On success; |
3175 | * - <0 - On error |
3176 | */ |
3177 | static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, |
3178 | u32 val, ktime_t *abs_time, u32 bitset, |
3179 | u32 __user *uaddr2) |
3180 | { |
3181 | struct hrtimer_sleeper timeout, *to = NULL; |
3182 | struct futex_pi_state *pi_state = NULL; |
3183 | struct rt_mutex_waiter rt_waiter; |
3184 | struct futex_hash_bucket *hb; |
3185 | union futex_key key2 = FUTEX_KEY_INIT; |
3186 | struct futex_q q = futex_q_init; |
3187 | int res, ret; |
3188 | |
3189 | if (!IS_ENABLED(CONFIG_FUTEX_PI)) |
3190 | return -ENOSYS; |
3191 | |
3192 | if (uaddr == uaddr2) |
3193 | return -EINVAL; |
3194 | |
3195 | if (!bitset) |
3196 | return -EINVAL; |
3197 | |
3198 | if (abs_time) { |
3199 | to = &timeout; |
3200 | hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ? |
3201 | CLOCK_REALTIME : CLOCK_MONOTONIC, |
3202 | HRTIMER_MODE_ABS); |
3203 | hrtimer_init_sleeper(to, current); |
3204 | hrtimer_set_expires_range_ns(&to->timer, *abs_time, |
3205 | current->timer_slack_ns); |
3206 | } |
3207 | |
3208 | /* |
3209 | * The waiter is allocated on our stack, manipulated by the requeue |
3210 | * code while we sleep on uaddr. |
3211 | */ |
3212 | rt_mutex_init_waiter(&rt_waiter); |
3213 | |
3214 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE); |
3215 | if (unlikely(ret != 0)) |
3216 | goto out; |
3217 | |
3218 | q.bitset = bitset; |
3219 | q.rt_waiter = &rt_waiter; |
3220 | q.requeue_pi_key = &key2; |
3221 | |
3222 | /* |
3223 | * Prepare to wait on uaddr. On success, increments q.key (key1) ref |
3224 | * count. |
3225 | */ |
3226 | ret = futex_wait_setup(uaddr, val, flags, &q, &hb); |
3227 | if (ret) |
3228 | goto out_key2; |
3229 | |
3230 | /* |
3231 | * The check above which compares uaddrs is not sufficient for |
3232 | * shared futexes. We need to compare the keys: |
3233 | */ |
3234 | if (match_futex(&q.key, &key2)) { |
3235 | queue_unlock(hb); |
3236 | ret = -EINVAL; |
3237 | goto out_put_keys; |
3238 | } |
3239 | |
3240 | /* Queue the futex_q, drop the hb lock, wait for wakeup. */ |
3241 | futex_wait_queue_me(hb, &q, to); |
3242 | |
3243 | spin_lock(&hb->lock); |
3244 | ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to); |
3245 | spin_unlock(&hb->lock); |
3246 | if (ret) |
3247 | goto out_put_keys; |
3248 | |
3249 | /* |
3250 | * In order for us to be here, we know our q.key == key2, and since |
3251 | * we took the hb->lock above, we also know that futex_requeue() has |
3252 | * completed and we no longer have to concern ourselves with a wakeup |
3253 | * race with the atomic proxy lock acquisition by the requeue code. The |
3254 | * futex_requeue dropped our key1 reference and incremented our key2 |
3255 | * reference count. |
3256 | */ |
3257 | |
3258 | /* Check if the requeue code acquired the second futex for us. */ |
3259 | if (!q.rt_waiter) { |
3260 | /* |
3261 | * Got the lock. We might not be the anticipated owner if we |
3262 | * did a lock-steal - fix up the PI-state in that case. |
3263 | */ |
3264 | if (q.pi_state && (q.pi_state->owner != current)) { |
3265 | spin_lock(q.lock_ptr); |
3266 | ret = fixup_pi_state_owner(uaddr2, &q, current); |
3267 | if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) { |
3268 | pi_state = q.pi_state; |
3269 | get_pi_state(pi_state); |
3270 | } |
3271 | /* |
3272 | * Drop the reference to the pi state which |
3273 | * the requeue_pi() code acquired for us. |
3274 | */ |
3275 | put_pi_state(q.pi_state); |
3276 | spin_unlock(q.lock_ptr); |
3277 | } |
3278 | } else { |
3279 | struct rt_mutex *pi_mutex; |
3280 | |
3281 | /* |
3282 | * We have been woken up by futex_unlock_pi(), a timeout, or a |
3283 | * signal. futex_unlock_pi() will not destroy the lock_ptr nor |
3284 | * the pi_state. |
3285 | */ |
3286 | WARN_ON(!q.pi_state); |
3287 | pi_mutex = &q.pi_state->pi_mutex; |
3288 | ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter); |
3289 | |
3290 | spin_lock(q.lock_ptr); |
3291 | if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter)) |
3292 | ret = 0; |
3293 | |
3294 | debug_rt_mutex_free_waiter(&rt_waiter); |
3295 | /* |
3296 | * Fixup the pi_state owner and possibly acquire the lock if we |
3297 | * haven't already. |
3298 | */ |
3299 | res = fixup_owner(uaddr2, &q, !ret); |
3300 | /* |
3301 | * If fixup_owner() returned an error, proprogate that. If it |
3302 | * acquired the lock, clear -ETIMEDOUT or -EINTR. |
3303 | */ |
3304 | if (res) |
3305 | ret = (res < 0) ? res : 0; |
3306 | |
3307 | /* |
3308 | * If fixup_pi_state_owner() faulted and was unable to handle |
3309 | * the fault, unlock the rt_mutex and return the fault to |
3310 | * userspace. |
3311 | */ |
3312 | if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) { |
3313 | pi_state = q.pi_state; |
3314 | get_pi_state(pi_state); |
3315 | } |
3316 | |
3317 | /* Unqueue and drop the lock. */ |
3318 | unqueue_me_pi(&q); |
3319 | } |
3320 | |
3321 | if (pi_state) { |
3322 | rt_mutex_futex_unlock(&pi_state->pi_mutex); |
3323 | put_pi_state(pi_state); |
3324 | } |
3325 | |
3326 | if (ret == -EINTR) { |
3327 | /* |
3328 | * We've already been requeued, but cannot restart by calling |
3329 | * futex_lock_pi() directly. We could restart this syscall, but |
3330 | * it would detect that the user space "val" changed and return |
3331 | * -EWOULDBLOCK. Save the overhead of the restart and return |
3332 | * -EWOULDBLOCK directly. |
3333 | */ |
3334 | ret = -EWOULDBLOCK; |
3335 | } |
3336 | |
3337 | out_put_keys: |
3338 | put_futex_key(&q.key); |
3339 | out_key2: |
3340 | put_futex_key(&key2); |
3341 | |
3342 | out: |
3343 | if (to) { |
3344 | hrtimer_cancel(&to->timer); |
3345 | destroy_hrtimer_on_stack(&to->timer); |
3346 | } |
3347 | return ret; |
3348 | } |
3349 | |
3350 | /* |
3351 | * Support for robust futexes: the kernel cleans up held futexes at |
3352 | * thread exit time. |
3353 | * |
3354 | * Implementation: user-space maintains a per-thread list of locks it |
3355 | * is holding. Upon do_exit(), the kernel carefully walks this list, |
3356 | * and marks all locks that are owned by this thread with the |
3357 | * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is |
3358 | * always manipulated with the lock held, so the list is private and |
3359 | * per-thread. Userspace also maintains a per-thread 'list_op_pending' |
3360 | * field, to allow the kernel to clean up if the thread dies after |
3361 | * acquiring the lock, but just before it could have added itself to |
3362 | * the list. There can only be one such pending lock. |
3363 | */ |
3364 | |
3365 | /** |
3366 | * sys_set_robust_list() - Set the robust-futex list head of a task |
3367 | * @head: pointer to the list-head |
3368 | * @len: length of the list-head, as userspace expects |
3369 | */ |
3370 | SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head, |
3371 | size_t, len) |
3372 | { |
3373 | if (!futex_cmpxchg_enabled) |
3374 | return -ENOSYS; |
3375 | /* |
3376 | * The kernel knows only one size for now: |
3377 | */ |
3378 | if (unlikely(len != sizeof(*head))) |
3379 | return -EINVAL; |
3380 | |
3381 | current->robust_list = head; |
3382 | |
3383 | return 0; |
3384 | } |
3385 | |
3386 | /** |
3387 | * sys_get_robust_list() - Get the robust-futex list head of a task |
3388 | * @pid: pid of the process [zero for current task] |
3389 | * @head_ptr: pointer to a list-head pointer, the kernel fills it in |
3390 | * @len_ptr: pointer to a length field, the kernel fills in the header size |
3391 | */ |
3392 | SYSCALL_DEFINE3(get_robust_list, int, pid, |
3393 | struct robust_list_head __user * __user *, head_ptr, |
3394 | size_t __user *, len_ptr) |
3395 | { |
3396 | struct robust_list_head __user *head; |
3397 | unsigned long ret; |
3398 | struct task_struct *p; |
3399 | |
3400 | if (!futex_cmpxchg_enabled) |
3401 | return -ENOSYS; |
3402 | |
3403 | rcu_read_lock(); |
3404 | |
3405 | ret = -ESRCH; |
3406 | if (!pid) |
3407 | p = current; |
3408 | else { |
3409 | p = find_task_by_vpid(pid); |
3410 | if (!p) |
3411 | goto err_unlock; |
3412 | } |
3413 | |
3414 | ret = -EPERM; |
3415 | if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS)) |
3416 | goto err_unlock; |
3417 | |
3418 | head = p->robust_list; |
3419 | rcu_read_unlock(); |
3420 | |
3421 | if (put_user(sizeof(*head), len_ptr)) |
3422 | return -EFAULT; |
3423 | return put_user(head, head_ptr); |
3424 | |
3425 | err_unlock: |
3426 | rcu_read_unlock(); |
3427 | |
3428 | return ret; |
3429 | } |
3430 | |
3431 | /* |
3432 | * Process a futex-list entry, check whether it's owned by the |
3433 | * dying task, and do notification if so: |
3434 | */ |
3435 | static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi) |
3436 | { |
3437 | u32 uval, uninitialized_var(nval), mval; |
3438 | |
3439 | /* Futex address must be 32bit aligned */ |
3440 | if ((((unsigned long)uaddr) % sizeof(*uaddr)) != 0) |
3441 | return -1; |
3442 | |
3443 | retry: |
3444 | if (get_user(uval, uaddr)) |
3445 | return -1; |
3446 | |
3447 | if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) { |
3448 | /* |
3449 | * Ok, this dying thread is truly holding a futex |
3450 | * of interest. Set the OWNER_DIED bit atomically |
3451 | * via cmpxchg, and if the value had FUTEX_WAITERS |
3452 | * set, wake up a waiter (if any). (We have to do a |
3453 | * futex_wake() even if OWNER_DIED is already set - |
3454 | * to handle the rare but possible case of recursive |
3455 | * thread-death.) The rest of the cleanup is done in |
3456 | * userspace. |
3457 | */ |
3458 | mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED; |
3459 | /* |
3460 | * We are not holding a lock here, but we want to have |
3461 | * the pagefault_disable/enable() protection because |
3462 | * we want to handle the fault gracefully. If the |
3463 | * access fails we try to fault in the futex with R/W |
3464 | * verification via get_user_pages. get_user() above |
3465 | * does not guarantee R/W access. If that fails we |
3466 | * give up and leave the futex locked. |
3467 | */ |
3468 | if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) { |
3469 | if (fault_in_user_writeable(uaddr)) |
3470 | return -1; |
3471 | goto retry; |
3472 | } |
3473 | if (nval != uval) |
3474 | goto retry; |
3475 | |
3476 | /* |
3477 | * Wake robust non-PI futexes here. The wakeup of |
3478 | * PI futexes happens in exit_pi_state(): |
3479 | */ |
3480 | if (!pi && (uval & FUTEX_WAITERS)) |
3481 | futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY); |
3482 | } |
3483 | return 0; |
3484 | } |
3485 | |
3486 | /* |
3487 | * Fetch a robust-list pointer. Bit 0 signals PI futexes: |
3488 | */ |
3489 | static inline int fetch_robust_entry(struct robust_list __user **entry, |
3490 | struct robust_list __user * __user *head, |
3491 | unsigned int *pi) |
3492 | { |
3493 | unsigned long uentry; |
3494 | |
3495 | if (get_user(uentry, (unsigned long __user *)head)) |
3496 | return -EFAULT; |
3497 | |
3498 | *entry = (void __user *)(uentry & ~1UL); |
3499 | *pi = uentry & 1; |
3500 | |
3501 | return 0; |
3502 | } |
3503 | |
3504 | /* |
3505 | * Walk curr->robust_list (very carefully, it's a userspace list!) |
3506 | * and mark any locks found there dead, and notify any waiters. |
3507 | * |
3508 | * We silently return on any sign of list-walking problem. |
3509 | */ |
3510 | void exit_robust_list(struct task_struct *curr) |
3511 | { |
3512 | struct robust_list_head __user *head = curr->robust_list; |
3513 | struct robust_list __user *entry, *next_entry, *pending; |
3514 | unsigned int limit = ROBUST_LIST_LIMIT, pi, pip; |
3515 | unsigned int uninitialized_var(next_pi); |
3516 | unsigned long futex_offset; |
3517 | int rc; |
3518 | |
3519 | if (!futex_cmpxchg_enabled) |
3520 | return; |
3521 | |
3522 | /* |
3523 | * Fetch the list head (which was registered earlier, via |
3524 | * sys_set_robust_list()): |
3525 | */ |
3526 | if (fetch_robust_entry(&entry, &head->list.next, &pi)) |
3527 | return; |
3528 | /* |
3529 | * Fetch the relative futex offset: |
3530 | */ |
3531 | if (get_user(futex_offset, &head->futex_offset)) |
3532 | return; |
3533 | /* |
3534 | * Fetch any possibly pending lock-add first, and handle it |
3535 | * if it exists: |
3536 | */ |
3537 | if (fetch_robust_entry(&pending, &head->list_op_pending, &pip)) |
3538 | return; |
3539 | |
3540 | next_entry = NULL; /* avoid warning with gcc */ |
3541 | while (entry != &head->list) { |
3542 | /* |
3543 | * Fetch the next entry in the list before calling |
3544 | * handle_futex_death: |
3545 | */ |
3546 | rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi); |
3547 | /* |
3548 | * A pending lock might already be on the list, so |
3549 | * don't process it twice: |
3550 | */ |
3551 | if (entry != pending) |
3552 | if (handle_futex_death((void __user *)entry + futex_offset, |
3553 | curr, pi)) |
3554 | return; |
3555 | if (rc) |
3556 | return; |
3557 | entry = next_entry; |
3558 | pi = next_pi; |
3559 | /* |
3560 | * Avoid excessively long or circular lists: |
3561 | */ |
3562 | if (!--limit) |
3563 | break; |
3564 | |
3565 | cond_resched(); |
3566 | } |
3567 | |
3568 | if (pending) |
3569 | handle_futex_death((void __user *)pending + futex_offset, |
3570 | curr, pip); |
3571 | } |
3572 | |
3573 | long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, |
3574 | u32 __user *uaddr2, u32 val2, u32 val3) |
3575 | { |
3576 | int cmd = op & FUTEX_CMD_MASK; |
3577 | unsigned int flags = 0; |
3578 | |
3579 | if (!(op & FUTEX_PRIVATE_FLAG)) |
3580 | flags |= FLAGS_SHARED; |
3581 | |
3582 | if (op & FUTEX_CLOCK_REALTIME) { |
3583 | flags |= FLAGS_CLOCKRT; |
3584 | if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \ |
3585 | cmd != FUTEX_WAIT_REQUEUE_PI) |
3586 | return -ENOSYS; |
3587 | } |
3588 | |
3589 | switch (cmd) { |
3590 | case FUTEX_LOCK_PI: |
3591 | case FUTEX_UNLOCK_PI: |
3592 | case FUTEX_TRYLOCK_PI: |
3593 | case FUTEX_WAIT_REQUEUE_PI: |
3594 | case FUTEX_CMP_REQUEUE_PI: |
3595 | if (!futex_cmpxchg_enabled) |
3596 | return -ENOSYS; |
3597 | } |
3598 | |
3599 | switch (cmd) { |
3600 | case FUTEX_WAIT: |
3601 | val3 = FUTEX_BITSET_MATCH_ANY; |
3602 | /* fall through */ |
3603 | case FUTEX_WAIT_BITSET: |
3604 | return futex_wait(uaddr, flags, val, timeout, val3); |
3605 | case FUTEX_WAKE: |
3606 | val3 = FUTEX_BITSET_MATCH_ANY; |
3607 | /* fall through */ |
3608 | case FUTEX_WAKE_BITSET: |
3609 | return futex_wake(uaddr, flags, val, val3); |
3610 | case FUTEX_REQUEUE: |
3611 | return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0); |
3612 | case FUTEX_CMP_REQUEUE: |
3613 | return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0); |
3614 | case FUTEX_WAKE_OP: |
3615 | return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3); |
3616 | case FUTEX_LOCK_PI: |
3617 | return futex_lock_pi(uaddr, flags, timeout, 0); |
3618 | case FUTEX_UNLOCK_PI: |
3619 | return futex_unlock_pi(uaddr, flags); |
3620 | case FUTEX_TRYLOCK_PI: |
3621 | return futex_lock_pi(uaddr, flags, NULL, 1); |
3622 | case FUTEX_WAIT_REQUEUE_PI: |
3623 | val3 = FUTEX_BITSET_MATCH_ANY; |
3624 | return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3, |
3625 | uaddr2); |
3626 | case FUTEX_CMP_REQUEUE_PI: |
3627 | return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1); |
3628 | } |
3629 | return -ENOSYS; |
3630 | } |
3631 | |
3632 | |
3633 | SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, |
3634 | struct __kernel_timespec __user *, utime, u32 __user *, uaddr2, |
3635 | u32, val3) |
3636 | { |
3637 | struct timespec64 ts; |
3638 | ktime_t t, *tp = NULL; |
3639 | u32 val2 = 0; |
3640 | int cmd = op & FUTEX_CMD_MASK; |
3641 | |
3642 | if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI || |
3643 | cmd == FUTEX_WAIT_BITSET || |
3644 | cmd == FUTEX_WAIT_REQUEUE_PI)) { |
3645 | if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG)))) |
3646 | return -EFAULT; |
3647 | if (get_timespec64(&ts, utime)) |
3648 | return -EFAULT; |
3649 | if (!timespec64_valid(&ts)) |
3650 | return -EINVAL; |
3651 | |
3652 | t = timespec64_to_ktime(ts); |
3653 | if (cmd == FUTEX_WAIT) |
3654 | t = ktime_add_safe(ktime_get(), t); |
3655 | tp = &t; |
3656 | } |
3657 | /* |
3658 | * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*. |
3659 | * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP. |
3660 | */ |
3661 | if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE || |
3662 | cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP) |
3663 | val2 = (u32) (unsigned long) utime; |
3664 | |
3665 | return do_futex(uaddr, op, val, tp, uaddr2, val2, val3); |
3666 | } |
3667 | |
3668 | #ifdef CONFIG_COMPAT |
3669 | /* |
3670 | * Fetch a robust-list pointer. Bit 0 signals PI futexes: |
3671 | */ |
3672 | static inline int |
3673 | compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry, |
3674 | compat_uptr_t __user *head, unsigned int *pi) |
3675 | { |
3676 | if (get_user(*uentry, head)) |
3677 | return -EFAULT; |
3678 | |
3679 | *entry = compat_ptr((*uentry) & ~1); |
3680 | *pi = (unsigned int)(*uentry) & 1; |
3681 | |
3682 | return 0; |
3683 | } |
3684 | |
3685 | static void __user *futex_uaddr(struct robust_list __user *entry, |
3686 | compat_long_t futex_offset) |
3687 | { |
3688 | compat_uptr_t base = ptr_to_compat(entry); |
3689 | void __user *uaddr = compat_ptr(base + futex_offset); |
3690 | |
3691 | return uaddr; |
3692 | } |
3693 | |
3694 | /* |
3695 | * Walk curr->robust_list (very carefully, it's a userspace list!) |
3696 | * and mark any locks found there dead, and notify any waiters. |
3697 | * |
3698 | * We silently return on any sign of list-walking problem. |
3699 | */ |
3700 | void compat_exit_robust_list(struct task_struct *curr) |
3701 | { |
3702 | struct compat_robust_list_head __user *head = curr->compat_robust_list; |
3703 | struct robust_list __user *entry, *next_entry, *pending; |
3704 | unsigned int limit = ROBUST_LIST_LIMIT, pi, pip; |
3705 | unsigned int uninitialized_var(next_pi); |
3706 | compat_uptr_t uentry, next_uentry, upending; |
3707 | compat_long_t futex_offset; |
3708 | int rc; |
3709 | |
3710 | if (!futex_cmpxchg_enabled) |
3711 | return; |
3712 | |
3713 | /* |
3714 | * Fetch the list head (which was registered earlier, via |
3715 | * sys_set_robust_list()): |
3716 | */ |
3717 | if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &pi)) |
3718 | return; |
3719 | /* |
3720 | * Fetch the relative futex offset: |
3721 | */ |
3722 | if (get_user(futex_offset, &head->futex_offset)) |
3723 | return; |
3724 | /* |
3725 | * Fetch any possibly pending lock-add first, and handle it |
3726 | * if it exists: |
3727 | */ |
3728 | if (compat_fetch_robust_entry(&upending, &pending, |
3729 | &head->list_op_pending, &pip)) |
3730 | return; |
3731 | |
3732 | next_entry = NULL; /* avoid warning with gcc */ |
3733 | while (entry != (struct robust_list __user *) &head->list) { |
3734 | /* |
3735 | * Fetch the next entry in the list before calling |
3736 | * handle_futex_death: |
3737 | */ |
3738 | rc = compat_fetch_robust_entry(&next_uentry, &next_entry, |
3739 | (compat_uptr_t __user *)&entry->next, &next_pi); |
3740 | /* |
3741 | * A pending lock might already be on the list, so |
3742 | * dont process it twice: |
3743 | */ |
3744 | if (entry != pending) { |
3745 | void __user *uaddr = futex_uaddr(entry, futex_offset); |
3746 | |
3747 | if (handle_futex_death(uaddr, curr, pi)) |
3748 | return; |
3749 | } |
3750 | if (rc) |
3751 | return; |
3752 | uentry = next_uentry; |
3753 | entry = next_entry; |
3754 | pi = next_pi; |
3755 | /* |
3756 | * Avoid excessively long or circular lists: |
3757 | */ |
3758 | if (!--limit) |
3759 | break; |
3760 | |
3761 | cond_resched(); |
3762 | } |
3763 | if (pending) { |
3764 | void __user *uaddr = futex_uaddr(pending, futex_offset); |
3765 | |
3766 | handle_futex_death(uaddr, curr, pip); |
3767 | } |
3768 | } |
3769 | |
3770 | COMPAT_SYSCALL_DEFINE2(set_robust_list, |
3771 | struct compat_robust_list_head __user *, head, |
3772 | compat_size_t, len) |
3773 | { |
3774 | if (!futex_cmpxchg_enabled) |
3775 | return -ENOSYS; |
3776 | |
3777 | if (unlikely(len != sizeof(*head))) |
3778 | return -EINVAL; |
3779 | |
3780 | current->compat_robust_list = head; |
3781 | |
3782 | return 0; |
3783 | } |
3784 | |
3785 | COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid, |
3786 | compat_uptr_t __user *, head_ptr, |
3787 | compat_size_t __user *, len_ptr) |
3788 | { |
3789 | struct compat_robust_list_head __user *head; |
3790 | unsigned long ret; |
3791 | struct task_struct *p; |
3792 | |
3793 | if (!futex_cmpxchg_enabled) |
3794 | return -ENOSYS; |
3795 | |
3796 | rcu_read_lock(); |
3797 | |
3798 | ret = -ESRCH; |
3799 | if (!pid) |
3800 | p = current; |
3801 | else { |
3802 | p = find_task_by_vpid(pid); |
3803 | if (!p) |
3804 | goto err_unlock; |
3805 | } |
3806 | |
3807 | ret = -EPERM; |
3808 | if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS)) |
3809 | goto err_unlock; |
3810 | |
3811 | head = p->compat_robust_list; |
3812 | rcu_read_unlock(); |
3813 | |
3814 | if (put_user(sizeof(*head), len_ptr)) |
3815 | return -EFAULT; |
3816 | return put_user(ptr_to_compat(head), head_ptr); |
3817 | |
3818 | err_unlock: |
3819 | rcu_read_unlock(); |
3820 | |
3821 | return ret; |
3822 | } |
3823 | #endif /* CONFIG_COMPAT */ |
3824 | |
3825 | #ifdef CONFIG_COMPAT_32BIT_TIME |
3826 | SYSCALL_DEFINE6(futex_time32, u32 __user *, uaddr, int, op, u32, val, |
3827 | struct old_timespec32 __user *, utime, u32 __user *, uaddr2, |
3828 | u32, val3) |
3829 | { |
3830 | struct timespec64 ts; |
3831 | ktime_t t, *tp = NULL; |
3832 | int val2 = 0; |
3833 | int cmd = op & FUTEX_CMD_MASK; |
3834 | |
3835 | if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI || |
3836 | cmd == FUTEX_WAIT_BITSET || |
3837 | cmd == FUTEX_WAIT_REQUEUE_PI)) { |
3838 | if (get_old_timespec32(&ts, utime)) |
3839 | return -EFAULT; |
3840 | if (!timespec64_valid(&ts)) |
3841 | return -EINVAL; |
3842 | |
3843 | t = timespec64_to_ktime(ts); |
3844 | if (cmd == FUTEX_WAIT) |
3845 | t = ktime_add_safe(ktime_get(), t); |
3846 | tp = &t; |
3847 | } |
3848 | if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE || |
3849 | cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP) |
3850 | val2 = (int) (unsigned long) utime; |
3851 | |
3852 | return do_futex(uaddr, op, val, tp, uaddr2, val2, val3); |
3853 | } |
3854 | #endif /* CONFIG_COMPAT_32BIT_TIME */ |
3855 | |
3856 | static void __init futex_detect_cmpxchg(void) |
3857 | { |
3858 | #ifndef CONFIG_HAVE_FUTEX_CMPXCHG |
3859 | u32 curval; |
3860 | |
3861 | /* |
3862 | * This will fail and we want it. Some arch implementations do |
3863 | * runtime detection of the futex_atomic_cmpxchg_inatomic() |
3864 | * functionality. We want to know that before we call in any |
3865 | * of the complex code paths. Also we want to prevent |
3866 | * registration of robust lists in that case. NULL is |
3867 | * guaranteed to fault and we get -EFAULT on functional |
3868 | * implementation, the non-functional ones will return |
3869 | * -ENOSYS. |
3870 | */ |
3871 | if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT) |
3872 | futex_cmpxchg_enabled = 1; |
3873 | #endif |
3874 | } |
3875 | |
3876 | static int __init futex_init(void) |
3877 | { |
3878 | unsigned int futex_shift; |
3879 | unsigned long i; |
3880 | |
3881 | #if CONFIG_BASE_SMALL |
3882 | futex_hashsize = 16; |
3883 | #else |
3884 | futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus()); |
3885 | #endif |
3886 | |
3887 | futex_queues = alloc_large_system_hash("futex" , sizeof(*futex_queues), |
3888 | futex_hashsize, 0, |
3889 | futex_hashsize < 256 ? HASH_SMALL : 0, |
3890 | &futex_shift, NULL, |
3891 | futex_hashsize, futex_hashsize); |
3892 | futex_hashsize = 1UL << futex_shift; |
3893 | |
3894 | futex_detect_cmpxchg(); |
3895 | |
3896 | for (i = 0; i < futex_hashsize; i++) { |
3897 | atomic_set(&futex_queues[i].waiters, 0); |
3898 | plist_head_init(&futex_queues[i].chain); |
3899 | spin_lock_init(&futex_queues[i].lock); |
3900 | } |
3901 | |
3902 | return 0; |
3903 | } |
3904 | core_initcall(futex_init); |
3905 | |