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>
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>
67 #include <asm/futex.h>
69 #include "rtmutex_common.h"
71 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
72 int __read_mostly futex_cmpxchg_enabled;
75 #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
78 * Futex flags used to encode options to functions and preserve them across
81 #define FLAGS_SHARED 0x01
82 #define FLAGS_CLOCKRT 0x02
83 #define FLAGS_HAS_TIMEOUT 0x04
86 * Priority Inheritance state:
88 struct futex_pi_state {
90 * list of 'owned' pi_state instances - these have to be
91 * cleaned up in do_exit() if the task exits prematurely:
93 struct list_head list;
98 struct rt_mutex pi_mutex;
100 struct task_struct *owner;
107 * struct futex_q - The hashed futex queue entry, one per waiting task
108 * @list: priority-sorted list of tasks waiting on this futex
109 * @task: the task waiting on the futex
110 * @lock_ptr: the hash bucket lock
111 * @key: the key the futex is hashed on
112 * @pi_state: optional priority inheritance state
113 * @rt_waiter: rt_waiter storage for use with requeue_pi
114 * @requeue_pi_key: the requeue_pi target futex key
115 * @bitset: bitset for the optional bitmasked wakeup
117 * We use this hashed waitqueue, instead of a normal wait_queue_t, so
118 * we can wake only the relevant ones (hashed queues may be shared).
120 * A futex_q has a woken state, just like tasks have TASK_RUNNING.
121 * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
122 * The order of wakeup is always to make the first condition true, then
125 * PI futexes are typically woken before they are removed from the hash list via
126 * the rt_mutex code. See unqueue_me_pi().
129 struct plist_node list;
131 struct task_struct *task;
132 spinlock_t *lock_ptr;
134 struct futex_pi_state *pi_state;
135 struct rt_mutex_waiter *rt_waiter;
136 union futex_key *requeue_pi_key;
140 static const struct futex_q futex_q_init = {
141 /* list gets initialized in queue_me()*/
142 .key = FUTEX_KEY_INIT,
143 .bitset = FUTEX_BITSET_MATCH_ANY
147 * Hash buckets are shared by all the futex_keys that hash to the same
148 * location. Each key may have multiple futex_q structures, one for each task
149 * waiting on a futex.
151 struct futex_hash_bucket {
153 struct plist_head chain;
156 static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
159 * We hash on the keys returned from get_futex_key (see below).
161 static struct futex_hash_bucket *hash_futex(union futex_key *key)
163 u32 hash = jhash2((u32*)&key->both.word,
164 (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
166 return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
170 * Return 1 if two futex_keys are equal, 0 otherwise.
172 static inline int match_futex(union futex_key *key1, union futex_key *key2)
175 && key1->both.word == key2->both.word
176 && key1->both.ptr == key2->both.ptr
177 && key1->both.offset == key2->both.offset);
181 * Take a reference to the resource addressed by a key.
182 * Can be called while holding spinlocks.
185 static void get_futex_key_refs(union futex_key *key)
190 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
192 ihold(key->shared.inode);
194 case FUT_OFF_MMSHARED:
195 atomic_inc(&key->private.mm->mm_count);
201 * Drop a reference to the resource addressed by a key.
202 * The hash bucket spinlock must not be held.
204 static void drop_futex_key_refs(union futex_key *key)
206 if (!key->both.ptr) {
207 /* If we're here then we tried to put a key we failed to get */
212 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
214 iput(key->shared.inode);
216 case FUT_OFF_MMSHARED:
217 mmdrop(key->private.mm);
223 * get_futex_key() - Get parameters which are the keys for a futex
224 * @uaddr: virtual address of the futex
225 * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
226 * @key: address where result is stored.
227 * @rw: mapping needs to be read/write (values: VERIFY_READ,
230 * Return: a negative error code or 0
232 * The key words are stored in *key on success.
234 * For shared mappings, it's (page->index, file_inode(vma->vm_file),
235 * offset_within_page). For private mappings, it's (uaddr, current->mm).
236 * We can usually work out the index without swapping in the page.
238 * lock_page() might sleep, the caller should not hold a spinlock.
241 get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
243 unsigned long address = (unsigned long)uaddr;
244 struct mm_struct *mm = current->mm;
245 struct page *page, *page_head;
249 * The futex address must be "naturally" aligned.
251 key->both.offset = address % PAGE_SIZE;
252 if (unlikely((address % sizeof(u32)) != 0))
254 address -= key->both.offset;
257 * PROCESS_PRIVATE futexes are fast.
258 * As the mm cannot disappear under us and the 'key' only needs
259 * virtual address, we dont even have to find the underlying vma.
260 * Note : We do have to check 'uaddr' is a valid user address,
261 * but access_ok() should be faster than find_vma()
264 if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))))
266 key->private.mm = mm;
267 key->private.address = address;
268 get_futex_key_refs(key);
273 err = get_user_pages_fast(address, 1, 1, &page);
275 * If write access is not required (eg. FUTEX_WAIT), try
276 * and get read-only access.
278 if (err == -EFAULT && rw == VERIFY_READ) {
279 err = get_user_pages_fast(address, 1, 0, &page);
287 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
289 if (unlikely(PageTail(page))) {
291 /* serialize against __split_huge_page_splitting() */
293 if (likely(__get_user_pages_fast(address, 1, !ro, &page) == 1)) {
294 page_head = compound_head(page);
296 * page_head is valid pointer but we must pin
297 * it before taking the PG_lock and/or
298 * PG_compound_lock. The moment we re-enable
299 * irqs __split_huge_page_splitting() can
300 * return and the head page can be freed from
301 * under us. We can't take the PG_lock and/or
302 * PG_compound_lock on a page that could be
303 * freed from under us.
305 if (page != page_head) {
316 page_head = compound_head(page);
317 if (page != page_head) {
323 lock_page(page_head);
326 * If page_head->mapping is NULL, then it cannot be a PageAnon
327 * page; but it might be the ZERO_PAGE or in the gate area or
328 * in a special mapping (all cases which we are happy to fail);
329 * or it may have been a good file page when get_user_pages_fast
330 * found it, but truncated or holepunched or subjected to
331 * invalidate_complete_page2 before we got the page lock (also
332 * cases which we are happy to fail). And we hold a reference,
333 * so refcount care in invalidate_complete_page's remove_mapping
334 * prevents drop_caches from setting mapping to NULL beneath us.
336 * The case we do have to guard against is when memory pressure made
337 * shmem_writepage move it from filecache to swapcache beneath us:
338 * an unlikely race, but we do need to retry for page_head->mapping.
340 if (!page_head->mapping) {
341 int shmem_swizzled = PageSwapCache(page_head);
342 unlock_page(page_head);
350 * Private mappings are handled in a simple way.
352 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
353 * it's a read-only handle, it's expected that futexes attach to
354 * the object not the particular process.
356 if (PageAnon(page_head)) {
358 * A RO anonymous page will never change and thus doesn't make
359 * sense for futex operations.
366 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
367 key->private.mm = mm;
368 key->private.address = address;
370 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
371 key->shared.inode = page_head->mapping->host;
372 key->shared.pgoff = basepage_index(page);
375 get_futex_key_refs(key);
378 unlock_page(page_head);
383 static inline void put_futex_key(union futex_key *key)
385 drop_futex_key_refs(key);
389 * fault_in_user_writeable() - Fault in user address and verify RW access
390 * @uaddr: pointer to faulting user space address
392 * Slow path to fixup the fault we just took in the atomic write
395 * We have no generic implementation of a non-destructive write to the
396 * user address. We know that we faulted in the atomic pagefault
397 * disabled section so we can as well avoid the #PF overhead by
398 * calling get_user_pages() right away.
400 static int fault_in_user_writeable(u32 __user *uaddr)
402 struct mm_struct *mm = current->mm;
405 down_read(&mm->mmap_sem);
406 ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
408 up_read(&mm->mmap_sem);
410 return ret < 0 ? ret : 0;
414 * futex_top_waiter() - Return the highest priority waiter on a futex
415 * @hb: the hash bucket the futex_q's reside in
416 * @key: the futex key (to distinguish it from other futex futex_q's)
418 * Must be called with the hb lock held.
420 static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
421 union futex_key *key)
423 struct futex_q *this;
425 plist_for_each_entry(this, &hb->chain, list) {
426 if (match_futex(&this->key, key))
432 static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
433 u32 uval, u32 newval)
438 ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
444 static int get_futex_value_locked(u32 *dest, u32 __user *from)
449 ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
452 return ret ? -EFAULT : 0;
459 static int refill_pi_state_cache(void)
461 struct futex_pi_state *pi_state;
463 if (likely(current->pi_state_cache))
466 pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
471 INIT_LIST_HEAD(&pi_state->list);
472 /* pi_mutex gets initialized later */
473 pi_state->owner = NULL;
474 atomic_set(&pi_state->refcount, 1);
475 pi_state->key = FUTEX_KEY_INIT;
477 current->pi_state_cache = pi_state;
482 static struct futex_pi_state * alloc_pi_state(void)
484 struct futex_pi_state *pi_state = current->pi_state_cache;
487 current->pi_state_cache = NULL;
492 static void free_pi_state(struct futex_pi_state *pi_state)
494 if (!atomic_dec_and_test(&pi_state->refcount))
498 * If pi_state->owner is NULL, the owner is most probably dying
499 * and has cleaned up the pi_state already
501 if (pi_state->owner) {
502 raw_spin_lock_irq(&pi_state->owner->pi_lock);
503 list_del_init(&pi_state->list);
504 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
506 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
509 if (current->pi_state_cache)
513 * pi_state->list is already empty.
514 * clear pi_state->owner.
515 * refcount is at 0 - put it back to 1.
517 pi_state->owner = NULL;
518 atomic_set(&pi_state->refcount, 1);
519 current->pi_state_cache = pi_state;
524 * Look up the task based on what TID userspace gave us.
527 static struct task_struct * futex_find_get_task(pid_t pid)
529 struct task_struct *p;
532 p = find_task_by_vpid(pid);
542 * This task is holding PI mutexes at exit time => bad.
543 * Kernel cleans up PI-state, but userspace is likely hosed.
544 * (Robust-futex cleanup is separate and might save the day for userspace.)
546 void exit_pi_state_list(struct task_struct *curr)
548 struct list_head *next, *head = &curr->pi_state_list;
549 struct futex_pi_state *pi_state;
550 struct futex_hash_bucket *hb;
551 union futex_key key = FUTEX_KEY_INIT;
553 if (!futex_cmpxchg_enabled)
556 * We are a ZOMBIE and nobody can enqueue itself on
557 * pi_state_list anymore, but we have to be careful
558 * versus waiters unqueueing themselves:
560 raw_spin_lock_irq(&curr->pi_lock);
561 while (!list_empty(head)) {
564 pi_state = list_entry(next, struct futex_pi_state, list);
566 hb = hash_futex(&key);
567 raw_spin_unlock_irq(&curr->pi_lock);
569 spin_lock(&hb->lock);
571 raw_spin_lock_irq(&curr->pi_lock);
573 * We dropped the pi-lock, so re-check whether this
574 * task still owns the PI-state:
576 if (head->next != next) {
577 spin_unlock(&hb->lock);
581 WARN_ON(pi_state->owner != curr);
582 WARN_ON(list_empty(&pi_state->list));
583 list_del_init(&pi_state->list);
584 pi_state->owner = NULL;
585 raw_spin_unlock_irq(&curr->pi_lock);
587 rt_mutex_unlock(&pi_state->pi_mutex);
589 spin_unlock(&hb->lock);
591 raw_spin_lock_irq(&curr->pi_lock);
593 raw_spin_unlock_irq(&curr->pi_lock);
597 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
598 union futex_key *key, struct futex_pi_state **ps)
600 struct futex_pi_state *pi_state = NULL;
601 struct futex_q *this, *next;
602 struct plist_head *head;
603 struct task_struct *p;
604 pid_t pid = uval & FUTEX_TID_MASK;
608 plist_for_each_entry_safe(this, next, head, list) {
609 if (match_futex(&this->key, key)) {
611 * Another waiter already exists - bump up
612 * the refcount and return its pi_state:
614 pi_state = this->pi_state;
616 * Userspace might have messed up non-PI and PI futexes
618 if (unlikely(!pi_state))
621 WARN_ON(!atomic_read(&pi_state->refcount));
624 * When pi_state->owner is NULL then the owner died
625 * and another waiter is on the fly. pi_state->owner
626 * is fixed up by the task which acquires
627 * pi_state->rt_mutex.
629 * We do not check for pid == 0 which can happen when
630 * the owner died and robust_list_exit() cleared the
633 if (pid && pi_state->owner) {
635 * Bail out if user space manipulated the
638 if (pid != task_pid_vnr(pi_state->owner))
642 atomic_inc(&pi_state->refcount);
650 * We are the first waiter - try to look up the real owner and attach
651 * the new pi_state to it, but bail out when TID = 0
655 p = futex_find_get_task(pid);
660 * We need to look at the task state flags to figure out,
661 * whether the task is exiting. To protect against the do_exit
662 * change of the task flags, we do this protected by
665 raw_spin_lock_irq(&p->pi_lock);
666 if (unlikely(p->flags & PF_EXITING)) {
668 * The task is on the way out. When PF_EXITPIDONE is
669 * set, we know that the task has finished the
672 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
674 raw_spin_unlock_irq(&p->pi_lock);
679 pi_state = alloc_pi_state();
682 * Initialize the pi_mutex in locked state and make 'p'
685 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
687 /* Store the key for possible exit cleanups: */
688 pi_state->key = *key;
690 WARN_ON(!list_empty(&pi_state->list));
691 list_add(&pi_state->list, &p->pi_state_list);
693 raw_spin_unlock_irq(&p->pi_lock);
703 * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
704 * @uaddr: the pi futex user address
705 * @hb: the pi futex hash bucket
706 * @key: the futex key associated with uaddr and hb
707 * @ps: the pi_state pointer where we store the result of the
709 * @task: the task to perform the atomic lock work for. This will
710 * be "current" except in the case of requeue pi.
711 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
715 * 1 - acquired the lock;
718 * The hb->lock and futex_key refs shall be held by the caller.
720 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
721 union futex_key *key,
722 struct futex_pi_state **ps,
723 struct task_struct *task, int set_waiters)
725 int lock_taken, ret, force_take = 0;
726 u32 uval, newval, curval, vpid = task_pid_vnr(task);
729 ret = lock_taken = 0;
732 * To avoid races, we attempt to take the lock here again
733 * (by doing a 0 -> TID atomic cmpxchg), while holding all
734 * the locks. It will most likely not succeed.
738 newval |= FUTEX_WAITERS;
740 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval)))
746 if ((unlikely((curval & FUTEX_TID_MASK) == vpid)))
750 * Surprise - we got the lock. Just return to userspace:
752 if (unlikely(!curval))
758 * Set the FUTEX_WAITERS flag, so the owner will know it has someone
759 * to wake at the next unlock.
761 newval = curval | FUTEX_WAITERS;
764 * Should we force take the futex? See below.
766 if (unlikely(force_take)) {
768 * Keep the OWNER_DIED and the WAITERS bit and set the
771 newval = (curval & ~FUTEX_TID_MASK) | vpid;
776 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
778 if (unlikely(curval != uval))
782 * We took the lock due to forced take over.
784 if (unlikely(lock_taken))
788 * We dont have the lock. Look up the PI state (or create it if
789 * we are the first waiter):
791 ret = lookup_pi_state(uval, hb, key, ps);
797 * We failed to find an owner for this
798 * futex. So we have no pi_state to block
799 * on. This can happen in two cases:
802 * 2) A stale FUTEX_WAITERS bit
804 * Re-read the futex value.
806 if (get_futex_value_locked(&curval, uaddr))
810 * If the owner died or we have a stale
811 * WAITERS bit the owner TID in the user space
814 if (!(curval & FUTEX_TID_MASK)) {
827 * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
828 * @q: The futex_q to unqueue
830 * The q->lock_ptr must not be NULL and must be held by the caller.
832 static void __unqueue_futex(struct futex_q *q)
834 struct futex_hash_bucket *hb;
836 if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
837 || WARN_ON(plist_node_empty(&q->list)))
840 hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
841 plist_del(&q->list, &hb->chain);
845 * The hash bucket lock must be held when this is called.
846 * Afterwards, the futex_q must not be accessed.
848 static void wake_futex(struct futex_q *q)
850 struct task_struct *p = q->task;
852 if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
856 * We set q->lock_ptr = NULL _before_ we wake up the task. If
857 * a non-futex wake up happens on another CPU then the task
858 * might exit and p would dereference a non-existing task
859 * struct. Prevent this by holding a reference on p across the
866 * The waiting task can free the futex_q as soon as
867 * q->lock_ptr = NULL is written, without taking any locks. A
868 * memory barrier is required here to prevent the following
869 * store to lock_ptr from getting ahead of the plist_del.
874 wake_up_state(p, TASK_NORMAL);
878 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
880 struct task_struct *new_owner;
881 struct futex_pi_state *pi_state = this->pi_state;
882 u32 uninitialized_var(curval), newval;
888 * If current does not own the pi_state then the futex is
889 * inconsistent and user space fiddled with the futex value.
891 if (pi_state->owner != current)
894 raw_spin_lock(&pi_state->pi_mutex.wait_lock);
895 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
898 * It is possible that the next waiter (the one that brought
899 * this owner to the kernel) timed out and is no longer
900 * waiting on the lock.
903 new_owner = this->task;
906 * We pass it to the next owner. (The WAITERS bit is always
907 * kept enabled while there is PI state around. We must also
908 * preserve the owner died bit.)
910 if (!(uval & FUTEX_OWNER_DIED)) {
913 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
915 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
917 else if (curval != uval)
920 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
925 raw_spin_lock_irq(&pi_state->owner->pi_lock);
926 WARN_ON(list_empty(&pi_state->list));
927 list_del_init(&pi_state->list);
928 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
930 raw_spin_lock_irq(&new_owner->pi_lock);
931 WARN_ON(!list_empty(&pi_state->list));
932 list_add(&pi_state->list, &new_owner->pi_state_list);
933 pi_state->owner = new_owner;
934 raw_spin_unlock_irq(&new_owner->pi_lock);
936 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
937 rt_mutex_unlock(&pi_state->pi_mutex);
942 static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
944 u32 uninitialized_var(oldval);
947 * There is no waiter, so we unlock the futex. The owner died
948 * bit has not to be preserved here. We are the owner:
950 if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0))
959 * Express the locking dependencies for lockdep:
962 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
965 spin_lock(&hb1->lock);
967 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
968 } else { /* hb1 > hb2 */
969 spin_lock(&hb2->lock);
970 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
975 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
977 spin_unlock(&hb1->lock);
979 spin_unlock(&hb2->lock);
983 * Wake up waiters matching bitset queued on this futex (uaddr).
986 futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
988 struct futex_hash_bucket *hb;
989 struct futex_q *this, *next;
990 struct plist_head *head;
991 union futex_key key = FUTEX_KEY_INIT;
997 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
998 if (unlikely(ret != 0))
1001 hb = hash_futex(&key);
1002 spin_lock(&hb->lock);
1005 plist_for_each_entry_safe(this, next, head, list) {
1006 if (match_futex (&this->key, &key)) {
1007 if (this->pi_state || this->rt_waiter) {
1012 /* Check if one of the bits is set in both bitsets */
1013 if (!(this->bitset & bitset))
1017 if (++ret >= nr_wake)
1022 spin_unlock(&hb->lock);
1023 put_futex_key(&key);
1029 * Wake up all waiters hashed on the physical page that is mapped
1030 * to this virtual address:
1033 futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
1034 int nr_wake, int nr_wake2, int op)
1036 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1037 struct futex_hash_bucket *hb1, *hb2;
1038 struct plist_head *head;
1039 struct futex_q *this, *next;
1043 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1044 if (unlikely(ret != 0))
1046 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
1047 if (unlikely(ret != 0))
1050 hb1 = hash_futex(&key1);
1051 hb2 = hash_futex(&key2);
1054 double_lock_hb(hb1, hb2);
1055 op_ret = futex_atomic_op_inuser(op, uaddr2);
1056 if (unlikely(op_ret < 0)) {
1058 double_unlock_hb(hb1, hb2);
1062 * we don't get EFAULT from MMU faults if we don't have an MMU,
1063 * but we might get them from range checking
1069 if (unlikely(op_ret != -EFAULT)) {
1074 ret = fault_in_user_writeable(uaddr2);
1078 if (!(flags & FLAGS_SHARED))
1081 put_futex_key(&key2);
1082 put_futex_key(&key1);
1088 plist_for_each_entry_safe(this, next, head, list) {
1089 if (match_futex (&this->key, &key1)) {
1090 if (this->pi_state || this->rt_waiter) {
1095 if (++ret >= nr_wake)
1104 plist_for_each_entry_safe(this, next, head, list) {
1105 if (match_futex (&this->key, &key2)) {
1106 if (this->pi_state || this->rt_waiter) {
1111 if (++op_ret >= nr_wake2)
1119 double_unlock_hb(hb1, hb2);
1121 put_futex_key(&key2);
1123 put_futex_key(&key1);
1129 * requeue_futex() - Requeue a futex_q from one hb to another
1130 * @q: the futex_q to requeue
1131 * @hb1: the source hash_bucket
1132 * @hb2: the target hash_bucket
1133 * @key2: the new key for the requeued futex_q
1136 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1137 struct futex_hash_bucket *hb2, union futex_key *key2)
1141 * If key1 and key2 hash to the same bucket, no need to
1144 if (likely(&hb1->chain != &hb2->chain)) {
1145 plist_del(&q->list, &hb1->chain);
1146 plist_add(&q->list, &hb2->chain);
1147 q->lock_ptr = &hb2->lock;
1149 get_futex_key_refs(key2);
1154 * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1156 * @key: the key of the requeue target futex
1157 * @hb: the hash_bucket of the requeue target futex
1159 * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1160 * target futex if it is uncontended or via a lock steal. Set the futex_q key
1161 * to the requeue target futex so the waiter can detect the wakeup on the right
1162 * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1163 * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
1164 * to protect access to the pi_state to fixup the owner later. Must be called
1165 * with both q->lock_ptr and hb->lock held.
1168 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1169 struct futex_hash_bucket *hb)
1171 get_futex_key_refs(key);
1176 WARN_ON(!q->rt_waiter);
1177 q->rt_waiter = NULL;
1179 q->lock_ptr = &hb->lock;
1181 wake_up_state(q->task, TASK_NORMAL);
1185 * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1186 * @pifutex: the user address of the to futex
1187 * @hb1: the from futex hash bucket, must be locked by the caller
1188 * @hb2: the to futex hash bucket, must be locked by the caller
1189 * @key1: the from futex key
1190 * @key2: the to futex key
1191 * @ps: address to store the pi_state pointer
1192 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1194 * Try and get the lock on behalf of the top waiter if we can do it atomically.
1195 * Wake the top waiter if we succeed. If the caller specified set_waiters,
1196 * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1197 * hb1 and hb2 must be held by the caller.
1200 * 0 - failed to acquire the lock atomically;
1201 * 1 - acquired the lock;
1204 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1205 struct futex_hash_bucket *hb1,
1206 struct futex_hash_bucket *hb2,
1207 union futex_key *key1, union futex_key *key2,
1208 struct futex_pi_state **ps, int set_waiters)
1210 struct futex_q *top_waiter = NULL;
1214 if (get_futex_value_locked(&curval, pifutex))
1218 * Find the top_waiter and determine if there are additional waiters.
1219 * If the caller intends to requeue more than 1 waiter to pifutex,
1220 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1221 * as we have means to handle the possible fault. If not, don't set
1222 * the bit unecessarily as it will force the subsequent unlock to enter
1225 top_waiter = futex_top_waiter(hb1, key1);
1227 /* There are no waiters, nothing for us to do. */
1231 /* Ensure we requeue to the expected futex. */
1232 if (!match_futex(top_waiter->requeue_pi_key, key2))
1236 * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
1237 * the contended case or if set_waiters is 1. The pi_state is returned
1238 * in ps in contended cases.
1240 ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1243 requeue_pi_wake_futex(top_waiter, key2, hb2);
1249 * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1250 * @uaddr1: source futex user address
1251 * @flags: futex flags (FLAGS_SHARED, etc.)
1252 * @uaddr2: target futex user address
1253 * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
1254 * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1255 * @cmpval: @uaddr1 expected value (or %NULL)
1256 * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1257 * pi futex (pi to pi requeue is not supported)
1259 * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1260 * uaddr2 atomically on behalf of the top waiter.
1263 * >=0 - on success, the number of tasks requeued or woken;
1266 static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1267 u32 __user *uaddr2, int nr_wake, int nr_requeue,
1268 u32 *cmpval, int requeue_pi)
1270 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1271 int drop_count = 0, task_count = 0, ret;
1272 struct futex_pi_state *pi_state = NULL;
1273 struct futex_hash_bucket *hb1, *hb2;
1274 struct plist_head *head1;
1275 struct futex_q *this, *next;
1280 * requeue_pi requires a pi_state, try to allocate it now
1281 * without any locks in case it fails.
1283 if (refill_pi_state_cache())
1286 * requeue_pi must wake as many tasks as it can, up to nr_wake
1287 * + nr_requeue, since it acquires the rt_mutex prior to
1288 * returning to userspace, so as to not leave the rt_mutex with
1289 * waiters and no owner. However, second and third wake-ups
1290 * cannot be predicted as they involve race conditions with the
1291 * first wake and a fault while looking up the pi_state. Both
1292 * pthread_cond_signal() and pthread_cond_broadcast() should
1300 if (pi_state != NULL) {
1302 * We will have to lookup the pi_state again, so free this one
1303 * to keep the accounting correct.
1305 free_pi_state(pi_state);
1309 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1310 if (unlikely(ret != 0))
1312 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
1313 requeue_pi ? VERIFY_WRITE : VERIFY_READ);
1314 if (unlikely(ret != 0))
1317 hb1 = hash_futex(&key1);
1318 hb2 = hash_futex(&key2);
1321 double_lock_hb(hb1, hb2);
1323 if (likely(cmpval != NULL)) {
1326 ret = get_futex_value_locked(&curval, uaddr1);
1328 if (unlikely(ret)) {
1329 double_unlock_hb(hb1, hb2);
1331 ret = get_user(curval, uaddr1);
1335 if (!(flags & FLAGS_SHARED))
1338 put_futex_key(&key2);
1339 put_futex_key(&key1);
1342 if (curval != *cmpval) {
1348 if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1350 * Attempt to acquire uaddr2 and wake the top waiter. If we
1351 * intend to requeue waiters, force setting the FUTEX_WAITERS
1352 * bit. We force this here where we are able to easily handle
1353 * faults rather in the requeue loop below.
1355 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1356 &key2, &pi_state, nr_requeue);
1359 * At this point the top_waiter has either taken uaddr2 or is
1360 * waiting on it. If the former, then the pi_state will not
1361 * exist yet, look it up one more time to ensure we have a
1368 ret = get_futex_value_locked(&curval2, uaddr2);
1370 ret = lookup_pi_state(curval2, hb2, &key2,
1378 double_unlock_hb(hb1, hb2);
1379 put_futex_key(&key2);
1380 put_futex_key(&key1);
1381 ret = fault_in_user_writeable(uaddr2);
1386 /* The owner was exiting, try again. */
1387 double_unlock_hb(hb1, hb2);
1388 put_futex_key(&key2);
1389 put_futex_key(&key1);
1397 head1 = &hb1->chain;
1398 plist_for_each_entry_safe(this, next, head1, list) {
1399 if (task_count - nr_wake >= nr_requeue)
1402 if (!match_futex(&this->key, &key1))
1406 * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1407 * be paired with each other and no other futex ops.
1409 * We should never be requeueing a futex_q with a pi_state,
1410 * which is awaiting a futex_unlock_pi().
1412 if ((requeue_pi && !this->rt_waiter) ||
1413 (!requeue_pi && this->rt_waiter) ||
1420 * Wake nr_wake waiters. For requeue_pi, if we acquired the
1421 * lock, we already woke the top_waiter. If not, it will be
1422 * woken by futex_unlock_pi().
1424 if (++task_count <= nr_wake && !requeue_pi) {
1429 /* Ensure we requeue to the expected futex for requeue_pi. */
1430 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1436 * Requeue nr_requeue waiters and possibly one more in the case
1437 * of requeue_pi if we couldn't acquire the lock atomically.
1440 /* Prepare the waiter to take the rt_mutex. */
1441 atomic_inc(&pi_state->refcount);
1442 this->pi_state = pi_state;
1443 ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1447 /* We got the lock. */
1448 requeue_pi_wake_futex(this, &key2, hb2);
1453 this->pi_state = NULL;
1454 free_pi_state(pi_state);
1458 requeue_futex(this, hb1, hb2, &key2);
1463 double_unlock_hb(hb1, hb2);
1466 * drop_futex_key_refs() must be called outside the spinlocks. During
1467 * the requeue we moved futex_q's from the hash bucket at key1 to the
1468 * one at key2 and updated their key pointer. We no longer need to
1469 * hold the references to key1.
1471 while (--drop_count >= 0)
1472 drop_futex_key_refs(&key1);
1475 put_futex_key(&key2);
1477 put_futex_key(&key1);
1479 if (pi_state != NULL)
1480 free_pi_state(pi_state);
1481 return ret ? ret : task_count;
1484 /* The key must be already stored in q->key. */
1485 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
1486 __acquires(&hb->lock)
1488 struct futex_hash_bucket *hb;
1490 hb = hash_futex(&q->key);
1491 q->lock_ptr = &hb->lock;
1493 spin_lock(&hb->lock);
1498 queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
1499 __releases(&hb->lock)
1501 spin_unlock(&hb->lock);
1505 * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1506 * @q: The futex_q to enqueue
1507 * @hb: The destination hash bucket
1509 * The hb->lock must be held by the caller, and is released here. A call to
1510 * queue_me() is typically paired with exactly one call to unqueue_me(). The
1511 * exceptions involve the PI related operations, which may use unqueue_me_pi()
1512 * or nothing if the unqueue is done as part of the wake process and the unqueue
1513 * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1516 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1517 __releases(&hb->lock)
1522 * The priority used to register this element is
1523 * - either the real thread-priority for the real-time threads
1524 * (i.e. threads with a priority lower than MAX_RT_PRIO)
1525 * - or MAX_RT_PRIO for non-RT threads.
1526 * Thus, all RT-threads are woken first in priority order, and
1527 * the others are woken last, in FIFO order.
1529 prio = min(current->normal_prio, MAX_RT_PRIO);
1531 plist_node_init(&q->list, prio);
1532 plist_add(&q->list, &hb->chain);
1534 spin_unlock(&hb->lock);
1538 * unqueue_me() - Remove the futex_q from its futex_hash_bucket
1539 * @q: The futex_q to unqueue
1541 * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
1542 * be paired with exactly one earlier call to queue_me().
1545 * 1 - if the futex_q was still queued (and we removed unqueued it);
1546 * 0 - if the futex_q was already removed by the waking thread
1548 static int unqueue_me(struct futex_q *q)
1550 spinlock_t *lock_ptr;
1553 /* In the common case we don't take the spinlock, which is nice. */
1555 lock_ptr = q->lock_ptr;
1557 if (lock_ptr != NULL) {
1558 spin_lock(lock_ptr);
1560 * q->lock_ptr can change between reading it and
1561 * spin_lock(), causing us to take the wrong lock. This
1562 * corrects the race condition.
1564 * Reasoning goes like this: if we have the wrong lock,
1565 * q->lock_ptr must have changed (maybe several times)
1566 * between reading it and the spin_lock(). It can
1567 * change again after the spin_lock() but only if it was
1568 * already changed before the spin_lock(). It cannot,
1569 * however, change back to the original value. Therefore
1570 * we can detect whether we acquired the correct lock.
1572 if (unlikely(lock_ptr != q->lock_ptr)) {
1573 spin_unlock(lock_ptr);
1578 BUG_ON(q->pi_state);
1580 spin_unlock(lock_ptr);
1584 drop_futex_key_refs(&q->key);
1589 * PI futexes can not be requeued and must remove themself from the
1590 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1593 static void unqueue_me_pi(struct futex_q *q)
1594 __releases(q->lock_ptr)
1598 BUG_ON(!q->pi_state);
1599 free_pi_state(q->pi_state);
1602 spin_unlock(q->lock_ptr);
1606 * Fixup the pi_state owner with the new owner.
1608 * Must be called with hash bucket lock held and mm->sem held for non
1611 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1612 struct task_struct *newowner)
1614 u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
1615 struct futex_pi_state *pi_state = q->pi_state;
1616 struct task_struct *oldowner = pi_state->owner;
1617 u32 uval, uninitialized_var(curval), newval;
1621 if (!pi_state->owner)
1622 newtid |= FUTEX_OWNER_DIED;
1625 * We are here either because we stole the rtmutex from the
1626 * previous highest priority waiter or we are the highest priority
1627 * waiter but failed to get the rtmutex the first time.
1628 * We have to replace the newowner TID in the user space variable.
1629 * This must be atomic as we have to preserve the owner died bit here.
1631 * Note: We write the user space value _before_ changing the pi_state
1632 * because we can fault here. Imagine swapped out pages or a fork
1633 * that marked all the anonymous memory readonly for cow.
1635 * Modifying pi_state _before_ the user space value would
1636 * leave the pi_state in an inconsistent state when we fault
1637 * here, because we need to drop the hash bucket lock to
1638 * handle the fault. This might be observed in the PID check
1639 * in lookup_pi_state.
1642 if (get_futex_value_locked(&uval, uaddr))
1646 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1648 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
1656 * We fixed up user space. Now we need to fix the pi_state
1659 if (pi_state->owner != NULL) {
1660 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1661 WARN_ON(list_empty(&pi_state->list));
1662 list_del_init(&pi_state->list);
1663 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1666 pi_state->owner = newowner;
1668 raw_spin_lock_irq(&newowner->pi_lock);
1669 WARN_ON(!list_empty(&pi_state->list));
1670 list_add(&pi_state->list, &newowner->pi_state_list);
1671 raw_spin_unlock_irq(&newowner->pi_lock);
1675 * To handle the page fault we need to drop the hash bucket
1676 * lock here. That gives the other task (either the highest priority
1677 * waiter itself or the task which stole the rtmutex) the
1678 * chance to try the fixup of the pi_state. So once we are
1679 * back from handling the fault we need to check the pi_state
1680 * after reacquiring the hash bucket lock and before trying to
1681 * do another fixup. When the fixup has been done already we
1685 spin_unlock(q->lock_ptr);
1687 ret = fault_in_user_writeable(uaddr);
1689 spin_lock(q->lock_ptr);
1692 * Check if someone else fixed it for us:
1694 if (pi_state->owner != oldowner)
1703 static long futex_wait_restart(struct restart_block *restart);
1706 * fixup_owner() - Post lock pi_state and corner case management
1707 * @uaddr: user address of the futex
1708 * @q: futex_q (contains pi_state and access to the rt_mutex)
1709 * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
1711 * After attempting to lock an rt_mutex, this function is called to cleanup
1712 * the pi_state owner as well as handle race conditions that may allow us to
1713 * acquire the lock. Must be called with the hb lock held.
1716 * 1 - success, lock taken;
1717 * 0 - success, lock not taken;
1718 * <0 - on error (-EFAULT)
1720 static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
1722 struct task_struct *owner;
1727 * Got the lock. We might not be the anticipated owner if we
1728 * did a lock-steal - fix up the PI-state in that case:
1730 if (q->pi_state->owner != current)
1731 ret = fixup_pi_state_owner(uaddr, q, current);
1736 * Catch the rare case, where the lock was released when we were on the
1737 * way back before we locked the hash bucket.
1739 if (q->pi_state->owner == current) {
1741 * Try to get the rt_mutex now. This might fail as some other
1742 * task acquired the rt_mutex after we removed ourself from the
1743 * rt_mutex waiters list.
1745 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
1751 * pi_state is incorrect, some other task did a lock steal and
1752 * we returned due to timeout or signal without taking the
1753 * rt_mutex. Too late.
1755 raw_spin_lock(&q->pi_state->pi_mutex.wait_lock);
1756 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
1758 owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
1759 raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock);
1760 ret = fixup_pi_state_owner(uaddr, q, owner);
1765 * Paranoia check. If we did not take the lock, then we should not be
1766 * the owner of the rt_mutex.
1768 if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
1769 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
1770 "pi-state %p\n", ret,
1771 q->pi_state->pi_mutex.owner,
1772 q->pi_state->owner);
1775 return ret ? ret : locked;
1779 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
1780 * @hb: the futex hash bucket, must be locked by the caller
1781 * @q: the futex_q to queue up on
1782 * @timeout: the prepared hrtimer_sleeper, or null for no timeout
1784 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
1785 struct hrtimer_sleeper *timeout)
1788 * The task state is guaranteed to be set before another task can
1789 * wake it. set_current_state() is implemented using set_mb() and
1790 * queue_me() calls spin_unlock() upon completion, both serializing
1791 * access to the hash list and forcing another memory barrier.
1793 set_current_state(TASK_INTERRUPTIBLE);
1798 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1799 if (!hrtimer_active(&timeout->timer))
1800 timeout->task = NULL;
1804 * If we have been removed from the hash list, then another task
1805 * has tried to wake us, and we can skip the call to schedule().
1807 if (likely(!plist_node_empty(&q->list))) {
1809 * If the timer has already expired, current will already be
1810 * flagged for rescheduling. Only call schedule if there
1811 * is no timeout, or if it has yet to expire.
1813 if (!timeout || timeout->task)
1814 freezable_schedule();
1816 __set_current_state(TASK_RUNNING);
1820 * futex_wait_setup() - Prepare to wait on a futex
1821 * @uaddr: the futex userspace address
1822 * @val: the expected value
1823 * @flags: futex flags (FLAGS_SHARED, etc.)
1824 * @q: the associated futex_q
1825 * @hb: storage for hash_bucket pointer to be returned to caller
1827 * Setup the futex_q and locate the hash_bucket. Get the futex value and
1828 * compare it with the expected value. Handle atomic faults internally.
1829 * Return with the hb lock held and a q.key reference on success, and unlocked
1830 * with no q.key reference on failure.
1833 * 0 - uaddr contains val and hb has been locked;
1834 * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
1836 static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
1837 struct futex_q *q, struct futex_hash_bucket **hb)
1843 * Access the page AFTER the hash-bucket is locked.
1844 * Order is important:
1846 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1847 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
1849 * The basic logical guarantee of a futex is that it blocks ONLY
1850 * if cond(var) is known to be true at the time of blocking, for
1851 * any cond. If we locked the hash-bucket after testing *uaddr, that
1852 * would open a race condition where we could block indefinitely with
1853 * cond(var) false, which would violate the guarantee.
1855 * On the other hand, we insert q and release the hash-bucket only
1856 * after testing *uaddr. This guarantees that futex_wait() will NOT
1857 * absorb a wakeup if *uaddr does not match the desired values
1858 * while the syscall executes.
1861 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
1862 if (unlikely(ret != 0))
1866 *hb = queue_lock(q);
1868 ret = get_futex_value_locked(&uval, uaddr);
1871 queue_unlock(q, *hb);
1873 ret = get_user(uval, uaddr);
1877 if (!(flags & FLAGS_SHARED))
1880 put_futex_key(&q->key);
1885 queue_unlock(q, *hb);
1891 put_futex_key(&q->key);
1895 static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
1896 ktime_t *abs_time, u32 bitset)
1898 struct hrtimer_sleeper timeout, *to = NULL;
1899 struct restart_block *restart;
1900 struct futex_hash_bucket *hb;
1901 struct futex_q q = futex_q_init;
1911 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
1912 CLOCK_REALTIME : CLOCK_MONOTONIC,
1914 hrtimer_init_sleeper(to, current);
1915 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
1916 current->timer_slack_ns);
1921 * Prepare to wait on uaddr. On success, holds hb lock and increments
1924 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
1928 /* queue_me and wait for wakeup, timeout, or a signal. */
1929 futex_wait_queue_me(hb, &q, to);
1931 /* If we were woken (and unqueued), we succeeded, whatever. */
1933 /* unqueue_me() drops q.key ref */
1934 if (!unqueue_me(&q))
1937 if (to && !to->task)
1941 * We expect signal_pending(current), but we might be the
1942 * victim of a spurious wakeup as well.
1944 if (!signal_pending(current))
1951 restart = ¤t_thread_info()->restart_block;
1952 restart->fn = futex_wait_restart;
1953 restart->futex.uaddr = uaddr;
1954 restart->futex.val = val;
1955 restart->futex.time = abs_time->tv64;
1956 restart->futex.bitset = bitset;
1957 restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
1959 ret = -ERESTART_RESTARTBLOCK;
1963 hrtimer_cancel(&to->timer);
1964 destroy_hrtimer_on_stack(&to->timer);
1970 static long futex_wait_restart(struct restart_block *restart)
1972 u32 __user *uaddr = restart->futex.uaddr;
1973 ktime_t t, *tp = NULL;
1975 if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
1976 t.tv64 = restart->futex.time;
1979 restart->fn = do_no_restart_syscall;
1981 return (long)futex_wait(uaddr, restart->futex.flags,
1982 restart->futex.val, tp, restart->futex.bitset);
1987 * Userspace tried a 0 -> TID atomic transition of the futex value
1988 * and failed. The kernel side here does the whole locking operation:
1989 * if there are waiters then it will block, it does PI, etc. (Due to
1990 * races the kernel might see a 0 value of the futex too.)
1992 static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect,
1993 ktime_t *time, int trylock)
1995 struct hrtimer_sleeper timeout, *to = NULL;
1996 struct futex_hash_bucket *hb;
1997 struct futex_q q = futex_q_init;
2000 if (refill_pi_state_cache())
2005 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
2007 hrtimer_init_sleeper(to, current);
2008 hrtimer_set_expires(&to->timer, *time);
2012 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
2013 if (unlikely(ret != 0))
2017 hb = queue_lock(&q);
2019 ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
2020 if (unlikely(ret)) {
2023 /* We got the lock. */
2025 goto out_unlock_put_key;
2030 * Task is exiting and we just wait for the
2033 queue_unlock(&q, hb);
2034 put_futex_key(&q.key);
2038 goto out_unlock_put_key;
2043 * Only actually queue now that the atomic ops are done:
2047 WARN_ON(!q.pi_state);
2049 * Block on the PI mutex:
2052 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
2054 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
2055 /* Fixup the trylock return value: */
2056 ret = ret ? 0 : -EWOULDBLOCK;
2059 spin_lock(q.lock_ptr);
2061 * Fixup the pi_state owner and possibly acquire the lock if we
2064 res = fixup_owner(uaddr, &q, !ret);
2066 * If fixup_owner() returned an error, proprogate that. If it acquired
2067 * the lock, clear our -ETIMEDOUT or -EINTR.
2070 ret = (res < 0) ? res : 0;
2073 * If fixup_owner() faulted and was unable to handle the fault, unlock
2074 * it and return the fault to userspace.
2076 if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
2077 rt_mutex_unlock(&q.pi_state->pi_mutex);
2079 /* Unqueue and drop the lock */
2085 queue_unlock(&q, hb);
2088 put_futex_key(&q.key);
2091 destroy_hrtimer_on_stack(&to->timer);
2092 return ret != -EINTR ? ret : -ERESTARTNOINTR;
2095 queue_unlock(&q, hb);
2097 ret = fault_in_user_writeable(uaddr);
2101 if (!(flags & FLAGS_SHARED))
2104 put_futex_key(&q.key);
2109 * Userspace attempted a TID -> 0 atomic transition, and failed.
2110 * This is the in-kernel slowpath: we look up the PI state (if any),
2111 * and do the rt-mutex unlock.
2113 static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
2115 struct futex_hash_bucket *hb;
2116 struct futex_q *this, *next;
2117 struct plist_head *head;
2118 union futex_key key = FUTEX_KEY_INIT;
2119 u32 uval, vpid = task_pid_vnr(current);
2123 if (get_user(uval, uaddr))
2126 * We release only a lock we actually own:
2128 if ((uval & FUTEX_TID_MASK) != vpid)
2131 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
2132 if (unlikely(ret != 0))
2135 hb = hash_futex(&key);
2136 spin_lock(&hb->lock);
2139 * To avoid races, try to do the TID -> 0 atomic transition
2140 * again. If it succeeds then we can return without waking
2143 if (!(uval & FUTEX_OWNER_DIED) &&
2144 cmpxchg_futex_value_locked(&uval, uaddr, vpid, 0))
2147 * Rare case: we managed to release the lock atomically,
2148 * no need to wake anyone else up:
2150 if (unlikely(uval == vpid))
2154 * Ok, other tasks may need to be woken up - check waiters
2155 * and do the wakeup if necessary:
2159 plist_for_each_entry_safe(this, next, head, list) {
2160 if (!match_futex (&this->key, &key))
2162 ret = wake_futex_pi(uaddr, uval, this);
2164 * The atomic access to the futex value
2165 * generated a pagefault, so retry the
2166 * user-access and the wakeup:
2173 * No waiters - kernel unlocks the futex:
2175 if (!(uval & FUTEX_OWNER_DIED)) {
2176 ret = unlock_futex_pi(uaddr, uval);
2182 spin_unlock(&hb->lock);
2183 put_futex_key(&key);
2189 spin_unlock(&hb->lock);
2190 put_futex_key(&key);
2192 ret = fault_in_user_writeable(uaddr);
2200 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2201 * @hb: the hash_bucket futex_q was original enqueued on
2202 * @q: the futex_q woken while waiting to be requeued
2203 * @key2: the futex_key of the requeue target futex
2204 * @timeout: the timeout associated with the wait (NULL if none)
2206 * Detect if the task was woken on the initial futex as opposed to the requeue
2207 * target futex. If so, determine if it was a timeout or a signal that caused
2208 * the wakeup and return the appropriate error code to the caller. Must be
2209 * called with the hb lock held.
2212 * 0 = no early wakeup detected;
2213 * <0 = -ETIMEDOUT or -ERESTARTNOINTR
2216 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2217 struct futex_q *q, union futex_key *key2,
2218 struct hrtimer_sleeper *timeout)
2223 * With the hb lock held, we avoid races while we process the wakeup.
2224 * We only need to hold hb (and not hb2) to ensure atomicity as the
2225 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2226 * It can't be requeued from uaddr2 to something else since we don't
2227 * support a PI aware source futex for requeue.
2229 if (!match_futex(&q->key, key2)) {
2230 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2232 * We were woken prior to requeue by a timeout or a signal.
2233 * Unqueue the futex_q and determine which it was.
2235 plist_del(&q->list, &hb->chain);
2237 /* Handle spurious wakeups gracefully */
2239 if (timeout && !timeout->task)
2241 else if (signal_pending(current))
2242 ret = -ERESTARTNOINTR;
2248 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2249 * @uaddr: the futex we initially wait on (non-pi)
2250 * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
2251 * the same type, no requeueing from private to shared, etc.
2252 * @val: the expected value of uaddr
2253 * @abs_time: absolute timeout
2254 * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
2255 * @uaddr2: the pi futex we will take prior to returning to user-space
2257 * The caller will wait on uaddr and will be requeued by futex_requeue() to
2258 * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
2259 * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
2260 * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
2261 * without one, the pi logic would not know which task to boost/deboost, if
2262 * there was a need to.
2264 * We call schedule in futex_wait_queue_me() when we enqueue and return there
2265 * via the following--
2266 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2267 * 2) wakeup on uaddr2 after a requeue
2271 * If 3, cleanup and return -ERESTARTNOINTR.
2273 * If 2, we may then block on trying to take the rt_mutex and return via:
2274 * 5) successful lock
2277 * 8) other lock acquisition failure
2279 * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2281 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2287 static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
2288 u32 val, ktime_t *abs_time, u32 bitset,
2291 struct hrtimer_sleeper timeout, *to = NULL;
2292 struct rt_mutex_waiter rt_waiter;
2293 struct rt_mutex *pi_mutex = NULL;
2294 struct futex_hash_bucket *hb;
2295 union futex_key key2 = FUTEX_KEY_INIT;
2296 struct futex_q q = futex_q_init;
2299 if (uaddr == uaddr2)
2307 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2308 CLOCK_REALTIME : CLOCK_MONOTONIC,
2310 hrtimer_init_sleeper(to, current);
2311 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2312 current->timer_slack_ns);
2316 * The waiter is allocated on our stack, manipulated by the requeue
2317 * code while we sleep on uaddr.
2319 debug_rt_mutex_init_waiter(&rt_waiter);
2320 rt_waiter.task = NULL;
2322 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
2323 if (unlikely(ret != 0))
2327 q.rt_waiter = &rt_waiter;
2328 q.requeue_pi_key = &key2;
2331 * Prepare to wait on uaddr. On success, increments q.key (key1) ref
2334 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2338 /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2339 futex_wait_queue_me(hb, &q, to);
2341 spin_lock(&hb->lock);
2342 ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2343 spin_unlock(&hb->lock);
2348 * In order for us to be here, we know our q.key == key2, and since
2349 * we took the hb->lock above, we also know that futex_requeue() has
2350 * completed and we no longer have to concern ourselves with a wakeup
2351 * race with the atomic proxy lock acquisition by the requeue code. The
2352 * futex_requeue dropped our key1 reference and incremented our key2
2356 /* Check if the requeue code acquired the second futex for us. */
2359 * Got the lock. We might not be the anticipated owner if we
2360 * did a lock-steal - fix up the PI-state in that case.
2362 if (q.pi_state && (q.pi_state->owner != current)) {
2363 spin_lock(q.lock_ptr);
2364 ret = fixup_pi_state_owner(uaddr2, &q, current);
2365 spin_unlock(q.lock_ptr);
2369 * We have been woken up by futex_unlock_pi(), a timeout, or a
2370 * signal. futex_unlock_pi() will not destroy the lock_ptr nor
2373 WARN_ON(!q.pi_state);
2374 pi_mutex = &q.pi_state->pi_mutex;
2375 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
2376 debug_rt_mutex_free_waiter(&rt_waiter);
2378 spin_lock(q.lock_ptr);
2380 * Fixup the pi_state owner and possibly acquire the lock if we
2383 res = fixup_owner(uaddr2, &q, !ret);
2385 * If fixup_owner() returned an error, proprogate that. If it
2386 * acquired the lock, clear -ETIMEDOUT or -EINTR.
2389 ret = (res < 0) ? res : 0;
2391 /* Unqueue and drop the lock. */
2396 * If fixup_pi_state_owner() faulted and was unable to handle the
2397 * fault, unlock the rt_mutex and return the fault to userspace.
2399 if (ret == -EFAULT) {
2400 if (pi_mutex && rt_mutex_owner(pi_mutex) == current)
2401 rt_mutex_unlock(pi_mutex);
2402 } else if (ret == -EINTR) {
2404 * We've already been requeued, but cannot restart by calling
2405 * futex_lock_pi() directly. We could restart this syscall, but
2406 * it would detect that the user space "val" changed and return
2407 * -EWOULDBLOCK. Save the overhead of the restart and return
2408 * -EWOULDBLOCK directly.
2414 put_futex_key(&q.key);
2416 put_futex_key(&key2);
2420 hrtimer_cancel(&to->timer);
2421 destroy_hrtimer_on_stack(&to->timer);
2427 * Support for robust futexes: the kernel cleans up held futexes at
2430 * Implementation: user-space maintains a per-thread list of locks it
2431 * is holding. Upon do_exit(), the kernel carefully walks this list,
2432 * and marks all locks that are owned by this thread with the
2433 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2434 * always manipulated with the lock held, so the list is private and
2435 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2436 * field, to allow the kernel to clean up if the thread dies after
2437 * acquiring the lock, but just before it could have added itself to
2438 * the list. There can only be one such pending lock.
2442 * sys_set_robust_list() - Set the robust-futex list head of a task
2443 * @head: pointer to the list-head
2444 * @len: length of the list-head, as userspace expects
2446 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2449 if (!futex_cmpxchg_enabled)
2452 * The kernel knows only one size for now:
2454 if (unlikely(len != sizeof(*head)))
2457 current->robust_list = head;
2463 * sys_get_robust_list() - Get the robust-futex list head of a task
2464 * @pid: pid of the process [zero for current task]
2465 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
2466 * @len_ptr: pointer to a length field, the kernel fills in the header size
2468 SYSCALL_DEFINE3(get_robust_list, int, pid,
2469 struct robust_list_head __user * __user *, head_ptr,
2470 size_t __user *, len_ptr)
2472 struct robust_list_head __user *head;
2474 struct task_struct *p;
2476 if (!futex_cmpxchg_enabled)
2485 p = find_task_by_vpid(pid);
2491 if (!ptrace_may_access(p, PTRACE_MODE_READ))
2494 head = p->robust_list;
2497 if (put_user(sizeof(*head), len_ptr))
2499 return put_user(head, head_ptr);
2508 * Process a futex-list entry, check whether it's owned by the
2509 * dying task, and do notification if so:
2511 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
2513 u32 uval, uninitialized_var(nval), mval;
2516 if (get_user(uval, uaddr))
2519 if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
2521 * Ok, this dying thread is truly holding a futex
2522 * of interest. Set the OWNER_DIED bit atomically
2523 * via cmpxchg, and if the value had FUTEX_WAITERS
2524 * set, wake up a waiter (if any). (We have to do a
2525 * futex_wake() even if OWNER_DIED is already set -
2526 * to handle the rare but possible case of recursive
2527 * thread-death.) The rest of the cleanup is done in
2530 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
2532 * We are not holding a lock here, but we want to have
2533 * the pagefault_disable/enable() protection because
2534 * we want to handle the fault gracefully. If the
2535 * access fails we try to fault in the futex with R/W
2536 * verification via get_user_pages. get_user() above
2537 * does not guarantee R/W access. If that fails we
2538 * give up and leave the futex locked.
2540 if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
2541 if (fault_in_user_writeable(uaddr))
2549 * Wake robust non-PI futexes here. The wakeup of
2550 * PI futexes happens in exit_pi_state():
2552 if (!pi && (uval & FUTEX_WAITERS))
2553 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
2559 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
2561 static inline int fetch_robust_entry(struct robust_list __user **entry,
2562 struct robust_list __user * __user *head,
2565 unsigned long uentry;
2567 if (get_user(uentry, (unsigned long __user *)head))
2570 *entry = (void __user *)(uentry & ~1UL);
2577 * Walk curr->robust_list (very carefully, it's a userspace list!)
2578 * and mark any locks found there dead, and notify any waiters.
2580 * We silently return on any sign of list-walking problem.
2582 void exit_robust_list(struct task_struct *curr)
2584 struct robust_list_head __user *head = curr->robust_list;
2585 struct robust_list __user *entry, *next_entry, *pending;
2586 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
2587 unsigned int uninitialized_var(next_pi);
2588 unsigned long futex_offset;
2591 if (!futex_cmpxchg_enabled)
2595 * Fetch the list head (which was registered earlier, via
2596 * sys_set_robust_list()):
2598 if (fetch_robust_entry(&entry, &head->list.next, &pi))
2601 * Fetch the relative futex offset:
2603 if (get_user(futex_offset, &head->futex_offset))
2606 * Fetch any possibly pending lock-add first, and handle it
2609 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
2612 next_entry = NULL; /* avoid warning with gcc */
2613 while (entry != &head->list) {
2615 * Fetch the next entry in the list before calling
2616 * handle_futex_death:
2618 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
2620 * A pending lock might already be on the list, so
2621 * don't process it twice:
2623 if (entry != pending)
2624 if (handle_futex_death((void __user *)entry + futex_offset,
2632 * Avoid excessively long or circular lists:
2641 handle_futex_death((void __user *)pending + futex_offset,
2645 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
2646 u32 __user *uaddr2, u32 val2, u32 val3)
2648 int cmd = op & FUTEX_CMD_MASK;
2649 unsigned int flags = 0;
2651 if (!(op & FUTEX_PRIVATE_FLAG))
2652 flags |= FLAGS_SHARED;
2654 if (op & FUTEX_CLOCK_REALTIME) {
2655 flags |= FLAGS_CLOCKRT;
2656 if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
2662 case FUTEX_UNLOCK_PI:
2663 case FUTEX_TRYLOCK_PI:
2664 case FUTEX_WAIT_REQUEUE_PI:
2665 case FUTEX_CMP_REQUEUE_PI:
2666 if (!futex_cmpxchg_enabled)
2672 val3 = FUTEX_BITSET_MATCH_ANY;
2673 case FUTEX_WAIT_BITSET:
2674 return futex_wait(uaddr, flags, val, timeout, val3);
2676 val3 = FUTEX_BITSET_MATCH_ANY;
2677 case FUTEX_WAKE_BITSET:
2678 return futex_wake(uaddr, flags, val, val3);
2680 return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
2681 case FUTEX_CMP_REQUEUE:
2682 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
2684 return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
2686 return futex_lock_pi(uaddr, flags, val, timeout, 0);
2687 case FUTEX_UNLOCK_PI:
2688 return futex_unlock_pi(uaddr, flags);
2689 case FUTEX_TRYLOCK_PI:
2690 return futex_lock_pi(uaddr, flags, 0, timeout, 1);
2691 case FUTEX_WAIT_REQUEUE_PI:
2692 val3 = FUTEX_BITSET_MATCH_ANY;
2693 return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
2695 case FUTEX_CMP_REQUEUE_PI:
2696 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
2702 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
2703 struct timespec __user *, utime, u32 __user *, uaddr2,
2707 ktime_t t, *tp = NULL;
2709 int cmd = op & FUTEX_CMD_MASK;
2711 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
2712 cmd == FUTEX_WAIT_BITSET ||
2713 cmd == FUTEX_WAIT_REQUEUE_PI)) {
2714 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
2716 if (!timespec_valid(&ts))
2719 t = timespec_to_ktime(ts);
2720 if (cmd == FUTEX_WAIT)
2721 t = ktime_add_safe(ktime_get(), t);
2725 * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
2726 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
2728 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
2729 cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
2730 val2 = (u32) (unsigned long) utime;
2732 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
2735 static void __init futex_detect_cmpxchg(void)
2737 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
2741 * This will fail and we want it. Some arch implementations do
2742 * runtime detection of the futex_atomic_cmpxchg_inatomic()
2743 * functionality. We want to know that before we call in any
2744 * of the complex code paths. Also we want to prevent
2745 * registration of robust lists in that case. NULL is
2746 * guaranteed to fault and we get -EFAULT on functional
2747 * implementation, the non-functional ones will return
2750 if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
2751 futex_cmpxchg_enabled = 1;
2755 static int __init futex_init(void)
2759 futex_detect_cmpxchg();
2761 for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
2762 plist_head_init(&futex_queues[i].chain);
2763 spin_lock_init(&futex_queues[i].lock);
2768 __initcall(futex_init);