add dma_mapping_ops for SWIOTLB
[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / kernel / futex.c
blob002aa189eb09ae0d66617f3236e4f53e31913547
1 /*
2 * Fast Userspace Mutexes (which I call "Futexes!").
3 * (C) Rusty Russell, IBM 2002
5 * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
6 * (C) Copyright 2003 Red Hat Inc, All Rights Reserved
8 * Removed page pinning, fix privately mapped COW pages and other cleanups
9 * (C) Copyright 2003, 2004 Jamie Lokier
11 * Robust futex support started by Ingo Molnar
12 * (C) Copyright 2006 Red Hat Inc, All Rights Reserved
13 * Thanks to Thomas Gleixner for suggestions, analysis and fixes.
15 * PI-futex support started by Ingo Molnar and Thomas Gleixner
16 * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
17 * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
19 * PRIVATE futexes by Eric Dumazet
20 * Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
22 * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
23 * enough at me, Linus for the original (flawed) idea, Matthew
24 * Kirkwood for proof-of-concept implementation.
26 * "The futexes are also cursed."
27 * "But they come in a choice of three flavours!"
29 * This program is free software; you can redistribute it and/or modify
30 * it under the terms of the GNU General Public License as published by
31 * the Free Software Foundation; either version 2 of the License, or
32 * (at your option) any later version.
34 * This program is distributed in the hope that it will be useful,
35 * but WITHOUT ANY WARRANTY; without even the implied warranty of
36 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
37 * GNU General Public License for more details.
39 * You should have received a copy of the GNU General Public License
40 * along with this program; if not, write to the Free Software
41 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
43 #include <linux/slab.h>
44 #include <linux/poll.h>
45 #include <linux/fs.h>
46 #include <linux/file.h>
47 #include <linux/jhash.h>
48 #include <linux/init.h>
49 #include <linux/futex.h>
50 #include <linux/mount.h>
51 #include <linux/pagemap.h>
52 #include <linux/syscalls.h>
53 #include <linux/signal.h>
54 #include <linux/module.h>
55 #include <linux/magic.h>
56 #include <linux/pid.h>
57 #include <linux/nsproxy.h>
59 #include <asm/futex.h>
61 #include "rtmutex_common.h"
63 int __read_mostly futex_cmpxchg_enabled;
65 #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
68 * Priority Inheritance state:
70 struct futex_pi_state {
72 * list of 'owned' pi_state instances - these have to be
73 * cleaned up in do_exit() if the task exits prematurely:
75 struct list_head list;
78 * The PI object:
80 struct rt_mutex pi_mutex;
82 struct task_struct *owner;
83 atomic_t refcount;
85 union futex_key key;
89 * We use this hashed waitqueue instead of a normal wait_queue_t, so
90 * we can wake only the relevant ones (hashed queues may be shared).
92 * A futex_q has a woken state, just like tasks have TASK_RUNNING.
93 * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
94 * The order of wakup is always to make the first condition true, then
95 * wake up q->waiter, then make the second condition true.
97 struct futex_q {
98 struct plist_node list;
99 /* There can only be a single waiter */
100 wait_queue_head_t waiter;
102 /* Which hash list lock to use: */
103 spinlock_t *lock_ptr;
105 /* Key which the futex is hashed on: */
106 union futex_key key;
108 /* Optional priority inheritance state: */
109 struct futex_pi_state *pi_state;
110 struct task_struct *task;
112 /* Bitset for the optional bitmasked wakeup */
113 u32 bitset;
117 * Split the global futex_lock into every hash list lock.
119 struct futex_hash_bucket {
120 spinlock_t lock;
121 struct plist_head chain;
124 static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
127 * We hash on the keys returned from get_futex_key (see below).
129 static struct futex_hash_bucket *hash_futex(union futex_key *key)
131 u32 hash = jhash2((u32*)&key->both.word,
132 (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
133 key->both.offset);
134 return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
138 * Return 1 if two futex_keys are equal, 0 otherwise.
140 static inline int match_futex(union futex_key *key1, union futex_key *key2)
142 return (key1->both.word == key2->both.word
143 && key1->both.ptr == key2->both.ptr
144 && key1->both.offset == key2->both.offset);
148 * Take a reference to the resource addressed by a key.
149 * Can be called while holding spinlocks.
152 static void get_futex_key_refs(union futex_key *key)
154 if (!key->both.ptr)
155 return;
157 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
158 case FUT_OFF_INODE:
159 atomic_inc(&key->shared.inode->i_count);
160 break;
161 case FUT_OFF_MMSHARED:
162 atomic_inc(&key->private.mm->mm_count);
163 break;
168 * Drop a reference to the resource addressed by a key.
169 * The hash bucket spinlock must not be held.
171 static void drop_futex_key_refs(union futex_key *key)
173 if (!key->both.ptr) {
174 /* If we're here then we tried to put a key we failed to get */
175 WARN_ON_ONCE(1);
176 return;
179 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
180 case FUT_OFF_INODE:
181 iput(key->shared.inode);
182 break;
183 case FUT_OFF_MMSHARED:
184 mmdrop(key->private.mm);
185 break;
190 * get_futex_key - Get parameters which are the keys for a futex.
191 * @uaddr: virtual address of the futex
192 * @shared: NULL for a PROCESS_PRIVATE futex,
193 * &current->mm->mmap_sem for a PROCESS_SHARED futex
194 * @key: address where result is stored.
196 * Returns a negative error code or 0
197 * The key words are stored in *key on success.
199 * For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,
200 * offset_within_page). For private mappings, it's (uaddr, current->mm).
201 * We can usually work out the index without swapping in the page.
203 * fshared is NULL for PROCESS_PRIVATE futexes
204 * For other futexes, it points to &current->mm->mmap_sem and
205 * caller must have taken the reader lock. but NOT any spinlocks.
207 static int get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key)
209 unsigned long address = (unsigned long)uaddr;
210 struct mm_struct *mm = current->mm;
211 struct page *page;
212 int err;
215 * The futex address must be "naturally" aligned.
217 key->both.offset = address % PAGE_SIZE;
218 if (unlikely((address % sizeof(u32)) != 0))
219 return -EINVAL;
220 address -= key->both.offset;
223 * PROCESS_PRIVATE futexes are fast.
224 * As the mm cannot disappear under us and the 'key' only needs
225 * virtual address, we dont even have to find the underlying vma.
226 * Note : We do have to check 'uaddr' is a valid user address,
227 * but access_ok() should be faster than find_vma()
229 if (!fshared) {
230 if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))))
231 return -EFAULT;
232 key->private.mm = mm;
233 key->private.address = address;
234 get_futex_key_refs(key);
235 return 0;
238 again:
239 err = get_user_pages_fast(address, 1, 0, &page);
240 if (err < 0)
241 return err;
243 lock_page(page);
244 if (!page->mapping) {
245 unlock_page(page);
246 put_page(page);
247 goto again;
251 * Private mappings are handled in a simple way.
253 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
254 * it's a read-only handle, it's expected that futexes attach to
255 * the object not the particular process.
257 if (PageAnon(page)) {
258 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
259 key->private.mm = mm;
260 key->private.address = address;
261 } else {
262 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
263 key->shared.inode = page->mapping->host;
264 key->shared.pgoff = page->index;
267 get_futex_key_refs(key);
269 unlock_page(page);
270 put_page(page);
271 return 0;
274 static inline
275 void put_futex_key(int fshared, union futex_key *key)
277 drop_futex_key_refs(key);
280 static u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval)
282 u32 curval;
284 pagefault_disable();
285 curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
286 pagefault_enable();
288 return curval;
291 static int get_futex_value_locked(u32 *dest, u32 __user *from)
293 int ret;
295 pagefault_disable();
296 ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
297 pagefault_enable();
299 return ret ? -EFAULT : 0;
303 * Fault handling.
305 static int futex_handle_fault(unsigned long address, int attempt)
307 struct vm_area_struct * vma;
308 struct mm_struct *mm = current->mm;
309 int ret = -EFAULT;
311 if (attempt > 2)
312 return ret;
314 down_read(&mm->mmap_sem);
315 vma = find_vma(mm, address);
316 if (vma && address >= vma->vm_start &&
317 (vma->vm_flags & VM_WRITE)) {
318 int fault;
319 fault = handle_mm_fault(mm, vma, address, 1);
320 if (unlikely((fault & VM_FAULT_ERROR))) {
321 #if 0
322 /* XXX: let's do this when we verify it is OK */
323 if (ret & VM_FAULT_OOM)
324 ret = -ENOMEM;
325 #endif
326 } else {
327 ret = 0;
328 if (fault & VM_FAULT_MAJOR)
329 current->maj_flt++;
330 else
331 current->min_flt++;
334 up_read(&mm->mmap_sem);
335 return ret;
339 * PI code:
341 static int refill_pi_state_cache(void)
343 struct futex_pi_state *pi_state;
345 if (likely(current->pi_state_cache))
346 return 0;
348 pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
350 if (!pi_state)
351 return -ENOMEM;
353 INIT_LIST_HEAD(&pi_state->list);
354 /* pi_mutex gets initialized later */
355 pi_state->owner = NULL;
356 atomic_set(&pi_state->refcount, 1);
357 pi_state->key = FUTEX_KEY_INIT;
359 current->pi_state_cache = pi_state;
361 return 0;
364 static struct futex_pi_state * alloc_pi_state(void)
366 struct futex_pi_state *pi_state = current->pi_state_cache;
368 WARN_ON(!pi_state);
369 current->pi_state_cache = NULL;
371 return pi_state;
374 static void free_pi_state(struct futex_pi_state *pi_state)
376 if (!atomic_dec_and_test(&pi_state->refcount))
377 return;
380 * If pi_state->owner is NULL, the owner is most probably dying
381 * and has cleaned up the pi_state already
383 if (pi_state->owner) {
384 spin_lock_irq(&pi_state->owner->pi_lock);
385 list_del_init(&pi_state->list);
386 spin_unlock_irq(&pi_state->owner->pi_lock);
388 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
391 if (current->pi_state_cache)
392 kfree(pi_state);
393 else {
395 * pi_state->list is already empty.
396 * clear pi_state->owner.
397 * refcount is at 0 - put it back to 1.
399 pi_state->owner = NULL;
400 atomic_set(&pi_state->refcount, 1);
401 current->pi_state_cache = pi_state;
406 * Look up the task based on what TID userspace gave us.
407 * We dont trust it.
409 static struct task_struct * futex_find_get_task(pid_t pid)
411 struct task_struct *p;
412 const struct cred *cred = current_cred(), *pcred;
414 rcu_read_lock();
415 p = find_task_by_vpid(pid);
416 if (!p) {
417 p = ERR_PTR(-ESRCH);
418 } else {
419 pcred = __task_cred(p);
420 if (cred->euid != pcred->euid &&
421 cred->euid != pcred->uid)
422 p = ERR_PTR(-ESRCH);
423 else
424 get_task_struct(p);
427 rcu_read_unlock();
429 return p;
433 * This task is holding PI mutexes at exit time => bad.
434 * Kernel cleans up PI-state, but userspace is likely hosed.
435 * (Robust-futex cleanup is separate and might save the day for userspace.)
437 void exit_pi_state_list(struct task_struct *curr)
439 struct list_head *next, *head = &curr->pi_state_list;
440 struct futex_pi_state *pi_state;
441 struct futex_hash_bucket *hb;
442 union futex_key key = FUTEX_KEY_INIT;
444 if (!futex_cmpxchg_enabled)
445 return;
447 * We are a ZOMBIE and nobody can enqueue itself on
448 * pi_state_list anymore, but we have to be careful
449 * versus waiters unqueueing themselves:
451 spin_lock_irq(&curr->pi_lock);
452 while (!list_empty(head)) {
454 next = head->next;
455 pi_state = list_entry(next, struct futex_pi_state, list);
456 key = pi_state->key;
457 hb = hash_futex(&key);
458 spin_unlock_irq(&curr->pi_lock);
460 spin_lock(&hb->lock);
462 spin_lock_irq(&curr->pi_lock);
464 * We dropped the pi-lock, so re-check whether this
465 * task still owns the PI-state:
467 if (head->next != next) {
468 spin_unlock(&hb->lock);
469 continue;
472 WARN_ON(pi_state->owner != curr);
473 WARN_ON(list_empty(&pi_state->list));
474 list_del_init(&pi_state->list);
475 pi_state->owner = NULL;
476 spin_unlock_irq(&curr->pi_lock);
478 rt_mutex_unlock(&pi_state->pi_mutex);
480 spin_unlock(&hb->lock);
482 spin_lock_irq(&curr->pi_lock);
484 spin_unlock_irq(&curr->pi_lock);
487 static int
488 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
489 union futex_key *key, struct futex_pi_state **ps)
491 struct futex_pi_state *pi_state = NULL;
492 struct futex_q *this, *next;
493 struct plist_head *head;
494 struct task_struct *p;
495 pid_t pid = uval & FUTEX_TID_MASK;
497 head = &hb->chain;
499 plist_for_each_entry_safe(this, next, head, list) {
500 if (match_futex(&this->key, key)) {
502 * Another waiter already exists - bump up
503 * the refcount and return its pi_state:
505 pi_state = this->pi_state;
507 * Userspace might have messed up non PI and PI futexes
509 if (unlikely(!pi_state))
510 return -EINVAL;
512 WARN_ON(!atomic_read(&pi_state->refcount));
513 WARN_ON(pid && pi_state->owner &&
514 pi_state->owner->pid != pid);
516 atomic_inc(&pi_state->refcount);
517 *ps = pi_state;
519 return 0;
524 * We are the first waiter - try to look up the real owner and attach
525 * the new pi_state to it, but bail out when TID = 0
527 if (!pid)
528 return -ESRCH;
529 p = futex_find_get_task(pid);
530 if (IS_ERR(p))
531 return PTR_ERR(p);
534 * We need to look at the task state flags to figure out,
535 * whether the task is exiting. To protect against the do_exit
536 * change of the task flags, we do this protected by
537 * p->pi_lock:
539 spin_lock_irq(&p->pi_lock);
540 if (unlikely(p->flags & PF_EXITING)) {
542 * The task is on the way out. When PF_EXITPIDONE is
543 * set, we know that the task has finished the
544 * cleanup:
546 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
548 spin_unlock_irq(&p->pi_lock);
549 put_task_struct(p);
550 return ret;
553 pi_state = alloc_pi_state();
556 * Initialize the pi_mutex in locked state and make 'p'
557 * the owner of it:
559 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
561 /* Store the key for possible exit cleanups: */
562 pi_state->key = *key;
564 WARN_ON(!list_empty(&pi_state->list));
565 list_add(&pi_state->list, &p->pi_state_list);
566 pi_state->owner = p;
567 spin_unlock_irq(&p->pi_lock);
569 put_task_struct(p);
571 *ps = pi_state;
573 return 0;
577 * The hash bucket lock must be held when this is called.
578 * Afterwards, the futex_q must not be accessed.
580 static void wake_futex(struct futex_q *q)
582 plist_del(&q->list, &q->list.plist);
584 * The lock in wake_up_all() is a crucial memory barrier after the
585 * plist_del() and also before assigning to q->lock_ptr.
587 wake_up(&q->waiter);
589 * The waiting task can free the futex_q as soon as this is written,
590 * without taking any locks. This must come last.
592 * A memory barrier is required here to prevent the following store
593 * to lock_ptr from getting ahead of the wakeup. Clearing the lock
594 * at the end of wake_up_all() does not prevent this store from
595 * moving.
597 smp_wmb();
598 q->lock_ptr = NULL;
601 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
603 struct task_struct *new_owner;
604 struct futex_pi_state *pi_state = this->pi_state;
605 u32 curval, newval;
607 if (!pi_state)
608 return -EINVAL;
610 spin_lock(&pi_state->pi_mutex.wait_lock);
611 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
614 * This happens when we have stolen the lock and the original
615 * pending owner did not enqueue itself back on the rt_mutex.
616 * Thats not a tragedy. We know that way, that a lock waiter
617 * is on the fly. We make the futex_q waiter the pending owner.
619 if (!new_owner)
620 new_owner = this->task;
623 * We pass it to the next owner. (The WAITERS bit is always
624 * kept enabled while there is PI state around. We must also
625 * preserve the owner died bit.)
627 if (!(uval & FUTEX_OWNER_DIED)) {
628 int ret = 0;
630 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
632 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
634 if (curval == -EFAULT)
635 ret = -EFAULT;
636 else if (curval != uval)
637 ret = -EINVAL;
638 if (ret) {
639 spin_unlock(&pi_state->pi_mutex.wait_lock);
640 return ret;
644 spin_lock_irq(&pi_state->owner->pi_lock);
645 WARN_ON(list_empty(&pi_state->list));
646 list_del_init(&pi_state->list);
647 spin_unlock_irq(&pi_state->owner->pi_lock);
649 spin_lock_irq(&new_owner->pi_lock);
650 WARN_ON(!list_empty(&pi_state->list));
651 list_add(&pi_state->list, &new_owner->pi_state_list);
652 pi_state->owner = new_owner;
653 spin_unlock_irq(&new_owner->pi_lock);
655 spin_unlock(&pi_state->pi_mutex.wait_lock);
656 rt_mutex_unlock(&pi_state->pi_mutex);
658 return 0;
661 static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
663 u32 oldval;
666 * There is no waiter, so we unlock the futex. The owner died
667 * bit has not to be preserved here. We are the owner:
669 oldval = cmpxchg_futex_value_locked(uaddr, uval, 0);
671 if (oldval == -EFAULT)
672 return oldval;
673 if (oldval != uval)
674 return -EAGAIN;
676 return 0;
680 * Express the locking dependencies for lockdep:
682 static inline void
683 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
685 if (hb1 <= hb2) {
686 spin_lock(&hb1->lock);
687 if (hb1 < hb2)
688 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
689 } else { /* hb1 > hb2 */
690 spin_lock(&hb2->lock);
691 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
696 * Wake up all waiters hashed on the physical page that is mapped
697 * to this virtual address:
699 static int futex_wake(u32 __user *uaddr, int fshared, int nr_wake, u32 bitset)
701 struct futex_hash_bucket *hb;
702 struct futex_q *this, *next;
703 struct plist_head *head;
704 union futex_key key = FUTEX_KEY_INIT;
705 int ret;
707 if (!bitset)
708 return -EINVAL;
710 ret = get_futex_key(uaddr, fshared, &key);
711 if (unlikely(ret != 0))
712 goto out;
714 hb = hash_futex(&key);
715 spin_lock(&hb->lock);
716 head = &hb->chain;
718 plist_for_each_entry_safe(this, next, head, list) {
719 if (match_futex (&this->key, &key)) {
720 if (this->pi_state) {
721 ret = -EINVAL;
722 break;
725 /* Check if one of the bits is set in both bitsets */
726 if (!(this->bitset & bitset))
727 continue;
729 wake_futex(this);
730 if (++ret >= nr_wake)
731 break;
735 spin_unlock(&hb->lock);
736 put_futex_key(fshared, &key);
737 out:
738 return ret;
742 * Wake up all waiters hashed on the physical page that is mapped
743 * to this virtual address:
745 static int
746 futex_wake_op(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
747 int nr_wake, int nr_wake2, int op)
749 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
750 struct futex_hash_bucket *hb1, *hb2;
751 struct plist_head *head;
752 struct futex_q *this, *next;
753 int ret, op_ret, attempt = 0;
755 retryfull:
756 ret = get_futex_key(uaddr1, fshared, &key1);
757 if (unlikely(ret != 0))
758 goto out;
759 ret = get_futex_key(uaddr2, fshared, &key2);
760 if (unlikely(ret != 0))
761 goto out_put_key1;
763 hb1 = hash_futex(&key1);
764 hb2 = hash_futex(&key2);
766 retry:
767 double_lock_hb(hb1, hb2);
769 op_ret = futex_atomic_op_inuser(op, uaddr2);
770 if (unlikely(op_ret < 0)) {
771 u32 dummy;
773 spin_unlock(&hb1->lock);
774 if (hb1 != hb2)
775 spin_unlock(&hb2->lock);
777 #ifndef CONFIG_MMU
779 * we don't get EFAULT from MMU faults if we don't have an MMU,
780 * but we might get them from range checking
782 ret = op_ret;
783 goto out_put_keys;
784 #endif
786 if (unlikely(op_ret != -EFAULT)) {
787 ret = op_ret;
788 goto out_put_keys;
792 * futex_atomic_op_inuser needs to both read and write
793 * *(int __user *)uaddr2, but we can't modify it
794 * non-atomically. Therefore, if get_user below is not
795 * enough, we need to handle the fault ourselves, while
796 * still holding the mmap_sem.
798 if (attempt++) {
799 ret = futex_handle_fault((unsigned long)uaddr2,
800 attempt);
801 if (ret)
802 goto out_put_keys;
803 goto retry;
806 ret = get_user(dummy, uaddr2);
807 if (ret)
808 return ret;
810 goto retryfull;
813 head = &hb1->chain;
815 plist_for_each_entry_safe(this, next, head, list) {
816 if (match_futex (&this->key, &key1)) {
817 wake_futex(this);
818 if (++ret >= nr_wake)
819 break;
823 if (op_ret > 0) {
824 head = &hb2->chain;
826 op_ret = 0;
827 plist_for_each_entry_safe(this, next, head, list) {
828 if (match_futex (&this->key, &key2)) {
829 wake_futex(this);
830 if (++op_ret >= nr_wake2)
831 break;
834 ret += op_ret;
837 spin_unlock(&hb1->lock);
838 if (hb1 != hb2)
839 spin_unlock(&hb2->lock);
840 out_put_keys:
841 put_futex_key(fshared, &key2);
842 out_put_key1:
843 put_futex_key(fshared, &key1);
844 out:
845 return ret;
849 * Requeue all waiters hashed on one physical page to another
850 * physical page.
852 static int futex_requeue(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
853 int nr_wake, int nr_requeue, u32 *cmpval)
855 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
856 struct futex_hash_bucket *hb1, *hb2;
857 struct plist_head *head1;
858 struct futex_q *this, *next;
859 int ret, drop_count = 0;
861 retry:
862 ret = get_futex_key(uaddr1, fshared, &key1);
863 if (unlikely(ret != 0))
864 goto out;
865 ret = get_futex_key(uaddr2, fshared, &key2);
866 if (unlikely(ret != 0))
867 goto out_put_key1;
869 hb1 = hash_futex(&key1);
870 hb2 = hash_futex(&key2);
872 double_lock_hb(hb1, hb2);
874 if (likely(cmpval != NULL)) {
875 u32 curval;
877 ret = get_futex_value_locked(&curval, uaddr1);
879 if (unlikely(ret)) {
880 spin_unlock(&hb1->lock);
881 if (hb1 != hb2)
882 spin_unlock(&hb2->lock);
884 ret = get_user(curval, uaddr1);
886 if (!ret)
887 goto retry;
889 goto out_put_keys;
891 if (curval != *cmpval) {
892 ret = -EAGAIN;
893 goto out_unlock;
897 head1 = &hb1->chain;
898 plist_for_each_entry_safe(this, next, head1, list) {
899 if (!match_futex (&this->key, &key1))
900 continue;
901 if (++ret <= nr_wake) {
902 wake_futex(this);
903 } else {
905 * If key1 and key2 hash to the same bucket, no need to
906 * requeue.
908 if (likely(head1 != &hb2->chain)) {
909 plist_del(&this->list, &hb1->chain);
910 plist_add(&this->list, &hb2->chain);
911 this->lock_ptr = &hb2->lock;
912 #ifdef CONFIG_DEBUG_PI_LIST
913 this->list.plist.lock = &hb2->lock;
914 #endif
916 this->key = key2;
917 get_futex_key_refs(&key2);
918 drop_count++;
920 if (ret - nr_wake >= nr_requeue)
921 break;
925 out_unlock:
926 spin_unlock(&hb1->lock);
927 if (hb1 != hb2)
928 spin_unlock(&hb2->lock);
930 /* drop_futex_key_refs() must be called outside the spinlocks. */
931 while (--drop_count >= 0)
932 drop_futex_key_refs(&key1);
934 out_put_keys:
935 put_futex_key(fshared, &key2);
936 out_put_key1:
937 put_futex_key(fshared, &key1);
938 out:
939 return ret;
942 /* The key must be already stored in q->key. */
943 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
945 struct futex_hash_bucket *hb;
947 init_waitqueue_head(&q->waiter);
949 get_futex_key_refs(&q->key);
950 hb = hash_futex(&q->key);
951 q->lock_ptr = &hb->lock;
953 spin_lock(&hb->lock);
954 return hb;
957 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
959 int prio;
962 * The priority used to register this element is
963 * - either the real thread-priority for the real-time threads
964 * (i.e. threads with a priority lower than MAX_RT_PRIO)
965 * - or MAX_RT_PRIO for non-RT threads.
966 * Thus, all RT-threads are woken first in priority order, and
967 * the others are woken last, in FIFO order.
969 prio = min(current->normal_prio, MAX_RT_PRIO);
971 plist_node_init(&q->list, prio);
972 #ifdef CONFIG_DEBUG_PI_LIST
973 q->list.plist.lock = &hb->lock;
974 #endif
975 plist_add(&q->list, &hb->chain);
976 q->task = current;
977 spin_unlock(&hb->lock);
980 static inline void
981 queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
983 spin_unlock(&hb->lock);
984 drop_futex_key_refs(&q->key);
988 * queue_me and unqueue_me must be called as a pair, each
989 * exactly once. They are called with the hashed spinlock held.
992 /* Return 1 if we were still queued (ie. 0 means we were woken) */
993 static int unqueue_me(struct futex_q *q)
995 spinlock_t *lock_ptr;
996 int ret = 0;
998 /* In the common case we don't take the spinlock, which is nice. */
999 retry:
1000 lock_ptr = q->lock_ptr;
1001 barrier();
1002 if (lock_ptr != NULL) {
1003 spin_lock(lock_ptr);
1005 * q->lock_ptr can change between reading it and
1006 * spin_lock(), causing us to take the wrong lock. This
1007 * corrects the race condition.
1009 * Reasoning goes like this: if we have the wrong lock,
1010 * q->lock_ptr must have changed (maybe several times)
1011 * between reading it and the spin_lock(). It can
1012 * change again after the spin_lock() but only if it was
1013 * already changed before the spin_lock(). It cannot,
1014 * however, change back to the original value. Therefore
1015 * we can detect whether we acquired the correct lock.
1017 if (unlikely(lock_ptr != q->lock_ptr)) {
1018 spin_unlock(lock_ptr);
1019 goto retry;
1021 WARN_ON(plist_node_empty(&q->list));
1022 plist_del(&q->list, &q->list.plist);
1024 BUG_ON(q->pi_state);
1026 spin_unlock(lock_ptr);
1027 ret = 1;
1030 drop_futex_key_refs(&q->key);
1031 return ret;
1035 * PI futexes can not be requeued and must remove themself from the
1036 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1037 * and dropped here.
1039 static void unqueue_me_pi(struct futex_q *q)
1041 WARN_ON(plist_node_empty(&q->list));
1042 plist_del(&q->list, &q->list.plist);
1044 BUG_ON(!q->pi_state);
1045 free_pi_state(q->pi_state);
1046 q->pi_state = NULL;
1048 spin_unlock(q->lock_ptr);
1050 drop_futex_key_refs(&q->key);
1054 * Fixup the pi_state owner with the new owner.
1056 * Must be called with hash bucket lock held and mm->sem held for non
1057 * private futexes.
1059 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1060 struct task_struct *newowner, int fshared)
1062 u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
1063 struct futex_pi_state *pi_state = q->pi_state;
1064 struct task_struct *oldowner = pi_state->owner;
1065 u32 uval, curval, newval;
1066 int ret, attempt = 0;
1068 /* Owner died? */
1069 if (!pi_state->owner)
1070 newtid |= FUTEX_OWNER_DIED;
1073 * We are here either because we stole the rtmutex from the
1074 * pending owner or we are the pending owner which failed to
1075 * get the rtmutex. We have to replace the pending owner TID
1076 * in the user space variable. This must be atomic as we have
1077 * to preserve the owner died bit here.
1079 * Note: We write the user space value _before_ changing the
1080 * pi_state because we can fault here. Imagine swapped out
1081 * pages or a fork, which was running right before we acquired
1082 * mmap_sem, that marked all the anonymous memory readonly for
1083 * cow.
1085 * Modifying pi_state _before_ the user space value would
1086 * leave the pi_state in an inconsistent state when we fault
1087 * here, because we need to drop the hash bucket lock to
1088 * handle the fault. This might be observed in the PID check
1089 * in lookup_pi_state.
1091 retry:
1092 if (get_futex_value_locked(&uval, uaddr))
1093 goto handle_fault;
1095 while (1) {
1096 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1098 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
1100 if (curval == -EFAULT)
1101 goto handle_fault;
1102 if (curval == uval)
1103 break;
1104 uval = curval;
1108 * We fixed up user space. Now we need to fix the pi_state
1109 * itself.
1111 if (pi_state->owner != NULL) {
1112 spin_lock_irq(&pi_state->owner->pi_lock);
1113 WARN_ON(list_empty(&pi_state->list));
1114 list_del_init(&pi_state->list);
1115 spin_unlock_irq(&pi_state->owner->pi_lock);
1118 pi_state->owner = newowner;
1120 spin_lock_irq(&newowner->pi_lock);
1121 WARN_ON(!list_empty(&pi_state->list));
1122 list_add(&pi_state->list, &newowner->pi_state_list);
1123 spin_unlock_irq(&newowner->pi_lock);
1124 return 0;
1127 * To handle the page fault we need to drop the hash bucket
1128 * lock here. That gives the other task (either the pending
1129 * owner itself or the task which stole the rtmutex) the
1130 * chance to try the fixup of the pi_state. So once we are
1131 * back from handling the fault we need to check the pi_state
1132 * after reacquiring the hash bucket lock and before trying to
1133 * do another fixup. When the fixup has been done already we
1134 * simply return.
1136 handle_fault:
1137 spin_unlock(q->lock_ptr);
1139 ret = futex_handle_fault((unsigned long)uaddr, attempt++);
1141 spin_lock(q->lock_ptr);
1144 * Check if someone else fixed it for us:
1146 if (pi_state->owner != oldowner)
1147 return 0;
1149 if (ret)
1150 return ret;
1152 goto retry;
1156 * In case we must use restart_block to restart a futex_wait,
1157 * we encode in the 'flags' shared capability
1159 #define FLAGS_SHARED 0x01
1160 #define FLAGS_CLOCKRT 0x02
1162 static long futex_wait_restart(struct restart_block *restart);
1164 static int futex_wait(u32 __user *uaddr, int fshared,
1165 u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
1167 struct task_struct *curr = current;
1168 DECLARE_WAITQUEUE(wait, curr);
1169 struct futex_hash_bucket *hb;
1170 struct futex_q q;
1171 u32 uval;
1172 int ret;
1173 struct hrtimer_sleeper t;
1174 int rem = 0;
1176 if (!bitset)
1177 return -EINVAL;
1179 q.pi_state = NULL;
1180 q.bitset = bitset;
1181 retry:
1182 q.key = FUTEX_KEY_INIT;
1183 ret = get_futex_key(uaddr, fshared, &q.key);
1184 if (unlikely(ret != 0))
1185 goto out;
1187 hb = queue_lock(&q);
1190 * Access the page AFTER the futex is queued.
1191 * Order is important:
1193 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1194 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
1196 * The basic logical guarantee of a futex is that it blocks ONLY
1197 * if cond(var) is known to be true at the time of blocking, for
1198 * any cond. If we queued after testing *uaddr, that would open
1199 * a race condition where we could block indefinitely with
1200 * cond(var) false, which would violate the guarantee.
1202 * A consequence is that futex_wait() can return zero and absorb
1203 * a wakeup when *uaddr != val on entry to the syscall. This is
1204 * rare, but normal.
1206 * for shared futexes, we hold the mmap semaphore, so the mapping
1207 * cannot have changed since we looked it up in get_futex_key.
1209 ret = get_futex_value_locked(&uval, uaddr);
1211 if (unlikely(ret)) {
1212 queue_unlock(&q, hb);
1213 put_futex_key(fshared, &q.key);
1215 ret = get_user(uval, uaddr);
1217 if (!ret)
1218 goto retry;
1219 return ret;
1221 ret = -EWOULDBLOCK;
1222 if (uval != val)
1223 goto out_unlock_put_key;
1225 /* Only actually queue if *uaddr contained val. */
1226 queue_me(&q, hb);
1229 * There might have been scheduling since the queue_me(), as we
1230 * cannot hold a spinlock across the get_user() in case it
1231 * faults, and we cannot just set TASK_INTERRUPTIBLE state when
1232 * queueing ourselves into the futex hash. This code thus has to
1233 * rely on the futex_wake() code removing us from hash when it
1234 * wakes us up.
1237 /* add_wait_queue is the barrier after __set_current_state. */
1238 __set_current_state(TASK_INTERRUPTIBLE);
1239 add_wait_queue(&q.waiter, &wait);
1241 * !plist_node_empty() is safe here without any lock.
1242 * q.lock_ptr != 0 is not safe, because of ordering against wakeup.
1244 if (likely(!plist_node_empty(&q.list))) {
1245 if (!abs_time)
1246 schedule();
1247 else {
1248 unsigned long slack;
1249 slack = current->timer_slack_ns;
1250 if (rt_task(current))
1251 slack = 0;
1252 hrtimer_init_on_stack(&t.timer,
1253 clockrt ? CLOCK_REALTIME :
1254 CLOCK_MONOTONIC,
1255 HRTIMER_MODE_ABS);
1256 hrtimer_init_sleeper(&t, current);
1257 hrtimer_set_expires_range_ns(&t.timer, *abs_time, slack);
1259 hrtimer_start_expires(&t.timer, HRTIMER_MODE_ABS);
1260 if (!hrtimer_active(&t.timer))
1261 t.task = NULL;
1264 * the timer could have already expired, in which
1265 * case current would be flagged for rescheduling.
1266 * Don't bother calling schedule.
1268 if (likely(t.task))
1269 schedule();
1271 hrtimer_cancel(&t.timer);
1273 /* Flag if a timeout occured */
1274 rem = (t.task == NULL);
1276 destroy_hrtimer_on_stack(&t.timer);
1279 __set_current_state(TASK_RUNNING);
1282 * NOTE: we don't remove ourselves from the waitqueue because
1283 * we are the only user of it.
1286 /* If we were woken (and unqueued), we succeeded, whatever. */
1287 if (!unqueue_me(&q))
1288 return 0;
1289 if (rem)
1290 return -ETIMEDOUT;
1293 * We expect signal_pending(current), but another thread may
1294 * have handled it for us already.
1296 if (!abs_time)
1297 return -ERESTARTSYS;
1298 else {
1299 struct restart_block *restart;
1300 restart = &current_thread_info()->restart_block;
1301 restart->fn = futex_wait_restart;
1302 restart->futex.uaddr = (u32 *)uaddr;
1303 restart->futex.val = val;
1304 restart->futex.time = abs_time->tv64;
1305 restart->futex.bitset = bitset;
1306 restart->futex.flags = 0;
1308 if (fshared)
1309 restart->futex.flags |= FLAGS_SHARED;
1310 if (clockrt)
1311 restart->futex.flags |= FLAGS_CLOCKRT;
1312 return -ERESTART_RESTARTBLOCK;
1315 out_unlock_put_key:
1316 queue_unlock(&q, hb);
1317 put_futex_key(fshared, &q.key);
1319 out:
1320 return ret;
1324 static long futex_wait_restart(struct restart_block *restart)
1326 u32 __user *uaddr = (u32 __user *)restart->futex.uaddr;
1327 int fshared = 0;
1328 ktime_t t;
1330 t.tv64 = restart->futex.time;
1331 restart->fn = do_no_restart_syscall;
1332 if (restart->futex.flags & FLAGS_SHARED)
1333 fshared = 1;
1334 return (long)futex_wait(uaddr, fshared, restart->futex.val, &t,
1335 restart->futex.bitset,
1336 restart->futex.flags & FLAGS_CLOCKRT);
1341 * Userspace tried a 0 -> TID atomic transition of the futex value
1342 * and failed. The kernel side here does the whole locking operation:
1343 * if there are waiters then it will block, it does PI, etc. (Due to
1344 * races the kernel might see a 0 value of the futex too.)
1346 static int futex_lock_pi(u32 __user *uaddr, int fshared,
1347 int detect, ktime_t *time, int trylock)
1349 struct hrtimer_sleeper timeout, *to = NULL;
1350 struct task_struct *curr = current;
1351 struct futex_hash_bucket *hb;
1352 u32 uval, newval, curval;
1353 struct futex_q q;
1354 int ret, lock_taken, ownerdied = 0, attempt = 0;
1356 if (refill_pi_state_cache())
1357 return -ENOMEM;
1359 if (time) {
1360 to = &timeout;
1361 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
1362 HRTIMER_MODE_ABS);
1363 hrtimer_init_sleeper(to, current);
1364 hrtimer_set_expires(&to->timer, *time);
1367 q.pi_state = NULL;
1368 retry:
1369 q.key = FUTEX_KEY_INIT;
1370 ret = get_futex_key(uaddr, fshared, &q.key);
1371 if (unlikely(ret != 0))
1372 goto out;
1374 retry_unlocked:
1375 hb = queue_lock(&q);
1377 retry_locked:
1378 ret = lock_taken = 0;
1381 * To avoid races, we attempt to take the lock here again
1382 * (by doing a 0 -> TID atomic cmpxchg), while holding all
1383 * the locks. It will most likely not succeed.
1385 newval = task_pid_vnr(current);
1387 curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
1389 if (unlikely(curval == -EFAULT))
1390 goto uaddr_faulted;
1393 * Detect deadlocks. In case of REQUEUE_PI this is a valid
1394 * situation and we return success to user space.
1396 if (unlikely((curval & FUTEX_TID_MASK) == task_pid_vnr(current))) {
1397 ret = -EDEADLK;
1398 goto out_unlock_put_key;
1402 * Surprise - we got the lock. Just return to userspace:
1404 if (unlikely(!curval))
1405 goto out_unlock_put_key;
1407 uval = curval;
1410 * Set the WAITERS flag, so the owner will know it has someone
1411 * to wake at next unlock
1413 newval = curval | FUTEX_WAITERS;
1416 * There are two cases, where a futex might have no owner (the
1417 * owner TID is 0): OWNER_DIED. We take over the futex in this
1418 * case. We also do an unconditional take over, when the owner
1419 * of the futex died.
1421 * This is safe as we are protected by the hash bucket lock !
1423 if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
1424 /* Keep the OWNER_DIED bit */
1425 newval = (curval & ~FUTEX_TID_MASK) | task_pid_vnr(current);
1426 ownerdied = 0;
1427 lock_taken = 1;
1430 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
1432 if (unlikely(curval == -EFAULT))
1433 goto uaddr_faulted;
1434 if (unlikely(curval != uval))
1435 goto retry_locked;
1438 * We took the lock due to owner died take over.
1440 if (unlikely(lock_taken))
1441 goto out_unlock_put_key;
1444 * We dont have the lock. Look up the PI state (or create it if
1445 * we are the first waiter):
1447 ret = lookup_pi_state(uval, hb, &q.key, &q.pi_state);
1449 if (unlikely(ret)) {
1450 switch (ret) {
1452 case -EAGAIN:
1454 * Task is exiting and we just wait for the
1455 * exit to complete.
1457 queue_unlock(&q, hb);
1458 cond_resched();
1459 goto retry;
1461 case -ESRCH:
1463 * No owner found for this futex. Check if the
1464 * OWNER_DIED bit is set to figure out whether
1465 * this is a robust futex or not.
1467 if (get_futex_value_locked(&curval, uaddr))
1468 goto uaddr_faulted;
1471 * We simply start over in case of a robust
1472 * futex. The code above will take the futex
1473 * and return happy.
1475 if (curval & FUTEX_OWNER_DIED) {
1476 ownerdied = 1;
1477 goto retry_locked;
1479 default:
1480 goto out_unlock_put_key;
1485 * Only actually queue now that the atomic ops are done:
1487 queue_me(&q, hb);
1489 WARN_ON(!q.pi_state);
1491 * Block on the PI mutex:
1493 if (!trylock)
1494 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
1495 else {
1496 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
1497 /* Fixup the trylock return value: */
1498 ret = ret ? 0 : -EWOULDBLOCK;
1501 spin_lock(q.lock_ptr);
1503 if (!ret) {
1505 * Got the lock. We might not be the anticipated owner
1506 * if we did a lock-steal - fix up the PI-state in
1507 * that case:
1509 if (q.pi_state->owner != curr)
1510 ret = fixup_pi_state_owner(uaddr, &q, curr, fshared);
1511 } else {
1513 * Catch the rare case, where the lock was released
1514 * when we were on the way back before we locked the
1515 * hash bucket.
1517 if (q.pi_state->owner == curr) {
1519 * Try to get the rt_mutex now. This might
1520 * fail as some other task acquired the
1521 * rt_mutex after we removed ourself from the
1522 * rt_mutex waiters list.
1524 if (rt_mutex_trylock(&q.pi_state->pi_mutex))
1525 ret = 0;
1526 else {
1528 * pi_state is incorrect, some other
1529 * task did a lock steal and we
1530 * returned due to timeout or signal
1531 * without taking the rt_mutex. Too
1532 * late. We can access the
1533 * rt_mutex_owner without locking, as
1534 * the other task is now blocked on
1535 * the hash bucket lock. Fix the state
1536 * up.
1538 struct task_struct *owner;
1539 int res;
1541 owner = rt_mutex_owner(&q.pi_state->pi_mutex);
1542 res = fixup_pi_state_owner(uaddr, &q, owner,
1543 fshared);
1545 /* propagate -EFAULT, if the fixup failed */
1546 if (res)
1547 ret = res;
1549 } else {
1551 * Paranoia check. If we did not take the lock
1552 * in the trylock above, then we should not be
1553 * the owner of the rtmutex, neither the real
1554 * nor the pending one:
1556 if (rt_mutex_owner(&q.pi_state->pi_mutex) == curr)
1557 printk(KERN_ERR "futex_lock_pi: ret = %d "
1558 "pi-mutex: %p pi-state %p\n", ret,
1559 q.pi_state->pi_mutex.owner,
1560 q.pi_state->owner);
1564 /* Unqueue and drop the lock */
1565 unqueue_me_pi(&q);
1567 if (to)
1568 destroy_hrtimer_on_stack(&to->timer);
1569 return ret != -EINTR ? ret : -ERESTARTNOINTR;
1571 out_unlock_put_key:
1572 queue_unlock(&q, hb);
1574 out_put_key:
1575 put_futex_key(fshared, &q.key);
1576 out:
1577 if (to)
1578 destroy_hrtimer_on_stack(&to->timer);
1579 return ret;
1581 uaddr_faulted:
1583 * We have to r/w *(int __user *)uaddr, and we have to modify it
1584 * atomically. Therefore, if we continue to fault after get_user()
1585 * below, we need to handle the fault ourselves, while still holding
1586 * the mmap_sem. This can occur if the uaddr is under contention as
1587 * we have to drop the mmap_sem in order to call get_user().
1589 queue_unlock(&q, hb);
1591 if (attempt++) {
1592 ret = futex_handle_fault((unsigned long)uaddr, attempt);
1593 if (ret)
1594 goto out_put_key;
1595 goto retry_unlocked;
1598 ret = get_user(uval, uaddr);
1599 if (!ret)
1600 goto retry;
1602 if (to)
1603 destroy_hrtimer_on_stack(&to->timer);
1604 return ret;
1608 * Userspace attempted a TID -> 0 atomic transition, and failed.
1609 * This is the in-kernel slowpath: we look up the PI state (if any),
1610 * and do the rt-mutex unlock.
1612 static int futex_unlock_pi(u32 __user *uaddr, int fshared)
1614 struct futex_hash_bucket *hb;
1615 struct futex_q *this, *next;
1616 u32 uval;
1617 struct plist_head *head;
1618 union futex_key key = FUTEX_KEY_INIT;
1619 int ret, attempt = 0;
1621 retry:
1622 if (get_user(uval, uaddr))
1623 return -EFAULT;
1625 * We release only a lock we actually own:
1627 if ((uval & FUTEX_TID_MASK) != task_pid_vnr(current))
1628 return -EPERM;
1630 ret = get_futex_key(uaddr, fshared, &key);
1631 if (unlikely(ret != 0))
1632 goto out;
1634 hb = hash_futex(&key);
1635 retry_unlocked:
1636 spin_lock(&hb->lock);
1639 * To avoid races, try to do the TID -> 0 atomic transition
1640 * again. If it succeeds then we can return without waking
1641 * anyone else up:
1643 if (!(uval & FUTEX_OWNER_DIED))
1644 uval = cmpxchg_futex_value_locked(uaddr, task_pid_vnr(current), 0);
1647 if (unlikely(uval == -EFAULT))
1648 goto pi_faulted;
1650 * Rare case: we managed to release the lock atomically,
1651 * no need to wake anyone else up:
1653 if (unlikely(uval == task_pid_vnr(current)))
1654 goto out_unlock;
1657 * Ok, other tasks may need to be woken up - check waiters
1658 * and do the wakeup if necessary:
1660 head = &hb->chain;
1662 plist_for_each_entry_safe(this, next, head, list) {
1663 if (!match_futex (&this->key, &key))
1664 continue;
1665 ret = wake_futex_pi(uaddr, uval, this);
1667 * The atomic access to the futex value
1668 * generated a pagefault, so retry the
1669 * user-access and the wakeup:
1671 if (ret == -EFAULT)
1672 goto pi_faulted;
1673 goto out_unlock;
1676 * No waiters - kernel unlocks the futex:
1678 if (!(uval & FUTEX_OWNER_DIED)) {
1679 ret = unlock_futex_pi(uaddr, uval);
1680 if (ret == -EFAULT)
1681 goto pi_faulted;
1684 out_unlock:
1685 spin_unlock(&hb->lock);
1686 put_futex_key(fshared, &key);
1688 out:
1689 return ret;
1691 pi_faulted:
1693 * We have to r/w *(int __user *)uaddr, and we have to modify it
1694 * atomically. Therefore, if we continue to fault after get_user()
1695 * below, we need to handle the fault ourselves, while still holding
1696 * the mmap_sem. This can occur if the uaddr is under contention as
1697 * we have to drop the mmap_sem in order to call get_user().
1699 spin_unlock(&hb->lock);
1701 if (attempt++) {
1702 ret = futex_handle_fault((unsigned long)uaddr, attempt);
1703 if (ret)
1704 goto out;
1705 uval = 0;
1706 goto retry_unlocked;
1709 ret = get_user(uval, uaddr);
1710 if (!ret)
1711 goto retry;
1713 return ret;
1717 * Support for robust futexes: the kernel cleans up held futexes at
1718 * thread exit time.
1720 * Implementation: user-space maintains a per-thread list of locks it
1721 * is holding. Upon do_exit(), the kernel carefully walks this list,
1722 * and marks all locks that are owned by this thread with the
1723 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
1724 * always manipulated with the lock held, so the list is private and
1725 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
1726 * field, to allow the kernel to clean up if the thread dies after
1727 * acquiring the lock, but just before it could have added itself to
1728 * the list. There can only be one such pending lock.
1732 * sys_set_robust_list - set the robust-futex list head of a task
1733 * @head: pointer to the list-head
1734 * @len: length of the list-head, as userspace expects
1736 asmlinkage long
1737 sys_set_robust_list(struct robust_list_head __user *head,
1738 size_t len)
1740 if (!futex_cmpxchg_enabled)
1741 return -ENOSYS;
1743 * The kernel knows only one size for now:
1745 if (unlikely(len != sizeof(*head)))
1746 return -EINVAL;
1748 current->robust_list = head;
1750 return 0;
1754 * sys_get_robust_list - get the robust-futex list head of a task
1755 * @pid: pid of the process [zero for current task]
1756 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
1757 * @len_ptr: pointer to a length field, the kernel fills in the header size
1759 asmlinkage long
1760 sys_get_robust_list(int pid, struct robust_list_head __user * __user *head_ptr,
1761 size_t __user *len_ptr)
1763 struct robust_list_head __user *head;
1764 unsigned long ret;
1765 const struct cred *cred = current_cred(), *pcred;
1767 if (!futex_cmpxchg_enabled)
1768 return -ENOSYS;
1770 if (!pid)
1771 head = current->robust_list;
1772 else {
1773 struct task_struct *p;
1775 ret = -ESRCH;
1776 rcu_read_lock();
1777 p = find_task_by_vpid(pid);
1778 if (!p)
1779 goto err_unlock;
1780 ret = -EPERM;
1781 pcred = __task_cred(p);
1782 if (cred->euid != pcred->euid &&
1783 cred->euid != pcred->uid &&
1784 !capable(CAP_SYS_PTRACE))
1785 goto err_unlock;
1786 head = p->robust_list;
1787 rcu_read_unlock();
1790 if (put_user(sizeof(*head), len_ptr))
1791 return -EFAULT;
1792 return put_user(head, head_ptr);
1794 err_unlock:
1795 rcu_read_unlock();
1797 return ret;
1801 * Process a futex-list entry, check whether it's owned by the
1802 * dying task, and do notification if so:
1804 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
1806 u32 uval, nval, mval;
1808 retry:
1809 if (get_user(uval, uaddr))
1810 return -1;
1812 if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
1814 * Ok, this dying thread is truly holding a futex
1815 * of interest. Set the OWNER_DIED bit atomically
1816 * via cmpxchg, and if the value had FUTEX_WAITERS
1817 * set, wake up a waiter (if any). (We have to do a
1818 * futex_wake() even if OWNER_DIED is already set -
1819 * to handle the rare but possible case of recursive
1820 * thread-death.) The rest of the cleanup is done in
1821 * userspace.
1823 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
1824 nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
1826 if (nval == -EFAULT)
1827 return -1;
1829 if (nval != uval)
1830 goto retry;
1833 * Wake robust non-PI futexes here. The wakeup of
1834 * PI futexes happens in exit_pi_state():
1836 if (!pi && (uval & FUTEX_WAITERS))
1837 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
1839 return 0;
1843 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
1845 static inline int fetch_robust_entry(struct robust_list __user **entry,
1846 struct robust_list __user * __user *head,
1847 int *pi)
1849 unsigned long uentry;
1851 if (get_user(uentry, (unsigned long __user *)head))
1852 return -EFAULT;
1854 *entry = (void __user *)(uentry & ~1UL);
1855 *pi = uentry & 1;
1857 return 0;
1861 * Walk curr->robust_list (very carefully, it's a userspace list!)
1862 * and mark any locks found there dead, and notify any waiters.
1864 * We silently return on any sign of list-walking problem.
1866 void exit_robust_list(struct task_struct *curr)
1868 struct robust_list_head __user *head = curr->robust_list;
1869 struct robust_list __user *entry, *next_entry, *pending;
1870 unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
1871 unsigned long futex_offset;
1872 int rc;
1874 if (!futex_cmpxchg_enabled)
1875 return;
1878 * Fetch the list head (which was registered earlier, via
1879 * sys_set_robust_list()):
1881 if (fetch_robust_entry(&entry, &head->list.next, &pi))
1882 return;
1884 * Fetch the relative futex offset:
1886 if (get_user(futex_offset, &head->futex_offset))
1887 return;
1889 * Fetch any possibly pending lock-add first, and handle it
1890 * if it exists:
1892 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
1893 return;
1895 next_entry = NULL; /* avoid warning with gcc */
1896 while (entry != &head->list) {
1898 * Fetch the next entry in the list before calling
1899 * handle_futex_death:
1901 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
1903 * A pending lock might already be on the list, so
1904 * don't process it twice:
1906 if (entry != pending)
1907 if (handle_futex_death((void __user *)entry + futex_offset,
1908 curr, pi))
1909 return;
1910 if (rc)
1911 return;
1912 entry = next_entry;
1913 pi = next_pi;
1915 * Avoid excessively long or circular lists:
1917 if (!--limit)
1918 break;
1920 cond_resched();
1923 if (pending)
1924 handle_futex_death((void __user *)pending + futex_offset,
1925 curr, pip);
1928 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
1929 u32 __user *uaddr2, u32 val2, u32 val3)
1931 int clockrt, ret = -ENOSYS;
1932 int cmd = op & FUTEX_CMD_MASK;
1933 int fshared = 0;
1935 if (!(op & FUTEX_PRIVATE_FLAG))
1936 fshared = 1;
1938 clockrt = op & FUTEX_CLOCK_REALTIME;
1939 if (clockrt && cmd != FUTEX_WAIT_BITSET)
1940 return -ENOSYS;
1942 switch (cmd) {
1943 case FUTEX_WAIT:
1944 val3 = FUTEX_BITSET_MATCH_ANY;
1945 case FUTEX_WAIT_BITSET:
1946 ret = futex_wait(uaddr, fshared, val, timeout, val3, clockrt);
1947 break;
1948 case FUTEX_WAKE:
1949 val3 = FUTEX_BITSET_MATCH_ANY;
1950 case FUTEX_WAKE_BITSET:
1951 ret = futex_wake(uaddr, fshared, val, val3);
1952 break;
1953 case FUTEX_REQUEUE:
1954 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL);
1955 break;
1956 case FUTEX_CMP_REQUEUE:
1957 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3);
1958 break;
1959 case FUTEX_WAKE_OP:
1960 ret = futex_wake_op(uaddr, fshared, uaddr2, val, val2, val3);
1961 break;
1962 case FUTEX_LOCK_PI:
1963 if (futex_cmpxchg_enabled)
1964 ret = futex_lock_pi(uaddr, fshared, val, timeout, 0);
1965 break;
1966 case FUTEX_UNLOCK_PI:
1967 if (futex_cmpxchg_enabled)
1968 ret = futex_unlock_pi(uaddr, fshared);
1969 break;
1970 case FUTEX_TRYLOCK_PI:
1971 if (futex_cmpxchg_enabled)
1972 ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1);
1973 break;
1974 default:
1975 ret = -ENOSYS;
1977 return ret;
1981 asmlinkage long sys_futex(u32 __user *uaddr, int op, u32 val,
1982 struct timespec __user *utime, u32 __user *uaddr2,
1983 u32 val3)
1985 struct timespec ts;
1986 ktime_t t, *tp = NULL;
1987 u32 val2 = 0;
1988 int cmd = op & FUTEX_CMD_MASK;
1990 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
1991 cmd == FUTEX_WAIT_BITSET)) {
1992 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
1993 return -EFAULT;
1994 if (!timespec_valid(&ts))
1995 return -EINVAL;
1997 t = timespec_to_ktime(ts);
1998 if (cmd == FUTEX_WAIT)
1999 t = ktime_add_safe(ktime_get(), t);
2000 tp = &t;
2003 * requeue parameter in 'utime' if cmd == FUTEX_REQUEUE.
2004 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
2006 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
2007 cmd == FUTEX_WAKE_OP)
2008 val2 = (u32) (unsigned long) utime;
2010 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
2013 static int __init futex_init(void)
2015 u32 curval;
2016 int i;
2019 * This will fail and we want it. Some arch implementations do
2020 * runtime detection of the futex_atomic_cmpxchg_inatomic()
2021 * functionality. We want to know that before we call in any
2022 * of the complex code paths. Also we want to prevent
2023 * registration of robust lists in that case. NULL is
2024 * guaranteed to fault and we get -EFAULT on functional
2025 * implementation, the non functional ones will return
2026 * -ENOSYS.
2028 curval = cmpxchg_futex_value_locked(NULL, 0, 0);
2029 if (curval == -EFAULT)
2030 futex_cmpxchg_enabled = 1;
2032 for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
2033 plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock);
2034 spin_lock_init(&futex_queues[i].lock);
2037 return 0;
2039 __initcall(futex_init);