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/module.h>
59 #include <linux/magic.h>
60 #include <linux/pid.h>
61 #include <linux/nsproxy.h>
63 #include <asm/futex.h>
65 #include "rtmutex_common.h"
67 int __read_mostly futex_cmpxchg_enabled
;
69 #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
72 * Priority Inheritance state:
74 struct futex_pi_state
{
76 * list of 'owned' pi_state instances - these have to be
77 * cleaned up in do_exit() if the task exits prematurely:
79 struct list_head list
;
84 struct rt_mutex pi_mutex
;
86 struct task_struct
*owner
;
93 * We use this hashed waitqueue instead of a normal wait_queue_t, so
94 * we can wake only the relevant ones (hashed queues may be shared).
96 * A futex_q has a woken state, just like tasks have TASK_RUNNING.
97 * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
98 * The order of wakup is always to make the first condition true, then
99 * wake up q->waiter, then make the second condition true.
102 struct plist_node list
;
103 /* Waiter reference */
104 struct task_struct
*task
;
106 /* Which hash list lock to use: */
107 spinlock_t
*lock_ptr
;
109 /* Key which the futex is hashed on: */
112 /* Optional priority inheritance state: */
113 struct futex_pi_state
*pi_state
;
115 /* rt_waiter storage for requeue_pi: */
116 struct rt_mutex_waiter
*rt_waiter
;
118 /* Bitset for the optional bitmasked wakeup */
123 * Hash buckets are shared by all the futex_keys that hash to the same
124 * location. Each key may have multiple futex_q structures, one for each task
125 * waiting on a futex.
127 struct futex_hash_bucket
{
129 struct plist_head chain
;
132 static struct futex_hash_bucket futex_queues
[1<<FUTEX_HASHBITS
];
135 * We hash on the keys returned from get_futex_key (see below).
137 static struct futex_hash_bucket
*hash_futex(union futex_key
*key
)
139 u32 hash
= jhash2((u32
*)&key
->both
.word
,
140 (sizeof(key
->both
.word
)+sizeof(key
->both
.ptr
))/4,
142 return &futex_queues
[hash
& ((1 << FUTEX_HASHBITS
)-1)];
146 * Return 1 if two futex_keys are equal, 0 otherwise.
148 static inline int match_futex(union futex_key
*key1
, union futex_key
*key2
)
150 return (key1
->both
.word
== key2
->both
.word
151 && key1
->both
.ptr
== key2
->both
.ptr
152 && key1
->both
.offset
== key2
->both
.offset
);
156 * Take a reference to the resource addressed by a key.
157 * Can be called while holding spinlocks.
160 static void get_futex_key_refs(union futex_key
*key
)
165 switch (key
->both
.offset
& (FUT_OFF_INODE
|FUT_OFF_MMSHARED
)) {
167 atomic_inc(&key
->shared
.inode
->i_count
);
169 case FUT_OFF_MMSHARED
:
170 atomic_inc(&key
->private.mm
->mm_count
);
176 * Drop a reference to the resource addressed by a key.
177 * The hash bucket spinlock must not be held.
179 static void drop_futex_key_refs(union futex_key
*key
)
181 if (!key
->both
.ptr
) {
182 /* If we're here then we tried to put a key we failed to get */
187 switch (key
->both
.offset
& (FUT_OFF_INODE
|FUT_OFF_MMSHARED
)) {
189 iput(key
->shared
.inode
);
191 case FUT_OFF_MMSHARED
:
192 mmdrop(key
->private.mm
);
198 * get_futex_key - Get parameters which are the keys for a futex.
199 * @uaddr: virtual address of the futex
200 * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
201 * @key: address where result is stored.
203 * Returns a negative error code or 0
204 * The key words are stored in *key on success.
206 * For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,
207 * offset_within_page). For private mappings, it's (uaddr, current->mm).
208 * We can usually work out the index without swapping in the page.
210 * lock_page() might sleep, the caller should not hold a spinlock.
212 static int get_futex_key(u32 __user
*uaddr
, int fshared
, union futex_key
*key
)
214 unsigned long address
= (unsigned long)uaddr
;
215 struct mm_struct
*mm
= current
->mm
;
220 * The futex address must be "naturally" aligned.
222 key
->both
.offset
= address
% PAGE_SIZE
;
223 if (unlikely((address
% sizeof(u32
)) != 0))
225 address
-= key
->both
.offset
;
228 * PROCESS_PRIVATE futexes are fast.
229 * As the mm cannot disappear under us and the 'key' only needs
230 * virtual address, we dont even have to find the underlying vma.
231 * Note : We do have to check 'uaddr' is a valid user address,
232 * but access_ok() should be faster than find_vma()
235 if (unlikely(!access_ok(VERIFY_WRITE
, uaddr
, sizeof(u32
))))
237 key
->private.mm
= mm
;
238 key
->private.address
= address
;
239 get_futex_key_refs(key
);
244 err
= get_user_pages_fast(address
, 1, 0, &page
);
249 if (!page
->mapping
) {
256 * Private mappings are handled in a simple way.
258 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
259 * it's a read-only handle, it's expected that futexes attach to
260 * the object not the particular process.
262 if (PageAnon(page
)) {
263 key
->both
.offset
|= FUT_OFF_MMSHARED
; /* ref taken on mm */
264 key
->private.mm
= mm
;
265 key
->private.address
= address
;
267 key
->both
.offset
|= FUT_OFF_INODE
; /* inode-based key */
268 key
->shared
.inode
= page
->mapping
->host
;
269 key
->shared
.pgoff
= page
->index
;
272 get_futex_key_refs(key
);
280 void put_futex_key(int fshared
, union futex_key
*key
)
282 drop_futex_key_refs(key
);
286 * futex_top_waiter() - Return the highest priority waiter on a futex
287 * @hb: the hash bucket the futex_q's reside in
288 * @key: the futex key (to distinguish it from other futex futex_q's)
290 * Must be called with the hb lock held.
292 static struct futex_q
*futex_top_waiter(struct futex_hash_bucket
*hb
,
293 union futex_key
*key
)
295 struct futex_q
*this;
297 plist_for_each_entry(this, &hb
->chain
, list
) {
298 if (match_futex(&this->key
, key
))
304 static u32
cmpxchg_futex_value_locked(u32 __user
*uaddr
, u32 uval
, u32 newval
)
309 curval
= futex_atomic_cmpxchg_inatomic(uaddr
, uval
, newval
);
315 static int get_futex_value_locked(u32
*dest
, u32 __user
*from
)
320 ret
= __copy_from_user_inatomic(dest
, from
, sizeof(u32
));
323 return ret
? -EFAULT
: 0;
330 static int refill_pi_state_cache(void)
332 struct futex_pi_state
*pi_state
;
334 if (likely(current
->pi_state_cache
))
337 pi_state
= kzalloc(sizeof(*pi_state
), GFP_KERNEL
);
342 INIT_LIST_HEAD(&pi_state
->list
);
343 /* pi_mutex gets initialized later */
344 pi_state
->owner
= NULL
;
345 atomic_set(&pi_state
->refcount
, 1);
346 pi_state
->key
= FUTEX_KEY_INIT
;
348 current
->pi_state_cache
= pi_state
;
353 static struct futex_pi_state
* alloc_pi_state(void)
355 struct futex_pi_state
*pi_state
= current
->pi_state_cache
;
358 current
->pi_state_cache
= NULL
;
363 static void free_pi_state(struct futex_pi_state
*pi_state
)
365 if (!atomic_dec_and_test(&pi_state
->refcount
))
369 * If pi_state->owner is NULL, the owner is most probably dying
370 * and has cleaned up the pi_state already
372 if (pi_state
->owner
) {
373 spin_lock_irq(&pi_state
->owner
->pi_lock
);
374 list_del_init(&pi_state
->list
);
375 spin_unlock_irq(&pi_state
->owner
->pi_lock
);
377 rt_mutex_proxy_unlock(&pi_state
->pi_mutex
, pi_state
->owner
);
380 if (current
->pi_state_cache
)
384 * pi_state->list is already empty.
385 * clear pi_state->owner.
386 * refcount is at 0 - put it back to 1.
388 pi_state
->owner
= NULL
;
389 atomic_set(&pi_state
->refcount
, 1);
390 current
->pi_state_cache
= pi_state
;
395 * Look up the task based on what TID userspace gave us.
398 static struct task_struct
* futex_find_get_task(pid_t pid
)
400 struct task_struct
*p
;
401 const struct cred
*cred
= current_cred(), *pcred
;
404 p
= find_task_by_vpid(pid
);
408 pcred
= __task_cred(p
);
409 if (cred
->euid
!= pcred
->euid
&&
410 cred
->euid
!= pcred
->uid
)
422 * This task is holding PI mutexes at exit time => bad.
423 * Kernel cleans up PI-state, but userspace is likely hosed.
424 * (Robust-futex cleanup is separate and might save the day for userspace.)
426 void exit_pi_state_list(struct task_struct
*curr
)
428 struct list_head
*next
, *head
= &curr
->pi_state_list
;
429 struct futex_pi_state
*pi_state
;
430 struct futex_hash_bucket
*hb
;
431 union futex_key key
= FUTEX_KEY_INIT
;
433 if (!futex_cmpxchg_enabled
)
436 * We are a ZOMBIE and nobody can enqueue itself on
437 * pi_state_list anymore, but we have to be careful
438 * versus waiters unqueueing themselves:
440 spin_lock_irq(&curr
->pi_lock
);
441 while (!list_empty(head
)) {
444 pi_state
= list_entry(next
, struct futex_pi_state
, list
);
446 hb
= hash_futex(&key
);
447 spin_unlock_irq(&curr
->pi_lock
);
449 spin_lock(&hb
->lock
);
451 spin_lock_irq(&curr
->pi_lock
);
453 * We dropped the pi-lock, so re-check whether this
454 * task still owns the PI-state:
456 if (head
->next
!= next
) {
457 spin_unlock(&hb
->lock
);
461 WARN_ON(pi_state
->owner
!= curr
);
462 WARN_ON(list_empty(&pi_state
->list
));
463 list_del_init(&pi_state
->list
);
464 pi_state
->owner
= NULL
;
465 spin_unlock_irq(&curr
->pi_lock
);
467 rt_mutex_unlock(&pi_state
->pi_mutex
);
469 spin_unlock(&hb
->lock
);
471 spin_lock_irq(&curr
->pi_lock
);
473 spin_unlock_irq(&curr
->pi_lock
);
477 lookup_pi_state(u32 uval
, struct futex_hash_bucket
*hb
,
478 union futex_key
*key
, struct futex_pi_state
**ps
)
480 struct futex_pi_state
*pi_state
= NULL
;
481 struct futex_q
*this, *next
;
482 struct plist_head
*head
;
483 struct task_struct
*p
;
484 pid_t pid
= uval
& FUTEX_TID_MASK
;
488 plist_for_each_entry_safe(this, next
, head
, list
) {
489 if (match_futex(&this->key
, key
)) {
491 * Another waiter already exists - bump up
492 * the refcount and return its pi_state:
494 pi_state
= this->pi_state
;
496 * Userspace might have messed up non PI and PI futexes
498 if (unlikely(!pi_state
))
501 WARN_ON(!atomic_read(&pi_state
->refcount
));
502 WARN_ON(pid
&& pi_state
->owner
&&
503 pi_state
->owner
->pid
!= pid
);
505 atomic_inc(&pi_state
->refcount
);
513 * We are the first waiter - try to look up the real owner and attach
514 * the new pi_state to it, but bail out when TID = 0
518 p
= futex_find_get_task(pid
);
523 * We need to look at the task state flags to figure out,
524 * whether the task is exiting. To protect against the do_exit
525 * change of the task flags, we do this protected by
528 spin_lock_irq(&p
->pi_lock
);
529 if (unlikely(p
->flags
& PF_EXITING
)) {
531 * The task is on the way out. When PF_EXITPIDONE is
532 * set, we know that the task has finished the
535 int ret
= (p
->flags
& PF_EXITPIDONE
) ? -ESRCH
: -EAGAIN
;
537 spin_unlock_irq(&p
->pi_lock
);
542 pi_state
= alloc_pi_state();
545 * Initialize the pi_mutex in locked state and make 'p'
548 rt_mutex_init_proxy_locked(&pi_state
->pi_mutex
, p
);
550 /* Store the key for possible exit cleanups: */
551 pi_state
->key
= *key
;
553 WARN_ON(!list_empty(&pi_state
->list
));
554 list_add(&pi_state
->list
, &p
->pi_state_list
);
556 spin_unlock_irq(&p
->pi_lock
);
566 * futex_lock_pi_atomic() - atomic work required to acquire a pi aware futex
567 * @uaddr: the pi futex user address
568 * @hb: the pi futex hash bucket
569 * @key: the futex key associated with uaddr and hb
570 * @ps: the pi_state pointer where we store the result of the
572 * @task: the task to perform the atomic lock work for. This will
573 * be "current" except in the case of requeue pi.
574 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
578 * 1 - acquired the lock
581 * The hb->lock and futex_key refs shall be held by the caller.
583 static int futex_lock_pi_atomic(u32 __user
*uaddr
, struct futex_hash_bucket
*hb
,
584 union futex_key
*key
,
585 struct futex_pi_state
**ps
,
586 struct task_struct
*task
, int set_waiters
)
588 int lock_taken
, ret
, ownerdied
= 0;
589 u32 uval
, newval
, curval
;
592 ret
= lock_taken
= 0;
595 * To avoid races, we attempt to take the lock here again
596 * (by doing a 0 -> TID atomic cmpxchg), while holding all
597 * the locks. It will most likely not succeed.
599 newval
= task_pid_vnr(task
);
601 newval
|= FUTEX_WAITERS
;
603 curval
= cmpxchg_futex_value_locked(uaddr
, 0, newval
);
605 if (unlikely(curval
== -EFAULT
))
611 if ((unlikely((curval
& FUTEX_TID_MASK
) == task_pid_vnr(task
))))
615 * Surprise - we got the lock. Just return to userspace:
617 if (unlikely(!curval
))
623 * Set the FUTEX_WAITERS flag, so the owner will know it has someone
624 * to wake at the next unlock.
626 newval
= curval
| FUTEX_WAITERS
;
629 * There are two cases, where a futex might have no owner (the
630 * owner TID is 0): OWNER_DIED. We take over the futex in this
631 * case. We also do an unconditional take over, when the owner
634 * This is safe as we are protected by the hash bucket lock !
636 if (unlikely(ownerdied
|| !(curval
& FUTEX_TID_MASK
))) {
637 /* Keep the OWNER_DIED bit */
638 newval
= (curval
& ~FUTEX_TID_MASK
) | task_pid_vnr(task
);
643 curval
= cmpxchg_futex_value_locked(uaddr
, uval
, newval
);
645 if (unlikely(curval
== -EFAULT
))
647 if (unlikely(curval
!= uval
))
651 * We took the lock due to owner died take over.
653 if (unlikely(lock_taken
))
657 * We dont have the lock. Look up the PI state (or create it if
658 * we are the first waiter):
660 ret
= lookup_pi_state(uval
, hb
, key
, ps
);
666 * No owner found for this futex. Check if the
667 * OWNER_DIED bit is set to figure out whether
668 * this is a robust futex or not.
670 if (get_futex_value_locked(&curval
, uaddr
))
674 * We simply start over in case of a robust
675 * futex. The code above will take the futex
678 if (curval
& FUTEX_OWNER_DIED
) {
691 * The hash bucket lock must be held when this is called.
692 * Afterwards, the futex_q must not be accessed.
694 static void wake_futex(struct futex_q
*q
)
696 struct task_struct
*p
= q
->task
;
699 * We set q->lock_ptr = NULL _before_ we wake up the task. If
700 * a non futex wake up happens on another CPU then the task
701 * might exit and p would dereference a non existing task
702 * struct. Prevent this by holding a reference on p across the
707 plist_del(&q
->list
, &q
->list
.plist
);
709 * The waiting task can free the futex_q as soon as
710 * q->lock_ptr = NULL is written, without taking any locks. A
711 * memory barrier is required here to prevent the following
712 * store to lock_ptr from getting ahead of the plist_del.
717 wake_up_state(p
, TASK_NORMAL
);
721 static int wake_futex_pi(u32 __user
*uaddr
, u32 uval
, struct futex_q
*this)
723 struct task_struct
*new_owner
;
724 struct futex_pi_state
*pi_state
= this->pi_state
;
730 spin_lock(&pi_state
->pi_mutex
.wait_lock
);
731 new_owner
= rt_mutex_next_owner(&pi_state
->pi_mutex
);
734 * This happens when we have stolen the lock and the original
735 * pending owner did not enqueue itself back on the rt_mutex.
736 * Thats not a tragedy. We know that way, that a lock waiter
737 * is on the fly. We make the futex_q waiter the pending owner.
740 new_owner
= this->task
;
743 * We pass it to the next owner. (The WAITERS bit is always
744 * kept enabled while there is PI state around. We must also
745 * preserve the owner died bit.)
747 if (!(uval
& FUTEX_OWNER_DIED
)) {
750 newval
= FUTEX_WAITERS
| task_pid_vnr(new_owner
);
752 curval
= cmpxchg_futex_value_locked(uaddr
, uval
, newval
);
754 if (curval
== -EFAULT
)
756 else if (curval
!= uval
)
759 spin_unlock(&pi_state
->pi_mutex
.wait_lock
);
764 spin_lock_irq(&pi_state
->owner
->pi_lock
);
765 WARN_ON(list_empty(&pi_state
->list
));
766 list_del_init(&pi_state
->list
);
767 spin_unlock_irq(&pi_state
->owner
->pi_lock
);
769 spin_lock_irq(&new_owner
->pi_lock
);
770 WARN_ON(!list_empty(&pi_state
->list
));
771 list_add(&pi_state
->list
, &new_owner
->pi_state_list
);
772 pi_state
->owner
= new_owner
;
773 spin_unlock_irq(&new_owner
->pi_lock
);
775 spin_unlock(&pi_state
->pi_mutex
.wait_lock
);
776 rt_mutex_unlock(&pi_state
->pi_mutex
);
781 static int unlock_futex_pi(u32 __user
*uaddr
, u32 uval
)
786 * There is no waiter, so we unlock the futex. The owner died
787 * bit has not to be preserved here. We are the owner:
789 oldval
= cmpxchg_futex_value_locked(uaddr
, uval
, 0);
791 if (oldval
== -EFAULT
)
800 * Express the locking dependencies for lockdep:
803 double_lock_hb(struct futex_hash_bucket
*hb1
, struct futex_hash_bucket
*hb2
)
806 spin_lock(&hb1
->lock
);
808 spin_lock_nested(&hb2
->lock
, SINGLE_DEPTH_NESTING
);
809 } else { /* hb1 > hb2 */
810 spin_lock(&hb2
->lock
);
811 spin_lock_nested(&hb1
->lock
, SINGLE_DEPTH_NESTING
);
816 double_unlock_hb(struct futex_hash_bucket
*hb1
, struct futex_hash_bucket
*hb2
)
818 spin_unlock(&hb1
->lock
);
820 spin_unlock(&hb2
->lock
);
824 * Wake up waiters matching bitset queued on this futex (uaddr).
826 static int futex_wake(u32 __user
*uaddr
, int fshared
, int nr_wake
, u32 bitset
)
828 struct futex_hash_bucket
*hb
;
829 struct futex_q
*this, *next
;
830 struct plist_head
*head
;
831 union futex_key key
= FUTEX_KEY_INIT
;
837 ret
= get_futex_key(uaddr
, fshared
, &key
);
838 if (unlikely(ret
!= 0))
841 hb
= hash_futex(&key
);
842 spin_lock(&hb
->lock
);
845 plist_for_each_entry_safe(this, next
, head
, list
) {
846 if (match_futex (&this->key
, &key
)) {
847 if (this->pi_state
|| this->rt_waiter
) {
852 /* Check if one of the bits is set in both bitsets */
853 if (!(this->bitset
& bitset
))
857 if (++ret
>= nr_wake
)
862 spin_unlock(&hb
->lock
);
863 put_futex_key(fshared
, &key
);
869 * Wake up all waiters hashed on the physical page that is mapped
870 * to this virtual address:
873 futex_wake_op(u32 __user
*uaddr1
, int fshared
, u32 __user
*uaddr2
,
874 int nr_wake
, int nr_wake2
, int op
)
876 union futex_key key1
= FUTEX_KEY_INIT
, key2
= FUTEX_KEY_INIT
;
877 struct futex_hash_bucket
*hb1
, *hb2
;
878 struct plist_head
*head
;
879 struct futex_q
*this, *next
;
883 ret
= get_futex_key(uaddr1
, fshared
, &key1
);
884 if (unlikely(ret
!= 0))
886 ret
= get_futex_key(uaddr2
, fshared
, &key2
);
887 if (unlikely(ret
!= 0))
890 hb1
= hash_futex(&key1
);
891 hb2
= hash_futex(&key2
);
893 double_lock_hb(hb1
, hb2
);
895 op_ret
= futex_atomic_op_inuser(op
, uaddr2
);
896 if (unlikely(op_ret
< 0)) {
899 double_unlock_hb(hb1
, hb2
);
903 * we don't get EFAULT from MMU faults if we don't have an MMU,
904 * but we might get them from range checking
910 if (unlikely(op_ret
!= -EFAULT
)) {
915 ret
= get_user(dummy
, uaddr2
);
922 put_futex_key(fshared
, &key2
);
923 put_futex_key(fshared
, &key1
);
929 plist_for_each_entry_safe(this, next
, head
, list
) {
930 if (match_futex (&this->key
, &key1
)) {
932 if (++ret
>= nr_wake
)
941 plist_for_each_entry_safe(this, next
, head
, list
) {
942 if (match_futex (&this->key
, &key2
)) {
944 if (++op_ret
>= nr_wake2
)
951 double_unlock_hb(hb1
, hb2
);
953 put_futex_key(fshared
, &key2
);
955 put_futex_key(fshared
, &key1
);
961 * requeue_futex() - Requeue a futex_q from one hb to another
962 * @q: the futex_q to requeue
963 * @hb1: the source hash_bucket
964 * @hb2: the target hash_bucket
965 * @key2: the new key for the requeued futex_q
968 void requeue_futex(struct futex_q
*q
, struct futex_hash_bucket
*hb1
,
969 struct futex_hash_bucket
*hb2
, union futex_key
*key2
)
973 * If key1 and key2 hash to the same bucket, no need to
976 if (likely(&hb1
->chain
!= &hb2
->chain
)) {
977 plist_del(&q
->list
, &hb1
->chain
);
978 plist_add(&q
->list
, &hb2
->chain
);
979 q
->lock_ptr
= &hb2
->lock
;
980 #ifdef CONFIG_DEBUG_PI_LIST
981 q
->list
.plist
.lock
= &hb2
->lock
;
984 get_futex_key_refs(key2
);
989 * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
991 * key: the key of the requeue target futex
993 * During futex_requeue, with requeue_pi=1, it is possible to acquire the
994 * target futex if it is uncontended or via a lock steal. Set the futex_q key
995 * to the requeue target futex so the waiter can detect the wakeup on the right
996 * futex, but remove it from the hb and NULL the rt_waiter so it can detect
997 * atomic lock acquisition. Must be called with the q->lock_ptr held.
1000 void requeue_pi_wake_futex(struct futex_q
*q
, union futex_key
*key
)
1002 drop_futex_key_refs(&q
->key
);
1003 get_futex_key_refs(key
);
1006 WARN_ON(plist_node_empty(&q
->list
));
1007 plist_del(&q
->list
, &q
->list
.plist
);
1009 WARN_ON(!q
->rt_waiter
);
1010 q
->rt_waiter
= NULL
;
1012 wake_up_state(q
->task
, TASK_NORMAL
);
1016 * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1017 * @pifutex: the user address of the to futex
1018 * @hb1: the from futex hash bucket, must be locked by the caller
1019 * @hb2: the to futex hash bucket, must be locked by the caller
1020 * @key1: the from futex key
1021 * @key2: the to futex key
1022 * @ps: address to store the pi_state pointer
1023 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1025 * Try and get the lock on behalf of the top waiter if we can do it atomically.
1026 * Wake the top waiter if we succeed. If the caller specified set_waiters,
1027 * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1028 * hb1 and hb2 must be held by the caller.
1031 * 0 - failed to acquire the lock atomicly
1032 * 1 - acquired the lock
1035 static int futex_proxy_trylock_atomic(u32 __user
*pifutex
,
1036 struct futex_hash_bucket
*hb1
,
1037 struct futex_hash_bucket
*hb2
,
1038 union futex_key
*key1
, union futex_key
*key2
,
1039 struct futex_pi_state
**ps
, int set_waiters
)
1041 struct futex_q
*top_waiter
= NULL
;
1045 if (get_futex_value_locked(&curval
, pifutex
))
1049 * Find the top_waiter and determine if there are additional waiters.
1050 * If the caller intends to requeue more than 1 waiter to pifutex,
1051 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1052 * as we have means to handle the possible fault. If not, don't set
1053 * the bit unecessarily as it will force the subsequent unlock to enter
1056 top_waiter
= futex_top_waiter(hb1
, key1
);
1058 /* There are no waiters, nothing for us to do. */
1063 * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
1064 * the contended case or if set_waiters is 1. The pi_state is returned
1065 * in ps in contended cases.
1067 ret
= futex_lock_pi_atomic(pifutex
, hb2
, key2
, ps
, top_waiter
->task
,
1070 requeue_pi_wake_futex(top_waiter
, key2
);
1076 * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1077 * uaddr1: source futex user address
1078 * uaddr2: target futex user address
1079 * nr_wake: number of waiters to wake (must be 1 for requeue_pi)
1080 * nr_requeue: number of waiters to requeue (0-INT_MAX)
1081 * requeue_pi: if we are attempting to requeue from a non-pi futex to a
1082 * pi futex (pi to pi requeue is not supported)
1084 * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1085 * uaddr2 atomically on behalf of the top waiter.
1088 * >=0 - on success, the number of tasks requeued or woken
1091 static int futex_requeue(u32 __user
*uaddr1
, int fshared
, u32 __user
*uaddr2
,
1092 int nr_wake
, int nr_requeue
, u32
*cmpval
,
1095 union futex_key key1
= FUTEX_KEY_INIT
, key2
= FUTEX_KEY_INIT
;
1096 int drop_count
= 0, task_count
= 0, ret
;
1097 struct futex_pi_state
*pi_state
= NULL
;
1098 struct futex_hash_bucket
*hb1
, *hb2
;
1099 struct plist_head
*head1
;
1100 struct futex_q
*this, *next
;
1105 * requeue_pi requires a pi_state, try to allocate it now
1106 * without any locks in case it fails.
1108 if (refill_pi_state_cache())
1111 * requeue_pi must wake as many tasks as it can, up to nr_wake
1112 * + nr_requeue, since it acquires the rt_mutex prior to
1113 * returning to userspace, so as to not leave the rt_mutex with
1114 * waiters and no owner. However, second and third wake-ups
1115 * cannot be predicted as they involve race conditions with the
1116 * first wake and a fault while looking up the pi_state. Both
1117 * pthread_cond_signal() and pthread_cond_broadcast() should
1125 if (pi_state
!= NULL
) {
1127 * We will have to lookup the pi_state again, so free this one
1128 * to keep the accounting correct.
1130 free_pi_state(pi_state
);
1134 ret
= get_futex_key(uaddr1
, fshared
, &key1
);
1135 if (unlikely(ret
!= 0))
1137 ret
= get_futex_key(uaddr2
, fshared
, &key2
);
1138 if (unlikely(ret
!= 0))
1141 hb1
= hash_futex(&key1
);
1142 hb2
= hash_futex(&key2
);
1145 double_lock_hb(hb1
, hb2
);
1147 if (likely(cmpval
!= NULL
)) {
1150 ret
= get_futex_value_locked(&curval
, uaddr1
);
1152 if (unlikely(ret
)) {
1153 double_unlock_hb(hb1
, hb2
);
1155 ret
= get_user(curval
, uaddr1
);
1162 put_futex_key(fshared
, &key2
);
1163 put_futex_key(fshared
, &key1
);
1166 if (curval
!= *cmpval
) {
1172 if (requeue_pi
&& (task_count
- nr_wake
< nr_requeue
)) {
1174 * Attempt to acquire uaddr2 and wake the top waiter. If we
1175 * intend to requeue waiters, force setting the FUTEX_WAITERS
1176 * bit. We force this here where we are able to easily handle
1177 * faults rather in the requeue loop below.
1179 ret
= futex_proxy_trylock_atomic(uaddr2
, hb1
, hb2
, &key1
,
1180 &key2
, &pi_state
, nr_requeue
);
1183 * At this point the top_waiter has either taken uaddr2 or is
1184 * waiting on it. If the former, then the pi_state will not
1185 * exist yet, look it up one more time to ensure we have a
1191 ret
= get_futex_value_locked(&curval2
, uaddr2
);
1193 ret
= lookup_pi_state(curval2
, hb2
, &key2
,
1201 double_unlock_hb(hb1
, hb2
);
1202 put_futex_key(fshared
, &key2
);
1203 put_futex_key(fshared
, &key1
);
1204 ret
= get_user(curval2
, uaddr2
);
1209 /* The owner was exiting, try again. */
1210 double_unlock_hb(hb1
, hb2
);
1211 put_futex_key(fshared
, &key2
);
1212 put_futex_key(fshared
, &key1
);
1220 head1
= &hb1
->chain
;
1221 plist_for_each_entry_safe(this, next
, head1
, list
) {
1222 if (task_count
- nr_wake
>= nr_requeue
)
1225 if (!match_futex(&this->key
, &key1
))
1228 WARN_ON(!requeue_pi
&& this->rt_waiter
);
1229 WARN_ON(requeue_pi
&& !this->rt_waiter
);
1232 * Wake nr_wake waiters. For requeue_pi, if we acquired the
1233 * lock, we already woke the top_waiter. If not, it will be
1234 * woken by futex_unlock_pi().
1236 if (++task_count
<= nr_wake
&& !requeue_pi
) {
1242 * Requeue nr_requeue waiters and possibly one more in the case
1243 * of requeue_pi if we couldn't acquire the lock atomically.
1246 /* Prepare the waiter to take the rt_mutex. */
1247 atomic_inc(&pi_state
->refcount
);
1248 this->pi_state
= pi_state
;
1249 ret
= rt_mutex_start_proxy_lock(&pi_state
->pi_mutex
,
1253 /* We got the lock. */
1254 requeue_pi_wake_futex(this, &key2
);
1258 this->pi_state
= NULL
;
1259 free_pi_state(pi_state
);
1263 requeue_futex(this, hb1
, hb2
, &key2
);
1268 double_unlock_hb(hb1
, hb2
);
1270 /* drop_futex_key_refs() must be called outside the spinlocks. */
1271 while (--drop_count
>= 0)
1272 drop_futex_key_refs(&key1
);
1275 put_futex_key(fshared
, &key2
);
1277 put_futex_key(fshared
, &key1
);
1279 if (pi_state
!= NULL
)
1280 free_pi_state(pi_state
);
1281 return ret
? ret
: task_count
;
1284 /* The key must be already stored in q->key. */
1285 static inline struct futex_hash_bucket
*queue_lock(struct futex_q
*q
)
1287 struct futex_hash_bucket
*hb
;
1289 get_futex_key_refs(&q
->key
);
1290 hb
= hash_futex(&q
->key
);
1291 q
->lock_ptr
= &hb
->lock
;
1293 spin_lock(&hb
->lock
);
1297 static inline void queue_me(struct futex_q
*q
, struct futex_hash_bucket
*hb
)
1302 * The priority used to register this element is
1303 * - either the real thread-priority for the real-time threads
1304 * (i.e. threads with a priority lower than MAX_RT_PRIO)
1305 * - or MAX_RT_PRIO for non-RT threads.
1306 * Thus, all RT-threads are woken first in priority order, and
1307 * the others are woken last, in FIFO order.
1309 prio
= min(current
->normal_prio
, MAX_RT_PRIO
);
1311 plist_node_init(&q
->list
, prio
);
1312 #ifdef CONFIG_DEBUG_PI_LIST
1313 q
->list
.plist
.lock
= &hb
->lock
;
1315 plist_add(&q
->list
, &hb
->chain
);
1317 spin_unlock(&hb
->lock
);
1321 queue_unlock(struct futex_q
*q
, struct futex_hash_bucket
*hb
)
1323 spin_unlock(&hb
->lock
);
1324 drop_futex_key_refs(&q
->key
);
1328 * queue_me and unqueue_me must be called as a pair, each
1329 * exactly once. They are called with the hashed spinlock held.
1332 /* Return 1 if we were still queued (ie. 0 means we were woken) */
1333 static int unqueue_me(struct futex_q
*q
)
1335 spinlock_t
*lock_ptr
;
1338 /* In the common case we don't take the spinlock, which is nice. */
1340 lock_ptr
= q
->lock_ptr
;
1342 if (lock_ptr
!= NULL
) {
1343 spin_lock(lock_ptr
);
1345 * q->lock_ptr can change between reading it and
1346 * spin_lock(), causing us to take the wrong lock. This
1347 * corrects the race condition.
1349 * Reasoning goes like this: if we have the wrong lock,
1350 * q->lock_ptr must have changed (maybe several times)
1351 * between reading it and the spin_lock(). It can
1352 * change again after the spin_lock() but only if it was
1353 * already changed before the spin_lock(). It cannot,
1354 * however, change back to the original value. Therefore
1355 * we can detect whether we acquired the correct lock.
1357 if (unlikely(lock_ptr
!= q
->lock_ptr
)) {
1358 spin_unlock(lock_ptr
);
1361 WARN_ON(plist_node_empty(&q
->list
));
1362 plist_del(&q
->list
, &q
->list
.plist
);
1364 BUG_ON(q
->pi_state
);
1366 spin_unlock(lock_ptr
);
1370 drop_futex_key_refs(&q
->key
);
1375 * PI futexes can not be requeued and must remove themself from the
1376 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1379 static void unqueue_me_pi(struct futex_q
*q
)
1381 WARN_ON(plist_node_empty(&q
->list
));
1382 plist_del(&q
->list
, &q
->list
.plist
);
1384 BUG_ON(!q
->pi_state
);
1385 free_pi_state(q
->pi_state
);
1388 spin_unlock(q
->lock_ptr
);
1390 drop_futex_key_refs(&q
->key
);
1394 * Fixup the pi_state owner with the new owner.
1396 * Must be called with hash bucket lock held and mm->sem held for non
1399 static int fixup_pi_state_owner(u32 __user
*uaddr
, struct futex_q
*q
,
1400 struct task_struct
*newowner
, int fshared
)
1402 u32 newtid
= task_pid_vnr(newowner
) | FUTEX_WAITERS
;
1403 struct futex_pi_state
*pi_state
= q
->pi_state
;
1404 struct task_struct
*oldowner
= pi_state
->owner
;
1405 u32 uval
, curval
, newval
;
1409 if (!pi_state
->owner
)
1410 newtid
|= FUTEX_OWNER_DIED
;
1413 * We are here either because we stole the rtmutex from the
1414 * pending owner or we are the pending owner which failed to
1415 * get the rtmutex. We have to replace the pending owner TID
1416 * in the user space variable. This must be atomic as we have
1417 * to preserve the owner died bit here.
1419 * Note: We write the user space value _before_ changing the pi_state
1420 * because we can fault here. Imagine swapped out pages or a fork
1421 * that marked all the anonymous memory readonly for cow.
1423 * Modifying pi_state _before_ the user space value would
1424 * leave the pi_state in an inconsistent state when we fault
1425 * here, because we need to drop the hash bucket lock to
1426 * handle the fault. This might be observed in the PID check
1427 * in lookup_pi_state.
1430 if (get_futex_value_locked(&uval
, uaddr
))
1434 newval
= (uval
& FUTEX_OWNER_DIED
) | newtid
;
1436 curval
= cmpxchg_futex_value_locked(uaddr
, uval
, newval
);
1438 if (curval
== -EFAULT
)
1446 * We fixed up user space. Now we need to fix the pi_state
1449 if (pi_state
->owner
!= NULL
) {
1450 spin_lock_irq(&pi_state
->owner
->pi_lock
);
1451 WARN_ON(list_empty(&pi_state
->list
));
1452 list_del_init(&pi_state
->list
);
1453 spin_unlock_irq(&pi_state
->owner
->pi_lock
);
1456 pi_state
->owner
= newowner
;
1458 spin_lock_irq(&newowner
->pi_lock
);
1459 WARN_ON(!list_empty(&pi_state
->list
));
1460 list_add(&pi_state
->list
, &newowner
->pi_state_list
);
1461 spin_unlock_irq(&newowner
->pi_lock
);
1465 * To handle the page fault we need to drop the hash bucket
1466 * lock here. That gives the other task (either the pending
1467 * owner itself or the task which stole the rtmutex) the
1468 * chance to try the fixup of the pi_state. So once we are
1469 * back from handling the fault we need to check the pi_state
1470 * after reacquiring the hash bucket lock and before trying to
1471 * do another fixup. When the fixup has been done already we
1475 spin_unlock(q
->lock_ptr
);
1477 ret
= get_user(uval
, uaddr
);
1479 spin_lock(q
->lock_ptr
);
1482 * Check if someone else fixed it for us:
1484 if (pi_state
->owner
!= oldowner
)
1494 * In case we must use restart_block to restart a futex_wait,
1495 * we encode in the 'flags' shared capability
1497 #define FLAGS_SHARED 0x01
1498 #define FLAGS_CLOCKRT 0x02
1499 #define FLAGS_HAS_TIMEOUT 0x04
1501 static long futex_wait_restart(struct restart_block
*restart
);
1502 static long futex_lock_pi_restart(struct restart_block
*restart
);
1505 * fixup_owner() - Post lock pi_state and corner case management
1506 * @uaddr: user address of the futex
1507 * @fshared: whether the futex is shared (1) or not (0)
1508 * @q: futex_q (contains pi_state and access to the rt_mutex)
1509 * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
1511 * After attempting to lock an rt_mutex, this function is called to cleanup
1512 * the pi_state owner as well as handle race conditions that may allow us to
1513 * acquire the lock. Must be called with the hb lock held.
1516 * 1 - success, lock taken
1517 * 0 - success, lock not taken
1518 * <0 - on error (-EFAULT)
1520 static int fixup_owner(u32 __user
*uaddr
, int fshared
, struct futex_q
*q
,
1523 struct task_struct
*owner
;
1528 * Got the lock. We might not be the anticipated owner if we
1529 * did a lock-steal - fix up the PI-state in that case:
1531 if (q
->pi_state
->owner
!= current
)
1532 ret
= fixup_pi_state_owner(uaddr
, q
, current
, fshared
);
1537 * Catch the rare case, where the lock was released when we were on the
1538 * way back before we locked the hash bucket.
1540 if (q
->pi_state
->owner
== current
) {
1542 * Try to get the rt_mutex now. This might fail as some other
1543 * task acquired the rt_mutex after we removed ourself from the
1544 * rt_mutex waiters list.
1546 if (rt_mutex_trylock(&q
->pi_state
->pi_mutex
)) {
1552 * pi_state is incorrect, some other task did a lock steal and
1553 * we returned due to timeout or signal without taking the
1554 * rt_mutex. Too late. We can access the rt_mutex_owner without
1555 * locking, as the other task is now blocked on the hash bucket
1556 * lock. Fix the state up.
1558 owner
= rt_mutex_owner(&q
->pi_state
->pi_mutex
);
1559 ret
= fixup_pi_state_owner(uaddr
, q
, owner
, fshared
);
1564 * Paranoia check. If we did not take the lock, then we should not be
1565 * the owner, nor the pending owner, of the rt_mutex.
1567 if (rt_mutex_owner(&q
->pi_state
->pi_mutex
) == current
)
1568 printk(KERN_ERR
"fixup_owner: ret = %d pi-mutex: %p "
1569 "pi-state %p\n", ret
,
1570 q
->pi_state
->pi_mutex
.owner
,
1571 q
->pi_state
->owner
);
1574 return ret
? ret
: locked
;
1578 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
1579 * @hb: the futex hash bucket, must be locked by the caller
1580 * @q: the futex_q to queue up on
1581 * @timeout: the prepared hrtimer_sleeper, or null for no timeout
1583 static void futex_wait_queue_me(struct futex_hash_bucket
*hb
, struct futex_q
*q
,
1584 struct hrtimer_sleeper
*timeout
)
1589 * There might have been scheduling since the queue_me(), as we
1590 * cannot hold a spinlock across the get_user() in case it
1591 * faults, and we cannot just set TASK_INTERRUPTIBLE state when
1592 * queueing ourselves into the futex hash. This code thus has to
1593 * rely on the futex_wake() code removing us from hash when it
1596 set_current_state(TASK_INTERRUPTIBLE
);
1600 hrtimer_start_expires(&timeout
->timer
, HRTIMER_MODE_ABS
);
1601 if (!hrtimer_active(&timeout
->timer
))
1602 timeout
->task
= NULL
;
1606 * !plist_node_empty() is safe here without any lock.
1607 * q.lock_ptr != 0 is not safe, because of ordering against wakeup.
1609 if (likely(!plist_node_empty(&q
->list
))) {
1611 * If the timer has already expired, current will already be
1612 * flagged for rescheduling. Only call schedule if there
1613 * is no timeout, or if it has yet to expire.
1615 if (!timeout
|| timeout
->task
)
1618 __set_current_state(TASK_RUNNING
);
1622 * futex_wait_setup() - Prepare to wait on a futex
1623 * @uaddr: the futex userspace address
1624 * @val: the expected value
1625 * @fshared: whether the futex is shared (1) or not (0)
1626 * @q: the associated futex_q
1627 * @hb: storage for hash_bucket pointer to be returned to caller
1629 * Setup the futex_q and locate the hash_bucket. Get the futex value and
1630 * compare it with the expected value. Handle atomic faults internally.
1631 * Return with the hb lock held and a q.key reference on success, and unlocked
1632 * with no q.key reference on failure.
1635 * 0 - uaddr contains val and hb has been locked
1636 * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlcoked
1638 static int futex_wait_setup(u32 __user
*uaddr
, u32 val
, int fshared
,
1639 struct futex_q
*q
, struct futex_hash_bucket
**hb
)
1645 * Access the page AFTER the hash-bucket is locked.
1646 * Order is important:
1648 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1649 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
1651 * The basic logical guarantee of a futex is that it blocks ONLY
1652 * if cond(var) is known to be true at the time of blocking, for
1653 * any cond. If we queued after testing *uaddr, that would open
1654 * a race condition where we could block indefinitely with
1655 * cond(var) false, which would violate the guarantee.
1657 * A consequence is that futex_wait() can return zero and absorb
1658 * a wakeup when *uaddr != val on entry to the syscall. This is
1662 q
->key
= FUTEX_KEY_INIT
;
1663 ret
= get_futex_key(uaddr
, fshared
, &q
->key
);
1664 if (unlikely(ret
!= 0))
1668 *hb
= queue_lock(q
);
1670 ret
= get_futex_value_locked(&uval
, uaddr
);
1673 queue_unlock(q
, *hb
);
1675 ret
= get_user(uval
, uaddr
);
1682 put_futex_key(fshared
, &q
->key
);
1687 queue_unlock(q
, *hb
);
1693 put_futex_key(fshared
, &q
->key
);
1697 static int futex_wait(u32 __user
*uaddr
, int fshared
,
1698 u32 val
, ktime_t
*abs_time
, u32 bitset
, int clockrt
)
1700 struct hrtimer_sleeper timeout
, *to
= NULL
;
1701 struct restart_block
*restart
;
1702 struct futex_hash_bucket
*hb
;
1716 hrtimer_init_on_stack(&to
->timer
, clockrt
? CLOCK_REALTIME
:
1717 CLOCK_MONOTONIC
, HRTIMER_MODE_ABS
);
1718 hrtimer_init_sleeper(to
, current
);
1719 hrtimer_set_expires_range_ns(&to
->timer
, *abs_time
,
1720 current
->timer_slack_ns
);
1723 /* Prepare to wait on uaddr. */
1724 ret
= futex_wait_setup(uaddr
, val
, fshared
, &q
, &hb
);
1728 /* queue_me and wait for wakeup, timeout, or a signal. */
1729 futex_wait_queue_me(hb
, &q
, to
);
1731 /* If we were woken (and unqueued), we succeeded, whatever. */
1733 if (!unqueue_me(&q
))
1736 if (to
&& !to
->task
)
1740 * We expect signal_pending(current), but another thread may
1741 * have handled it for us already.
1747 restart
= ¤t_thread_info()->restart_block
;
1748 restart
->fn
= futex_wait_restart
;
1749 restart
->futex
.uaddr
= (u32
*)uaddr
;
1750 restart
->futex
.val
= val
;
1751 restart
->futex
.time
= abs_time
->tv64
;
1752 restart
->futex
.bitset
= bitset
;
1753 restart
->futex
.flags
= FLAGS_HAS_TIMEOUT
;
1756 restart
->futex
.flags
|= FLAGS_SHARED
;
1758 restart
->futex
.flags
|= FLAGS_CLOCKRT
;
1760 ret
= -ERESTART_RESTARTBLOCK
;
1763 put_futex_key(fshared
, &q
.key
);
1766 hrtimer_cancel(&to
->timer
);
1767 destroy_hrtimer_on_stack(&to
->timer
);
1773 static long futex_wait_restart(struct restart_block
*restart
)
1775 u32 __user
*uaddr
= (u32 __user
*)restart
->futex
.uaddr
;
1777 ktime_t t
, *tp
= NULL
;
1779 if (restart
->futex
.flags
& FLAGS_HAS_TIMEOUT
) {
1780 t
.tv64
= restart
->futex
.time
;
1783 restart
->fn
= do_no_restart_syscall
;
1784 if (restart
->futex
.flags
& FLAGS_SHARED
)
1786 return (long)futex_wait(uaddr
, fshared
, restart
->futex
.val
, tp
,
1787 restart
->futex
.bitset
,
1788 restart
->futex
.flags
& FLAGS_CLOCKRT
);
1793 * Userspace tried a 0 -> TID atomic transition of the futex value
1794 * and failed. The kernel side here does the whole locking operation:
1795 * if there are waiters then it will block, it does PI, etc. (Due to
1796 * races the kernel might see a 0 value of the futex too.)
1798 static int futex_lock_pi(u32 __user
*uaddr
, int fshared
,
1799 int detect
, ktime_t
*time
, int trylock
)
1801 struct hrtimer_sleeper timeout
, *to
= NULL
;
1802 struct futex_hash_bucket
*hb
;
1807 if (refill_pi_state_cache())
1812 hrtimer_init_on_stack(&to
->timer
, CLOCK_REALTIME
,
1814 hrtimer_init_sleeper(to
, current
);
1815 hrtimer_set_expires(&to
->timer
, *time
);
1821 q
.key
= FUTEX_KEY_INIT
;
1822 ret
= get_futex_key(uaddr
, fshared
, &q
.key
);
1823 if (unlikely(ret
!= 0))
1827 hb
= queue_lock(&q
);
1829 ret
= futex_lock_pi_atomic(uaddr
, hb
, &q
.key
, &q
.pi_state
, current
, 0);
1830 if (unlikely(ret
)) {
1833 /* We got the lock. */
1835 goto out_unlock_put_key
;
1840 * Task is exiting and we just wait for the
1843 queue_unlock(&q
, hb
);
1844 put_futex_key(fshared
, &q
.key
);
1848 goto out_unlock_put_key
;
1853 * Only actually queue now that the atomic ops are done:
1857 WARN_ON(!q
.pi_state
);
1859 * Block on the PI mutex:
1862 ret
= rt_mutex_timed_lock(&q
.pi_state
->pi_mutex
, to
, 1);
1864 ret
= rt_mutex_trylock(&q
.pi_state
->pi_mutex
);
1865 /* Fixup the trylock return value: */
1866 ret
= ret
? 0 : -EWOULDBLOCK
;
1869 spin_lock(q
.lock_ptr
);
1871 * Fixup the pi_state owner and possibly acquire the lock if we
1874 res
= fixup_owner(uaddr
, fshared
, &q
, !ret
);
1876 * If fixup_owner() returned an error, proprogate that. If it acquired
1877 * the lock, clear our -ETIMEDOUT or -EINTR.
1880 ret
= (res
< 0) ? res
: 0;
1883 * If fixup_owner() faulted and was unable to handle the fault, unlock
1884 * it and return the fault to userspace.
1886 if (ret
&& (rt_mutex_owner(&q
.pi_state
->pi_mutex
) == current
))
1887 rt_mutex_unlock(&q
.pi_state
->pi_mutex
);
1889 /* Unqueue and drop the lock */
1895 queue_unlock(&q
, hb
);
1898 put_futex_key(fshared
, &q
.key
);
1901 destroy_hrtimer_on_stack(&to
->timer
);
1902 return ret
!= -EINTR
? ret
: -ERESTARTNOINTR
;
1906 * We have to r/w *(int __user *)uaddr, and we have to modify it
1907 * atomically. Therefore, if we continue to fault after get_user()
1908 * below, we need to handle the fault ourselves, while still holding
1909 * the mmap_sem. This can occur if the uaddr is under contention as
1910 * we have to drop the mmap_sem in order to call get_user().
1912 queue_unlock(&q
, hb
);
1914 ret
= get_user(uval
, uaddr
);
1921 put_futex_key(fshared
, &q
.key
);
1925 static long futex_lock_pi_restart(struct restart_block
*restart
)
1927 u32 __user
*uaddr
= (u32 __user
*)restart
->futex
.uaddr
;
1928 ktime_t t
, *tp
= NULL
;
1929 int fshared
= restart
->futex
.flags
& FLAGS_SHARED
;
1931 if (restart
->futex
.flags
& FLAGS_HAS_TIMEOUT
) {
1932 t
.tv64
= restart
->futex
.time
;
1935 restart
->fn
= do_no_restart_syscall
;
1937 return (long)futex_lock_pi(uaddr
, fshared
, restart
->futex
.val
, tp
, 0);
1941 * Userspace attempted a TID -> 0 atomic transition, and failed.
1942 * This is the in-kernel slowpath: we look up the PI state (if any),
1943 * and do the rt-mutex unlock.
1945 static int futex_unlock_pi(u32 __user
*uaddr
, int fshared
)
1947 struct futex_hash_bucket
*hb
;
1948 struct futex_q
*this, *next
;
1950 struct plist_head
*head
;
1951 union futex_key key
= FUTEX_KEY_INIT
;
1955 if (get_user(uval
, uaddr
))
1958 * We release only a lock we actually own:
1960 if ((uval
& FUTEX_TID_MASK
) != task_pid_vnr(current
))
1963 ret
= get_futex_key(uaddr
, fshared
, &key
);
1964 if (unlikely(ret
!= 0))
1967 hb
= hash_futex(&key
);
1968 spin_lock(&hb
->lock
);
1971 * To avoid races, try to do the TID -> 0 atomic transition
1972 * again. If it succeeds then we can return without waking
1975 if (!(uval
& FUTEX_OWNER_DIED
))
1976 uval
= cmpxchg_futex_value_locked(uaddr
, task_pid_vnr(current
), 0);
1979 if (unlikely(uval
== -EFAULT
))
1982 * Rare case: we managed to release the lock atomically,
1983 * no need to wake anyone else up:
1985 if (unlikely(uval
== task_pid_vnr(current
)))
1989 * Ok, other tasks may need to be woken up - check waiters
1990 * and do the wakeup if necessary:
1994 plist_for_each_entry_safe(this, next
, head
, list
) {
1995 if (!match_futex (&this->key
, &key
))
1997 ret
= wake_futex_pi(uaddr
, uval
, this);
1999 * The atomic access to the futex value
2000 * generated a pagefault, so retry the
2001 * user-access and the wakeup:
2008 * No waiters - kernel unlocks the futex:
2010 if (!(uval
& FUTEX_OWNER_DIED
)) {
2011 ret
= unlock_futex_pi(uaddr
, uval
);
2017 spin_unlock(&hb
->lock
);
2018 put_futex_key(fshared
, &key
);
2025 * We have to r/w *(int __user *)uaddr, and we have to modify it
2026 * atomically. Therefore, if we continue to fault after get_user()
2027 * below, we need to handle the fault ourselves, while still holding
2028 * the mmap_sem. This can occur if the uaddr is under contention as
2029 * we have to drop the mmap_sem in order to call get_user().
2031 spin_unlock(&hb
->lock
);
2032 put_futex_key(fshared
, &key
);
2034 ret
= get_user(uval
, uaddr
);
2042 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2043 * @hb: the hash_bucket futex_q was original enqueued on
2044 * @q: the futex_q woken while waiting to be requeued
2045 * @key2: the futex_key of the requeue target futex
2046 * @timeout: the timeout associated with the wait (NULL if none)
2048 * Detect if the task was woken on the initial futex as opposed to the requeue
2049 * target futex. If so, determine if it was a timeout or a signal that caused
2050 * the wakeup and return the appropriate error code to the caller. Must be
2051 * called with the hb lock held.
2054 * 0 - no early wakeup detected
2055 * <0 - -ETIMEDOUT or -ERESTARTSYS (FIXME: or ERESTARTNOINTR?)
2058 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket
*hb
,
2059 struct futex_q
*q
, union futex_key
*key2
,
2060 struct hrtimer_sleeper
*timeout
)
2065 * With the hb lock held, we avoid races while we process the wakeup.
2066 * We only need to hold hb (and not hb2) to ensure atomicity as the
2067 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2068 * It can't be requeued from uaddr2 to something else since we don't
2069 * support a PI aware source futex for requeue.
2071 if (!match_futex(&q
->key
, key2
)) {
2072 WARN_ON(q
->lock_ptr
&& (&hb
->lock
!= q
->lock_ptr
));
2074 * We were woken prior to requeue by a timeout or a signal.
2075 * Unqueue the futex_q and determine which it was.
2077 plist_del(&q
->list
, &q
->list
.plist
);
2078 drop_futex_key_refs(&q
->key
);
2080 if (timeout
&& !timeout
->task
)
2084 * We expect signal_pending(current), but another
2085 * thread may have handled it for us already.
2087 /* FIXME: ERESTARTSYS or ERESTARTNOINTR? Do we care if
2088 * the user specified SA_RESTART or not? */
2096 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2097 * @uaddr: the futex we initialyl wait on (non-pi)
2098 * @fshared: whether the futexes are shared (1) or not (0). They must be
2099 * the same type, no requeueing from private to shared, etc.
2100 * @val: the expected value of uaddr
2101 * @abs_time: absolute timeout
2102 * @bitset: 32 bit wakeup bitset set by userspace, defaults to all.
2103 * @clockrt: whether to use CLOCK_REALTIME (1) or CLOCK_MONOTONIC (0)
2104 * @uaddr2: the pi futex we will take prior to returning to user-space
2106 * The caller will wait on uaddr and will be requeued by futex_requeue() to
2107 * uaddr2 which must be PI aware. Normal wakeup will wake on uaddr2 and
2108 * complete the acquisition of the rt_mutex prior to returning to userspace.
2109 * This ensures the rt_mutex maintains an owner when it has waiters; without
2110 * one, the pi logic wouldn't know which task to boost/deboost, if there was a
2113 * We call schedule in futex_wait_queue_me() when we enqueue and return there
2114 * via the following:
2115 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2116 * 2) wakeup on uaddr2 after a requeue and subsequent unlock
2117 * 3) signal (before or after requeue)
2118 * 4) timeout (before or after requeue)
2120 * If 3, we setup a restart_block with futex_wait_requeue_pi() as the function.
2122 * If 2, we may then block on trying to take the rt_mutex and return via:
2123 * 5) successful lock
2126 * 8) other lock acquisition failure
2128 * If 6, we setup a restart_block with futex_lock_pi() as the function.
2130 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2136 static int futex_wait_requeue_pi(u32 __user
*uaddr
, int fshared
,
2137 u32 val
, ktime_t
*abs_time
, u32 bitset
,
2138 int clockrt
, u32 __user
*uaddr2
)
2140 struct hrtimer_sleeper timeout
, *to
= NULL
;
2141 struct rt_mutex_waiter rt_waiter
;
2142 struct rt_mutex
*pi_mutex
= NULL
;
2143 struct restart_block
*restart
;
2144 struct futex_hash_bucket
*hb
;
2145 union futex_key key2
;
2155 hrtimer_init_on_stack(&to
->timer
, clockrt
? CLOCK_REALTIME
:
2156 CLOCK_MONOTONIC
, HRTIMER_MODE_ABS
);
2157 hrtimer_init_sleeper(to
, current
);
2158 hrtimer_set_expires_range_ns(&to
->timer
, *abs_time
,
2159 current
->timer_slack_ns
);
2163 * The waiter is allocated on our stack, manipulated by the requeue
2164 * code while we sleep on uaddr.
2166 debug_rt_mutex_init_waiter(&rt_waiter
);
2167 rt_waiter
.task
= NULL
;
2171 q
.rt_waiter
= &rt_waiter
;
2173 key2
= FUTEX_KEY_INIT
;
2174 ret
= get_futex_key(uaddr2
, fshared
, &key2
);
2175 if (unlikely(ret
!= 0))
2178 /* Prepare to wait on uaddr. */
2179 ret
= futex_wait_setup(uaddr
, val
, fshared
, &q
, &hb
);
2181 put_futex_key(fshared
, &key2
);
2185 /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2186 futex_wait_queue_me(hb
, &q
, to
);
2188 spin_lock(&hb
->lock
);
2189 ret
= handle_early_requeue_pi_wakeup(hb
, &q
, &key2
, to
);
2190 spin_unlock(&hb
->lock
);
2195 * In order for us to be here, we know our q.key == key2, and since
2196 * we took the hb->lock above, we also know that futex_requeue() has
2197 * completed and we no longer have to concern ourselves with a wakeup
2198 * race with the atomic proxy lock acquition by the requeue code.
2201 /* Check if the requeue code acquired the second futex for us. */
2204 * Got the lock. We might not be the anticipated owner if we
2205 * did a lock-steal - fix up the PI-state in that case.
2207 if (q
.pi_state
&& (q
.pi_state
->owner
!= current
)) {
2208 spin_lock(q
.lock_ptr
);
2209 ret
= fixup_pi_state_owner(uaddr2
, &q
, current
,
2211 spin_unlock(q
.lock_ptr
);
2215 * We have been woken up by futex_unlock_pi(), a timeout, or a
2216 * signal. futex_unlock_pi() will not destroy the lock_ptr nor
2219 WARN_ON(!&q
.pi_state
);
2220 pi_mutex
= &q
.pi_state
->pi_mutex
;
2221 ret
= rt_mutex_finish_proxy_lock(pi_mutex
, to
, &rt_waiter
, 1);
2222 debug_rt_mutex_free_waiter(&rt_waiter
);
2224 spin_lock(q
.lock_ptr
);
2226 * Fixup the pi_state owner and possibly acquire the lock if we
2229 res
= fixup_owner(uaddr2
, fshared
, &q
, !ret
);
2231 * If fixup_owner() returned an error, proprogate that. If it
2232 * acquired the lock, clear our -ETIMEDOUT or -EINTR.
2235 ret
= (res
< 0) ? res
: 0;
2237 /* Unqueue and drop the lock. */
2242 * If fixup_pi_state_owner() faulted and was unable to handle the
2243 * fault, unlock the rt_mutex and return the fault to userspace.
2245 if (ret
== -EFAULT
) {
2246 if (rt_mutex_owner(pi_mutex
) == current
)
2247 rt_mutex_unlock(pi_mutex
);
2248 } else if (ret
== -EINTR
) {
2250 if (get_user(uval
, uaddr2
))
2254 * We've already been requeued, so restart by calling
2255 * futex_lock_pi() directly, rather then returning to this
2258 ret
= -ERESTART_RESTARTBLOCK
;
2259 restart
= ¤t_thread_info()->restart_block
;
2260 restart
->fn
= futex_lock_pi_restart
;
2261 restart
->futex
.uaddr
= (u32
*)uaddr2
;
2262 restart
->futex
.val
= uval
;
2263 restart
->futex
.flags
= 0;
2265 restart
->futex
.flags
|= FLAGS_HAS_TIMEOUT
;
2266 restart
->futex
.time
= abs_time
->tv64
;
2270 restart
->futex
.flags
|= FLAGS_SHARED
;
2272 restart
->futex
.flags
|= FLAGS_CLOCKRT
;
2276 put_futex_key(fshared
, &q
.key
);
2277 put_futex_key(fshared
, &key2
);
2281 hrtimer_cancel(&to
->timer
);
2282 destroy_hrtimer_on_stack(&to
->timer
);
2288 * Support for robust futexes: the kernel cleans up held futexes at
2291 * Implementation: user-space maintains a per-thread list of locks it
2292 * is holding. Upon do_exit(), the kernel carefully walks this list,
2293 * and marks all locks that are owned by this thread with the
2294 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2295 * always manipulated with the lock held, so the list is private and
2296 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2297 * field, to allow the kernel to clean up if the thread dies after
2298 * acquiring the lock, but just before it could have added itself to
2299 * the list. There can only be one such pending lock.
2303 * sys_set_robust_list - set the robust-futex list head of a task
2304 * @head: pointer to the list-head
2305 * @len: length of the list-head, as userspace expects
2307 SYSCALL_DEFINE2(set_robust_list
, struct robust_list_head __user
*, head
,
2310 if (!futex_cmpxchg_enabled
)
2313 * The kernel knows only one size for now:
2315 if (unlikely(len
!= sizeof(*head
)))
2318 current
->robust_list
= head
;
2324 * sys_get_robust_list - get the robust-futex list head of a task
2325 * @pid: pid of the process [zero for current task]
2326 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
2327 * @len_ptr: pointer to a length field, the kernel fills in the header size
2329 SYSCALL_DEFINE3(get_robust_list
, int, pid
,
2330 struct robust_list_head __user
* __user
*, head_ptr
,
2331 size_t __user
*, len_ptr
)
2333 struct robust_list_head __user
*head
;
2335 const struct cred
*cred
= current_cred(), *pcred
;
2337 if (!futex_cmpxchg_enabled
)
2341 head
= current
->robust_list
;
2343 struct task_struct
*p
;
2347 p
= find_task_by_vpid(pid
);
2351 pcred
= __task_cred(p
);
2352 if (cred
->euid
!= pcred
->euid
&&
2353 cred
->euid
!= pcred
->uid
&&
2354 !capable(CAP_SYS_PTRACE
))
2356 head
= p
->robust_list
;
2360 if (put_user(sizeof(*head
), len_ptr
))
2362 return put_user(head
, head_ptr
);
2371 * Process a futex-list entry, check whether it's owned by the
2372 * dying task, and do notification if so:
2374 int handle_futex_death(u32 __user
*uaddr
, struct task_struct
*curr
, int pi
)
2376 u32 uval
, nval
, mval
;
2379 if (get_user(uval
, uaddr
))
2382 if ((uval
& FUTEX_TID_MASK
) == task_pid_vnr(curr
)) {
2384 * Ok, this dying thread is truly holding a futex
2385 * of interest. Set the OWNER_DIED bit atomically
2386 * via cmpxchg, and if the value had FUTEX_WAITERS
2387 * set, wake up a waiter (if any). (We have to do a
2388 * futex_wake() even if OWNER_DIED is already set -
2389 * to handle the rare but possible case of recursive
2390 * thread-death.) The rest of the cleanup is done in
2393 mval
= (uval
& FUTEX_WAITERS
) | FUTEX_OWNER_DIED
;
2394 nval
= futex_atomic_cmpxchg_inatomic(uaddr
, uval
, mval
);
2396 if (nval
== -EFAULT
)
2403 * Wake robust non-PI futexes here. The wakeup of
2404 * PI futexes happens in exit_pi_state():
2406 if (!pi
&& (uval
& FUTEX_WAITERS
))
2407 futex_wake(uaddr
, 1, 1, FUTEX_BITSET_MATCH_ANY
);
2413 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
2415 static inline int fetch_robust_entry(struct robust_list __user
**entry
,
2416 struct robust_list __user
* __user
*head
,
2419 unsigned long uentry
;
2421 if (get_user(uentry
, (unsigned long __user
*)head
))
2424 *entry
= (void __user
*)(uentry
& ~1UL);
2431 * Walk curr->robust_list (very carefully, it's a userspace list!)
2432 * and mark any locks found there dead, and notify any waiters.
2434 * We silently return on any sign of list-walking problem.
2436 void exit_robust_list(struct task_struct
*curr
)
2438 struct robust_list_head __user
*head
= curr
->robust_list
;
2439 struct robust_list __user
*entry
, *next_entry
, *pending
;
2440 unsigned int limit
= ROBUST_LIST_LIMIT
, pi
, next_pi
, pip
;
2441 unsigned long futex_offset
;
2444 if (!futex_cmpxchg_enabled
)
2448 * Fetch the list head (which was registered earlier, via
2449 * sys_set_robust_list()):
2451 if (fetch_robust_entry(&entry
, &head
->list
.next
, &pi
))
2454 * Fetch the relative futex offset:
2456 if (get_user(futex_offset
, &head
->futex_offset
))
2459 * Fetch any possibly pending lock-add first, and handle it
2462 if (fetch_robust_entry(&pending
, &head
->list_op_pending
, &pip
))
2465 next_entry
= NULL
; /* avoid warning with gcc */
2466 while (entry
!= &head
->list
) {
2468 * Fetch the next entry in the list before calling
2469 * handle_futex_death:
2471 rc
= fetch_robust_entry(&next_entry
, &entry
->next
, &next_pi
);
2473 * A pending lock might already be on the list, so
2474 * don't process it twice:
2476 if (entry
!= pending
)
2477 if (handle_futex_death((void __user
*)entry
+ futex_offset
,
2485 * Avoid excessively long or circular lists:
2494 handle_futex_death((void __user
*)pending
+ futex_offset
,
2498 long do_futex(u32 __user
*uaddr
, int op
, u32 val
, ktime_t
*timeout
,
2499 u32 __user
*uaddr2
, u32 val2
, u32 val3
)
2501 int clockrt
, ret
= -ENOSYS
;
2502 int cmd
= op
& FUTEX_CMD_MASK
;
2505 if (!(op
& FUTEX_PRIVATE_FLAG
))
2508 clockrt
= op
& FUTEX_CLOCK_REALTIME
;
2509 if (clockrt
&& cmd
!= FUTEX_WAIT_BITSET
&& cmd
!= FUTEX_WAIT_REQUEUE_PI
)
2514 val3
= FUTEX_BITSET_MATCH_ANY
;
2515 case FUTEX_WAIT_BITSET
:
2516 ret
= futex_wait(uaddr
, fshared
, val
, timeout
, val3
, clockrt
);
2519 val3
= FUTEX_BITSET_MATCH_ANY
;
2520 case FUTEX_WAKE_BITSET
:
2521 ret
= futex_wake(uaddr
, fshared
, val
, val3
);
2524 ret
= futex_requeue(uaddr
, fshared
, uaddr2
, val
, val2
, NULL
, 0);
2526 case FUTEX_CMP_REQUEUE
:
2527 ret
= futex_requeue(uaddr
, fshared
, uaddr2
, val
, val2
, &val3
,
2531 ret
= futex_wake_op(uaddr
, fshared
, uaddr2
, val
, val2
, val3
);
2534 if (futex_cmpxchg_enabled
)
2535 ret
= futex_lock_pi(uaddr
, fshared
, val
, timeout
, 0);
2537 case FUTEX_UNLOCK_PI
:
2538 if (futex_cmpxchg_enabled
)
2539 ret
= futex_unlock_pi(uaddr
, fshared
);
2541 case FUTEX_TRYLOCK_PI
:
2542 if (futex_cmpxchg_enabled
)
2543 ret
= futex_lock_pi(uaddr
, fshared
, 0, timeout
, 1);
2545 case FUTEX_WAIT_REQUEUE_PI
:
2546 val3
= FUTEX_BITSET_MATCH_ANY
;
2547 ret
= futex_wait_requeue_pi(uaddr
, fshared
, val
, timeout
, val3
,
2550 case FUTEX_CMP_REQUEUE_PI
:
2551 ret
= futex_requeue(uaddr
, fshared
, uaddr2
, val
, val2
, &val3
,
2561 SYSCALL_DEFINE6(futex
, u32 __user
*, uaddr
, int, op
, u32
, val
,
2562 struct timespec __user
*, utime
, u32 __user
*, uaddr2
,
2566 ktime_t t
, *tp
= NULL
;
2568 int cmd
= op
& FUTEX_CMD_MASK
;
2570 if (utime
&& (cmd
== FUTEX_WAIT
|| cmd
== FUTEX_LOCK_PI
||
2571 cmd
== FUTEX_WAIT_BITSET
||
2572 cmd
== FUTEX_WAIT_REQUEUE_PI
)) {
2573 if (copy_from_user(&ts
, utime
, sizeof(ts
)) != 0)
2575 if (!timespec_valid(&ts
))
2578 t
= timespec_to_ktime(ts
);
2579 if (cmd
== FUTEX_WAIT
)
2580 t
= ktime_add_safe(ktime_get(), t
);
2584 * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
2585 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
2587 if (cmd
== FUTEX_REQUEUE
|| cmd
== FUTEX_CMP_REQUEUE
||
2588 cmd
== FUTEX_CMP_REQUEUE_PI
|| cmd
== FUTEX_WAKE_OP
)
2589 val2
= (u32
) (unsigned long) utime
;
2591 return do_futex(uaddr
, op
, val
, tp
, uaddr2
, val2
, val3
);
2594 static int __init
futex_init(void)
2600 * This will fail and we want it. Some arch implementations do
2601 * runtime detection of the futex_atomic_cmpxchg_inatomic()
2602 * functionality. We want to know that before we call in any
2603 * of the complex code paths. Also we want to prevent
2604 * registration of robust lists in that case. NULL is
2605 * guaranteed to fault and we get -EFAULT on functional
2606 * implementation, the non functional ones will return
2609 curval
= cmpxchg_futex_value_locked(NULL
, 0, 0);
2610 if (curval
== -EFAULT
)
2611 futex_cmpxchg_enabled
= 1;
2613 for (i
= 0; i
< ARRAY_SIZE(futex_queues
); i
++) {
2614 plist_head_init(&futex_queues
[i
].chain
, &futex_queues
[i
].lock
);
2615 spin_lock_init(&futex_queues
[i
].lock
);
2620 __initcall(futex_init
);