ia64/linux-2.6.18-xen.hg

view kernel/futex.c @ 562:66faefe721eb

pvSCSI backend driver

Signed-off-by: Tomonari Horikoshi <t.horikoshi@jp.fujitsu.com>
Signed-off-by: Jun Kamada <kama@jp.fujitsu.com>
author Keir Fraser <keir.fraser@citrix.com>
date Mon Jun 02 09:58:27 2008 +0100 (2008-06-02)
parents 831230e53067
children
line source
1 /*
2 * Fast Userspace Mutexes (which I call "Futexes!").
3 * (C) Rusty Russell, IBM 2002
4 *
5 * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
6 * (C) Copyright 2003 Red Hat Inc, All Rights Reserved
7 *
8 * Removed page pinning, fix privately mapped COW pages and other cleanups
9 * (C) Copyright 2003, 2004 Jamie Lokier
10 *
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.
14 *
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>
18 *
19 * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
20 * enough at me, Linus for the original (flawed) idea, Matthew
21 * Kirkwood for proof-of-concept implementation.
22 *
23 * "The futexes are also cursed."
24 * "But they come in a choice of three flavours!"
25 *
26 * This program is free software; you can redistribute it and/or modify
27 * it under the terms of the GNU General Public License as published by
28 * the Free Software Foundation; either version 2 of the License, or
29 * (at your option) any later version.
30 *
31 * This program is distributed in the hope that it will be useful,
32 * but WITHOUT ANY WARRANTY; without even the implied warranty of
33 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
34 * GNU General Public License for more details.
35 *
36 * You should have received a copy of the GNU General Public License
37 * along with this program; if not, write to the Free Software
38 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
39 */
40 #include <linux/slab.h>
41 #include <linux/poll.h>
42 #include <linux/fs.h>
43 #include <linux/file.h>
44 #include <linux/jhash.h>
45 #include <linux/init.h>
46 #include <linux/futex.h>
47 #include <linux/mount.h>
48 #include <linux/pagemap.h>
49 #include <linux/syscalls.h>
50 #include <linux/signal.h>
51 #include <asm/futex.h>
53 #include "rtmutex_common.h"
55 #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
57 /*
58 * Futexes are matched on equal values of this key.
59 * The key type depends on whether it's a shared or private mapping.
60 * Don't rearrange members without looking at hash_futex().
61 *
62 * offset is aligned to a multiple of sizeof(u32) (== 4) by definition.
63 * We set bit 0 to indicate if it's an inode-based key.
64 */
65 union futex_key {
66 struct {
67 unsigned long pgoff;
68 struct inode *inode;
69 int offset;
70 } shared;
71 struct {
72 unsigned long address;
73 struct mm_struct *mm;
74 int offset;
75 } private;
76 struct {
77 unsigned long word;
78 void *ptr;
79 int offset;
80 } both;
81 };
83 /*
84 * Priority Inheritance state:
85 */
86 struct futex_pi_state {
87 /*
88 * list of 'owned' pi_state instances - these have to be
89 * cleaned up in do_exit() if the task exits prematurely:
90 */
91 struct list_head list;
93 /*
94 * The PI object:
95 */
96 struct rt_mutex pi_mutex;
98 struct task_struct *owner;
99 atomic_t refcount;
101 union futex_key key;
102 };
104 /*
105 * We use this hashed waitqueue instead of a normal wait_queue_t, so
106 * we can wake only the relevant ones (hashed queues may be shared).
107 *
108 * A futex_q has a woken state, just like tasks have TASK_RUNNING.
109 * It is considered woken when list_empty(&q->list) || q->lock_ptr == 0.
110 * The order of wakup is always to make the first condition true, then
111 * wake up q->waiters, then make the second condition true.
112 */
113 struct futex_q {
114 struct list_head list;
115 wait_queue_head_t waiters;
117 /* Which hash list lock to use: */
118 spinlock_t *lock_ptr;
120 /* Key which the futex is hashed on: */
121 union futex_key key;
123 /* For fd, sigio sent using these: */
124 int fd;
125 struct file *filp;
127 /* Optional priority inheritance state: */
128 struct futex_pi_state *pi_state;
129 struct task_struct *task;
130 };
132 /*
133 * Split the global futex_lock into every hash list lock.
134 */
135 struct futex_hash_bucket {
136 spinlock_t lock;
137 struct list_head chain;
138 };
140 static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
142 /* Futex-fs vfsmount entry: */
143 static struct vfsmount *futex_mnt;
145 /*
146 * We hash on the keys returned from get_futex_key (see below).
147 */
148 static struct futex_hash_bucket *hash_futex(union futex_key *key)
149 {
150 u32 hash = jhash2((u32*)&key->both.word,
151 (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
152 key->both.offset);
153 return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
154 }
156 /*
157 * Return 1 if two futex_keys are equal, 0 otherwise.
158 */
159 static inline int match_futex(union futex_key *key1, union futex_key *key2)
160 {
161 return (key1->both.word == key2->both.word
162 && key1->both.ptr == key2->both.ptr
163 && key1->both.offset == key2->both.offset);
164 }
166 /*
167 * Get parameters which are the keys for a futex.
168 *
169 * For shared mappings, it's (page->index, vma->vm_file->f_dentry->d_inode,
170 * offset_within_page). For private mappings, it's (uaddr, current->mm).
171 * We can usually work out the index without swapping in the page.
172 *
173 * Returns: 0, or negative error code.
174 * The key words are stored in *key on success.
175 *
176 * Should be called with &current->mm->mmap_sem but NOT any spinlocks.
177 */
178 static int get_futex_key(u32 __user *uaddr, union futex_key *key)
179 {
180 unsigned long address = (unsigned long)uaddr;
181 struct mm_struct *mm = current->mm;
182 struct vm_area_struct *vma;
183 struct page *page;
184 int err;
186 /*
187 * The futex address must be "naturally" aligned.
188 */
189 key->both.offset = address % PAGE_SIZE;
190 if (unlikely((key->both.offset % sizeof(u32)) != 0))
191 return -EINVAL;
192 address -= key->both.offset;
194 /*
195 * The futex is hashed differently depending on whether
196 * it's in a shared or private mapping. So check vma first.
197 */
198 vma = find_extend_vma(mm, address);
199 if (unlikely(!vma))
200 return -EFAULT;
202 /*
203 * Permissions.
204 */
205 if (unlikely((vma->vm_flags & (VM_IO|VM_READ)) != VM_READ))
206 return (vma->vm_flags & VM_IO) ? -EPERM : -EACCES;
208 /*
209 * Private mappings are handled in a simple way.
210 *
211 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
212 * it's a read-only handle, it's expected that futexes attach to
213 * the object not the particular process. Therefore we use
214 * VM_MAYSHARE here, not VM_SHARED which is restricted to shared
215 * mappings of _writable_ handles.
216 */
217 if (likely(!(vma->vm_flags & VM_MAYSHARE))) {
218 key->private.mm = mm;
219 key->private.address = address;
220 return 0;
221 }
223 /*
224 * Linear file mappings are also simple.
225 */
226 key->shared.inode = vma->vm_file->f_dentry->d_inode;
227 key->both.offset++; /* Bit 0 of offset indicates inode-based key. */
228 if (likely(!(vma->vm_flags & VM_NONLINEAR))) {
229 key->shared.pgoff = (((address - vma->vm_start) >> PAGE_SHIFT)
230 + vma->vm_pgoff);
231 return 0;
232 }
234 /*
235 * We could walk the page table to read the non-linear
236 * pte, and get the page index without fetching the page
237 * from swap. But that's a lot of code to duplicate here
238 * for a rare case, so we simply fetch the page.
239 */
240 err = get_user_pages(current, mm, address, 1, 0, 0, &page, NULL);
241 if (err >= 0) {
242 key->shared.pgoff =
243 page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
244 put_page(page);
245 return 0;
246 }
247 return err;
248 }
250 /*
251 * Take a reference to the resource addressed by a key.
252 * Can be called while holding spinlocks.
253 *
254 * NOTE: mmap_sem MUST be held between get_futex_key() and calling this
255 * function, if it is called at all. mmap_sem keeps key->shared.inode valid.
256 */
257 static inline void get_key_refs(union futex_key *key)
258 {
259 if (key->both.ptr != 0) {
260 if (key->both.offset & 1)
261 atomic_inc(&key->shared.inode->i_count);
262 else
263 atomic_inc(&key->private.mm->mm_count);
264 }
265 }
267 /*
268 * Drop a reference to the resource addressed by a key.
269 * The hash bucket spinlock must not be held.
270 */
271 static void drop_key_refs(union futex_key *key)
272 {
273 if (key->both.ptr != 0) {
274 if (key->both.offset & 1)
275 iput(key->shared.inode);
276 else
277 mmdrop(key->private.mm);
278 }
279 }
281 static inline int get_futex_value_locked(u32 *dest, u32 __user *from)
282 {
283 int ret;
285 inc_preempt_count();
286 ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
287 dec_preempt_count();
289 return ret ? -EFAULT : 0;
290 }
292 /*
293 * Fault handling. Called with current->mm->mmap_sem held.
294 */
295 static int futex_handle_fault(unsigned long address, int attempt)
296 {
297 struct vm_area_struct * vma;
298 struct mm_struct *mm = current->mm;
300 if (attempt > 2 || !(vma = find_vma(mm, address)) ||
301 vma->vm_start > address || !(vma->vm_flags & VM_WRITE))
302 return -EFAULT;
304 switch (handle_mm_fault(mm, vma, address, 1)) {
305 case VM_FAULT_MINOR:
306 current->min_flt++;
307 break;
308 case VM_FAULT_MAJOR:
309 current->maj_flt++;
310 break;
311 default:
312 return -EFAULT;
313 }
314 return 0;
315 }
317 /*
318 * PI code:
319 */
320 static int refill_pi_state_cache(void)
321 {
322 struct futex_pi_state *pi_state;
324 if (likely(current->pi_state_cache))
325 return 0;
327 pi_state = kmalloc(sizeof(*pi_state), GFP_KERNEL);
329 if (!pi_state)
330 return -ENOMEM;
332 memset(pi_state, 0, sizeof(*pi_state));
333 INIT_LIST_HEAD(&pi_state->list);
334 /* pi_mutex gets initialized later */
335 pi_state->owner = NULL;
336 atomic_set(&pi_state->refcount, 1);
338 current->pi_state_cache = pi_state;
340 return 0;
341 }
343 static struct futex_pi_state * alloc_pi_state(void)
344 {
345 struct futex_pi_state *pi_state = current->pi_state_cache;
347 WARN_ON(!pi_state);
348 current->pi_state_cache = NULL;
350 return pi_state;
351 }
353 static void free_pi_state(struct futex_pi_state *pi_state)
354 {
355 if (!atomic_dec_and_test(&pi_state->refcount))
356 return;
358 /*
359 * If pi_state->owner is NULL, the owner is most probably dying
360 * and has cleaned up the pi_state already
361 */
362 if (pi_state->owner) {
363 spin_lock_irq(&pi_state->owner->pi_lock);
364 list_del_init(&pi_state->list);
365 spin_unlock_irq(&pi_state->owner->pi_lock);
367 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
368 }
370 if (current->pi_state_cache)
371 kfree(pi_state);
372 else {
373 /*
374 * pi_state->list is already empty.
375 * clear pi_state->owner.
376 * refcount is at 0 - put it back to 1.
377 */
378 pi_state->owner = NULL;
379 atomic_set(&pi_state->refcount, 1);
380 current->pi_state_cache = pi_state;
381 }
382 }
384 /*
385 * Look up the task based on what TID userspace gave us.
386 * We dont trust it.
387 */
388 static struct task_struct * futex_find_get_task(pid_t pid)
389 {
390 struct task_struct *p;
392 read_lock(&tasklist_lock);
393 p = find_task_by_pid(pid);
394 if (!p)
395 goto out_unlock;
396 if ((current->euid != p->euid) && (current->euid != p->uid)) {
397 p = NULL;
398 goto out_unlock;
399 }
400 if (p->exit_state != 0) {
401 p = NULL;
402 goto out_unlock;
403 }
404 get_task_struct(p);
405 out_unlock:
406 read_unlock(&tasklist_lock);
408 return p;
409 }
411 /*
412 * This task is holding PI mutexes at exit time => bad.
413 * Kernel cleans up PI-state, but userspace is likely hosed.
414 * (Robust-futex cleanup is separate and might save the day for userspace.)
415 */
416 void exit_pi_state_list(struct task_struct *curr)
417 {
418 struct list_head *next, *head = &curr->pi_state_list;
419 struct futex_pi_state *pi_state;
420 struct futex_hash_bucket *hb;
421 union futex_key key;
423 /*
424 * We are a ZOMBIE and nobody can enqueue itself on
425 * pi_state_list anymore, but we have to be careful
426 * versus waiters unqueueing themselves:
427 */
428 spin_lock_irq(&curr->pi_lock);
429 while (!list_empty(head)) {
431 next = head->next;
432 pi_state = list_entry(next, struct futex_pi_state, list);
433 key = pi_state->key;
434 hb = hash_futex(&key);
435 spin_unlock_irq(&curr->pi_lock);
437 spin_lock(&hb->lock);
439 spin_lock_irq(&curr->pi_lock);
440 /*
441 * We dropped the pi-lock, so re-check whether this
442 * task still owns the PI-state:
443 */
444 if (head->next != next) {
445 spin_unlock(&hb->lock);
446 continue;
447 }
449 WARN_ON(pi_state->owner != curr);
450 WARN_ON(list_empty(&pi_state->list));
451 list_del_init(&pi_state->list);
452 pi_state->owner = NULL;
453 spin_unlock_irq(&curr->pi_lock);
455 rt_mutex_unlock(&pi_state->pi_mutex);
457 spin_unlock(&hb->lock);
459 spin_lock_irq(&curr->pi_lock);
460 }
461 spin_unlock_irq(&curr->pi_lock);
462 }
464 static int
465 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, struct futex_q *me)
466 {
467 struct futex_pi_state *pi_state = NULL;
468 struct futex_q *this, *next;
469 struct list_head *head;
470 struct task_struct *p;
471 pid_t pid;
473 head = &hb->chain;
475 list_for_each_entry_safe(this, next, head, list) {
476 if (match_futex(&this->key, &me->key)) {
477 /*
478 * Another waiter already exists - bump up
479 * the refcount and return its pi_state:
480 */
481 pi_state = this->pi_state;
482 /*
483 * Userspace might have messed up non PI and PI futexes
484 */
485 if (unlikely(!pi_state))
486 return -EINVAL;
488 WARN_ON(!atomic_read(&pi_state->refcount));
490 atomic_inc(&pi_state->refcount);
491 me->pi_state = pi_state;
493 return 0;
494 }
495 }
497 /*
498 * We are the first waiter - try to look up the real owner and attach
499 * the new pi_state to it, but bail out when the owner died bit is set
500 * and TID = 0:
501 */
502 pid = uval & FUTEX_TID_MASK;
503 if (!pid && (uval & FUTEX_OWNER_DIED))
504 return -ESRCH;
505 p = futex_find_get_task(pid);
506 if (!p)
507 return -ESRCH;
509 pi_state = alloc_pi_state();
511 /*
512 * Initialize the pi_mutex in locked state and make 'p'
513 * the owner of it:
514 */
515 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
517 /* Store the key for possible exit cleanups: */
518 pi_state->key = me->key;
520 spin_lock_irq(&p->pi_lock);
521 WARN_ON(!list_empty(&pi_state->list));
522 list_add(&pi_state->list, &p->pi_state_list);
523 pi_state->owner = p;
524 spin_unlock_irq(&p->pi_lock);
526 put_task_struct(p);
528 me->pi_state = pi_state;
530 return 0;
531 }
533 /*
534 * The hash bucket lock must be held when this is called.
535 * Afterwards, the futex_q must not be accessed.
536 */
537 static void wake_futex(struct futex_q *q)
538 {
539 list_del_init(&q->list);
540 if (q->filp)
541 send_sigio(&q->filp->f_owner, q->fd, POLL_IN);
542 /*
543 * The lock in wake_up_all() is a crucial memory barrier after the
544 * list_del_init() and also before assigning to q->lock_ptr.
545 */
546 wake_up_all(&q->waiters);
547 /*
548 * The waiting task can free the futex_q as soon as this is written,
549 * without taking any locks. This must come last.
550 *
551 * A memory barrier is required here to prevent the following store
552 * to lock_ptr from getting ahead of the wakeup. Clearing the lock
553 * at the end of wake_up_all() does not prevent this store from
554 * moving.
555 */
556 wmb();
557 q->lock_ptr = NULL;
558 }
560 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
561 {
562 struct task_struct *new_owner;
563 struct futex_pi_state *pi_state = this->pi_state;
564 u32 curval, newval;
566 if (!pi_state)
567 return -EINVAL;
569 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
571 /*
572 * This happens when we have stolen the lock and the original
573 * pending owner did not enqueue itself back on the rt_mutex.
574 * Thats not a tragedy. We know that way, that a lock waiter
575 * is on the fly. We make the futex_q waiter the pending owner.
576 */
577 if (!new_owner)
578 new_owner = this->task;
580 /*
581 * We pass it to the next owner. (The WAITERS bit is always
582 * kept enabled while there is PI state around. We must also
583 * preserve the owner died bit.)
584 */
585 if (!(uval & FUTEX_OWNER_DIED)) {
586 newval = FUTEX_WAITERS | new_owner->pid;
588 inc_preempt_count();
589 curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
590 dec_preempt_count();
591 if (curval == -EFAULT)
592 return -EFAULT;
593 if (curval != uval)
594 return -EINVAL;
595 }
597 spin_lock_irq(&pi_state->owner->pi_lock);
598 WARN_ON(list_empty(&pi_state->list));
599 list_del_init(&pi_state->list);
600 spin_unlock_irq(&pi_state->owner->pi_lock);
602 spin_lock_irq(&new_owner->pi_lock);
603 WARN_ON(!list_empty(&pi_state->list));
604 list_add(&pi_state->list, &new_owner->pi_state_list);
605 pi_state->owner = new_owner;
606 spin_unlock_irq(&new_owner->pi_lock);
608 rt_mutex_unlock(&pi_state->pi_mutex);
610 return 0;
611 }
613 static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
614 {
615 u32 oldval;
617 /*
618 * There is no waiter, so we unlock the futex. The owner died
619 * bit has not to be preserved here. We are the owner:
620 */
621 inc_preempt_count();
622 oldval = futex_atomic_cmpxchg_inatomic(uaddr, uval, 0);
623 dec_preempt_count();
625 if (oldval == -EFAULT)
626 return oldval;
627 if (oldval != uval)
628 return -EAGAIN;
630 return 0;
631 }
633 /*
634 * Express the locking dependencies for lockdep:
635 */
636 static inline void
637 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
638 {
639 if (hb1 <= hb2) {
640 spin_lock(&hb1->lock);
641 if (hb1 < hb2)
642 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
643 } else { /* hb1 > hb2 */
644 spin_lock(&hb2->lock);
645 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
646 }
647 }
649 /*
650 * Wake up all waiters hashed on the physical page that is mapped
651 * to this virtual address:
652 */
653 static int futex_wake(u32 __user *uaddr, int nr_wake)
654 {
655 struct futex_hash_bucket *hb;
656 struct futex_q *this, *next;
657 struct list_head *head;
658 union futex_key key;
659 int ret;
661 down_read(&current->mm->mmap_sem);
663 ret = get_futex_key(uaddr, &key);
664 if (unlikely(ret != 0))
665 goto out;
667 hb = hash_futex(&key);
668 spin_lock(&hb->lock);
669 head = &hb->chain;
671 list_for_each_entry_safe(this, next, head, list) {
672 if (match_futex (&this->key, &key)) {
673 if (this->pi_state) {
674 ret = -EINVAL;
675 break;
676 }
677 wake_futex(this);
678 if (++ret >= nr_wake)
679 break;
680 }
681 }
683 spin_unlock(&hb->lock);
684 out:
685 up_read(&current->mm->mmap_sem);
686 return ret;
687 }
689 /*
690 * Wake up all waiters hashed on the physical page that is mapped
691 * to this virtual address:
692 */
693 static int
694 futex_wake_op(u32 __user *uaddr1, u32 __user *uaddr2,
695 int nr_wake, int nr_wake2, int op)
696 {
697 union futex_key key1, key2;
698 struct futex_hash_bucket *hb1, *hb2;
699 struct list_head *head;
700 struct futex_q *this, *next;
701 int ret, op_ret, attempt = 0;
703 retryfull:
704 down_read(&current->mm->mmap_sem);
706 ret = get_futex_key(uaddr1, &key1);
707 if (unlikely(ret != 0))
708 goto out;
709 ret = get_futex_key(uaddr2, &key2);
710 if (unlikely(ret != 0))
711 goto out;
713 hb1 = hash_futex(&key1);
714 hb2 = hash_futex(&key2);
716 retry:
717 double_lock_hb(hb1, hb2);
719 op_ret = futex_atomic_op_inuser(op, uaddr2);
720 if (unlikely(op_ret < 0)) {
721 u32 dummy;
723 spin_unlock(&hb1->lock);
724 if (hb1 != hb2)
725 spin_unlock(&hb2->lock);
727 #ifndef CONFIG_MMU
728 /*
729 * we don't get EFAULT from MMU faults if we don't have an MMU,
730 * but we might get them from range checking
731 */
732 ret = op_ret;
733 goto out;
734 #endif
736 if (unlikely(op_ret != -EFAULT)) {
737 ret = op_ret;
738 goto out;
739 }
741 /*
742 * futex_atomic_op_inuser needs to both read and write
743 * *(int __user *)uaddr2, but we can't modify it
744 * non-atomically. Therefore, if get_user below is not
745 * enough, we need to handle the fault ourselves, while
746 * still holding the mmap_sem.
747 */
748 if (attempt++) {
749 if (futex_handle_fault((unsigned long)uaddr2,
750 attempt)) {
751 ret = -EFAULT;
752 goto out;
753 }
754 goto retry;
755 }
757 /*
758 * If we would have faulted, release mmap_sem,
759 * fault it in and start all over again.
760 */
761 up_read(&current->mm->mmap_sem);
763 ret = get_user(dummy, uaddr2);
764 if (ret)
765 return ret;
767 goto retryfull;
768 }
770 head = &hb1->chain;
772 list_for_each_entry_safe(this, next, head, list) {
773 if (match_futex (&this->key, &key1)) {
774 wake_futex(this);
775 if (++ret >= nr_wake)
776 break;
777 }
778 }
780 if (op_ret > 0) {
781 head = &hb2->chain;
783 op_ret = 0;
784 list_for_each_entry_safe(this, next, head, list) {
785 if (match_futex (&this->key, &key2)) {
786 wake_futex(this);
787 if (++op_ret >= nr_wake2)
788 break;
789 }
790 }
791 ret += op_ret;
792 }
794 spin_unlock(&hb1->lock);
795 if (hb1 != hb2)
796 spin_unlock(&hb2->lock);
797 out:
798 up_read(&current->mm->mmap_sem);
799 return ret;
800 }
802 /*
803 * Requeue all waiters hashed on one physical page to another
804 * physical page.
805 */
806 static int futex_requeue(u32 __user *uaddr1, u32 __user *uaddr2,
807 int nr_wake, int nr_requeue, u32 *cmpval)
808 {
809 union futex_key key1, key2;
810 struct futex_hash_bucket *hb1, *hb2;
811 struct list_head *head1;
812 struct futex_q *this, *next;
813 int ret, drop_count = 0;
815 retry:
816 down_read(&current->mm->mmap_sem);
818 ret = get_futex_key(uaddr1, &key1);
819 if (unlikely(ret != 0))
820 goto out;
821 ret = get_futex_key(uaddr2, &key2);
822 if (unlikely(ret != 0))
823 goto out;
825 hb1 = hash_futex(&key1);
826 hb2 = hash_futex(&key2);
828 double_lock_hb(hb1, hb2);
830 if (likely(cmpval != NULL)) {
831 u32 curval;
833 ret = get_futex_value_locked(&curval, uaddr1);
835 if (unlikely(ret)) {
836 spin_unlock(&hb1->lock);
837 if (hb1 != hb2)
838 spin_unlock(&hb2->lock);
840 /*
841 * If we would have faulted, release mmap_sem, fault
842 * it in and start all over again.
843 */
844 up_read(&current->mm->mmap_sem);
846 ret = get_user(curval, uaddr1);
848 if (!ret)
849 goto retry;
851 return ret;
852 }
853 if (curval != *cmpval) {
854 ret = -EAGAIN;
855 goto out_unlock;
856 }
857 }
859 head1 = &hb1->chain;
860 list_for_each_entry_safe(this, next, head1, list) {
861 if (!match_futex (&this->key, &key1))
862 continue;
863 if (++ret <= nr_wake) {
864 wake_futex(this);
865 } else {
866 /*
867 * If key1 and key2 hash to the same bucket, no need to
868 * requeue.
869 */
870 if (likely(head1 != &hb2->chain)) {
871 list_move_tail(&this->list, &hb2->chain);
872 this->lock_ptr = &hb2->lock;
873 }
874 this->key = key2;
875 get_key_refs(&key2);
876 drop_count++;
878 if (ret - nr_wake >= nr_requeue)
879 break;
880 }
881 }
883 out_unlock:
884 spin_unlock(&hb1->lock);
885 if (hb1 != hb2)
886 spin_unlock(&hb2->lock);
888 /* drop_key_refs() must be called outside the spinlocks. */
889 while (--drop_count >= 0)
890 drop_key_refs(&key1);
892 out:
893 up_read(&current->mm->mmap_sem);
894 return ret;
895 }
897 /* The key must be already stored in q->key. */
898 static inline struct futex_hash_bucket *
899 queue_lock(struct futex_q *q, int fd, struct file *filp)
900 {
901 struct futex_hash_bucket *hb;
903 q->fd = fd;
904 q->filp = filp;
906 init_waitqueue_head(&q->waiters);
908 get_key_refs(&q->key);
909 hb = hash_futex(&q->key);
910 q->lock_ptr = &hb->lock;
912 spin_lock(&hb->lock);
913 return hb;
914 }
916 static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
917 {
918 list_add_tail(&q->list, &hb->chain);
919 q->task = current;
920 spin_unlock(&hb->lock);
921 }
923 static inline void
924 queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
925 {
926 spin_unlock(&hb->lock);
927 drop_key_refs(&q->key);
928 }
930 /*
931 * queue_me and unqueue_me must be called as a pair, each
932 * exactly once. They are called with the hashed spinlock held.
933 */
935 /* The key must be already stored in q->key. */
936 static void queue_me(struct futex_q *q, int fd, struct file *filp)
937 {
938 struct futex_hash_bucket *hb;
940 hb = queue_lock(q, fd, filp);
941 __queue_me(q, hb);
942 }
944 /* Return 1 if we were still queued (ie. 0 means we were woken) */
945 static int unqueue_me(struct futex_q *q)
946 {
947 spinlock_t *lock_ptr;
948 int ret = 0;
950 /* In the common case we don't take the spinlock, which is nice. */
951 retry:
952 lock_ptr = q->lock_ptr;
953 barrier();
954 if (lock_ptr != 0) {
955 spin_lock(lock_ptr);
956 /*
957 * q->lock_ptr can change between reading it and
958 * spin_lock(), causing us to take the wrong lock. This
959 * corrects the race condition.
960 *
961 * Reasoning goes like this: if we have the wrong lock,
962 * q->lock_ptr must have changed (maybe several times)
963 * between reading it and the spin_lock(). It can
964 * change again after the spin_lock() but only if it was
965 * already changed before the spin_lock(). It cannot,
966 * however, change back to the original value. Therefore
967 * we can detect whether we acquired the correct lock.
968 */
969 if (unlikely(lock_ptr != q->lock_ptr)) {
970 spin_unlock(lock_ptr);
971 goto retry;
972 }
973 WARN_ON(list_empty(&q->list));
974 list_del(&q->list);
976 BUG_ON(q->pi_state);
978 spin_unlock(lock_ptr);
979 ret = 1;
980 }
982 drop_key_refs(&q->key);
983 return ret;
984 }
986 /*
987 * PI futexes can not be requeued and must remove themself from the
988 * hash bucket. The hash bucket lock is held on entry and dropped here.
989 */
990 static void unqueue_me_pi(struct futex_q *q, struct futex_hash_bucket *hb)
991 {
992 WARN_ON(list_empty(&q->list));
993 list_del(&q->list);
995 BUG_ON(!q->pi_state);
996 free_pi_state(q->pi_state);
997 q->pi_state = NULL;
999 spin_unlock(&hb->lock);
1001 drop_key_refs(&q->key);
1004 static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time)
1006 struct task_struct *curr = current;
1007 DECLARE_WAITQUEUE(wait, curr);
1008 struct futex_hash_bucket *hb;
1009 struct futex_q q;
1010 u32 uval;
1011 int ret;
1013 q.pi_state = NULL;
1014 retry:
1015 down_read(&curr->mm->mmap_sem);
1017 ret = get_futex_key(uaddr, &q.key);
1018 if (unlikely(ret != 0))
1019 goto out_release_sem;
1021 hb = queue_lock(&q, -1, NULL);
1023 /*
1024 * Access the page AFTER the futex is queued.
1025 * Order is important:
1027 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1028 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
1030 * The basic logical guarantee of a futex is that it blocks ONLY
1031 * if cond(var) is known to be true at the time of blocking, for
1032 * any cond. If we queued after testing *uaddr, that would open
1033 * a race condition where we could block indefinitely with
1034 * cond(var) false, which would violate the guarantee.
1036 * A consequence is that futex_wait() can return zero and absorb
1037 * a wakeup when *uaddr != val on entry to the syscall. This is
1038 * rare, but normal.
1040 * We hold the mmap semaphore, so the mapping cannot have changed
1041 * since we looked it up in get_futex_key.
1042 */
1043 ret = get_futex_value_locked(&uval, uaddr);
1045 if (unlikely(ret)) {
1046 queue_unlock(&q, hb);
1048 /*
1049 * If we would have faulted, release mmap_sem, fault it in and
1050 * start all over again.
1051 */
1052 up_read(&curr->mm->mmap_sem);
1054 ret = get_user(uval, uaddr);
1056 if (!ret)
1057 goto retry;
1058 return ret;
1060 ret = -EWOULDBLOCK;
1061 if (uval != val)
1062 goto out_unlock_release_sem;
1064 /* Only actually queue if *uaddr contained val. */
1065 __queue_me(&q, hb);
1067 /*
1068 * Now the futex is queued and we have checked the data, we
1069 * don't want to hold mmap_sem while we sleep.
1070 */
1071 up_read(&curr->mm->mmap_sem);
1073 /*
1074 * There might have been scheduling since the queue_me(), as we
1075 * cannot hold a spinlock across the get_user() in case it
1076 * faults, and we cannot just set TASK_INTERRUPTIBLE state when
1077 * queueing ourselves into the futex hash. This code thus has to
1078 * rely on the futex_wake() code removing us from hash when it
1079 * wakes us up.
1080 */
1082 /* add_wait_queue is the barrier after __set_current_state. */
1083 __set_current_state(TASK_INTERRUPTIBLE);
1084 add_wait_queue(&q.waiters, &wait);
1085 /*
1086 * !list_empty() is safe here without any lock.
1087 * q.lock_ptr != 0 is not safe, because of ordering against wakeup.
1088 */
1089 if (likely(!list_empty(&q.list)))
1090 time = schedule_timeout(time);
1091 __set_current_state(TASK_RUNNING);
1093 /*
1094 * NOTE: we don't remove ourselves from the waitqueue because
1095 * we are the only user of it.
1096 */
1098 /* If we were woken (and unqueued), we succeeded, whatever. */
1099 if (!unqueue_me(&q))
1100 return 0;
1101 if (time == 0)
1102 return -ETIMEDOUT;
1103 /*
1104 * We expect signal_pending(current), but another thread may
1105 * have handled it for us already.
1106 */
1107 return -EINTR;
1109 out_unlock_release_sem:
1110 queue_unlock(&q, hb);
1112 out_release_sem:
1113 up_read(&curr->mm->mmap_sem);
1114 return ret;
1117 /*
1118 * Userspace tried a 0 -> TID atomic transition of the futex value
1119 * and failed. The kernel side here does the whole locking operation:
1120 * if there are waiters then it will block, it does PI, etc. (Due to
1121 * races the kernel might see a 0 value of the futex too.)
1122 */
1123 static int futex_lock_pi(u32 __user *uaddr, int detect, unsigned long sec,
1124 long nsec, int trylock)
1126 struct hrtimer_sleeper timeout, *to = NULL;
1127 struct task_struct *curr = current;
1128 struct futex_hash_bucket *hb;
1129 u32 uval, newval, curval;
1130 struct futex_q q;
1131 int ret, attempt = 0;
1133 if (refill_pi_state_cache())
1134 return -ENOMEM;
1136 if (sec != MAX_SCHEDULE_TIMEOUT) {
1137 to = &timeout;
1138 hrtimer_init(&to->timer, CLOCK_REALTIME, HRTIMER_ABS);
1139 hrtimer_init_sleeper(to, current);
1140 to->timer.expires = ktime_set(sec, nsec);
1143 q.pi_state = NULL;
1144 retry:
1145 down_read(&curr->mm->mmap_sem);
1147 ret = get_futex_key(uaddr, &q.key);
1148 if (unlikely(ret != 0))
1149 goto out_release_sem;
1151 hb = queue_lock(&q, -1, NULL);
1153 retry_locked:
1154 /*
1155 * To avoid races, we attempt to take the lock here again
1156 * (by doing a 0 -> TID atomic cmpxchg), while holding all
1157 * the locks. It will most likely not succeed.
1158 */
1159 newval = current->pid;
1161 inc_preempt_count();
1162 curval = futex_atomic_cmpxchg_inatomic(uaddr, 0, newval);
1163 dec_preempt_count();
1165 if (unlikely(curval == -EFAULT))
1166 goto uaddr_faulted;
1168 /* We own the lock already */
1169 if (unlikely((curval & FUTEX_TID_MASK) == current->pid)) {
1170 if (!detect && 0)
1171 force_sig(SIGKILL, current);
1172 ret = -EDEADLK;
1173 goto out_unlock_release_sem;
1176 /*
1177 * Surprise - we got the lock. Just return
1178 * to userspace:
1179 */
1180 if (unlikely(!curval))
1181 goto out_unlock_release_sem;
1183 uval = curval;
1184 newval = uval | FUTEX_WAITERS;
1186 inc_preempt_count();
1187 curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
1188 dec_preempt_count();
1190 if (unlikely(curval == -EFAULT))
1191 goto uaddr_faulted;
1192 if (unlikely(curval != uval))
1193 goto retry_locked;
1195 /*
1196 * We dont have the lock. Look up the PI state (or create it if
1197 * we are the first waiter):
1198 */
1199 ret = lookup_pi_state(uval, hb, &q);
1201 if (unlikely(ret)) {
1202 /*
1203 * There were no waiters and the owner task lookup
1204 * failed. When the OWNER_DIED bit is set, then we
1205 * know that this is a robust futex and we actually
1206 * take the lock. This is safe as we are protected by
1207 * the hash bucket lock. We also set the waiters bit
1208 * unconditionally here, to simplify glibc handling of
1209 * multiple tasks racing to acquire the lock and
1210 * cleanup the problems which were left by the dead
1211 * owner.
1212 */
1213 if (curval & FUTEX_OWNER_DIED) {
1214 uval = newval;
1215 newval = current->pid |
1216 FUTEX_OWNER_DIED | FUTEX_WAITERS;
1218 inc_preempt_count();
1219 curval = futex_atomic_cmpxchg_inatomic(uaddr,
1220 uval, newval);
1221 dec_preempt_count();
1223 if (unlikely(curval == -EFAULT))
1224 goto uaddr_faulted;
1225 if (unlikely(curval != uval))
1226 goto retry_locked;
1227 ret = 0;
1229 goto out_unlock_release_sem;
1232 /*
1233 * Only actually queue now that the atomic ops are done:
1234 */
1235 __queue_me(&q, hb);
1237 /*
1238 * Now the futex is queued and we have checked the data, we
1239 * don't want to hold mmap_sem while we sleep.
1240 */
1241 up_read(&curr->mm->mmap_sem);
1243 WARN_ON(!q.pi_state);
1244 /*
1245 * Block on the PI mutex:
1246 */
1247 if (!trylock)
1248 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
1249 else {
1250 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
1251 /* Fixup the trylock return value: */
1252 ret = ret ? 0 : -EWOULDBLOCK;
1255 down_read(&curr->mm->mmap_sem);
1256 spin_lock(q.lock_ptr);
1258 /*
1259 * Got the lock. We might not be the anticipated owner if we
1260 * did a lock-steal - fix up the PI-state in that case.
1261 */
1262 if (!ret && q.pi_state->owner != curr) {
1263 u32 newtid = current->pid | FUTEX_WAITERS;
1265 /* Owner died? */
1266 if (q.pi_state->owner != NULL) {
1267 spin_lock_irq(&q.pi_state->owner->pi_lock);
1268 WARN_ON(list_empty(&q.pi_state->list));
1269 list_del_init(&q.pi_state->list);
1270 spin_unlock_irq(&q.pi_state->owner->pi_lock);
1271 } else
1272 newtid |= FUTEX_OWNER_DIED;
1274 q.pi_state->owner = current;
1276 spin_lock_irq(&current->pi_lock);
1277 WARN_ON(!list_empty(&q.pi_state->list));
1278 list_add(&q.pi_state->list, &current->pi_state_list);
1279 spin_unlock_irq(&current->pi_lock);
1281 /* Unqueue and drop the lock */
1282 unqueue_me_pi(&q, hb);
1283 up_read(&curr->mm->mmap_sem);
1284 /*
1285 * We own it, so we have to replace the pending owner
1286 * TID. This must be atomic as we have preserve the
1287 * owner died bit here.
1288 */
1289 ret = get_user(uval, uaddr);
1290 while (!ret) {
1291 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1292 curval = futex_atomic_cmpxchg_inatomic(uaddr,
1293 uval, newval);
1294 if (curval == -EFAULT)
1295 ret = -EFAULT;
1296 if (curval == uval)
1297 break;
1298 uval = curval;
1300 } else {
1301 /*
1302 * Catch the rare case, where the lock was released
1303 * when we were on the way back before we locked
1304 * the hash bucket.
1305 */
1306 if (ret && q.pi_state->owner == curr) {
1307 if (rt_mutex_trylock(&q.pi_state->pi_mutex))
1308 ret = 0;
1310 /* Unqueue and drop the lock */
1311 unqueue_me_pi(&q, hb);
1312 up_read(&curr->mm->mmap_sem);
1315 if (!detect && ret == -EDEADLK && 0)
1316 force_sig(SIGKILL, current);
1318 return ret != -EINTR ? ret : -ERESTARTNOINTR;
1320 out_unlock_release_sem:
1321 queue_unlock(&q, hb);
1323 out_release_sem:
1324 up_read(&curr->mm->mmap_sem);
1325 return ret;
1327 uaddr_faulted:
1328 /*
1329 * We have to r/w *(int __user *)uaddr, but we can't modify it
1330 * non-atomically. Therefore, if get_user below is not
1331 * enough, we need to handle the fault ourselves, while
1332 * still holding the mmap_sem.
1333 */
1334 if (attempt++) {
1335 if (futex_handle_fault((unsigned long)uaddr, attempt)) {
1336 ret = -EFAULT;
1337 goto out_unlock_release_sem;
1339 goto retry_locked;
1342 queue_unlock(&q, hb);
1343 up_read(&curr->mm->mmap_sem);
1345 ret = get_user(uval, uaddr);
1346 if (!ret && (uval != -EFAULT))
1347 goto retry;
1349 return ret;
1352 /*
1353 * Userspace attempted a TID -> 0 atomic transition, and failed.
1354 * This is the in-kernel slowpath: we look up the PI state (if any),
1355 * and do the rt-mutex unlock.
1356 */
1357 static int futex_unlock_pi(u32 __user *uaddr)
1359 struct futex_hash_bucket *hb;
1360 struct futex_q *this, *next;
1361 u32 uval;
1362 struct list_head *head;
1363 union futex_key key;
1364 int ret, attempt = 0;
1366 retry:
1367 if (get_user(uval, uaddr))
1368 return -EFAULT;
1369 /*
1370 * We release only a lock we actually own:
1371 */
1372 if ((uval & FUTEX_TID_MASK) != current->pid)
1373 return -EPERM;
1374 /*
1375 * First take all the futex related locks:
1376 */
1377 down_read(&current->mm->mmap_sem);
1379 ret = get_futex_key(uaddr, &key);
1380 if (unlikely(ret != 0))
1381 goto out;
1383 hb = hash_futex(&key);
1384 spin_lock(&hb->lock);
1386 retry_locked:
1387 /*
1388 * To avoid races, try to do the TID -> 0 atomic transition
1389 * again. If it succeeds then we can return without waking
1390 * anyone else up:
1391 */
1392 if (!(uval & FUTEX_OWNER_DIED)) {
1393 inc_preempt_count();
1394 uval = futex_atomic_cmpxchg_inatomic(uaddr, current->pid, 0);
1395 dec_preempt_count();
1398 if (unlikely(uval == -EFAULT))
1399 goto pi_faulted;
1400 /*
1401 * Rare case: we managed to release the lock atomically,
1402 * no need to wake anyone else up:
1403 */
1404 if (unlikely(uval == current->pid))
1405 goto out_unlock;
1407 /*
1408 * Ok, other tasks may need to be woken up - check waiters
1409 * and do the wakeup if necessary:
1410 */
1411 head = &hb->chain;
1413 list_for_each_entry_safe(this, next, head, list) {
1414 if (!match_futex (&this->key, &key))
1415 continue;
1416 ret = wake_futex_pi(uaddr, uval, this);
1417 /*
1418 * The atomic access to the futex value
1419 * generated a pagefault, so retry the
1420 * user-access and the wakeup:
1421 */
1422 if (ret == -EFAULT)
1423 goto pi_faulted;
1424 goto out_unlock;
1426 /*
1427 * No waiters - kernel unlocks the futex:
1428 */
1429 if (!(uval & FUTEX_OWNER_DIED)) {
1430 ret = unlock_futex_pi(uaddr, uval);
1431 if (ret == -EFAULT)
1432 goto pi_faulted;
1435 out_unlock:
1436 spin_unlock(&hb->lock);
1437 out:
1438 up_read(&current->mm->mmap_sem);
1440 return ret;
1442 pi_faulted:
1443 /*
1444 * We have to r/w *(int __user *)uaddr, but we can't modify it
1445 * non-atomically. Therefore, if get_user below is not
1446 * enough, we need to handle the fault ourselves, while
1447 * still holding the mmap_sem.
1448 */
1449 if (attempt++) {
1450 if (futex_handle_fault((unsigned long)uaddr, attempt)) {
1451 ret = -EFAULT;
1452 goto out_unlock;
1454 goto retry_locked;
1457 spin_unlock(&hb->lock);
1458 up_read(&current->mm->mmap_sem);
1460 ret = get_user(uval, uaddr);
1461 if (!ret && (uval != -EFAULT))
1462 goto retry;
1464 return ret;
1467 static int futex_close(struct inode *inode, struct file *filp)
1469 struct futex_q *q = filp->private_data;
1471 unqueue_me(q);
1472 kfree(q);
1474 return 0;
1477 /* This is one-shot: once it's gone off you need a new fd */
1478 static unsigned int futex_poll(struct file *filp,
1479 struct poll_table_struct *wait)
1481 struct futex_q *q = filp->private_data;
1482 int ret = 0;
1484 poll_wait(filp, &q->waiters, wait);
1486 /*
1487 * list_empty() is safe here without any lock.
1488 * q->lock_ptr != 0 is not safe, because of ordering against wakeup.
1489 */
1490 if (list_empty(&q->list))
1491 ret = POLLIN | POLLRDNORM;
1493 return ret;
1496 static struct file_operations futex_fops = {
1497 .release = futex_close,
1498 .poll = futex_poll,
1499 };
1501 /*
1502 * Signal allows caller to avoid the race which would occur if they
1503 * set the sigio stuff up afterwards.
1504 */
1505 static int futex_fd(u32 __user *uaddr, int signal)
1507 struct futex_q *q;
1508 struct file *filp;
1509 int ret, err;
1511 ret = -EINVAL;
1512 if (!valid_signal(signal))
1513 goto out;
1515 ret = get_unused_fd();
1516 if (ret < 0)
1517 goto out;
1518 filp = get_empty_filp();
1519 if (!filp) {
1520 put_unused_fd(ret);
1521 ret = -ENFILE;
1522 goto out;
1524 filp->f_op = &futex_fops;
1525 filp->f_vfsmnt = mntget(futex_mnt);
1526 filp->f_dentry = dget(futex_mnt->mnt_root);
1527 filp->f_mapping = filp->f_dentry->d_inode->i_mapping;
1529 if (signal) {
1530 err = f_setown(filp, current->pid, 1);
1531 if (err < 0) {
1532 goto error;
1534 filp->f_owner.signum = signal;
1537 q = kmalloc(sizeof(*q), GFP_KERNEL);
1538 if (!q) {
1539 err = -ENOMEM;
1540 goto error;
1542 q->pi_state = NULL;
1544 down_read(&current->mm->mmap_sem);
1545 err = get_futex_key(uaddr, &q->key);
1547 if (unlikely(err != 0)) {
1548 up_read(&current->mm->mmap_sem);
1549 kfree(q);
1550 goto error;
1553 /*
1554 * queue_me() must be called before releasing mmap_sem, because
1555 * key->shared.inode needs to be referenced while holding it.
1556 */
1557 filp->private_data = q;
1559 queue_me(q, ret, filp);
1560 up_read(&current->mm->mmap_sem);
1562 /* Now we map fd to filp, so userspace can access it */
1563 fd_install(ret, filp);
1564 out:
1565 return ret;
1566 error:
1567 put_unused_fd(ret);
1568 put_filp(filp);
1569 ret = err;
1570 goto out;
1573 /*
1574 * Support for robust futexes: the kernel cleans up held futexes at
1575 * thread exit time.
1577 * Implementation: user-space maintains a per-thread list of locks it
1578 * is holding. Upon do_exit(), the kernel carefully walks this list,
1579 * and marks all locks that are owned by this thread with the
1580 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
1581 * always manipulated with the lock held, so the list is private and
1582 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
1583 * field, to allow the kernel to clean up if the thread dies after
1584 * acquiring the lock, but just before it could have added itself to
1585 * the list. There can only be one such pending lock.
1586 */
1588 /**
1589 * sys_set_robust_list - set the robust-futex list head of a task
1590 * @head: pointer to the list-head
1591 * @len: length of the list-head, as userspace expects
1592 */
1593 asmlinkage long
1594 sys_set_robust_list(struct robust_list_head __user *head,
1595 size_t len)
1597 /*
1598 * The kernel knows only one size for now:
1599 */
1600 if (unlikely(len != sizeof(*head)))
1601 return -EINVAL;
1603 current->robust_list = head;
1605 return 0;
1608 /**
1609 * sys_get_robust_list - get the robust-futex list head of a task
1610 * @pid: pid of the process [zero for current task]
1611 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
1612 * @len_ptr: pointer to a length field, the kernel fills in the header size
1613 */
1614 asmlinkage long
1615 sys_get_robust_list(int pid, struct robust_list_head __user **head_ptr,
1616 size_t __user *len_ptr)
1618 struct robust_list_head *head;
1619 unsigned long ret;
1621 if (!pid)
1622 head = current->robust_list;
1623 else {
1624 struct task_struct *p;
1626 ret = -ESRCH;
1627 read_lock(&tasklist_lock);
1628 p = find_task_by_pid(pid);
1629 if (!p)
1630 goto err_unlock;
1631 ret = -EPERM;
1632 if ((current->euid != p->euid) && (current->euid != p->uid) &&
1633 !capable(CAP_SYS_PTRACE))
1634 goto err_unlock;
1635 head = p->robust_list;
1636 read_unlock(&tasklist_lock);
1639 if (put_user(sizeof(*head), len_ptr))
1640 return -EFAULT;
1641 return put_user(head, head_ptr);
1643 err_unlock:
1644 read_unlock(&tasklist_lock);
1646 return ret;
1649 /*
1650 * Process a futex-list entry, check whether it's owned by the
1651 * dying task, and do notification if so:
1652 */
1653 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
1655 u32 uval, nval, mval;
1657 retry:
1658 if (get_user(uval, uaddr))
1659 return -1;
1661 if ((uval & FUTEX_TID_MASK) == curr->pid) {
1662 /*
1663 * Ok, this dying thread is truly holding a futex
1664 * of interest. Set the OWNER_DIED bit atomically
1665 * via cmpxchg, and if the value had FUTEX_WAITERS
1666 * set, wake up a waiter (if any). (We have to do a
1667 * futex_wake() even if OWNER_DIED is already set -
1668 * to handle the rare but possible case of recursive
1669 * thread-death.) The rest of the cleanup is done in
1670 * userspace.
1671 */
1672 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
1673 nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
1675 if (nval == -EFAULT)
1676 return -1;
1678 if (nval != uval)
1679 goto retry;
1681 /*
1682 * Wake robust non-PI futexes here. The wakeup of
1683 * PI futexes happens in exit_pi_state():
1684 */
1685 if (!pi) {
1686 if (uval & FUTEX_WAITERS)
1687 futex_wake(uaddr, 1);
1690 return 0;
1693 /*
1694 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
1695 */
1696 static inline int fetch_robust_entry(struct robust_list __user **entry,
1697 struct robust_list __user **head, int *pi)
1699 unsigned long uentry;
1701 if (get_user(uentry, (unsigned long *)head))
1702 return -EFAULT;
1704 *entry = (void *)(uentry & ~1UL);
1705 *pi = uentry & 1;
1707 return 0;
1710 /*
1711 * Walk curr->robust_list (very carefully, it's a userspace list!)
1712 * and mark any locks found there dead, and notify any waiters.
1714 * We silently return on any sign of list-walking problem.
1715 */
1716 void exit_robust_list(struct task_struct *curr)
1718 struct robust_list_head __user *head = curr->robust_list;
1719 struct robust_list __user *entry, *pending;
1720 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
1721 unsigned long futex_offset;
1723 /*
1724 * Fetch the list head (which was registered earlier, via
1725 * sys_set_robust_list()):
1726 */
1727 if (fetch_robust_entry(&entry, &head->list.next, &pi))
1728 return;
1729 /*
1730 * Fetch the relative futex offset:
1731 */
1732 if (get_user(futex_offset, &head->futex_offset))
1733 return;
1734 /*
1735 * Fetch any possibly pending lock-add first, and handle it
1736 * if it exists:
1737 */
1738 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
1739 return;
1741 if (pending)
1742 handle_futex_death((void *)pending + futex_offset, curr, pip);
1744 while (entry != &head->list) {
1745 /*
1746 * A pending lock might already be on the list, so
1747 * don't process it twice:
1748 */
1749 if (entry != pending)
1750 if (handle_futex_death((void *)entry + futex_offset,
1751 curr, pi))
1752 return;
1753 /*
1754 * Fetch the next entry in the list:
1755 */
1756 if (fetch_robust_entry(&entry, &entry->next, &pi))
1757 return;
1758 /*
1759 * Avoid excessively long or circular lists:
1760 */
1761 if (!--limit)
1762 break;
1764 cond_resched();
1768 long do_futex(u32 __user *uaddr, int op, u32 val, unsigned long timeout,
1769 u32 __user *uaddr2, u32 val2, u32 val3)
1771 int ret;
1773 switch (op) {
1774 case FUTEX_WAIT:
1775 ret = futex_wait(uaddr, val, timeout);
1776 break;
1777 case FUTEX_WAKE:
1778 ret = futex_wake(uaddr, val);
1779 break;
1780 case FUTEX_FD:
1781 /* non-zero val means F_SETOWN(getpid()) & F_SETSIG(val) */
1782 ret = futex_fd(uaddr, val);
1783 break;
1784 case FUTEX_REQUEUE:
1785 ret = futex_requeue(uaddr, uaddr2, val, val2, NULL);
1786 break;
1787 case FUTEX_CMP_REQUEUE:
1788 ret = futex_requeue(uaddr, uaddr2, val, val2, &val3);
1789 break;
1790 case FUTEX_WAKE_OP:
1791 ret = futex_wake_op(uaddr, uaddr2, val, val2, val3);
1792 break;
1793 case FUTEX_LOCK_PI:
1794 ret = futex_lock_pi(uaddr, val, timeout, val2, 0);
1795 break;
1796 case FUTEX_UNLOCK_PI:
1797 ret = futex_unlock_pi(uaddr);
1798 break;
1799 case FUTEX_TRYLOCK_PI:
1800 ret = futex_lock_pi(uaddr, 0, timeout, val2, 1);
1801 break;
1802 default:
1803 ret = -ENOSYS;
1805 return ret;
1809 asmlinkage long sys_futex(u32 __user *uaddr, int op, u32 val,
1810 struct timespec __user *utime, u32 __user *uaddr2,
1811 u32 val3)
1813 struct timespec t;
1814 unsigned long timeout = MAX_SCHEDULE_TIMEOUT;
1815 u32 val2 = 0;
1817 if (utime && (op == FUTEX_WAIT || op == FUTEX_LOCK_PI)) {
1818 if (copy_from_user(&t, utime, sizeof(t)) != 0)
1819 return -EFAULT;
1820 if (!timespec_valid(&t))
1821 return -EINVAL;
1822 if (op == FUTEX_WAIT)
1823 timeout = timespec_to_jiffies(&t) + 1;
1824 else {
1825 timeout = t.tv_sec;
1826 val2 = t.tv_nsec;
1829 /*
1830 * requeue parameter in 'utime' if op == FUTEX_REQUEUE.
1831 */
1832 if (op == FUTEX_REQUEUE || op == FUTEX_CMP_REQUEUE)
1833 val2 = (u32) (unsigned long) utime;
1835 return do_futex(uaddr, op, val, timeout, uaddr2, val2, val3);
1838 static int futexfs_get_sb(struct file_system_type *fs_type,
1839 int flags, const char *dev_name, void *data,
1840 struct vfsmount *mnt)
1842 return get_sb_pseudo(fs_type, "futex", NULL, 0xBAD1DEA, mnt);
1845 static struct file_system_type futex_fs_type = {
1846 .name = "futexfs",
1847 .get_sb = futexfs_get_sb,
1848 .kill_sb = kill_anon_super,
1849 };
1851 static int __init init(void)
1853 unsigned int i;
1855 register_filesystem(&futex_fs_type);
1856 futex_mnt = kern_mount(&futex_fs_type);
1858 for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
1859 INIT_LIST_HEAD(&futex_queues[i].chain);
1860 spin_lock_init(&futex_queues[i].lock);
1862 return 0;
1864 __initcall(init);