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 /* There can only be a single waiter */
104 wait_queue_head_t waiter;
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;
114 struct task_struct *task;
116 /* rt_waiter storage for requeue_pi: */
117 struct rt_mutex_waiter *rt_waiter;
119 /* Bitset for the optional bitmasked wakeup */
124 * Hash buckets are shared by all the futex_keys that hash to the same
125 * location. Each key may have multiple futex_q structures, one for each task
126 * waiting on a futex.
128 struct futex_hash_bucket {
130 struct plist_head chain;
133 static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
136 * We hash on the keys returned from get_futex_key (see below).
138 static struct futex_hash_bucket *hash_futex(union futex_key *key)
140 u32 hash = jhash2((u32*)&key->both.word,
141 (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
143 return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
147 * Return 1 if two futex_keys are equal, 0 otherwise.
149 static inline int match_futex(union futex_key *key1, union futex_key *key2)
151 return (key1->both.word == key2->both.word
152 && key1->both.ptr == key2->both.ptr
153 && key1->both.offset == key2->both.offset);
157 * Take a reference to the resource addressed by a key.
158 * Can be called while holding spinlocks.
161 static void get_futex_key_refs(union futex_key *key)
166 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
168 atomic_inc(&key->shared.inode->i_count);
170 case FUT_OFF_MMSHARED:
171 atomic_inc(&key->private.mm->mm_count);
177 * Drop a reference to the resource addressed by a key.
178 * The hash bucket spinlock must not be held.
180 static void drop_futex_key_refs(union futex_key *key)
182 if (!key->both.ptr) {
183 /* If we're here then we tried to put a key we failed to get */
188 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
190 iput(key->shared.inode);
192 case FUT_OFF_MMSHARED:
193 mmdrop(key->private.mm);
199 * get_futex_key - Get parameters which are the keys for a futex.
200 * @uaddr: virtual address of the futex
201 * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
202 * @key: address where result is stored.
204 * Returns a negative error code or 0
205 * The key words are stored in *key on success.
207 * For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,
208 * offset_within_page). For private mappings, it's (uaddr, current->mm).
209 * We can usually work out the index without swapping in the page.
211 * lock_page() might sleep, the caller should not hold a spinlock.
213 static int get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key)
215 unsigned long address = (unsigned long)uaddr;
216 struct mm_struct *mm = current->mm;
221 * The futex address must be "naturally" aligned.
223 key->both.offset = address % PAGE_SIZE;
224 if (unlikely((address % sizeof(u32)) != 0))
226 address -= key->both.offset;
229 * PROCESS_PRIVATE futexes are fast.
230 * As the mm cannot disappear under us and the 'key' only needs
231 * virtual address, we dont even have to find the underlying vma.
232 * Note : We do have to check 'uaddr' is a valid user address,
233 * but access_ok() should be faster than find_vma()
236 if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))))
238 key->private.mm = mm;
239 key->private.address = address;
240 get_futex_key_refs(key);
245 err = get_user_pages_fast(address, 1, 0, &page);
250 if (!page->mapping) {
257 * Private mappings are handled in a simple way.
259 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
260 * it's a read-only handle, it's expected that futexes attach to
261 * the object not the particular process.
263 if (PageAnon(page)) {
264 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
265 key->private.mm = mm;
266 key->private.address = address;
268 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
269 key->shared.inode = page->mapping->host;
270 key->shared.pgoff = page->index;
273 get_futex_key_refs(key);
281 void put_futex_key(int fshared, union futex_key *key)
283 drop_futex_key_refs(key);
287 * futex_top_waiter() - Return the highest priority waiter on a futex
288 * @hb: the hash bucket the futex_q's reside in
289 * @key: the futex key (to distinguish it from other futex futex_q's)
291 * Must be called with the hb lock held.
293 static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
294 union futex_key *key)
296 struct futex_q *this;
298 plist_for_each_entry(this, &hb->chain, list) {
299 if (match_futex(&this->key, key))
305 static u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval)
310 curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
316 static int get_futex_value_locked(u32 *dest, u32 __user *from)
321 ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
324 return ret ? -EFAULT : 0;
331 static int refill_pi_state_cache(void)
333 struct futex_pi_state *pi_state;
335 if (likely(current->pi_state_cache))
338 pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
343 INIT_LIST_HEAD(&pi_state->list);
344 /* pi_mutex gets initialized later */
345 pi_state->owner = NULL;
346 atomic_set(&pi_state->refcount, 1);
347 pi_state->key = FUTEX_KEY_INIT;
349 current->pi_state_cache = pi_state;
354 static struct futex_pi_state * alloc_pi_state(void)
356 struct futex_pi_state *pi_state = current->pi_state_cache;
359 current->pi_state_cache = NULL;
364 static void free_pi_state(struct futex_pi_state *pi_state)
366 if (!atomic_dec_and_test(&pi_state->refcount))
370 * If pi_state->owner is NULL, the owner is most probably dying
371 * and has cleaned up the pi_state already
373 if (pi_state->owner) {
374 spin_lock_irq(&pi_state->owner->pi_lock);
375 list_del_init(&pi_state->list);
376 spin_unlock_irq(&pi_state->owner->pi_lock);
378 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
381 if (current->pi_state_cache)
385 * pi_state->list is already empty.
386 * clear pi_state->owner.
387 * refcount is at 0 - put it back to 1.
389 pi_state->owner = NULL;
390 atomic_set(&pi_state->refcount, 1);
391 current->pi_state_cache = pi_state;
396 * Look up the task based on what TID userspace gave us.
399 static struct task_struct * futex_find_get_task(pid_t pid)
401 struct task_struct *p;
402 const struct cred *cred = current_cred(), *pcred;
405 p = find_task_by_vpid(pid);
409 pcred = __task_cred(p);
410 if (cred->euid != pcred->euid &&
411 cred->euid != pcred->uid)
423 * This task is holding PI mutexes at exit time => bad.
424 * Kernel cleans up PI-state, but userspace is likely hosed.
425 * (Robust-futex cleanup is separate and might save the day for userspace.)
427 void exit_pi_state_list(struct task_struct *curr)
429 struct list_head *next, *head = &curr->pi_state_list;
430 struct futex_pi_state *pi_state;
431 struct futex_hash_bucket *hb;
432 union futex_key key = FUTEX_KEY_INIT;
434 if (!futex_cmpxchg_enabled)
437 * We are a ZOMBIE and nobody can enqueue itself on
438 * pi_state_list anymore, but we have to be careful
439 * versus waiters unqueueing themselves:
441 spin_lock_irq(&curr->pi_lock);
442 while (!list_empty(head)) {
445 pi_state = list_entry(next, struct futex_pi_state, list);
447 hb = hash_futex(&key);
448 spin_unlock_irq(&curr->pi_lock);
450 spin_lock(&hb->lock);
452 spin_lock_irq(&curr->pi_lock);
454 * We dropped the pi-lock, so re-check whether this
455 * task still owns the PI-state:
457 if (head->next != next) {
458 spin_unlock(&hb->lock);
462 WARN_ON(pi_state->owner != curr);
463 WARN_ON(list_empty(&pi_state->list));
464 list_del_init(&pi_state->list);
465 pi_state->owner = NULL;
466 spin_unlock_irq(&curr->pi_lock);
468 rt_mutex_unlock(&pi_state->pi_mutex);
470 spin_unlock(&hb->lock);
472 spin_lock_irq(&curr->pi_lock);
474 spin_unlock_irq(&curr->pi_lock);
478 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
479 union futex_key *key, struct futex_pi_state **ps)
481 struct futex_pi_state *pi_state = NULL;
482 struct futex_q *this, *next;
483 struct plist_head *head;
484 struct task_struct *p;
485 pid_t pid = uval & FUTEX_TID_MASK;
489 plist_for_each_entry_safe(this, next, head, list) {
490 if (match_futex(&this->key, key)) {
492 * Another waiter already exists - bump up
493 * the refcount and return its pi_state:
495 pi_state = this->pi_state;
497 * Userspace might have messed up non PI and PI futexes
499 if (unlikely(!pi_state))
502 WARN_ON(!atomic_read(&pi_state->refcount));
503 WARN_ON(pid && pi_state->owner &&
504 pi_state->owner->pid != pid);
506 atomic_inc(&pi_state->refcount);
514 * We are the first waiter - try to look up the real owner and attach
515 * the new pi_state to it, but bail out when TID = 0
519 p = futex_find_get_task(pid);
524 * We need to look at the task state flags to figure out,
525 * whether the task is exiting. To protect against the do_exit
526 * change of the task flags, we do this protected by
529 spin_lock_irq(&p->pi_lock);
530 if (unlikely(p->flags & PF_EXITING)) {
532 * The task is on the way out. When PF_EXITPIDONE is
533 * set, we know that the task has finished the
536 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
538 spin_unlock_irq(&p->pi_lock);
543 pi_state = alloc_pi_state();
546 * Initialize the pi_mutex in locked state and make 'p'
549 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
551 /* Store the key for possible exit cleanups: */
552 pi_state->key = *key;
554 WARN_ON(!list_empty(&pi_state->list));
555 list_add(&pi_state->list, &p->pi_state_list);
557 spin_unlock_irq(&p->pi_lock);
567 * futex_lock_pi_atomic() - atomic work required to acquire a pi aware futex
568 * @uaddr: the pi futex user address
569 * @hb: the pi futex hash bucket
570 * @key: the futex key associated with uaddr and hb
571 * @ps: the pi_state pointer where we store the result of the
573 * @task: the task to perform the atomic lock work for. This will
574 * be "current" except in the case of requeue pi.
575 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
579 * 1 - acquired the lock
582 * The hb->lock and futex_key refs shall be held by the caller.
584 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
585 union futex_key *key,
586 struct futex_pi_state **ps,
587 struct task_struct *task, int set_waiters)
589 int lock_taken, ret, ownerdied = 0;
590 u32 uval, newval, curval;
593 ret = lock_taken = 0;
596 * To avoid races, we attempt to take the lock here again
597 * (by doing a 0 -> TID atomic cmpxchg), while holding all
598 * the locks. It will most likely not succeed.
600 newval = task_pid_vnr(task);
602 newval |= FUTEX_WAITERS;
604 curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
606 if (unlikely(curval == -EFAULT))
612 if ((unlikely((curval & FUTEX_TID_MASK) == task_pid_vnr(task))))
616 * Surprise - we got the lock. Just return to userspace:
618 if (unlikely(!curval))
624 * Set the FUTEX_WAITERS flag, so the owner will know it has someone
625 * to wake at the next unlock.
627 newval = curval | FUTEX_WAITERS;
630 * There are two cases, where a futex might have no owner (the
631 * owner TID is 0): OWNER_DIED. We take over the futex in this
632 * case. We also do an unconditional take over, when the owner
635 * This is safe as we are protected by the hash bucket lock !
637 if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
638 /* Keep the OWNER_DIED bit */
639 newval = (curval & ~FUTEX_TID_MASK) | task_pid_vnr(task);
644 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
646 if (unlikely(curval == -EFAULT))
648 if (unlikely(curval != uval))
652 * We took the lock due to owner died take over.
654 if (unlikely(lock_taken))
658 * We dont have the lock. Look up the PI state (or create it if
659 * we are the first waiter):
661 ret = lookup_pi_state(uval, hb, key, ps);
667 * No owner found for this futex. Check if the
668 * OWNER_DIED bit is set to figure out whether
669 * this is a robust futex or not.
671 if (get_futex_value_locked(&curval, uaddr))
675 * We simply start over in case of a robust
676 * futex. The code above will take the futex
679 if (curval & FUTEX_OWNER_DIED) {
692 * The hash bucket lock must be held when this is called.
693 * Afterwards, the futex_q must not be accessed.
695 static void wake_futex(struct futex_q *q)
697 plist_del(&q->list, &q->list.plist);
699 * The lock in wake_up_all() is a crucial memory barrier after the
700 * plist_del() and also before assigning to q->lock_ptr.
704 * The waiting task can free the futex_q as soon as this is written,
705 * without taking any locks. This must come last.
707 * A memory barrier is required here to prevent the following store to
708 * lock_ptr from getting ahead of the wakeup. Clearing the lock at the
709 * end of wake_up() does not prevent this store from moving.
715 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
717 struct task_struct *new_owner;
718 struct futex_pi_state *pi_state = this->pi_state;
724 spin_lock(&pi_state->pi_mutex.wait_lock);
725 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
728 * This happens when we have stolen the lock and the original
729 * pending owner did not enqueue itself back on the rt_mutex.
730 * Thats not a tragedy. We know that way, that a lock waiter
731 * is on the fly. We make the futex_q waiter the pending owner.
734 new_owner = this->task;
737 * We pass it to the next owner. (The WAITERS bit is always
738 * kept enabled while there is PI state around. We must also
739 * preserve the owner died bit.)
741 if (!(uval & FUTEX_OWNER_DIED)) {
744 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
746 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
748 if (curval == -EFAULT)
750 else if (curval != uval)
753 spin_unlock(&pi_state->pi_mutex.wait_lock);
758 spin_lock_irq(&pi_state->owner->pi_lock);
759 WARN_ON(list_empty(&pi_state->list));
760 list_del_init(&pi_state->list);
761 spin_unlock_irq(&pi_state->owner->pi_lock);
763 spin_lock_irq(&new_owner->pi_lock);
764 WARN_ON(!list_empty(&pi_state->list));
765 list_add(&pi_state->list, &new_owner->pi_state_list);
766 pi_state->owner = new_owner;
767 spin_unlock_irq(&new_owner->pi_lock);
769 spin_unlock(&pi_state->pi_mutex.wait_lock);
770 rt_mutex_unlock(&pi_state->pi_mutex);
775 static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
780 * There is no waiter, so we unlock the futex. The owner died
781 * bit has not to be preserved here. We are the owner:
783 oldval = cmpxchg_futex_value_locked(uaddr, uval, 0);
785 if (oldval == -EFAULT)
794 * Express the locking dependencies for lockdep:
797 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
800 spin_lock(&hb1->lock);
802 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
803 } else { /* hb1 > hb2 */
804 spin_lock(&hb2->lock);
805 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
810 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
812 spin_unlock(&hb1->lock);
814 spin_unlock(&hb2->lock);
818 * Wake up waiters matching bitset queued on this futex (uaddr).
820 static int futex_wake(u32 __user *uaddr, int fshared, int nr_wake, u32 bitset)
822 struct futex_hash_bucket *hb;
823 struct futex_q *this, *next;
824 struct plist_head *head;
825 union futex_key key = FUTEX_KEY_INIT;
831 ret = get_futex_key(uaddr, fshared, &key);
832 if (unlikely(ret != 0))
835 hb = hash_futex(&key);
836 spin_lock(&hb->lock);
839 plist_for_each_entry_safe(this, next, head, list) {
840 if (match_futex (&this->key, &key)) {
841 if (this->pi_state || this->rt_waiter) {
846 /* Check if one of the bits is set in both bitsets */
847 if (!(this->bitset & bitset))
851 if (++ret >= nr_wake)
856 spin_unlock(&hb->lock);
857 put_futex_key(fshared, &key);
863 * Wake up all waiters hashed on the physical page that is mapped
864 * to this virtual address:
867 futex_wake_op(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
868 int nr_wake, int nr_wake2, int op)
870 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
871 struct futex_hash_bucket *hb1, *hb2;
872 struct plist_head *head;
873 struct futex_q *this, *next;
877 ret = get_futex_key(uaddr1, fshared, &key1);
878 if (unlikely(ret != 0))
880 ret = get_futex_key(uaddr2, fshared, &key2);
881 if (unlikely(ret != 0))
884 hb1 = hash_futex(&key1);
885 hb2 = hash_futex(&key2);
887 double_lock_hb(hb1, hb2);
889 op_ret = futex_atomic_op_inuser(op, uaddr2);
890 if (unlikely(op_ret < 0)) {
893 double_unlock_hb(hb1, hb2);
897 * we don't get EFAULT from MMU faults if we don't have an MMU,
898 * but we might get them from range checking
904 if (unlikely(op_ret != -EFAULT)) {
909 ret = get_user(dummy, uaddr2);
916 put_futex_key(fshared, &key2);
917 put_futex_key(fshared, &key1);
923 plist_for_each_entry_safe(this, next, head, list) {
924 if (match_futex (&this->key, &key1)) {
926 if (++ret >= nr_wake)
935 plist_for_each_entry_safe(this, next, head, list) {
936 if (match_futex (&this->key, &key2)) {
938 if (++op_ret >= nr_wake2)
945 double_unlock_hb(hb1, hb2);
947 put_futex_key(fshared, &key2);
949 put_futex_key(fshared, &key1);
955 * requeue_futex() - Requeue a futex_q from one hb to another
956 * @q: the futex_q to requeue
957 * @hb1: the source hash_bucket
958 * @hb2: the target hash_bucket
959 * @key2: the new key for the requeued futex_q
962 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
963 struct futex_hash_bucket *hb2, union futex_key *key2)
967 * If key1 and key2 hash to the same bucket, no need to
970 if (likely(&hb1->chain != &hb2->chain)) {
971 plist_del(&q->list, &hb1->chain);
972 plist_add(&q->list, &hb2->chain);
973 q->lock_ptr = &hb2->lock;
974 #ifdef CONFIG_DEBUG_PI_LIST
975 q->list.plist.lock = &hb2->lock;
978 get_futex_key_refs(key2);
983 * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
985 * key: the key of the requeue target futex
987 * During futex_requeue, with requeue_pi=1, it is possible to acquire the
988 * target futex if it is uncontended or via a lock steal. Set the futex_q key
989 * to the requeue target futex so the waiter can detect the wakeup on the right
990 * futex, but remove it from the hb and NULL the rt_waiter so it can detect
991 * atomic lock acquisition. Must be called with the q->lock_ptr held.
994 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key)
996 drop_futex_key_refs(&q->key);
997 get_futex_key_refs(key);
1000 WARN_ON(plist_node_empty(&q->list));
1001 plist_del(&q->list, &q->list.plist);
1003 WARN_ON(!q->rt_waiter);
1004 q->rt_waiter = NULL;
1006 wake_up(&q->waiter);
1010 * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1011 * @pifutex: the user address of the to futex
1012 * @hb1: the from futex hash bucket, must be locked by the caller
1013 * @hb2: the to futex hash bucket, must be locked by the caller
1014 * @key1: the from futex key
1015 * @key2: the to futex key
1016 * @ps: address to store the pi_state pointer
1017 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1019 * Try and get the lock on behalf of the top waiter if we can do it atomically.
1020 * Wake the top waiter if we succeed. If the caller specified set_waiters,
1021 * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1022 * hb1 and hb2 must be held by the caller.
1025 * 0 - failed to acquire the lock atomicly
1026 * 1 - acquired the lock
1029 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1030 struct futex_hash_bucket *hb1,
1031 struct futex_hash_bucket *hb2,
1032 union futex_key *key1, union futex_key *key2,
1033 struct futex_pi_state **ps, int set_waiters)
1035 struct futex_q *top_waiter = NULL;
1039 if (get_futex_value_locked(&curval, pifutex))
1043 * Find the top_waiter and determine if there are additional waiters.
1044 * If the caller intends to requeue more than 1 waiter to pifutex,
1045 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1046 * as we have means to handle the possible fault. If not, don't set
1047 * the bit unecessarily as it will force the subsequent unlock to enter
1050 top_waiter = futex_top_waiter(hb1, key1);
1052 /* There are no waiters, nothing for us to do. */
1057 * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
1058 * the contended case or if set_waiters is 1. The pi_state is returned
1059 * in ps in contended cases.
1061 ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1064 requeue_pi_wake_futex(top_waiter, key2);
1070 * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1071 * uaddr1: source futex user address
1072 * uaddr2: target futex user address
1073 * nr_wake: number of waiters to wake (must be 1 for requeue_pi)
1074 * nr_requeue: number of waiters to requeue (0-INT_MAX)
1075 * requeue_pi: if we are attempting to requeue from a non-pi futex to a
1076 * pi futex (pi to pi requeue is not supported)
1078 * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1079 * uaddr2 atomically on behalf of the top waiter.
1082 * >=0 - on success, the number of tasks requeued or woken
1085 static int futex_requeue(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
1086 int nr_wake, int nr_requeue, u32 *cmpval,
1089 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1090 int drop_count = 0, task_count = 0, ret;
1091 struct futex_pi_state *pi_state = NULL;
1092 struct futex_hash_bucket *hb1, *hb2;
1093 struct plist_head *head1;
1094 struct futex_q *this, *next;
1099 * requeue_pi requires a pi_state, try to allocate it now
1100 * without any locks in case it fails.
1102 if (refill_pi_state_cache())
1105 * requeue_pi must wake as many tasks as it can, up to nr_wake
1106 * + nr_requeue, since it acquires the rt_mutex prior to
1107 * returning to userspace, so as to not leave the rt_mutex with
1108 * waiters and no owner. However, second and third wake-ups
1109 * cannot be predicted as they involve race conditions with the
1110 * first wake and a fault while looking up the pi_state. Both
1111 * pthread_cond_signal() and pthread_cond_broadcast() should
1119 if (pi_state != NULL) {
1121 * We will have to lookup the pi_state again, so free this one
1122 * to keep the accounting correct.
1124 free_pi_state(pi_state);
1128 ret = get_futex_key(uaddr1, fshared, &key1);
1129 if (unlikely(ret != 0))
1131 ret = get_futex_key(uaddr2, fshared, &key2);
1132 if (unlikely(ret != 0))
1135 hb1 = hash_futex(&key1);
1136 hb2 = hash_futex(&key2);
1139 double_lock_hb(hb1, hb2);
1141 if (likely(cmpval != NULL)) {
1144 ret = get_futex_value_locked(&curval, uaddr1);
1146 if (unlikely(ret)) {
1147 double_unlock_hb(hb1, hb2);
1149 ret = get_user(curval, uaddr1);
1156 put_futex_key(fshared, &key2);
1157 put_futex_key(fshared, &key1);
1160 if (curval != *cmpval) {
1166 if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1168 * Attempt to acquire uaddr2 and wake the top waiter. If we
1169 * intend to requeue waiters, force setting the FUTEX_WAITERS
1170 * bit. We force this here where we are able to easily handle
1171 * faults rather in the requeue loop below.
1173 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1174 &key2, &pi_state, nr_requeue);
1177 * At this point the top_waiter has either taken uaddr2 or is
1178 * waiting on it. If the former, then the pi_state will not
1179 * exist yet, look it up one more time to ensure we have a
1185 ret = get_futex_value_locked(&curval2, uaddr2);
1187 ret = lookup_pi_state(curval2, hb2, &key2,
1195 double_unlock_hb(hb1, hb2);
1196 put_futex_key(fshared, &key2);
1197 put_futex_key(fshared, &key1);
1198 ret = get_user(curval2, uaddr2);
1203 /* The owner was exiting, try again. */
1204 double_unlock_hb(hb1, hb2);
1205 put_futex_key(fshared, &key2);
1206 put_futex_key(fshared, &key1);
1214 head1 = &hb1->chain;
1215 plist_for_each_entry_safe(this, next, head1, list) {
1216 if (task_count - nr_wake >= nr_requeue)
1219 if (!match_futex(&this->key, &key1))
1222 WARN_ON(!requeue_pi && this->rt_waiter);
1223 WARN_ON(requeue_pi && !this->rt_waiter);
1226 * Wake nr_wake waiters. For requeue_pi, if we acquired the
1227 * lock, we already woke the top_waiter. If not, it will be
1228 * woken by futex_unlock_pi().
1230 if (++task_count <= nr_wake && !requeue_pi) {
1236 * Requeue nr_requeue waiters and possibly one more in the case
1237 * of requeue_pi if we couldn't acquire the lock atomically.
1240 /* Prepare the waiter to take the rt_mutex. */
1241 atomic_inc(&pi_state->refcount);
1242 this->pi_state = pi_state;
1243 ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1247 /* We got the lock. */
1248 requeue_pi_wake_futex(this, &key2);
1252 this->pi_state = NULL;
1253 free_pi_state(pi_state);
1257 requeue_futex(this, hb1, hb2, &key2);
1262 double_unlock_hb(hb1, hb2);
1264 /* drop_futex_key_refs() must be called outside the spinlocks. */
1265 while (--drop_count >= 0)
1266 drop_futex_key_refs(&key1);
1269 put_futex_key(fshared, &key2);
1271 put_futex_key(fshared, &key1);
1273 if (pi_state != NULL)
1274 free_pi_state(pi_state);
1275 return ret ? ret : task_count;
1278 /* The key must be already stored in q->key. */
1279 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
1281 struct futex_hash_bucket *hb;
1283 init_waitqueue_head(&q->waiter);
1285 get_futex_key_refs(&q->key);
1286 hb = hash_futex(&q->key);
1287 q->lock_ptr = &hb->lock;
1289 spin_lock(&hb->lock);
1293 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1298 * The priority used to register this element is
1299 * - either the real thread-priority for the real-time threads
1300 * (i.e. threads with a priority lower than MAX_RT_PRIO)
1301 * - or MAX_RT_PRIO for non-RT threads.
1302 * Thus, all RT-threads are woken first in priority order, and
1303 * the others are woken last, in FIFO order.
1305 prio = min(current->normal_prio, MAX_RT_PRIO);
1307 plist_node_init(&q->list, prio);
1308 #ifdef CONFIG_DEBUG_PI_LIST
1309 q->list.plist.lock = &hb->lock;
1311 plist_add(&q->list, &hb->chain);
1313 spin_unlock(&hb->lock);
1317 queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
1319 spin_unlock(&hb->lock);
1320 drop_futex_key_refs(&q->key);
1324 * queue_me and unqueue_me must be called as a pair, each
1325 * exactly once. They are called with the hashed spinlock held.
1328 /* Return 1 if we were still queued (ie. 0 means we were woken) */
1329 static int unqueue_me(struct futex_q *q)
1331 spinlock_t *lock_ptr;
1334 /* In the common case we don't take the spinlock, which is nice. */
1336 lock_ptr = q->lock_ptr;
1338 if (lock_ptr != NULL) {
1339 spin_lock(lock_ptr);
1341 * q->lock_ptr can change between reading it and
1342 * spin_lock(), causing us to take the wrong lock. This
1343 * corrects the race condition.
1345 * Reasoning goes like this: if we have the wrong lock,
1346 * q->lock_ptr must have changed (maybe several times)
1347 * between reading it and the spin_lock(). It can
1348 * change again after the spin_lock() but only if it was
1349 * already changed before the spin_lock(). It cannot,
1350 * however, change back to the original value. Therefore
1351 * we can detect whether we acquired the correct lock.
1353 if (unlikely(lock_ptr != q->lock_ptr)) {
1354 spin_unlock(lock_ptr);
1357 WARN_ON(plist_node_empty(&q->list));
1358 plist_del(&q->list, &q->list.plist);
1360 BUG_ON(q->pi_state);
1362 spin_unlock(lock_ptr);
1366 drop_futex_key_refs(&q->key);
1371 * PI futexes can not be requeued and must remove themself from the
1372 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1375 static void unqueue_me_pi(struct futex_q *q)
1377 WARN_ON(plist_node_empty(&q->list));
1378 plist_del(&q->list, &q->list.plist);
1380 BUG_ON(!q->pi_state);
1381 free_pi_state(q->pi_state);
1384 spin_unlock(q->lock_ptr);
1386 drop_futex_key_refs(&q->key);
1390 * Fixup the pi_state owner with the new owner.
1392 * Must be called with hash bucket lock held and mm->sem held for non
1395 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1396 struct task_struct *newowner, int fshared)
1398 u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
1399 struct futex_pi_state *pi_state = q->pi_state;
1400 struct task_struct *oldowner = pi_state->owner;
1401 u32 uval, curval, newval;
1405 if (!pi_state->owner)
1406 newtid |= FUTEX_OWNER_DIED;
1409 * We are here either because we stole the rtmutex from the
1410 * pending owner or we are the pending owner which failed to
1411 * get the rtmutex. We have to replace the pending owner TID
1412 * in the user space variable. This must be atomic as we have
1413 * to preserve the owner died bit here.
1415 * Note: We write the user space value _before_ changing the pi_state
1416 * because we can fault here. Imagine swapped out pages or a fork
1417 * that marked all the anonymous memory readonly for cow.
1419 * Modifying pi_state _before_ the user space value would
1420 * leave the pi_state in an inconsistent state when we fault
1421 * here, because we need to drop the hash bucket lock to
1422 * handle the fault. This might be observed in the PID check
1423 * in lookup_pi_state.
1426 if (get_futex_value_locked(&uval, uaddr))
1430 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1432 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
1434 if (curval == -EFAULT)
1442 * We fixed up user space. Now we need to fix the pi_state
1445 if (pi_state->owner != NULL) {
1446 spin_lock_irq(&pi_state->owner->pi_lock);
1447 WARN_ON(list_empty(&pi_state->list));
1448 list_del_init(&pi_state->list);
1449 spin_unlock_irq(&pi_state->owner->pi_lock);
1452 pi_state->owner = newowner;
1454 spin_lock_irq(&newowner->pi_lock);
1455 WARN_ON(!list_empty(&pi_state->list));
1456 list_add(&pi_state->list, &newowner->pi_state_list);
1457 spin_unlock_irq(&newowner->pi_lock);
1461 * To handle the page fault we need to drop the hash bucket
1462 * lock here. That gives the other task (either the pending
1463 * owner itself or the task which stole the rtmutex) the
1464 * chance to try the fixup of the pi_state. So once we are
1465 * back from handling the fault we need to check the pi_state
1466 * after reacquiring the hash bucket lock and before trying to
1467 * do another fixup. When the fixup has been done already we
1471 spin_unlock(q->lock_ptr);
1473 ret = get_user(uval, uaddr);
1475 spin_lock(q->lock_ptr);
1478 * Check if someone else fixed it for us:
1480 if (pi_state->owner != oldowner)
1490 * In case we must use restart_block to restart a futex_wait,
1491 * we encode in the 'flags' shared capability
1493 #define FLAGS_SHARED 0x01
1494 #define FLAGS_CLOCKRT 0x02
1495 #define FLAGS_HAS_TIMEOUT 0x04
1497 static long futex_wait_restart(struct restart_block *restart);
1498 static long futex_lock_pi_restart(struct restart_block *restart);
1501 * fixup_owner() - Post lock pi_state and corner case management
1502 * @uaddr: user address of the futex
1503 * @fshared: whether the futex is shared (1) or not (0)
1504 * @q: futex_q (contains pi_state and access to the rt_mutex)
1505 * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
1507 * After attempting to lock an rt_mutex, this function is called to cleanup
1508 * the pi_state owner as well as handle race conditions that may allow us to
1509 * acquire the lock. Must be called with the hb lock held.
1512 * 1 - success, lock taken
1513 * 0 - success, lock not taken
1514 * <0 - on error (-EFAULT)
1516 static int fixup_owner(u32 __user *uaddr, int fshared, struct futex_q *q,
1519 struct task_struct *owner;
1524 * Got the lock. We might not be the anticipated owner if we
1525 * did a lock-steal - fix up the PI-state in that case:
1527 if (q->pi_state->owner != current)
1528 ret = fixup_pi_state_owner(uaddr, q, current, fshared);
1533 * Catch the rare case, where the lock was released when we were on the
1534 * way back before we locked the hash bucket.
1536 if (q->pi_state->owner == current) {
1538 * Try to get the rt_mutex now. This might fail as some other
1539 * task acquired the rt_mutex after we removed ourself from the
1540 * rt_mutex waiters list.
1542 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
1548 * pi_state is incorrect, some other task did a lock steal and
1549 * we returned due to timeout or signal without taking the
1550 * rt_mutex. Too late. We can access the rt_mutex_owner without
1551 * locking, as the other task is now blocked on the hash bucket
1552 * lock. Fix the state up.
1554 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
1555 ret = fixup_pi_state_owner(uaddr, q, owner, fshared);
1560 * Paranoia check. If we did not take the lock, then we should not be
1561 * the owner, nor the pending owner, of the rt_mutex.
1563 if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
1564 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
1565 "pi-state %p\n", ret,
1566 q->pi_state->pi_mutex.owner,
1567 q->pi_state->owner);
1570 return ret ? ret : locked;
1574 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
1575 * @hb: the futex hash bucket, must be locked by the caller
1576 * @q: the futex_q to queue up on
1577 * @timeout: the prepared hrtimer_sleeper, or null for no timeout
1578 * @wait: the wait_queue to add to the futex_q after queueing in the hb
1580 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
1581 struct hrtimer_sleeper *timeout,
1587 * There might have been scheduling since the queue_me(), as we
1588 * cannot hold a spinlock across the get_user() in case it
1589 * faults, and we cannot just set TASK_INTERRUPTIBLE state when
1590 * queueing ourselves into the futex hash. This code thus has to
1591 * rely on the futex_wake() code removing us from hash when it
1595 /* add_wait_queue is the barrier after __set_current_state. */
1596 __set_current_state(TASK_INTERRUPTIBLE);
1599 * Add current as the futex_q waiter. We don't remove ourselves from
1600 * the wait_queue because we are the only user of it.
1602 add_wait_queue(&q->waiter, wait);
1606 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1607 if (!hrtimer_active(&timeout->timer))
1608 timeout->task = NULL;
1612 * !plist_node_empty() is safe here without any lock.
1613 * q.lock_ptr != 0 is not safe, because of ordering against wakeup.
1615 if (likely(!plist_node_empty(&q->list))) {
1617 * If the timer has already expired, current will already be
1618 * flagged for rescheduling. Only call schedule if there
1619 * is no timeout, or if it has yet to expire.
1621 if (!timeout || timeout->task)
1624 __set_current_state(TASK_RUNNING);
1628 * futex_wait_setup() - Prepare to wait on a futex
1629 * @uaddr: the futex userspace address
1630 * @val: the expected value
1631 * @fshared: whether the futex is shared (1) or not (0)
1632 * @q: the associated futex_q
1633 * @hb: storage for hash_bucket pointer to be returned to caller
1635 * Setup the futex_q and locate the hash_bucket. Get the futex value and
1636 * compare it with the expected value. Handle atomic faults internally.
1637 * Return with the hb lock held and a q.key reference on success, and unlocked
1638 * with no q.key reference on failure.
1641 * 0 - uaddr contains val and hb has been locked
1642 * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlcoked
1644 static int futex_wait_setup(u32 __user *uaddr, u32 val, int fshared,
1645 struct futex_q *q, struct futex_hash_bucket **hb)
1651 * Access the page AFTER the hash-bucket is locked.
1652 * Order is important:
1654 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1655 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
1657 * The basic logical guarantee of a futex is that it blocks ONLY
1658 * if cond(var) is known to be true at the time of blocking, for
1659 * any cond. If we queued after testing *uaddr, that would open
1660 * a race condition where we could block indefinitely with
1661 * cond(var) false, which would violate the guarantee.
1663 * A consequence is that futex_wait() can return zero and absorb
1664 * a wakeup when *uaddr != val on entry to the syscall. This is
1668 q->key = FUTEX_KEY_INIT;
1669 ret = get_futex_key(uaddr, fshared, &q->key);
1670 if (unlikely(ret != 0))
1674 *hb = queue_lock(q);
1676 ret = get_futex_value_locked(&uval, uaddr);
1679 queue_unlock(q, *hb);
1681 ret = get_user(uval, uaddr);
1688 put_futex_key(fshared, &q->key);
1693 queue_unlock(q, *hb);
1699 put_futex_key(fshared, &q->key);
1703 static int futex_wait(u32 __user *uaddr, int fshared,
1704 u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
1706 struct hrtimer_sleeper timeout, *to = NULL;
1707 DECLARE_WAITQUEUE(wait, current);
1708 struct restart_block *restart;
1709 struct futex_hash_bucket *hb;
1723 hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
1724 CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1725 hrtimer_init_sleeper(to, current);
1726 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
1727 current->timer_slack_ns);
1730 /* Prepare to wait on uaddr. */
1731 ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
1735 /* queue_me and wait for wakeup, timeout, or a signal. */
1736 futex_wait_queue_me(hb, &q, to, &wait);
1738 /* If we were woken (and unqueued), we succeeded, whatever. */
1740 if (!unqueue_me(&q))
1743 if (to && !to->task)
1747 * We expect signal_pending(current), but another thread may
1748 * have handled it for us already.
1754 restart = ¤t_thread_info()->restart_block;
1755 restart->fn = futex_wait_restart;
1756 restart->futex.uaddr = (u32 *)uaddr;
1757 restart->futex.val = val;
1758 restart->futex.time = abs_time->tv64;
1759 restart->futex.bitset = bitset;
1760 restart->futex.flags = FLAGS_HAS_TIMEOUT;
1763 restart->futex.flags |= FLAGS_SHARED;
1765 restart->futex.flags |= FLAGS_CLOCKRT;
1767 ret = -ERESTART_RESTARTBLOCK;
1770 put_futex_key(fshared, &q.key);
1773 hrtimer_cancel(&to->timer);
1774 destroy_hrtimer_on_stack(&to->timer);
1780 static long futex_wait_restart(struct restart_block *restart)
1782 u32 __user *uaddr = (u32 __user *)restart->futex.uaddr;
1784 ktime_t t, *tp = NULL;
1786 if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
1787 t.tv64 = restart->futex.time;
1790 restart->fn = do_no_restart_syscall;
1791 if (restart->futex.flags & FLAGS_SHARED)
1793 return (long)futex_wait(uaddr, fshared, restart->futex.val, tp,
1794 restart->futex.bitset,
1795 restart->futex.flags & FLAGS_CLOCKRT);
1800 * Userspace tried a 0 -> TID atomic transition of the futex value
1801 * and failed. The kernel side here does the whole locking operation:
1802 * if there are waiters then it will block, it does PI, etc. (Due to
1803 * races the kernel might see a 0 value of the futex too.)
1805 static int futex_lock_pi(u32 __user *uaddr, int fshared,
1806 int detect, ktime_t *time, int trylock)
1808 struct hrtimer_sleeper timeout, *to = NULL;
1809 struct futex_hash_bucket *hb;
1814 if (refill_pi_state_cache())
1819 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
1821 hrtimer_init_sleeper(to, current);
1822 hrtimer_set_expires(&to->timer, *time);
1828 q.key = FUTEX_KEY_INIT;
1829 ret = get_futex_key(uaddr, fshared, &q.key);
1830 if (unlikely(ret != 0))
1834 hb = queue_lock(&q);
1836 ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
1837 if (unlikely(ret)) {
1840 /* We got the lock. */
1842 goto out_unlock_put_key;
1847 * Task is exiting and we just wait for the
1850 queue_unlock(&q, hb);
1851 put_futex_key(fshared, &q.key);
1855 goto out_unlock_put_key;
1860 * Only actually queue now that the atomic ops are done:
1864 WARN_ON(!q.pi_state);
1866 * Block on the PI mutex:
1869 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
1871 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
1872 /* Fixup the trylock return value: */
1873 ret = ret ? 0 : -EWOULDBLOCK;
1876 spin_lock(q.lock_ptr);
1878 * Fixup the pi_state owner and possibly acquire the lock if we
1881 res = fixup_owner(uaddr, fshared, &q, !ret);
1883 * If fixup_owner() returned an error, proprogate that. If it acquired
1884 * the lock, clear our -ETIMEDOUT or -EINTR.
1887 ret = (res < 0) ? res : 0;
1890 * If fixup_owner() faulted and was unable to handle the fault, unlock
1891 * it and return the fault to userspace.
1893 if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
1894 rt_mutex_unlock(&q.pi_state->pi_mutex);
1896 /* Unqueue and drop the lock */
1902 queue_unlock(&q, hb);
1905 put_futex_key(fshared, &q.key);
1908 destroy_hrtimer_on_stack(&to->timer);
1909 return ret != -EINTR ? ret : -ERESTARTNOINTR;
1913 * We have to r/w *(int __user *)uaddr, and we have to modify it
1914 * atomically. Therefore, if we continue to fault after get_user()
1915 * below, we need to handle the fault ourselves, while still holding
1916 * the mmap_sem. This can occur if the uaddr is under contention as
1917 * we have to drop the mmap_sem in order to call get_user().
1919 queue_unlock(&q, hb);
1921 ret = get_user(uval, uaddr);
1928 put_futex_key(fshared, &q.key);
1932 static long futex_lock_pi_restart(struct restart_block *restart)
1934 u32 __user *uaddr = (u32 __user *)restart->futex.uaddr;
1935 ktime_t t, *tp = NULL;
1936 int fshared = restart->futex.flags & FLAGS_SHARED;
1938 if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
1939 t.tv64 = restart->futex.time;
1942 restart->fn = do_no_restart_syscall;
1944 return (long)futex_lock_pi(uaddr, fshared, restart->futex.val, tp, 0);
1948 * Userspace attempted a TID -> 0 atomic transition, and failed.
1949 * This is the in-kernel slowpath: we look up the PI state (if any),
1950 * and do the rt-mutex unlock.
1952 static int futex_unlock_pi(u32 __user *uaddr, int fshared)
1954 struct futex_hash_bucket *hb;
1955 struct futex_q *this, *next;
1957 struct plist_head *head;
1958 union futex_key key = FUTEX_KEY_INIT;
1962 if (get_user(uval, uaddr))
1965 * We release only a lock we actually own:
1967 if ((uval & FUTEX_TID_MASK) != task_pid_vnr(current))
1970 ret = get_futex_key(uaddr, fshared, &key);
1971 if (unlikely(ret != 0))
1974 hb = hash_futex(&key);
1975 spin_lock(&hb->lock);
1978 * To avoid races, try to do the TID -> 0 atomic transition
1979 * again. If it succeeds then we can return without waking
1982 if (!(uval & FUTEX_OWNER_DIED))
1983 uval = cmpxchg_futex_value_locked(uaddr, task_pid_vnr(current), 0);
1986 if (unlikely(uval == -EFAULT))
1989 * Rare case: we managed to release the lock atomically,
1990 * no need to wake anyone else up:
1992 if (unlikely(uval == task_pid_vnr(current)))
1996 * Ok, other tasks may need to be woken up - check waiters
1997 * and do the wakeup if necessary:
2001 plist_for_each_entry_safe(this, next, head, list) {
2002 if (!match_futex (&this->key, &key))
2004 ret = wake_futex_pi(uaddr, uval, this);
2006 * The atomic access to the futex value
2007 * generated a pagefault, so retry the
2008 * user-access and the wakeup:
2015 * No waiters - kernel unlocks the futex:
2017 if (!(uval & FUTEX_OWNER_DIED)) {
2018 ret = unlock_futex_pi(uaddr, uval);
2024 spin_unlock(&hb->lock);
2025 put_futex_key(fshared, &key);
2032 * We have to r/w *(int __user *)uaddr, and we have to modify it
2033 * atomically. Therefore, if we continue to fault after get_user()
2034 * below, we need to handle the fault ourselves, while still holding
2035 * the mmap_sem. This can occur if the uaddr is under contention as
2036 * we have to drop the mmap_sem in order to call get_user().
2038 spin_unlock(&hb->lock);
2039 put_futex_key(fshared, &key);
2041 ret = get_user(uval, uaddr);
2049 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2050 * @hb: the hash_bucket futex_q was original enqueued on
2051 * @q: the futex_q woken while waiting to be requeued
2052 * @key2: the futex_key of the requeue target futex
2053 * @timeout: the timeout associated with the wait (NULL if none)
2055 * Detect if the task was woken on the initial futex as opposed to the requeue
2056 * target futex. If so, determine if it was a timeout or a signal that caused
2057 * the wakeup and return the appropriate error code to the caller. Must be
2058 * called with the hb lock held.
2061 * 0 - no early wakeup detected
2062 * <0 - -ETIMEDOUT or -ERESTARTSYS (FIXME: or ERESTARTNOINTR?)
2065 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2066 struct futex_q *q, union futex_key *key2,
2067 struct hrtimer_sleeper *timeout)
2072 * With the hb lock held, we avoid races while we process the wakeup.
2073 * We only need to hold hb (and not hb2) to ensure atomicity as the
2074 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2075 * It can't be requeued from uaddr2 to something else since we don't
2076 * support a PI aware source futex for requeue.
2078 if (!match_futex(&q->key, key2)) {
2079 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2081 * We were woken prior to requeue by a timeout or a signal.
2082 * Unqueue the futex_q and determine which it was.
2084 plist_del(&q->list, &q->list.plist);
2085 drop_futex_key_refs(&q->key);
2087 if (timeout && !timeout->task)
2091 * We expect signal_pending(current), but another
2092 * thread may have handled it for us already.
2094 /* FIXME: ERESTARTSYS or ERESTARTNOINTR? Do we care if
2095 * the user specified SA_RESTART or not? */
2103 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2104 * @uaddr: the futex we initialyl wait on (non-pi)
2105 * @fshared: whether the futexes are shared (1) or not (0). They must be
2106 * the same type, no requeueing from private to shared, etc.
2107 * @val: the expected value of uaddr
2108 * @abs_time: absolute timeout
2109 * @bitset: 32 bit wakeup bitset set by userspace, defaults to all.
2110 * @clockrt: whether to use CLOCK_REALTIME (1) or CLOCK_MONOTONIC (0)
2111 * @uaddr2: the pi futex we will take prior to returning to user-space
2113 * The caller will wait on uaddr and will be requeued by futex_requeue() to
2114 * uaddr2 which must be PI aware. Normal wakeup will wake on uaddr2 and
2115 * complete the acquisition of the rt_mutex prior to returning to userspace.
2116 * This ensures the rt_mutex maintains an owner when it has waiters; without
2117 * one, the pi logic wouldn't know which task to boost/deboost, if there was a
2120 * We call schedule in futex_wait_queue_me() when we enqueue and return there
2121 * via the following:
2122 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2123 * 2) wakeup on uaddr2 after a requeue and subsequent unlock
2124 * 3) signal (before or after requeue)
2125 * 4) timeout (before or after requeue)
2127 * If 3, we setup a restart_block with futex_wait_requeue_pi() as the function.
2129 * If 2, we may then block on trying to take the rt_mutex and return via:
2130 * 5) successful lock
2133 * 8) other lock acquisition failure
2135 * If 6, we setup a restart_block with futex_lock_pi() as the function.
2137 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2143 static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
2144 u32 val, ktime_t *abs_time, u32 bitset,
2145 int clockrt, u32 __user *uaddr2)
2147 struct hrtimer_sleeper timeout, *to = NULL;
2148 struct rt_mutex_waiter rt_waiter;
2149 struct rt_mutex *pi_mutex = NULL;
2150 DECLARE_WAITQUEUE(wait, current);
2151 struct restart_block *restart;
2152 struct futex_hash_bucket *hb;
2153 union futex_key key2;
2163 hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
2164 CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
2165 hrtimer_init_sleeper(to, current);
2166 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2167 current->timer_slack_ns);
2171 * The waiter is allocated on our stack, manipulated by the requeue
2172 * code while we sleep on uaddr.
2174 debug_rt_mutex_init_waiter(&rt_waiter);
2175 rt_waiter.task = NULL;
2179 q.rt_waiter = &rt_waiter;
2181 key2 = FUTEX_KEY_INIT;
2182 ret = get_futex_key(uaddr2, fshared, &key2);
2183 if (unlikely(ret != 0))
2186 /* Prepare to wait on uaddr. */
2187 ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
2189 put_futex_key(fshared, &key2);
2193 /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2194 futex_wait_queue_me(hb, &q, to, &wait);
2196 spin_lock(&hb->lock);
2197 ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2198 spin_unlock(&hb->lock);
2203 * In order for us to be here, we know our q.key == key2, and since
2204 * we took the hb->lock above, we also know that futex_requeue() has
2205 * completed and we no longer have to concern ourselves with a wakeup
2206 * race with the atomic proxy lock acquition by the requeue code.
2209 /* Check if the requeue code acquired the second futex for us. */
2212 * Got the lock. We might not be the anticipated owner if we
2213 * did a lock-steal - fix up the PI-state in that case.
2215 if (q.pi_state && (q.pi_state->owner != current)) {
2216 spin_lock(q.lock_ptr);
2217 ret = fixup_pi_state_owner(uaddr2, &q, current,
2219 spin_unlock(q.lock_ptr);
2223 * We have been woken up by futex_unlock_pi(), a timeout, or a
2224 * signal. futex_unlock_pi() will not destroy the lock_ptr nor
2227 WARN_ON(!&q.pi_state);
2228 pi_mutex = &q.pi_state->pi_mutex;
2229 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
2230 debug_rt_mutex_free_waiter(&rt_waiter);
2232 spin_lock(q.lock_ptr);
2234 * Fixup the pi_state owner and possibly acquire the lock if we
2237 res = fixup_owner(uaddr2, fshared, &q, !ret);
2239 * If fixup_owner() returned an error, proprogate that. If it
2240 * acquired the lock, clear our -ETIMEDOUT or -EINTR.
2243 ret = (res < 0) ? res : 0;
2245 /* Unqueue and drop the lock. */
2250 * If fixup_pi_state_owner() faulted and was unable to handle the
2251 * fault, unlock the rt_mutex and return the fault to userspace.
2253 if (ret == -EFAULT) {
2254 if (rt_mutex_owner(pi_mutex) == current)
2255 rt_mutex_unlock(pi_mutex);
2256 } else if (ret == -EINTR) {
2258 if (get_user(uval, uaddr2))
2262 * We've already been requeued, so restart by calling
2263 * futex_lock_pi() directly, rather then returning to this
2266 ret = -ERESTART_RESTARTBLOCK;
2267 restart = ¤t_thread_info()->restart_block;
2268 restart->fn = futex_lock_pi_restart;
2269 restart->futex.uaddr = (u32 *)uaddr2;
2270 restart->futex.val = uval;
2271 restart->futex.flags = 0;
2273 restart->futex.flags |= FLAGS_HAS_TIMEOUT;
2274 restart->futex.time = abs_time->tv64;
2278 restart->futex.flags |= FLAGS_SHARED;
2280 restart->futex.flags |= FLAGS_CLOCKRT;
2284 put_futex_key(fshared, &q.key);
2285 put_futex_key(fshared, &key2);
2289 hrtimer_cancel(&to->timer);
2290 destroy_hrtimer_on_stack(&to->timer);
2296 * Support for robust futexes: the kernel cleans up held futexes at
2299 * Implementation: user-space maintains a per-thread list of locks it
2300 * is holding. Upon do_exit(), the kernel carefully walks this list,
2301 * and marks all locks that are owned by this thread with the
2302 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2303 * always manipulated with the lock held, so the list is private and
2304 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2305 * field, to allow the kernel to clean up if the thread dies after
2306 * acquiring the lock, but just before it could have added itself to
2307 * the list. There can only be one such pending lock.
2311 * sys_set_robust_list - set the robust-futex list head of a task
2312 * @head: pointer to the list-head
2313 * @len: length of the list-head, as userspace expects
2315 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2318 if (!futex_cmpxchg_enabled)
2321 * The kernel knows only one size for now:
2323 if (unlikely(len != sizeof(*head)))
2326 current->robust_list = head;
2332 * sys_get_robust_list - get the robust-futex list head of a task
2333 * @pid: pid of the process [zero for current task]
2334 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
2335 * @len_ptr: pointer to a length field, the kernel fills in the header size
2337 SYSCALL_DEFINE3(get_robust_list, int, pid,
2338 struct robust_list_head __user * __user *, head_ptr,
2339 size_t __user *, len_ptr)
2341 struct robust_list_head __user *head;
2343 const struct cred *cred = current_cred(), *pcred;
2345 if (!futex_cmpxchg_enabled)
2349 head = current->robust_list;
2351 struct task_struct *p;
2355 p = find_task_by_vpid(pid);
2359 pcred = __task_cred(p);
2360 if (cred->euid != pcred->euid &&
2361 cred->euid != pcred->uid &&
2362 !capable(CAP_SYS_PTRACE))
2364 head = p->robust_list;
2368 if (put_user(sizeof(*head), len_ptr))
2370 return put_user(head, head_ptr);
2379 * Process a futex-list entry, check whether it's owned by the
2380 * dying task, and do notification if so:
2382 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
2384 u32 uval, nval, mval;
2387 if (get_user(uval, uaddr))
2390 if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
2392 * Ok, this dying thread is truly holding a futex
2393 * of interest. Set the OWNER_DIED bit atomically
2394 * via cmpxchg, and if the value had FUTEX_WAITERS
2395 * set, wake up a waiter (if any). (We have to do a
2396 * futex_wake() even if OWNER_DIED is already set -
2397 * to handle the rare but possible case of recursive
2398 * thread-death.) The rest of the cleanup is done in
2401 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
2402 nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
2404 if (nval == -EFAULT)
2411 * Wake robust non-PI futexes here. The wakeup of
2412 * PI futexes happens in exit_pi_state():
2414 if (!pi && (uval & FUTEX_WAITERS))
2415 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
2421 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
2423 static inline int fetch_robust_entry(struct robust_list __user **entry,
2424 struct robust_list __user * __user *head,
2427 unsigned long uentry;
2429 if (get_user(uentry, (unsigned long __user *)head))
2432 *entry = (void __user *)(uentry & ~1UL);
2439 * Walk curr->robust_list (very carefully, it's a userspace list!)
2440 * and mark any locks found there dead, and notify any waiters.
2442 * We silently return on any sign of list-walking problem.
2444 void exit_robust_list(struct task_struct *curr)
2446 struct robust_list_head __user *head = curr->robust_list;
2447 struct robust_list __user *entry, *next_entry, *pending;
2448 unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
2449 unsigned long futex_offset;
2452 if (!futex_cmpxchg_enabled)
2456 * Fetch the list head (which was registered earlier, via
2457 * sys_set_robust_list()):
2459 if (fetch_robust_entry(&entry, &head->list.next, &pi))
2462 * Fetch the relative futex offset:
2464 if (get_user(futex_offset, &head->futex_offset))
2467 * Fetch any possibly pending lock-add first, and handle it
2470 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
2473 next_entry = NULL; /* avoid warning with gcc */
2474 while (entry != &head->list) {
2476 * Fetch the next entry in the list before calling
2477 * handle_futex_death:
2479 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
2481 * A pending lock might already be on the list, so
2482 * don't process it twice:
2484 if (entry != pending)
2485 if (handle_futex_death((void __user *)entry + futex_offset,
2493 * Avoid excessively long or circular lists:
2502 handle_futex_death((void __user *)pending + futex_offset,
2506 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
2507 u32 __user *uaddr2, u32 val2, u32 val3)
2509 int clockrt, ret = -ENOSYS;
2510 int cmd = op & FUTEX_CMD_MASK;
2513 if (!(op & FUTEX_PRIVATE_FLAG))
2516 clockrt = op & FUTEX_CLOCK_REALTIME;
2517 if (clockrt && cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
2522 val3 = FUTEX_BITSET_MATCH_ANY;
2523 case FUTEX_WAIT_BITSET:
2524 ret = futex_wait(uaddr, fshared, val, timeout, val3, clockrt);
2527 val3 = FUTEX_BITSET_MATCH_ANY;
2528 case FUTEX_WAKE_BITSET:
2529 ret = futex_wake(uaddr, fshared, val, val3);
2532 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL, 0);
2534 case FUTEX_CMP_REQUEUE:
2535 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
2539 ret = futex_wake_op(uaddr, fshared, uaddr2, val, val2, val3);
2542 if (futex_cmpxchg_enabled)
2543 ret = futex_lock_pi(uaddr, fshared, val, timeout, 0);
2545 case FUTEX_UNLOCK_PI:
2546 if (futex_cmpxchg_enabled)
2547 ret = futex_unlock_pi(uaddr, fshared);
2549 case FUTEX_TRYLOCK_PI:
2550 if (futex_cmpxchg_enabled)
2551 ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1);
2553 case FUTEX_WAIT_REQUEUE_PI:
2554 val3 = FUTEX_BITSET_MATCH_ANY;
2555 ret = futex_wait_requeue_pi(uaddr, fshared, val, timeout, val3,
2558 case FUTEX_REQUEUE_PI:
2559 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL, 1);
2561 case FUTEX_CMP_REQUEUE_PI:
2562 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
2572 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
2573 struct timespec __user *, utime, u32 __user *, uaddr2,
2577 ktime_t t, *tp = NULL;
2579 int cmd = op & FUTEX_CMD_MASK;
2581 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
2582 cmd == FUTEX_WAIT_BITSET ||
2583 cmd == FUTEX_WAIT_REQUEUE_PI)) {
2584 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
2586 if (!timespec_valid(&ts))
2589 t = timespec_to_ktime(ts);
2590 if (cmd == FUTEX_WAIT)
2591 t = ktime_add_safe(ktime_get(), t);
2595 * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
2596 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
2598 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
2599 cmd == FUTEX_REQUEUE_PI || cmd == FUTEX_CMP_REQUEUE_PI ||
2600 cmd == FUTEX_WAKE_OP)
2601 val2 = (u32) (unsigned long) utime;
2603 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
2606 static int __init futex_init(void)
2612 * This will fail and we want it. Some arch implementations do
2613 * runtime detection of the futex_atomic_cmpxchg_inatomic()
2614 * functionality. We want to know that before we call in any
2615 * of the complex code paths. Also we want to prevent
2616 * registration of robust lists in that case. NULL is
2617 * guaranteed to fault and we get -EFAULT on functional
2618 * implementation, the non functional ones will return
2621 curval = cmpxchg_futex_value_locked(NULL, 0, 0);
2622 if (curval == -EFAULT)
2623 futex_cmpxchg_enabled = 1;
2625 for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
2626 plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock);
2627 spin_lock_init(&futex_queues[i].lock);
2632 __initcall(futex_init);