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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/memblock.h>
38#include <linux/fault-inject.h>
39#include <linux/slab.h>
40
41#include "futex.h"
42#include "../locking/rtmutex_common.h"
43
44/*
45 * The base of the bucket array and its size are always used together
46 * (after initialization only in futex_hash()), so ensure that they
47 * reside in the same cacheline.
48 */
49static struct {
50 struct futex_hash_bucket *queues;
51 unsigned long hashsize;
52} __futex_data __read_mostly __aligned(2*sizeof(long));
53#define futex_queues (__futex_data.queues)
54#define futex_hashsize (__futex_data.hashsize)
55
56
57/*
58 * Fault injections for futexes.
59 */
60#ifdef CONFIG_FAIL_FUTEX
61
62static struct {
63 struct fault_attr attr;
64
65 bool ignore_private;
66} fail_futex = {
67 .attr = FAULT_ATTR_INITIALIZER,
68 .ignore_private = false,
69};
70
71static int __init setup_fail_futex(char *str)
72{
73 return setup_fault_attr(&fail_futex.attr, str);
74}
75__setup("fail_futex=", setup_fail_futex);
76
77bool should_fail_futex(bool fshared)
78{
79 if (fail_futex.ignore_private && !fshared)
80 return false;
81
82 return should_fail(&fail_futex.attr, 1);
83}
84
85#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
86
87static int __init fail_futex_debugfs(void)
88{
89 umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
90 struct dentry *dir;
91
92 dir = fault_create_debugfs_attr("fail_futex", NULL,
93 &fail_futex.attr);
94 if (IS_ERR(dir))
95 return PTR_ERR(dir);
96
97 debugfs_create_bool("ignore-private", mode, dir,
98 &fail_futex.ignore_private);
99 return 0;
100}
101
102late_initcall(fail_futex_debugfs);
103
104#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
105
106#endif /* CONFIG_FAIL_FUTEX */
107
108/**
109 * futex_hash - Return the hash bucket in the global hash
110 * @key: Pointer to the futex key for which the hash is calculated
111 *
112 * We hash on the keys returned from get_futex_key (see below) and return the
113 * corresponding hash bucket in the global hash.
114 */
115struct futex_hash_bucket *futex_hash(union futex_key *key)
116{
117 u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
118 key->both.offset);
119
120 return &futex_queues[hash & (futex_hashsize - 1)];
121}
122
123
124/**
125 * futex_setup_timer - set up the sleeping hrtimer.
126 * @time: ptr to the given timeout value
127 * @timeout: the hrtimer_sleeper structure to be set up
128 * @flags: futex flags
129 * @range_ns: optional range in ns
130 *
131 * Return: Initialized hrtimer_sleeper structure or NULL if no timeout
132 * value given
133 */
134struct hrtimer_sleeper *
135futex_setup_timer(ktime_t *time, struct hrtimer_sleeper *timeout,
136 int flags, u64 range_ns)
137{
138 if (!time)
139 return NULL;
140
141 hrtimer_init_sleeper_on_stack(timeout, (flags & FLAGS_CLOCKRT) ?
142 CLOCK_REALTIME : CLOCK_MONOTONIC,
143 HRTIMER_MODE_ABS);
144 /*
145 * If range_ns is 0, calling hrtimer_set_expires_range_ns() is
146 * effectively the same as calling hrtimer_set_expires().
147 */
148 hrtimer_set_expires_range_ns(&timeout->timer, *time, range_ns);
149
150 return timeout;
151}
152
153/*
154 * Generate a machine wide unique identifier for this inode.
155 *
156 * This relies on u64 not wrapping in the life-time of the machine; which with
157 * 1ns resolution means almost 585 years.
158 *
159 * This further relies on the fact that a well formed program will not unmap
160 * the file while it has a (shared) futex waiting on it. This mapping will have
161 * a file reference which pins the mount and inode.
162 *
163 * If for some reason an inode gets evicted and read back in again, it will get
164 * a new sequence number and will _NOT_ match, even though it is the exact same
165 * file.
166 *
167 * It is important that futex_match() will never have a false-positive, esp.
168 * for PI futexes that can mess up the state. The above argues that false-negatives
169 * are only possible for malformed programs.
170 */
171static u64 get_inode_sequence_number(struct inode *inode)
172{
173 static atomic64_t i_seq;
174 u64 old;
175
176 /* Does the inode already have a sequence number? */
177 old = atomic64_read(&inode->i_sequence);
178 if (likely(old))
179 return old;
180
181 for (;;) {
182 u64 new = atomic64_add_return(1, &i_seq);
183 if (WARN_ON_ONCE(!new))
184 continue;
185
186 old = atomic64_cmpxchg_relaxed(&inode->i_sequence, 0, new);
187 if (old)
188 return old;
189 return new;
190 }
191}
192
193/**
194 * get_futex_key() - Get parameters which are the keys for a futex
195 * @uaddr: virtual address of the futex
196 * @fshared: false for a PROCESS_PRIVATE futex, true for PROCESS_SHARED
197 * @key: address where result is stored.
198 * @rw: mapping needs to be read/write (values: FUTEX_READ,
199 * FUTEX_WRITE)
200 *
201 * Return: a negative error code or 0
202 *
203 * The key words are stored in @key on success.
204 *
205 * For shared mappings (when @fshared), the key is:
206 *
207 * ( inode->i_sequence, page->index, offset_within_page )
208 *
209 * [ also see get_inode_sequence_number() ]
210 *
211 * For private mappings (or when !@fshared), the key is:
212 *
213 * ( current->mm, address, 0 )
214 *
215 * This allows (cross process, where applicable) identification of the futex
216 * without keeping the page pinned for the duration of the FUTEX_WAIT.
217 *
218 * lock_page() might sleep, the caller should not hold a spinlock.
219 */
220int get_futex_key(u32 __user *uaddr, bool fshared, union futex_key *key,
221 enum futex_access rw)
222{
223 unsigned long address = (unsigned long)uaddr;
224 struct mm_struct *mm = current->mm;
225 struct page *page, *tail;
226 struct address_space *mapping;
227 int err, ro = 0;
228
229 /*
230 * The futex address must be "naturally" aligned.
231 */
232 key->both.offset = address % PAGE_SIZE;
233 if (unlikely((address % sizeof(u32)) != 0))
234 return -EINVAL;
235 address -= key->both.offset;
236
237 if (unlikely(!access_ok(uaddr, sizeof(u32))))
238 return -EFAULT;
239
240 if (unlikely(should_fail_futex(fshared)))
241 return -EFAULT;
242
243 /*
244 * PROCESS_PRIVATE futexes are fast.
245 * As the mm cannot disappear under us and the 'key' only needs
246 * virtual address, we dont even have to find the underlying vma.
247 * Note : We do have to check 'uaddr' is a valid user address,
248 * but access_ok() should be faster than find_vma()
249 */
250 if (!fshared) {
251 key->private.mm = mm;
252 key->private.address = address;
253 return 0;
254 }
255
256again:
257 /* Ignore any VERIFY_READ mapping (futex common case) */
258 if (unlikely(should_fail_futex(true)))
259 return -EFAULT;
260
261 err = get_user_pages_fast(address, 1, FOLL_WRITE, &page);
262 /*
263 * If write access is not required (eg. FUTEX_WAIT), try
264 * and get read-only access.
265 */
266 if (err == -EFAULT && rw == FUTEX_READ) {
267 err = get_user_pages_fast(address, 1, 0, &page);
268 ro = 1;
269 }
270 if (err < 0)
271 return err;
272 else
273 err = 0;
274
275 /*
276 * The treatment of mapping from this point on is critical. The page
277 * lock protects many things but in this context the page lock
278 * stabilizes mapping, prevents inode freeing in the shared
279 * file-backed region case and guards against movement to swap cache.
280 *
281 * Strictly speaking the page lock is not needed in all cases being
282 * considered here and page lock forces unnecessarily serialization
283 * From this point on, mapping will be re-verified if necessary and
284 * page lock will be acquired only if it is unavoidable
285 *
286 * Mapping checks require the head page for any compound page so the
287 * head page and mapping is looked up now. For anonymous pages, it
288 * does not matter if the page splits in the future as the key is
289 * based on the address. For filesystem-backed pages, the tail is
290 * required as the index of the page determines the key. For
291 * base pages, there is no tail page and tail == page.
292 */
293 tail = page;
294 page = compound_head(page);
295 mapping = READ_ONCE(page->mapping);
296
297 /*
298 * If page->mapping is NULL, then it cannot be a PageAnon
299 * page; but it might be the ZERO_PAGE or in the gate area or
300 * in a special mapping (all cases which we are happy to fail);
301 * or it may have been a good file page when get_user_pages_fast
302 * found it, but truncated or holepunched or subjected to
303 * invalidate_complete_page2 before we got the page lock (also
304 * cases which we are happy to fail). And we hold a reference,
305 * so refcount care in invalidate_inode_page's remove_mapping
306 * prevents drop_caches from setting mapping to NULL beneath us.
307 *
308 * The case we do have to guard against is when memory pressure made
309 * shmem_writepage move it from filecache to swapcache beneath us:
310 * an unlikely race, but we do need to retry for page->mapping.
311 */
312 if (unlikely(!mapping)) {
313 int shmem_swizzled;
314
315 /*
316 * Page lock is required to identify which special case above
317 * applies. If this is really a shmem page then the page lock
318 * will prevent unexpected transitions.
319 */
320 lock_page(page);
321 shmem_swizzled = PageSwapCache(page) || page->mapping;
322 unlock_page(page);
323 put_page(page);
324
325 if (shmem_swizzled)
326 goto again;
327
328 return -EFAULT;
329 }
330
331 /*
332 * Private mappings are handled in a simple way.
333 *
334 * If the futex key is stored on an anonymous page, then the associated
335 * object is the mm which is implicitly pinned by the calling process.
336 *
337 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
338 * it's a read-only handle, it's expected that futexes attach to
339 * the object not the particular process.
340 */
341 if (PageAnon(page)) {
342 /*
343 * A RO anonymous page will never change and thus doesn't make
344 * sense for futex operations.
345 */
346 if (unlikely(should_fail_futex(true)) || ro) {
347 err = -EFAULT;
348 goto out;
349 }
350
351 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
352 key->private.mm = mm;
353 key->private.address = address;
354
355 } else {
356 struct inode *inode;
357
358 /*
359 * The associated futex object in this case is the inode and
360 * the page->mapping must be traversed. Ordinarily this should
361 * be stabilised under page lock but it's not strictly
362 * necessary in this case as we just want to pin the inode, not
363 * update the radix tree or anything like that.
364 *
365 * The RCU read lock is taken as the inode is finally freed
366 * under RCU. If the mapping still matches expectations then the
367 * mapping->host can be safely accessed as being a valid inode.
368 */
369 rcu_read_lock();
370
371 if (READ_ONCE(page->mapping) != mapping) {
372 rcu_read_unlock();
373 put_page(page);
374
375 goto again;
376 }
377
378 inode = READ_ONCE(mapping->host);
379 if (!inode) {
380 rcu_read_unlock();
381 put_page(page);
382
383 goto again;
384 }
385
386 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
387 key->shared.i_seq = get_inode_sequence_number(inode);
388 key->shared.pgoff = page_to_pgoff(tail);
389 rcu_read_unlock();
390 }
391
392out:
393 put_page(page);
394 return err;
395}
396
397/**
398 * fault_in_user_writeable() - Fault in user address and verify RW access
399 * @uaddr: pointer to faulting user space address
400 *
401 * Slow path to fixup the fault we just took in the atomic write
402 * access to @uaddr.
403 *
404 * We have no generic implementation of a non-destructive write to the
405 * user address. We know that we faulted in the atomic pagefault
406 * disabled section so we can as well avoid the #PF overhead by
407 * calling get_user_pages() right away.
408 */
409int fault_in_user_writeable(u32 __user *uaddr)
410{
411 struct mm_struct *mm = current->mm;
412 int ret;
413
414 mmap_read_lock(mm);
415 ret = fixup_user_fault(mm, (unsigned long)uaddr,
416 FAULT_FLAG_WRITE, NULL);
417 mmap_read_unlock(mm);
418
419 return ret < 0 ? ret : 0;
420}
421
422/**
423 * futex_top_waiter() - Return the highest priority waiter on a futex
424 * @hb: the hash bucket the futex_q's reside in
425 * @key: the futex key (to distinguish it from other futex futex_q's)
426 *
427 * Must be called with the hb lock held.
428 */
429struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb, union futex_key *key)
430{
431 struct futex_q *this;
432
433 plist_for_each_entry(this, &hb->chain, list) {
434 if (futex_match(&this->key, key))
435 return this;
436 }
437 return NULL;
438}
439
440int futex_cmpxchg_value_locked(u32 *curval, u32 __user *uaddr, u32 uval, u32 newval)
441{
442 int ret;
443
444 pagefault_disable();
445 ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
446 pagefault_enable();
447
448 return ret;
449}
450
451int futex_get_value_locked(u32 *dest, u32 __user *from)
452{
453 int ret;
454
455 pagefault_disable();
456 ret = __get_user(*dest, from);
457 pagefault_enable();
458
459 return ret ? -EFAULT : 0;
460}
461
462/**
463 * wait_for_owner_exiting - Block until the owner has exited
464 * @ret: owner's current futex lock status
465 * @exiting: Pointer to the exiting task
466 *
467 * Caller must hold a refcount on @exiting.
468 */
469void wait_for_owner_exiting(int ret, struct task_struct *exiting)
470{
471 if (ret != -EBUSY) {
472 WARN_ON_ONCE(exiting);
473 return;
474 }
475
476 if (WARN_ON_ONCE(ret == -EBUSY && !exiting))
477 return;
478
479 mutex_lock(&exiting->futex_exit_mutex);
480 /*
481 * No point in doing state checking here. If the waiter got here
482 * while the task was in exec()->exec_futex_release() then it can
483 * have any FUTEX_STATE_* value when the waiter has acquired the
484 * mutex. OK, if running, EXITING or DEAD if it reached exit()
485 * already. Highly unlikely and not a problem. Just one more round
486 * through the futex maze.
487 */
488 mutex_unlock(&exiting->futex_exit_mutex);
489
490 put_task_struct(exiting);
491}
492
493/**
494 * __futex_unqueue() - Remove the futex_q from its futex_hash_bucket
495 * @q: The futex_q to unqueue
496 *
497 * The q->lock_ptr must not be NULL and must be held by the caller.
498 */
499void __futex_unqueue(struct futex_q *q)
500{
501 struct futex_hash_bucket *hb;
502
503 if (WARN_ON_SMP(!q->lock_ptr) || WARN_ON(plist_node_empty(&q->list)))
504 return;
505 lockdep_assert_held(q->lock_ptr);
506
507 hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
508 plist_del(&q->list, &hb->chain);
509 futex_hb_waiters_dec(hb);
510}
511
512/* The key must be already stored in q->key. */
513struct futex_hash_bucket *futex_q_lock(struct futex_q *q)
514 __acquires(&hb->lock)
515{
516 struct futex_hash_bucket *hb;
517
518 hb = futex_hash(&q->key);
519
520 /*
521 * Increment the counter before taking the lock so that
522 * a potential waker won't miss a to-be-slept task that is
523 * waiting for the spinlock. This is safe as all futex_q_lock()
524 * users end up calling futex_queue(). Similarly, for housekeeping,
525 * decrement the counter at futex_q_unlock() when some error has
526 * occurred and we don't end up adding the task to the list.
527 */
528 futex_hb_waiters_inc(hb); /* implies smp_mb(); (A) */
529
530 q->lock_ptr = &hb->lock;
531
532 spin_lock(&hb->lock);
533 return hb;
534}
535
536void futex_q_unlock(struct futex_hash_bucket *hb)
537 __releases(&hb->lock)
538{
539 spin_unlock(&hb->lock);
540 futex_hb_waiters_dec(hb);
541}
542
543void __futex_queue(struct futex_q *q, struct futex_hash_bucket *hb)
544{
545 int prio;
546
547 /*
548 * The priority used to register this element is
549 * - either the real thread-priority for the real-time threads
550 * (i.e. threads with a priority lower than MAX_RT_PRIO)
551 * - or MAX_RT_PRIO for non-RT threads.
552 * Thus, all RT-threads are woken first in priority order, and
553 * the others are woken last, in FIFO order.
554 */
555 prio = min(current->normal_prio, MAX_RT_PRIO);
556
557 plist_node_init(&q->list, prio);
558 plist_add(&q->list, &hb->chain);
559 q->task = current;
560}
561
562/**
563 * futex_unqueue() - Remove the futex_q from its futex_hash_bucket
564 * @q: The futex_q to unqueue
565 *
566 * The q->lock_ptr must not be held by the caller. A call to futex_unqueue() must
567 * be paired with exactly one earlier call to futex_queue().
568 *
569 * Return:
570 * - 1 - if the futex_q was still queued (and we removed unqueued it);
571 * - 0 - if the futex_q was already removed by the waking thread
572 */
573int futex_unqueue(struct futex_q *q)
574{
575 spinlock_t *lock_ptr;
576 int ret = 0;
577
578 /* In the common case we don't take the spinlock, which is nice. */
579retry:
580 /*
581 * q->lock_ptr can change between this read and the following spin_lock.
582 * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
583 * optimizing lock_ptr out of the logic below.
584 */
585 lock_ptr = READ_ONCE(q->lock_ptr);
586 if (lock_ptr != NULL) {
587 spin_lock(lock_ptr);
588 /*
589 * q->lock_ptr can change between reading it and
590 * spin_lock(), causing us to take the wrong lock. This
591 * corrects the race condition.
592 *
593 * Reasoning goes like this: if we have the wrong lock,
594 * q->lock_ptr must have changed (maybe several times)
595 * between reading it and the spin_lock(). It can
596 * change again after the spin_lock() but only if it was
597 * already changed before the spin_lock(). It cannot,
598 * however, change back to the original value. Therefore
599 * we can detect whether we acquired the correct lock.
600 */
601 if (unlikely(lock_ptr != q->lock_ptr)) {
602 spin_unlock(lock_ptr);
603 goto retry;
604 }
605 __futex_unqueue(q);
606
607 BUG_ON(q->pi_state);
608
609 spin_unlock(lock_ptr);
610 ret = 1;
611 }
612
613 return ret;
614}
615
616/*
617 * PI futexes can not be requeued and must remove themselves from the
618 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held.
619 */
620void futex_unqueue_pi(struct futex_q *q)
621{
622 __futex_unqueue(q);
623
624 BUG_ON(!q->pi_state);
625 put_pi_state(q->pi_state);
626 q->pi_state = NULL;
627}
628
629/* Constants for the pending_op argument of handle_futex_death */
630#define HANDLE_DEATH_PENDING true
631#define HANDLE_DEATH_LIST false
632
633/*
634 * Process a futex-list entry, check whether it's owned by the
635 * dying task, and do notification if so:
636 */
637static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr,
638 bool pi, bool pending_op)
639{
640 u32 uval, nval, mval;
641 pid_t owner;
642 int err;
643
644 /* Futex address must be 32bit aligned */
645 if ((((unsigned long)uaddr) % sizeof(*uaddr)) != 0)
646 return -1;
647
648retry:
649 if (get_user(uval, uaddr))
650 return -1;
651
652 /*
653 * Special case for regular (non PI) futexes. The unlock path in
654 * user space has two race scenarios:
655 *
656 * 1. The unlock path releases the user space futex value and
657 * before it can execute the futex() syscall to wake up
658 * waiters it is killed.
659 *
660 * 2. A woken up waiter is killed before it can acquire the
661 * futex in user space.
662 *
663 * In the second case, the wake up notification could be generated
664 * by the unlock path in user space after setting the futex value
665 * to zero or by the kernel after setting the OWNER_DIED bit below.
666 *
667 * In both cases the TID validation below prevents a wakeup of
668 * potential waiters which can cause these waiters to block
669 * forever.
670 *
671 * In both cases the following conditions are met:
672 *
673 * 1) task->robust_list->list_op_pending != NULL
674 * @pending_op == true
675 * 2) The owner part of user space futex value == 0
676 * 3) Regular futex: @pi == false
677 *
678 * If these conditions are met, it is safe to attempt waking up a
679 * potential waiter without touching the user space futex value and
680 * trying to set the OWNER_DIED bit. If the futex value is zero,
681 * the rest of the user space mutex state is consistent, so a woken
682 * waiter will just take over the uncontended futex. Setting the
683 * OWNER_DIED bit would create inconsistent state and malfunction
684 * of the user space owner died handling. Otherwise, the OWNER_DIED
685 * bit is already set, and the woken waiter is expected to deal with
686 * this.
687 */
688 owner = uval & FUTEX_TID_MASK;
689
690 if (pending_op && !pi && !owner) {
691 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
692 return 0;
693 }
694
695 if (owner != task_pid_vnr(curr))
696 return 0;
697
698 /*
699 * Ok, this dying thread is truly holding a futex
700 * of interest. Set the OWNER_DIED bit atomically
701 * via cmpxchg, and if the value had FUTEX_WAITERS
702 * set, wake up a waiter (if any). (We have to do a
703 * futex_wake() even if OWNER_DIED is already set -
704 * to handle the rare but possible case of recursive
705 * thread-death.) The rest of the cleanup is done in
706 * userspace.
707 */
708 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
709
710 /*
711 * We are not holding a lock here, but we want to have
712 * the pagefault_disable/enable() protection because
713 * we want to handle the fault gracefully. If the
714 * access fails we try to fault in the futex with R/W
715 * verification via get_user_pages. get_user() above
716 * does not guarantee R/W access. If that fails we
717 * give up and leave the futex locked.
718 */
719 if ((err = futex_cmpxchg_value_locked(&nval, uaddr, uval, mval))) {
720 switch (err) {
721 case -EFAULT:
722 if (fault_in_user_writeable(uaddr))
723 return -1;
724 goto retry;
725
726 case -EAGAIN:
727 cond_resched();
728 goto retry;
729
730 default:
731 WARN_ON_ONCE(1);
732 return err;
733 }
734 }
735
736 if (nval != uval)
737 goto retry;
738
739 /*
740 * Wake robust non-PI futexes here. The wakeup of
741 * PI futexes happens in exit_pi_state():
742 */
743 if (!pi && (uval & FUTEX_WAITERS))
744 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
745
746 return 0;
747}
748
749/*
750 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
751 */
752static inline int fetch_robust_entry(struct robust_list __user **entry,
753 struct robust_list __user * __user *head,
754 unsigned int *pi)
755{
756 unsigned long uentry;
757
758 if (get_user(uentry, (unsigned long __user *)head))
759 return -EFAULT;
760
761 *entry = (void __user *)(uentry & ~1UL);
762 *pi = uentry & 1;
763
764 return 0;
765}
766
767/*
768 * Walk curr->robust_list (very carefully, it's a userspace list!)
769 * and mark any locks found there dead, and notify any waiters.
770 *
771 * We silently return on any sign of list-walking problem.
772 */
773static void exit_robust_list(struct task_struct *curr)
774{
775 struct robust_list_head __user *head = curr->robust_list;
776 struct robust_list __user *entry, *next_entry, *pending;
777 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
778 unsigned int next_pi;
779 unsigned long futex_offset;
780 int rc;
781
782 /*
783 * Fetch the list head (which was registered earlier, via
784 * sys_set_robust_list()):
785 */
786 if (fetch_robust_entry(&entry, &head->list.next, &pi))
787 return;
788 /*
789 * Fetch the relative futex offset:
790 */
791 if (get_user(futex_offset, &head->futex_offset))
792 return;
793 /*
794 * Fetch any possibly pending lock-add first, and handle it
795 * if it exists:
796 */
797 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
798 return;
799
800 next_entry = NULL; /* avoid warning with gcc */
801 while (entry != &head->list) {
802 /*
803 * Fetch the next entry in the list before calling
804 * handle_futex_death:
805 */
806 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
807 /*
808 * A pending lock might already be on the list, so
809 * don't process it twice:
810 */
811 if (entry != pending) {
812 if (handle_futex_death((void __user *)entry + futex_offset,
813 curr, pi, HANDLE_DEATH_LIST))
814 return;
815 }
816 if (rc)
817 return;
818 entry = next_entry;
819 pi = next_pi;
820 /*
821 * Avoid excessively long or circular lists:
822 */
823 if (!--limit)
824 break;
825
826 cond_resched();
827 }
828
829 if (pending) {
830 handle_futex_death((void __user *)pending + futex_offset,
831 curr, pip, HANDLE_DEATH_PENDING);
832 }
833}
834
835#ifdef CONFIG_COMPAT
836static void __user *futex_uaddr(struct robust_list __user *entry,
837 compat_long_t futex_offset)
838{
839 compat_uptr_t base = ptr_to_compat(entry);
840 void __user *uaddr = compat_ptr(base + futex_offset);
841
842 return uaddr;
843}
844
845/*
846 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
847 */
848static inline int
849compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry,
850 compat_uptr_t __user *head, unsigned int *pi)
851{
852 if (get_user(*uentry, head))
853 return -EFAULT;
854
855 *entry = compat_ptr((*uentry) & ~1);
856 *pi = (unsigned int)(*uentry) & 1;
857
858 return 0;
859}
860
861/*
862 * Walk curr->robust_list (very carefully, it's a userspace list!)
863 * and mark any locks found there dead, and notify any waiters.
864 *
865 * We silently return on any sign of list-walking problem.
866 */
867static void compat_exit_robust_list(struct task_struct *curr)
868{
869 struct compat_robust_list_head __user *head = curr->compat_robust_list;
870 struct robust_list __user *entry, *next_entry, *pending;
871 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
872 unsigned int next_pi;
873 compat_uptr_t uentry, next_uentry, upending;
874 compat_long_t futex_offset;
875 int rc;
876
877 /*
878 * Fetch the list head (which was registered earlier, via
879 * sys_set_robust_list()):
880 */
881 if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &pi))
882 return;
883 /*
884 * Fetch the relative futex offset:
885 */
886 if (get_user(futex_offset, &head->futex_offset))
887 return;
888 /*
889 * Fetch any possibly pending lock-add first, and handle it
890 * if it exists:
891 */
892 if (compat_fetch_robust_entry(&upending, &pending,
893 &head->list_op_pending, &pip))
894 return;
895
896 next_entry = NULL; /* avoid warning with gcc */
897 while (entry != (struct robust_list __user *) &head->list) {
898 /*
899 * Fetch the next entry in the list before calling
900 * handle_futex_death:
901 */
902 rc = compat_fetch_robust_entry(&next_uentry, &next_entry,
903 (compat_uptr_t __user *)&entry->next, &next_pi);
904 /*
905 * A pending lock might already be on the list, so
906 * dont process it twice:
907 */
908 if (entry != pending) {
909 void __user *uaddr = futex_uaddr(entry, futex_offset);
910
911 if (handle_futex_death(uaddr, curr, pi,
912 HANDLE_DEATH_LIST))
913 return;
914 }
915 if (rc)
916 return;
917 uentry = next_uentry;
918 entry = next_entry;
919 pi = next_pi;
920 /*
921 * Avoid excessively long or circular lists:
922 */
923 if (!--limit)
924 break;
925
926 cond_resched();
927 }
928 if (pending) {
929 void __user *uaddr = futex_uaddr(pending, futex_offset);
930
931 handle_futex_death(uaddr, curr, pip, HANDLE_DEATH_PENDING);
932 }
933}
934#endif
935
936#ifdef CONFIG_FUTEX_PI
937
938/*
939 * This task is holding PI mutexes at exit time => bad.
940 * Kernel cleans up PI-state, but userspace is likely hosed.
941 * (Robust-futex cleanup is separate and might save the day for userspace.)
942 */
943static void exit_pi_state_list(struct task_struct *curr)
944{
945 struct list_head *next, *head = &curr->pi_state_list;
946 struct futex_pi_state *pi_state;
947 struct futex_hash_bucket *hb;
948 union futex_key key = FUTEX_KEY_INIT;
949
950 /*
951 * We are a ZOMBIE and nobody can enqueue itself on
952 * pi_state_list anymore, but we have to be careful
953 * versus waiters unqueueing themselves:
954 */
955 raw_spin_lock_irq(&curr->pi_lock);
956 while (!list_empty(head)) {
957 next = head->next;
958 pi_state = list_entry(next, struct futex_pi_state, list);
959 key = pi_state->key;
960 hb = futex_hash(&key);
961
962 /*
963 * We can race against put_pi_state() removing itself from the
964 * list (a waiter going away). put_pi_state() will first
965 * decrement the reference count and then modify the list, so
966 * its possible to see the list entry but fail this reference
967 * acquire.
968 *
969 * In that case; drop the locks to let put_pi_state() make
970 * progress and retry the loop.
971 */
972 if (!refcount_inc_not_zero(&pi_state->refcount)) {
973 raw_spin_unlock_irq(&curr->pi_lock);
974 cpu_relax();
975 raw_spin_lock_irq(&curr->pi_lock);
976 continue;
977 }
978 raw_spin_unlock_irq(&curr->pi_lock);
979
980 spin_lock(&hb->lock);
981 raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
982 raw_spin_lock(&curr->pi_lock);
983 /*
984 * We dropped the pi-lock, so re-check whether this
985 * task still owns the PI-state:
986 */
987 if (head->next != next) {
988 /* retain curr->pi_lock for the loop invariant */
989 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
990 spin_unlock(&hb->lock);
991 put_pi_state(pi_state);
992 continue;
993 }
994
995 WARN_ON(pi_state->owner != curr);
996 WARN_ON(list_empty(&pi_state->list));
997 list_del_init(&pi_state->list);
998 pi_state->owner = NULL;
999
1000 raw_spin_unlock(&curr->pi_lock);
1001 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1002 spin_unlock(&hb->lock);
1003
1004 rt_mutex_futex_unlock(&pi_state->pi_mutex);
1005 put_pi_state(pi_state);
1006
1007 raw_spin_lock_irq(&curr->pi_lock);
1008 }
1009 raw_spin_unlock_irq(&curr->pi_lock);
1010}
1011#else
1012static inline void exit_pi_state_list(struct task_struct *curr) { }
1013#endif
1014
1015static void futex_cleanup(struct task_struct *tsk)
1016{
1017 if (unlikely(tsk->robust_list)) {
1018 exit_robust_list(tsk);
1019 tsk->robust_list = NULL;
1020 }
1021
1022#ifdef CONFIG_COMPAT
1023 if (unlikely(tsk->compat_robust_list)) {
1024 compat_exit_robust_list(tsk);
1025 tsk->compat_robust_list = NULL;
1026 }
1027#endif
1028
1029 if (unlikely(!list_empty(&tsk->pi_state_list)))
1030 exit_pi_state_list(tsk);
1031}
1032
1033/**
1034 * futex_exit_recursive - Set the tasks futex state to FUTEX_STATE_DEAD
1035 * @tsk: task to set the state on
1036 *
1037 * Set the futex exit state of the task lockless. The futex waiter code
1038 * observes that state when a task is exiting and loops until the task has
1039 * actually finished the futex cleanup. The worst case for this is that the
1040 * waiter runs through the wait loop until the state becomes visible.
1041 *
1042 * This is called from the recursive fault handling path in make_task_dead().
1043 *
1044 * This is best effort. Either the futex exit code has run already or
1045 * not. If the OWNER_DIED bit has been set on the futex then the waiter can
1046 * take it over. If not, the problem is pushed back to user space. If the
1047 * futex exit code did not run yet, then an already queued waiter might
1048 * block forever, but there is nothing which can be done about that.
1049 */
1050void futex_exit_recursive(struct task_struct *tsk)
1051{
1052 /* If the state is FUTEX_STATE_EXITING then futex_exit_mutex is held */
1053 if (tsk->futex_state == FUTEX_STATE_EXITING)
1054 mutex_unlock(&tsk->futex_exit_mutex);
1055 tsk->futex_state = FUTEX_STATE_DEAD;
1056}
1057
1058static void futex_cleanup_begin(struct task_struct *tsk)
1059{
1060 /*
1061 * Prevent various race issues against a concurrent incoming waiter
1062 * including live locks by forcing the waiter to block on
1063 * tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in
1064 * attach_to_pi_owner().
1065 */
1066 mutex_lock(&tsk->futex_exit_mutex);
1067
1068 /*
1069 * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock.
1070 *
1071 * This ensures that all subsequent checks of tsk->futex_state in
1072 * attach_to_pi_owner() must observe FUTEX_STATE_EXITING with
1073 * tsk->pi_lock held.
1074 *
1075 * It guarantees also that a pi_state which was queued right before
1076 * the state change under tsk->pi_lock by a concurrent waiter must
1077 * be observed in exit_pi_state_list().
1078 */
1079 raw_spin_lock_irq(&tsk->pi_lock);
1080 tsk->futex_state = FUTEX_STATE_EXITING;
1081 raw_spin_unlock_irq(&tsk->pi_lock);
1082}
1083
1084static void futex_cleanup_end(struct task_struct *tsk, int state)
1085{
1086 /*
1087 * Lockless store. The only side effect is that an observer might
1088 * take another loop until it becomes visible.
1089 */
1090 tsk->futex_state = state;
1091 /*
1092 * Drop the exit protection. This unblocks waiters which observed
1093 * FUTEX_STATE_EXITING to reevaluate the state.
1094 */
1095 mutex_unlock(&tsk->futex_exit_mutex);
1096}
1097
1098void futex_exec_release(struct task_struct *tsk)
1099{
1100 /*
1101 * The state handling is done for consistency, but in the case of
1102 * exec() there is no way to prevent further damage as the PID stays
1103 * the same. But for the unlikely and arguably buggy case that a
1104 * futex is held on exec(), this provides at least as much state
1105 * consistency protection which is possible.
1106 */
1107 futex_cleanup_begin(tsk);
1108 futex_cleanup(tsk);
1109 /*
1110 * Reset the state to FUTEX_STATE_OK. The task is alive and about
1111 * exec a new binary.
1112 */
1113 futex_cleanup_end(tsk, FUTEX_STATE_OK);
1114}
1115
1116void futex_exit_release(struct task_struct *tsk)
1117{
1118 futex_cleanup_begin(tsk);
1119 futex_cleanup(tsk);
1120 futex_cleanup_end(tsk, FUTEX_STATE_DEAD);
1121}
1122
1123static int __init futex_init(void)
1124{
1125 unsigned int futex_shift;
1126 unsigned long i;
1127
1128#if CONFIG_BASE_SMALL
1129 futex_hashsize = 16;
1130#else
1131 futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
1132#endif
1133
1134 futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
1135 futex_hashsize, 0,
1136 futex_hashsize < 256 ? HASH_SMALL : 0,
1137 &futex_shift, NULL,
1138 futex_hashsize, futex_hashsize);
1139 futex_hashsize = 1UL << futex_shift;
1140
1141 for (i = 0; i < futex_hashsize; i++) {
1142 atomic_set(&futex_queues[i].waiters, 0);
1143 plist_head_init(&futex_queues[i].chain);
1144 spin_lock_init(&futex_queues[i].lock);
1145 }
1146
1147 return 0;
1148}
1149core_initcall(futex_init);