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 * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
23 * enough at me, Linus for the original (flawed) idea, Matthew
24 * Kirkwood for proof-of-concept implementation.
26 * "The futexes are also cursed."
27 * "But they come in a choice of three flavours!"
29 * This program is free software; you can redistribute it and/or modify
30 * it under the terms of the GNU General Public License as published by
31 * the Free Software Foundation; either version 2 of the License, or
32 * (at your option) any later version.
34 * This program is distributed in the hope that it will be useful,
35 * but WITHOUT ANY WARRANTY; without even the implied warranty of
36 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
37 * GNU General Public License for more details.
39 * You should have received a copy of the GNU General Public License
40 * along with this program; if not, write to the Free Software
41 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
43 #include <linux/slab.h>
44 #include <linux/poll.h>
46 #include <linux/file.h>
47 #include <linux/jhash.h>
48 #include <linux/init.h>
49 #include <linux/futex.h>
50 #include <linux/mount.h>
51 #include <linux/pagemap.h>
52 #include <linux/syscalls.h>
53 #include <linux/signal.h>
54 #include <linux/module.h>
55 #include <linux/magic.h>
56 #include <linux/pid.h>
57 #include <linux/nsproxy.h>
59 #include <asm/futex.h>
61 #include "rtmutex_common.h"
63 int __read_mostly futex_cmpxchg_enabled;
65 #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
68 * Priority Inheritance state:
70 struct futex_pi_state {
72 * list of 'owned' pi_state instances - these have to be
73 * cleaned up in do_exit() if the task exits prematurely:
75 struct list_head list;
80 struct rt_mutex pi_mutex;
82 struct task_struct *owner;
89 * We use this hashed waitqueue instead of a normal wait_queue_t, so
90 * we can wake only the relevant ones (hashed queues may be shared).
92 * A futex_q has a woken state, just like tasks have TASK_RUNNING.
93 * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
94 * The order of wakup is always to make the first condition true, then
95 * wake up q->waiter, then make the second condition true.
98 struct plist_node list;
99 /* There can only be a single waiter */
100 wait_queue_head_t waiter;
102 /* Which hash list lock to use: */
103 spinlock_t *lock_ptr;
105 /* Key which the futex is hashed on: */
108 /* Optional priority inheritance state: */
109 struct futex_pi_state *pi_state;
110 struct task_struct *task;
112 /* Bitset for the optional bitmasked wakeup */
117 * Hash buckets are shared by all the futex_keys that hash to the same
118 * location. Each key may have multiple futex_q structures, one for each task
119 * waiting on a futex.
121 struct futex_hash_bucket {
123 struct plist_head chain;
126 static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
129 * We hash on the keys returned from get_futex_key (see below).
131 static struct futex_hash_bucket *hash_futex(union futex_key *key)
133 u32 hash = jhash2((u32*)&key->both.word,
134 (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
136 return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
140 * Return 1 if two futex_keys are equal, 0 otherwise.
142 static inline int match_futex(union futex_key *key1, union futex_key *key2)
144 return (key1->both.word == key2->both.word
145 && key1->both.ptr == key2->both.ptr
146 && key1->both.offset == key2->both.offset);
150 * Take a reference to the resource addressed by a key.
151 * Can be called while holding spinlocks.
154 static void get_futex_key_refs(union futex_key *key)
159 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
161 atomic_inc(&key->shared.inode->i_count);
163 case FUT_OFF_MMSHARED:
164 atomic_inc(&key->private.mm->mm_count);
170 * Drop a reference to the resource addressed by a key.
171 * The hash bucket spinlock must not be held.
173 static void drop_futex_key_refs(union futex_key *key)
175 if (!key->both.ptr) {
176 /* If we're here then we tried to put a key we failed to get */
181 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
183 iput(key->shared.inode);
185 case FUT_OFF_MMSHARED:
186 mmdrop(key->private.mm);
192 * get_futex_key - Get parameters which are the keys for a futex.
193 * @uaddr: virtual address of the futex
194 * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
195 * @key: address where result is stored.
197 * Returns a negative error code or 0
198 * The key words are stored in *key on success.
200 * For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,
201 * offset_within_page). For private mappings, it's (uaddr, current->mm).
202 * We can usually work out the index without swapping in the page.
204 * lock_page() might sleep, the caller should not hold a spinlock.
206 static int get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key)
208 unsigned long address = (unsigned long)uaddr;
209 struct mm_struct *mm = current->mm;
214 * The futex address must be "naturally" aligned.
216 key->both.offset = address % PAGE_SIZE;
217 if (unlikely((address % sizeof(u32)) != 0))
219 address -= key->both.offset;
222 * PROCESS_PRIVATE futexes are fast.
223 * As the mm cannot disappear under us and the 'key' only needs
224 * virtual address, we dont even have to find the underlying vma.
225 * Note : We do have to check 'uaddr' is a valid user address,
226 * but access_ok() should be faster than find_vma()
229 if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))))
231 key->private.mm = mm;
232 key->private.address = address;
233 get_futex_key_refs(key);
238 err = get_user_pages_fast(address, 1, 0, &page);
243 if (!page->mapping) {
250 * Private mappings are handled in a simple way.
252 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
253 * it's a read-only handle, it's expected that futexes attach to
254 * the object not the particular process.
256 if (PageAnon(page)) {
257 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
258 key->private.mm = mm;
259 key->private.address = address;
261 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
262 key->shared.inode = page->mapping->host;
263 key->shared.pgoff = page->index;
266 get_futex_key_refs(key);
274 void put_futex_key(int fshared, union futex_key *key)
276 drop_futex_key_refs(key);
279 static u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval)
284 curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
290 static int get_futex_value_locked(u32 *dest, u32 __user *from)
295 ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
298 return ret ? -EFAULT : 0;
305 static int refill_pi_state_cache(void)
307 struct futex_pi_state *pi_state;
309 if (likely(current->pi_state_cache))
312 pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
317 INIT_LIST_HEAD(&pi_state->list);
318 /* pi_mutex gets initialized later */
319 pi_state->owner = NULL;
320 atomic_set(&pi_state->refcount, 1);
321 pi_state->key = FUTEX_KEY_INIT;
323 current->pi_state_cache = pi_state;
328 static struct futex_pi_state * alloc_pi_state(void)
330 struct futex_pi_state *pi_state = current->pi_state_cache;
333 current->pi_state_cache = NULL;
338 static void free_pi_state(struct futex_pi_state *pi_state)
340 if (!atomic_dec_and_test(&pi_state->refcount))
344 * If pi_state->owner is NULL, the owner is most probably dying
345 * and has cleaned up the pi_state already
347 if (pi_state->owner) {
348 spin_lock_irq(&pi_state->owner->pi_lock);
349 list_del_init(&pi_state->list);
350 spin_unlock_irq(&pi_state->owner->pi_lock);
352 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
355 if (current->pi_state_cache)
359 * pi_state->list is already empty.
360 * clear pi_state->owner.
361 * refcount is at 0 - put it back to 1.
363 pi_state->owner = NULL;
364 atomic_set(&pi_state->refcount, 1);
365 current->pi_state_cache = pi_state;
370 * Look up the task based on what TID userspace gave us.
373 static struct task_struct * futex_find_get_task(pid_t pid)
375 struct task_struct *p;
376 const struct cred *cred = current_cred(), *pcred;
379 p = find_task_by_vpid(pid);
383 pcred = __task_cred(p);
384 if (cred->euid != pcred->euid &&
385 cred->euid != pcred->uid)
397 * This task is holding PI mutexes at exit time => bad.
398 * Kernel cleans up PI-state, but userspace is likely hosed.
399 * (Robust-futex cleanup is separate and might save the day for userspace.)
401 void exit_pi_state_list(struct task_struct *curr)
403 struct list_head *next, *head = &curr->pi_state_list;
404 struct futex_pi_state *pi_state;
405 struct futex_hash_bucket *hb;
406 union futex_key key = FUTEX_KEY_INIT;
408 if (!futex_cmpxchg_enabled)
411 * We are a ZOMBIE and nobody can enqueue itself on
412 * pi_state_list anymore, but we have to be careful
413 * versus waiters unqueueing themselves:
415 spin_lock_irq(&curr->pi_lock);
416 while (!list_empty(head)) {
419 pi_state = list_entry(next, struct futex_pi_state, list);
421 hb = hash_futex(&key);
422 spin_unlock_irq(&curr->pi_lock);
424 spin_lock(&hb->lock);
426 spin_lock_irq(&curr->pi_lock);
428 * We dropped the pi-lock, so re-check whether this
429 * task still owns the PI-state:
431 if (head->next != next) {
432 spin_unlock(&hb->lock);
436 WARN_ON(pi_state->owner != curr);
437 WARN_ON(list_empty(&pi_state->list));
438 list_del_init(&pi_state->list);
439 pi_state->owner = NULL;
440 spin_unlock_irq(&curr->pi_lock);
442 rt_mutex_unlock(&pi_state->pi_mutex);
444 spin_unlock(&hb->lock);
446 spin_lock_irq(&curr->pi_lock);
448 spin_unlock_irq(&curr->pi_lock);
452 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
453 union futex_key *key, struct futex_pi_state **ps)
455 struct futex_pi_state *pi_state = NULL;
456 struct futex_q *this, *next;
457 struct plist_head *head;
458 struct task_struct *p;
459 pid_t pid = uval & FUTEX_TID_MASK;
463 plist_for_each_entry_safe(this, next, head, list) {
464 if (match_futex(&this->key, key)) {
466 * Another waiter already exists - bump up
467 * the refcount and return its pi_state:
469 pi_state = this->pi_state;
471 * Userspace might have messed up non PI and PI futexes
473 if (unlikely(!pi_state))
476 WARN_ON(!atomic_read(&pi_state->refcount));
477 WARN_ON(pid && pi_state->owner &&
478 pi_state->owner->pid != pid);
480 atomic_inc(&pi_state->refcount);
488 * We are the first waiter - try to look up the real owner and attach
489 * the new pi_state to it, but bail out when TID = 0
493 p = futex_find_get_task(pid);
498 * We need to look at the task state flags to figure out,
499 * whether the task is exiting. To protect against the do_exit
500 * change of the task flags, we do this protected by
503 spin_lock_irq(&p->pi_lock);
504 if (unlikely(p->flags & PF_EXITING)) {
506 * The task is on the way out. When PF_EXITPIDONE is
507 * set, we know that the task has finished the
510 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
512 spin_unlock_irq(&p->pi_lock);
517 pi_state = alloc_pi_state();
520 * Initialize the pi_mutex in locked state and make 'p'
523 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
525 /* Store the key for possible exit cleanups: */
526 pi_state->key = *key;
528 WARN_ON(!list_empty(&pi_state->list));
529 list_add(&pi_state->list, &p->pi_state_list);
531 spin_unlock_irq(&p->pi_lock);
541 * The hash bucket lock must be held when this is called.
542 * Afterwards, the futex_q must not be accessed.
544 static void wake_futex(struct futex_q *q)
546 plist_del(&q->list, &q->list.plist);
548 * The lock in wake_up_all() is a crucial memory barrier after the
549 * plist_del() and also before assigning to q->lock_ptr.
553 * The waiting task can free the futex_q as soon as this is written,
554 * without taking any locks. This must come last.
556 * A memory barrier is required here to prevent the following store to
557 * lock_ptr from getting ahead of the wakeup. Clearing the lock at the
558 * end of wake_up() does not prevent this store from moving.
564 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
566 struct task_struct *new_owner;
567 struct futex_pi_state *pi_state = this->pi_state;
573 spin_lock(&pi_state->pi_mutex.wait_lock);
574 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
577 * This happens when we have stolen the lock and the original
578 * pending owner did not enqueue itself back on the rt_mutex.
579 * Thats not a tragedy. We know that way, that a lock waiter
580 * is on the fly. We make the futex_q waiter the pending owner.
583 new_owner = this->task;
586 * We pass it to the next owner. (The WAITERS bit is always
587 * kept enabled while there is PI state around. We must also
588 * preserve the owner died bit.)
590 if (!(uval & FUTEX_OWNER_DIED)) {
593 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
595 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
597 if (curval == -EFAULT)
599 else if (curval != uval)
602 spin_unlock(&pi_state->pi_mutex.wait_lock);
607 spin_lock_irq(&pi_state->owner->pi_lock);
608 WARN_ON(list_empty(&pi_state->list));
609 list_del_init(&pi_state->list);
610 spin_unlock_irq(&pi_state->owner->pi_lock);
612 spin_lock_irq(&new_owner->pi_lock);
613 WARN_ON(!list_empty(&pi_state->list));
614 list_add(&pi_state->list, &new_owner->pi_state_list);
615 pi_state->owner = new_owner;
616 spin_unlock_irq(&new_owner->pi_lock);
618 spin_unlock(&pi_state->pi_mutex.wait_lock);
619 rt_mutex_unlock(&pi_state->pi_mutex);
624 static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
629 * There is no waiter, so we unlock the futex. The owner died
630 * bit has not to be preserved here. We are the owner:
632 oldval = cmpxchg_futex_value_locked(uaddr, uval, 0);
634 if (oldval == -EFAULT)
643 * Express the locking dependencies for lockdep:
646 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
649 spin_lock(&hb1->lock);
651 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
652 } else { /* hb1 > hb2 */
653 spin_lock(&hb2->lock);
654 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
659 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
661 spin_unlock(&hb1->lock);
663 spin_unlock(&hb2->lock);
667 * Wake up waiters matching bitset queued on this futex (uaddr).
669 static int futex_wake(u32 __user *uaddr, int fshared, int nr_wake, u32 bitset)
671 struct futex_hash_bucket *hb;
672 struct futex_q *this, *next;
673 struct plist_head *head;
674 union futex_key key = FUTEX_KEY_INIT;
680 ret = get_futex_key(uaddr, fshared, &key);
681 if (unlikely(ret != 0))
684 hb = hash_futex(&key);
685 spin_lock(&hb->lock);
688 plist_for_each_entry_safe(this, next, head, list) {
689 if (match_futex (&this->key, &key)) {
690 if (this->pi_state) {
695 /* Check if one of the bits is set in both bitsets */
696 if (!(this->bitset & bitset))
700 if (++ret >= nr_wake)
705 spin_unlock(&hb->lock);
706 put_futex_key(fshared, &key);
712 * Wake up all waiters hashed on the physical page that is mapped
713 * to this virtual address:
716 futex_wake_op(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
717 int nr_wake, int nr_wake2, int op)
719 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
720 struct futex_hash_bucket *hb1, *hb2;
721 struct plist_head *head;
722 struct futex_q *this, *next;
726 ret = get_futex_key(uaddr1, fshared, &key1);
727 if (unlikely(ret != 0))
729 ret = get_futex_key(uaddr2, fshared, &key2);
730 if (unlikely(ret != 0))
733 hb1 = hash_futex(&key1);
734 hb2 = hash_futex(&key2);
736 double_lock_hb(hb1, hb2);
738 op_ret = futex_atomic_op_inuser(op, uaddr2);
739 if (unlikely(op_ret < 0)) {
742 double_unlock_hb(hb1, hb2);
746 * we don't get EFAULT from MMU faults if we don't have an MMU,
747 * but we might get them from range checking
753 if (unlikely(op_ret != -EFAULT)) {
758 ret = get_user(dummy, uaddr2);
765 put_futex_key(fshared, &key2);
766 put_futex_key(fshared, &key1);
772 plist_for_each_entry_safe(this, next, head, list) {
773 if (match_futex (&this->key, &key1)) {
775 if (++ret >= nr_wake)
784 plist_for_each_entry_safe(this, next, head, list) {
785 if (match_futex (&this->key, &key2)) {
787 if (++op_ret >= nr_wake2)
794 double_unlock_hb(hb1, hb2);
796 put_futex_key(fshared, &key2);
798 put_futex_key(fshared, &key1);
804 * Requeue all waiters hashed on one physical page to another
807 static int futex_requeue(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
808 int nr_wake, int nr_requeue, u32 *cmpval)
810 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
811 struct futex_hash_bucket *hb1, *hb2;
812 struct plist_head *head1;
813 struct futex_q *this, *next;
814 int ret, drop_count = 0;
817 ret = get_futex_key(uaddr1, fshared, &key1);
818 if (unlikely(ret != 0))
820 ret = get_futex_key(uaddr2, fshared, &key2);
821 if (unlikely(ret != 0))
824 hb1 = hash_futex(&key1);
825 hb2 = hash_futex(&key2);
828 double_lock_hb(hb1, hb2);
830 if (likely(cmpval != NULL)) {
833 ret = get_futex_value_locked(&curval, uaddr1);
836 double_unlock_hb(hb1, hb2);
838 ret = get_user(curval, uaddr1);
845 put_futex_key(fshared, &key2);
846 put_futex_key(fshared, &key1);
849 if (curval != *cmpval) {
856 plist_for_each_entry_safe(this, next, head1, list) {
857 if (!match_futex (&this->key, &key1))
859 if (++ret <= nr_wake) {
863 * If key1 and key2 hash to the same bucket, no need to
866 if (likely(head1 != &hb2->chain)) {
867 plist_del(&this->list, &hb1->chain);
868 plist_add(&this->list, &hb2->chain);
869 this->lock_ptr = &hb2->lock;
870 #ifdef CONFIG_DEBUG_PI_LIST
871 this->list.plist.lock = &hb2->lock;
875 get_futex_key_refs(&key2);
878 if (ret - nr_wake >= nr_requeue)
884 double_unlock_hb(hb1, hb2);
886 /* drop_futex_key_refs() must be called outside the spinlocks. */
887 while (--drop_count >= 0)
888 drop_futex_key_refs(&key1);
891 put_futex_key(fshared, &key2);
893 put_futex_key(fshared, &key1);
898 /* The key must be already stored in q->key. */
899 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
901 struct futex_hash_bucket *hb;
903 init_waitqueue_head(&q->waiter);
905 get_futex_key_refs(&q->key);
906 hb = hash_futex(&q->key);
907 q->lock_ptr = &hb->lock;
909 spin_lock(&hb->lock);
913 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
918 * The priority used to register this element is
919 * - either the real thread-priority for the real-time threads
920 * (i.e. threads with a priority lower than MAX_RT_PRIO)
921 * - or MAX_RT_PRIO for non-RT threads.
922 * Thus, all RT-threads are woken first in priority order, and
923 * the others are woken last, in FIFO order.
925 prio = min(current->normal_prio, MAX_RT_PRIO);
927 plist_node_init(&q->list, prio);
928 #ifdef CONFIG_DEBUG_PI_LIST
929 q->list.plist.lock = &hb->lock;
931 plist_add(&q->list, &hb->chain);
933 spin_unlock(&hb->lock);
937 queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
939 spin_unlock(&hb->lock);
940 drop_futex_key_refs(&q->key);
944 * queue_me and unqueue_me must be called as a pair, each
945 * exactly once. They are called with the hashed spinlock held.
948 /* Return 1 if we were still queued (ie. 0 means we were woken) */
949 static int unqueue_me(struct futex_q *q)
951 spinlock_t *lock_ptr;
954 /* In the common case we don't take the spinlock, which is nice. */
956 lock_ptr = q->lock_ptr;
958 if (lock_ptr != NULL) {
961 * q->lock_ptr can change between reading it and
962 * spin_lock(), causing us to take the wrong lock. This
963 * corrects the race condition.
965 * Reasoning goes like this: if we have the wrong lock,
966 * q->lock_ptr must have changed (maybe several times)
967 * between reading it and the spin_lock(). It can
968 * change again after the spin_lock() but only if it was
969 * already changed before the spin_lock(). It cannot,
970 * however, change back to the original value. Therefore
971 * we can detect whether we acquired the correct lock.
973 if (unlikely(lock_ptr != q->lock_ptr)) {
974 spin_unlock(lock_ptr);
977 WARN_ON(plist_node_empty(&q->list));
978 plist_del(&q->list, &q->list.plist);
982 spin_unlock(lock_ptr);
986 drop_futex_key_refs(&q->key);
991 * PI futexes can not be requeued and must remove themself from the
992 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
995 static void unqueue_me_pi(struct futex_q *q)
997 WARN_ON(plist_node_empty(&q->list));
998 plist_del(&q->list, &q->list.plist);
1000 BUG_ON(!q->pi_state);
1001 free_pi_state(q->pi_state);
1004 spin_unlock(q->lock_ptr);
1006 drop_futex_key_refs(&q->key);
1010 * Fixup the pi_state owner with the new owner.
1012 * Must be called with hash bucket lock held and mm->sem held for non
1015 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1016 struct task_struct *newowner, int fshared)
1018 u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
1019 struct futex_pi_state *pi_state = q->pi_state;
1020 struct task_struct *oldowner = pi_state->owner;
1021 u32 uval, curval, newval;
1025 if (!pi_state->owner)
1026 newtid |= FUTEX_OWNER_DIED;
1029 * We are here either because we stole the rtmutex from the
1030 * pending owner or we are the pending owner which failed to
1031 * get the rtmutex. We have to replace the pending owner TID
1032 * in the user space variable. This must be atomic as we have
1033 * to preserve the owner died bit here.
1035 * Note: We write the user space value _before_ changing the pi_state
1036 * because we can fault here. Imagine swapped out pages or a fork
1037 * that marked all the anonymous memory readonly for cow.
1039 * Modifying pi_state _before_ the user space value would
1040 * leave the pi_state in an inconsistent state when we fault
1041 * here, because we need to drop the hash bucket lock to
1042 * handle the fault. This might be observed in the PID check
1043 * in lookup_pi_state.
1046 if (get_futex_value_locked(&uval, uaddr))
1050 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1052 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
1054 if (curval == -EFAULT)
1062 * We fixed up user space. Now we need to fix the pi_state
1065 if (pi_state->owner != NULL) {
1066 spin_lock_irq(&pi_state->owner->pi_lock);
1067 WARN_ON(list_empty(&pi_state->list));
1068 list_del_init(&pi_state->list);
1069 spin_unlock_irq(&pi_state->owner->pi_lock);
1072 pi_state->owner = newowner;
1074 spin_lock_irq(&newowner->pi_lock);
1075 WARN_ON(!list_empty(&pi_state->list));
1076 list_add(&pi_state->list, &newowner->pi_state_list);
1077 spin_unlock_irq(&newowner->pi_lock);
1081 * To handle the page fault we need to drop the hash bucket
1082 * lock here. That gives the other task (either the pending
1083 * owner itself or the task which stole the rtmutex) the
1084 * chance to try the fixup of the pi_state. So once we are
1085 * back from handling the fault we need to check the pi_state
1086 * after reacquiring the hash bucket lock and before trying to
1087 * do another fixup. When the fixup has been done already we
1091 spin_unlock(q->lock_ptr);
1093 ret = get_user(uval, uaddr);
1095 spin_lock(q->lock_ptr);
1098 * Check if someone else fixed it for us:
1100 if (pi_state->owner != oldowner)
1110 * In case we must use restart_block to restart a futex_wait,
1111 * we encode in the 'flags' shared capability
1113 #define FLAGS_SHARED 0x01
1114 #define FLAGS_CLOCKRT 0x02
1116 static long futex_wait_restart(struct restart_block *restart);
1119 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
1120 * @hb: the futex hash bucket, must be locked by the caller
1121 * @q: the futex_q to queue up on
1122 * @timeout: the prepared hrtimer_sleeper, or null for no timeout
1123 * @wait: the wait_queue to add to the futex_q after queueing in the hb
1125 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
1126 struct hrtimer_sleeper *timeout,
1132 * There might have been scheduling since the queue_me(), as we
1133 * cannot hold a spinlock across the get_user() in case it
1134 * faults, and we cannot just set TASK_INTERRUPTIBLE state when
1135 * queueing ourselves into the futex hash. This code thus has to
1136 * rely on the futex_wake() code removing us from hash when it
1140 /* add_wait_queue is the barrier after __set_current_state. */
1141 __set_current_state(TASK_INTERRUPTIBLE);
1144 * Add current as the futex_q waiter. We don't remove ourselves from
1145 * the wait_queue because we are the only user of it.
1147 add_wait_queue(&q->waiter, wait);
1151 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1152 if (!hrtimer_active(&timeout->timer))
1153 timeout->task = NULL;
1157 * !plist_node_empty() is safe here without any lock.
1158 * q.lock_ptr != 0 is not safe, because of ordering against wakeup.
1160 if (likely(!plist_node_empty(&q->list))) {
1162 * If the timer has already expired, current will already be
1163 * flagged for rescheduling. Only call schedule if there
1164 * is no timeout, or if it has yet to expire.
1166 if (!timeout || timeout->task)
1169 __set_current_state(TASK_RUNNING);
1172 static int futex_wait(u32 __user *uaddr, int fshared,
1173 u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
1175 struct hrtimer_sleeper timeout, *to = NULL;
1176 DECLARE_WAITQUEUE(wait, current);
1177 struct restart_block *restart;
1178 struct futex_hash_bucket *hb;
1192 hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
1193 CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1194 hrtimer_init_sleeper(to, current);
1195 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
1196 current->timer_slack_ns);
1200 q.key = FUTEX_KEY_INIT;
1201 ret = get_futex_key(uaddr, fshared, &q.key);
1202 if (unlikely(ret != 0))
1206 hb = queue_lock(&q);
1209 * Access the page AFTER the hash-bucket is locked.
1210 * Order is important:
1212 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1213 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
1215 * The basic logical guarantee of a futex is that it blocks ONLY
1216 * if cond(var) is known to be true at the time of blocking, for
1217 * any cond. If we queued after testing *uaddr, that would open
1218 * a race condition where we could block indefinitely with
1219 * cond(var) false, which would violate the guarantee.
1221 * A consequence is that futex_wait() can return zero and absorb
1222 * a wakeup when *uaddr != val on entry to the syscall. This is
1225 * For shared futexes, we hold the mmap semaphore, so the mapping
1226 * cannot have changed since we looked it up in get_futex_key.
1228 ret = get_futex_value_locked(&uval, uaddr);
1230 if (unlikely(ret)) {
1231 queue_unlock(&q, hb);
1233 ret = get_user(uval, uaddr);
1240 put_futex_key(fshared, &q.key);
1245 /* Only actually queue if *uaddr contained val. */
1246 if (unlikely(uval != val)) {
1247 queue_unlock(&q, hb);
1251 /* queue_me and wait for wakeup, timeout, or a signal. */
1252 futex_wait_queue_me(hb, &q, to, &wait);
1254 /* If we were woken (and unqueued), we succeeded, whatever. */
1256 if (!unqueue_me(&q))
1259 if (to && !to->task)
1263 * We expect signal_pending(current), but another thread may
1264 * have handled it for us already.
1270 restart = ¤t_thread_info()->restart_block;
1271 restart->fn = futex_wait_restart;
1272 restart->futex.uaddr = (u32 *)uaddr;
1273 restart->futex.val = val;
1274 restart->futex.time = abs_time->tv64;
1275 restart->futex.bitset = bitset;
1276 restart->futex.flags = 0;
1279 restart->futex.flags |= FLAGS_SHARED;
1281 restart->futex.flags |= FLAGS_CLOCKRT;
1283 ret = -ERESTART_RESTARTBLOCK;
1286 put_futex_key(fshared, &q.key);
1289 hrtimer_cancel(&to->timer);
1290 destroy_hrtimer_on_stack(&to->timer);
1296 static long futex_wait_restart(struct restart_block *restart)
1298 u32 __user *uaddr = (u32 __user *)restart->futex.uaddr;
1302 t.tv64 = restart->futex.time;
1303 restart->fn = do_no_restart_syscall;
1304 if (restart->futex.flags & FLAGS_SHARED)
1306 return (long)futex_wait(uaddr, fshared, restart->futex.val, &t,
1307 restart->futex.bitset,
1308 restart->futex.flags & FLAGS_CLOCKRT);
1313 * Userspace tried a 0 -> TID atomic transition of the futex value
1314 * and failed. The kernel side here does the whole locking operation:
1315 * if there are waiters then it will block, it does PI, etc. (Due to
1316 * races the kernel might see a 0 value of the futex too.)
1318 static int futex_lock_pi(u32 __user *uaddr, int fshared,
1319 int detect, ktime_t *time, int trylock)
1321 struct hrtimer_sleeper timeout, *to = NULL;
1322 struct task_struct *curr = current;
1323 struct futex_hash_bucket *hb;
1324 u32 uval, newval, curval;
1326 int ret, lock_taken, ownerdied = 0;
1328 if (refill_pi_state_cache())
1333 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
1335 hrtimer_init_sleeper(to, current);
1336 hrtimer_set_expires(&to->timer, *time);
1341 q.key = FUTEX_KEY_INIT;
1342 ret = get_futex_key(uaddr, fshared, &q.key);
1343 if (unlikely(ret != 0))
1347 hb = queue_lock(&q);
1350 ret = lock_taken = 0;
1353 * To avoid races, we attempt to take the lock here again
1354 * (by doing a 0 -> TID atomic cmpxchg), while holding all
1355 * the locks. It will most likely not succeed.
1357 newval = task_pid_vnr(current);
1359 curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
1361 if (unlikely(curval == -EFAULT))
1365 * Detect deadlocks. In case of REQUEUE_PI this is a valid
1366 * situation and we return success to user space.
1368 if (unlikely((curval & FUTEX_TID_MASK) == task_pid_vnr(current))) {
1370 goto out_unlock_put_key;
1374 * Surprise - we got the lock. Just return to userspace:
1376 if (unlikely(!curval))
1377 goto out_unlock_put_key;
1382 * Set the WAITERS flag, so the owner will know it has someone
1383 * to wake at next unlock
1385 newval = curval | FUTEX_WAITERS;
1388 * There are two cases, where a futex might have no owner (the
1389 * owner TID is 0): OWNER_DIED. We take over the futex in this
1390 * case. We also do an unconditional take over, when the owner
1391 * of the futex died.
1393 * This is safe as we are protected by the hash bucket lock !
1395 if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
1396 /* Keep the OWNER_DIED bit */
1397 newval = (curval & ~FUTEX_TID_MASK) | task_pid_vnr(current);
1402 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
1404 if (unlikely(curval == -EFAULT))
1406 if (unlikely(curval != uval))
1410 * We took the lock due to owner died take over.
1412 if (unlikely(lock_taken))
1413 goto out_unlock_put_key;
1416 * We dont have the lock. Look up the PI state (or create it if
1417 * we are the first waiter):
1419 ret = lookup_pi_state(uval, hb, &q.key, &q.pi_state);
1421 if (unlikely(ret)) {
1426 * Task is exiting and we just wait for the
1429 queue_unlock(&q, hb);
1430 put_futex_key(fshared, &q.key);
1436 * No owner found for this futex. Check if the
1437 * OWNER_DIED bit is set to figure out whether
1438 * this is a robust futex or not.
1440 if (get_futex_value_locked(&curval, uaddr))
1444 * We simply start over in case of a robust
1445 * futex. The code above will take the futex
1448 if (curval & FUTEX_OWNER_DIED) {
1453 goto out_unlock_put_key;
1458 * Only actually queue now that the atomic ops are done:
1462 WARN_ON(!q.pi_state);
1464 * Block on the PI mutex:
1467 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
1469 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
1470 /* Fixup the trylock return value: */
1471 ret = ret ? 0 : -EWOULDBLOCK;
1474 spin_lock(q.lock_ptr);
1478 * Got the lock. We might not be the anticipated owner
1479 * if we did a lock-steal - fix up the PI-state in
1482 if (q.pi_state->owner != curr)
1483 ret = fixup_pi_state_owner(uaddr, &q, curr, fshared);
1486 * Catch the rare case, where the lock was released
1487 * when we were on the way back before we locked the
1490 if (q.pi_state->owner == curr) {
1492 * Try to get the rt_mutex now. This might
1493 * fail as some other task acquired the
1494 * rt_mutex after we removed ourself from the
1495 * rt_mutex waiters list.
1497 if (rt_mutex_trylock(&q.pi_state->pi_mutex))
1501 * pi_state is incorrect, some other
1502 * task did a lock steal and we
1503 * returned due to timeout or signal
1504 * without taking the rt_mutex. Too
1505 * late. We can access the
1506 * rt_mutex_owner without locking, as
1507 * the other task is now blocked on
1508 * the hash bucket lock. Fix the state
1511 struct task_struct *owner;
1514 owner = rt_mutex_owner(&q.pi_state->pi_mutex);
1515 res = fixup_pi_state_owner(uaddr, &q, owner,
1518 /* propagate -EFAULT, if the fixup failed */
1524 * Paranoia check. If we did not take the lock
1525 * in the trylock above, then we should not be
1526 * the owner of the rtmutex, neither the real
1527 * nor the pending one:
1529 if (rt_mutex_owner(&q.pi_state->pi_mutex) == curr)
1530 printk(KERN_ERR "futex_lock_pi: ret = %d "
1531 "pi-mutex: %p pi-state %p\n", ret,
1532 q.pi_state->pi_mutex.owner,
1538 * If fixup_pi_state_owner() faulted and was unable to handle the
1539 * fault, unlock it and return the fault to userspace.
1541 if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
1542 rt_mutex_unlock(&q.pi_state->pi_mutex);
1544 /* Unqueue and drop the lock */
1548 destroy_hrtimer_on_stack(&to->timer);
1549 return ret != -EINTR ? ret : -ERESTARTNOINTR;
1552 queue_unlock(&q, hb);
1555 put_futex_key(fshared, &q.key);
1558 destroy_hrtimer_on_stack(&to->timer);
1563 * We have to r/w *(int __user *)uaddr, and we have to modify it
1564 * atomically. Therefore, if we continue to fault after get_user()
1565 * below, we need to handle the fault ourselves, while still holding
1566 * the mmap_sem. This can occur if the uaddr is under contention as
1567 * we have to drop the mmap_sem in order to call get_user().
1569 queue_unlock(&q, hb);
1571 ret = get_user(uval, uaddr);
1578 put_futex_key(fshared, &q.key);
1584 * Userspace attempted a TID -> 0 atomic transition, and failed.
1585 * This is the in-kernel slowpath: we look up the PI state (if any),
1586 * and do the rt-mutex unlock.
1588 static int futex_unlock_pi(u32 __user *uaddr, int fshared)
1590 struct futex_hash_bucket *hb;
1591 struct futex_q *this, *next;
1593 struct plist_head *head;
1594 union futex_key key = FUTEX_KEY_INIT;
1598 if (get_user(uval, uaddr))
1601 * We release only a lock we actually own:
1603 if ((uval & FUTEX_TID_MASK) != task_pid_vnr(current))
1606 ret = get_futex_key(uaddr, fshared, &key);
1607 if (unlikely(ret != 0))
1610 hb = hash_futex(&key);
1611 spin_lock(&hb->lock);
1614 * To avoid races, try to do the TID -> 0 atomic transition
1615 * again. If it succeeds then we can return without waking
1618 if (!(uval & FUTEX_OWNER_DIED))
1619 uval = cmpxchg_futex_value_locked(uaddr, task_pid_vnr(current), 0);
1622 if (unlikely(uval == -EFAULT))
1625 * Rare case: we managed to release the lock atomically,
1626 * no need to wake anyone else up:
1628 if (unlikely(uval == task_pid_vnr(current)))
1632 * Ok, other tasks may need to be woken up - check waiters
1633 * and do the wakeup if necessary:
1637 plist_for_each_entry_safe(this, next, head, list) {
1638 if (!match_futex (&this->key, &key))
1640 ret = wake_futex_pi(uaddr, uval, this);
1642 * The atomic access to the futex value
1643 * generated a pagefault, so retry the
1644 * user-access and the wakeup:
1651 * No waiters - kernel unlocks the futex:
1653 if (!(uval & FUTEX_OWNER_DIED)) {
1654 ret = unlock_futex_pi(uaddr, uval);
1660 spin_unlock(&hb->lock);
1661 put_futex_key(fshared, &key);
1668 * We have to r/w *(int __user *)uaddr, and we have to modify it
1669 * atomically. Therefore, if we continue to fault after get_user()
1670 * below, we need to handle the fault ourselves, while still holding
1671 * the mmap_sem. This can occur if the uaddr is under contention as
1672 * we have to drop the mmap_sem in order to call get_user().
1674 spin_unlock(&hb->lock);
1675 put_futex_key(fshared, &key);
1677 ret = get_user(uval, uaddr);
1685 * Support for robust futexes: the kernel cleans up held futexes at
1688 * Implementation: user-space maintains a per-thread list of locks it
1689 * is holding. Upon do_exit(), the kernel carefully walks this list,
1690 * and marks all locks that are owned by this thread with the
1691 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
1692 * always manipulated with the lock held, so the list is private and
1693 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
1694 * field, to allow the kernel to clean up if the thread dies after
1695 * acquiring the lock, but just before it could have added itself to
1696 * the list. There can only be one such pending lock.
1700 * sys_set_robust_list - set the robust-futex list head of a task
1701 * @head: pointer to the list-head
1702 * @len: length of the list-head, as userspace expects
1704 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
1707 if (!futex_cmpxchg_enabled)
1710 * The kernel knows only one size for now:
1712 if (unlikely(len != sizeof(*head)))
1715 current->robust_list = head;
1721 * sys_get_robust_list - get the robust-futex list head of a task
1722 * @pid: pid of the process [zero for current task]
1723 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
1724 * @len_ptr: pointer to a length field, the kernel fills in the header size
1726 SYSCALL_DEFINE3(get_robust_list, int, pid,
1727 struct robust_list_head __user * __user *, head_ptr,
1728 size_t __user *, len_ptr)
1730 struct robust_list_head __user *head;
1732 const struct cred *cred = current_cred(), *pcred;
1734 if (!futex_cmpxchg_enabled)
1738 head = current->robust_list;
1740 struct task_struct *p;
1744 p = find_task_by_vpid(pid);
1748 pcred = __task_cred(p);
1749 if (cred->euid != pcred->euid &&
1750 cred->euid != pcred->uid &&
1751 !capable(CAP_SYS_PTRACE))
1753 head = p->robust_list;
1757 if (put_user(sizeof(*head), len_ptr))
1759 return put_user(head, head_ptr);
1768 * Process a futex-list entry, check whether it's owned by the
1769 * dying task, and do notification if so:
1771 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
1773 u32 uval, nval, mval;
1776 if (get_user(uval, uaddr))
1779 if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
1781 * Ok, this dying thread is truly holding a futex
1782 * of interest. Set the OWNER_DIED bit atomically
1783 * via cmpxchg, and if the value had FUTEX_WAITERS
1784 * set, wake up a waiter (if any). (We have to do a
1785 * futex_wake() even if OWNER_DIED is already set -
1786 * to handle the rare but possible case of recursive
1787 * thread-death.) The rest of the cleanup is done in
1790 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
1791 nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
1793 if (nval == -EFAULT)
1800 * Wake robust non-PI futexes here. The wakeup of
1801 * PI futexes happens in exit_pi_state():
1803 if (!pi && (uval & FUTEX_WAITERS))
1804 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
1810 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
1812 static inline int fetch_robust_entry(struct robust_list __user **entry,
1813 struct robust_list __user * __user *head,
1816 unsigned long uentry;
1818 if (get_user(uentry, (unsigned long __user *)head))
1821 *entry = (void __user *)(uentry & ~1UL);
1828 * Walk curr->robust_list (very carefully, it's a userspace list!)
1829 * and mark any locks found there dead, and notify any waiters.
1831 * We silently return on any sign of list-walking problem.
1833 void exit_robust_list(struct task_struct *curr)
1835 struct robust_list_head __user *head = curr->robust_list;
1836 struct robust_list __user *entry, *next_entry, *pending;
1837 unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
1838 unsigned long futex_offset;
1841 if (!futex_cmpxchg_enabled)
1845 * Fetch the list head (which was registered earlier, via
1846 * sys_set_robust_list()):
1848 if (fetch_robust_entry(&entry, &head->list.next, &pi))
1851 * Fetch the relative futex offset:
1853 if (get_user(futex_offset, &head->futex_offset))
1856 * Fetch any possibly pending lock-add first, and handle it
1859 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
1862 next_entry = NULL; /* avoid warning with gcc */
1863 while (entry != &head->list) {
1865 * Fetch the next entry in the list before calling
1866 * handle_futex_death:
1868 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
1870 * A pending lock might already be on the list, so
1871 * don't process it twice:
1873 if (entry != pending)
1874 if (handle_futex_death((void __user *)entry + futex_offset,
1882 * Avoid excessively long or circular lists:
1891 handle_futex_death((void __user *)pending + futex_offset,
1895 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
1896 u32 __user *uaddr2, u32 val2, u32 val3)
1898 int clockrt, ret = -ENOSYS;
1899 int cmd = op & FUTEX_CMD_MASK;
1902 if (!(op & FUTEX_PRIVATE_FLAG))
1905 clockrt = op & FUTEX_CLOCK_REALTIME;
1906 if (clockrt && cmd != FUTEX_WAIT_BITSET)
1911 val3 = FUTEX_BITSET_MATCH_ANY;
1912 case FUTEX_WAIT_BITSET:
1913 ret = futex_wait(uaddr, fshared, val, timeout, val3, clockrt);
1916 val3 = FUTEX_BITSET_MATCH_ANY;
1917 case FUTEX_WAKE_BITSET:
1918 ret = futex_wake(uaddr, fshared, val, val3);
1921 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL);
1923 case FUTEX_CMP_REQUEUE:
1924 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3);
1927 ret = futex_wake_op(uaddr, fshared, uaddr2, val, val2, val3);
1930 if (futex_cmpxchg_enabled)
1931 ret = futex_lock_pi(uaddr, fshared, val, timeout, 0);
1933 case FUTEX_UNLOCK_PI:
1934 if (futex_cmpxchg_enabled)
1935 ret = futex_unlock_pi(uaddr, fshared);
1937 case FUTEX_TRYLOCK_PI:
1938 if (futex_cmpxchg_enabled)
1939 ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1);
1948 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
1949 struct timespec __user *, utime, u32 __user *, uaddr2,
1953 ktime_t t, *tp = NULL;
1955 int cmd = op & FUTEX_CMD_MASK;
1957 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
1958 cmd == FUTEX_WAIT_BITSET)) {
1959 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
1961 if (!timespec_valid(&ts))
1964 t = timespec_to_ktime(ts);
1965 if (cmd == FUTEX_WAIT)
1966 t = ktime_add_safe(ktime_get(), t);
1970 * requeue parameter in 'utime' if cmd == FUTEX_REQUEUE.
1971 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
1973 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
1974 cmd == FUTEX_WAKE_OP)
1975 val2 = (u32) (unsigned long) utime;
1977 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
1980 static int __init futex_init(void)
1986 * This will fail and we want it. Some arch implementations do
1987 * runtime detection of the futex_atomic_cmpxchg_inatomic()
1988 * functionality. We want to know that before we call in any
1989 * of the complex code paths. Also we want to prevent
1990 * registration of robust lists in that case. NULL is
1991 * guaranteed to fault and we get -EFAULT on functional
1992 * implementation, the non functional ones will return
1995 curval = cmpxchg_futex_value_locked(NULL, 0, 0);
1996 if (curval == -EFAULT)
1997 futex_cmpxchg_enabled = 1;
1999 for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
2000 plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock);
2001 spin_lock_init(&futex_queues[i].lock);
2006 __initcall(futex_init);