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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/jhash.h>
36#include <linux/pagemap.h>
37#include <linux/debugfs.h>
38#include <linux/plist.h>
39#include <linux/memblock.h>
40#include <linux/fault-inject.h>
41#include <linux/slab.h>
42
43#include "futex.h"
44#include "../locking/rtmutex_common.h"
45
46/*
47 * The base of the bucket array and its size are always used together
48 * (after initialization only in futex_hash()), so ensure that they
49 * reside in the same cacheline.
50 */
51static struct {
52 struct futex_hash_bucket *queues;
53 unsigned long hashsize;
54} __futex_data __read_mostly __aligned(2*sizeof(long));
55#define futex_queues (__futex_data.queues)
56#define futex_hashsize (__futex_data.hashsize)
57
58
59/*
60 * Fault injections for futexes.
61 */
62#ifdef CONFIG_FAIL_FUTEX
63
64static struct {
65 struct fault_attr attr;
66
67 bool ignore_private;
68} fail_futex = {
69 .attr = FAULT_ATTR_INITIALIZER,
70 .ignore_private = false,
71};
72
73static int __init setup_fail_futex(char *str)
74{
75 return setup_fault_attr(&fail_futex.attr, str);
76}
77__setup("fail_futex=", setup_fail_futex);
78
79bool should_fail_futex(bool fshared)
80{
81 if (fail_futex.ignore_private && !fshared)
82 return false;
83
84 return should_fail(&fail_futex.attr, 1);
85}
86
87#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
88
89static int __init fail_futex_debugfs(void)
90{
91 umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
92 struct dentry *dir;
93
94 dir = fault_create_debugfs_attr("fail_futex", NULL,
95 &fail_futex.attr);
96 if (IS_ERR(dir))
97 return PTR_ERR(dir);
98
99 debugfs_create_bool("ignore-private", mode, dir,
100 &fail_futex.ignore_private);
101 return 0;
102}
103
104late_initcall(fail_futex_debugfs);
105
106#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
107
108#endif /* CONFIG_FAIL_FUTEX */
109
110/**
111 * futex_hash - Return the hash bucket in the global hash
112 * @key: Pointer to the futex key for which the hash is calculated
113 *
114 * We hash on the keys returned from get_futex_key (see below) and return the
115 * corresponding hash bucket in the global hash.
116 */
117struct futex_hash_bucket *futex_hash(union futex_key *key)
118{
119 u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
120 key->both.offset);
121
122 return &futex_queues[hash & (futex_hashsize - 1)];
123}
124
125
126/**
127 * futex_setup_timer - set up the sleeping hrtimer.
128 * @time: ptr to the given timeout value
129 * @timeout: the hrtimer_sleeper structure to be set up
130 * @flags: futex flags
131 * @range_ns: optional range in ns
132 *
133 * Return: Initialized hrtimer_sleeper structure or NULL if no timeout
134 * value given
135 */
136struct hrtimer_sleeper *
137futex_setup_timer(ktime_t *time, struct hrtimer_sleeper *timeout,
138 int flags, u64 range_ns)
139{
140 if (!time)
141 return NULL;
142
143 hrtimer_setup_sleeper_on_stack(timeout,
144 (flags & FLAGS_CLOCKRT) ? CLOCK_REALTIME : CLOCK_MONOTONIC,
145 HRTIMER_MODE_ABS);
146 /*
147 * If range_ns is 0, calling hrtimer_set_expires_range_ns() is
148 * effectively the same as calling hrtimer_set_expires().
149 */
150 hrtimer_set_expires_range_ns(&timeout->timer, *time, range_ns);
151
152 return timeout;
153}
154
155/*
156 * Generate a machine wide unique identifier for this inode.
157 *
158 * This relies on u64 not wrapping in the life-time of the machine; which with
159 * 1ns resolution means almost 585 years.
160 *
161 * This further relies on the fact that a well formed program will not unmap
162 * the file while it has a (shared) futex waiting on it. This mapping will have
163 * a file reference which pins the mount and inode.
164 *
165 * If for some reason an inode gets evicted and read back in again, it will get
166 * a new sequence number and will _NOT_ match, even though it is the exact same
167 * file.
168 *
169 * It is important that futex_match() will never have a false-positive, esp.
170 * for PI futexes that can mess up the state. The above argues that false-negatives
171 * are only possible for malformed programs.
172 */
173static u64 get_inode_sequence_number(struct inode *inode)
174{
175 static atomic64_t i_seq;
176 u64 old;
177
178 /* Does the inode already have a sequence number? */
179 old = atomic64_read(&inode->i_sequence);
180 if (likely(old))
181 return old;
182
183 for (;;) {
184 u64 new = atomic64_inc_return(&i_seq);
185 if (WARN_ON_ONCE(!new))
186 continue;
187
188 old = 0;
189 if (!atomic64_try_cmpxchg_relaxed(&inode->i_sequence, &old, new))
190 return old;
191 return new;
192 }
193}
194
195/**
196 * get_futex_key() - Get parameters which are the keys for a futex
197 * @uaddr: virtual address of the futex
198 * @flags: FLAGS_*
199 * @key: address where result is stored.
200 * @rw: mapping needs to be read/write (values: FUTEX_READ,
201 * FUTEX_WRITE)
202 *
203 * Return: a negative error code or 0
204 *
205 * The key words are stored in @key on success.
206 *
207 * For shared mappings (when @fshared), the key is:
208 *
209 * ( inode->i_sequence, page->index, offset_within_page )
210 *
211 * [ also see get_inode_sequence_number() ]
212 *
213 * For private mappings (or when !@fshared), the key is:
214 *
215 * ( current->mm, address, 0 )
216 *
217 * This allows (cross process, where applicable) identification of the futex
218 * without keeping the page pinned for the duration of the FUTEX_WAIT.
219 *
220 * lock_page() might sleep, the caller should not hold a spinlock.
221 */
222int get_futex_key(u32 __user *uaddr, unsigned int flags, union futex_key *key,
223 enum futex_access rw)
224{
225 unsigned long address = (unsigned long)uaddr;
226 struct mm_struct *mm = current->mm;
227 struct page *page;
228 struct folio *folio;
229 struct address_space *mapping;
230 int err, ro = 0;
231 bool fshared;
232
233 fshared = flags & FLAGS_SHARED;
234
235 /*
236 * The futex address must be "naturally" aligned.
237 */
238 key->both.offset = address % PAGE_SIZE;
239 if (unlikely((address % sizeof(u32)) != 0))
240 return -EINVAL;
241 address -= key->both.offset;
242
243 if (unlikely(!access_ok(uaddr, sizeof(u32))))
244 return -EFAULT;
245
246 if (unlikely(should_fail_futex(fshared)))
247 return -EFAULT;
248
249 /*
250 * PROCESS_PRIVATE futexes are fast.
251 * As the mm cannot disappear under us and the 'key' only needs
252 * virtual address, we dont even have to find the underlying vma.
253 * Note : We do have to check 'uaddr' is a valid user address,
254 * but access_ok() should be faster than find_vma()
255 */
256 if (!fshared) {
257 /*
258 * On no-MMU, shared futexes are treated as private, therefore
259 * we must not include the current process in the key. Since
260 * there is only one address space, the address is a unique key
261 * on its own.
262 */
263 if (IS_ENABLED(CONFIG_MMU))
264 key->private.mm = mm;
265 else
266 key->private.mm = NULL;
267
268 key->private.address = address;
269 return 0;
270 }
271
272again:
273 /* Ignore any VERIFY_READ mapping (futex common case) */
274 if (unlikely(should_fail_futex(true)))
275 return -EFAULT;
276
277 err = get_user_pages_fast(address, 1, FOLL_WRITE, &page);
278 /*
279 * If write access is not required (eg. FUTEX_WAIT), try
280 * and get read-only access.
281 */
282 if (err == -EFAULT && rw == FUTEX_READ) {
283 err = get_user_pages_fast(address, 1, 0, &page);
284 ro = 1;
285 }
286 if (err < 0)
287 return err;
288 else
289 err = 0;
290
291 /*
292 * The treatment of mapping from this point on is critical. The folio
293 * lock protects many things but in this context the folio lock
294 * stabilizes mapping, prevents inode freeing in the shared
295 * file-backed region case and guards against movement to swap cache.
296 *
297 * Strictly speaking the folio lock is not needed in all cases being
298 * considered here and folio lock forces unnecessarily serialization.
299 * From this point on, mapping will be re-verified if necessary and
300 * folio lock will be acquired only if it is unavoidable
301 *
302 * Mapping checks require the folio so it is looked up now. For
303 * anonymous pages, it does not matter if the folio is split
304 * in the future as the key is based on the address. For
305 * filesystem-backed pages, the precise page is required as the
306 * index of the page determines the key.
307 */
308 folio = page_folio(page);
309 mapping = READ_ONCE(folio->mapping);
310
311 /*
312 * If folio->mapping is NULL, then it cannot be an anonymous
313 * page; but it might be the ZERO_PAGE or in the gate area or
314 * in a special mapping (all cases which we are happy to fail);
315 * or it may have been a good file page when get_user_pages_fast
316 * found it, but truncated or holepunched or subjected to
317 * invalidate_complete_page2 before we got the folio lock (also
318 * cases which we are happy to fail). And we hold a reference,
319 * so refcount care in invalidate_inode_page's remove_mapping
320 * prevents drop_caches from setting mapping to NULL beneath us.
321 *
322 * The case we do have to guard against is when memory pressure made
323 * shmem_writepage move it from filecache to swapcache beneath us:
324 * an unlikely race, but we do need to retry for folio->mapping.
325 */
326 if (unlikely(!mapping)) {
327 int shmem_swizzled;
328
329 /*
330 * Folio lock is required to identify which special case above
331 * applies. If this is really a shmem page then the folio lock
332 * will prevent unexpected transitions.
333 */
334 folio_lock(folio);
335 shmem_swizzled = folio_test_swapcache(folio) || folio->mapping;
336 folio_unlock(folio);
337 folio_put(folio);
338
339 if (shmem_swizzled)
340 goto again;
341
342 return -EFAULT;
343 }
344
345 /*
346 * Private mappings are handled in a simple way.
347 *
348 * If the futex key is stored in anonymous memory, then the associated
349 * object is the mm which is implicitly pinned by the calling process.
350 *
351 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
352 * it's a read-only handle, it's expected that futexes attach to
353 * the object not the particular process.
354 */
355 if (folio_test_anon(folio)) {
356 /*
357 * A RO anonymous page will never change and thus doesn't make
358 * sense for futex operations.
359 */
360 if (unlikely(should_fail_futex(true)) || ro) {
361 err = -EFAULT;
362 goto out;
363 }
364
365 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
366 key->private.mm = mm;
367 key->private.address = address;
368
369 } else {
370 struct inode *inode;
371
372 /*
373 * The associated futex object in this case is the inode and
374 * the folio->mapping must be traversed. Ordinarily this should
375 * be stabilised under folio lock but it's not strictly
376 * necessary in this case as we just want to pin the inode, not
377 * update i_pages or anything like that.
378 *
379 * The RCU read lock is taken as the inode is finally freed
380 * under RCU. If the mapping still matches expectations then the
381 * mapping->host can be safely accessed as being a valid inode.
382 */
383 rcu_read_lock();
384
385 if (READ_ONCE(folio->mapping) != mapping) {
386 rcu_read_unlock();
387 folio_put(folio);
388
389 goto again;
390 }
391
392 inode = READ_ONCE(mapping->host);
393 if (!inode) {
394 rcu_read_unlock();
395 folio_put(folio);
396
397 goto again;
398 }
399
400 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
401 key->shared.i_seq = get_inode_sequence_number(inode);
402 key->shared.pgoff = page_pgoff(folio, page);
403 rcu_read_unlock();
404 }
405
406out:
407 folio_put(folio);
408 return err;
409}
410
411/**
412 * fault_in_user_writeable() - Fault in user address and verify RW access
413 * @uaddr: pointer to faulting user space address
414 *
415 * Slow path to fixup the fault we just took in the atomic write
416 * access to @uaddr.
417 *
418 * We have no generic implementation of a non-destructive write to the
419 * user address. We know that we faulted in the atomic pagefault
420 * disabled section so we can as well avoid the #PF overhead by
421 * calling get_user_pages() right away.
422 */
423int fault_in_user_writeable(u32 __user *uaddr)
424{
425 struct mm_struct *mm = current->mm;
426 int ret;
427
428 mmap_read_lock(mm);
429 ret = fixup_user_fault(mm, (unsigned long)uaddr,
430 FAULT_FLAG_WRITE, NULL);
431 mmap_read_unlock(mm);
432
433 return ret < 0 ? ret : 0;
434}
435
436/**
437 * futex_top_waiter() - Return the highest priority waiter on a futex
438 * @hb: the hash bucket the futex_q's reside in
439 * @key: the futex key (to distinguish it from other futex futex_q's)
440 *
441 * Must be called with the hb lock held.
442 */
443struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb, union futex_key *key)
444{
445 struct futex_q *this;
446
447 plist_for_each_entry(this, &hb->chain, list) {
448 if (futex_match(&this->key, key))
449 return this;
450 }
451 return NULL;
452}
453
454/**
455 * wait_for_owner_exiting - Block until the owner has exited
456 * @ret: owner's current futex lock status
457 * @exiting: Pointer to the exiting task
458 *
459 * Caller must hold a refcount on @exiting.
460 */
461void wait_for_owner_exiting(int ret, struct task_struct *exiting)
462{
463 if (ret != -EBUSY) {
464 WARN_ON_ONCE(exiting);
465 return;
466 }
467
468 if (WARN_ON_ONCE(ret == -EBUSY && !exiting))
469 return;
470
471 mutex_lock(&exiting->futex_exit_mutex);
472 /*
473 * No point in doing state checking here. If the waiter got here
474 * while the task was in exec()->exec_futex_release() then it can
475 * have any FUTEX_STATE_* value when the waiter has acquired the
476 * mutex. OK, if running, EXITING or DEAD if it reached exit()
477 * already. Highly unlikely and not a problem. Just one more round
478 * through the futex maze.
479 */
480 mutex_unlock(&exiting->futex_exit_mutex);
481
482 put_task_struct(exiting);
483}
484
485/**
486 * __futex_unqueue() - Remove the futex_q from its futex_hash_bucket
487 * @q: The futex_q to unqueue
488 *
489 * The q->lock_ptr must not be NULL and must be held by the caller.
490 */
491void __futex_unqueue(struct futex_q *q)
492{
493 struct futex_hash_bucket *hb;
494
495 if (WARN_ON_SMP(!q->lock_ptr) || WARN_ON(plist_node_empty(&q->list)))
496 return;
497 lockdep_assert_held(q->lock_ptr);
498
499 hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
500 plist_del(&q->list, &hb->chain);
501 futex_hb_waiters_dec(hb);
502}
503
504/* The key must be already stored in q->key. */
505struct futex_hash_bucket *futex_q_lock(struct futex_q *q)
506 __acquires(&hb->lock)
507{
508 struct futex_hash_bucket *hb;
509
510 hb = futex_hash(&q->key);
511
512 /*
513 * Increment the counter before taking the lock so that
514 * a potential waker won't miss a to-be-slept task that is
515 * waiting for the spinlock. This is safe as all futex_q_lock()
516 * users end up calling futex_queue(). Similarly, for housekeeping,
517 * decrement the counter at futex_q_unlock() when some error has
518 * occurred and we don't end up adding the task to the list.
519 */
520 futex_hb_waiters_inc(hb); /* implies smp_mb(); (A) */
521
522 q->lock_ptr = &hb->lock;
523
524 spin_lock(&hb->lock);
525 return hb;
526}
527
528void futex_q_unlock(struct futex_hash_bucket *hb)
529 __releases(&hb->lock)
530{
531 spin_unlock(&hb->lock);
532 futex_hb_waiters_dec(hb);
533}
534
535void __futex_queue(struct futex_q *q, struct futex_hash_bucket *hb)
536{
537 int prio;
538
539 /*
540 * The priority used to register this element is
541 * - either the real thread-priority for the real-time threads
542 * (i.e. threads with a priority lower than MAX_RT_PRIO)
543 * - or MAX_RT_PRIO for non-RT threads.
544 * Thus, all RT-threads are woken first in priority order, and
545 * the others are woken last, in FIFO order.
546 */
547 prio = min(current->normal_prio, MAX_RT_PRIO);
548
549 plist_node_init(&q->list, prio);
550 plist_add(&q->list, &hb->chain);
551 q->task = current;
552}
553
554/**
555 * futex_unqueue() - Remove the futex_q from its futex_hash_bucket
556 * @q: The futex_q to unqueue
557 *
558 * The q->lock_ptr must not be held by the caller. A call to futex_unqueue() must
559 * be paired with exactly one earlier call to futex_queue().
560 *
561 * Return:
562 * - 1 - if the futex_q was still queued (and we removed unqueued it);
563 * - 0 - if the futex_q was already removed by the waking thread
564 */
565int futex_unqueue(struct futex_q *q)
566{
567 spinlock_t *lock_ptr;
568 int ret = 0;
569
570 /* In the common case we don't take the spinlock, which is nice. */
571retry:
572 /*
573 * q->lock_ptr can change between this read and the following spin_lock.
574 * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
575 * optimizing lock_ptr out of the logic below.
576 */
577 lock_ptr = READ_ONCE(q->lock_ptr);
578 if (lock_ptr != NULL) {
579 spin_lock(lock_ptr);
580 /*
581 * q->lock_ptr can change between reading it and
582 * spin_lock(), causing us to take the wrong lock. This
583 * corrects the race condition.
584 *
585 * Reasoning goes like this: if we have the wrong lock,
586 * q->lock_ptr must have changed (maybe several times)
587 * between reading it and the spin_lock(). It can
588 * change again after the spin_lock() but only if it was
589 * already changed before the spin_lock(). It cannot,
590 * however, change back to the original value. Therefore
591 * we can detect whether we acquired the correct lock.
592 */
593 if (unlikely(lock_ptr != q->lock_ptr)) {
594 spin_unlock(lock_ptr);
595 goto retry;
596 }
597 __futex_unqueue(q);
598
599 BUG_ON(q->pi_state);
600
601 spin_unlock(lock_ptr);
602 ret = 1;
603 }
604
605 return ret;
606}
607
608/*
609 * PI futexes can not be requeued and must remove themselves from the hash
610 * bucket. The hash bucket lock (i.e. lock_ptr) is held.
611 */
612void futex_unqueue_pi(struct futex_q *q)
613{
614 /*
615 * If the lock was not acquired (due to timeout or signal) then the
616 * rt_waiter is removed before futex_q is. If this is observed by
617 * an unlocker after dropping the rtmutex wait lock and before
618 * acquiring the hash bucket lock, then the unlocker dequeues the
619 * futex_q from the hash bucket list to guarantee consistent state
620 * vs. userspace. Therefore the dequeue here must be conditional.
621 */
622 if (!plist_node_empty(&q->list))
623 __futex_unqueue(q);
624
625 BUG_ON(!q->pi_state);
626 put_pi_state(q->pi_state);
627 q->pi_state = NULL;
628}
629
630/* Constants for the pending_op argument of handle_futex_death */
631#define HANDLE_DEATH_PENDING true
632#define HANDLE_DEATH_LIST false
633
634/*
635 * Process a futex-list entry, check whether it's owned by the
636 * dying task, and do notification if so:
637 */
638static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr,
639 bool pi, bool pending_op)
640{
641 u32 uval, nval, mval;
642 pid_t owner;
643 int err;
644
645 /* Futex address must be 32bit aligned */
646 if ((((unsigned long)uaddr) % sizeof(*uaddr)) != 0)
647 return -1;
648
649retry:
650 if (get_user(uval, uaddr))
651 return -1;
652
653 /*
654 * Special case for regular (non PI) futexes. The unlock path in
655 * user space has two race scenarios:
656 *
657 * 1. The unlock path releases the user space futex value and
658 * before it can execute the futex() syscall to wake up
659 * waiters it is killed.
660 *
661 * 2. A woken up waiter is killed before it can acquire the
662 * futex in user space.
663 *
664 * In the second case, the wake up notification could be generated
665 * by the unlock path in user space after setting the futex value
666 * to zero or by the kernel after setting the OWNER_DIED bit below.
667 *
668 * In both cases the TID validation below prevents a wakeup of
669 * potential waiters which can cause these waiters to block
670 * forever.
671 *
672 * In both cases the following conditions are met:
673 *
674 * 1) task->robust_list->list_op_pending != NULL
675 * @pending_op == true
676 * 2) The owner part of user space futex value == 0
677 * 3) Regular futex: @pi == false
678 *
679 * If these conditions are met, it is safe to attempt waking up a
680 * potential waiter without touching the user space futex value and
681 * trying to set the OWNER_DIED bit. If the futex value is zero,
682 * the rest of the user space mutex state is consistent, so a woken
683 * waiter will just take over the uncontended futex. Setting the
684 * OWNER_DIED bit would create inconsistent state and malfunction
685 * of the user space owner died handling. Otherwise, the OWNER_DIED
686 * bit is already set, and the woken waiter is expected to deal with
687 * this.
688 */
689 owner = uval & FUTEX_TID_MASK;
690
691 if (pending_op && !pi && !owner) {
692 futex_wake(uaddr, FLAGS_SIZE_32 | FLAGS_SHARED, 1,
693 FUTEX_BITSET_MATCH_ANY);
694 return 0;
695 }
696
697 if (owner != task_pid_vnr(curr))
698 return 0;
699
700 /*
701 * Ok, this dying thread is truly holding a futex
702 * of interest. Set the OWNER_DIED bit atomically
703 * via cmpxchg, and if the value had FUTEX_WAITERS
704 * set, wake up a waiter (if any). (We have to do a
705 * futex_wake() even if OWNER_DIED is already set -
706 * to handle the rare but possible case of recursive
707 * thread-death.) The rest of the cleanup is done in
708 * userspace.
709 */
710 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
711
712 /*
713 * We are not holding a lock here, but we want to have
714 * the pagefault_disable/enable() protection because
715 * we want to handle the fault gracefully. If the
716 * access fails we try to fault in the futex with R/W
717 * verification via get_user_pages. get_user() above
718 * does not guarantee R/W access. If that fails we
719 * give up and leave the futex locked.
720 */
721 if ((err = futex_cmpxchg_value_locked(&nval, uaddr, uval, mval))) {
722 switch (err) {
723 case -EFAULT:
724 if (fault_in_user_writeable(uaddr))
725 return -1;
726 goto retry;
727
728 case -EAGAIN:
729 cond_resched();
730 goto retry;
731
732 default:
733 WARN_ON_ONCE(1);
734 return err;
735 }
736 }
737
738 if (nval != uval)
739 goto retry;
740
741 /*
742 * Wake robust non-PI futexes here. The wakeup of
743 * PI futexes happens in exit_pi_state():
744 */
745 if (!pi && (uval & FUTEX_WAITERS)) {
746 futex_wake(uaddr, FLAGS_SIZE_32 | FLAGS_SHARED, 1,
747 FUTEX_BITSET_MATCH_ANY);
748 }
749
750 return 0;
751}
752
753/*
754 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
755 */
756static inline int fetch_robust_entry(struct robust_list __user **entry,
757 struct robust_list __user * __user *head,
758 unsigned int *pi)
759{
760 unsigned long uentry;
761
762 if (get_user(uentry, (unsigned long __user *)head))
763 return -EFAULT;
764
765 *entry = (void __user *)(uentry & ~1UL);
766 *pi = uentry & 1;
767
768 return 0;
769}
770
771/*
772 * Walk curr->robust_list (very carefully, it's a userspace list!)
773 * and mark any locks found there dead, and notify any waiters.
774 *
775 * We silently return on any sign of list-walking problem.
776 */
777static void exit_robust_list(struct task_struct *curr)
778{
779 struct robust_list_head __user *head = curr->robust_list;
780 struct robust_list __user *entry, *next_entry, *pending;
781 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
782 unsigned int next_pi;
783 unsigned long futex_offset;
784 int rc;
785
786 /*
787 * Fetch the list head (which was registered earlier, via
788 * sys_set_robust_list()):
789 */
790 if (fetch_robust_entry(&entry, &head->list.next, &pi))
791 return;
792 /*
793 * Fetch the relative futex offset:
794 */
795 if (get_user(futex_offset, &head->futex_offset))
796 return;
797 /*
798 * Fetch any possibly pending lock-add first, and handle it
799 * if it exists:
800 */
801 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
802 return;
803
804 next_entry = NULL; /* avoid warning with gcc */
805 while (entry != &head->list) {
806 /*
807 * Fetch the next entry in the list before calling
808 * handle_futex_death:
809 */
810 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
811 /*
812 * A pending lock might already be on the list, so
813 * don't process it twice:
814 */
815 if (entry != pending) {
816 if (handle_futex_death((void __user *)entry + futex_offset,
817 curr, pi, HANDLE_DEATH_LIST))
818 return;
819 }
820 if (rc)
821 return;
822 entry = next_entry;
823 pi = next_pi;
824 /*
825 * Avoid excessively long or circular lists:
826 */
827 if (!--limit)
828 break;
829
830 cond_resched();
831 }
832
833 if (pending) {
834 handle_futex_death((void __user *)pending + futex_offset,
835 curr, pip, HANDLE_DEATH_PENDING);
836 }
837}
838
839#ifdef CONFIG_COMPAT
840static void __user *futex_uaddr(struct robust_list __user *entry,
841 compat_long_t futex_offset)
842{
843 compat_uptr_t base = ptr_to_compat(entry);
844 void __user *uaddr = compat_ptr(base + futex_offset);
845
846 return uaddr;
847}
848
849/*
850 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
851 */
852static inline int
853compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry,
854 compat_uptr_t __user *head, unsigned int *pi)
855{
856 if (get_user(*uentry, head))
857 return -EFAULT;
858
859 *entry = compat_ptr((*uentry) & ~1);
860 *pi = (unsigned int)(*uentry) & 1;
861
862 return 0;
863}
864
865/*
866 * Walk curr->robust_list (very carefully, it's a userspace list!)
867 * and mark any locks found there dead, and notify any waiters.
868 *
869 * We silently return on any sign of list-walking problem.
870 */
871static void compat_exit_robust_list(struct task_struct *curr)
872{
873 struct compat_robust_list_head __user *head = curr->compat_robust_list;
874 struct robust_list __user *entry, *next_entry, *pending;
875 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
876 unsigned int next_pi;
877 compat_uptr_t uentry, next_uentry, upending;
878 compat_long_t futex_offset;
879 int rc;
880
881 /*
882 * Fetch the list head (which was registered earlier, via
883 * sys_set_robust_list()):
884 */
885 if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &pi))
886 return;
887 /*
888 * Fetch the relative futex offset:
889 */
890 if (get_user(futex_offset, &head->futex_offset))
891 return;
892 /*
893 * Fetch any possibly pending lock-add first, and handle it
894 * if it exists:
895 */
896 if (compat_fetch_robust_entry(&upending, &pending,
897 &head->list_op_pending, &pip))
898 return;
899
900 next_entry = NULL; /* avoid warning with gcc */
901 while (entry != (struct robust_list __user *) &head->list) {
902 /*
903 * Fetch the next entry in the list before calling
904 * handle_futex_death:
905 */
906 rc = compat_fetch_robust_entry(&next_uentry, &next_entry,
907 (compat_uptr_t __user *)&entry->next, &next_pi);
908 /*
909 * A pending lock might already be on the list, so
910 * dont process it twice:
911 */
912 if (entry != pending) {
913 void __user *uaddr = futex_uaddr(entry, futex_offset);
914
915 if (handle_futex_death(uaddr, curr, pi,
916 HANDLE_DEATH_LIST))
917 return;
918 }
919 if (rc)
920 return;
921 uentry = next_uentry;
922 entry = next_entry;
923 pi = next_pi;
924 /*
925 * Avoid excessively long or circular lists:
926 */
927 if (!--limit)
928 break;
929
930 cond_resched();
931 }
932 if (pending) {
933 void __user *uaddr = futex_uaddr(pending, futex_offset);
934
935 handle_futex_death(uaddr, curr, pip, HANDLE_DEATH_PENDING);
936 }
937}
938#endif
939
940#ifdef CONFIG_FUTEX_PI
941
942/*
943 * This task is holding PI mutexes at exit time => bad.
944 * Kernel cleans up PI-state, but userspace is likely hosed.
945 * (Robust-futex cleanup is separate and might save the day for userspace.)
946 */
947static void exit_pi_state_list(struct task_struct *curr)
948{
949 struct list_head *next, *head = &curr->pi_state_list;
950 struct futex_pi_state *pi_state;
951 struct futex_hash_bucket *hb;
952 union futex_key key = FUTEX_KEY_INIT;
953
954 /*
955 * We are a ZOMBIE and nobody can enqueue itself on
956 * pi_state_list anymore, but we have to be careful
957 * versus waiters unqueueing themselves:
958 */
959 raw_spin_lock_irq(&curr->pi_lock);
960 while (!list_empty(head)) {
961 next = head->next;
962 pi_state = list_entry(next, struct futex_pi_state, list);
963 key = pi_state->key;
964 hb = futex_hash(&key);
965
966 /*
967 * We can race against put_pi_state() removing itself from the
968 * list (a waiter going away). put_pi_state() will first
969 * decrement the reference count and then modify the list, so
970 * its possible to see the list entry but fail this reference
971 * acquire.
972 *
973 * In that case; drop the locks to let put_pi_state() make
974 * progress and retry the loop.
975 */
976 if (!refcount_inc_not_zero(&pi_state->refcount)) {
977 raw_spin_unlock_irq(&curr->pi_lock);
978 cpu_relax();
979 raw_spin_lock_irq(&curr->pi_lock);
980 continue;
981 }
982 raw_spin_unlock_irq(&curr->pi_lock);
983
984 spin_lock(&hb->lock);
985 raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
986 raw_spin_lock(&curr->pi_lock);
987 /*
988 * We dropped the pi-lock, so re-check whether this
989 * task still owns the PI-state:
990 */
991 if (head->next != next) {
992 /* retain curr->pi_lock for the loop invariant */
993 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
994 spin_unlock(&hb->lock);
995 put_pi_state(pi_state);
996 continue;
997 }
998
999 WARN_ON(pi_state->owner != curr);
1000 WARN_ON(list_empty(&pi_state->list));
1001 list_del_init(&pi_state->list);
1002 pi_state->owner = NULL;
1003
1004 raw_spin_unlock(&curr->pi_lock);
1005 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1006 spin_unlock(&hb->lock);
1007
1008 rt_mutex_futex_unlock(&pi_state->pi_mutex);
1009 put_pi_state(pi_state);
1010
1011 raw_spin_lock_irq(&curr->pi_lock);
1012 }
1013 raw_spin_unlock_irq(&curr->pi_lock);
1014}
1015#else
1016static inline void exit_pi_state_list(struct task_struct *curr) { }
1017#endif
1018
1019static void futex_cleanup(struct task_struct *tsk)
1020{
1021 if (unlikely(tsk->robust_list)) {
1022 exit_robust_list(tsk);
1023 tsk->robust_list = NULL;
1024 }
1025
1026#ifdef CONFIG_COMPAT
1027 if (unlikely(tsk->compat_robust_list)) {
1028 compat_exit_robust_list(tsk);
1029 tsk->compat_robust_list = NULL;
1030 }
1031#endif
1032
1033 if (unlikely(!list_empty(&tsk->pi_state_list)))
1034 exit_pi_state_list(tsk);
1035}
1036
1037/**
1038 * futex_exit_recursive - Set the tasks futex state to FUTEX_STATE_DEAD
1039 * @tsk: task to set the state on
1040 *
1041 * Set the futex exit state of the task lockless. The futex waiter code
1042 * observes that state when a task is exiting and loops until the task has
1043 * actually finished the futex cleanup. The worst case for this is that the
1044 * waiter runs through the wait loop until the state becomes visible.
1045 *
1046 * This is called from the recursive fault handling path in make_task_dead().
1047 *
1048 * This is best effort. Either the futex exit code has run already or
1049 * not. If the OWNER_DIED bit has been set on the futex then the waiter can
1050 * take it over. If not, the problem is pushed back to user space. If the
1051 * futex exit code did not run yet, then an already queued waiter might
1052 * block forever, but there is nothing which can be done about that.
1053 */
1054void futex_exit_recursive(struct task_struct *tsk)
1055{
1056 /* If the state is FUTEX_STATE_EXITING then futex_exit_mutex is held */
1057 if (tsk->futex_state == FUTEX_STATE_EXITING)
1058 mutex_unlock(&tsk->futex_exit_mutex);
1059 tsk->futex_state = FUTEX_STATE_DEAD;
1060}
1061
1062static void futex_cleanup_begin(struct task_struct *tsk)
1063{
1064 /*
1065 * Prevent various race issues against a concurrent incoming waiter
1066 * including live locks by forcing the waiter to block on
1067 * tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in
1068 * attach_to_pi_owner().
1069 */
1070 mutex_lock(&tsk->futex_exit_mutex);
1071
1072 /*
1073 * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock.
1074 *
1075 * This ensures that all subsequent checks of tsk->futex_state in
1076 * attach_to_pi_owner() must observe FUTEX_STATE_EXITING with
1077 * tsk->pi_lock held.
1078 *
1079 * It guarantees also that a pi_state which was queued right before
1080 * the state change under tsk->pi_lock by a concurrent waiter must
1081 * be observed in exit_pi_state_list().
1082 */
1083 raw_spin_lock_irq(&tsk->pi_lock);
1084 tsk->futex_state = FUTEX_STATE_EXITING;
1085 raw_spin_unlock_irq(&tsk->pi_lock);
1086}
1087
1088static void futex_cleanup_end(struct task_struct *tsk, int state)
1089{
1090 /*
1091 * Lockless store. The only side effect is that an observer might
1092 * take another loop until it becomes visible.
1093 */
1094 tsk->futex_state = state;
1095 /*
1096 * Drop the exit protection. This unblocks waiters which observed
1097 * FUTEX_STATE_EXITING to reevaluate the state.
1098 */
1099 mutex_unlock(&tsk->futex_exit_mutex);
1100}
1101
1102void futex_exec_release(struct task_struct *tsk)
1103{
1104 /*
1105 * The state handling is done for consistency, but in the case of
1106 * exec() there is no way to prevent further damage as the PID stays
1107 * the same. But for the unlikely and arguably buggy case that a
1108 * futex is held on exec(), this provides at least as much state
1109 * consistency protection which is possible.
1110 */
1111 futex_cleanup_begin(tsk);
1112 futex_cleanup(tsk);
1113 /*
1114 * Reset the state to FUTEX_STATE_OK. The task is alive and about
1115 * exec a new binary.
1116 */
1117 futex_cleanup_end(tsk, FUTEX_STATE_OK);
1118}
1119
1120void futex_exit_release(struct task_struct *tsk)
1121{
1122 futex_cleanup_begin(tsk);
1123 futex_cleanup(tsk);
1124 futex_cleanup_end(tsk, FUTEX_STATE_DEAD);
1125}
1126
1127static int __init futex_init(void)
1128{
1129 unsigned int futex_shift;
1130 unsigned long i;
1131
1132#ifdef CONFIG_BASE_SMALL
1133 futex_hashsize = 16;
1134#else
1135 futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
1136#endif
1137
1138 futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
1139 futex_hashsize, 0, 0,
1140 &futex_shift, NULL,
1141 futex_hashsize, futex_hashsize);
1142 futex_hashsize = 1UL << futex_shift;
1143
1144 for (i = 0; i < futex_hashsize; i++) {
1145 atomic_set(&futex_queues[i].waiters, 0);
1146 plist_head_init(&futex_queues[i].chain);
1147 spin_lock_init(&futex_queues[i].lock);
1148 }
1149
1150 return 0;
1151}
1152core_initcall(futex_init);