md:raid1: fix a dead loop when read from a WriteMostly disk
[linux/fpc-iii.git] / kernel / futex.c
blob3057dabf726f723d014b12e9cc99a612e4d972a4
1 /*
2 * Fast Userspace Mutexes (which I call "Futexes!").
3 * (C) Rusty Russell, IBM 2002
5 * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
6 * (C) Copyright 2003 Red Hat Inc, All Rights Reserved
8 * Removed page pinning, fix privately mapped COW pages and other cleanups
9 * (C) Copyright 2003, 2004 Jamie Lokier
11 * Robust futex support started by Ingo Molnar
12 * (C) Copyright 2006 Red Hat Inc, All Rights Reserved
13 * Thanks to Thomas Gleixner for suggestions, analysis and fixes.
15 * PI-futex support started by Ingo Molnar and Thomas Gleixner
16 * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
17 * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
19 * PRIVATE futexes by Eric Dumazet
20 * Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
22 * Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
23 * Copyright (C) IBM Corporation, 2009
24 * Thanks to Thomas Gleixner for conceptual design and careful reviews.
26 * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
27 * enough at me, Linus for the original (flawed) idea, Matthew
28 * Kirkwood for proof-of-concept implementation.
30 * "The futexes are also cursed."
31 * "But they come in a choice of three flavours!"
33 * This program is free software; you can redistribute it and/or modify
34 * it under the terms of the GNU General Public License as published by
35 * the Free Software Foundation; either version 2 of the License, or
36 * (at your option) any later version.
38 * This program is distributed in the hope that it will be useful,
39 * but WITHOUT ANY WARRANTY; without even the implied warranty of
40 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
41 * GNU General Public License for more details.
43 * You should have received a copy of the GNU General Public License
44 * along with this program; if not, write to the Free Software
45 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
47 #include <linux/slab.h>
48 #include <linux/poll.h>
49 #include <linux/fs.h>
50 #include <linux/file.h>
51 #include <linux/jhash.h>
52 #include <linux/init.h>
53 #include <linux/futex.h>
54 #include <linux/mount.h>
55 #include <linux/pagemap.h>
56 #include <linux/syscalls.h>
57 #include <linux/signal.h>
58 #include <linux/export.h>
59 #include <linux/magic.h>
60 #include <linux/pid.h>
61 #include <linux/nsproxy.h>
62 #include <linux/ptrace.h>
63 #include <linux/sched/rt.h>
64 #include <linux/hugetlb.h>
65 #include <linux/freezer.h>
66 #include <linux/bootmem.h>
67 #include <linux/fault-inject.h>
69 #include <asm/futex.h>
71 #include "locking/rtmutex_common.h"
74 * READ this before attempting to hack on futexes!
76 * Basic futex operation and ordering guarantees
77 * =============================================
79 * The waiter reads the futex value in user space and calls
80 * futex_wait(). This function computes the hash bucket and acquires
81 * the hash bucket lock. After that it reads the futex user space value
82 * again and verifies that the data has not changed. If it has not changed
83 * it enqueues itself into the hash bucket, releases the hash bucket lock
84 * and schedules.
86 * The waker side modifies the user space value of the futex and calls
87 * futex_wake(). This function computes the hash bucket and acquires the
88 * hash bucket lock. Then it looks for waiters on that futex in the hash
89 * bucket and wakes them.
91 * In futex wake up scenarios where no tasks are blocked on a futex, taking
92 * the hb spinlock can be avoided and simply return. In order for this
93 * optimization to work, ordering guarantees must exist so that the waiter
94 * being added to the list is acknowledged when the list is concurrently being
95 * checked by the waker, avoiding scenarios like the following:
97 * CPU 0 CPU 1
98 * val = *futex;
99 * sys_futex(WAIT, futex, val);
100 * futex_wait(futex, val);
101 * uval = *futex;
102 * *futex = newval;
103 * sys_futex(WAKE, futex);
104 * futex_wake(futex);
105 * if (queue_empty())
106 * return;
107 * if (uval == val)
108 * lock(hash_bucket(futex));
109 * queue();
110 * unlock(hash_bucket(futex));
111 * schedule();
113 * This would cause the waiter on CPU 0 to wait forever because it
114 * missed the transition of the user space value from val to newval
115 * and the waker did not find the waiter in the hash bucket queue.
117 * The correct serialization ensures that a waiter either observes
118 * the changed user space value before blocking or is woken by a
119 * concurrent waker:
121 * CPU 0 CPU 1
122 * val = *futex;
123 * sys_futex(WAIT, futex, val);
124 * futex_wait(futex, val);
126 * waiters++; (a)
127 * mb(); (A) <-- paired with -.
129 * lock(hash_bucket(futex)); |
131 * uval = *futex; |
132 * | *futex = newval;
133 * | sys_futex(WAKE, futex);
134 * | futex_wake(futex);
136 * `-------> mb(); (B)
137 * if (uval == val)
138 * queue();
139 * unlock(hash_bucket(futex));
140 * schedule(); if (waiters)
141 * lock(hash_bucket(futex));
142 * else wake_waiters(futex);
143 * waiters--; (b) unlock(hash_bucket(futex));
145 * Where (A) orders the waiters increment and the futex value read through
146 * atomic operations (see hb_waiters_inc) and where (B) orders the write
147 * to futex and the waiters read -- this is done by the barriers for both
148 * shared and private futexes in get_futex_key_refs().
150 * This yields the following case (where X:=waiters, Y:=futex):
152 * X = Y = 0
154 * w[X]=1 w[Y]=1
155 * MB MB
156 * r[Y]=y r[X]=x
158 * Which guarantees that x==0 && y==0 is impossible; which translates back into
159 * the guarantee that we cannot both miss the futex variable change and the
160 * enqueue.
162 * Note that a new waiter is accounted for in (a) even when it is possible that
163 * the wait call can return error, in which case we backtrack from it in (b).
164 * Refer to the comment in queue_lock().
166 * Similarly, in order to account for waiters being requeued on another
167 * address we always increment the waiters for the destination bucket before
168 * acquiring the lock. It then decrements them again after releasing it -
169 * the code that actually moves the futex(es) between hash buckets (requeue_futex)
170 * will do the additional required waiter count housekeeping. This is done for
171 * double_lock_hb() and double_unlock_hb(), respectively.
174 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
175 int __read_mostly futex_cmpxchg_enabled;
176 #endif
179 * Futex flags used to encode options to functions and preserve them across
180 * restarts.
182 #define FLAGS_SHARED 0x01
183 #define FLAGS_CLOCKRT 0x02
184 #define FLAGS_HAS_TIMEOUT 0x04
187 * Priority Inheritance state:
189 struct futex_pi_state {
191 * list of 'owned' pi_state instances - these have to be
192 * cleaned up in do_exit() if the task exits prematurely:
194 struct list_head list;
197 * The PI object:
199 struct rt_mutex pi_mutex;
201 struct task_struct *owner;
202 atomic_t refcount;
204 union futex_key key;
208 * struct futex_q - The hashed futex queue entry, one per waiting task
209 * @list: priority-sorted list of tasks waiting on this futex
210 * @task: the task waiting on the futex
211 * @lock_ptr: the hash bucket lock
212 * @key: the key the futex is hashed on
213 * @pi_state: optional priority inheritance state
214 * @rt_waiter: rt_waiter storage for use with requeue_pi
215 * @requeue_pi_key: the requeue_pi target futex key
216 * @bitset: bitset for the optional bitmasked wakeup
218 * We use this hashed waitqueue, instead of a normal wait_queue_t, so
219 * we can wake only the relevant ones (hashed queues may be shared).
221 * A futex_q has a woken state, just like tasks have TASK_RUNNING.
222 * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
223 * The order of wakeup is always to make the first condition true, then
224 * the second.
226 * PI futexes are typically woken before they are removed from the hash list via
227 * the rt_mutex code. See unqueue_me_pi().
229 struct futex_q {
230 struct plist_node list;
232 struct task_struct *task;
233 spinlock_t *lock_ptr;
234 union futex_key key;
235 struct futex_pi_state *pi_state;
236 struct rt_mutex_waiter *rt_waiter;
237 union futex_key *requeue_pi_key;
238 u32 bitset;
241 static const struct futex_q futex_q_init = {
242 /* list gets initialized in queue_me()*/
243 .key = FUTEX_KEY_INIT,
244 .bitset = FUTEX_BITSET_MATCH_ANY
248 * Hash buckets are shared by all the futex_keys that hash to the same
249 * location. Each key may have multiple futex_q structures, one for each task
250 * waiting on a futex.
252 struct futex_hash_bucket {
253 atomic_t waiters;
254 spinlock_t lock;
255 struct plist_head chain;
256 } ____cacheline_aligned_in_smp;
259 * The base of the bucket array and its size are always used together
260 * (after initialization only in hash_futex()), so ensure that they
261 * reside in the same cacheline.
263 static struct {
264 struct futex_hash_bucket *queues;
265 unsigned long hashsize;
266 } __futex_data __read_mostly __aligned(2*sizeof(long));
267 #define futex_queues (__futex_data.queues)
268 #define futex_hashsize (__futex_data.hashsize)
272 * Fault injections for futexes.
274 #ifdef CONFIG_FAIL_FUTEX
276 static struct {
277 struct fault_attr attr;
279 bool ignore_private;
280 } fail_futex = {
281 .attr = FAULT_ATTR_INITIALIZER,
282 .ignore_private = false,
285 static int __init setup_fail_futex(char *str)
287 return setup_fault_attr(&fail_futex.attr, str);
289 __setup("fail_futex=", setup_fail_futex);
291 static bool should_fail_futex(bool fshared)
293 if (fail_futex.ignore_private && !fshared)
294 return false;
296 return should_fail(&fail_futex.attr, 1);
299 #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
301 static int __init fail_futex_debugfs(void)
303 umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
304 struct dentry *dir;
306 dir = fault_create_debugfs_attr("fail_futex", NULL,
307 &fail_futex.attr);
308 if (IS_ERR(dir))
309 return PTR_ERR(dir);
311 if (!debugfs_create_bool("ignore-private", mode, dir,
312 &fail_futex.ignore_private)) {
313 debugfs_remove_recursive(dir);
314 return -ENOMEM;
317 return 0;
320 late_initcall(fail_futex_debugfs);
322 #endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
324 #else
325 static inline bool should_fail_futex(bool fshared)
327 return false;
329 #endif /* CONFIG_FAIL_FUTEX */
331 static inline void futex_get_mm(union futex_key *key)
333 atomic_inc(&key->private.mm->mm_count);
335 * Ensure futex_get_mm() implies a full barrier such that
336 * get_futex_key() implies a full barrier. This is relied upon
337 * as full barrier (B), see the ordering comment above.
339 smp_mb__after_atomic();
343 * Reflects a new waiter being added to the waitqueue.
345 static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
347 #ifdef CONFIG_SMP
348 atomic_inc(&hb->waiters);
350 * Full barrier (A), see the ordering comment above.
352 smp_mb__after_atomic();
353 #endif
357 * Reflects a waiter being removed from the waitqueue by wakeup
358 * paths.
360 static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
362 #ifdef CONFIG_SMP
363 atomic_dec(&hb->waiters);
364 #endif
367 static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
369 #ifdef CONFIG_SMP
370 return atomic_read(&hb->waiters);
371 #else
372 return 1;
373 #endif
377 * We hash on the keys returned from get_futex_key (see below).
379 static struct futex_hash_bucket *hash_futex(union futex_key *key)
381 u32 hash = jhash2((u32*)&key->both.word,
382 (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
383 key->both.offset);
384 return &futex_queues[hash & (futex_hashsize - 1)];
388 * Return 1 if two futex_keys are equal, 0 otherwise.
390 static inline int match_futex(union futex_key *key1, union futex_key *key2)
392 return (key1 && key2
393 && key1->both.word == key2->both.word
394 && key1->both.ptr == key2->both.ptr
395 && key1->both.offset == key2->both.offset);
399 * Take a reference to the resource addressed by a key.
400 * Can be called while holding spinlocks.
403 static void get_futex_key_refs(union futex_key *key)
405 if (!key->both.ptr)
406 return;
408 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
409 case FUT_OFF_INODE:
410 ihold(key->shared.inode); /* implies MB (B) */
411 break;
412 case FUT_OFF_MMSHARED:
413 futex_get_mm(key); /* implies MB (B) */
414 break;
415 default:
417 * Private futexes do not hold reference on an inode or
418 * mm, therefore the only purpose of calling get_futex_key_refs
419 * is because we need the barrier for the lockless waiter check.
421 smp_mb(); /* explicit MB (B) */
426 * Drop a reference to the resource addressed by a key.
427 * The hash bucket spinlock must not be held. This is
428 * a no-op for private futexes, see comment in the get
429 * counterpart.
431 static void drop_futex_key_refs(union futex_key *key)
433 if (!key->both.ptr) {
434 /* If we're here then we tried to put a key we failed to get */
435 WARN_ON_ONCE(1);
436 return;
439 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
440 case FUT_OFF_INODE:
441 iput(key->shared.inode);
442 break;
443 case FUT_OFF_MMSHARED:
444 mmdrop(key->private.mm);
445 break;
450 * get_futex_key() - Get parameters which are the keys for a futex
451 * @uaddr: virtual address of the futex
452 * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
453 * @key: address where result is stored.
454 * @rw: mapping needs to be read/write (values: VERIFY_READ,
455 * VERIFY_WRITE)
457 * Return: a negative error code or 0
459 * The key words are stored in *key on success.
461 * For shared mappings, it's (page->index, file_inode(vma->vm_file),
462 * offset_within_page). For private mappings, it's (uaddr, current->mm).
463 * We can usually work out the index without swapping in the page.
465 * lock_page() might sleep, the caller should not hold a spinlock.
467 static int
468 get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
470 unsigned long address = (unsigned long)uaddr;
471 struct mm_struct *mm = current->mm;
472 struct page *page, *page_head;
473 int err, ro = 0;
476 * The futex address must be "naturally" aligned.
478 key->both.offset = address % PAGE_SIZE;
479 if (unlikely((address % sizeof(u32)) != 0))
480 return -EINVAL;
481 address -= key->both.offset;
483 if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
484 return -EFAULT;
486 if (unlikely(should_fail_futex(fshared)))
487 return -EFAULT;
490 * PROCESS_PRIVATE futexes are fast.
491 * As the mm cannot disappear under us and the 'key' only needs
492 * virtual address, we dont even have to find the underlying vma.
493 * Note : We do have to check 'uaddr' is a valid user address,
494 * but access_ok() should be faster than find_vma()
496 if (!fshared) {
497 key->private.mm = mm;
498 key->private.address = address;
499 get_futex_key_refs(key); /* implies MB (B) */
500 return 0;
503 again:
504 /* Ignore any VERIFY_READ mapping (futex common case) */
505 if (unlikely(should_fail_futex(fshared)))
506 return -EFAULT;
508 err = get_user_pages_fast(address, 1, 1, &page);
510 * If write access is not required (eg. FUTEX_WAIT), try
511 * and get read-only access.
513 if (err == -EFAULT && rw == VERIFY_READ) {
514 err = get_user_pages_fast(address, 1, 0, &page);
515 ro = 1;
517 if (err < 0)
518 return err;
519 else
520 err = 0;
522 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
523 page_head = page;
524 if (unlikely(PageTail(page))) {
525 put_page(page);
526 /* serialize against __split_huge_page_splitting() */
527 local_irq_disable();
528 if (likely(__get_user_pages_fast(address, 1, !ro, &page) == 1)) {
529 page_head = compound_head(page);
531 * page_head is valid pointer but we must pin
532 * it before taking the PG_lock and/or
533 * PG_compound_lock. The moment we re-enable
534 * irqs __split_huge_page_splitting() can
535 * return and the head page can be freed from
536 * under us. We can't take the PG_lock and/or
537 * PG_compound_lock on a page that could be
538 * freed from under us.
540 if (page != page_head) {
541 get_page(page_head);
542 put_page(page);
544 local_irq_enable();
545 } else {
546 local_irq_enable();
547 goto again;
550 #else
551 page_head = compound_head(page);
552 if (page != page_head) {
553 get_page(page_head);
554 put_page(page);
556 #endif
558 lock_page(page_head);
561 * If page_head->mapping is NULL, then it cannot be a PageAnon
562 * page; but it might be the ZERO_PAGE or in the gate area or
563 * in a special mapping (all cases which we are happy to fail);
564 * or it may have been a good file page when get_user_pages_fast
565 * found it, but truncated or holepunched or subjected to
566 * invalidate_complete_page2 before we got the page lock (also
567 * cases which we are happy to fail). And we hold a reference,
568 * so refcount care in invalidate_complete_page's remove_mapping
569 * prevents drop_caches from setting mapping to NULL beneath us.
571 * The case we do have to guard against is when memory pressure made
572 * shmem_writepage move it from filecache to swapcache beneath us:
573 * an unlikely race, but we do need to retry for page_head->mapping.
575 if (!page_head->mapping) {
576 int shmem_swizzled = PageSwapCache(page_head);
577 unlock_page(page_head);
578 put_page(page_head);
579 if (shmem_swizzled)
580 goto again;
581 return -EFAULT;
585 * Private mappings are handled in a simple way.
587 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
588 * it's a read-only handle, it's expected that futexes attach to
589 * the object not the particular process.
591 if (PageAnon(page_head)) {
593 * A RO anonymous page will never change and thus doesn't make
594 * sense for futex operations.
596 if (unlikely(should_fail_futex(fshared)) || ro) {
597 err = -EFAULT;
598 goto out;
601 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
602 key->private.mm = mm;
603 key->private.address = address;
604 } else {
605 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
606 key->shared.inode = page_head->mapping->host;
607 key->shared.pgoff = basepage_index(page);
610 get_futex_key_refs(key); /* implies MB (B) */
612 out:
613 unlock_page(page_head);
614 put_page(page_head);
615 return err;
618 static inline void put_futex_key(union futex_key *key)
620 drop_futex_key_refs(key);
624 * fault_in_user_writeable() - Fault in user address and verify RW access
625 * @uaddr: pointer to faulting user space address
627 * Slow path to fixup the fault we just took in the atomic write
628 * access to @uaddr.
630 * We have no generic implementation of a non-destructive write to the
631 * user address. We know that we faulted in the atomic pagefault
632 * disabled section so we can as well avoid the #PF overhead by
633 * calling get_user_pages() right away.
635 static int fault_in_user_writeable(u32 __user *uaddr)
637 struct mm_struct *mm = current->mm;
638 int ret;
640 down_read(&mm->mmap_sem);
641 ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
642 FAULT_FLAG_WRITE);
643 up_read(&mm->mmap_sem);
645 return ret < 0 ? ret : 0;
649 * futex_top_waiter() - Return the highest priority waiter on a futex
650 * @hb: the hash bucket the futex_q's reside in
651 * @key: the futex key (to distinguish it from other futex futex_q's)
653 * Must be called with the hb lock held.
655 static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
656 union futex_key *key)
658 struct futex_q *this;
660 plist_for_each_entry(this, &hb->chain, list) {
661 if (match_futex(&this->key, key))
662 return this;
664 return NULL;
667 static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
668 u32 uval, u32 newval)
670 int ret;
672 pagefault_disable();
673 ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
674 pagefault_enable();
676 return ret;
679 static int get_futex_value_locked(u32 *dest, u32 __user *from)
681 int ret;
683 pagefault_disable();
684 ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
685 pagefault_enable();
687 return ret ? -EFAULT : 0;
692 * PI code:
694 static int refill_pi_state_cache(void)
696 struct futex_pi_state *pi_state;
698 if (likely(current->pi_state_cache))
699 return 0;
701 pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
703 if (!pi_state)
704 return -ENOMEM;
706 INIT_LIST_HEAD(&pi_state->list);
707 /* pi_mutex gets initialized later */
708 pi_state->owner = NULL;
709 atomic_set(&pi_state->refcount, 1);
710 pi_state->key = FUTEX_KEY_INIT;
712 current->pi_state_cache = pi_state;
714 return 0;
717 static struct futex_pi_state * alloc_pi_state(void)
719 struct futex_pi_state *pi_state = current->pi_state_cache;
721 WARN_ON(!pi_state);
722 current->pi_state_cache = NULL;
724 return pi_state;
728 * Must be called with the hb lock held.
730 static void free_pi_state(struct futex_pi_state *pi_state)
732 if (!pi_state)
733 return;
735 if (!atomic_dec_and_test(&pi_state->refcount))
736 return;
739 * If pi_state->owner is NULL, the owner is most probably dying
740 * and has cleaned up the pi_state already
742 if (pi_state->owner) {
743 raw_spin_lock_irq(&pi_state->owner->pi_lock);
744 list_del_init(&pi_state->list);
745 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
747 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
750 if (current->pi_state_cache)
751 kfree(pi_state);
752 else {
754 * pi_state->list is already empty.
755 * clear pi_state->owner.
756 * refcount is at 0 - put it back to 1.
758 pi_state->owner = NULL;
759 atomic_set(&pi_state->refcount, 1);
760 current->pi_state_cache = pi_state;
765 * Look up the task based on what TID userspace gave us.
766 * We dont trust it.
768 static struct task_struct * futex_find_get_task(pid_t pid)
770 struct task_struct *p;
772 rcu_read_lock();
773 p = find_task_by_vpid(pid);
774 if (p)
775 get_task_struct(p);
777 rcu_read_unlock();
779 return p;
783 * This task is holding PI mutexes at exit time => bad.
784 * Kernel cleans up PI-state, but userspace is likely hosed.
785 * (Robust-futex cleanup is separate and might save the day for userspace.)
787 void exit_pi_state_list(struct task_struct *curr)
789 struct list_head *next, *head = &curr->pi_state_list;
790 struct futex_pi_state *pi_state;
791 struct futex_hash_bucket *hb;
792 union futex_key key = FUTEX_KEY_INIT;
794 if (!futex_cmpxchg_enabled)
795 return;
797 * We are a ZOMBIE and nobody can enqueue itself on
798 * pi_state_list anymore, but we have to be careful
799 * versus waiters unqueueing themselves:
801 raw_spin_lock_irq(&curr->pi_lock);
802 while (!list_empty(head)) {
804 next = head->next;
805 pi_state = list_entry(next, struct futex_pi_state, list);
806 key = pi_state->key;
807 hb = hash_futex(&key);
808 raw_spin_unlock_irq(&curr->pi_lock);
810 spin_lock(&hb->lock);
812 raw_spin_lock_irq(&curr->pi_lock);
814 * We dropped the pi-lock, so re-check whether this
815 * task still owns the PI-state:
817 if (head->next != next) {
818 spin_unlock(&hb->lock);
819 continue;
822 WARN_ON(pi_state->owner != curr);
823 WARN_ON(list_empty(&pi_state->list));
824 list_del_init(&pi_state->list);
825 pi_state->owner = NULL;
826 raw_spin_unlock_irq(&curr->pi_lock);
828 rt_mutex_unlock(&pi_state->pi_mutex);
830 spin_unlock(&hb->lock);
832 raw_spin_lock_irq(&curr->pi_lock);
834 raw_spin_unlock_irq(&curr->pi_lock);
838 * We need to check the following states:
840 * Waiter | pi_state | pi->owner | uTID | uODIED | ?
842 * [1] NULL | --- | --- | 0 | 0/1 | Valid
843 * [2] NULL | --- | --- | >0 | 0/1 | Valid
845 * [3] Found | NULL | -- | Any | 0/1 | Invalid
847 * [4] Found | Found | NULL | 0 | 1 | Valid
848 * [5] Found | Found | NULL | >0 | 1 | Invalid
850 * [6] Found | Found | task | 0 | 1 | Valid
852 * [7] Found | Found | NULL | Any | 0 | Invalid
854 * [8] Found | Found | task | ==taskTID | 0/1 | Valid
855 * [9] Found | Found | task | 0 | 0 | Invalid
856 * [10] Found | Found | task | !=taskTID | 0/1 | Invalid
858 * [1] Indicates that the kernel can acquire the futex atomically. We
859 * came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
861 * [2] Valid, if TID does not belong to a kernel thread. If no matching
862 * thread is found then it indicates that the owner TID has died.
864 * [3] Invalid. The waiter is queued on a non PI futex
866 * [4] Valid state after exit_robust_list(), which sets the user space
867 * value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
869 * [5] The user space value got manipulated between exit_robust_list()
870 * and exit_pi_state_list()
872 * [6] Valid state after exit_pi_state_list() which sets the new owner in
873 * the pi_state but cannot access the user space value.
875 * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
877 * [8] Owner and user space value match
879 * [9] There is no transient state which sets the user space TID to 0
880 * except exit_robust_list(), but this is indicated by the
881 * FUTEX_OWNER_DIED bit. See [4]
883 * [10] There is no transient state which leaves owner and user space
884 * TID out of sync.
888 * Validate that the existing waiter has a pi_state and sanity check
889 * the pi_state against the user space value. If correct, attach to
890 * it.
892 static int attach_to_pi_state(u32 uval, struct futex_pi_state *pi_state,
893 struct futex_pi_state **ps)
895 pid_t pid = uval & FUTEX_TID_MASK;
898 * Userspace might have messed up non-PI and PI futexes [3]
900 if (unlikely(!pi_state))
901 return -EINVAL;
903 WARN_ON(!atomic_read(&pi_state->refcount));
906 * Handle the owner died case:
908 if (uval & FUTEX_OWNER_DIED) {
910 * exit_pi_state_list sets owner to NULL and wakes the
911 * topmost waiter. The task which acquires the
912 * pi_state->rt_mutex will fixup owner.
914 if (!pi_state->owner) {
916 * No pi state owner, but the user space TID
917 * is not 0. Inconsistent state. [5]
919 if (pid)
920 return -EINVAL;
922 * Take a ref on the state and return success. [4]
924 goto out_state;
928 * If TID is 0, then either the dying owner has not
929 * yet executed exit_pi_state_list() or some waiter
930 * acquired the rtmutex in the pi state, but did not
931 * yet fixup the TID in user space.
933 * Take a ref on the state and return success. [6]
935 if (!pid)
936 goto out_state;
937 } else {
939 * If the owner died bit is not set, then the pi_state
940 * must have an owner. [7]
942 if (!pi_state->owner)
943 return -EINVAL;
947 * Bail out if user space manipulated the futex value. If pi
948 * state exists then the owner TID must be the same as the
949 * user space TID. [9/10]
951 if (pid != task_pid_vnr(pi_state->owner))
952 return -EINVAL;
953 out_state:
954 atomic_inc(&pi_state->refcount);
955 *ps = pi_state;
956 return 0;
960 * Lookup the task for the TID provided from user space and attach to
961 * it after doing proper sanity checks.
963 static int attach_to_pi_owner(u32 uval, union futex_key *key,
964 struct futex_pi_state **ps)
966 pid_t pid = uval & FUTEX_TID_MASK;
967 struct futex_pi_state *pi_state;
968 struct task_struct *p;
971 * We are the first waiter - try to look up the real owner and attach
972 * the new pi_state to it, but bail out when TID = 0 [1]
974 if (!pid)
975 return -ESRCH;
976 p = futex_find_get_task(pid);
977 if (!p)
978 return -ESRCH;
980 if (unlikely(p->flags & PF_KTHREAD)) {
981 put_task_struct(p);
982 return -EPERM;
986 * We need to look at the task state flags to figure out,
987 * whether the task is exiting. To protect against the do_exit
988 * change of the task flags, we do this protected by
989 * p->pi_lock:
991 raw_spin_lock_irq(&p->pi_lock);
992 if (unlikely(p->flags & PF_EXITING)) {
994 * The task is on the way out. When PF_EXITPIDONE is
995 * set, we know that the task has finished the
996 * cleanup:
998 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
1000 raw_spin_unlock_irq(&p->pi_lock);
1001 put_task_struct(p);
1002 return ret;
1006 * No existing pi state. First waiter. [2]
1008 pi_state = alloc_pi_state();
1011 * Initialize the pi_mutex in locked state and make @p
1012 * the owner of it:
1014 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
1016 /* Store the key for possible exit cleanups: */
1017 pi_state->key = *key;
1019 WARN_ON(!list_empty(&pi_state->list));
1020 list_add(&pi_state->list, &p->pi_state_list);
1021 pi_state->owner = p;
1022 raw_spin_unlock_irq(&p->pi_lock);
1024 put_task_struct(p);
1026 *ps = pi_state;
1028 return 0;
1031 static int lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
1032 union futex_key *key, struct futex_pi_state **ps)
1034 struct futex_q *match = futex_top_waiter(hb, key);
1037 * If there is a waiter on that futex, validate it and
1038 * attach to the pi_state when the validation succeeds.
1040 if (match)
1041 return attach_to_pi_state(uval, match->pi_state, ps);
1044 * We are the first waiter - try to look up the owner based on
1045 * @uval and attach to it.
1047 return attach_to_pi_owner(uval, key, ps);
1050 static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
1052 u32 uninitialized_var(curval);
1054 if (unlikely(should_fail_futex(true)))
1055 return -EFAULT;
1057 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
1058 return -EFAULT;
1060 /*If user space value changed, let the caller retry */
1061 return curval != uval ? -EAGAIN : 0;
1065 * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
1066 * @uaddr: the pi futex user address
1067 * @hb: the pi futex hash bucket
1068 * @key: the futex key associated with uaddr and hb
1069 * @ps: the pi_state pointer where we store the result of the
1070 * lookup
1071 * @task: the task to perform the atomic lock work for. This will
1072 * be "current" except in the case of requeue pi.
1073 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1075 * Return:
1076 * 0 - ready to wait;
1077 * 1 - acquired the lock;
1078 * <0 - error
1080 * The hb->lock and futex_key refs shall be held by the caller.
1082 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
1083 union futex_key *key,
1084 struct futex_pi_state **ps,
1085 struct task_struct *task, int set_waiters)
1087 u32 uval, newval, vpid = task_pid_vnr(task);
1088 struct futex_q *match;
1089 int ret;
1092 * Read the user space value first so we can validate a few
1093 * things before proceeding further.
1095 if (get_futex_value_locked(&uval, uaddr))
1096 return -EFAULT;
1098 if (unlikely(should_fail_futex(true)))
1099 return -EFAULT;
1102 * Detect deadlocks.
1104 if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
1105 return -EDEADLK;
1107 if ((unlikely(should_fail_futex(true))))
1108 return -EDEADLK;
1111 * Lookup existing state first. If it exists, try to attach to
1112 * its pi_state.
1114 match = futex_top_waiter(hb, key);
1115 if (match)
1116 return attach_to_pi_state(uval, match->pi_state, ps);
1119 * No waiter and user TID is 0. We are here because the
1120 * waiters or the owner died bit is set or called from
1121 * requeue_cmp_pi or for whatever reason something took the
1122 * syscall.
1124 if (!(uval & FUTEX_TID_MASK)) {
1126 * We take over the futex. No other waiters and the user space
1127 * TID is 0. We preserve the owner died bit.
1129 newval = uval & FUTEX_OWNER_DIED;
1130 newval |= vpid;
1132 /* The futex requeue_pi code can enforce the waiters bit */
1133 if (set_waiters)
1134 newval |= FUTEX_WAITERS;
1136 ret = lock_pi_update_atomic(uaddr, uval, newval);
1137 /* If the take over worked, return 1 */
1138 return ret < 0 ? ret : 1;
1142 * First waiter. Set the waiters bit before attaching ourself to
1143 * the owner. If owner tries to unlock, it will be forced into
1144 * the kernel and blocked on hb->lock.
1146 newval = uval | FUTEX_WAITERS;
1147 ret = lock_pi_update_atomic(uaddr, uval, newval);
1148 if (ret)
1149 return ret;
1151 * If the update of the user space value succeeded, we try to
1152 * attach to the owner. If that fails, no harm done, we only
1153 * set the FUTEX_WAITERS bit in the user space variable.
1155 return attach_to_pi_owner(uval, key, ps);
1159 * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
1160 * @q: The futex_q to unqueue
1162 * The q->lock_ptr must not be NULL and must be held by the caller.
1164 static void __unqueue_futex(struct futex_q *q)
1166 struct futex_hash_bucket *hb;
1168 if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
1169 || WARN_ON(plist_node_empty(&q->list)))
1170 return;
1172 hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
1173 plist_del(&q->list, &hb->chain);
1174 hb_waiters_dec(hb);
1178 * The hash bucket lock must be held when this is called.
1179 * Afterwards, the futex_q must not be accessed. Callers
1180 * must ensure to later call wake_up_q() for the actual
1181 * wakeups to occur.
1183 static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
1185 struct task_struct *p = q->task;
1187 if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
1188 return;
1191 * Queue the task for later wakeup for after we've released
1192 * the hb->lock. wake_q_add() grabs reference to p.
1194 wake_q_add(wake_q, p);
1195 __unqueue_futex(q);
1197 * The waiting task can free the futex_q as soon as
1198 * q->lock_ptr = NULL is written, without taking any locks. A
1199 * memory barrier is required here to prevent the following
1200 * store to lock_ptr from getting ahead of the plist_del.
1202 smp_wmb();
1203 q->lock_ptr = NULL;
1206 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this,
1207 struct futex_hash_bucket *hb)
1209 struct task_struct *new_owner;
1210 struct futex_pi_state *pi_state = this->pi_state;
1211 u32 uninitialized_var(curval), newval;
1212 WAKE_Q(wake_q);
1213 bool deboost;
1214 int ret = 0;
1216 if (!pi_state)
1217 return -EINVAL;
1220 * If current does not own the pi_state then the futex is
1221 * inconsistent and user space fiddled with the futex value.
1223 if (pi_state->owner != current)
1224 return -EINVAL;
1226 raw_spin_lock(&pi_state->pi_mutex.wait_lock);
1227 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
1230 * It is possible that the next waiter (the one that brought
1231 * this owner to the kernel) timed out and is no longer
1232 * waiting on the lock.
1234 if (!new_owner)
1235 new_owner = this->task;
1238 * We pass it to the next owner. The WAITERS bit is always
1239 * kept enabled while there is PI state around. We cleanup the
1240 * owner died bit, because we are the owner.
1242 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
1244 if (unlikely(should_fail_futex(true)))
1245 ret = -EFAULT;
1247 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) {
1248 ret = -EFAULT;
1249 } else if (curval != uval) {
1251 * If a unconditional UNLOCK_PI operation (user space did not
1252 * try the TID->0 transition) raced with a waiter setting the
1253 * FUTEX_WAITERS flag between get_user() and locking the hash
1254 * bucket lock, retry the operation.
1256 if ((FUTEX_TID_MASK & curval) == uval)
1257 ret = -EAGAIN;
1258 else
1259 ret = -EINVAL;
1261 if (ret) {
1262 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
1263 return ret;
1266 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1267 WARN_ON(list_empty(&pi_state->list));
1268 list_del_init(&pi_state->list);
1269 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1271 raw_spin_lock_irq(&new_owner->pi_lock);
1272 WARN_ON(!list_empty(&pi_state->list));
1273 list_add(&pi_state->list, &new_owner->pi_state_list);
1274 pi_state->owner = new_owner;
1275 raw_spin_unlock_irq(&new_owner->pi_lock);
1277 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
1279 deboost = rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
1282 * First unlock HB so the waiter does not spin on it once he got woken
1283 * up. Second wake up the waiter before the priority is adjusted. If we
1284 * deboost first (and lose our higher priority), then the task might get
1285 * scheduled away before the wake up can take place.
1287 spin_unlock(&hb->lock);
1288 wake_up_q(&wake_q);
1289 if (deboost)
1290 rt_mutex_adjust_prio(current);
1292 return 0;
1296 * Express the locking dependencies for lockdep:
1298 static inline void
1299 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1301 if (hb1 <= hb2) {
1302 spin_lock(&hb1->lock);
1303 if (hb1 < hb2)
1304 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
1305 } else { /* hb1 > hb2 */
1306 spin_lock(&hb2->lock);
1307 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
1311 static inline void
1312 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1314 spin_unlock(&hb1->lock);
1315 if (hb1 != hb2)
1316 spin_unlock(&hb2->lock);
1320 * Wake up waiters matching bitset queued on this futex (uaddr).
1322 static int
1323 futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
1325 struct futex_hash_bucket *hb;
1326 struct futex_q *this, *next;
1327 union futex_key key = FUTEX_KEY_INIT;
1328 int ret;
1329 WAKE_Q(wake_q);
1331 if (!bitset)
1332 return -EINVAL;
1334 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
1335 if (unlikely(ret != 0))
1336 goto out;
1338 hb = hash_futex(&key);
1340 /* Make sure we really have tasks to wakeup */
1341 if (!hb_waiters_pending(hb))
1342 goto out_put_key;
1344 spin_lock(&hb->lock);
1346 plist_for_each_entry_safe(this, next, &hb->chain, list) {
1347 if (match_futex (&this->key, &key)) {
1348 if (this->pi_state || this->rt_waiter) {
1349 ret = -EINVAL;
1350 break;
1353 /* Check if one of the bits is set in both bitsets */
1354 if (!(this->bitset & bitset))
1355 continue;
1357 mark_wake_futex(&wake_q, this);
1358 if (++ret >= nr_wake)
1359 break;
1363 spin_unlock(&hb->lock);
1364 wake_up_q(&wake_q);
1365 out_put_key:
1366 put_futex_key(&key);
1367 out:
1368 return ret;
1372 * Wake up all waiters hashed on the physical page that is mapped
1373 * to this virtual address:
1375 static int
1376 futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
1377 int nr_wake, int nr_wake2, int op)
1379 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1380 struct futex_hash_bucket *hb1, *hb2;
1381 struct futex_q *this, *next;
1382 int ret, op_ret;
1383 WAKE_Q(wake_q);
1385 retry:
1386 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1387 if (unlikely(ret != 0))
1388 goto out;
1389 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
1390 if (unlikely(ret != 0))
1391 goto out_put_key1;
1393 hb1 = hash_futex(&key1);
1394 hb2 = hash_futex(&key2);
1396 retry_private:
1397 double_lock_hb(hb1, hb2);
1398 op_ret = futex_atomic_op_inuser(op, uaddr2);
1399 if (unlikely(op_ret < 0)) {
1401 double_unlock_hb(hb1, hb2);
1403 #ifndef CONFIG_MMU
1405 * we don't get EFAULT from MMU faults if we don't have an MMU,
1406 * but we might get them from range checking
1408 ret = op_ret;
1409 goto out_put_keys;
1410 #endif
1412 if (unlikely(op_ret != -EFAULT)) {
1413 ret = op_ret;
1414 goto out_put_keys;
1417 ret = fault_in_user_writeable(uaddr2);
1418 if (ret)
1419 goto out_put_keys;
1421 if (!(flags & FLAGS_SHARED))
1422 goto retry_private;
1424 put_futex_key(&key2);
1425 put_futex_key(&key1);
1426 goto retry;
1429 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1430 if (match_futex (&this->key, &key1)) {
1431 if (this->pi_state || this->rt_waiter) {
1432 ret = -EINVAL;
1433 goto out_unlock;
1435 mark_wake_futex(&wake_q, this);
1436 if (++ret >= nr_wake)
1437 break;
1441 if (op_ret > 0) {
1442 op_ret = 0;
1443 plist_for_each_entry_safe(this, next, &hb2->chain, list) {
1444 if (match_futex (&this->key, &key2)) {
1445 if (this->pi_state || this->rt_waiter) {
1446 ret = -EINVAL;
1447 goto out_unlock;
1449 mark_wake_futex(&wake_q, this);
1450 if (++op_ret >= nr_wake2)
1451 break;
1454 ret += op_ret;
1457 out_unlock:
1458 double_unlock_hb(hb1, hb2);
1459 wake_up_q(&wake_q);
1460 out_put_keys:
1461 put_futex_key(&key2);
1462 out_put_key1:
1463 put_futex_key(&key1);
1464 out:
1465 return ret;
1469 * requeue_futex() - Requeue a futex_q from one hb to another
1470 * @q: the futex_q to requeue
1471 * @hb1: the source hash_bucket
1472 * @hb2: the target hash_bucket
1473 * @key2: the new key for the requeued futex_q
1475 static inline
1476 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1477 struct futex_hash_bucket *hb2, union futex_key *key2)
1481 * If key1 and key2 hash to the same bucket, no need to
1482 * requeue.
1484 if (likely(&hb1->chain != &hb2->chain)) {
1485 plist_del(&q->list, &hb1->chain);
1486 hb_waiters_dec(hb1);
1487 hb_waiters_inc(hb2);
1488 plist_add(&q->list, &hb2->chain);
1489 q->lock_ptr = &hb2->lock;
1491 get_futex_key_refs(key2);
1492 q->key = *key2;
1496 * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1497 * @q: the futex_q
1498 * @key: the key of the requeue target futex
1499 * @hb: the hash_bucket of the requeue target futex
1501 * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1502 * target futex if it is uncontended or via a lock steal. Set the futex_q key
1503 * to the requeue target futex so the waiter can detect the wakeup on the right
1504 * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1505 * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
1506 * to protect access to the pi_state to fixup the owner later. Must be called
1507 * with both q->lock_ptr and hb->lock held.
1509 static inline
1510 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1511 struct futex_hash_bucket *hb)
1513 get_futex_key_refs(key);
1514 q->key = *key;
1516 __unqueue_futex(q);
1518 WARN_ON(!q->rt_waiter);
1519 q->rt_waiter = NULL;
1521 q->lock_ptr = &hb->lock;
1523 wake_up_state(q->task, TASK_NORMAL);
1527 * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1528 * @pifutex: the user address of the to futex
1529 * @hb1: the from futex hash bucket, must be locked by the caller
1530 * @hb2: the to futex hash bucket, must be locked by the caller
1531 * @key1: the from futex key
1532 * @key2: the to futex key
1533 * @ps: address to store the pi_state pointer
1534 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1536 * Try and get the lock on behalf of the top waiter if we can do it atomically.
1537 * Wake the top waiter if we succeed. If the caller specified set_waiters,
1538 * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1539 * hb1 and hb2 must be held by the caller.
1541 * Return:
1542 * 0 - failed to acquire the lock atomically;
1543 * >0 - acquired the lock, return value is vpid of the top_waiter
1544 * <0 - error
1546 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1547 struct futex_hash_bucket *hb1,
1548 struct futex_hash_bucket *hb2,
1549 union futex_key *key1, union futex_key *key2,
1550 struct futex_pi_state **ps, int set_waiters)
1552 struct futex_q *top_waiter = NULL;
1553 u32 curval;
1554 int ret, vpid;
1556 if (get_futex_value_locked(&curval, pifutex))
1557 return -EFAULT;
1559 if (unlikely(should_fail_futex(true)))
1560 return -EFAULT;
1563 * Find the top_waiter and determine if there are additional waiters.
1564 * If the caller intends to requeue more than 1 waiter to pifutex,
1565 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1566 * as we have means to handle the possible fault. If not, don't set
1567 * the bit unecessarily as it will force the subsequent unlock to enter
1568 * the kernel.
1570 top_waiter = futex_top_waiter(hb1, key1);
1572 /* There are no waiters, nothing for us to do. */
1573 if (!top_waiter)
1574 return 0;
1576 /* Ensure we requeue to the expected futex. */
1577 if (!match_futex(top_waiter->requeue_pi_key, key2))
1578 return -EINVAL;
1581 * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
1582 * the contended case or if set_waiters is 1. The pi_state is returned
1583 * in ps in contended cases.
1585 vpid = task_pid_vnr(top_waiter->task);
1586 ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1587 set_waiters);
1588 if (ret == 1) {
1589 requeue_pi_wake_futex(top_waiter, key2, hb2);
1590 return vpid;
1592 return ret;
1596 * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1597 * @uaddr1: source futex user address
1598 * @flags: futex flags (FLAGS_SHARED, etc.)
1599 * @uaddr2: target futex user address
1600 * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
1601 * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1602 * @cmpval: @uaddr1 expected value (or %NULL)
1603 * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1604 * pi futex (pi to pi requeue is not supported)
1606 * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1607 * uaddr2 atomically on behalf of the top waiter.
1609 * Return:
1610 * >=0 - on success, the number of tasks requeued or woken;
1611 * <0 - on error
1613 static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1614 u32 __user *uaddr2, int nr_wake, int nr_requeue,
1615 u32 *cmpval, int requeue_pi)
1617 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1618 int drop_count = 0, task_count = 0, ret;
1619 struct futex_pi_state *pi_state = NULL;
1620 struct futex_hash_bucket *hb1, *hb2;
1621 struct futex_q *this, *next;
1622 WAKE_Q(wake_q);
1624 if (requeue_pi) {
1626 * Requeue PI only works on two distinct uaddrs. This
1627 * check is only valid for private futexes. See below.
1629 if (uaddr1 == uaddr2)
1630 return -EINVAL;
1633 * requeue_pi requires a pi_state, try to allocate it now
1634 * without any locks in case it fails.
1636 if (refill_pi_state_cache())
1637 return -ENOMEM;
1639 * requeue_pi must wake as many tasks as it can, up to nr_wake
1640 * + nr_requeue, since it acquires the rt_mutex prior to
1641 * returning to userspace, so as to not leave the rt_mutex with
1642 * waiters and no owner. However, second and third wake-ups
1643 * cannot be predicted as they involve race conditions with the
1644 * first wake and a fault while looking up the pi_state. Both
1645 * pthread_cond_signal() and pthread_cond_broadcast() should
1646 * use nr_wake=1.
1648 if (nr_wake != 1)
1649 return -EINVAL;
1652 retry:
1653 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1654 if (unlikely(ret != 0))
1655 goto out;
1656 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
1657 requeue_pi ? VERIFY_WRITE : VERIFY_READ);
1658 if (unlikely(ret != 0))
1659 goto out_put_key1;
1662 * The check above which compares uaddrs is not sufficient for
1663 * shared futexes. We need to compare the keys:
1665 if (requeue_pi && match_futex(&key1, &key2)) {
1666 ret = -EINVAL;
1667 goto out_put_keys;
1670 hb1 = hash_futex(&key1);
1671 hb2 = hash_futex(&key2);
1673 retry_private:
1674 hb_waiters_inc(hb2);
1675 double_lock_hb(hb1, hb2);
1677 if (likely(cmpval != NULL)) {
1678 u32 curval;
1680 ret = get_futex_value_locked(&curval, uaddr1);
1682 if (unlikely(ret)) {
1683 double_unlock_hb(hb1, hb2);
1684 hb_waiters_dec(hb2);
1686 ret = get_user(curval, uaddr1);
1687 if (ret)
1688 goto out_put_keys;
1690 if (!(flags & FLAGS_SHARED))
1691 goto retry_private;
1693 put_futex_key(&key2);
1694 put_futex_key(&key1);
1695 goto retry;
1697 if (curval != *cmpval) {
1698 ret = -EAGAIN;
1699 goto out_unlock;
1703 if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1705 * Attempt to acquire uaddr2 and wake the top waiter. If we
1706 * intend to requeue waiters, force setting the FUTEX_WAITERS
1707 * bit. We force this here where we are able to easily handle
1708 * faults rather in the requeue loop below.
1710 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1711 &key2, &pi_state, nr_requeue);
1714 * At this point the top_waiter has either taken uaddr2 or is
1715 * waiting on it. If the former, then the pi_state will not
1716 * exist yet, look it up one more time to ensure we have a
1717 * reference to it. If the lock was taken, ret contains the
1718 * vpid of the top waiter task.
1720 if (ret > 0) {
1721 WARN_ON(pi_state);
1722 drop_count++;
1723 task_count++;
1725 * If we acquired the lock, then the user
1726 * space value of uaddr2 should be vpid. It
1727 * cannot be changed by the top waiter as it
1728 * is blocked on hb2 lock if it tries to do
1729 * so. If something fiddled with it behind our
1730 * back the pi state lookup might unearth
1731 * it. So we rather use the known value than
1732 * rereading and handing potential crap to
1733 * lookup_pi_state.
1735 ret = lookup_pi_state(ret, hb2, &key2, &pi_state);
1738 switch (ret) {
1739 case 0:
1740 break;
1741 case -EFAULT:
1742 free_pi_state(pi_state);
1743 pi_state = NULL;
1744 double_unlock_hb(hb1, hb2);
1745 hb_waiters_dec(hb2);
1746 put_futex_key(&key2);
1747 put_futex_key(&key1);
1748 ret = fault_in_user_writeable(uaddr2);
1749 if (!ret)
1750 goto retry;
1751 goto out;
1752 case -EAGAIN:
1754 * Two reasons for this:
1755 * - Owner is exiting and we just wait for the
1756 * exit to complete.
1757 * - The user space value changed.
1759 free_pi_state(pi_state);
1760 pi_state = NULL;
1761 double_unlock_hb(hb1, hb2);
1762 hb_waiters_dec(hb2);
1763 put_futex_key(&key2);
1764 put_futex_key(&key1);
1765 cond_resched();
1766 goto retry;
1767 default:
1768 goto out_unlock;
1772 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1773 if (task_count - nr_wake >= nr_requeue)
1774 break;
1776 if (!match_futex(&this->key, &key1))
1777 continue;
1780 * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1781 * be paired with each other and no other futex ops.
1783 * We should never be requeueing a futex_q with a pi_state,
1784 * which is awaiting a futex_unlock_pi().
1786 if ((requeue_pi && !this->rt_waiter) ||
1787 (!requeue_pi && this->rt_waiter) ||
1788 this->pi_state) {
1789 ret = -EINVAL;
1790 break;
1794 * Wake nr_wake waiters. For requeue_pi, if we acquired the
1795 * lock, we already woke the top_waiter. If not, it will be
1796 * woken by futex_unlock_pi().
1798 if (++task_count <= nr_wake && !requeue_pi) {
1799 mark_wake_futex(&wake_q, this);
1800 continue;
1803 /* Ensure we requeue to the expected futex for requeue_pi. */
1804 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1805 ret = -EINVAL;
1806 break;
1810 * Requeue nr_requeue waiters and possibly one more in the case
1811 * of requeue_pi if we couldn't acquire the lock atomically.
1813 if (requeue_pi) {
1814 /* Prepare the waiter to take the rt_mutex. */
1815 atomic_inc(&pi_state->refcount);
1816 this->pi_state = pi_state;
1817 ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1818 this->rt_waiter,
1819 this->task);
1820 if (ret == 1) {
1821 /* We got the lock. */
1822 requeue_pi_wake_futex(this, &key2, hb2);
1823 drop_count++;
1824 continue;
1825 } else if (ret) {
1826 /* -EDEADLK */
1827 this->pi_state = NULL;
1828 free_pi_state(pi_state);
1829 goto out_unlock;
1832 requeue_futex(this, hb1, hb2, &key2);
1833 drop_count++;
1836 out_unlock:
1837 free_pi_state(pi_state);
1838 double_unlock_hb(hb1, hb2);
1839 wake_up_q(&wake_q);
1840 hb_waiters_dec(hb2);
1843 * drop_futex_key_refs() must be called outside the spinlocks. During
1844 * the requeue we moved futex_q's from the hash bucket at key1 to the
1845 * one at key2 and updated their key pointer. We no longer need to
1846 * hold the references to key1.
1848 while (--drop_count >= 0)
1849 drop_futex_key_refs(&key1);
1851 out_put_keys:
1852 put_futex_key(&key2);
1853 out_put_key1:
1854 put_futex_key(&key1);
1855 out:
1856 return ret ? ret : task_count;
1859 /* The key must be already stored in q->key. */
1860 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
1861 __acquires(&hb->lock)
1863 struct futex_hash_bucket *hb;
1865 hb = hash_futex(&q->key);
1868 * Increment the counter before taking the lock so that
1869 * a potential waker won't miss a to-be-slept task that is
1870 * waiting for the spinlock. This is safe as all queue_lock()
1871 * users end up calling queue_me(). Similarly, for housekeeping,
1872 * decrement the counter at queue_unlock() when some error has
1873 * occurred and we don't end up adding the task to the list.
1875 hb_waiters_inc(hb);
1877 q->lock_ptr = &hb->lock;
1879 spin_lock(&hb->lock); /* implies MB (A) */
1880 return hb;
1883 static inline void
1884 queue_unlock(struct futex_hash_bucket *hb)
1885 __releases(&hb->lock)
1887 spin_unlock(&hb->lock);
1888 hb_waiters_dec(hb);
1892 * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1893 * @q: The futex_q to enqueue
1894 * @hb: The destination hash bucket
1896 * The hb->lock must be held by the caller, and is released here. A call to
1897 * queue_me() is typically paired with exactly one call to unqueue_me(). The
1898 * exceptions involve the PI related operations, which may use unqueue_me_pi()
1899 * or nothing if the unqueue is done as part of the wake process and the unqueue
1900 * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1901 * an example).
1903 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1904 __releases(&hb->lock)
1906 int prio;
1909 * The priority used to register this element is
1910 * - either the real thread-priority for the real-time threads
1911 * (i.e. threads with a priority lower than MAX_RT_PRIO)
1912 * - or MAX_RT_PRIO for non-RT threads.
1913 * Thus, all RT-threads are woken first in priority order, and
1914 * the others are woken last, in FIFO order.
1916 prio = min(current->normal_prio, MAX_RT_PRIO);
1918 plist_node_init(&q->list, prio);
1919 plist_add(&q->list, &hb->chain);
1920 q->task = current;
1921 spin_unlock(&hb->lock);
1925 * unqueue_me() - Remove the futex_q from its futex_hash_bucket
1926 * @q: The futex_q to unqueue
1928 * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
1929 * be paired with exactly one earlier call to queue_me().
1931 * Return:
1932 * 1 - if the futex_q was still queued (and we removed unqueued it);
1933 * 0 - if the futex_q was already removed by the waking thread
1935 static int unqueue_me(struct futex_q *q)
1937 spinlock_t *lock_ptr;
1938 int ret = 0;
1940 /* In the common case we don't take the spinlock, which is nice. */
1941 retry:
1942 lock_ptr = q->lock_ptr;
1943 barrier();
1944 if (lock_ptr != NULL) {
1945 spin_lock(lock_ptr);
1947 * q->lock_ptr can change between reading it and
1948 * spin_lock(), causing us to take the wrong lock. This
1949 * corrects the race condition.
1951 * Reasoning goes like this: if we have the wrong lock,
1952 * q->lock_ptr must have changed (maybe several times)
1953 * between reading it and the spin_lock(). It can
1954 * change again after the spin_lock() but only if it was
1955 * already changed before the spin_lock(). It cannot,
1956 * however, change back to the original value. Therefore
1957 * we can detect whether we acquired the correct lock.
1959 if (unlikely(lock_ptr != q->lock_ptr)) {
1960 spin_unlock(lock_ptr);
1961 goto retry;
1963 __unqueue_futex(q);
1965 BUG_ON(q->pi_state);
1967 spin_unlock(lock_ptr);
1968 ret = 1;
1971 drop_futex_key_refs(&q->key);
1972 return ret;
1976 * PI futexes can not be requeued and must remove themself from the
1977 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1978 * and dropped here.
1980 static void unqueue_me_pi(struct futex_q *q)
1981 __releases(q->lock_ptr)
1983 __unqueue_futex(q);
1985 BUG_ON(!q->pi_state);
1986 free_pi_state(q->pi_state);
1987 q->pi_state = NULL;
1989 spin_unlock(q->lock_ptr);
1993 * Fixup the pi_state owner with the new owner.
1995 * Must be called with hash bucket lock held and mm->sem held for non
1996 * private futexes.
1998 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1999 struct task_struct *newowner)
2001 u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
2002 struct futex_pi_state *pi_state = q->pi_state;
2003 struct task_struct *oldowner = pi_state->owner;
2004 u32 uval, uninitialized_var(curval), newval;
2005 int ret;
2007 /* Owner died? */
2008 if (!pi_state->owner)
2009 newtid |= FUTEX_OWNER_DIED;
2012 * We are here either because we stole the rtmutex from the
2013 * previous highest priority waiter or we are the highest priority
2014 * waiter but failed to get the rtmutex the first time.
2015 * We have to replace the newowner TID in the user space variable.
2016 * This must be atomic as we have to preserve the owner died bit here.
2018 * Note: We write the user space value _before_ changing the pi_state
2019 * because we can fault here. Imagine swapped out pages or a fork
2020 * that marked all the anonymous memory readonly for cow.
2022 * Modifying pi_state _before_ the user space value would
2023 * leave the pi_state in an inconsistent state when we fault
2024 * here, because we need to drop the hash bucket lock to
2025 * handle the fault. This might be observed in the PID check
2026 * in lookup_pi_state.
2028 retry:
2029 if (get_futex_value_locked(&uval, uaddr))
2030 goto handle_fault;
2032 while (1) {
2033 newval = (uval & FUTEX_OWNER_DIED) | newtid;
2035 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
2036 goto handle_fault;
2037 if (curval == uval)
2038 break;
2039 uval = curval;
2043 * We fixed up user space. Now we need to fix the pi_state
2044 * itself.
2046 if (pi_state->owner != NULL) {
2047 raw_spin_lock_irq(&pi_state->owner->pi_lock);
2048 WARN_ON(list_empty(&pi_state->list));
2049 list_del_init(&pi_state->list);
2050 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
2053 pi_state->owner = newowner;
2055 raw_spin_lock_irq(&newowner->pi_lock);
2056 WARN_ON(!list_empty(&pi_state->list));
2057 list_add(&pi_state->list, &newowner->pi_state_list);
2058 raw_spin_unlock_irq(&newowner->pi_lock);
2059 return 0;
2062 * To handle the page fault we need to drop the hash bucket
2063 * lock here. That gives the other task (either the highest priority
2064 * waiter itself or the task which stole the rtmutex) the
2065 * chance to try the fixup of the pi_state. So once we are
2066 * back from handling the fault we need to check the pi_state
2067 * after reacquiring the hash bucket lock and before trying to
2068 * do another fixup. When the fixup has been done already we
2069 * simply return.
2071 handle_fault:
2072 spin_unlock(q->lock_ptr);
2074 ret = fault_in_user_writeable(uaddr);
2076 spin_lock(q->lock_ptr);
2079 * Check if someone else fixed it for us:
2081 if (pi_state->owner != oldowner)
2082 return 0;
2084 if (ret)
2085 return ret;
2087 goto retry;
2090 static long futex_wait_restart(struct restart_block *restart);
2093 * fixup_owner() - Post lock pi_state and corner case management
2094 * @uaddr: user address of the futex
2095 * @q: futex_q (contains pi_state and access to the rt_mutex)
2096 * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
2098 * After attempting to lock an rt_mutex, this function is called to cleanup
2099 * the pi_state owner as well as handle race conditions that may allow us to
2100 * acquire the lock. Must be called with the hb lock held.
2102 * Return:
2103 * 1 - success, lock taken;
2104 * 0 - success, lock not taken;
2105 * <0 - on error (-EFAULT)
2107 static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
2109 struct task_struct *owner;
2110 int ret = 0;
2112 if (locked) {
2114 * Got the lock. We might not be the anticipated owner if we
2115 * did a lock-steal - fix up the PI-state in that case:
2117 if (q->pi_state->owner != current)
2118 ret = fixup_pi_state_owner(uaddr, q, current);
2119 goto out;
2123 * Catch the rare case, where the lock was released when we were on the
2124 * way back before we locked the hash bucket.
2126 if (q->pi_state->owner == current) {
2128 * Try to get the rt_mutex now. This might fail as some other
2129 * task acquired the rt_mutex after we removed ourself from the
2130 * rt_mutex waiters list.
2132 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
2133 locked = 1;
2134 goto out;
2138 * pi_state is incorrect, some other task did a lock steal and
2139 * we returned due to timeout or signal without taking the
2140 * rt_mutex. Too late.
2142 raw_spin_lock(&q->pi_state->pi_mutex.wait_lock);
2143 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
2144 if (!owner)
2145 owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
2146 raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock);
2147 ret = fixup_pi_state_owner(uaddr, q, owner);
2148 goto out;
2152 * Paranoia check. If we did not take the lock, then we should not be
2153 * the owner of the rt_mutex.
2155 if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
2156 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
2157 "pi-state %p\n", ret,
2158 q->pi_state->pi_mutex.owner,
2159 q->pi_state->owner);
2161 out:
2162 return ret ? ret : locked;
2166 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
2167 * @hb: the futex hash bucket, must be locked by the caller
2168 * @q: the futex_q to queue up on
2169 * @timeout: the prepared hrtimer_sleeper, or null for no timeout
2171 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
2172 struct hrtimer_sleeper *timeout)
2175 * The task state is guaranteed to be set before another task can
2176 * wake it. set_current_state() is implemented using smp_store_mb() and
2177 * queue_me() calls spin_unlock() upon completion, both serializing
2178 * access to the hash list and forcing another memory barrier.
2180 set_current_state(TASK_INTERRUPTIBLE);
2181 queue_me(q, hb);
2183 /* Arm the timer */
2184 if (timeout)
2185 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
2188 * If we have been removed from the hash list, then another task
2189 * has tried to wake us, and we can skip the call to schedule().
2191 if (likely(!plist_node_empty(&q->list))) {
2193 * If the timer has already expired, current will already be
2194 * flagged for rescheduling. Only call schedule if there
2195 * is no timeout, or if it has yet to expire.
2197 if (!timeout || timeout->task)
2198 freezable_schedule();
2200 __set_current_state(TASK_RUNNING);
2204 * futex_wait_setup() - Prepare to wait on a futex
2205 * @uaddr: the futex userspace address
2206 * @val: the expected value
2207 * @flags: futex flags (FLAGS_SHARED, etc.)
2208 * @q: the associated futex_q
2209 * @hb: storage for hash_bucket pointer to be returned to caller
2211 * Setup the futex_q and locate the hash_bucket. Get the futex value and
2212 * compare it with the expected value. Handle atomic faults internally.
2213 * Return with the hb lock held and a q.key reference on success, and unlocked
2214 * with no q.key reference on failure.
2216 * Return:
2217 * 0 - uaddr contains val and hb has been locked;
2218 * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
2220 static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
2221 struct futex_q *q, struct futex_hash_bucket **hb)
2223 u32 uval;
2224 int ret;
2227 * Access the page AFTER the hash-bucket is locked.
2228 * Order is important:
2230 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
2231 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
2233 * The basic logical guarantee of a futex is that it blocks ONLY
2234 * if cond(var) is known to be true at the time of blocking, for
2235 * any cond. If we locked the hash-bucket after testing *uaddr, that
2236 * would open a race condition where we could block indefinitely with
2237 * cond(var) false, which would violate the guarantee.
2239 * On the other hand, we insert q and release the hash-bucket only
2240 * after testing *uaddr. This guarantees that futex_wait() will NOT
2241 * absorb a wakeup if *uaddr does not match the desired values
2242 * while the syscall executes.
2244 retry:
2245 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
2246 if (unlikely(ret != 0))
2247 return ret;
2249 retry_private:
2250 *hb = queue_lock(q);
2252 ret = get_futex_value_locked(&uval, uaddr);
2254 if (ret) {
2255 queue_unlock(*hb);
2257 ret = get_user(uval, uaddr);
2258 if (ret)
2259 goto out;
2261 if (!(flags & FLAGS_SHARED))
2262 goto retry_private;
2264 put_futex_key(&q->key);
2265 goto retry;
2268 if (uval != val) {
2269 queue_unlock(*hb);
2270 ret = -EWOULDBLOCK;
2273 out:
2274 if (ret)
2275 put_futex_key(&q->key);
2276 return ret;
2279 static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
2280 ktime_t *abs_time, u32 bitset)
2282 struct hrtimer_sleeper timeout, *to = NULL;
2283 struct restart_block *restart;
2284 struct futex_hash_bucket *hb;
2285 struct futex_q q = futex_q_init;
2286 int ret;
2288 if (!bitset)
2289 return -EINVAL;
2290 q.bitset = bitset;
2292 if (abs_time) {
2293 to = &timeout;
2295 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2296 CLOCK_REALTIME : CLOCK_MONOTONIC,
2297 HRTIMER_MODE_ABS);
2298 hrtimer_init_sleeper(to, current);
2299 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2300 current->timer_slack_ns);
2303 retry:
2305 * Prepare to wait on uaddr. On success, holds hb lock and increments
2306 * q.key refs.
2308 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2309 if (ret)
2310 goto out;
2312 /* queue_me and wait for wakeup, timeout, or a signal. */
2313 futex_wait_queue_me(hb, &q, to);
2315 /* If we were woken (and unqueued), we succeeded, whatever. */
2316 ret = 0;
2317 /* unqueue_me() drops q.key ref */
2318 if (!unqueue_me(&q))
2319 goto out;
2320 ret = -ETIMEDOUT;
2321 if (to && !to->task)
2322 goto out;
2325 * We expect signal_pending(current), but we might be the
2326 * victim of a spurious wakeup as well.
2328 if (!signal_pending(current))
2329 goto retry;
2331 ret = -ERESTARTSYS;
2332 if (!abs_time)
2333 goto out;
2335 restart = &current->restart_block;
2336 restart->fn = futex_wait_restart;
2337 restart->futex.uaddr = uaddr;
2338 restart->futex.val = val;
2339 restart->futex.time = abs_time->tv64;
2340 restart->futex.bitset = bitset;
2341 restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
2343 ret = -ERESTART_RESTARTBLOCK;
2345 out:
2346 if (to) {
2347 hrtimer_cancel(&to->timer);
2348 destroy_hrtimer_on_stack(&to->timer);
2350 return ret;
2354 static long futex_wait_restart(struct restart_block *restart)
2356 u32 __user *uaddr = restart->futex.uaddr;
2357 ktime_t t, *tp = NULL;
2359 if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
2360 t.tv64 = restart->futex.time;
2361 tp = &t;
2363 restart->fn = do_no_restart_syscall;
2365 return (long)futex_wait(uaddr, restart->futex.flags,
2366 restart->futex.val, tp, restart->futex.bitset);
2371 * Userspace tried a 0 -> TID atomic transition of the futex value
2372 * and failed. The kernel side here does the whole locking operation:
2373 * if there are waiters then it will block as a consequence of relying
2374 * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
2375 * a 0 value of the futex too.).
2377 * Also serves as futex trylock_pi()'ing, and due semantics.
2379 static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
2380 ktime_t *time, int trylock)
2382 struct hrtimer_sleeper timeout, *to = NULL;
2383 struct futex_hash_bucket *hb;
2384 struct futex_q q = futex_q_init;
2385 int res, ret;
2387 if (refill_pi_state_cache())
2388 return -ENOMEM;
2390 if (time) {
2391 to = &timeout;
2392 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
2393 HRTIMER_MODE_ABS);
2394 hrtimer_init_sleeper(to, current);
2395 hrtimer_set_expires(&to->timer, *time);
2398 retry:
2399 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
2400 if (unlikely(ret != 0))
2401 goto out;
2403 retry_private:
2404 hb = queue_lock(&q);
2406 ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
2407 if (unlikely(ret)) {
2409 * Atomic work succeeded and we got the lock,
2410 * or failed. Either way, we do _not_ block.
2412 switch (ret) {
2413 case 1:
2414 /* We got the lock. */
2415 ret = 0;
2416 goto out_unlock_put_key;
2417 case -EFAULT:
2418 goto uaddr_faulted;
2419 case -EAGAIN:
2421 * Two reasons for this:
2422 * - Task is exiting and we just wait for the
2423 * exit to complete.
2424 * - The user space value changed.
2426 queue_unlock(hb);
2427 put_futex_key(&q.key);
2428 cond_resched();
2429 goto retry;
2430 default:
2431 goto out_unlock_put_key;
2436 * Only actually queue now that the atomic ops are done:
2438 queue_me(&q, hb);
2440 WARN_ON(!q.pi_state);
2442 * Block on the PI mutex:
2444 if (!trylock) {
2445 ret = rt_mutex_timed_futex_lock(&q.pi_state->pi_mutex, to);
2446 } else {
2447 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
2448 /* Fixup the trylock return value: */
2449 ret = ret ? 0 : -EWOULDBLOCK;
2452 spin_lock(q.lock_ptr);
2454 * Fixup the pi_state owner and possibly acquire the lock if we
2455 * haven't already.
2457 res = fixup_owner(uaddr, &q, !ret);
2459 * If fixup_owner() returned an error, proprogate that. If it acquired
2460 * the lock, clear our -ETIMEDOUT or -EINTR.
2462 if (res)
2463 ret = (res < 0) ? res : 0;
2466 * If fixup_owner() faulted and was unable to handle the fault, unlock
2467 * it and return the fault to userspace.
2469 if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
2470 rt_mutex_unlock(&q.pi_state->pi_mutex);
2472 /* Unqueue and drop the lock */
2473 unqueue_me_pi(&q);
2475 goto out_put_key;
2477 out_unlock_put_key:
2478 queue_unlock(hb);
2480 out_put_key:
2481 put_futex_key(&q.key);
2482 out:
2483 if (to)
2484 destroy_hrtimer_on_stack(&to->timer);
2485 return ret != -EINTR ? ret : -ERESTARTNOINTR;
2487 uaddr_faulted:
2488 queue_unlock(hb);
2490 ret = fault_in_user_writeable(uaddr);
2491 if (ret)
2492 goto out_put_key;
2494 if (!(flags & FLAGS_SHARED))
2495 goto retry_private;
2497 put_futex_key(&q.key);
2498 goto retry;
2502 * Userspace attempted a TID -> 0 atomic transition, and failed.
2503 * This is the in-kernel slowpath: we look up the PI state (if any),
2504 * and do the rt-mutex unlock.
2506 static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
2508 u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current);
2509 union futex_key key = FUTEX_KEY_INIT;
2510 struct futex_hash_bucket *hb;
2511 struct futex_q *match;
2512 int ret;
2514 retry:
2515 if (get_user(uval, uaddr))
2516 return -EFAULT;
2518 * We release only a lock we actually own:
2520 if ((uval & FUTEX_TID_MASK) != vpid)
2521 return -EPERM;
2523 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
2524 if (ret)
2525 return ret;
2527 hb = hash_futex(&key);
2528 spin_lock(&hb->lock);
2531 * Check waiters first. We do not trust user space values at
2532 * all and we at least want to know if user space fiddled
2533 * with the futex value instead of blindly unlocking.
2535 match = futex_top_waiter(hb, &key);
2536 if (match) {
2537 ret = wake_futex_pi(uaddr, uval, match, hb);
2539 * In case of success wake_futex_pi dropped the hash
2540 * bucket lock.
2542 if (!ret)
2543 goto out_putkey;
2545 * The atomic access to the futex value generated a
2546 * pagefault, so retry the user-access and the wakeup:
2548 if (ret == -EFAULT)
2549 goto pi_faulted;
2551 * A unconditional UNLOCK_PI op raced against a waiter
2552 * setting the FUTEX_WAITERS bit. Try again.
2554 if (ret == -EAGAIN) {
2555 spin_unlock(&hb->lock);
2556 put_futex_key(&key);
2557 goto retry;
2560 * wake_futex_pi has detected invalid state. Tell user
2561 * space.
2563 goto out_unlock;
2567 * We have no kernel internal state, i.e. no waiters in the
2568 * kernel. Waiters which are about to queue themselves are stuck
2569 * on hb->lock. So we can safely ignore them. We do neither
2570 * preserve the WAITERS bit not the OWNER_DIED one. We are the
2571 * owner.
2573 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))
2574 goto pi_faulted;
2577 * If uval has changed, let user space handle it.
2579 ret = (curval == uval) ? 0 : -EAGAIN;
2581 out_unlock:
2582 spin_unlock(&hb->lock);
2583 out_putkey:
2584 put_futex_key(&key);
2585 return ret;
2587 pi_faulted:
2588 spin_unlock(&hb->lock);
2589 put_futex_key(&key);
2591 ret = fault_in_user_writeable(uaddr);
2592 if (!ret)
2593 goto retry;
2595 return ret;
2599 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2600 * @hb: the hash_bucket futex_q was original enqueued on
2601 * @q: the futex_q woken while waiting to be requeued
2602 * @key2: the futex_key of the requeue target futex
2603 * @timeout: the timeout associated with the wait (NULL if none)
2605 * Detect if the task was woken on the initial futex as opposed to the requeue
2606 * target futex. If so, determine if it was a timeout or a signal that caused
2607 * the wakeup and return the appropriate error code to the caller. Must be
2608 * called with the hb lock held.
2610 * Return:
2611 * 0 = no early wakeup detected;
2612 * <0 = -ETIMEDOUT or -ERESTARTNOINTR
2614 static inline
2615 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2616 struct futex_q *q, union futex_key *key2,
2617 struct hrtimer_sleeper *timeout)
2619 int ret = 0;
2622 * With the hb lock held, we avoid races while we process the wakeup.
2623 * We only need to hold hb (and not hb2) to ensure atomicity as the
2624 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2625 * It can't be requeued from uaddr2 to something else since we don't
2626 * support a PI aware source futex for requeue.
2628 if (!match_futex(&q->key, key2)) {
2629 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2631 * We were woken prior to requeue by a timeout or a signal.
2632 * Unqueue the futex_q and determine which it was.
2634 plist_del(&q->list, &hb->chain);
2635 hb_waiters_dec(hb);
2637 /* Handle spurious wakeups gracefully */
2638 ret = -EWOULDBLOCK;
2639 if (timeout && !timeout->task)
2640 ret = -ETIMEDOUT;
2641 else if (signal_pending(current))
2642 ret = -ERESTARTNOINTR;
2644 return ret;
2648 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2649 * @uaddr: the futex we initially wait on (non-pi)
2650 * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
2651 * the same type, no requeueing from private to shared, etc.
2652 * @val: the expected value of uaddr
2653 * @abs_time: absolute timeout
2654 * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
2655 * @uaddr2: the pi futex we will take prior to returning to user-space
2657 * The caller will wait on uaddr and will be requeued by futex_requeue() to
2658 * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
2659 * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
2660 * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
2661 * without one, the pi logic would not know which task to boost/deboost, if
2662 * there was a need to.
2664 * We call schedule in futex_wait_queue_me() when we enqueue and return there
2665 * via the following--
2666 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2667 * 2) wakeup on uaddr2 after a requeue
2668 * 3) signal
2669 * 4) timeout
2671 * If 3, cleanup and return -ERESTARTNOINTR.
2673 * If 2, we may then block on trying to take the rt_mutex and return via:
2674 * 5) successful lock
2675 * 6) signal
2676 * 7) timeout
2677 * 8) other lock acquisition failure
2679 * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2681 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2683 * Return:
2684 * 0 - On success;
2685 * <0 - On error
2687 static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
2688 u32 val, ktime_t *abs_time, u32 bitset,
2689 u32 __user *uaddr2)
2691 struct hrtimer_sleeper timeout, *to = NULL;
2692 struct rt_mutex_waiter rt_waiter;
2693 struct futex_hash_bucket *hb;
2694 union futex_key key2 = FUTEX_KEY_INIT;
2695 struct futex_q q = futex_q_init;
2696 int res, ret;
2698 if (uaddr == uaddr2)
2699 return -EINVAL;
2701 if (!bitset)
2702 return -EINVAL;
2704 if (abs_time) {
2705 to = &timeout;
2706 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2707 CLOCK_REALTIME : CLOCK_MONOTONIC,
2708 HRTIMER_MODE_ABS);
2709 hrtimer_init_sleeper(to, current);
2710 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2711 current->timer_slack_ns);
2715 * The waiter is allocated on our stack, manipulated by the requeue
2716 * code while we sleep on uaddr.
2718 debug_rt_mutex_init_waiter(&rt_waiter);
2719 RB_CLEAR_NODE(&rt_waiter.pi_tree_entry);
2720 RB_CLEAR_NODE(&rt_waiter.tree_entry);
2721 rt_waiter.task = NULL;
2723 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
2724 if (unlikely(ret != 0))
2725 goto out;
2727 q.bitset = bitset;
2728 q.rt_waiter = &rt_waiter;
2729 q.requeue_pi_key = &key2;
2732 * Prepare to wait on uaddr. On success, increments q.key (key1) ref
2733 * count.
2735 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2736 if (ret)
2737 goto out_key2;
2740 * The check above which compares uaddrs is not sufficient for
2741 * shared futexes. We need to compare the keys:
2743 if (match_futex(&q.key, &key2)) {
2744 queue_unlock(hb);
2745 ret = -EINVAL;
2746 goto out_put_keys;
2749 /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2750 futex_wait_queue_me(hb, &q, to);
2752 spin_lock(&hb->lock);
2753 ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2754 spin_unlock(&hb->lock);
2755 if (ret)
2756 goto out_put_keys;
2759 * In order for us to be here, we know our q.key == key2, and since
2760 * we took the hb->lock above, we also know that futex_requeue() has
2761 * completed and we no longer have to concern ourselves with a wakeup
2762 * race with the atomic proxy lock acquisition by the requeue code. The
2763 * futex_requeue dropped our key1 reference and incremented our key2
2764 * reference count.
2767 /* Check if the requeue code acquired the second futex for us. */
2768 if (!q.rt_waiter) {
2770 * Got the lock. We might not be the anticipated owner if we
2771 * did a lock-steal - fix up the PI-state in that case.
2773 if (q.pi_state && (q.pi_state->owner != current)) {
2774 spin_lock(q.lock_ptr);
2775 ret = fixup_pi_state_owner(uaddr2, &q, current);
2776 if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current)
2777 rt_mutex_unlock(&q.pi_state->pi_mutex);
2779 * Drop the reference to the pi state which
2780 * the requeue_pi() code acquired for us.
2782 free_pi_state(q.pi_state);
2783 spin_unlock(q.lock_ptr);
2785 } else {
2786 struct rt_mutex *pi_mutex;
2789 * We have been woken up by futex_unlock_pi(), a timeout, or a
2790 * signal. futex_unlock_pi() will not destroy the lock_ptr nor
2791 * the pi_state.
2793 WARN_ON(!q.pi_state);
2794 pi_mutex = &q.pi_state->pi_mutex;
2795 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter);
2796 debug_rt_mutex_free_waiter(&rt_waiter);
2798 spin_lock(q.lock_ptr);
2800 * Fixup the pi_state owner and possibly acquire the lock if we
2801 * haven't already.
2803 res = fixup_owner(uaddr2, &q, !ret);
2805 * If fixup_owner() returned an error, proprogate that. If it
2806 * acquired the lock, clear -ETIMEDOUT or -EINTR.
2808 if (res)
2809 ret = (res < 0) ? res : 0;
2812 * If fixup_pi_state_owner() faulted and was unable to handle
2813 * the fault, unlock the rt_mutex and return the fault to
2814 * userspace.
2816 if (ret && rt_mutex_owner(pi_mutex) == current)
2817 rt_mutex_unlock(pi_mutex);
2819 /* Unqueue and drop the lock. */
2820 unqueue_me_pi(&q);
2823 if (ret == -EINTR) {
2825 * We've already been requeued, but cannot restart by calling
2826 * futex_lock_pi() directly. We could restart this syscall, but
2827 * it would detect that the user space "val" changed and return
2828 * -EWOULDBLOCK. Save the overhead of the restart and return
2829 * -EWOULDBLOCK directly.
2831 ret = -EWOULDBLOCK;
2834 out_put_keys:
2835 put_futex_key(&q.key);
2836 out_key2:
2837 put_futex_key(&key2);
2839 out:
2840 if (to) {
2841 hrtimer_cancel(&to->timer);
2842 destroy_hrtimer_on_stack(&to->timer);
2844 return ret;
2848 * Support for robust futexes: the kernel cleans up held futexes at
2849 * thread exit time.
2851 * Implementation: user-space maintains a per-thread list of locks it
2852 * is holding. Upon do_exit(), the kernel carefully walks this list,
2853 * and marks all locks that are owned by this thread with the
2854 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2855 * always manipulated with the lock held, so the list is private and
2856 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2857 * field, to allow the kernel to clean up if the thread dies after
2858 * acquiring the lock, but just before it could have added itself to
2859 * the list. There can only be one such pending lock.
2863 * sys_set_robust_list() - Set the robust-futex list head of a task
2864 * @head: pointer to the list-head
2865 * @len: length of the list-head, as userspace expects
2867 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2868 size_t, len)
2870 if (!futex_cmpxchg_enabled)
2871 return -ENOSYS;
2873 * The kernel knows only one size for now:
2875 if (unlikely(len != sizeof(*head)))
2876 return -EINVAL;
2878 current->robust_list = head;
2880 return 0;
2884 * sys_get_robust_list() - Get the robust-futex list head of a task
2885 * @pid: pid of the process [zero for current task]
2886 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
2887 * @len_ptr: pointer to a length field, the kernel fills in the header size
2889 SYSCALL_DEFINE3(get_robust_list, int, pid,
2890 struct robust_list_head __user * __user *, head_ptr,
2891 size_t __user *, len_ptr)
2893 struct robust_list_head __user *head;
2894 unsigned long ret;
2895 struct task_struct *p;
2897 if (!futex_cmpxchg_enabled)
2898 return -ENOSYS;
2900 rcu_read_lock();
2902 ret = -ESRCH;
2903 if (!pid)
2904 p = current;
2905 else {
2906 p = find_task_by_vpid(pid);
2907 if (!p)
2908 goto err_unlock;
2911 ret = -EPERM;
2912 if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
2913 goto err_unlock;
2915 head = p->robust_list;
2916 rcu_read_unlock();
2918 if (put_user(sizeof(*head), len_ptr))
2919 return -EFAULT;
2920 return put_user(head, head_ptr);
2922 err_unlock:
2923 rcu_read_unlock();
2925 return ret;
2929 * Process a futex-list entry, check whether it's owned by the
2930 * dying task, and do notification if so:
2932 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
2934 u32 uval, uninitialized_var(nval), mval;
2936 retry:
2937 if (get_user(uval, uaddr))
2938 return -1;
2940 if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
2942 * Ok, this dying thread is truly holding a futex
2943 * of interest. Set the OWNER_DIED bit atomically
2944 * via cmpxchg, and if the value had FUTEX_WAITERS
2945 * set, wake up a waiter (if any). (We have to do a
2946 * futex_wake() even if OWNER_DIED is already set -
2947 * to handle the rare but possible case of recursive
2948 * thread-death.) The rest of the cleanup is done in
2949 * userspace.
2951 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
2953 * We are not holding a lock here, but we want to have
2954 * the pagefault_disable/enable() protection because
2955 * we want to handle the fault gracefully. If the
2956 * access fails we try to fault in the futex with R/W
2957 * verification via get_user_pages. get_user() above
2958 * does not guarantee R/W access. If that fails we
2959 * give up and leave the futex locked.
2961 if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
2962 if (fault_in_user_writeable(uaddr))
2963 return -1;
2964 goto retry;
2966 if (nval != uval)
2967 goto retry;
2970 * Wake robust non-PI futexes here. The wakeup of
2971 * PI futexes happens in exit_pi_state():
2973 if (!pi && (uval & FUTEX_WAITERS))
2974 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
2976 return 0;
2980 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
2982 static inline int fetch_robust_entry(struct robust_list __user **entry,
2983 struct robust_list __user * __user *head,
2984 unsigned int *pi)
2986 unsigned long uentry;
2988 if (get_user(uentry, (unsigned long __user *)head))
2989 return -EFAULT;
2991 *entry = (void __user *)(uentry & ~1UL);
2992 *pi = uentry & 1;
2994 return 0;
2998 * Walk curr->robust_list (very carefully, it's a userspace list!)
2999 * and mark any locks found there dead, and notify any waiters.
3001 * We silently return on any sign of list-walking problem.
3003 void exit_robust_list(struct task_struct *curr)
3005 struct robust_list_head __user *head = curr->robust_list;
3006 struct robust_list __user *entry, *next_entry, *pending;
3007 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
3008 unsigned int uninitialized_var(next_pi);
3009 unsigned long futex_offset;
3010 int rc;
3012 if (!futex_cmpxchg_enabled)
3013 return;
3016 * Fetch the list head (which was registered earlier, via
3017 * sys_set_robust_list()):
3019 if (fetch_robust_entry(&entry, &head->list.next, &pi))
3020 return;
3022 * Fetch the relative futex offset:
3024 if (get_user(futex_offset, &head->futex_offset))
3025 return;
3027 * Fetch any possibly pending lock-add first, and handle it
3028 * if it exists:
3030 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
3031 return;
3033 next_entry = NULL; /* avoid warning with gcc */
3034 while (entry != &head->list) {
3036 * Fetch the next entry in the list before calling
3037 * handle_futex_death:
3039 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
3041 * A pending lock might already be on the list, so
3042 * don't process it twice:
3044 if (entry != pending)
3045 if (handle_futex_death((void __user *)entry + futex_offset,
3046 curr, pi))
3047 return;
3048 if (rc)
3049 return;
3050 entry = next_entry;
3051 pi = next_pi;
3053 * Avoid excessively long or circular lists:
3055 if (!--limit)
3056 break;
3058 cond_resched();
3061 if (pending)
3062 handle_futex_death((void __user *)pending + futex_offset,
3063 curr, pip);
3066 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
3067 u32 __user *uaddr2, u32 val2, u32 val3)
3069 int cmd = op & FUTEX_CMD_MASK;
3070 unsigned int flags = 0;
3072 if (!(op & FUTEX_PRIVATE_FLAG))
3073 flags |= FLAGS_SHARED;
3075 if (op & FUTEX_CLOCK_REALTIME) {
3076 flags |= FLAGS_CLOCKRT;
3077 if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
3078 return -ENOSYS;
3081 switch (cmd) {
3082 case FUTEX_LOCK_PI:
3083 case FUTEX_UNLOCK_PI:
3084 case FUTEX_TRYLOCK_PI:
3085 case FUTEX_WAIT_REQUEUE_PI:
3086 case FUTEX_CMP_REQUEUE_PI:
3087 if (!futex_cmpxchg_enabled)
3088 return -ENOSYS;
3091 switch (cmd) {
3092 case FUTEX_WAIT:
3093 val3 = FUTEX_BITSET_MATCH_ANY;
3094 case FUTEX_WAIT_BITSET:
3095 return futex_wait(uaddr, flags, val, timeout, val3);
3096 case FUTEX_WAKE:
3097 val3 = FUTEX_BITSET_MATCH_ANY;
3098 case FUTEX_WAKE_BITSET:
3099 return futex_wake(uaddr, flags, val, val3);
3100 case FUTEX_REQUEUE:
3101 return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
3102 case FUTEX_CMP_REQUEUE:
3103 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
3104 case FUTEX_WAKE_OP:
3105 return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
3106 case FUTEX_LOCK_PI:
3107 return futex_lock_pi(uaddr, flags, timeout, 0);
3108 case FUTEX_UNLOCK_PI:
3109 return futex_unlock_pi(uaddr, flags);
3110 case FUTEX_TRYLOCK_PI:
3111 return futex_lock_pi(uaddr, flags, NULL, 1);
3112 case FUTEX_WAIT_REQUEUE_PI:
3113 val3 = FUTEX_BITSET_MATCH_ANY;
3114 return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
3115 uaddr2);
3116 case FUTEX_CMP_REQUEUE_PI:
3117 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
3119 return -ENOSYS;
3123 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
3124 struct timespec __user *, utime, u32 __user *, uaddr2,
3125 u32, val3)
3127 struct timespec ts;
3128 ktime_t t, *tp = NULL;
3129 u32 val2 = 0;
3130 int cmd = op & FUTEX_CMD_MASK;
3132 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
3133 cmd == FUTEX_WAIT_BITSET ||
3134 cmd == FUTEX_WAIT_REQUEUE_PI)) {
3135 if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
3136 return -EFAULT;
3137 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
3138 return -EFAULT;
3139 if (!timespec_valid(&ts))
3140 return -EINVAL;
3142 t = timespec_to_ktime(ts);
3143 if (cmd == FUTEX_WAIT)
3144 t = ktime_add_safe(ktime_get(), t);
3145 tp = &t;
3148 * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
3149 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
3151 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
3152 cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
3153 val2 = (u32) (unsigned long) utime;
3155 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
3158 static void __init futex_detect_cmpxchg(void)
3160 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
3161 u32 curval;
3164 * This will fail and we want it. Some arch implementations do
3165 * runtime detection of the futex_atomic_cmpxchg_inatomic()
3166 * functionality. We want to know that before we call in any
3167 * of the complex code paths. Also we want to prevent
3168 * registration of robust lists in that case. NULL is
3169 * guaranteed to fault and we get -EFAULT on functional
3170 * implementation, the non-functional ones will return
3171 * -ENOSYS.
3173 if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
3174 futex_cmpxchg_enabled = 1;
3175 #endif
3178 static int __init futex_init(void)
3180 unsigned int futex_shift;
3181 unsigned long i;
3183 #if CONFIG_BASE_SMALL
3184 futex_hashsize = 16;
3185 #else
3186 futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
3187 #endif
3189 futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
3190 futex_hashsize, 0,
3191 futex_hashsize < 256 ? HASH_SMALL : 0,
3192 &futex_shift, NULL,
3193 futex_hashsize, futex_hashsize);
3194 futex_hashsize = 1UL << futex_shift;
3196 futex_detect_cmpxchg();
3198 for (i = 0; i < futex_hashsize; i++) {
3199 atomic_set(&futex_queues[i].waiters, 0);
3200 plist_head_init(&futex_queues[i].chain);
3201 spin_lock_init(&futex_queues[i].lock);
3204 return 0;
3206 core_initcall(futex_init);