Branch data Line data Source code
1 : : // SPDX-License-Identifier: GPL-2.0-or-later
2 : : /*
3 : : * Fast Userspace Mutexes (which I call "Futexes!").
4 : : * (C) Rusty Russell, IBM 2002
5 : : *
6 : : * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
7 : : * (C) Copyright 2003 Red Hat Inc, All Rights Reserved
8 : : *
9 : : * Removed page pinning, fix privately mapped COW pages and other cleanups
10 : : * (C) Copyright 2003, 2004 Jamie Lokier
11 : : *
12 : : * Robust futex support started by Ingo Molnar
13 : : * (C) Copyright 2006 Red Hat Inc, All Rights Reserved
14 : : * Thanks to Thomas Gleixner for suggestions, analysis and fixes.
15 : : *
16 : : * PI-futex support started by Ingo Molnar and Thomas Gleixner
17 : : * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
18 : : * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
19 : : *
20 : : * PRIVATE futexes by Eric Dumazet
21 : : * Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
22 : : *
23 : : * Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
24 : : * Copyright (C) IBM Corporation, 2009
25 : : * Thanks to Thomas Gleixner for conceptual design and careful reviews.
26 : : *
27 : : * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
28 : : * enough at me, Linus for the original (flawed) idea, Matthew
29 : : * Kirkwood for proof-of-concept implementation.
30 : : *
31 : : * "The futexes are also cursed."
32 : : * "But they come in a choice of three flavours!"
33 : : */
34 : : #include <linux/compat.h>
35 : : #include <linux/slab.h>
36 : : #include <linux/poll.h>
37 : : #include <linux/fs.h>
38 : : #include <linux/file.h>
39 : : #include <linux/jhash.h>
40 : : #include <linux/init.h>
41 : : #include <linux/futex.h>
42 : : #include <linux/mount.h>
43 : : #include <linux/pagemap.h>
44 : : #include <linux/syscalls.h>
45 : : #include <linux/signal.h>
46 : : #include <linux/export.h>
47 : : #include <linux/magic.h>
48 : : #include <linux/pid.h>
49 : : #include <linux/nsproxy.h>
50 : : #include <linux/ptrace.h>
51 : : #include <linux/sched/rt.h>
52 : : #include <linux/sched/wake_q.h>
53 : : #include <linux/sched/mm.h>
54 : : #include <linux/hugetlb.h>
55 : : #include <linux/freezer.h>
56 : : #include <linux/memblock.h>
57 : : #include <linux/fault-inject.h>
58 : : #include <linux/refcount.h>
59 : :
60 : : #include <asm/futex.h>
61 : :
62 : : #include "locking/rtmutex_common.h"
63 : :
64 : : /*
65 : : * READ this before attempting to hack on futexes!
66 : : *
67 : : * Basic futex operation and ordering guarantees
68 : : * =============================================
69 : : *
70 : : * The waiter reads the futex value in user space and calls
71 : : * futex_wait(). This function computes the hash bucket and acquires
72 : : * the hash bucket lock. After that it reads the futex user space value
73 : : * again and verifies that the data has not changed. If it has not changed
74 : : * it enqueues itself into the hash bucket, releases the hash bucket lock
75 : : * and schedules.
76 : : *
77 : : * The waker side modifies the user space value of the futex and calls
78 : : * futex_wake(). This function computes the hash bucket and acquires the
79 : : * hash bucket lock. Then it looks for waiters on that futex in the hash
80 : : * bucket and wakes them.
81 : : *
82 : : * In futex wake up scenarios where no tasks are blocked on a futex, taking
83 : : * the hb spinlock can be avoided and simply return. In order for this
84 : : * optimization to work, ordering guarantees must exist so that the waiter
85 : : * being added to the list is acknowledged when the list is concurrently being
86 : : * checked by the waker, avoiding scenarios like the following:
87 : : *
88 : : * CPU 0 CPU 1
89 : : * val = *futex;
90 : : * sys_futex(WAIT, futex, val);
91 : : * futex_wait(futex, val);
92 : : * uval = *futex;
93 : : * *futex = newval;
94 : : * sys_futex(WAKE, futex);
95 : : * futex_wake(futex);
96 : : * if (queue_empty())
97 : : * return;
98 : : * if (uval == val)
99 : : * lock(hash_bucket(futex));
100 : : * queue();
101 : : * unlock(hash_bucket(futex));
102 : : * schedule();
103 : : *
104 : : * This would cause the waiter on CPU 0 to wait forever because it
105 : : * missed the transition of the user space value from val to newval
106 : : * and the waker did not find the waiter in the hash bucket queue.
107 : : *
108 : : * The correct serialization ensures that a waiter either observes
109 : : * the changed user space value before blocking or is woken by a
110 : : * concurrent waker:
111 : : *
112 : : * CPU 0 CPU 1
113 : : * val = *futex;
114 : : * sys_futex(WAIT, futex, val);
115 : : * futex_wait(futex, val);
116 : : *
117 : : * waiters++; (a)
118 : : * smp_mb(); (A) <-- paired with -.
119 : : * |
120 : : * lock(hash_bucket(futex)); |
121 : : * |
122 : : * uval = *futex; |
123 : : * | *futex = newval;
124 : : * | sys_futex(WAKE, futex);
125 : : * | futex_wake(futex);
126 : : * |
127 : : * `--------> smp_mb(); (B)
128 : : * if (uval == val)
129 : : * queue();
130 : : * unlock(hash_bucket(futex));
131 : : * schedule(); if (waiters)
132 : : * lock(hash_bucket(futex));
133 : : * else wake_waiters(futex);
134 : : * waiters--; (b) unlock(hash_bucket(futex));
135 : : *
136 : : * Where (A) orders the waiters increment and the futex value read through
137 : : * atomic operations (see hb_waiters_inc) and where (B) orders the write
138 : : * to futex and the waiters read -- this is done by the barriers for both
139 : : * shared and private futexes in get_futex_key_refs().
140 : : *
141 : : * This yields the following case (where X:=waiters, Y:=futex):
142 : : *
143 : : * X = Y = 0
144 : : *
145 : : * w[X]=1 w[Y]=1
146 : : * MB MB
147 : : * r[Y]=y r[X]=x
148 : : *
149 : : * Which guarantees that x==0 && y==0 is impossible; which translates back into
150 : : * the guarantee that we cannot both miss the futex variable change and the
151 : : * enqueue.
152 : : *
153 : : * Note that a new waiter is accounted for in (a) even when it is possible that
154 : : * the wait call can return error, in which case we backtrack from it in (b).
155 : : * Refer to the comment in queue_lock().
156 : : *
157 : : * Similarly, in order to account for waiters being requeued on another
158 : : * address we always increment the waiters for the destination bucket before
159 : : * acquiring the lock. It then decrements them again after releasing it -
160 : : * the code that actually moves the futex(es) between hash buckets (requeue_futex)
161 : : * will do the additional required waiter count housekeeping. This is done for
162 : : * double_lock_hb() and double_unlock_hb(), respectively.
163 : : */
164 : :
165 : : #ifdef CONFIG_HAVE_FUTEX_CMPXCHG
166 : : #define futex_cmpxchg_enabled 1
167 : : #else
168 : : static int __read_mostly futex_cmpxchg_enabled;
169 : : #endif
170 : :
171 : : /*
172 : : * Futex flags used to encode options to functions and preserve them across
173 : : * restarts.
174 : : */
175 : : #ifdef CONFIG_MMU
176 : : # define FLAGS_SHARED 0x01
177 : : #else
178 : : /*
179 : : * NOMMU does not have per process address space. Let the compiler optimize
180 : : * code away.
181 : : */
182 : : # define FLAGS_SHARED 0x00
183 : : #endif
184 : : #define FLAGS_CLOCKRT 0x02
185 : : #define FLAGS_HAS_TIMEOUT 0x04
186 : :
187 : : /*
188 : : * Priority Inheritance state:
189 : : */
190 : : struct futex_pi_state {
191 : : /*
192 : : * list of 'owned' pi_state instances - these have to be
193 : : * cleaned up in do_exit() if the task exits prematurely:
194 : : */
195 : : struct list_head list;
196 : :
197 : : /*
198 : : * The PI object:
199 : : */
200 : : struct rt_mutex pi_mutex;
201 : :
202 : : struct task_struct *owner;
203 : : refcount_t refcount;
204 : :
205 : : union futex_key key;
206 : : } __randomize_layout;
207 : :
208 : : /**
209 : : * struct futex_q - The hashed futex queue entry, one per waiting task
210 : : * @list: priority-sorted list of tasks waiting on this futex
211 : : * @task: the task waiting on the futex
212 : : * @lock_ptr: the hash bucket lock
213 : : * @key: the key the futex is hashed on
214 : : * @pi_state: optional priority inheritance state
215 : : * @rt_waiter: rt_waiter storage for use with requeue_pi
216 : : * @requeue_pi_key: the requeue_pi target futex key
217 : : * @bitset: bitset for the optional bitmasked wakeup
218 : : *
219 : : * We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so
220 : : * we can wake only the relevant ones (hashed queues may be shared).
221 : : *
222 : : * A futex_q has a woken state, just like tasks have TASK_RUNNING.
223 : : * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
224 : : * The order of wakeup is always to make the first condition true, then
225 : : * the second.
226 : : *
227 : : * PI futexes are typically woken before they are removed from the hash list via
228 : : * the rt_mutex code. See unqueue_me_pi().
229 : : */
230 : : struct futex_q {
231 : : struct plist_node list;
232 : :
233 : : struct task_struct *task;
234 : : spinlock_t *lock_ptr;
235 : : union futex_key key;
236 : : struct futex_pi_state *pi_state;
237 : : struct rt_mutex_waiter *rt_waiter;
238 : : union futex_key *requeue_pi_key;
239 : : u32 bitset;
240 : : } __randomize_layout;
241 : :
242 : : static const struct futex_q futex_q_init = {
243 : : /* list gets initialized in queue_me()*/
244 : : .key = FUTEX_KEY_INIT,
245 : : .bitset = FUTEX_BITSET_MATCH_ANY
246 : : };
247 : :
248 : : /*
249 : : * Hash buckets are shared by all the futex_keys that hash to the same
250 : : * location. Each key may have multiple futex_q structures, one for each task
251 : : * waiting on a futex.
252 : : */
253 : : struct futex_hash_bucket {
254 : : atomic_t waiters;
255 : : spinlock_t lock;
256 : : struct plist_head chain;
257 : : } ____cacheline_aligned_in_smp;
258 : :
259 : : /*
260 : : * The base of the bucket array and its size are always used together
261 : : * (after initialization only in hash_futex()), so ensure that they
262 : : * reside in the same cacheline.
263 : : */
264 : : static struct {
265 : : struct futex_hash_bucket *queues;
266 : : unsigned long hashsize;
267 : : } __futex_data __read_mostly __aligned(2*sizeof(long));
268 : : #define futex_queues (__futex_data.queues)
269 : : #define futex_hashsize (__futex_data.hashsize)
270 : :
271 : :
272 : : /*
273 : : * Fault injections for futexes.
274 : : */
275 : : #ifdef CONFIG_FAIL_FUTEX
276 : :
277 : : static struct {
278 : : struct fault_attr attr;
279 : :
280 : : bool ignore_private;
281 : : } fail_futex = {
282 : : .attr = FAULT_ATTR_INITIALIZER,
283 : : .ignore_private = false,
284 : : };
285 : :
286 : : static int __init setup_fail_futex(char *str)
287 : : {
288 : : return setup_fault_attr(&fail_futex.attr, str);
289 : : }
290 : : __setup("fail_futex=", setup_fail_futex);
291 : :
292 : : static bool should_fail_futex(bool fshared)
293 : : {
294 : : if (fail_futex.ignore_private && !fshared)
295 : : return false;
296 : :
297 : : return should_fail(&fail_futex.attr, 1);
298 : : }
299 : :
300 : : #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
301 : :
302 : : static int __init fail_futex_debugfs(void)
303 : : {
304 : : umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
305 : : struct dentry *dir;
306 : :
307 : : dir = fault_create_debugfs_attr("fail_futex", NULL,
308 : : &fail_futex.attr);
309 : : if (IS_ERR(dir))
310 : : return PTR_ERR(dir);
311 : :
312 : : debugfs_create_bool("ignore-private", mode, dir,
313 : : &fail_futex.ignore_private);
314 : : return 0;
315 : : }
316 : :
317 : : late_initcall(fail_futex_debugfs);
318 : :
319 : : #endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
320 : :
321 : : #else
322 : : static inline bool should_fail_futex(bool fshared)
323 : : {
324 : : return false;
325 : : }
326 : : #endif /* CONFIG_FAIL_FUTEX */
327 : :
328 : : #ifdef CONFIG_COMPAT
329 : : static void compat_exit_robust_list(struct task_struct *curr);
330 : : #else
331 : : static inline void compat_exit_robust_list(struct task_struct *curr) { }
332 : : #endif
333 : :
334 : 3 : static inline void futex_get_mm(union futex_key *key)
335 : : {
336 : 3 : mmgrab(key->private.mm);
337 : : /*
338 : : * Ensure futex_get_mm() implies a full barrier such that
339 : : * get_futex_key() implies a full barrier. This is relied upon
340 : : * as smp_mb(); (B), see the ordering comment above.
341 : : */
342 : 3 : smp_mb__after_atomic();
343 : 3 : }
344 : :
345 : : /*
346 : : * Reflects a new waiter being added to the waitqueue.
347 : : */
348 : 3 : static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
349 : : {
350 : : #ifdef CONFIG_SMP
351 : 3 : atomic_inc(&hb->waiters);
352 : : /*
353 : : * Full barrier (A), see the ordering comment above.
354 : : */
355 : 3 : smp_mb__after_atomic();
356 : : #endif
357 : 3 : }
358 : :
359 : : /*
360 : : * Reflects a waiter being removed from the waitqueue by wakeup
361 : : * paths.
362 : : */
363 : : static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
364 : : {
365 : : #ifdef CONFIG_SMP
366 : 3 : atomic_dec(&hb->waiters);
367 : : #endif
368 : : }
369 : :
370 : : static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
371 : : {
372 : : #ifdef CONFIG_SMP
373 : : return atomic_read(&hb->waiters);
374 : : #else
375 : : return 1;
376 : : #endif
377 : : }
378 : :
379 : : /**
380 : : * hash_futex - Return the hash bucket in the global hash
381 : : * @key: Pointer to the futex key for which the hash is calculated
382 : : *
383 : : * We hash on the keys returned from get_futex_key (see below) and return the
384 : : * corresponding hash bucket in the global hash.
385 : : */
386 : 3 : static struct futex_hash_bucket *hash_futex(union futex_key *key)
387 : : {
388 : 3 : u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
389 : : key->both.offset);
390 : :
391 : 3 : return &futex_queues[hash & (futex_hashsize - 1)];
392 : : }
393 : :
394 : :
395 : : /**
396 : : * match_futex - Check whether two futex keys are equal
397 : : * @key1: Pointer to key1
398 : : * @key2: Pointer to key2
399 : : *
400 : : * Return 1 if two futex_keys are equal, 0 otherwise.
401 : : */
402 : : static inline int match_futex(union futex_key *key1, union futex_key *key2)
403 : : {
404 : 0 : return (key1 && key2
405 : 3 : && key1->both.word == key2->both.word
406 : 3 : && key1->both.ptr == key2->both.ptr
407 : 3 : && key1->both.offset == key2->both.offset);
408 : : }
409 : :
410 : : /*
411 : : * Take a reference to the resource addressed by a key.
412 : : * Can be called while holding spinlocks.
413 : : *
414 : : */
415 : 3 : static void get_futex_key_refs(union futex_key *key)
416 : : {
417 : 3 : if (!key->both.ptr)
418 : : return;
419 : :
420 : : /*
421 : : * On MMU less systems futexes are always "private" as there is no per
422 : : * process address space. We need the smp wmb nevertheless - yes,
423 : : * arch/blackfin has MMU less SMP ...
424 : : */
425 : : if (!IS_ENABLED(CONFIG_MMU)) {
426 : : smp_mb(); /* explicit smp_mb(); (B) */
427 : : return;
428 : : }
429 : :
430 : 3 : switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
431 : : case FUT_OFF_INODE:
432 : 0 : smp_mb(); /* explicit smp_mb(); (B) */
433 : 0 : break;
434 : : case FUT_OFF_MMSHARED:
435 : 3 : futex_get_mm(key); /* implies smp_mb(); (B) */
436 : 3 : break;
437 : : default:
438 : : /*
439 : : * Private futexes do not hold reference on an inode or
440 : : * mm, therefore the only purpose of calling get_futex_key_refs
441 : : * is because we need the barrier for the lockless waiter check.
442 : : */
443 : 3 : smp_mb(); /* explicit smp_mb(); (B) */
444 : : }
445 : : }
446 : :
447 : : /*
448 : : * Drop a reference to the resource addressed by a key.
449 : : * The hash bucket spinlock must not be held. This is
450 : : * a no-op for private futexes, see comment in the get
451 : : * counterpart.
452 : : */
453 : 3 : static void drop_futex_key_refs(union futex_key *key)
454 : : {
455 : 3 : if (!key->both.ptr) {
456 : : /* If we're here then we tried to put a key we failed to get */
457 : 0 : WARN_ON_ONCE(1);
458 : : return;
459 : : }
460 : :
461 : : if (!IS_ENABLED(CONFIG_MMU))
462 : : return;
463 : :
464 : 3 : switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
465 : : case FUT_OFF_INODE:
466 : : break;
467 : : case FUT_OFF_MMSHARED:
468 : 3 : mmdrop(key->private.mm);
469 : 3 : break;
470 : : }
471 : : }
472 : :
473 : : enum futex_access {
474 : : FUTEX_READ,
475 : : FUTEX_WRITE
476 : : };
477 : :
478 : : /**
479 : : * futex_setup_timer - set up the sleeping hrtimer.
480 : : * @time: ptr to the given timeout value
481 : : * @timeout: the hrtimer_sleeper structure to be set up
482 : : * @flags: futex flags
483 : : * @range_ns: optional range in ns
484 : : *
485 : : * Return: Initialized hrtimer_sleeper structure or NULL if no timeout
486 : : * value given
487 : : */
488 : : static inline struct hrtimer_sleeper *
489 : 3 : futex_setup_timer(ktime_t *time, struct hrtimer_sleeper *timeout,
490 : : int flags, u64 range_ns)
491 : : {
492 : 3 : if (!time)
493 : : return NULL;
494 : :
495 : 3 : hrtimer_init_sleeper_on_stack(timeout, (flags & FLAGS_CLOCKRT) ?
496 : : CLOCK_REALTIME : CLOCK_MONOTONIC,
497 : : HRTIMER_MODE_ABS);
498 : : /*
499 : : * If range_ns is 0, calling hrtimer_set_expires_range_ns() is
500 : : * effectively the same as calling hrtimer_set_expires().
501 : : */
502 : 3 : hrtimer_set_expires_range_ns(&timeout->timer, *time, range_ns);
503 : :
504 : 3 : return timeout;
505 : : }
506 : :
507 : : /*
508 : : * Generate a machine wide unique identifier for this inode.
509 : : *
510 : : * This relies on u64 not wrapping in the life-time of the machine; which with
511 : : * 1ns resolution means almost 585 years.
512 : : *
513 : : * This further relies on the fact that a well formed program will not unmap
514 : : * the file while it has a (shared) futex waiting on it. This mapping will have
515 : : * a file reference which pins the mount and inode.
516 : : *
517 : : * If for some reason an inode gets evicted and read back in again, it will get
518 : : * a new sequence number and will _NOT_ match, even though it is the exact same
519 : : * file.
520 : : *
521 : : * It is important that match_futex() will never have a false-positive, esp.
522 : : * for PI futexes that can mess up the state. The above argues that false-negatives
523 : : * are only possible for malformed programs.
524 : : */
525 : 0 : static u64 get_inode_sequence_number(struct inode *inode)
526 : : {
527 : : static atomic64_t i_seq;
528 : : u64 old;
529 : :
530 : : /* Does the inode already have a sequence number? */
531 : 0 : old = atomic64_read(&inode->i_sequence);
532 : 0 : if (likely(old))
533 : : return old;
534 : :
535 : : for (;;) {
536 : 0 : u64 new = atomic64_add_return(1, &i_seq);
537 : 0 : if (WARN_ON_ONCE(!new))
538 : 0 : continue;
539 : :
540 : 0 : old = atomic64_cmpxchg_relaxed(&inode->i_sequence, 0, new);
541 : 0 : if (old)
542 : : return old;
543 : 0 : return new;
544 : 0 : }
545 : : }
546 : :
547 : : /**
548 : : * get_futex_key() - Get parameters which are the keys for a futex
549 : : * @uaddr: virtual address of the futex
550 : : * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
551 : : * @key: address where result is stored.
552 : : * @rw: mapping needs to be read/write (values: FUTEX_READ,
553 : : * FUTEX_WRITE)
554 : : *
555 : : * Return: a negative error code or 0
556 : : *
557 : : * The key words are stored in @key on success.
558 : : *
559 : : * For shared mappings (when @fshared), the key is:
560 : : * ( inode->i_sequence, page->index, offset_within_page )
561 : : * [ also see get_inode_sequence_number() ]
562 : : *
563 : : * For private mappings (or when !@fshared), the key is:
564 : : * ( current->mm, address, 0 )
565 : : *
566 : : * This allows (cross process, where applicable) identification of the futex
567 : : * without keeping the page pinned for the duration of the FUTEX_WAIT.
568 : : *
569 : : * lock_page() might sleep, the caller should not hold a spinlock.
570 : : */
571 : : static int
572 : 3 : get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, enum futex_access rw)
573 : : {
574 : 3 : unsigned long address = (unsigned long)uaddr;
575 : 3 : struct mm_struct *mm = current->mm;
576 : : struct page *page, *tail;
577 : : struct address_space *mapping;
578 : : int err, ro = 0;
579 : :
580 : : /*
581 : : * The futex address must be "naturally" aligned.
582 : : */
583 : 3 : key->both.offset = address % PAGE_SIZE;
584 : 3 : if (unlikely((address % sizeof(u32)) != 0))
585 : : return -EINVAL;
586 : 3 : address -= key->both.offset;
587 : :
588 : 3 : if (unlikely(!access_ok(uaddr, sizeof(u32))))
589 : : return -EFAULT;
590 : :
591 : : if (unlikely(should_fail_futex(fshared)))
592 : : return -EFAULT;
593 : :
594 : : /*
595 : : * PROCESS_PRIVATE futexes are fast.
596 : : * As the mm cannot disappear under us and the 'key' only needs
597 : : * virtual address, we dont even have to find the underlying vma.
598 : : * Note : We do have to check 'uaddr' is a valid user address,
599 : : * but access_ok() should be faster than find_vma()
600 : : */
601 : 3 : if (!fshared) {
602 : 3 : key->private.mm = mm;
603 : 3 : key->private.address = address;
604 : 3 : get_futex_key_refs(key); /* implies smp_mb(); (B) */
605 : 3 : return 0;
606 : : }
607 : :
608 : : again:
609 : : /* Ignore any VERIFY_READ mapping (futex common case) */
610 : : if (unlikely(should_fail_futex(fshared)))
611 : : return -EFAULT;
612 : :
613 : 3 : err = get_user_pages_fast(address, 1, FOLL_WRITE, &page);
614 : : /*
615 : : * If write access is not required (eg. FUTEX_WAIT), try
616 : : * and get read-only access.
617 : : */
618 : 3 : if (err == -EFAULT && rw == FUTEX_READ) {
619 : 0 : err = get_user_pages_fast(address, 1, 0, &page);
620 : : ro = 1;
621 : : }
622 : 3 : if (err < 0)
623 : 0 : return err;
624 : : else
625 : : err = 0;
626 : :
627 : : /*
628 : : * The treatment of mapping from this point on is critical. The page
629 : : * lock protects many things but in this context the page lock
630 : : * stabilizes mapping, prevents inode freeing in the shared
631 : : * file-backed region case and guards against movement to swap cache.
632 : : *
633 : : * Strictly speaking the page lock is not needed in all cases being
634 : : * considered here and page lock forces unnecessarily serialization
635 : : * From this point on, mapping will be re-verified if necessary and
636 : : * page lock will be acquired only if it is unavoidable
637 : : *
638 : : * Mapping checks require the head page for any compound page so the
639 : : * head page and mapping is looked up now. For anonymous pages, it
640 : : * does not matter if the page splits in the future as the key is
641 : : * based on the address. For filesystem-backed pages, the tail is
642 : : * required as the index of the page determines the key. For
643 : : * base pages, there is no tail page and tail == page.
644 : : */
645 : 3 : tail = page;
646 : 3 : page = compound_head(page);
647 : 3 : mapping = READ_ONCE(page->mapping);
648 : :
649 : : /*
650 : : * If page->mapping is NULL, then it cannot be a PageAnon
651 : : * page; but it might be the ZERO_PAGE or in the gate area or
652 : : * in a special mapping (all cases which we are happy to fail);
653 : : * or it may have been a good file page when get_user_pages_fast
654 : : * found it, but truncated or holepunched or subjected to
655 : : * invalidate_complete_page2 before we got the page lock (also
656 : : * cases which we are happy to fail). And we hold a reference,
657 : : * so refcount care in invalidate_complete_page's remove_mapping
658 : : * prevents drop_caches from setting mapping to NULL beneath us.
659 : : *
660 : : * The case we do have to guard against is when memory pressure made
661 : : * shmem_writepage move it from filecache to swapcache beneath us:
662 : : * an unlikely race, but we do need to retry for page->mapping.
663 : : */
664 : 3 : if (unlikely(!mapping)) {
665 : : int shmem_swizzled;
666 : :
667 : : /*
668 : : * Page lock is required to identify which special case above
669 : : * applies. If this is really a shmem page then the page lock
670 : : * will prevent unexpected transitions.
671 : : */
672 : 0 : lock_page(page);
673 : 0 : shmem_swizzled = PageSwapCache(page) || page->mapping;
674 : 0 : unlock_page(page);
675 : 0 : put_page(page);
676 : :
677 : 0 : if (shmem_swizzled)
678 : : goto again;
679 : :
680 : : return -EFAULT;
681 : : }
682 : :
683 : : /*
684 : : * Private mappings are handled in a simple way.
685 : : *
686 : : * If the futex key is stored on an anonymous page, then the associated
687 : : * object is the mm which is implicitly pinned by the calling process.
688 : : *
689 : : * NOTE: When userspace waits on a MAP_SHARED mapping, even if
690 : : * it's a read-only handle, it's expected that futexes attach to
691 : : * the object not the particular process.
692 : : */
693 : 3 : if (PageAnon(page)) {
694 : : /*
695 : : * A RO anonymous page will never change and thus doesn't make
696 : : * sense for futex operations.
697 : : */
698 : 3 : if (unlikely(should_fail_futex(fshared)) || ro) {
699 : : err = -EFAULT;
700 : : goto out;
701 : : }
702 : :
703 : 3 : key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
704 : 3 : key->private.mm = mm;
705 : 3 : key->private.address = address;
706 : :
707 : : } else {
708 : : struct inode *inode;
709 : :
710 : : /*
711 : : * The associated futex object in this case is the inode and
712 : : * the page->mapping must be traversed. Ordinarily this should
713 : : * be stabilised under page lock but it's not strictly
714 : : * necessary in this case as we just want to pin the inode, not
715 : : * update the radix tree or anything like that.
716 : : *
717 : : * The RCU read lock is taken as the inode is finally freed
718 : : * under RCU. If the mapping still matches expectations then the
719 : : * mapping->host can be safely accessed as being a valid inode.
720 : : */
721 : : rcu_read_lock();
722 : :
723 : 0 : if (READ_ONCE(page->mapping) != mapping) {
724 : : rcu_read_unlock();
725 : 0 : put_page(page);
726 : :
727 : 0 : goto again;
728 : : }
729 : :
730 : 0 : inode = READ_ONCE(mapping->host);
731 : 0 : if (!inode) {
732 : : rcu_read_unlock();
733 : 0 : put_page(page);
734 : :
735 : 0 : goto again;
736 : : }
737 : :
738 : 0 : key->both.offset |= FUT_OFF_INODE; /* inode-based key */
739 : 0 : key->shared.i_seq = get_inode_sequence_number(inode);
740 : 0 : key->shared.pgoff = basepage_index(tail);
741 : : rcu_read_unlock();
742 : : }
743 : :
744 : 3 : get_futex_key_refs(key); /* implies smp_mb(); (B) */
745 : :
746 : : out:
747 : 3 : put_page(page);
748 : 3 : return err;
749 : : }
750 : :
751 : : static inline void put_futex_key(union futex_key *key)
752 : : {
753 : 3 : drop_futex_key_refs(key);
754 : : }
755 : :
756 : : /**
757 : : * fault_in_user_writeable() - Fault in user address and verify RW access
758 : : * @uaddr: pointer to faulting user space address
759 : : *
760 : : * Slow path to fixup the fault we just took in the atomic write
761 : : * access to @uaddr.
762 : : *
763 : : * We have no generic implementation of a non-destructive write to the
764 : : * user address. We know that we faulted in the atomic pagefault
765 : : * disabled section so we can as well avoid the #PF overhead by
766 : : * calling get_user_pages() right away.
767 : : */
768 : 0 : static int fault_in_user_writeable(u32 __user *uaddr)
769 : : {
770 : 0 : struct mm_struct *mm = current->mm;
771 : : int ret;
772 : :
773 : 0 : down_read(&mm->mmap_sem);
774 : 0 : ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
775 : : FAULT_FLAG_WRITE, NULL);
776 : 0 : up_read(&mm->mmap_sem);
777 : :
778 : 0 : return ret < 0 ? ret : 0;
779 : : }
780 : :
781 : : /**
782 : : * futex_top_waiter() - Return the highest priority waiter on a futex
783 : : * @hb: the hash bucket the futex_q's reside in
784 : : * @key: the futex key (to distinguish it from other futex futex_q's)
785 : : *
786 : : * Must be called with the hb lock held.
787 : : */
788 : 0 : static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
789 : : union futex_key *key)
790 : : {
791 : : struct futex_q *this;
792 : :
793 : 0 : plist_for_each_entry(this, &hb->chain, list) {
794 : 0 : if (match_futex(&this->key, key))
795 : 0 : return this;
796 : : }
797 : : return NULL;
798 : : }
799 : :
800 : 3 : static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
801 : : u32 uval, u32 newval)
802 : : {
803 : : int ret;
804 : :
805 : : pagefault_disable();
806 : 3 : ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
807 : : pagefault_enable();
808 : :
809 : 3 : return ret;
810 : : }
811 : :
812 : 3 : static int get_futex_value_locked(u32 *dest, u32 __user *from)
813 : : {
814 : : int ret;
815 : :
816 : : pagefault_disable();
817 : 3 : ret = __get_user(*dest, from);
818 : : pagefault_enable();
819 : :
820 : 3 : return ret ? -EFAULT : 0;
821 : : }
822 : :
823 : :
824 : : /*
825 : : * PI code:
826 : : */
827 : 0 : static int refill_pi_state_cache(void)
828 : : {
829 : : struct futex_pi_state *pi_state;
830 : :
831 : 0 : if (likely(current->pi_state_cache))
832 : : return 0;
833 : :
834 : 0 : pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
835 : :
836 : 0 : if (!pi_state)
837 : : return -ENOMEM;
838 : :
839 : 0 : INIT_LIST_HEAD(&pi_state->list);
840 : : /* pi_mutex gets initialized later */
841 : 0 : pi_state->owner = NULL;
842 : : refcount_set(&pi_state->refcount, 1);
843 : 0 : pi_state->key = FUTEX_KEY_INIT;
844 : :
845 : 0 : current->pi_state_cache = pi_state;
846 : :
847 : 0 : return 0;
848 : : }
849 : :
850 : 0 : static struct futex_pi_state *alloc_pi_state(void)
851 : : {
852 : 0 : struct futex_pi_state *pi_state = current->pi_state_cache;
853 : :
854 : 0 : WARN_ON(!pi_state);
855 : 0 : current->pi_state_cache = NULL;
856 : :
857 : 0 : return pi_state;
858 : : }
859 : :
860 : 0 : static void get_pi_state(struct futex_pi_state *pi_state)
861 : : {
862 : 0 : WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount));
863 : 0 : }
864 : :
865 : : /*
866 : : * Drops a reference to the pi_state object and frees or caches it
867 : : * when the last reference is gone.
868 : : */
869 : 0 : static void put_pi_state(struct futex_pi_state *pi_state)
870 : : {
871 : 0 : if (!pi_state)
872 : : return;
873 : :
874 : 0 : if (!refcount_dec_and_test(&pi_state->refcount))
875 : : return;
876 : :
877 : : /*
878 : : * If pi_state->owner is NULL, the owner is most probably dying
879 : : * and has cleaned up the pi_state already
880 : : */
881 : 0 : if (pi_state->owner) {
882 : : struct task_struct *owner;
883 : :
884 : 0 : raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
885 : 0 : owner = pi_state->owner;
886 : 0 : if (owner) {
887 : 0 : raw_spin_lock(&owner->pi_lock);
888 : 0 : list_del_init(&pi_state->list);
889 : : raw_spin_unlock(&owner->pi_lock);
890 : : }
891 : 0 : rt_mutex_proxy_unlock(&pi_state->pi_mutex, owner);
892 : 0 : raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
893 : : }
894 : :
895 : 0 : if (current->pi_state_cache) {
896 : 0 : kfree(pi_state);
897 : : } else {
898 : : /*
899 : : * pi_state->list is already empty.
900 : : * clear pi_state->owner.
901 : : * refcount is at 0 - put it back to 1.
902 : : */
903 : 0 : pi_state->owner = NULL;
904 : : refcount_set(&pi_state->refcount, 1);
905 : 0 : current->pi_state_cache = pi_state;
906 : : }
907 : : }
908 : :
909 : : #ifdef CONFIG_FUTEX_PI
910 : :
911 : : /*
912 : : * This task is holding PI mutexes at exit time => bad.
913 : : * Kernel cleans up PI-state, but userspace is likely hosed.
914 : : * (Robust-futex cleanup is separate and might save the day for userspace.)
915 : : */
916 : 0 : static void exit_pi_state_list(struct task_struct *curr)
917 : : {
918 : 0 : struct list_head *next, *head = &curr->pi_state_list;
919 : : struct futex_pi_state *pi_state;
920 : : struct futex_hash_bucket *hb;
921 : 0 : union futex_key key = FUTEX_KEY_INIT;
922 : :
923 : 0 : if (!futex_cmpxchg_enabled)
924 : 0 : return;
925 : : /*
926 : : * We are a ZOMBIE and nobody can enqueue itself on
927 : : * pi_state_list anymore, but we have to be careful
928 : : * versus waiters unqueueing themselves:
929 : : */
930 : 0 : raw_spin_lock_irq(&curr->pi_lock);
931 : 0 : while (!list_empty(head)) {
932 : 0 : next = head->next;
933 : : pi_state = list_entry(next, struct futex_pi_state, list);
934 : 0 : key = pi_state->key;
935 : 0 : hb = hash_futex(&key);
936 : :
937 : : /*
938 : : * We can race against put_pi_state() removing itself from the
939 : : * list (a waiter going away). put_pi_state() will first
940 : : * decrement the reference count and then modify the list, so
941 : : * its possible to see the list entry but fail this reference
942 : : * acquire.
943 : : *
944 : : * In that case; drop the locks to let put_pi_state() make
945 : : * progress and retry the loop.
946 : : */
947 : 0 : if (!refcount_inc_not_zero(&pi_state->refcount)) {
948 : 0 : raw_spin_unlock_irq(&curr->pi_lock);
949 : 0 : cpu_relax();
950 : 0 : raw_spin_lock_irq(&curr->pi_lock);
951 : 0 : continue;
952 : : }
953 : 0 : raw_spin_unlock_irq(&curr->pi_lock);
954 : :
955 : : spin_lock(&hb->lock);
956 : 0 : raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
957 : 0 : raw_spin_lock(&curr->pi_lock);
958 : : /*
959 : : * We dropped the pi-lock, so re-check whether this
960 : : * task still owns the PI-state:
961 : : */
962 : 0 : if (head->next != next) {
963 : : /* retain curr->pi_lock for the loop invariant */
964 : : raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
965 : : spin_unlock(&hb->lock);
966 : 0 : put_pi_state(pi_state);
967 : 0 : continue;
968 : : }
969 : :
970 : 0 : WARN_ON(pi_state->owner != curr);
971 : 0 : WARN_ON(list_empty(&pi_state->list));
972 : : list_del_init(&pi_state->list);
973 : 0 : pi_state->owner = NULL;
974 : :
975 : : raw_spin_unlock(&curr->pi_lock);
976 : 0 : raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
977 : : spin_unlock(&hb->lock);
978 : :
979 : 0 : rt_mutex_futex_unlock(&pi_state->pi_mutex);
980 : 0 : put_pi_state(pi_state);
981 : :
982 : 0 : raw_spin_lock_irq(&curr->pi_lock);
983 : : }
984 : 0 : raw_spin_unlock_irq(&curr->pi_lock);
985 : : }
986 : : #else
987 : : static inline void exit_pi_state_list(struct task_struct *curr) { }
988 : : #endif
989 : :
990 : : /*
991 : : * We need to check the following states:
992 : : *
993 : : * Waiter | pi_state | pi->owner | uTID | uODIED | ?
994 : : *
995 : : * [1] NULL | --- | --- | 0 | 0/1 | Valid
996 : : * [2] NULL | --- | --- | >0 | 0/1 | Valid
997 : : *
998 : : * [3] Found | NULL | -- | Any | 0/1 | Invalid
999 : : *
1000 : : * [4] Found | Found | NULL | 0 | 1 | Valid
1001 : : * [5] Found | Found | NULL | >0 | 1 | Invalid
1002 : : *
1003 : : * [6] Found | Found | task | 0 | 1 | Valid
1004 : : *
1005 : : * [7] Found | Found | NULL | Any | 0 | Invalid
1006 : : *
1007 : : * [8] Found | Found | task | ==taskTID | 0/1 | Valid
1008 : : * [9] Found | Found | task | 0 | 0 | Invalid
1009 : : * [10] Found | Found | task | !=taskTID | 0/1 | Invalid
1010 : : *
1011 : : * [1] Indicates that the kernel can acquire the futex atomically. We
1012 : : * came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
1013 : : *
1014 : : * [2] Valid, if TID does not belong to a kernel thread. If no matching
1015 : : * thread is found then it indicates that the owner TID has died.
1016 : : *
1017 : : * [3] Invalid. The waiter is queued on a non PI futex
1018 : : *
1019 : : * [4] Valid state after exit_robust_list(), which sets the user space
1020 : : * value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
1021 : : *
1022 : : * [5] The user space value got manipulated between exit_robust_list()
1023 : : * and exit_pi_state_list()
1024 : : *
1025 : : * [6] Valid state after exit_pi_state_list() which sets the new owner in
1026 : : * the pi_state but cannot access the user space value.
1027 : : *
1028 : : * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
1029 : : *
1030 : : * [8] Owner and user space value match
1031 : : *
1032 : : * [9] There is no transient state which sets the user space TID to 0
1033 : : * except exit_robust_list(), but this is indicated by the
1034 : : * FUTEX_OWNER_DIED bit. See [4]
1035 : : *
1036 : : * [10] There is no transient state which leaves owner and user space
1037 : : * TID out of sync.
1038 : : *
1039 : : *
1040 : : * Serialization and lifetime rules:
1041 : : *
1042 : : * hb->lock:
1043 : : *
1044 : : * hb -> futex_q, relation
1045 : : * futex_q -> pi_state, relation
1046 : : *
1047 : : * (cannot be raw because hb can contain arbitrary amount
1048 : : * of futex_q's)
1049 : : *
1050 : : * pi_mutex->wait_lock:
1051 : : *
1052 : : * {uval, pi_state}
1053 : : *
1054 : : * (and pi_mutex 'obviously')
1055 : : *
1056 : : * p->pi_lock:
1057 : : *
1058 : : * p->pi_state_list -> pi_state->list, relation
1059 : : *
1060 : : * pi_state->refcount:
1061 : : *
1062 : : * pi_state lifetime
1063 : : *
1064 : : *
1065 : : * Lock order:
1066 : : *
1067 : : * hb->lock
1068 : : * pi_mutex->wait_lock
1069 : : * p->pi_lock
1070 : : *
1071 : : */
1072 : :
1073 : : /*
1074 : : * Validate that the existing waiter has a pi_state and sanity check
1075 : : * the pi_state against the user space value. If correct, attach to
1076 : : * it.
1077 : : */
1078 : 0 : static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
1079 : : struct futex_pi_state *pi_state,
1080 : : struct futex_pi_state **ps)
1081 : : {
1082 : 0 : pid_t pid = uval & FUTEX_TID_MASK;
1083 : : u32 uval2;
1084 : : int ret;
1085 : :
1086 : : /*
1087 : : * Userspace might have messed up non-PI and PI futexes [3]
1088 : : */
1089 : 0 : if (unlikely(!pi_state))
1090 : : return -EINVAL;
1091 : :
1092 : : /*
1093 : : * We get here with hb->lock held, and having found a
1094 : : * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
1095 : : * has dropped the hb->lock in between queue_me() and unqueue_me_pi(),
1096 : : * which in turn means that futex_lock_pi() still has a reference on
1097 : : * our pi_state.
1098 : : *
1099 : : * The waiter holding a reference on @pi_state also protects against
1100 : : * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
1101 : : * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
1102 : : * free pi_state before we can take a reference ourselves.
1103 : : */
1104 : 0 : WARN_ON(!refcount_read(&pi_state->refcount));
1105 : :
1106 : : /*
1107 : : * Now that we have a pi_state, we can acquire wait_lock
1108 : : * and do the state validation.
1109 : : */
1110 : 0 : raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
1111 : :
1112 : : /*
1113 : : * Since {uval, pi_state} is serialized by wait_lock, and our current
1114 : : * uval was read without holding it, it can have changed. Verify it
1115 : : * still is what we expect it to be, otherwise retry the entire
1116 : : * operation.
1117 : : */
1118 : 0 : if (get_futex_value_locked(&uval2, uaddr))
1119 : : goto out_efault;
1120 : :
1121 : 0 : if (uval != uval2)
1122 : : goto out_eagain;
1123 : :
1124 : : /*
1125 : : * Handle the owner died case:
1126 : : */
1127 : 0 : if (uval & FUTEX_OWNER_DIED) {
1128 : : /*
1129 : : * exit_pi_state_list sets owner to NULL and wakes the
1130 : : * topmost waiter. The task which acquires the
1131 : : * pi_state->rt_mutex will fixup owner.
1132 : : */
1133 : 0 : if (!pi_state->owner) {
1134 : : /*
1135 : : * No pi state owner, but the user space TID
1136 : : * is not 0. Inconsistent state. [5]
1137 : : */
1138 : 0 : if (pid)
1139 : : goto out_einval;
1140 : : /*
1141 : : * Take a ref on the state and return success. [4]
1142 : : */
1143 : : goto out_attach;
1144 : : }
1145 : :
1146 : : /*
1147 : : * If TID is 0, then either the dying owner has not
1148 : : * yet executed exit_pi_state_list() or some waiter
1149 : : * acquired the rtmutex in the pi state, but did not
1150 : : * yet fixup the TID in user space.
1151 : : *
1152 : : * Take a ref on the state and return success. [6]
1153 : : */
1154 : 0 : if (!pid)
1155 : : goto out_attach;
1156 : : } else {
1157 : : /*
1158 : : * If the owner died bit is not set, then the pi_state
1159 : : * must have an owner. [7]
1160 : : */
1161 : 0 : if (!pi_state->owner)
1162 : : goto out_einval;
1163 : : }
1164 : :
1165 : : /*
1166 : : * Bail out if user space manipulated the futex value. If pi
1167 : : * state exists then the owner TID must be the same as the
1168 : : * user space TID. [9/10]
1169 : : */
1170 : 0 : if (pid != task_pid_vnr(pi_state->owner))
1171 : : goto out_einval;
1172 : :
1173 : : out_attach:
1174 : 0 : get_pi_state(pi_state);
1175 : 0 : raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1176 : 0 : *ps = pi_state;
1177 : 0 : return 0;
1178 : :
1179 : : out_einval:
1180 : : ret = -EINVAL;
1181 : : goto out_error;
1182 : :
1183 : : out_eagain:
1184 : : ret = -EAGAIN;
1185 : : goto out_error;
1186 : :
1187 : : out_efault:
1188 : : ret = -EFAULT;
1189 : : goto out_error;
1190 : :
1191 : : out_error:
1192 : 0 : raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1193 : 0 : return ret;
1194 : : }
1195 : :
1196 : : /**
1197 : : * wait_for_owner_exiting - Block until the owner has exited
1198 : : * @exiting: Pointer to the exiting task
1199 : : *
1200 : : * Caller must hold a refcount on @exiting.
1201 : : */
1202 : 0 : static void wait_for_owner_exiting(int ret, struct task_struct *exiting)
1203 : : {
1204 : 0 : if (ret != -EBUSY) {
1205 : 0 : WARN_ON_ONCE(exiting);
1206 : : return;
1207 : : }
1208 : :
1209 : 0 : if (WARN_ON_ONCE(ret == -EBUSY && !exiting))
1210 : : return;
1211 : :
1212 : 0 : mutex_lock(&exiting->futex_exit_mutex);
1213 : : /*
1214 : : * No point in doing state checking here. If the waiter got here
1215 : : * while the task was in exec()->exec_futex_release() then it can
1216 : : * have any FUTEX_STATE_* value when the waiter has acquired the
1217 : : * mutex. OK, if running, EXITING or DEAD if it reached exit()
1218 : : * already. Highly unlikely and not a problem. Just one more round
1219 : : * through the futex maze.
1220 : : */
1221 : 0 : mutex_unlock(&exiting->futex_exit_mutex);
1222 : :
1223 : 0 : put_task_struct(exiting);
1224 : : }
1225 : :
1226 : 0 : static int handle_exit_race(u32 __user *uaddr, u32 uval,
1227 : : struct task_struct *tsk)
1228 : : {
1229 : : u32 uval2;
1230 : :
1231 : : /*
1232 : : * If the futex exit state is not yet FUTEX_STATE_DEAD, tell the
1233 : : * caller that the alleged owner is busy.
1234 : : */
1235 : 0 : if (tsk && tsk->futex_state != FUTEX_STATE_DEAD)
1236 : : return -EBUSY;
1237 : :
1238 : : /*
1239 : : * Reread the user space value to handle the following situation:
1240 : : *
1241 : : * CPU0 CPU1
1242 : : *
1243 : : * sys_exit() sys_futex()
1244 : : * do_exit() futex_lock_pi()
1245 : : * futex_lock_pi_atomic()
1246 : : * exit_signals(tsk) No waiters:
1247 : : * tsk->flags |= PF_EXITING; *uaddr == 0x00000PID
1248 : : * mm_release(tsk) Set waiter bit
1249 : : * exit_robust_list(tsk) { *uaddr = 0x80000PID;
1250 : : * Set owner died attach_to_pi_owner() {
1251 : : * *uaddr = 0xC0000000; tsk = get_task(PID);
1252 : : * } if (!tsk->flags & PF_EXITING) {
1253 : : * ... attach();
1254 : : * tsk->futex_state = } else {
1255 : : * FUTEX_STATE_DEAD; if (tsk->futex_state !=
1256 : : * FUTEX_STATE_DEAD)
1257 : : * return -EAGAIN;
1258 : : * return -ESRCH; <--- FAIL
1259 : : * }
1260 : : *
1261 : : * Returning ESRCH unconditionally is wrong here because the
1262 : : * user space value has been changed by the exiting task.
1263 : : *
1264 : : * The same logic applies to the case where the exiting task is
1265 : : * already gone.
1266 : : */
1267 : 0 : if (get_futex_value_locked(&uval2, uaddr))
1268 : : return -EFAULT;
1269 : :
1270 : : /* If the user space value has changed, try again. */
1271 : 0 : if (uval2 != uval)
1272 : : return -EAGAIN;
1273 : :
1274 : : /*
1275 : : * The exiting task did not have a robust list, the robust list was
1276 : : * corrupted or the user space value in *uaddr is simply bogus.
1277 : : * Give up and tell user space.
1278 : : */
1279 : 0 : return -ESRCH;
1280 : : }
1281 : :
1282 : : /*
1283 : : * Lookup the task for the TID provided from user space and attach to
1284 : : * it after doing proper sanity checks.
1285 : : */
1286 : 0 : static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key,
1287 : : struct futex_pi_state **ps,
1288 : : struct task_struct **exiting)
1289 : : {
1290 : 0 : pid_t pid = uval & FUTEX_TID_MASK;
1291 : : struct futex_pi_state *pi_state;
1292 : : struct task_struct *p;
1293 : :
1294 : : /*
1295 : : * We are the first waiter - try to look up the real owner and attach
1296 : : * the new pi_state to it, but bail out when TID = 0 [1]
1297 : : *
1298 : : * The !pid check is paranoid. None of the call sites should end up
1299 : : * with pid == 0, but better safe than sorry. Let the caller retry
1300 : : */
1301 : 0 : if (!pid)
1302 : : return -EAGAIN;
1303 : 0 : p = find_get_task_by_vpid(pid);
1304 : 0 : if (!p)
1305 : 0 : return handle_exit_race(uaddr, uval, NULL);
1306 : :
1307 : 0 : if (unlikely(p->flags & PF_KTHREAD)) {
1308 : 0 : put_task_struct(p);
1309 : 0 : return -EPERM;
1310 : : }
1311 : :
1312 : : /*
1313 : : * We need to look at the task state to figure out, whether the
1314 : : * task is exiting. To protect against the change of the task state
1315 : : * in futex_exit_release(), we do this protected by p->pi_lock:
1316 : : */
1317 : 0 : raw_spin_lock_irq(&p->pi_lock);
1318 : 0 : if (unlikely(p->futex_state != FUTEX_STATE_OK)) {
1319 : : /*
1320 : : * The task is on the way out. When the futex state is
1321 : : * FUTEX_STATE_DEAD, we know that the task has finished
1322 : : * the cleanup:
1323 : : */
1324 : 0 : int ret = handle_exit_race(uaddr, uval, p);
1325 : :
1326 : 0 : raw_spin_unlock_irq(&p->pi_lock);
1327 : : /*
1328 : : * If the owner task is between FUTEX_STATE_EXITING and
1329 : : * FUTEX_STATE_DEAD then store the task pointer and keep
1330 : : * the reference on the task struct. The calling code will
1331 : : * drop all locks, wait for the task to reach
1332 : : * FUTEX_STATE_DEAD and then drop the refcount. This is
1333 : : * required to prevent a live lock when the current task
1334 : : * preempted the exiting task between the two states.
1335 : : */
1336 : 0 : if (ret == -EBUSY)
1337 : 0 : *exiting = p;
1338 : : else
1339 : 0 : put_task_struct(p);
1340 : 0 : return ret;
1341 : : }
1342 : :
1343 : : /*
1344 : : * No existing pi state. First waiter. [2]
1345 : : *
1346 : : * This creates pi_state, we have hb->lock held, this means nothing can
1347 : : * observe this state, wait_lock is irrelevant.
1348 : : */
1349 : 0 : pi_state = alloc_pi_state();
1350 : :
1351 : : /*
1352 : : * Initialize the pi_mutex in locked state and make @p
1353 : : * the owner of it:
1354 : : */
1355 : 0 : rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
1356 : :
1357 : : /* Store the key for possible exit cleanups: */
1358 : 0 : pi_state->key = *key;
1359 : :
1360 : 0 : WARN_ON(!list_empty(&pi_state->list));
1361 : 0 : list_add(&pi_state->list, &p->pi_state_list);
1362 : : /*
1363 : : * Assignment without holding pi_state->pi_mutex.wait_lock is safe
1364 : : * because there is no concurrency as the object is not published yet.
1365 : : */
1366 : 0 : pi_state->owner = p;
1367 : 0 : raw_spin_unlock_irq(&p->pi_lock);
1368 : :
1369 : 0 : put_task_struct(p);
1370 : :
1371 : 0 : *ps = pi_state;
1372 : :
1373 : 0 : return 0;
1374 : : }
1375 : :
1376 : 0 : static int lookup_pi_state(u32 __user *uaddr, u32 uval,
1377 : : struct futex_hash_bucket *hb,
1378 : : union futex_key *key, struct futex_pi_state **ps,
1379 : : struct task_struct **exiting)
1380 : : {
1381 : 0 : struct futex_q *top_waiter = futex_top_waiter(hb, key);
1382 : :
1383 : : /*
1384 : : * If there is a waiter on that futex, validate it and
1385 : : * attach to the pi_state when the validation succeeds.
1386 : : */
1387 : 0 : if (top_waiter)
1388 : 0 : return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
1389 : :
1390 : : /*
1391 : : * We are the first waiter - try to look up the owner based on
1392 : : * @uval and attach to it.
1393 : : */
1394 : 0 : return attach_to_pi_owner(uaddr, uval, key, ps, exiting);
1395 : : }
1396 : :
1397 : 0 : static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
1398 : : {
1399 : : int err;
1400 : : u32 uninitialized_var(curval);
1401 : :
1402 : : if (unlikely(should_fail_futex(true)))
1403 : : return -EFAULT;
1404 : :
1405 : 0 : err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
1406 : 0 : if (unlikely(err))
1407 : : return err;
1408 : :
1409 : : /* If user space value changed, let the caller retry */
1410 : 0 : return curval != uval ? -EAGAIN : 0;
1411 : : }
1412 : :
1413 : : /**
1414 : : * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
1415 : : * @uaddr: the pi futex user address
1416 : : * @hb: the pi futex hash bucket
1417 : : * @key: the futex key associated with uaddr and hb
1418 : : * @ps: the pi_state pointer where we store the result of the
1419 : : * lookup
1420 : : * @task: the task to perform the atomic lock work for. This will
1421 : : * be "current" except in the case of requeue pi.
1422 : : * @exiting: Pointer to store the task pointer of the owner task
1423 : : * which is in the middle of exiting
1424 : : * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1425 : : *
1426 : : * Return:
1427 : : * - 0 - ready to wait;
1428 : : * - 1 - acquired the lock;
1429 : : * - <0 - error
1430 : : *
1431 : : * The hb->lock and futex_key refs shall be held by the caller.
1432 : : *
1433 : : * @exiting is only set when the return value is -EBUSY. If so, this holds
1434 : : * a refcount on the exiting task on return and the caller needs to drop it
1435 : : * after waiting for the exit to complete.
1436 : : */
1437 : 0 : static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
1438 : : union futex_key *key,
1439 : : struct futex_pi_state **ps,
1440 : : struct task_struct *task,
1441 : : struct task_struct **exiting,
1442 : : int set_waiters)
1443 : : {
1444 : 0 : u32 uval, newval, vpid = task_pid_vnr(task);
1445 : : struct futex_q *top_waiter;
1446 : : int ret;
1447 : :
1448 : : /*
1449 : : * Read the user space value first so we can validate a few
1450 : : * things before proceeding further.
1451 : : */
1452 : 0 : if (get_futex_value_locked(&uval, uaddr))
1453 : : return -EFAULT;
1454 : :
1455 : : if (unlikely(should_fail_futex(true)))
1456 : : return -EFAULT;
1457 : :
1458 : : /*
1459 : : * Detect deadlocks.
1460 : : */
1461 : 0 : if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
1462 : : return -EDEADLK;
1463 : :
1464 : : if ((unlikely(should_fail_futex(true))))
1465 : : return -EDEADLK;
1466 : :
1467 : : /*
1468 : : * Lookup existing state first. If it exists, try to attach to
1469 : : * its pi_state.
1470 : : */
1471 : 0 : top_waiter = futex_top_waiter(hb, key);
1472 : 0 : if (top_waiter)
1473 : 0 : return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
1474 : :
1475 : : /*
1476 : : * No waiter and user TID is 0. We are here because the
1477 : : * waiters or the owner died bit is set or called from
1478 : : * requeue_cmp_pi or for whatever reason something took the
1479 : : * syscall.
1480 : : */
1481 : 0 : if (!(uval & FUTEX_TID_MASK)) {
1482 : : /*
1483 : : * We take over the futex. No other waiters and the user space
1484 : : * TID is 0. We preserve the owner died bit.
1485 : : */
1486 : 0 : newval = uval & FUTEX_OWNER_DIED;
1487 : 0 : newval |= vpid;
1488 : :
1489 : : /* The futex requeue_pi code can enforce the waiters bit */
1490 : 0 : if (set_waiters)
1491 : 0 : newval |= FUTEX_WAITERS;
1492 : :
1493 : 0 : ret = lock_pi_update_atomic(uaddr, uval, newval);
1494 : : /* If the take over worked, return 1 */
1495 : 0 : return ret < 0 ? ret : 1;
1496 : : }
1497 : :
1498 : : /*
1499 : : * First waiter. Set the waiters bit before attaching ourself to
1500 : : * the owner. If owner tries to unlock, it will be forced into
1501 : : * the kernel and blocked on hb->lock.
1502 : : */
1503 : 0 : newval = uval | FUTEX_WAITERS;
1504 : 0 : ret = lock_pi_update_atomic(uaddr, uval, newval);
1505 : 0 : if (ret)
1506 : : return ret;
1507 : : /*
1508 : : * If the update of the user space value succeeded, we try to
1509 : : * attach to the owner. If that fails, no harm done, we only
1510 : : * set the FUTEX_WAITERS bit in the user space variable.
1511 : : */
1512 : 0 : return attach_to_pi_owner(uaddr, newval, key, ps, exiting);
1513 : : }
1514 : :
1515 : : /**
1516 : : * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
1517 : : * @q: The futex_q to unqueue
1518 : : *
1519 : : * The q->lock_ptr must not be NULL and must be held by the caller.
1520 : : */
1521 : 3 : static void __unqueue_futex(struct futex_q *q)
1522 : : {
1523 : : struct futex_hash_bucket *hb;
1524 : :
1525 : 3 : if (WARN_ON_SMP(!q->lock_ptr) || WARN_ON(plist_node_empty(&q->list)))
1526 : 3 : return;
1527 : : lockdep_assert_held(q->lock_ptr);
1528 : :
1529 : 3 : hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
1530 : 3 : plist_del(&q->list, &hb->chain);
1531 : : hb_waiters_dec(hb);
1532 : : }
1533 : :
1534 : : /*
1535 : : * The hash bucket lock must be held when this is called.
1536 : : * Afterwards, the futex_q must not be accessed. Callers
1537 : : * must ensure to later call wake_up_q() for the actual
1538 : : * wakeups to occur.
1539 : : */
1540 : 3 : static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
1541 : : {
1542 : 3 : struct task_struct *p = q->task;
1543 : :
1544 : 3 : if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
1545 : 3 : return;
1546 : :
1547 : : get_task_struct(p);
1548 : 3 : __unqueue_futex(q);
1549 : : /*
1550 : : * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
1551 : : * is written, without taking any locks. This is possible in the event
1552 : : * of a spurious wakeup, for example. A memory barrier is required here
1553 : : * to prevent the following store to lock_ptr from getting ahead of the
1554 : : * plist_del in __unqueue_futex().
1555 : : */
1556 : 3 : smp_store_release(&q->lock_ptr, NULL);
1557 : :
1558 : : /*
1559 : : * Queue the task for later wakeup for after we've released
1560 : : * the hb->lock. wake_q_add() grabs reference to p.
1561 : : */
1562 : 3 : wake_q_add_safe(wake_q, p);
1563 : : }
1564 : :
1565 : : /*
1566 : : * Caller must hold a reference on @pi_state.
1567 : : */
1568 : 0 : static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
1569 : : {
1570 : : u32 uninitialized_var(curval), newval;
1571 : : struct task_struct *new_owner;
1572 : : bool postunlock = false;
1573 : 0 : DEFINE_WAKE_Q(wake_q);
1574 : : int ret = 0;
1575 : :
1576 : 0 : new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
1577 : 0 : if (WARN_ON_ONCE(!new_owner)) {
1578 : : /*
1579 : : * As per the comment in futex_unlock_pi() this should not happen.
1580 : : *
1581 : : * When this happens, give up our locks and try again, giving
1582 : : * the futex_lock_pi() instance time to complete, either by
1583 : : * waiting on the rtmutex or removing itself from the futex
1584 : : * queue.
1585 : : */
1586 : : ret = -EAGAIN;
1587 : : goto out_unlock;
1588 : : }
1589 : :
1590 : : /*
1591 : : * We pass it to the next owner. The WAITERS bit is always kept
1592 : : * enabled while there is PI state around. We cleanup the owner
1593 : : * died bit, because we are the owner.
1594 : : */
1595 : 0 : newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
1596 : :
1597 : : if (unlikely(should_fail_futex(true)))
1598 : : ret = -EFAULT;
1599 : :
1600 : 0 : ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
1601 : 0 : if (!ret && (curval != uval)) {
1602 : : /*
1603 : : * If a unconditional UNLOCK_PI operation (user space did not
1604 : : * try the TID->0 transition) raced with a waiter setting the
1605 : : * FUTEX_WAITERS flag between get_user() and locking the hash
1606 : : * bucket lock, retry the operation.
1607 : : */
1608 : 0 : if ((FUTEX_TID_MASK & curval) == uval)
1609 : : ret = -EAGAIN;
1610 : : else
1611 : : ret = -EINVAL;
1612 : : }
1613 : :
1614 : 0 : if (ret)
1615 : : goto out_unlock;
1616 : :
1617 : : /*
1618 : : * This is a point of no return; once we modify the uval there is no
1619 : : * going back and subsequent operations must not fail.
1620 : : */
1621 : :
1622 : 0 : raw_spin_lock(&pi_state->owner->pi_lock);
1623 : 0 : WARN_ON(list_empty(&pi_state->list));
1624 : : list_del_init(&pi_state->list);
1625 : 0 : raw_spin_unlock(&pi_state->owner->pi_lock);
1626 : :
1627 : 0 : raw_spin_lock(&new_owner->pi_lock);
1628 : 0 : WARN_ON(!list_empty(&pi_state->list));
1629 : 0 : list_add(&pi_state->list, &new_owner->pi_state_list);
1630 : 0 : pi_state->owner = new_owner;
1631 : : raw_spin_unlock(&new_owner->pi_lock);
1632 : :
1633 : 0 : postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
1634 : :
1635 : : out_unlock:
1636 : 0 : raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1637 : :
1638 : 0 : if (postunlock)
1639 : 0 : rt_mutex_postunlock(&wake_q);
1640 : :
1641 : 0 : return ret;
1642 : : }
1643 : :
1644 : : /*
1645 : : * Express the locking dependencies for lockdep:
1646 : : */
1647 : : static inline void
1648 : 0 : double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1649 : : {
1650 : 0 : if (hb1 <= hb2) {
1651 : : spin_lock(&hb1->lock);
1652 : 0 : if (hb1 < hb2)
1653 : 0 : spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
1654 : : } else { /* hb1 > hb2 */
1655 : : spin_lock(&hb2->lock);
1656 : 0 : spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
1657 : : }
1658 : 0 : }
1659 : :
1660 : : static inline void
1661 : : double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1662 : : {
1663 : : spin_unlock(&hb1->lock);
1664 : 0 : if (hb1 != hb2)
1665 : : spin_unlock(&hb2->lock);
1666 : : }
1667 : :
1668 : : /*
1669 : : * Wake up waiters matching bitset queued on this futex (uaddr).
1670 : : */
1671 : : static int
1672 : 3 : futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
1673 : : {
1674 : : struct futex_hash_bucket *hb;
1675 : : struct futex_q *this, *next;
1676 : 3 : union futex_key key = FUTEX_KEY_INIT;
1677 : : int ret;
1678 : 3 : DEFINE_WAKE_Q(wake_q);
1679 : :
1680 : 3 : if (!bitset)
1681 : : return -EINVAL;
1682 : :
1683 : 3 : ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_READ);
1684 : 3 : if (unlikely(ret != 0))
1685 : : goto out;
1686 : :
1687 : 3 : hb = hash_futex(&key);
1688 : :
1689 : : /* Make sure we really have tasks to wakeup */
1690 : 3 : if (!hb_waiters_pending(hb))
1691 : : goto out_put_key;
1692 : :
1693 : : spin_lock(&hb->lock);
1694 : :
1695 : 3 : plist_for_each_entry_safe(this, next, &hb->chain, list) {
1696 : 3 : if (match_futex (&this->key, &key)) {
1697 : 3 : if (this->pi_state || this->rt_waiter) {
1698 : : ret = -EINVAL;
1699 : : break;
1700 : : }
1701 : :
1702 : : /* Check if one of the bits is set in both bitsets */
1703 : 3 : if (!(this->bitset & bitset))
1704 : 0 : continue;
1705 : :
1706 : 3 : mark_wake_futex(&wake_q, this);
1707 : 3 : if (++ret >= nr_wake)
1708 : : break;
1709 : : }
1710 : : }
1711 : :
1712 : : spin_unlock(&hb->lock);
1713 : 3 : wake_up_q(&wake_q);
1714 : : out_put_key:
1715 : : put_futex_key(&key);
1716 : : out:
1717 : 3 : return ret;
1718 : : }
1719 : :
1720 : 0 : static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
1721 : : {
1722 : 0 : unsigned int op = (encoded_op & 0x70000000) >> 28;
1723 : 0 : unsigned int cmp = (encoded_op & 0x0f000000) >> 24;
1724 : 0 : int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11);
1725 : 0 : int cmparg = sign_extend32(encoded_op & 0x00000fff, 11);
1726 : : int oldval, ret;
1727 : :
1728 : 0 : if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
1729 : 0 : if (oparg < 0 || oparg > 31) {
1730 : : char comm[sizeof(current->comm)];
1731 : : /*
1732 : : * kill this print and return -EINVAL when userspace
1733 : : * is sane again
1734 : : */
1735 : 0 : pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n",
1736 : : get_task_comm(comm, current), oparg);
1737 : 0 : oparg &= 31;
1738 : : }
1739 : 0 : oparg = 1 << oparg;
1740 : : }
1741 : :
1742 : 0 : if (!access_ok(uaddr, sizeof(u32)))
1743 : : return -EFAULT;
1744 : :
1745 : 0 : ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
1746 : 0 : if (ret)
1747 : : return ret;
1748 : :
1749 : 0 : switch (cmp) {
1750 : : case FUTEX_OP_CMP_EQ:
1751 : 0 : return oldval == cmparg;
1752 : : case FUTEX_OP_CMP_NE:
1753 : 0 : return oldval != cmparg;
1754 : : case FUTEX_OP_CMP_LT:
1755 : 0 : return oldval < cmparg;
1756 : : case FUTEX_OP_CMP_GE:
1757 : 0 : return oldval >= cmparg;
1758 : : case FUTEX_OP_CMP_LE:
1759 : 0 : return oldval <= cmparg;
1760 : : case FUTEX_OP_CMP_GT:
1761 : 0 : return oldval > cmparg;
1762 : : default:
1763 : : return -ENOSYS;
1764 : : }
1765 : : }
1766 : :
1767 : : /*
1768 : : * Wake up all waiters hashed on the physical page that is mapped
1769 : : * to this virtual address:
1770 : : */
1771 : : static int
1772 : 0 : futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
1773 : : int nr_wake, int nr_wake2, int op)
1774 : : {
1775 : 0 : union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1776 : : struct futex_hash_bucket *hb1, *hb2;
1777 : : struct futex_q *this, *next;
1778 : : int ret, op_ret;
1779 : 0 : DEFINE_WAKE_Q(wake_q);
1780 : :
1781 : : retry:
1782 : 0 : ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
1783 : 0 : if (unlikely(ret != 0))
1784 : : goto out;
1785 : 0 : ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
1786 : 0 : if (unlikely(ret != 0))
1787 : : goto out_put_key1;
1788 : :
1789 : 0 : hb1 = hash_futex(&key1);
1790 : 0 : hb2 = hash_futex(&key2);
1791 : :
1792 : : retry_private:
1793 : 0 : double_lock_hb(hb1, hb2);
1794 : 0 : op_ret = futex_atomic_op_inuser(op, uaddr2);
1795 : 0 : if (unlikely(op_ret < 0)) {
1796 : : double_unlock_hb(hb1, hb2);
1797 : :
1798 : 0 : if (!IS_ENABLED(CONFIG_MMU) ||
1799 : 0 : unlikely(op_ret != -EFAULT && op_ret != -EAGAIN)) {
1800 : : /*
1801 : : * we don't get EFAULT from MMU faults if we don't have
1802 : : * an MMU, but we might get them from range checking
1803 : : */
1804 : 0 : ret = op_ret;
1805 : 0 : goto out_put_keys;
1806 : : }
1807 : :
1808 : 0 : if (op_ret == -EFAULT) {
1809 : 0 : ret = fault_in_user_writeable(uaddr2);
1810 : 0 : if (ret)
1811 : : goto out_put_keys;
1812 : : }
1813 : :
1814 : 0 : if (!(flags & FLAGS_SHARED)) {
1815 : 0 : cond_resched();
1816 : 0 : goto retry_private;
1817 : : }
1818 : :
1819 : : put_futex_key(&key2);
1820 : : put_futex_key(&key1);
1821 : 0 : cond_resched();
1822 : 0 : goto retry;
1823 : : }
1824 : :
1825 : 0 : plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1826 : 0 : if (match_futex (&this->key, &key1)) {
1827 : 0 : if (this->pi_state || this->rt_waiter) {
1828 : : ret = -EINVAL;
1829 : : goto out_unlock;
1830 : : }
1831 : 0 : mark_wake_futex(&wake_q, this);
1832 : 0 : if (++ret >= nr_wake)
1833 : : break;
1834 : : }
1835 : : }
1836 : :
1837 : 0 : if (op_ret > 0) {
1838 : : op_ret = 0;
1839 : 0 : plist_for_each_entry_safe(this, next, &hb2->chain, list) {
1840 : 0 : if (match_futex (&this->key, &key2)) {
1841 : 0 : if (this->pi_state || this->rt_waiter) {
1842 : : ret = -EINVAL;
1843 : : goto out_unlock;
1844 : : }
1845 : 0 : mark_wake_futex(&wake_q, this);
1846 : 0 : if (++op_ret >= nr_wake2)
1847 : : break;
1848 : : }
1849 : : }
1850 : 0 : ret += op_ret;
1851 : : }
1852 : :
1853 : : out_unlock:
1854 : : double_unlock_hb(hb1, hb2);
1855 : 0 : wake_up_q(&wake_q);
1856 : : out_put_keys:
1857 : : put_futex_key(&key2);
1858 : : out_put_key1:
1859 : : put_futex_key(&key1);
1860 : : out:
1861 : 0 : return ret;
1862 : : }
1863 : :
1864 : : /**
1865 : : * requeue_futex() - Requeue a futex_q from one hb to another
1866 : : * @q: the futex_q to requeue
1867 : : * @hb1: the source hash_bucket
1868 : : * @hb2: the target hash_bucket
1869 : : * @key2: the new key for the requeued futex_q
1870 : : */
1871 : : static inline
1872 : 0 : void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1873 : : struct futex_hash_bucket *hb2, union futex_key *key2)
1874 : : {
1875 : :
1876 : : /*
1877 : : * If key1 and key2 hash to the same bucket, no need to
1878 : : * requeue.
1879 : : */
1880 : 0 : if (likely(&hb1->chain != &hb2->chain)) {
1881 : 0 : plist_del(&q->list, &hb1->chain);
1882 : : hb_waiters_dec(hb1);
1883 : 0 : hb_waiters_inc(hb2);
1884 : 0 : plist_add(&q->list, &hb2->chain);
1885 : 0 : q->lock_ptr = &hb2->lock;
1886 : : }
1887 : 0 : get_futex_key_refs(key2);
1888 : 0 : q->key = *key2;
1889 : 0 : }
1890 : :
1891 : : /**
1892 : : * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1893 : : * @q: the futex_q
1894 : : * @key: the key of the requeue target futex
1895 : : * @hb: the hash_bucket of the requeue target futex
1896 : : *
1897 : : * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1898 : : * target futex if it is uncontended or via a lock steal. Set the futex_q key
1899 : : * to the requeue target futex so the waiter can detect the wakeup on the right
1900 : : * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1901 : : * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
1902 : : * to protect access to the pi_state to fixup the owner later. Must be called
1903 : : * with both q->lock_ptr and hb->lock held.
1904 : : */
1905 : : static inline
1906 : 0 : void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1907 : : struct futex_hash_bucket *hb)
1908 : : {
1909 : 0 : get_futex_key_refs(key);
1910 : 0 : q->key = *key;
1911 : :
1912 : 0 : __unqueue_futex(q);
1913 : :
1914 : 0 : WARN_ON(!q->rt_waiter);
1915 : 0 : q->rt_waiter = NULL;
1916 : :
1917 : 0 : q->lock_ptr = &hb->lock;
1918 : :
1919 : 0 : wake_up_state(q->task, TASK_NORMAL);
1920 : 0 : }
1921 : :
1922 : : /**
1923 : : * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1924 : : * @pifutex: the user address of the to futex
1925 : : * @hb1: the from futex hash bucket, must be locked by the caller
1926 : : * @hb2: the to futex hash bucket, must be locked by the caller
1927 : : * @key1: the from futex key
1928 : : * @key2: the to futex key
1929 : : * @ps: address to store the pi_state pointer
1930 : : * @exiting: Pointer to store the task pointer of the owner task
1931 : : * which is in the middle of exiting
1932 : : * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1933 : : *
1934 : : * Try and get the lock on behalf of the top waiter if we can do it atomically.
1935 : : * Wake the top waiter if we succeed. If the caller specified set_waiters,
1936 : : * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1937 : : * hb1 and hb2 must be held by the caller.
1938 : : *
1939 : : * @exiting is only set when the return value is -EBUSY. If so, this holds
1940 : : * a refcount on the exiting task on return and the caller needs to drop it
1941 : : * after waiting for the exit to complete.
1942 : : *
1943 : : * Return:
1944 : : * - 0 - failed to acquire the lock atomically;
1945 : : * - >0 - acquired the lock, return value is vpid of the top_waiter
1946 : : * - <0 - error
1947 : : */
1948 : : static int
1949 : 0 : futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1,
1950 : : struct futex_hash_bucket *hb2, union futex_key *key1,
1951 : : union futex_key *key2, struct futex_pi_state **ps,
1952 : : struct task_struct **exiting, int set_waiters)
1953 : : {
1954 : : struct futex_q *top_waiter = NULL;
1955 : : u32 curval;
1956 : : int ret, vpid;
1957 : :
1958 : 0 : if (get_futex_value_locked(&curval, pifutex))
1959 : : return -EFAULT;
1960 : :
1961 : : if (unlikely(should_fail_futex(true)))
1962 : : return -EFAULT;
1963 : :
1964 : : /*
1965 : : * Find the top_waiter and determine if there are additional waiters.
1966 : : * If the caller intends to requeue more than 1 waiter to pifutex,
1967 : : * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1968 : : * as we have means to handle the possible fault. If not, don't set
1969 : : * the bit unecessarily as it will force the subsequent unlock to enter
1970 : : * the kernel.
1971 : : */
1972 : 0 : top_waiter = futex_top_waiter(hb1, key1);
1973 : :
1974 : : /* There are no waiters, nothing for us to do. */
1975 : 0 : if (!top_waiter)
1976 : : return 0;
1977 : :
1978 : : /* Ensure we requeue to the expected futex. */
1979 : 0 : if (!match_futex(top_waiter->requeue_pi_key, key2))
1980 : : return -EINVAL;
1981 : :
1982 : : /*
1983 : : * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
1984 : : * the contended case or if set_waiters is 1. The pi_state is returned
1985 : : * in ps in contended cases.
1986 : : */
1987 : 0 : vpid = task_pid_vnr(top_waiter->task);
1988 : 0 : ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1989 : : exiting, set_waiters);
1990 : 0 : if (ret == 1) {
1991 : 0 : requeue_pi_wake_futex(top_waiter, key2, hb2);
1992 : 0 : return vpid;
1993 : : }
1994 : : return ret;
1995 : : }
1996 : :
1997 : : /**
1998 : : * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1999 : : * @uaddr1: source futex user address
2000 : : * @flags: futex flags (FLAGS_SHARED, etc.)
2001 : : * @uaddr2: target futex user address
2002 : : * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
2003 : : * @nr_requeue: number of waiters to requeue (0-INT_MAX)
2004 : : * @cmpval: @uaddr1 expected value (or %NULL)
2005 : : * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
2006 : : * pi futex (pi to pi requeue is not supported)
2007 : : *
2008 : : * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
2009 : : * uaddr2 atomically on behalf of the top waiter.
2010 : : *
2011 : : * Return:
2012 : : * - >=0 - on success, the number of tasks requeued or woken;
2013 : : * - <0 - on error
2014 : : */
2015 : 0 : static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
2016 : : u32 __user *uaddr2, int nr_wake, int nr_requeue,
2017 : : u32 *cmpval, int requeue_pi)
2018 : : {
2019 : 0 : union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
2020 : : int drop_count = 0, task_count = 0, ret;
2021 : 0 : struct futex_pi_state *pi_state = NULL;
2022 : : struct futex_hash_bucket *hb1, *hb2;
2023 : : struct futex_q *this, *next;
2024 : 0 : DEFINE_WAKE_Q(wake_q);
2025 : :
2026 : 0 : if (nr_wake < 0 || nr_requeue < 0)
2027 : : return -EINVAL;
2028 : :
2029 : : /*
2030 : : * When PI not supported: return -ENOSYS if requeue_pi is true,
2031 : : * consequently the compiler knows requeue_pi is always false past
2032 : : * this point which will optimize away all the conditional code
2033 : : * further down.
2034 : : */
2035 : : if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi)
2036 : : return -ENOSYS;
2037 : :
2038 : 0 : if (requeue_pi) {
2039 : : /*
2040 : : * Requeue PI only works on two distinct uaddrs. This
2041 : : * check is only valid for private futexes. See below.
2042 : : */
2043 : 0 : if (uaddr1 == uaddr2)
2044 : : return -EINVAL;
2045 : :
2046 : : /*
2047 : : * requeue_pi requires a pi_state, try to allocate it now
2048 : : * without any locks in case it fails.
2049 : : */
2050 : 0 : if (refill_pi_state_cache())
2051 : : return -ENOMEM;
2052 : : /*
2053 : : * requeue_pi must wake as many tasks as it can, up to nr_wake
2054 : : * + nr_requeue, since it acquires the rt_mutex prior to
2055 : : * returning to userspace, so as to not leave the rt_mutex with
2056 : : * waiters and no owner. However, second and third wake-ups
2057 : : * cannot be predicted as they involve race conditions with the
2058 : : * first wake and a fault while looking up the pi_state. Both
2059 : : * pthread_cond_signal() and pthread_cond_broadcast() should
2060 : : * use nr_wake=1.
2061 : : */
2062 : 0 : if (nr_wake != 1)
2063 : : return -EINVAL;
2064 : : }
2065 : :
2066 : : retry:
2067 : 0 : ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
2068 : 0 : if (unlikely(ret != 0))
2069 : : goto out;
2070 : 0 : ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
2071 : : requeue_pi ? FUTEX_WRITE : FUTEX_READ);
2072 : 0 : if (unlikely(ret != 0))
2073 : : goto out_put_key1;
2074 : :
2075 : : /*
2076 : : * The check above which compares uaddrs is not sufficient for
2077 : : * shared futexes. We need to compare the keys:
2078 : : */
2079 : 0 : if (requeue_pi && match_futex(&key1, &key2)) {
2080 : : ret = -EINVAL;
2081 : : goto out_put_keys;
2082 : : }
2083 : :
2084 : 0 : hb1 = hash_futex(&key1);
2085 : 0 : hb2 = hash_futex(&key2);
2086 : :
2087 : : retry_private:
2088 : 0 : hb_waiters_inc(hb2);
2089 : 0 : double_lock_hb(hb1, hb2);
2090 : :
2091 : 0 : if (likely(cmpval != NULL)) {
2092 : : u32 curval;
2093 : :
2094 : 0 : ret = get_futex_value_locked(&curval, uaddr1);
2095 : :
2096 : 0 : if (unlikely(ret)) {
2097 : : double_unlock_hb(hb1, hb2);
2098 : : hb_waiters_dec(hb2);
2099 : :
2100 : 0 : ret = get_user(curval, uaddr1);
2101 : 0 : if (ret)
2102 : : goto out_put_keys;
2103 : :
2104 : 0 : if (!(flags & FLAGS_SHARED))
2105 : : goto retry_private;
2106 : :
2107 : : put_futex_key(&key2);
2108 : : put_futex_key(&key1);
2109 : 0 : goto retry;
2110 : : }
2111 : 0 : if (curval != *cmpval) {
2112 : : ret = -EAGAIN;
2113 : 0 : goto out_unlock;
2114 : : }
2115 : : }
2116 : :
2117 : 0 : if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
2118 : 0 : struct task_struct *exiting = NULL;
2119 : :
2120 : : /*
2121 : : * Attempt to acquire uaddr2 and wake the top waiter. If we
2122 : : * intend to requeue waiters, force setting the FUTEX_WAITERS
2123 : : * bit. We force this here where we are able to easily handle
2124 : : * faults rather in the requeue loop below.
2125 : : */
2126 : 0 : ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
2127 : : &key2, &pi_state,
2128 : : &exiting, nr_requeue);
2129 : :
2130 : : /*
2131 : : * At this point the top_waiter has either taken uaddr2 or is
2132 : : * waiting on it. If the former, then the pi_state will not
2133 : : * exist yet, look it up one more time to ensure we have a
2134 : : * reference to it. If the lock was taken, ret contains the
2135 : : * vpid of the top waiter task.
2136 : : * If the lock was not taken, we have pi_state and an initial
2137 : : * refcount on it. In case of an error we have nothing.
2138 : : */
2139 : 0 : if (ret > 0) {
2140 : 0 : WARN_ON(pi_state);
2141 : 0 : drop_count++;
2142 : 0 : task_count++;
2143 : : /*
2144 : : * If we acquired the lock, then the user space value
2145 : : * of uaddr2 should be vpid. It cannot be changed by
2146 : : * the top waiter as it is blocked on hb2 lock if it
2147 : : * tries to do so. If something fiddled with it behind
2148 : : * our back the pi state lookup might unearth it. So
2149 : : * we rather use the known value than rereading and
2150 : : * handing potential crap to lookup_pi_state.
2151 : : *
2152 : : * If that call succeeds then we have pi_state and an
2153 : : * initial refcount on it.
2154 : : */
2155 : 0 : ret = lookup_pi_state(uaddr2, ret, hb2, &key2,
2156 : : &pi_state, &exiting);
2157 : : }
2158 : :
2159 : 0 : switch (ret) {
2160 : : case 0:
2161 : : /* We hold a reference on the pi state. */
2162 : : break;
2163 : :
2164 : : /* If the above failed, then pi_state is NULL */
2165 : : case -EFAULT:
2166 : : double_unlock_hb(hb1, hb2);
2167 : : hb_waiters_dec(hb2);
2168 : : put_futex_key(&key2);
2169 : : put_futex_key(&key1);
2170 : 0 : ret = fault_in_user_writeable(uaddr2);
2171 : 0 : if (!ret)
2172 : : goto retry;
2173 : 0 : goto out;
2174 : : case -EBUSY:
2175 : : case -EAGAIN:
2176 : : /*
2177 : : * Two reasons for this:
2178 : : * - EBUSY: Owner is exiting and we just wait for the
2179 : : * exit to complete.
2180 : : * - EAGAIN: The user space value changed.
2181 : : */
2182 : : double_unlock_hb(hb1, hb2);
2183 : : hb_waiters_dec(hb2);
2184 : : put_futex_key(&key2);
2185 : : put_futex_key(&key1);
2186 : : /*
2187 : : * Handle the case where the owner is in the middle of
2188 : : * exiting. Wait for the exit to complete otherwise
2189 : : * this task might loop forever, aka. live lock.
2190 : : */
2191 : 0 : wait_for_owner_exiting(ret, exiting);
2192 : 0 : cond_resched();
2193 : 0 : goto retry;
2194 : : default:
2195 : 0 : goto out_unlock;
2196 : : }
2197 : : }
2198 : :
2199 : 0 : plist_for_each_entry_safe(this, next, &hb1->chain, list) {
2200 : 0 : if (task_count - nr_wake >= nr_requeue)
2201 : : break;
2202 : :
2203 : 0 : if (!match_futex(&this->key, &key1))
2204 : 0 : continue;
2205 : :
2206 : : /*
2207 : : * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
2208 : : * be paired with each other and no other futex ops.
2209 : : *
2210 : : * We should never be requeueing a futex_q with a pi_state,
2211 : : * which is awaiting a futex_unlock_pi().
2212 : : */
2213 : 0 : if ((requeue_pi && !this->rt_waiter) ||
2214 : 0 : (!requeue_pi && this->rt_waiter) ||
2215 : 0 : this->pi_state) {
2216 : : ret = -EINVAL;
2217 : : break;
2218 : : }
2219 : :
2220 : : /*
2221 : : * Wake nr_wake waiters. For requeue_pi, if we acquired the
2222 : : * lock, we already woke the top_waiter. If not, it will be
2223 : : * woken by futex_unlock_pi().
2224 : : */
2225 : 0 : if (++task_count <= nr_wake && !requeue_pi) {
2226 : 0 : mark_wake_futex(&wake_q, this);
2227 : 0 : continue;
2228 : : }
2229 : :
2230 : : /* Ensure we requeue to the expected futex for requeue_pi. */
2231 : 0 : if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
2232 : : ret = -EINVAL;
2233 : : break;
2234 : : }
2235 : :
2236 : : /*
2237 : : * Requeue nr_requeue waiters and possibly one more in the case
2238 : : * of requeue_pi if we couldn't acquire the lock atomically.
2239 : : */
2240 : 0 : if (requeue_pi) {
2241 : : /*
2242 : : * Prepare the waiter to take the rt_mutex. Take a
2243 : : * refcount on the pi_state and store the pointer in
2244 : : * the futex_q object of the waiter.
2245 : : */
2246 : 0 : get_pi_state(pi_state);
2247 : 0 : this->pi_state = pi_state;
2248 : 0 : ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
2249 : : this->rt_waiter,
2250 : : this->task);
2251 : 0 : if (ret == 1) {
2252 : : /*
2253 : : * We got the lock. We do neither drop the
2254 : : * refcount on pi_state nor clear
2255 : : * this->pi_state because the waiter needs the
2256 : : * pi_state for cleaning up the user space
2257 : : * value. It will drop the refcount after
2258 : : * doing so.
2259 : : */
2260 : 0 : requeue_pi_wake_futex(this, &key2, hb2);
2261 : 0 : drop_count++;
2262 : 0 : continue;
2263 : 0 : } else if (ret) {
2264 : : /*
2265 : : * rt_mutex_start_proxy_lock() detected a
2266 : : * potential deadlock when we tried to queue
2267 : : * that waiter. Drop the pi_state reference
2268 : : * which we took above and remove the pointer
2269 : : * to the state from the waiters futex_q
2270 : : * object.
2271 : : */
2272 : 0 : this->pi_state = NULL;
2273 : 0 : put_pi_state(pi_state);
2274 : : /*
2275 : : * We stop queueing more waiters and let user
2276 : : * space deal with the mess.
2277 : : */
2278 : 0 : break;
2279 : : }
2280 : : }
2281 : 0 : requeue_futex(this, hb1, hb2, &key2);
2282 : 0 : drop_count++;
2283 : : }
2284 : :
2285 : : /*
2286 : : * We took an extra initial reference to the pi_state either
2287 : : * in futex_proxy_trylock_atomic() or in lookup_pi_state(). We
2288 : : * need to drop it here again.
2289 : : */
2290 : 0 : put_pi_state(pi_state);
2291 : :
2292 : : out_unlock:
2293 : : double_unlock_hb(hb1, hb2);
2294 : 0 : wake_up_q(&wake_q);
2295 : : hb_waiters_dec(hb2);
2296 : :
2297 : : /*
2298 : : * drop_futex_key_refs() must be called outside the spinlocks. During
2299 : : * the requeue we moved futex_q's from the hash bucket at key1 to the
2300 : : * one at key2 and updated their key pointer. We no longer need to
2301 : : * hold the references to key1.
2302 : : */
2303 : 0 : while (--drop_count >= 0)
2304 : 0 : drop_futex_key_refs(&key1);
2305 : :
2306 : : out_put_keys:
2307 : : put_futex_key(&key2);
2308 : : out_put_key1:
2309 : : put_futex_key(&key1);
2310 : : out:
2311 : 0 : return ret ? ret : task_count;
2312 : : }
2313 : :
2314 : : /* The key must be already stored in q->key. */
2315 : 3 : static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
2316 : : __acquires(&hb->lock)
2317 : : {
2318 : : struct futex_hash_bucket *hb;
2319 : :
2320 : 3 : hb = hash_futex(&q->key);
2321 : :
2322 : : /*
2323 : : * Increment the counter before taking the lock so that
2324 : : * a potential waker won't miss a to-be-slept task that is
2325 : : * waiting for the spinlock. This is safe as all queue_lock()
2326 : : * users end up calling queue_me(). Similarly, for housekeeping,
2327 : : * decrement the counter at queue_unlock() when some error has
2328 : : * occurred and we don't end up adding the task to the list.
2329 : : */
2330 : 3 : hb_waiters_inc(hb); /* implies smp_mb(); (A) */
2331 : :
2332 : 3 : q->lock_ptr = &hb->lock;
2333 : :
2334 : : spin_lock(&hb->lock);
2335 : 3 : return hb;
2336 : : }
2337 : :
2338 : : static inline void
2339 : 3 : queue_unlock(struct futex_hash_bucket *hb)
2340 : : __releases(&hb->lock)
2341 : : {
2342 : : spin_unlock(&hb->lock);
2343 : : hb_waiters_dec(hb);
2344 : 3 : }
2345 : :
2346 : 3 : static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
2347 : : {
2348 : : int prio;
2349 : :
2350 : : /*
2351 : : * The priority used to register this element is
2352 : : * - either the real thread-priority for the real-time threads
2353 : : * (i.e. threads with a priority lower than MAX_RT_PRIO)
2354 : : * - or MAX_RT_PRIO for non-RT threads.
2355 : : * Thus, all RT-threads are woken first in priority order, and
2356 : : * the others are woken last, in FIFO order.
2357 : : */
2358 : 3 : prio = min(current->normal_prio, MAX_RT_PRIO);
2359 : :
2360 : : plist_node_init(&q->list, prio);
2361 : 3 : plist_add(&q->list, &hb->chain);
2362 : 3 : q->task = current;
2363 : 3 : }
2364 : :
2365 : : /**
2366 : : * queue_me() - Enqueue the futex_q on the futex_hash_bucket
2367 : : * @q: The futex_q to enqueue
2368 : : * @hb: The destination hash bucket
2369 : : *
2370 : : * The hb->lock must be held by the caller, and is released here. A call to
2371 : : * queue_me() is typically paired with exactly one call to unqueue_me(). The
2372 : : * exceptions involve the PI related operations, which may use unqueue_me_pi()
2373 : : * or nothing if the unqueue is done as part of the wake process and the unqueue
2374 : : * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
2375 : : * an example).
2376 : : */
2377 : : static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
2378 : : __releases(&hb->lock)
2379 : : {
2380 : 3 : __queue_me(q, hb);
2381 : : spin_unlock(&hb->lock);
2382 : : }
2383 : :
2384 : : /**
2385 : : * unqueue_me() - Remove the futex_q from its futex_hash_bucket
2386 : : * @q: The futex_q to unqueue
2387 : : *
2388 : : * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
2389 : : * be paired with exactly one earlier call to queue_me().
2390 : : *
2391 : : * Return:
2392 : : * - 1 - if the futex_q was still queued (and we removed unqueued it);
2393 : : * - 0 - if the futex_q was already removed by the waking thread
2394 : : */
2395 : 3 : static int unqueue_me(struct futex_q *q)
2396 : : {
2397 : : spinlock_t *lock_ptr;
2398 : : int ret = 0;
2399 : :
2400 : : /* In the common case we don't take the spinlock, which is nice. */
2401 : : retry:
2402 : : /*
2403 : : * q->lock_ptr can change between this read and the following spin_lock.
2404 : : * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
2405 : : * optimizing lock_ptr out of the logic below.
2406 : : */
2407 : 3 : lock_ptr = READ_ONCE(q->lock_ptr);
2408 : 3 : if (lock_ptr != NULL) {
2409 : : spin_lock(lock_ptr);
2410 : : /*
2411 : : * q->lock_ptr can change between reading it and
2412 : : * spin_lock(), causing us to take the wrong lock. This
2413 : : * corrects the race condition.
2414 : : *
2415 : : * Reasoning goes like this: if we have the wrong lock,
2416 : : * q->lock_ptr must have changed (maybe several times)
2417 : : * between reading it and the spin_lock(). It can
2418 : : * change again after the spin_lock() but only if it was
2419 : : * already changed before the spin_lock(). It cannot,
2420 : : * however, change back to the original value. Therefore
2421 : : * we can detect whether we acquired the correct lock.
2422 : : */
2423 : 3 : if (unlikely(lock_ptr != q->lock_ptr)) {
2424 : : spin_unlock(lock_ptr);
2425 : : goto retry;
2426 : : }
2427 : 3 : __unqueue_futex(q);
2428 : :
2429 : 3 : BUG_ON(q->pi_state);
2430 : :
2431 : : spin_unlock(lock_ptr);
2432 : : ret = 1;
2433 : : }
2434 : :
2435 : 3 : drop_futex_key_refs(&q->key);
2436 : 3 : return ret;
2437 : : }
2438 : :
2439 : : /*
2440 : : * PI futexes can not be requeued and must remove themself from the
2441 : : * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
2442 : : * and dropped here.
2443 : : */
2444 : 0 : static void unqueue_me_pi(struct futex_q *q)
2445 : : __releases(q->lock_ptr)
2446 : : {
2447 : 0 : __unqueue_futex(q);
2448 : :
2449 : 0 : BUG_ON(!q->pi_state);
2450 : 0 : put_pi_state(q->pi_state);
2451 : 0 : q->pi_state = NULL;
2452 : :
2453 : 0 : spin_unlock(q->lock_ptr);
2454 : 0 : }
2455 : :
2456 : 0 : static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
2457 : : struct task_struct *argowner)
2458 : : {
2459 : 0 : struct futex_pi_state *pi_state = q->pi_state;
2460 : : u32 uval, uninitialized_var(curval), newval;
2461 : : struct task_struct *oldowner, *newowner;
2462 : : u32 newtid;
2463 : : int ret, err = 0;
2464 : :
2465 : : lockdep_assert_held(q->lock_ptr);
2466 : :
2467 : 0 : raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
2468 : :
2469 : 0 : oldowner = pi_state->owner;
2470 : :
2471 : : /*
2472 : : * We are here because either:
2473 : : *
2474 : : * - we stole the lock and pi_state->owner needs updating to reflect
2475 : : * that (@argowner == current),
2476 : : *
2477 : : * or:
2478 : : *
2479 : : * - someone stole our lock and we need to fix things to point to the
2480 : : * new owner (@argowner == NULL).
2481 : : *
2482 : : * Either way, we have to replace the TID in the user space variable.
2483 : : * This must be atomic as we have to preserve the owner died bit here.
2484 : : *
2485 : : * Note: We write the user space value _before_ changing the pi_state
2486 : : * because we can fault here. Imagine swapped out pages or a fork
2487 : : * that marked all the anonymous memory readonly for cow.
2488 : : *
2489 : : * Modifying pi_state _before_ the user space value would leave the
2490 : : * pi_state in an inconsistent state when we fault here, because we
2491 : : * need to drop the locks to handle the fault. This might be observed
2492 : : * in the PID check in lookup_pi_state.
2493 : : */
2494 : : retry:
2495 : 0 : if (!argowner) {
2496 : 0 : if (oldowner != current) {
2497 : : /*
2498 : : * We raced against a concurrent self; things are
2499 : : * already fixed up. Nothing to do.
2500 : : */
2501 : : ret = 0;
2502 : : goto out_unlock;
2503 : : }
2504 : :
2505 : 0 : if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) {
2506 : : /* We got the lock after all, nothing to fix. */
2507 : : ret = 0;
2508 : : goto out_unlock;
2509 : : }
2510 : :
2511 : : /*
2512 : : * Since we just failed the trylock; there must be an owner.
2513 : : */
2514 : : newowner = rt_mutex_owner(&pi_state->pi_mutex);
2515 : 0 : BUG_ON(!newowner);
2516 : : } else {
2517 : 0 : WARN_ON_ONCE(argowner != current);
2518 : 0 : if (oldowner == current) {
2519 : : /*
2520 : : * We raced against a concurrent self; things are
2521 : : * already fixed up. Nothing to do.
2522 : : */
2523 : : ret = 0;
2524 : : goto out_unlock;
2525 : : }
2526 : : newowner = argowner;
2527 : : }
2528 : :
2529 : 0 : newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
2530 : : /* Owner died? */
2531 : 0 : if (!pi_state->owner)
2532 : 0 : newtid |= FUTEX_OWNER_DIED;
2533 : :
2534 : 0 : err = get_futex_value_locked(&uval, uaddr);
2535 : 0 : if (err)
2536 : : goto handle_err;
2537 : :
2538 : : for (;;) {
2539 : 0 : newval = (uval & FUTEX_OWNER_DIED) | newtid;
2540 : :
2541 : 0 : err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
2542 : 0 : if (err)
2543 : : goto handle_err;
2544 : :
2545 : 0 : if (curval == uval)
2546 : : break;
2547 : 0 : uval = curval;
2548 : 0 : }
2549 : :
2550 : : /*
2551 : : * We fixed up user space. Now we need to fix the pi_state
2552 : : * itself.
2553 : : */
2554 : 0 : if (pi_state->owner != NULL) {
2555 : 0 : raw_spin_lock(&pi_state->owner->pi_lock);
2556 : 0 : WARN_ON(list_empty(&pi_state->list));
2557 : : list_del_init(&pi_state->list);
2558 : 0 : raw_spin_unlock(&pi_state->owner->pi_lock);
2559 : : }
2560 : :
2561 : 0 : pi_state->owner = newowner;
2562 : :
2563 : 0 : raw_spin_lock(&newowner->pi_lock);
2564 : 0 : WARN_ON(!list_empty(&pi_state->list));
2565 : 0 : list_add(&pi_state->list, &newowner->pi_state_list);
2566 : : raw_spin_unlock(&newowner->pi_lock);
2567 : 0 : raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
2568 : :
2569 : 0 : return 0;
2570 : :
2571 : : /*
2572 : : * In order to reschedule or handle a page fault, we need to drop the
2573 : : * locks here. In the case of a fault, this gives the other task
2574 : : * (either the highest priority waiter itself or the task which stole
2575 : : * the rtmutex) the chance to try the fixup of the pi_state. So once we
2576 : : * are back from handling the fault we need to check the pi_state after
2577 : : * reacquiring the locks and before trying to do another fixup. When
2578 : : * the fixup has been done already we simply return.
2579 : : *
2580 : : * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
2581 : : * drop hb->lock since the caller owns the hb -> futex_q relation.
2582 : : * Dropping the pi_mutex->wait_lock requires the state revalidate.
2583 : : */
2584 : : handle_err:
2585 : 0 : raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
2586 : 0 : spin_unlock(q->lock_ptr);
2587 : :
2588 : 0 : switch (err) {
2589 : : case -EFAULT:
2590 : 0 : ret = fault_in_user_writeable(uaddr);
2591 : 0 : break;
2592 : :
2593 : : case -EAGAIN:
2594 : 0 : cond_resched();
2595 : : ret = 0;
2596 : 0 : break;
2597 : :
2598 : : default:
2599 : 0 : WARN_ON_ONCE(1);
2600 : : ret = err;
2601 : 0 : break;
2602 : : }
2603 : :
2604 : 0 : spin_lock(q->lock_ptr);
2605 : 0 : raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
2606 : :
2607 : : /*
2608 : : * Check if someone else fixed it for us:
2609 : : */
2610 : 0 : if (pi_state->owner != oldowner) {
2611 : : ret = 0;
2612 : : goto out_unlock;
2613 : : }
2614 : :
2615 : 0 : if (ret)
2616 : : goto out_unlock;
2617 : :
2618 : : goto retry;
2619 : :
2620 : : out_unlock:
2621 : 0 : raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
2622 : 0 : return ret;
2623 : : }
2624 : :
2625 : : static long futex_wait_restart(struct restart_block *restart);
2626 : :
2627 : : /**
2628 : : * fixup_owner() - Post lock pi_state and corner case management
2629 : : * @uaddr: user address of the futex
2630 : : * @q: futex_q (contains pi_state and access to the rt_mutex)
2631 : : * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
2632 : : *
2633 : : * After attempting to lock an rt_mutex, this function is called to cleanup
2634 : : * the pi_state owner as well as handle race conditions that may allow us to
2635 : : * acquire the lock. Must be called with the hb lock held.
2636 : : *
2637 : : * Return:
2638 : : * - 1 - success, lock taken;
2639 : : * - 0 - success, lock not taken;
2640 : : * - <0 - on error (-EFAULT)
2641 : : */
2642 : 0 : static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
2643 : : {
2644 : : int ret = 0;
2645 : :
2646 : 0 : if (locked) {
2647 : : /*
2648 : : * Got the lock. We might not be the anticipated owner if we
2649 : : * did a lock-steal - fix up the PI-state in that case:
2650 : : *
2651 : : * Speculative pi_state->owner read (we don't hold wait_lock);
2652 : : * since we own the lock pi_state->owner == current is the
2653 : : * stable state, anything else needs more attention.
2654 : : */
2655 : 0 : if (q->pi_state->owner != current)
2656 : 0 : ret = fixup_pi_state_owner(uaddr, q, current);
2657 : : goto out;
2658 : : }
2659 : :
2660 : : /*
2661 : : * If we didn't get the lock; check if anybody stole it from us. In
2662 : : * that case, we need to fix up the uval to point to them instead of
2663 : : * us, otherwise bad things happen. [10]
2664 : : *
2665 : : * Another speculative read; pi_state->owner == current is unstable
2666 : : * but needs our attention.
2667 : : */
2668 : 0 : if (q->pi_state->owner == current) {
2669 : 0 : ret = fixup_pi_state_owner(uaddr, q, NULL);
2670 : 0 : goto out;
2671 : : }
2672 : :
2673 : : /*
2674 : : * Paranoia check. If we did not take the lock, then we should not be
2675 : : * the owner of the rt_mutex.
2676 : : */
2677 : 0 : if (rt_mutex_owner(&q->pi_state->pi_mutex) == current) {
2678 : 0 : printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
2679 : : "pi-state %p\n", ret,
2680 : : q->pi_state->pi_mutex.owner,
2681 : : q->pi_state->owner);
2682 : : }
2683 : :
2684 : : out:
2685 : 0 : return ret ? ret : locked;
2686 : : }
2687 : :
2688 : : /**
2689 : : * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
2690 : : * @hb: the futex hash bucket, must be locked by the caller
2691 : : * @q: the futex_q to queue up on
2692 : : * @timeout: the prepared hrtimer_sleeper, or null for no timeout
2693 : : */
2694 : 3 : static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
2695 : : struct hrtimer_sleeper *timeout)
2696 : : {
2697 : : /*
2698 : : * The task state is guaranteed to be set before another task can
2699 : : * wake it. set_current_state() is implemented using smp_store_mb() and
2700 : : * queue_me() calls spin_unlock() upon completion, both serializing
2701 : : * access to the hash list and forcing another memory barrier.
2702 : : */
2703 : 3 : set_current_state(TASK_INTERRUPTIBLE);
2704 : : queue_me(q, hb);
2705 : :
2706 : : /* Arm the timer */
2707 : 3 : if (timeout)
2708 : 3 : hrtimer_sleeper_start_expires(timeout, HRTIMER_MODE_ABS);
2709 : :
2710 : : /*
2711 : : * If we have been removed from the hash list, then another task
2712 : : * has tried to wake us, and we can skip the call to schedule().
2713 : : */
2714 : 3 : if (likely(!plist_node_empty(&q->list))) {
2715 : : /*
2716 : : * If the timer has already expired, current will already be
2717 : : * flagged for rescheduling. Only call schedule if there
2718 : : * is no timeout, or if it has yet to expire.
2719 : : */
2720 : 3 : if (!timeout || timeout->task)
2721 : 3 : freezable_schedule();
2722 : : }
2723 : 3 : __set_current_state(TASK_RUNNING);
2724 : 3 : }
2725 : :
2726 : : /**
2727 : : * futex_wait_setup() - Prepare to wait on a futex
2728 : : * @uaddr: the futex userspace address
2729 : : * @val: the expected value
2730 : : * @flags: futex flags (FLAGS_SHARED, etc.)
2731 : : * @q: the associated futex_q
2732 : : * @hb: storage for hash_bucket pointer to be returned to caller
2733 : : *
2734 : : * Setup the futex_q and locate the hash_bucket. Get the futex value and
2735 : : * compare it with the expected value. Handle atomic faults internally.
2736 : : * Return with the hb lock held and a q.key reference on success, and unlocked
2737 : : * with no q.key reference on failure.
2738 : : *
2739 : : * Return:
2740 : : * - 0 - uaddr contains val and hb has been locked;
2741 : : * - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
2742 : : */
2743 : 3 : static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
2744 : : struct futex_q *q, struct futex_hash_bucket **hb)
2745 : : {
2746 : : u32 uval;
2747 : : int ret;
2748 : :
2749 : : /*
2750 : : * Access the page AFTER the hash-bucket is locked.
2751 : : * Order is important:
2752 : : *
2753 : : * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
2754 : : * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
2755 : : *
2756 : : * The basic logical guarantee of a futex is that it blocks ONLY
2757 : : * if cond(var) is known to be true at the time of blocking, for
2758 : : * any cond. If we locked the hash-bucket after testing *uaddr, that
2759 : : * would open a race condition where we could block indefinitely with
2760 : : * cond(var) false, which would violate the guarantee.
2761 : : *
2762 : : * On the other hand, we insert q and release the hash-bucket only
2763 : : * after testing *uaddr. This guarantees that futex_wait() will NOT
2764 : : * absorb a wakeup if *uaddr does not match the desired values
2765 : : * while the syscall executes.
2766 : : */
2767 : : retry:
2768 : 3 : ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, FUTEX_READ);
2769 : 3 : if (unlikely(ret != 0))
2770 : 0 : return ret;
2771 : :
2772 : : retry_private:
2773 : 3 : *hb = queue_lock(q);
2774 : :
2775 : 3 : ret = get_futex_value_locked(&uval, uaddr);
2776 : :
2777 : 3 : if (ret) {
2778 : 0 : queue_unlock(*hb);
2779 : :
2780 : 0 : ret = get_user(uval, uaddr);
2781 : 0 : if (ret)
2782 : : goto out;
2783 : :
2784 : 0 : if (!(flags & FLAGS_SHARED))
2785 : : goto retry_private;
2786 : :
2787 : : put_futex_key(&q->key);
2788 : : goto retry;
2789 : : }
2790 : :
2791 : 3 : if (uval != val) {
2792 : 3 : queue_unlock(*hb);
2793 : : ret = -EWOULDBLOCK;
2794 : : }
2795 : :
2796 : : out:
2797 : 3 : if (ret)
2798 : 3 : put_futex_key(&q->key);
2799 : 3 : return ret;
2800 : : }
2801 : :
2802 : 3 : static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
2803 : : ktime_t *abs_time, u32 bitset)
2804 : : {
2805 : : struct hrtimer_sleeper timeout, *to;
2806 : : struct restart_block *restart;
2807 : : struct futex_hash_bucket *hb;
2808 : 3 : struct futex_q q = futex_q_init;
2809 : : int ret;
2810 : :
2811 : 3 : if (!bitset)
2812 : : return -EINVAL;
2813 : 3 : q.bitset = bitset;
2814 : :
2815 : 3 : to = futex_setup_timer(abs_time, &timeout, flags,
2816 : 3 : current->timer_slack_ns);
2817 : : retry:
2818 : : /*
2819 : : * Prepare to wait on uaddr. On success, holds hb lock and increments
2820 : : * q.key refs.
2821 : : */
2822 : 3 : ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2823 : 3 : if (ret)
2824 : : goto out;
2825 : :
2826 : : /* queue_me and wait for wakeup, timeout, or a signal. */
2827 : 3 : futex_wait_queue_me(hb, &q, to);
2828 : :
2829 : : /* If we were woken (and unqueued), we succeeded, whatever. */
2830 : : ret = 0;
2831 : : /* unqueue_me() drops q.key ref */
2832 : 3 : if (!unqueue_me(&q))
2833 : : goto out;
2834 : : ret = -ETIMEDOUT;
2835 : 3 : if (to && !to->task)
2836 : : goto out;
2837 : :
2838 : : /*
2839 : : * We expect signal_pending(current), but we might be the
2840 : : * victim of a spurious wakeup as well.
2841 : : */
2842 : 3 : if (!signal_pending(current))
2843 : : goto retry;
2844 : :
2845 : : ret = -ERESTARTSYS;
2846 : 3 : if (!abs_time)
2847 : : goto out;
2848 : :
2849 : 3 : restart = ¤t->restart_block;
2850 : 3 : restart->fn = futex_wait_restart;
2851 : 3 : restart->futex.uaddr = uaddr;
2852 : 3 : restart->futex.val = val;
2853 : 3 : restart->futex.time = *abs_time;
2854 : 3 : restart->futex.bitset = bitset;
2855 : 3 : restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
2856 : :
2857 : : ret = -ERESTART_RESTARTBLOCK;
2858 : :
2859 : : out:
2860 : 3 : if (to) {
2861 : 3 : hrtimer_cancel(&to->timer);
2862 : : destroy_hrtimer_on_stack(&to->timer);
2863 : : }
2864 : 3 : return ret;
2865 : : }
2866 : :
2867 : :
2868 : 0 : static long futex_wait_restart(struct restart_block *restart)
2869 : : {
2870 : 0 : u32 __user *uaddr = restart->futex.uaddr;
2871 : : ktime_t t, *tp = NULL;
2872 : :
2873 : 0 : if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
2874 : 0 : t = restart->futex.time;
2875 : : tp = &t;
2876 : : }
2877 : 0 : restart->fn = do_no_restart_syscall;
2878 : :
2879 : 0 : return (long)futex_wait(uaddr, restart->futex.flags,
2880 : : restart->futex.val, tp, restart->futex.bitset);
2881 : : }
2882 : :
2883 : :
2884 : : /*
2885 : : * Userspace tried a 0 -> TID atomic transition of the futex value
2886 : : * and failed. The kernel side here does the whole locking operation:
2887 : : * if there are waiters then it will block as a consequence of relying
2888 : : * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
2889 : : * a 0 value of the futex too.).
2890 : : *
2891 : : * Also serves as futex trylock_pi()'ing, and due semantics.
2892 : : */
2893 : 0 : static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
2894 : : ktime_t *time, int trylock)
2895 : : {
2896 : : struct hrtimer_sleeper timeout, *to;
2897 : : struct futex_pi_state *pi_state = NULL;
2898 : 0 : struct task_struct *exiting = NULL;
2899 : : struct rt_mutex_waiter rt_waiter;
2900 : : struct futex_hash_bucket *hb;
2901 : 0 : struct futex_q q = futex_q_init;
2902 : : int res, ret;
2903 : :
2904 : : if (!IS_ENABLED(CONFIG_FUTEX_PI))
2905 : : return -ENOSYS;
2906 : :
2907 : 0 : if (refill_pi_state_cache())
2908 : : return -ENOMEM;
2909 : :
2910 : 0 : to = futex_setup_timer(time, &timeout, FLAGS_CLOCKRT, 0);
2911 : :
2912 : : retry:
2913 : 0 : ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE);
2914 : 0 : if (unlikely(ret != 0))
2915 : : goto out;
2916 : :
2917 : : retry_private:
2918 : 0 : hb = queue_lock(&q);
2919 : :
2920 : 0 : ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current,
2921 : : &exiting, 0);
2922 : 0 : if (unlikely(ret)) {
2923 : : /*
2924 : : * Atomic work succeeded and we got the lock,
2925 : : * or failed. Either way, we do _not_ block.
2926 : : */
2927 : 0 : switch (ret) {
2928 : : case 1:
2929 : : /* We got the lock. */
2930 : : ret = 0;
2931 : 0 : goto out_unlock_put_key;
2932 : : case -EFAULT:
2933 : : goto uaddr_faulted;
2934 : : case -EBUSY:
2935 : : case -EAGAIN:
2936 : : /*
2937 : : * Two reasons for this:
2938 : : * - EBUSY: Task is exiting and we just wait for the
2939 : : * exit to complete.
2940 : : * - EAGAIN: The user space value changed.
2941 : : */
2942 : 0 : queue_unlock(hb);
2943 : : put_futex_key(&q.key);
2944 : : /*
2945 : : * Handle the case where the owner is in the middle of
2946 : : * exiting. Wait for the exit to complete otherwise
2947 : : * this task might loop forever, aka. live lock.
2948 : : */
2949 : 0 : wait_for_owner_exiting(ret, exiting);
2950 : 0 : cond_resched();
2951 : 0 : goto retry;
2952 : : default:
2953 : : goto out_unlock_put_key;
2954 : : }
2955 : : }
2956 : :
2957 : 0 : WARN_ON(!q.pi_state);
2958 : :
2959 : : /*
2960 : : * Only actually queue now that the atomic ops are done:
2961 : : */
2962 : 0 : __queue_me(&q, hb);
2963 : :
2964 : 0 : if (trylock) {
2965 : 0 : ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
2966 : : /* Fixup the trylock return value: */
2967 : 0 : ret = ret ? 0 : -EWOULDBLOCK;
2968 : 0 : goto no_block;
2969 : : }
2970 : :
2971 : 0 : rt_mutex_init_waiter(&rt_waiter);
2972 : :
2973 : : /*
2974 : : * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
2975 : : * hold it while doing rt_mutex_start_proxy(), because then it will
2976 : : * include hb->lock in the blocking chain, even through we'll not in
2977 : : * fact hold it while blocking. This will lead it to report -EDEADLK
2978 : : * and BUG when futex_unlock_pi() interleaves with this.
2979 : : *
2980 : : * Therefore acquire wait_lock while holding hb->lock, but drop the
2981 : : * latter before calling __rt_mutex_start_proxy_lock(). This
2982 : : * interleaves with futex_unlock_pi() -- which does a similar lock
2983 : : * handoff -- such that the latter can observe the futex_q::pi_state
2984 : : * before __rt_mutex_start_proxy_lock() is done.
2985 : : */
2986 : 0 : raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
2987 : 0 : spin_unlock(q.lock_ptr);
2988 : : /*
2989 : : * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
2990 : : * such that futex_unlock_pi() is guaranteed to observe the waiter when
2991 : : * it sees the futex_q::pi_state.
2992 : : */
2993 : 0 : ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
2994 : 0 : raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
2995 : :
2996 : 0 : if (ret) {
2997 : 0 : if (ret == 1)
2998 : : ret = 0;
2999 : : goto cleanup;
3000 : : }
3001 : :
3002 : 0 : if (unlikely(to))
3003 : 0 : hrtimer_sleeper_start_expires(to, HRTIMER_MODE_ABS);
3004 : :
3005 : 0 : ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
3006 : :
3007 : : cleanup:
3008 : 0 : spin_lock(q.lock_ptr);
3009 : : /*
3010 : : * If we failed to acquire the lock (deadlock/signal/timeout), we must
3011 : : * first acquire the hb->lock before removing the lock from the
3012 : : * rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait
3013 : : * lists consistent.
3014 : : *
3015 : : * In particular; it is important that futex_unlock_pi() can not
3016 : : * observe this inconsistency.
3017 : : */
3018 : 0 : if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
3019 : : ret = 0;
3020 : :
3021 : : no_block:
3022 : : /*
3023 : : * Fixup the pi_state owner and possibly acquire the lock if we
3024 : : * haven't already.
3025 : : */
3026 : 0 : res = fixup_owner(uaddr, &q, !ret);
3027 : : /*
3028 : : * If fixup_owner() returned an error, proprogate that. If it acquired
3029 : : * the lock, clear our -ETIMEDOUT or -EINTR.
3030 : : */
3031 : 0 : if (res)
3032 : 0 : ret = (res < 0) ? res : 0;
3033 : :
3034 : : /*
3035 : : * If fixup_owner() faulted and was unable to handle the fault, unlock
3036 : : * it and return the fault to userspace.
3037 : : */
3038 : 0 : if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) {
3039 : : pi_state = q.pi_state;
3040 : 0 : get_pi_state(pi_state);
3041 : : }
3042 : :
3043 : : /* Unqueue and drop the lock */
3044 : 0 : unqueue_me_pi(&q);
3045 : :
3046 : 0 : if (pi_state) {
3047 : 0 : rt_mutex_futex_unlock(&pi_state->pi_mutex);
3048 : 0 : put_pi_state(pi_state);
3049 : : }
3050 : :
3051 : : goto out_put_key;
3052 : :
3053 : : out_unlock_put_key:
3054 : 0 : queue_unlock(hb);
3055 : :
3056 : : out_put_key:
3057 : : put_futex_key(&q.key);
3058 : : out:
3059 : 0 : if (to) {
3060 : 0 : hrtimer_cancel(&to->timer);
3061 : : destroy_hrtimer_on_stack(&to->timer);
3062 : : }
3063 : 0 : return ret != -EINTR ? ret : -ERESTARTNOINTR;
3064 : :
3065 : : uaddr_faulted:
3066 : 0 : queue_unlock(hb);
3067 : :
3068 : 0 : ret = fault_in_user_writeable(uaddr);
3069 : 0 : if (ret)
3070 : : goto out_put_key;
3071 : :
3072 : 0 : if (!(flags & FLAGS_SHARED))
3073 : : goto retry_private;
3074 : :
3075 : : put_futex_key(&q.key);
3076 : : goto retry;
3077 : : }
3078 : :
3079 : : /*
3080 : : * Userspace attempted a TID -> 0 atomic transition, and failed.
3081 : : * This is the in-kernel slowpath: we look up the PI state (if any),
3082 : : * and do the rt-mutex unlock.
3083 : : */
3084 : 1 : static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
3085 : : {
3086 : 1 : u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current);
3087 : 1 : union futex_key key = FUTEX_KEY_INIT;
3088 : : struct futex_hash_bucket *hb;
3089 : : struct futex_q *top_waiter;
3090 : : int ret;
3091 : :
3092 : : if (!IS_ENABLED(CONFIG_FUTEX_PI))
3093 : : return -ENOSYS;
3094 : :
3095 : : retry:
3096 : 1 : if (get_user(uval, uaddr))
3097 : : return -EFAULT;
3098 : : /*
3099 : : * We release only a lock we actually own:
3100 : : */
3101 : 1 : if ((uval & FUTEX_TID_MASK) != vpid)
3102 : : return -EPERM;
3103 : :
3104 : 0 : ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_WRITE);
3105 : 0 : if (ret)
3106 : 0 : return ret;
3107 : :
3108 : 0 : hb = hash_futex(&key);
3109 : : spin_lock(&hb->lock);
3110 : :
3111 : : /*
3112 : : * Check waiters first. We do not trust user space values at
3113 : : * all and we at least want to know if user space fiddled
3114 : : * with the futex value instead of blindly unlocking.
3115 : : */
3116 : 0 : top_waiter = futex_top_waiter(hb, &key);
3117 : 0 : if (top_waiter) {
3118 : 0 : struct futex_pi_state *pi_state = top_waiter->pi_state;
3119 : :
3120 : : ret = -EINVAL;
3121 : 0 : if (!pi_state)
3122 : : goto out_unlock;
3123 : :
3124 : : /*
3125 : : * If current does not own the pi_state then the futex is
3126 : : * inconsistent and user space fiddled with the futex value.
3127 : : */
3128 : 0 : if (pi_state->owner != current)
3129 : : goto out_unlock;
3130 : :
3131 : 0 : get_pi_state(pi_state);
3132 : : /*
3133 : : * By taking wait_lock while still holding hb->lock, we ensure
3134 : : * there is no point where we hold neither; and therefore
3135 : : * wake_futex_pi() must observe a state consistent with what we
3136 : : * observed.
3137 : : *
3138 : : * In particular; this forces __rt_mutex_start_proxy() to
3139 : : * complete such that we're guaranteed to observe the
3140 : : * rt_waiter. Also see the WARN in wake_futex_pi().
3141 : : */
3142 : 0 : raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
3143 : : spin_unlock(&hb->lock);
3144 : :
3145 : : /* drops pi_state->pi_mutex.wait_lock */
3146 : 0 : ret = wake_futex_pi(uaddr, uval, pi_state);
3147 : :
3148 : 0 : put_pi_state(pi_state);
3149 : :
3150 : : /*
3151 : : * Success, we're done! No tricky corner cases.
3152 : : */
3153 : 0 : if (!ret)
3154 : : goto out_putkey;
3155 : : /*
3156 : : * The atomic access to the futex value generated a
3157 : : * pagefault, so retry the user-access and the wakeup:
3158 : : */
3159 : 0 : if (ret == -EFAULT)
3160 : : goto pi_faulted;
3161 : : /*
3162 : : * A unconditional UNLOCK_PI op raced against a waiter
3163 : : * setting the FUTEX_WAITERS bit. Try again.
3164 : : */
3165 : 0 : if (ret == -EAGAIN)
3166 : : goto pi_retry;
3167 : : /*
3168 : : * wake_futex_pi has detected invalid state. Tell user
3169 : : * space.
3170 : : */
3171 : : goto out_putkey;
3172 : : }
3173 : :
3174 : : /*
3175 : : * We have no kernel internal state, i.e. no waiters in the
3176 : : * kernel. Waiters which are about to queue themselves are stuck
3177 : : * on hb->lock. So we can safely ignore them. We do neither
3178 : : * preserve the WAITERS bit not the OWNER_DIED one. We are the
3179 : : * owner.
3180 : : */
3181 : 0 : if ((ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))) {
3182 : : spin_unlock(&hb->lock);
3183 : 0 : switch (ret) {
3184 : : case -EFAULT:
3185 : : goto pi_faulted;
3186 : :
3187 : : case -EAGAIN:
3188 : : goto pi_retry;
3189 : :
3190 : : default:
3191 : 0 : WARN_ON_ONCE(1);
3192 : : goto out_putkey;
3193 : : }
3194 : : }
3195 : :
3196 : : /*
3197 : : * If uval has changed, let user space handle it.
3198 : : */
3199 : 0 : ret = (curval == uval) ? 0 : -EAGAIN;
3200 : :
3201 : : out_unlock:
3202 : : spin_unlock(&hb->lock);
3203 : : out_putkey:
3204 : : put_futex_key(&key);
3205 : 0 : return ret;
3206 : :
3207 : : pi_retry:
3208 : : put_futex_key(&key);
3209 : 0 : cond_resched();
3210 : 0 : goto retry;
3211 : :
3212 : : pi_faulted:
3213 : : put_futex_key(&key);
3214 : :
3215 : 0 : ret = fault_in_user_writeable(uaddr);
3216 : 0 : if (!ret)
3217 : : goto retry;
3218 : :
3219 : 0 : return ret;
3220 : : }
3221 : :
3222 : : /**
3223 : : * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
3224 : : * @hb: the hash_bucket futex_q was original enqueued on
3225 : : * @q: the futex_q woken while waiting to be requeued
3226 : : * @key2: the futex_key of the requeue target futex
3227 : : * @timeout: the timeout associated with the wait (NULL if none)
3228 : : *
3229 : : * Detect if the task was woken on the initial futex as opposed to the requeue
3230 : : * target futex. If so, determine if it was a timeout or a signal that caused
3231 : : * the wakeup and return the appropriate error code to the caller. Must be
3232 : : * called with the hb lock held.
3233 : : *
3234 : : * Return:
3235 : : * - 0 = no early wakeup detected;
3236 : : * - <0 = -ETIMEDOUT or -ERESTARTNOINTR
3237 : : */
3238 : : static inline
3239 : 0 : int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
3240 : : struct futex_q *q, union futex_key *key2,
3241 : : struct hrtimer_sleeper *timeout)
3242 : : {
3243 : : int ret = 0;
3244 : :
3245 : : /*
3246 : : * With the hb lock held, we avoid races while we process the wakeup.
3247 : : * We only need to hold hb (and not hb2) to ensure atomicity as the
3248 : : * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
3249 : : * It can't be requeued from uaddr2 to something else since we don't
3250 : : * support a PI aware source futex for requeue.
3251 : : */
3252 : 0 : if (!match_futex(&q->key, key2)) {
3253 : 0 : WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
3254 : : /*
3255 : : * We were woken prior to requeue by a timeout or a signal.
3256 : : * Unqueue the futex_q and determine which it was.
3257 : : */
3258 : 0 : plist_del(&q->list, &hb->chain);
3259 : : hb_waiters_dec(hb);
3260 : :
3261 : : /* Handle spurious wakeups gracefully */
3262 : : ret = -EWOULDBLOCK;
3263 : 0 : if (timeout && !timeout->task)
3264 : : ret = -ETIMEDOUT;
3265 : 0 : else if (signal_pending(current))
3266 : : ret = -ERESTARTNOINTR;
3267 : : }
3268 : 0 : return ret;
3269 : : }
3270 : :
3271 : : /**
3272 : : * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
3273 : : * @uaddr: the futex we initially wait on (non-pi)
3274 : : * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
3275 : : * the same type, no requeueing from private to shared, etc.
3276 : : * @val: the expected value of uaddr
3277 : : * @abs_time: absolute timeout
3278 : : * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
3279 : : * @uaddr2: the pi futex we will take prior to returning to user-space
3280 : : *
3281 : : * The caller will wait on uaddr and will be requeued by futex_requeue() to
3282 : : * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
3283 : : * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
3284 : : * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
3285 : : * without one, the pi logic would not know which task to boost/deboost, if
3286 : : * there was a need to.
3287 : : *
3288 : : * We call schedule in futex_wait_queue_me() when we enqueue and return there
3289 : : * via the following--
3290 : : * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
3291 : : * 2) wakeup on uaddr2 after a requeue
3292 : : * 3) signal
3293 : : * 4) timeout
3294 : : *
3295 : : * If 3, cleanup and return -ERESTARTNOINTR.
3296 : : *
3297 : : * If 2, we may then block on trying to take the rt_mutex and return via:
3298 : : * 5) successful lock
3299 : : * 6) signal
3300 : : * 7) timeout
3301 : : * 8) other lock acquisition failure
3302 : : *
3303 : : * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
3304 : : *
3305 : : * If 4 or 7, we cleanup and return with -ETIMEDOUT.
3306 : : *
3307 : : * Return:
3308 : : * - 0 - On success;
3309 : : * - <0 - On error
3310 : : */
3311 : 0 : static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
3312 : : u32 val, ktime_t *abs_time, u32 bitset,
3313 : : u32 __user *uaddr2)
3314 : : {
3315 : : struct hrtimer_sleeper timeout, *to;
3316 : : struct futex_pi_state *pi_state = NULL;
3317 : : struct rt_mutex_waiter rt_waiter;
3318 : : struct futex_hash_bucket *hb;
3319 : 0 : union futex_key key2 = FUTEX_KEY_INIT;
3320 : 0 : struct futex_q q = futex_q_init;
3321 : : int res, ret;
3322 : :
3323 : : if (!IS_ENABLED(CONFIG_FUTEX_PI))
3324 : : return -ENOSYS;
3325 : :
3326 : 0 : if (uaddr == uaddr2)
3327 : : return -EINVAL;
3328 : :
3329 : 0 : if (!bitset)
3330 : : return -EINVAL;
3331 : :
3332 : 0 : to = futex_setup_timer(abs_time, &timeout, flags,
3333 : 0 : current->timer_slack_ns);
3334 : :
3335 : : /*
3336 : : * The waiter is allocated on our stack, manipulated by the requeue
3337 : : * code while we sleep on uaddr.
3338 : : */
3339 : 0 : rt_mutex_init_waiter(&rt_waiter);
3340 : :
3341 : 0 : ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
3342 : 0 : if (unlikely(ret != 0))
3343 : : goto out;
3344 : :
3345 : 0 : q.bitset = bitset;
3346 : 0 : q.rt_waiter = &rt_waiter;
3347 : 0 : q.requeue_pi_key = &key2;
3348 : :
3349 : : /*
3350 : : * Prepare to wait on uaddr. On success, increments q.key (key1) ref
3351 : : * count.
3352 : : */
3353 : 0 : ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
3354 : 0 : if (ret)
3355 : : goto out_key2;
3356 : :
3357 : : /*
3358 : : * The check above which compares uaddrs is not sufficient for
3359 : : * shared futexes. We need to compare the keys:
3360 : : */
3361 : 0 : if (match_futex(&q.key, &key2)) {
3362 : 0 : queue_unlock(hb);
3363 : : ret = -EINVAL;
3364 : 0 : goto out_put_keys;
3365 : : }
3366 : :
3367 : : /* Queue the futex_q, drop the hb lock, wait for wakeup. */
3368 : 0 : futex_wait_queue_me(hb, &q, to);
3369 : :
3370 : 0 : spin_lock(&hb->lock);
3371 : 0 : ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
3372 : 0 : spin_unlock(&hb->lock);
3373 : 0 : if (ret)
3374 : : goto out_put_keys;
3375 : :
3376 : : /*
3377 : : * In order for us to be here, we know our q.key == key2, and since
3378 : : * we took the hb->lock above, we also know that futex_requeue() has
3379 : : * completed and we no longer have to concern ourselves with a wakeup
3380 : : * race with the atomic proxy lock acquisition by the requeue code. The
3381 : : * futex_requeue dropped our key1 reference and incremented our key2
3382 : : * reference count.
3383 : : */
3384 : :
3385 : : /* Check if the requeue code acquired the second futex for us. */
3386 : 0 : if (!q.rt_waiter) {
3387 : : /*
3388 : : * Got the lock. We might not be the anticipated owner if we
3389 : : * did a lock-steal - fix up the PI-state in that case.
3390 : : */
3391 : 0 : if (q.pi_state && (q.pi_state->owner != current)) {
3392 : 0 : spin_lock(q.lock_ptr);
3393 : 0 : ret = fixup_pi_state_owner(uaddr2, &q, current);
3394 : 0 : if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
3395 : : pi_state = q.pi_state;
3396 : 0 : get_pi_state(pi_state);
3397 : : }
3398 : : /*
3399 : : * Drop the reference to the pi state which
3400 : : * the requeue_pi() code acquired for us.
3401 : : */
3402 : 0 : put_pi_state(q.pi_state);
3403 : 0 : spin_unlock(q.lock_ptr);
3404 : : }
3405 : : } else {
3406 : : struct rt_mutex *pi_mutex;
3407 : :
3408 : : /*
3409 : : * We have been woken up by futex_unlock_pi(), a timeout, or a
3410 : : * signal. futex_unlock_pi() will not destroy the lock_ptr nor
3411 : : * the pi_state.
3412 : : */
3413 : 0 : WARN_ON(!q.pi_state);
3414 : 0 : pi_mutex = &q.pi_state->pi_mutex;
3415 : 0 : ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);
3416 : :
3417 : 0 : spin_lock(q.lock_ptr);
3418 : 0 : if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
3419 : : ret = 0;
3420 : :
3421 : : debug_rt_mutex_free_waiter(&rt_waiter);
3422 : : /*
3423 : : * Fixup the pi_state owner and possibly acquire the lock if we
3424 : : * haven't already.
3425 : : */
3426 : 0 : res = fixup_owner(uaddr2, &q, !ret);
3427 : : /*
3428 : : * If fixup_owner() returned an error, proprogate that. If it
3429 : : * acquired the lock, clear -ETIMEDOUT or -EINTR.
3430 : : */
3431 : 0 : if (res)
3432 : 0 : ret = (res < 0) ? res : 0;
3433 : :
3434 : : /*
3435 : : * If fixup_pi_state_owner() faulted and was unable to handle
3436 : : * the fault, unlock the rt_mutex and return the fault to
3437 : : * userspace.
3438 : : */
3439 : 0 : if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
3440 : : pi_state = q.pi_state;
3441 : 0 : get_pi_state(pi_state);
3442 : : }
3443 : :
3444 : : /* Unqueue and drop the lock. */
3445 : 0 : unqueue_me_pi(&q);
3446 : : }
3447 : :
3448 : 0 : if (pi_state) {
3449 : 0 : rt_mutex_futex_unlock(&pi_state->pi_mutex);
3450 : 0 : put_pi_state(pi_state);
3451 : : }
3452 : :
3453 : 0 : if (ret == -EINTR) {
3454 : : /*
3455 : : * We've already been requeued, but cannot restart by calling
3456 : : * futex_lock_pi() directly. We could restart this syscall, but
3457 : : * it would detect that the user space "val" changed and return
3458 : : * -EWOULDBLOCK. Save the overhead of the restart and return
3459 : : * -EWOULDBLOCK directly.
3460 : : */
3461 : : ret = -EWOULDBLOCK;
3462 : : }
3463 : :
3464 : : out_put_keys:
3465 : : put_futex_key(&q.key);
3466 : : out_key2:
3467 : : put_futex_key(&key2);
3468 : :
3469 : : out:
3470 : 0 : if (to) {
3471 : 0 : hrtimer_cancel(&to->timer);
3472 : : destroy_hrtimer_on_stack(&to->timer);
3473 : : }
3474 : 0 : return ret;
3475 : : }
3476 : :
3477 : : /*
3478 : : * Support for robust futexes: the kernel cleans up held futexes at
3479 : : * thread exit time.
3480 : : *
3481 : : * Implementation: user-space maintains a per-thread list of locks it
3482 : : * is holding. Upon do_exit(), the kernel carefully walks this list,
3483 : : * and marks all locks that are owned by this thread with the
3484 : : * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
3485 : : * always manipulated with the lock held, so the list is private and
3486 : : * per-thread. Userspace also maintains a per-thread 'list_op_pending'
3487 : : * field, to allow the kernel to clean up if the thread dies after
3488 : : * acquiring the lock, but just before it could have added itself to
3489 : : * the list. There can only be one such pending lock.
3490 : : */
3491 : :
3492 : : /**
3493 : : * sys_set_robust_list() - Set the robust-futex list head of a task
3494 : : * @head: pointer to the list-head
3495 : : * @len: length of the list-head, as userspace expects
3496 : : */
3497 : 3 : SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
3498 : : size_t, len)
3499 : : {
3500 : 3 : if (!futex_cmpxchg_enabled)
3501 : : return -ENOSYS;
3502 : : /*
3503 : : * The kernel knows only one size for now:
3504 : : */
3505 : 3 : if (unlikely(len != sizeof(*head)))
3506 : : return -EINVAL;
3507 : :
3508 : 3 : current->robust_list = head;
3509 : :
3510 : : return 0;
3511 : : }
3512 : :
3513 : : /**
3514 : : * sys_get_robust_list() - Get the robust-futex list head of a task
3515 : : * @pid: pid of the process [zero for current task]
3516 : : * @head_ptr: pointer to a list-head pointer, the kernel fills it in
3517 : : * @len_ptr: pointer to a length field, the kernel fills in the header size
3518 : : */
3519 : 0 : SYSCALL_DEFINE3(get_robust_list, int, pid,
3520 : : struct robust_list_head __user * __user *, head_ptr,
3521 : : size_t __user *, len_ptr)
3522 : : {
3523 : : struct robust_list_head __user *head;
3524 : : unsigned long ret;
3525 : : struct task_struct *p;
3526 : :
3527 : 0 : if (!futex_cmpxchg_enabled)
3528 : : return -ENOSYS;
3529 : :
3530 : : rcu_read_lock();
3531 : :
3532 : : ret = -ESRCH;
3533 : 0 : if (!pid)
3534 : 0 : p = current;
3535 : : else {
3536 : 0 : p = find_task_by_vpid(pid);
3537 : 0 : if (!p)
3538 : : goto err_unlock;
3539 : : }
3540 : :
3541 : : ret = -EPERM;
3542 : 0 : if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
3543 : : goto err_unlock;
3544 : :
3545 : 0 : head = p->robust_list;
3546 : : rcu_read_unlock();
3547 : :
3548 : 0 : if (put_user(sizeof(*head), len_ptr))
3549 : : return -EFAULT;
3550 : 0 : return put_user(head, head_ptr);
3551 : :
3552 : : err_unlock:
3553 : : rcu_read_unlock();
3554 : :
3555 : 0 : return ret;
3556 : : }
3557 : :
3558 : : /* Constants for the pending_op argument of handle_futex_death */
3559 : : #define HANDLE_DEATH_PENDING true
3560 : : #define HANDLE_DEATH_LIST false
3561 : :
3562 : : /*
3563 : : * Process a futex-list entry, check whether it's owned by the
3564 : : * dying task, and do notification if so:
3565 : : */
3566 : 0 : static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr,
3567 : : bool pi, bool pending_op)
3568 : : {
3569 : : u32 uval, uninitialized_var(nval), mval;
3570 : : int err;
3571 : :
3572 : : /* Futex address must be 32bit aligned */
3573 : 0 : if ((((unsigned long)uaddr) % sizeof(*uaddr)) != 0)
3574 : : return -1;
3575 : :
3576 : : retry:
3577 : 0 : if (get_user(uval, uaddr))
3578 : : return -1;
3579 : :
3580 : : /*
3581 : : * Special case for regular (non PI) futexes. The unlock path in
3582 : : * user space has two race scenarios:
3583 : : *
3584 : : * 1. The unlock path releases the user space futex value and
3585 : : * before it can execute the futex() syscall to wake up
3586 : : * waiters it is killed.
3587 : : *
3588 : : * 2. A woken up waiter is killed before it can acquire the
3589 : : * futex in user space.
3590 : : *
3591 : : * In both cases the TID validation below prevents a wakeup of
3592 : : * potential waiters which can cause these waiters to block
3593 : : * forever.
3594 : : *
3595 : : * In both cases the following conditions are met:
3596 : : *
3597 : : * 1) task->robust_list->list_op_pending != NULL
3598 : : * @pending_op == true
3599 : : * 2) User space futex value == 0
3600 : : * 3) Regular futex: @pi == false
3601 : : *
3602 : : * If these conditions are met, it is safe to attempt waking up a
3603 : : * potential waiter without touching the user space futex value and
3604 : : * trying to set the OWNER_DIED bit. The user space futex value is
3605 : : * uncontended and the rest of the user space mutex state is
3606 : : * consistent, so a woken waiter will just take over the
3607 : : * uncontended futex. Setting the OWNER_DIED bit would create
3608 : : * inconsistent state and malfunction of the user space owner died
3609 : : * handling.
3610 : : */
3611 : 0 : if (pending_op && !pi && !uval) {
3612 : 0 : futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
3613 : 0 : return 0;
3614 : : }
3615 : :
3616 : 0 : if ((uval & FUTEX_TID_MASK) != task_pid_vnr(curr))
3617 : : return 0;
3618 : :
3619 : : /*
3620 : : * Ok, this dying thread is truly holding a futex
3621 : : * of interest. Set the OWNER_DIED bit atomically
3622 : : * via cmpxchg, and if the value had FUTEX_WAITERS
3623 : : * set, wake up a waiter (if any). (We have to do a
3624 : : * futex_wake() even if OWNER_DIED is already set -
3625 : : * to handle the rare but possible case of recursive
3626 : : * thread-death.) The rest of the cleanup is done in
3627 : : * userspace.
3628 : : */
3629 : 0 : mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
3630 : :
3631 : : /*
3632 : : * We are not holding a lock here, but we want to have
3633 : : * the pagefault_disable/enable() protection because
3634 : : * we want to handle the fault gracefully. If the
3635 : : * access fails we try to fault in the futex with R/W
3636 : : * verification via get_user_pages. get_user() above
3637 : : * does not guarantee R/W access. If that fails we
3638 : : * give up and leave the futex locked.
3639 : : */
3640 : 0 : if ((err = cmpxchg_futex_value_locked(&nval, uaddr, uval, mval))) {
3641 : 0 : switch (err) {
3642 : : case -EFAULT:
3643 : 0 : if (fault_in_user_writeable(uaddr))
3644 : : return -1;
3645 : : goto retry;
3646 : :
3647 : : case -EAGAIN:
3648 : 0 : cond_resched();
3649 : 0 : goto retry;
3650 : :
3651 : : default:
3652 : 0 : WARN_ON_ONCE(1);
3653 : 0 : return err;
3654 : : }
3655 : : }
3656 : :
3657 : 0 : if (nval != uval)
3658 : : goto retry;
3659 : :
3660 : : /*
3661 : : * Wake robust non-PI futexes here. The wakeup of
3662 : : * PI futexes happens in exit_pi_state():
3663 : : */
3664 : 0 : if (!pi && (uval & FUTEX_WAITERS))
3665 : 0 : futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
3666 : :
3667 : : return 0;
3668 : : }
3669 : :
3670 : : /*
3671 : : * Fetch a robust-list pointer. Bit 0 signals PI futexes:
3672 : : */
3673 : 3 : static inline int fetch_robust_entry(struct robust_list __user **entry,
3674 : : struct robust_list __user * __user *head,
3675 : : unsigned int *pi)
3676 : : {
3677 : : unsigned long uentry;
3678 : :
3679 : 3 : if (get_user(uentry, (unsigned long __user *)head))
3680 : : return -EFAULT;
3681 : :
3682 : 3 : *entry = (void __user *)(uentry & ~1UL);
3683 : 3 : *pi = uentry & 1;
3684 : :
3685 : 3 : return 0;
3686 : : }
3687 : :
3688 : : /*
3689 : : * Walk curr->robust_list (very carefully, it's a userspace list!)
3690 : : * and mark any locks found there dead, and notify any waiters.
3691 : : *
3692 : : * We silently return on any sign of list-walking problem.
3693 : : */
3694 : 3 : static void exit_robust_list(struct task_struct *curr)
3695 : : {
3696 : 3 : struct robust_list_head __user *head = curr->robust_list;
3697 : : struct robust_list __user *entry, *next_entry, *pending;
3698 : : unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
3699 : : unsigned int uninitialized_var(next_pi);
3700 : : unsigned long futex_offset;
3701 : : int rc;
3702 : :
3703 : 3 : if (!futex_cmpxchg_enabled)
3704 : 0 : return;
3705 : :
3706 : : /*
3707 : : * Fetch the list head (which was registered earlier, via
3708 : : * sys_set_robust_list()):
3709 : : */
3710 : 3 : if (fetch_robust_entry(&entry, &head->list.next, &pi))
3711 : : return;
3712 : : /*
3713 : : * Fetch the relative futex offset:
3714 : : */
3715 : 3 : if (get_user(futex_offset, &head->futex_offset))
3716 : : return;
3717 : : /*
3718 : : * Fetch any possibly pending lock-add first, and handle it
3719 : : * if it exists:
3720 : : */
3721 : 3 : if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
3722 : : return;
3723 : :
3724 : 3 : next_entry = NULL; /* avoid warning with gcc */
3725 : 3 : while (entry != &head->list) {
3726 : : /*
3727 : : * Fetch the next entry in the list before calling
3728 : : * handle_futex_death:
3729 : : */
3730 : 0 : rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
3731 : : /*
3732 : : * A pending lock might already be on the list, so
3733 : : * don't process it twice:
3734 : : */
3735 : 0 : if (entry != pending) {
3736 : 0 : if (handle_futex_death((void __user *)entry + futex_offset,
3737 : : curr, pi, HANDLE_DEATH_LIST))
3738 : : return;
3739 : : }
3740 : 0 : if (rc)
3741 : : return;
3742 : 0 : entry = next_entry;
3743 : 0 : pi = next_pi;
3744 : : /*
3745 : : * Avoid excessively long or circular lists:
3746 : : */
3747 : 0 : if (!--limit)
3748 : : break;
3749 : :
3750 : 0 : cond_resched();
3751 : : }
3752 : :
3753 : 3 : if (pending) {
3754 : 0 : handle_futex_death((void __user *)pending + futex_offset,
3755 : : curr, pip, HANDLE_DEATH_PENDING);
3756 : : }
3757 : : }
3758 : :
3759 : 3 : static void futex_cleanup(struct task_struct *tsk)
3760 : : {
3761 : 3 : if (unlikely(tsk->robust_list)) {
3762 : 3 : exit_robust_list(tsk);
3763 : 3 : tsk->robust_list = NULL;
3764 : : }
3765 : :
3766 : : #ifdef CONFIG_COMPAT
3767 : : if (unlikely(tsk->compat_robust_list)) {
3768 : : compat_exit_robust_list(tsk);
3769 : : tsk->compat_robust_list = NULL;
3770 : : }
3771 : : #endif
3772 : :
3773 : 3 : if (unlikely(!list_empty(&tsk->pi_state_list)))
3774 : 0 : exit_pi_state_list(tsk);
3775 : 3 : }
3776 : :
3777 : : /**
3778 : : * futex_exit_recursive - Set the tasks futex state to FUTEX_STATE_DEAD
3779 : : * @tsk: task to set the state on
3780 : : *
3781 : : * Set the futex exit state of the task lockless. The futex waiter code
3782 : : * observes that state when a task is exiting and loops until the task has
3783 : : * actually finished the futex cleanup. The worst case for this is that the
3784 : : * waiter runs through the wait loop until the state becomes visible.
3785 : : *
3786 : : * This is called from the recursive fault handling path in do_exit().
3787 : : *
3788 : : * This is best effort. Either the futex exit code has run already or
3789 : : * not. If the OWNER_DIED bit has been set on the futex then the waiter can
3790 : : * take it over. If not, the problem is pushed back to user space. If the
3791 : : * futex exit code did not run yet, then an already queued waiter might
3792 : : * block forever, but there is nothing which can be done about that.
3793 : : */
3794 : 0 : void futex_exit_recursive(struct task_struct *tsk)
3795 : : {
3796 : : /* If the state is FUTEX_STATE_EXITING then futex_exit_mutex is held */
3797 : 0 : if (tsk->futex_state == FUTEX_STATE_EXITING)
3798 : 0 : mutex_unlock(&tsk->futex_exit_mutex);
3799 : 0 : tsk->futex_state = FUTEX_STATE_DEAD;
3800 : 0 : }
3801 : :
3802 : 3 : static void futex_cleanup_begin(struct task_struct *tsk)
3803 : : {
3804 : : /*
3805 : : * Prevent various race issues against a concurrent incoming waiter
3806 : : * including live locks by forcing the waiter to block on
3807 : : * tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in
3808 : : * attach_to_pi_owner().
3809 : : */
3810 : 3 : mutex_lock(&tsk->futex_exit_mutex);
3811 : :
3812 : : /*
3813 : : * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock.
3814 : : *
3815 : : * This ensures that all subsequent checks of tsk->futex_state in
3816 : : * attach_to_pi_owner() must observe FUTEX_STATE_EXITING with
3817 : : * tsk->pi_lock held.
3818 : : *
3819 : : * It guarantees also that a pi_state which was queued right before
3820 : : * the state change under tsk->pi_lock by a concurrent waiter must
3821 : : * be observed in exit_pi_state_list().
3822 : : */
3823 : 3 : raw_spin_lock_irq(&tsk->pi_lock);
3824 : 3 : tsk->futex_state = FUTEX_STATE_EXITING;
3825 : 3 : raw_spin_unlock_irq(&tsk->pi_lock);
3826 : 3 : }
3827 : :
3828 : : static void futex_cleanup_end(struct task_struct *tsk, int state)
3829 : : {
3830 : : /*
3831 : : * Lockless store. The only side effect is that an observer might
3832 : : * take another loop until it becomes visible.
3833 : : */
3834 : 3 : tsk->futex_state = state;
3835 : : /*
3836 : : * Drop the exit protection. This unblocks waiters which observed
3837 : : * FUTEX_STATE_EXITING to reevaluate the state.
3838 : : */
3839 : 3 : mutex_unlock(&tsk->futex_exit_mutex);
3840 : : }
3841 : :
3842 : 3 : void futex_exec_release(struct task_struct *tsk)
3843 : : {
3844 : : /*
3845 : : * The state handling is done for consistency, but in the case of
3846 : : * exec() there is no way to prevent futher damage as the PID stays
3847 : : * the same. But for the unlikely and arguably buggy case that a
3848 : : * futex is held on exec(), this provides at least as much state
3849 : : * consistency protection which is possible.
3850 : : */
3851 : 3 : futex_cleanup_begin(tsk);
3852 : 3 : futex_cleanup(tsk);
3853 : : /*
3854 : : * Reset the state to FUTEX_STATE_OK. The task is alive and about
3855 : : * exec a new binary.
3856 : : */
3857 : : futex_cleanup_end(tsk, FUTEX_STATE_OK);
3858 : 3 : }
3859 : :
3860 : 3 : void futex_exit_release(struct task_struct *tsk)
3861 : : {
3862 : 3 : futex_cleanup_begin(tsk);
3863 : 3 : futex_cleanup(tsk);
3864 : : futex_cleanup_end(tsk, FUTEX_STATE_DEAD);
3865 : 3 : }
3866 : :
3867 : 3 : long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
3868 : : u32 __user *uaddr2, u32 val2, u32 val3)
3869 : : {
3870 : 3 : int cmd = op & FUTEX_CMD_MASK;
3871 : : unsigned int flags = 0;
3872 : :
3873 : 3 : if (!(op & FUTEX_PRIVATE_FLAG))
3874 : : flags |= FLAGS_SHARED;
3875 : :
3876 : 3 : if (op & FUTEX_CLOCK_REALTIME) {
3877 : 3 : flags |= FLAGS_CLOCKRT;
3878 : 3 : if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \
3879 : : cmd != FUTEX_WAIT_REQUEUE_PI)
3880 : : return -ENOSYS;
3881 : : }
3882 : :
3883 : 3 : switch (cmd) {
3884 : : case FUTEX_LOCK_PI:
3885 : : case FUTEX_UNLOCK_PI:
3886 : : case FUTEX_TRYLOCK_PI:
3887 : : case FUTEX_WAIT_REQUEUE_PI:
3888 : : case FUTEX_CMP_REQUEUE_PI:
3889 : 1 : if (!futex_cmpxchg_enabled)
3890 : : return -ENOSYS;
3891 : : }
3892 : :
3893 : 3 : switch (cmd) {
3894 : : case FUTEX_WAIT:
3895 : 3 : val3 = FUTEX_BITSET_MATCH_ANY;
3896 : : /* fall through */
3897 : : case FUTEX_WAIT_BITSET:
3898 : 3 : return futex_wait(uaddr, flags, val, timeout, val3);
3899 : : case FUTEX_WAKE:
3900 : 3 : val3 = FUTEX_BITSET_MATCH_ANY;
3901 : : /* fall through */
3902 : : case FUTEX_WAKE_BITSET:
3903 : 3 : return futex_wake(uaddr, flags, val, val3);
3904 : : case FUTEX_REQUEUE:
3905 : 0 : return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
3906 : : case FUTEX_CMP_REQUEUE:
3907 : 0 : return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
3908 : : case FUTEX_WAKE_OP:
3909 : 0 : return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
3910 : : case FUTEX_LOCK_PI:
3911 : 0 : return futex_lock_pi(uaddr, flags, timeout, 0);
3912 : : case FUTEX_UNLOCK_PI:
3913 : 1 : return futex_unlock_pi(uaddr, flags);
3914 : : case FUTEX_TRYLOCK_PI:
3915 : 0 : return futex_lock_pi(uaddr, flags, NULL, 1);
3916 : : case FUTEX_WAIT_REQUEUE_PI:
3917 : 0 : val3 = FUTEX_BITSET_MATCH_ANY;
3918 : 0 : return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
3919 : : uaddr2);
3920 : : case FUTEX_CMP_REQUEUE_PI:
3921 : 0 : return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
3922 : : }
3923 : : return -ENOSYS;
3924 : : }
3925 : :
3926 : :
3927 : 0 : SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
3928 : : struct __kernel_timespec __user *, utime, u32 __user *, uaddr2,
3929 : : u32, val3)
3930 : : {
3931 : : struct timespec64 ts;
3932 : : ktime_t t, *tp = NULL;
3933 : : u32 val2 = 0;
3934 : 0 : int cmd = op & FUTEX_CMD_MASK;
3935 : :
3936 : 0 : if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
3937 : 0 : cmd == FUTEX_WAIT_BITSET ||
3938 : 0 : cmd == FUTEX_WAIT_REQUEUE_PI)) {
3939 : : if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
3940 : : return -EFAULT;
3941 : 0 : if (get_timespec64(&ts, utime))
3942 : : return -EFAULT;
3943 : 0 : if (!timespec64_valid(&ts))
3944 : : return -EINVAL;
3945 : :
3946 : 0 : t = timespec64_to_ktime(ts);
3947 : 0 : if (cmd == FUTEX_WAIT)
3948 : 0 : t = ktime_add_safe(ktime_get(), t);
3949 : : tp = &t;
3950 : : }
3951 : : /*
3952 : : * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
3953 : : * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
3954 : : */
3955 : 0 : if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
3956 : 0 : cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
3957 : 0 : val2 = (u32) (unsigned long) utime;
3958 : :
3959 : 0 : return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
3960 : : }
3961 : :
3962 : : #ifdef CONFIG_COMPAT
3963 : : /*
3964 : : * Fetch a robust-list pointer. Bit 0 signals PI futexes:
3965 : : */
3966 : : static inline int
3967 : : compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry,
3968 : : compat_uptr_t __user *head, unsigned int *pi)
3969 : : {
3970 : : if (get_user(*uentry, head))
3971 : : return -EFAULT;
3972 : :
3973 : : *entry = compat_ptr((*uentry) & ~1);
3974 : : *pi = (unsigned int)(*uentry) & 1;
3975 : :
3976 : : return 0;
3977 : : }
3978 : :
3979 : : static void __user *futex_uaddr(struct robust_list __user *entry,
3980 : : compat_long_t futex_offset)
3981 : : {
3982 : : compat_uptr_t base = ptr_to_compat(entry);
3983 : : void __user *uaddr = compat_ptr(base + futex_offset);
3984 : :
3985 : : return uaddr;
3986 : : }
3987 : :
3988 : : /*
3989 : : * Walk curr->robust_list (very carefully, it's a userspace list!)
3990 : : * and mark any locks found there dead, and notify any waiters.
3991 : : *
3992 : : * We silently return on any sign of list-walking problem.
3993 : : */
3994 : : static void compat_exit_robust_list(struct task_struct *curr)
3995 : : {
3996 : : struct compat_robust_list_head __user *head = curr->compat_robust_list;
3997 : : struct robust_list __user *entry, *next_entry, *pending;
3998 : : unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
3999 : : unsigned int uninitialized_var(next_pi);
4000 : : compat_uptr_t uentry, next_uentry, upending;
4001 : : compat_long_t futex_offset;
4002 : : int rc;
4003 : :
4004 : : if (!futex_cmpxchg_enabled)
4005 : : return;
4006 : :
4007 : : /*
4008 : : * Fetch the list head (which was registered earlier, via
4009 : : * sys_set_robust_list()):
4010 : : */
4011 : : if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &pi))
4012 : : return;
4013 : : /*
4014 : : * Fetch the relative futex offset:
4015 : : */
4016 : : if (get_user(futex_offset, &head->futex_offset))
4017 : : return;
4018 : : /*
4019 : : * Fetch any possibly pending lock-add first, and handle it
4020 : : * if it exists:
4021 : : */
4022 : : if (compat_fetch_robust_entry(&upending, &pending,
4023 : : &head->list_op_pending, &pip))
4024 : : return;
4025 : :
4026 : : next_entry = NULL; /* avoid warning with gcc */
4027 : : while (entry != (struct robust_list __user *) &head->list) {
4028 : : /*
4029 : : * Fetch the next entry in the list before calling
4030 : : * handle_futex_death:
4031 : : */
4032 : : rc = compat_fetch_robust_entry(&next_uentry, &next_entry,
4033 : : (compat_uptr_t __user *)&entry->next, &next_pi);
4034 : : /*
4035 : : * A pending lock might already be on the list, so
4036 : : * dont process it twice:
4037 : : */
4038 : : if (entry != pending) {
4039 : : void __user *uaddr = futex_uaddr(entry, futex_offset);
4040 : :
4041 : : if (handle_futex_death(uaddr, curr, pi,
4042 : : HANDLE_DEATH_LIST))
4043 : : return;
4044 : : }
4045 : : if (rc)
4046 : : return;
4047 : : uentry = next_uentry;
4048 : : entry = next_entry;
4049 : : pi = next_pi;
4050 : : /*
4051 : : * Avoid excessively long or circular lists:
4052 : : */
4053 : : if (!--limit)
4054 : : break;
4055 : :
4056 : : cond_resched();
4057 : : }
4058 : : if (pending) {
4059 : : void __user *uaddr = futex_uaddr(pending, futex_offset);
4060 : :
4061 : : handle_futex_death(uaddr, curr, pip, HANDLE_DEATH_PENDING);
4062 : : }
4063 : : }
4064 : :
4065 : : COMPAT_SYSCALL_DEFINE2(set_robust_list,
4066 : : struct compat_robust_list_head __user *, head,
4067 : : compat_size_t, len)
4068 : : {
4069 : : if (!futex_cmpxchg_enabled)
4070 : : return -ENOSYS;
4071 : :
4072 : : if (unlikely(len != sizeof(*head)))
4073 : : return -EINVAL;
4074 : :
4075 : : current->compat_robust_list = head;
4076 : :
4077 : : return 0;
4078 : : }
4079 : :
4080 : : COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
4081 : : compat_uptr_t __user *, head_ptr,
4082 : : compat_size_t __user *, len_ptr)
4083 : : {
4084 : : struct compat_robust_list_head __user *head;
4085 : : unsigned long ret;
4086 : : struct task_struct *p;
4087 : :
4088 : : if (!futex_cmpxchg_enabled)
4089 : : return -ENOSYS;
4090 : :
4091 : : rcu_read_lock();
4092 : :
4093 : : ret = -ESRCH;
4094 : : if (!pid)
4095 : : p = current;
4096 : : else {
4097 : : p = find_task_by_vpid(pid);
4098 : : if (!p)
4099 : : goto err_unlock;
4100 : : }
4101 : :
4102 : : ret = -EPERM;
4103 : : if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
4104 : : goto err_unlock;
4105 : :
4106 : : head = p->compat_robust_list;
4107 : : rcu_read_unlock();
4108 : :
4109 : : if (put_user(sizeof(*head), len_ptr))
4110 : : return -EFAULT;
4111 : : return put_user(ptr_to_compat(head), head_ptr);
4112 : :
4113 : : err_unlock:
4114 : : rcu_read_unlock();
4115 : :
4116 : : return ret;
4117 : : }
4118 : : #endif /* CONFIG_COMPAT */
4119 : :
4120 : : #ifdef CONFIG_COMPAT_32BIT_TIME
4121 : 3 : SYSCALL_DEFINE6(futex_time32, u32 __user *, uaddr, int, op, u32, val,
4122 : : struct old_timespec32 __user *, utime, u32 __user *, uaddr2,
4123 : : u32, val3)
4124 : : {
4125 : : struct timespec64 ts;
4126 : : ktime_t t, *tp = NULL;
4127 : : int val2 = 0;
4128 : 3 : int cmd = op & FUTEX_CMD_MASK;
4129 : :
4130 : 3 : if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
4131 : 0 : cmd == FUTEX_WAIT_BITSET ||
4132 : 0 : cmd == FUTEX_WAIT_REQUEUE_PI)) {
4133 : 3 : if (get_old_timespec32(&ts, utime))
4134 : : return -EFAULT;
4135 : 3 : if (!timespec64_valid(&ts))
4136 : : return -EINVAL;
4137 : :
4138 : 3 : t = timespec64_to_ktime(ts);
4139 : 3 : if (cmd == FUTEX_WAIT)
4140 : 3 : t = ktime_add_safe(ktime_get(), t);
4141 : : tp = &t;
4142 : : }
4143 : 3 : if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
4144 : 3 : cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
4145 : 0 : val2 = (int) (unsigned long) utime;
4146 : :
4147 : 3 : return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
4148 : : }
4149 : : #endif /* CONFIG_COMPAT_32BIT_TIME */
4150 : :
4151 : 3 : static void __init futex_detect_cmpxchg(void)
4152 : : {
4153 : : #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
4154 : : u32 curval;
4155 : :
4156 : : /*
4157 : : * This will fail and we want it. Some arch implementations do
4158 : : * runtime detection of the futex_atomic_cmpxchg_inatomic()
4159 : : * functionality. We want to know that before we call in any
4160 : : * of the complex code paths. Also we want to prevent
4161 : : * registration of robust lists in that case. NULL is
4162 : : * guaranteed to fault and we get -EFAULT on functional
4163 : : * implementation, the non-functional ones will return
4164 : : * -ENOSYS.
4165 : : */
4166 : 3 : if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
4167 : 3 : futex_cmpxchg_enabled = 1;
4168 : : #endif
4169 : 3 : }
4170 : :
4171 : 3 : static int __init futex_init(void)
4172 : : {
4173 : : unsigned int futex_shift;
4174 : : unsigned long i;
4175 : :
4176 : : #if CONFIG_BASE_SMALL
4177 : : futex_hashsize = 16;
4178 : : #else
4179 : 3 : futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
4180 : : #endif
4181 : :
4182 : 3 : futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
4183 : : futex_hashsize, 0,
4184 : : futex_hashsize < 256 ? HASH_SMALL : 0,
4185 : : &futex_shift, NULL,
4186 : : futex_hashsize, futex_hashsize);
4187 : 3 : futex_hashsize = 1UL << futex_shift;
4188 : :
4189 : 3 : futex_detect_cmpxchg();
4190 : :
4191 : 3 : for (i = 0; i < futex_hashsize; i++) {
4192 : 3 : atomic_set(&futex_queues[i].waiters, 0);
4193 : : plist_head_init(&futex_queues[i].chain);
4194 : 3 : spin_lock_init(&futex_queues[i].lock);
4195 : : }
4196 : :
4197 : 3 : return 0;
4198 : : }
4199 : : core_initcall(futex_init);
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