2 * Fast Userspace Mutexes (which I call "Futexes!").
3 * (C) Rusty Russell, IBM 2002
5 * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
6 * (C) Copyright 2003 Red Hat Inc, All Rights Reserved
8 * Removed page pinning, fix privately mapped COW pages and other cleanups
9 * (C) Copyright 2003, 2004 Jamie Lokier
11 * Robust futex support started by Ingo Molnar
12 * (C) Copyright 2006 Red Hat Inc, All Rights Reserved
13 * Thanks to Thomas Gleixner for suggestions, analysis and fixes.
15 * PI-futex support started by Ingo Molnar and Thomas Gleixner
16 * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
17 * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
19 * PRIVATE futexes by Eric Dumazet
20 * Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
22 * Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
23 * Copyright (C) IBM Corporation, 2009
24 * Thanks to Thomas Gleixner for conceptual design and careful reviews.
26 * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
27 * enough at me, Linus for the original (flawed) idea, Matthew
28 * Kirkwood for proof-of-concept implementation.
30 * "The futexes are also cursed."
31 * "But they come in a choice of three flavours!"
33 * This program is free software; you can redistribute it and/or modify
34 * it under the terms of the GNU General Public License as published by
35 * the Free Software Foundation; either version 2 of the License, or
36 * (at your option) any later version.
38 * This program is distributed in the hope that it will be useful,
39 * but WITHOUT ANY WARRANTY; without even the implied warranty of
40 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
41 * GNU General Public License for more details.
43 * You should have received a copy of the GNU General Public License
44 * along with this program; if not, write to the Free Software
45 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
47 #include <linux/slab.h>
48 #include <linux/poll.h>
50 #include <linux/file.h>
51 #include <linux/jhash.h>
52 #include <linux/init.h>
53 #include <linux/futex.h>
54 #include <linux/mount.h>
55 #include <linux/pagemap.h>
56 #include <linux/syscalls.h>
57 #include <linux/signal.h>
58 #include <linux/module.h>
59 #include <linux/magic.h>
60 #include <linux/pid.h>
61 #include <linux/nsproxy.h>
63 #include <asm/futex.h>
65 #include "rtmutex_common.h"
67 int __read_mostly futex_cmpxchg_enabled;
69 #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
72 * Priority Inheritance state:
74 struct futex_pi_state {
76 * list of 'owned' pi_state instances - these have to be
77 * cleaned up in do_exit() if the task exits prematurely:
79 struct list_head list;
84 struct rt_mutex pi_mutex;
86 struct task_struct *owner;
93 * struct futex_q - The hashed futex queue entry, one per waiting task
94 * @task: the task waiting on the futex
95 * @lock_ptr: the hash bucket lock
96 * @key: the key the futex is hashed on
97 * @pi_state: optional priority inheritance state
98 * @rt_waiter: rt_waiter storage for use with requeue_pi
99 * @requeue_pi_key: the requeue_pi target futex key
100 * @bitset: bitset for the optional bitmasked wakeup
102 * We use this hashed waitqueue, instead of a normal wait_queue_t, so
103 * we can wake only the relevant ones (hashed queues may be shared).
105 * A futex_q has a woken state, just like tasks have TASK_RUNNING.
106 * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
107 * The order of wakup is always to make the first condition true, then
110 * PI futexes are typically woken before they are removed from the hash list via
111 * the rt_mutex code. See unqueue_me_pi().
114 struct plist_node list;
116 struct task_struct *task;
117 spinlock_t *lock_ptr;
119 struct futex_pi_state *pi_state;
120 struct rt_mutex_waiter *rt_waiter;
121 union futex_key *requeue_pi_key;
126 * Hash buckets are shared by all the futex_keys that hash to the same
127 * location. Each key may have multiple futex_q structures, one for each task
128 * waiting on a futex.
130 struct futex_hash_bucket {
132 struct plist_head chain;
135 static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
138 * We hash on the keys returned from get_futex_key (see below).
140 static struct futex_hash_bucket *hash_futex(union futex_key *key)
142 u32 hash = jhash2((u32*)&key->both.word,
143 (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
145 return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
149 * Return 1 if two futex_keys are equal, 0 otherwise.
151 static inline int match_futex(union futex_key *key1, union futex_key *key2)
154 && key1->both.word == key2->both.word
155 && key1->both.ptr == key2->both.ptr
156 && key1->both.offset == key2->both.offset);
160 * Take a reference to the resource addressed by a key.
161 * Can be called while holding spinlocks.
164 static void get_futex_key_refs(union futex_key *key)
169 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
171 atomic_inc(&key->shared.inode->i_count);
173 case FUT_OFF_MMSHARED:
174 atomic_inc(&key->private.mm->mm_count);
180 * Drop a reference to the resource addressed by a key.
181 * The hash bucket spinlock must not be held.
183 static void drop_futex_key_refs(union futex_key *key)
185 if (!key->both.ptr) {
186 /* If we're here then we tried to put a key we failed to get */
191 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
193 iput(key->shared.inode);
195 case FUT_OFF_MMSHARED:
196 mmdrop(key->private.mm);
202 * get_futex_key() - Get parameters which are the keys for a futex
203 * @uaddr: virtual address of the futex
204 * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
205 * @key: address where result is stored.
207 * Returns a negative error code or 0
208 * The key words are stored in *key on success.
210 * For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,
211 * offset_within_page). For private mappings, it's (uaddr, current->mm).
212 * We can usually work out the index without swapping in the page.
214 * lock_page() might sleep, the caller should not hold a spinlock.
217 get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key)
219 unsigned long address = (unsigned long)uaddr;
220 struct mm_struct *mm = current->mm;
225 * The futex address must be "naturally" aligned.
227 key->both.offset = address % PAGE_SIZE;
228 if (unlikely((address % sizeof(u32)) != 0))
230 address -= key->both.offset;
233 * PROCESS_PRIVATE futexes are fast.
234 * As the mm cannot disappear under us and the 'key' only needs
235 * virtual address, we dont even have to find the underlying vma.
236 * Note : We do have to check 'uaddr' is a valid user address,
237 * but access_ok() should be faster than find_vma()
240 if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))))
242 key->private.mm = mm;
243 key->private.address = address;
244 get_futex_key_refs(key);
249 err = get_user_pages_fast(address, 1, 1, &page);
253 page = compound_head(page);
255 if (!page->mapping) {
262 * Private mappings are handled in a simple way.
264 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
265 * it's a read-only handle, it's expected that futexes attach to
266 * the object not the particular process.
268 if (PageAnon(page)) {
269 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
270 key->private.mm = mm;
271 key->private.address = address;
273 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
274 key->shared.inode = page->mapping->host;
275 key->shared.pgoff = page->index;
278 get_futex_key_refs(key);
286 void put_futex_key(int fshared, union futex_key *key)
288 drop_futex_key_refs(key);
292 * fault_in_user_writeable() - Fault in user address and verify RW access
293 * @uaddr: pointer to faulting user space address
295 * Slow path to fixup the fault we just took in the atomic write
298 * We have no generic implementation of a non destructive write to the
299 * user address. We know that we faulted in the atomic pagefault
300 * disabled section so we can as well avoid the #PF overhead by
301 * calling get_user_pages() right away.
303 static int fault_in_user_writeable(u32 __user *uaddr)
305 struct mm_struct *mm = current->mm;
308 down_read(&mm->mmap_sem);
309 ret = get_user_pages(current, mm, (unsigned long)uaddr,
310 1, 1, 0, NULL, NULL);
311 up_read(&mm->mmap_sem);
313 return ret < 0 ? ret : 0;
317 * futex_top_waiter() - Return the highest priority waiter on a futex
318 * @hb: the hash bucket the futex_q's reside in
319 * @key: the futex key (to distinguish it from other futex futex_q's)
321 * Must be called with the hb lock held.
323 static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
324 union futex_key *key)
326 struct futex_q *this;
328 plist_for_each_entry(this, &hb->chain, list) {
329 if (match_futex(&this->key, key))
335 static u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval)
340 curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
346 static int get_futex_value_locked(u32 *dest, u32 __user *from)
351 ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
354 return ret ? -EFAULT : 0;
361 static int refill_pi_state_cache(void)
363 struct futex_pi_state *pi_state;
365 if (likely(current->pi_state_cache))
368 pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
373 INIT_LIST_HEAD(&pi_state->list);
374 /* pi_mutex gets initialized later */
375 pi_state->owner = NULL;
376 atomic_set(&pi_state->refcount, 1);
377 pi_state->key = FUTEX_KEY_INIT;
379 current->pi_state_cache = pi_state;
384 static struct futex_pi_state * alloc_pi_state(void)
386 struct futex_pi_state *pi_state = current->pi_state_cache;
389 current->pi_state_cache = NULL;
394 static void free_pi_state(struct futex_pi_state *pi_state)
396 if (!atomic_dec_and_test(&pi_state->refcount))
400 * If pi_state->owner is NULL, the owner is most probably dying
401 * and has cleaned up the pi_state already
403 if (pi_state->owner) {
404 raw_spin_lock_irq(&pi_state->owner->pi_lock);
405 list_del_init(&pi_state->list);
406 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
408 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
411 if (current->pi_state_cache)
415 * pi_state->list is already empty.
416 * clear pi_state->owner.
417 * refcount is at 0 - put it back to 1.
419 pi_state->owner = NULL;
420 atomic_set(&pi_state->refcount, 1);
421 current->pi_state_cache = pi_state;
426 * Look up the task based on what TID userspace gave us.
429 static struct task_struct * futex_find_get_task(pid_t pid)
431 struct task_struct *p;
434 p = find_task_by_vpid(pid);
444 * This task is holding PI mutexes at exit time => bad.
445 * Kernel cleans up PI-state, but userspace is likely hosed.
446 * (Robust-futex cleanup is separate and might save the day for userspace.)
448 void exit_pi_state_list(struct task_struct *curr)
450 struct list_head *next, *head = &curr->pi_state_list;
451 struct futex_pi_state *pi_state;
452 struct futex_hash_bucket *hb;
453 union futex_key key = FUTEX_KEY_INIT;
455 if (!futex_cmpxchg_enabled)
458 * We are a ZOMBIE and nobody can enqueue itself on
459 * pi_state_list anymore, but we have to be careful
460 * versus waiters unqueueing themselves:
462 raw_spin_lock_irq(&curr->pi_lock);
463 while (!list_empty(head)) {
466 pi_state = list_entry(next, struct futex_pi_state, list);
468 hb = hash_futex(&key);
469 raw_spin_unlock_irq(&curr->pi_lock);
471 spin_lock(&hb->lock);
473 raw_spin_lock_irq(&curr->pi_lock);
475 * We dropped the pi-lock, so re-check whether this
476 * task still owns the PI-state:
478 if (head->next != next) {
479 spin_unlock(&hb->lock);
483 WARN_ON(pi_state->owner != curr);
484 WARN_ON(list_empty(&pi_state->list));
485 list_del_init(&pi_state->list);
486 pi_state->owner = NULL;
487 raw_spin_unlock_irq(&curr->pi_lock);
489 rt_mutex_unlock(&pi_state->pi_mutex);
491 spin_unlock(&hb->lock);
493 raw_spin_lock_irq(&curr->pi_lock);
495 raw_spin_unlock_irq(&curr->pi_lock);
499 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
500 union futex_key *key, struct futex_pi_state **ps)
502 struct futex_pi_state *pi_state = NULL;
503 struct futex_q *this, *next;
504 struct plist_head *head;
505 struct task_struct *p;
506 pid_t pid = uval & FUTEX_TID_MASK;
510 plist_for_each_entry_safe(this, next, head, list) {
511 if (match_futex(&this->key, key)) {
513 * Another waiter already exists - bump up
514 * the refcount and return its pi_state:
516 pi_state = this->pi_state;
518 * Userspace might have messed up non PI and PI futexes
520 if (unlikely(!pi_state))
523 WARN_ON(!atomic_read(&pi_state->refcount));
526 * When pi_state->owner is NULL then the owner died
527 * and another waiter is on the fly. pi_state->owner
528 * is fixed up by the task which acquires
529 * pi_state->rt_mutex.
531 * We do not check for pid == 0 which can happen when
532 * the owner died and robust_list_exit() cleared the
535 if (pid && pi_state->owner) {
537 * Bail out if user space manipulated the
540 if (pid != task_pid_vnr(pi_state->owner))
544 atomic_inc(&pi_state->refcount);
552 * We are the first waiter - try to look up the real owner and attach
553 * the new pi_state to it, but bail out when TID = 0
557 p = futex_find_get_task(pid);
562 * We need to look at the task state flags to figure out,
563 * whether the task is exiting. To protect against the do_exit
564 * change of the task flags, we do this protected by
567 raw_spin_lock_irq(&p->pi_lock);
568 if (unlikely(p->flags & PF_EXITING)) {
570 * The task is on the way out. When PF_EXITPIDONE is
571 * set, we know that the task has finished the
574 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
576 raw_spin_unlock_irq(&p->pi_lock);
581 pi_state = alloc_pi_state();
584 * Initialize the pi_mutex in locked state and make 'p'
587 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
589 /* Store the key for possible exit cleanups: */
590 pi_state->key = *key;
592 WARN_ON(!list_empty(&pi_state->list));
593 list_add(&pi_state->list, &p->pi_state_list);
595 raw_spin_unlock_irq(&p->pi_lock);
605 * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
606 * @uaddr: the pi futex user address
607 * @hb: the pi futex hash bucket
608 * @key: the futex key associated with uaddr and hb
609 * @ps: the pi_state pointer where we store the result of the
611 * @task: the task to perform the atomic lock work for. This will
612 * be "current" except in the case of requeue pi.
613 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
617 * 1 - acquired the lock
620 * The hb->lock and futex_key refs shall be held by the caller.
622 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
623 union futex_key *key,
624 struct futex_pi_state **ps,
625 struct task_struct *task, int set_waiters)
627 int lock_taken, ret, ownerdied = 0;
628 u32 uval, newval, curval;
631 ret = lock_taken = 0;
634 * To avoid races, we attempt to take the lock here again
635 * (by doing a 0 -> TID atomic cmpxchg), while holding all
636 * the locks. It will most likely not succeed.
638 newval = task_pid_vnr(task);
640 newval |= FUTEX_WAITERS;
642 curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
644 if (unlikely(curval == -EFAULT))
650 if ((unlikely((curval & FUTEX_TID_MASK) == task_pid_vnr(task))))
654 * Surprise - we got the lock. Just return to userspace:
656 if (unlikely(!curval))
662 * Set the FUTEX_WAITERS flag, so the owner will know it has someone
663 * to wake at the next unlock.
665 newval = curval | FUTEX_WAITERS;
668 * There are two cases, where a futex might have no owner (the
669 * owner TID is 0): OWNER_DIED. We take over the futex in this
670 * case. We also do an unconditional take over, when the owner
673 * This is safe as we are protected by the hash bucket lock !
675 if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
676 /* Keep the OWNER_DIED bit */
677 newval = (curval & ~FUTEX_TID_MASK) | task_pid_vnr(task);
682 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
684 if (unlikely(curval == -EFAULT))
686 if (unlikely(curval != uval))
690 * We took the lock due to owner died take over.
692 if (unlikely(lock_taken))
696 * We dont have the lock. Look up the PI state (or create it if
697 * we are the first waiter):
699 ret = lookup_pi_state(uval, hb, key, ps);
705 * No owner found for this futex. Check if the
706 * OWNER_DIED bit is set to figure out whether
707 * this is a robust futex or not.
709 if (get_futex_value_locked(&curval, uaddr))
713 * We simply start over in case of a robust
714 * futex. The code above will take the futex
717 if (curval & FUTEX_OWNER_DIED) {
730 * The hash bucket lock must be held when this is called.
731 * Afterwards, the futex_q must not be accessed.
733 static void wake_futex(struct futex_q *q)
735 struct task_struct *p = q->task;
738 * We set q->lock_ptr = NULL _before_ we wake up the task. If
739 * a non futex wake up happens on another CPU then the task
740 * might exit and p would dereference a non existing task
741 * struct. Prevent this by holding a reference on p across the
746 plist_del(&q->list, &q->list.plist);
748 * The waiting task can free the futex_q as soon as
749 * q->lock_ptr = NULL is written, without taking any locks. A
750 * memory barrier is required here to prevent the following
751 * store to lock_ptr from getting ahead of the plist_del.
756 wake_up_state(p, TASK_NORMAL);
760 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
762 struct task_struct *new_owner;
763 struct futex_pi_state *pi_state = this->pi_state;
770 * If current does not own the pi_state then the futex is
771 * inconsistent and user space fiddled with the futex value.
773 if (pi_state->owner != current)
776 raw_spin_lock(&pi_state->pi_mutex.wait_lock);
777 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
780 * This happens when we have stolen the lock and the original
781 * pending owner did not enqueue itself back on the rt_mutex.
782 * Thats not a tragedy. We know that way, that a lock waiter
783 * is on the fly. We make the futex_q waiter the pending owner.
786 new_owner = this->task;
789 * We pass it to the next owner. (The WAITERS bit is always
790 * kept enabled while there is PI state around. We must also
791 * preserve the owner died bit.)
793 if (!(uval & FUTEX_OWNER_DIED)) {
796 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
798 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
800 if (curval == -EFAULT)
802 else if (curval != uval)
805 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
810 raw_spin_lock_irq(&pi_state->owner->pi_lock);
811 WARN_ON(list_empty(&pi_state->list));
812 list_del_init(&pi_state->list);
813 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
815 raw_spin_lock_irq(&new_owner->pi_lock);
816 WARN_ON(!list_empty(&pi_state->list));
817 list_add(&pi_state->list, &new_owner->pi_state_list);
818 pi_state->owner = new_owner;
819 raw_spin_unlock_irq(&new_owner->pi_lock);
821 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
822 rt_mutex_unlock(&pi_state->pi_mutex);
827 static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
832 * There is no waiter, so we unlock the futex. The owner died
833 * bit has not to be preserved here. We are the owner:
835 oldval = cmpxchg_futex_value_locked(uaddr, uval, 0);
837 if (oldval == -EFAULT)
846 * Express the locking dependencies for lockdep:
849 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
852 spin_lock(&hb1->lock);
854 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
855 } else { /* hb1 > hb2 */
856 spin_lock(&hb2->lock);
857 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
862 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
864 spin_unlock(&hb1->lock);
866 spin_unlock(&hb2->lock);
870 * Wake up waiters matching bitset queued on this futex (uaddr).
872 static int futex_wake(u32 __user *uaddr, int fshared, int nr_wake, u32 bitset)
874 struct futex_hash_bucket *hb;
875 struct futex_q *this, *next;
876 struct plist_head *head;
877 union futex_key key = FUTEX_KEY_INIT;
883 ret = get_futex_key(uaddr, fshared, &key);
884 if (unlikely(ret != 0))
887 hb = hash_futex(&key);
888 spin_lock(&hb->lock);
891 plist_for_each_entry_safe(this, next, head, list) {
892 if (match_futex (&this->key, &key)) {
893 if (this->pi_state || this->rt_waiter) {
898 /* Check if one of the bits is set in both bitsets */
899 if (!(this->bitset & bitset))
903 if (++ret >= nr_wake)
908 spin_unlock(&hb->lock);
909 put_futex_key(fshared, &key);
915 * Wake up all waiters hashed on the physical page that is mapped
916 * to this virtual address:
919 futex_wake_op(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
920 int nr_wake, int nr_wake2, int op)
922 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
923 struct futex_hash_bucket *hb1, *hb2;
924 struct plist_head *head;
925 struct futex_q *this, *next;
929 ret = get_futex_key(uaddr1, fshared, &key1);
930 if (unlikely(ret != 0))
932 ret = get_futex_key(uaddr2, fshared, &key2);
933 if (unlikely(ret != 0))
936 hb1 = hash_futex(&key1);
937 hb2 = hash_futex(&key2);
940 double_lock_hb(hb1, hb2);
941 op_ret = futex_atomic_op_inuser(op, uaddr2);
942 if (unlikely(op_ret < 0)) {
944 double_unlock_hb(hb1, hb2);
948 * we don't get EFAULT from MMU faults if we don't have an MMU,
949 * but we might get them from range checking
955 if (unlikely(op_ret != -EFAULT)) {
960 ret = fault_in_user_writeable(uaddr2);
967 put_futex_key(fshared, &key2);
968 put_futex_key(fshared, &key1);
974 plist_for_each_entry_safe(this, next, head, list) {
975 if (match_futex (&this->key, &key1)) {
977 if (++ret >= nr_wake)
986 plist_for_each_entry_safe(this, next, head, list) {
987 if (match_futex (&this->key, &key2)) {
989 if (++op_ret >= nr_wake2)
996 double_unlock_hb(hb1, hb2);
998 put_futex_key(fshared, &key2);
1000 put_futex_key(fshared, &key1);
1006 * requeue_futex() - Requeue a futex_q from one hb to another
1007 * @q: the futex_q to requeue
1008 * @hb1: the source hash_bucket
1009 * @hb2: the target hash_bucket
1010 * @key2: the new key for the requeued futex_q
1013 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1014 struct futex_hash_bucket *hb2, union futex_key *key2)
1018 * If key1 and key2 hash to the same bucket, no need to
1021 if (likely(&hb1->chain != &hb2->chain)) {
1022 plist_del(&q->list, &hb1->chain);
1023 plist_add(&q->list, &hb2->chain);
1024 q->lock_ptr = &hb2->lock;
1025 #ifdef CONFIG_DEBUG_PI_LIST
1026 q->list.plist.spinlock = &hb2->lock;
1029 get_futex_key_refs(key2);
1034 * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1036 * @key: the key of the requeue target futex
1037 * @hb: the hash_bucket of the requeue target futex
1039 * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1040 * target futex if it is uncontended or via a lock steal. Set the futex_q key
1041 * to the requeue target futex so the waiter can detect the wakeup on the right
1042 * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1043 * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
1044 * to protect access to the pi_state to fixup the owner later. Must be called
1045 * with both q->lock_ptr and hb->lock held.
1048 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1049 struct futex_hash_bucket *hb)
1051 get_futex_key_refs(key);
1054 WARN_ON(plist_node_empty(&q->list));
1055 plist_del(&q->list, &q->list.plist);
1057 WARN_ON(!q->rt_waiter);
1058 q->rt_waiter = NULL;
1060 q->lock_ptr = &hb->lock;
1061 #ifdef CONFIG_DEBUG_PI_LIST
1062 q->list.plist.spinlock = &hb->lock;
1065 wake_up_state(q->task, TASK_NORMAL);
1069 * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1070 * @pifutex: the user address of the to futex
1071 * @hb1: the from futex hash bucket, must be locked by the caller
1072 * @hb2: the to futex hash bucket, must be locked by the caller
1073 * @key1: the from futex key
1074 * @key2: the to futex key
1075 * @ps: address to store the pi_state pointer
1076 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1078 * Try and get the lock on behalf of the top waiter if we can do it atomically.
1079 * Wake the top waiter if we succeed. If the caller specified set_waiters,
1080 * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1081 * hb1 and hb2 must be held by the caller.
1084 * 0 - failed to acquire the lock atomicly
1085 * 1 - acquired the lock
1088 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1089 struct futex_hash_bucket *hb1,
1090 struct futex_hash_bucket *hb2,
1091 union futex_key *key1, union futex_key *key2,
1092 struct futex_pi_state **ps, int set_waiters)
1094 struct futex_q *top_waiter = NULL;
1098 if (get_futex_value_locked(&curval, pifutex))
1102 * Find the top_waiter and determine if there are additional waiters.
1103 * If the caller intends to requeue more than 1 waiter to pifutex,
1104 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1105 * as we have means to handle the possible fault. If not, don't set
1106 * the bit unecessarily as it will force the subsequent unlock to enter
1109 top_waiter = futex_top_waiter(hb1, key1);
1111 /* There are no waiters, nothing for us to do. */
1115 /* Ensure we requeue to the expected futex. */
1116 if (!match_futex(top_waiter->requeue_pi_key, key2))
1120 * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
1121 * the contended case or if set_waiters is 1. The pi_state is returned
1122 * in ps in contended cases.
1124 ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1127 requeue_pi_wake_futex(top_waiter, key2, hb2);
1133 * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1134 * uaddr1: source futex user address
1135 * uaddr2: target futex user address
1136 * nr_wake: number of waiters to wake (must be 1 for requeue_pi)
1137 * nr_requeue: number of waiters to requeue (0-INT_MAX)
1138 * requeue_pi: if we are attempting to requeue from a non-pi futex to a
1139 * pi futex (pi to pi requeue is not supported)
1141 * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1142 * uaddr2 atomically on behalf of the top waiter.
1145 * >=0 - on success, the number of tasks requeued or woken
1148 static int futex_requeue(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
1149 int nr_wake, int nr_requeue, u32 *cmpval,
1152 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1153 int drop_count = 0, task_count = 0, ret;
1154 struct futex_pi_state *pi_state = NULL;
1155 struct futex_hash_bucket *hb1, *hb2;
1156 struct plist_head *head1;
1157 struct futex_q *this, *next;
1162 * requeue_pi requires a pi_state, try to allocate it now
1163 * without any locks in case it fails.
1165 if (refill_pi_state_cache())
1168 * requeue_pi must wake as many tasks as it can, up to nr_wake
1169 * + nr_requeue, since it acquires the rt_mutex prior to
1170 * returning to userspace, so as to not leave the rt_mutex with
1171 * waiters and no owner. However, second and third wake-ups
1172 * cannot be predicted as they involve race conditions with the
1173 * first wake and a fault while looking up the pi_state. Both
1174 * pthread_cond_signal() and pthread_cond_broadcast() should
1182 if (pi_state != NULL) {
1184 * We will have to lookup the pi_state again, so free this one
1185 * to keep the accounting correct.
1187 free_pi_state(pi_state);
1191 ret = get_futex_key(uaddr1, fshared, &key1);
1192 if (unlikely(ret != 0))
1194 ret = get_futex_key(uaddr2, fshared, &key2);
1195 if (unlikely(ret != 0))
1198 hb1 = hash_futex(&key1);
1199 hb2 = hash_futex(&key2);
1202 double_lock_hb(hb1, hb2);
1204 if (likely(cmpval != NULL)) {
1207 ret = get_futex_value_locked(&curval, uaddr1);
1209 if (unlikely(ret)) {
1210 double_unlock_hb(hb1, hb2);
1212 ret = get_user(curval, uaddr1);
1219 put_futex_key(fshared, &key2);
1220 put_futex_key(fshared, &key1);
1223 if (curval != *cmpval) {
1229 if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1231 * Attempt to acquire uaddr2 and wake the top waiter. If we
1232 * intend to requeue waiters, force setting the FUTEX_WAITERS
1233 * bit. We force this here where we are able to easily handle
1234 * faults rather in the requeue loop below.
1236 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1237 &key2, &pi_state, nr_requeue);
1240 * At this point the top_waiter has either taken uaddr2 or is
1241 * waiting on it. If the former, then the pi_state will not
1242 * exist yet, look it up one more time to ensure we have a
1249 ret = get_futex_value_locked(&curval2, uaddr2);
1251 ret = lookup_pi_state(curval2, hb2, &key2,
1259 double_unlock_hb(hb1, hb2);
1260 put_futex_key(fshared, &key2);
1261 put_futex_key(fshared, &key1);
1262 ret = fault_in_user_writeable(uaddr2);
1267 /* The owner was exiting, try again. */
1268 double_unlock_hb(hb1, hb2);
1269 put_futex_key(fshared, &key2);
1270 put_futex_key(fshared, &key1);
1278 head1 = &hb1->chain;
1279 plist_for_each_entry_safe(this, next, head1, list) {
1280 if (task_count - nr_wake >= nr_requeue)
1283 if (!match_futex(&this->key, &key1))
1287 * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1288 * be paired with each other and no other futex ops.
1290 if ((requeue_pi && !this->rt_waiter) ||
1291 (!requeue_pi && this->rt_waiter)) {
1297 * Wake nr_wake waiters. For requeue_pi, if we acquired the
1298 * lock, we already woke the top_waiter. If not, it will be
1299 * woken by futex_unlock_pi().
1301 if (++task_count <= nr_wake && !requeue_pi) {
1306 /* Ensure we requeue to the expected futex for requeue_pi. */
1307 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1313 * Requeue nr_requeue waiters and possibly one more in the case
1314 * of requeue_pi if we couldn't acquire the lock atomically.
1317 /* Prepare the waiter to take the rt_mutex. */
1318 atomic_inc(&pi_state->refcount);
1319 this->pi_state = pi_state;
1320 ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1324 /* We got the lock. */
1325 requeue_pi_wake_futex(this, &key2, hb2);
1330 this->pi_state = NULL;
1331 free_pi_state(pi_state);
1335 requeue_futex(this, hb1, hb2, &key2);
1340 double_unlock_hb(hb1, hb2);
1343 * drop_futex_key_refs() must be called outside the spinlocks. During
1344 * the requeue we moved futex_q's from the hash bucket at key1 to the
1345 * one at key2 and updated their key pointer. We no longer need to
1346 * hold the references to key1.
1348 while (--drop_count >= 0)
1349 drop_futex_key_refs(&key1);
1352 put_futex_key(fshared, &key2);
1354 put_futex_key(fshared, &key1);
1356 if (pi_state != NULL)
1357 free_pi_state(pi_state);
1358 return ret ? ret : task_count;
1361 /* The key must be already stored in q->key. */
1362 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
1364 struct futex_hash_bucket *hb;
1366 get_futex_key_refs(&q->key);
1367 hb = hash_futex(&q->key);
1368 q->lock_ptr = &hb->lock;
1370 spin_lock(&hb->lock);
1375 queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
1377 spin_unlock(&hb->lock);
1378 drop_futex_key_refs(&q->key);
1382 * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1383 * @q: The futex_q to enqueue
1384 * @hb: The destination hash bucket
1386 * The hb->lock must be held by the caller, and is released here. A call to
1387 * queue_me() is typically paired with exactly one call to unqueue_me(). The
1388 * exceptions involve the PI related operations, which may use unqueue_me_pi()
1389 * or nothing if the unqueue is done as part of the wake process and the unqueue
1390 * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1393 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1398 * The priority used to register this element is
1399 * - either the real thread-priority for the real-time threads
1400 * (i.e. threads with a priority lower than MAX_RT_PRIO)
1401 * - or MAX_RT_PRIO for non-RT threads.
1402 * Thus, all RT-threads are woken first in priority order, and
1403 * the others are woken last, in FIFO order.
1405 prio = min(current->normal_prio, MAX_RT_PRIO);
1407 plist_node_init(&q->list, prio);
1408 #ifdef CONFIG_DEBUG_PI_LIST
1409 q->list.plist.spinlock = &hb->lock;
1411 plist_add(&q->list, &hb->chain);
1413 spin_unlock(&hb->lock);
1417 * unqueue_me() - Remove the futex_q from its futex_hash_bucket
1418 * @q: The futex_q to unqueue
1420 * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
1421 * be paired with exactly one earlier call to queue_me().
1424 * 1 - if the futex_q was still queued (and we removed unqueued it)
1425 * 0 - if the futex_q was already removed by the waking thread
1427 static int unqueue_me(struct futex_q *q)
1429 spinlock_t *lock_ptr;
1432 /* In the common case we don't take the spinlock, which is nice. */
1434 lock_ptr = q->lock_ptr;
1436 if (lock_ptr != NULL) {
1437 spin_lock(lock_ptr);
1439 * q->lock_ptr can change between reading it and
1440 * spin_lock(), causing us to take the wrong lock. This
1441 * corrects the race condition.
1443 * Reasoning goes like this: if we have the wrong lock,
1444 * q->lock_ptr must have changed (maybe several times)
1445 * between reading it and the spin_lock(). It can
1446 * change again after the spin_lock() but only if it was
1447 * already changed before the spin_lock(). It cannot,
1448 * however, change back to the original value. Therefore
1449 * we can detect whether we acquired the correct lock.
1451 if (unlikely(lock_ptr != q->lock_ptr)) {
1452 spin_unlock(lock_ptr);
1455 WARN_ON(plist_node_empty(&q->list));
1456 plist_del(&q->list, &q->list.plist);
1458 BUG_ON(q->pi_state);
1460 spin_unlock(lock_ptr);
1464 drop_futex_key_refs(&q->key);
1469 * PI futexes can not be requeued and must remove themself from the
1470 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1473 static void unqueue_me_pi(struct futex_q *q)
1475 WARN_ON(plist_node_empty(&q->list));
1476 plist_del(&q->list, &q->list.plist);
1478 BUG_ON(!q->pi_state);
1479 free_pi_state(q->pi_state);
1482 spin_unlock(q->lock_ptr);
1484 drop_futex_key_refs(&q->key);
1488 * Fixup the pi_state owner with the new owner.
1490 * Must be called with hash bucket lock held and mm->sem held for non
1493 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1494 struct task_struct *newowner, int fshared)
1496 u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
1497 struct futex_pi_state *pi_state = q->pi_state;
1498 struct task_struct *oldowner = pi_state->owner;
1499 u32 uval, curval, newval;
1503 if (!pi_state->owner)
1504 newtid |= FUTEX_OWNER_DIED;
1507 * We are here either because we stole the rtmutex from the
1508 * pending owner or we are the pending owner which failed to
1509 * get the rtmutex. We have to replace the pending owner TID
1510 * in the user space variable. This must be atomic as we have
1511 * to preserve the owner died bit here.
1513 * Note: We write the user space value _before_ changing the pi_state
1514 * because we can fault here. Imagine swapped out pages or a fork
1515 * that marked all the anonymous memory readonly for cow.
1517 * Modifying pi_state _before_ the user space value would
1518 * leave the pi_state in an inconsistent state when we fault
1519 * here, because we need to drop the hash bucket lock to
1520 * handle the fault. This might be observed in the PID check
1521 * in lookup_pi_state.
1524 if (get_futex_value_locked(&uval, uaddr))
1528 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1530 curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
1532 if (curval == -EFAULT)
1540 * We fixed up user space. Now we need to fix the pi_state
1543 if (pi_state->owner != NULL) {
1544 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1545 WARN_ON(list_empty(&pi_state->list));
1546 list_del_init(&pi_state->list);
1547 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1550 pi_state->owner = newowner;
1552 raw_spin_lock_irq(&newowner->pi_lock);
1553 WARN_ON(!list_empty(&pi_state->list));
1554 list_add(&pi_state->list, &newowner->pi_state_list);
1555 raw_spin_unlock_irq(&newowner->pi_lock);
1559 * To handle the page fault we need to drop the hash bucket
1560 * lock here. That gives the other task (either the pending
1561 * owner itself or the task which stole the rtmutex) the
1562 * chance to try the fixup of the pi_state. So once we are
1563 * back from handling the fault we need to check the pi_state
1564 * after reacquiring the hash bucket lock and before trying to
1565 * do another fixup. When the fixup has been done already we
1569 spin_unlock(q->lock_ptr);
1571 ret = fault_in_user_writeable(uaddr);
1573 spin_lock(q->lock_ptr);
1576 * Check if someone else fixed it for us:
1578 if (pi_state->owner != oldowner)
1588 * In case we must use restart_block to restart a futex_wait,
1589 * we encode in the 'flags' shared capability
1591 #define FLAGS_SHARED 0x01
1592 #define FLAGS_CLOCKRT 0x02
1593 #define FLAGS_HAS_TIMEOUT 0x04
1595 static long futex_wait_restart(struct restart_block *restart);
1598 * fixup_owner() - Post lock pi_state and corner case management
1599 * @uaddr: user address of the futex
1600 * @fshared: whether the futex is shared (1) or not (0)
1601 * @q: futex_q (contains pi_state and access to the rt_mutex)
1602 * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
1604 * After attempting to lock an rt_mutex, this function is called to cleanup
1605 * the pi_state owner as well as handle race conditions that may allow us to
1606 * acquire the lock. Must be called with the hb lock held.
1609 * 1 - success, lock taken
1610 * 0 - success, lock not taken
1611 * <0 - on error (-EFAULT)
1613 static int fixup_owner(u32 __user *uaddr, int fshared, struct futex_q *q,
1616 struct task_struct *owner;
1621 * Got the lock. We might not be the anticipated owner if we
1622 * did a lock-steal - fix up the PI-state in that case:
1624 if (q->pi_state->owner != current)
1625 ret = fixup_pi_state_owner(uaddr, q, current, fshared);
1630 * Catch the rare case, where the lock was released when we were on the
1631 * way back before we locked the hash bucket.
1633 if (q->pi_state->owner == current) {
1635 * Try to get the rt_mutex now. This might fail as some other
1636 * task acquired the rt_mutex after we removed ourself from the
1637 * rt_mutex waiters list.
1639 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
1645 * pi_state is incorrect, some other task did a lock steal and
1646 * we returned due to timeout or signal without taking the
1647 * rt_mutex. Too late. We can access the rt_mutex_owner without
1648 * locking, as the other task is now blocked on the hash bucket
1649 * lock. Fix the state up.
1651 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
1652 ret = fixup_pi_state_owner(uaddr, q, owner, fshared);
1657 * Paranoia check. If we did not take the lock, then we should not be
1658 * the owner, nor the pending owner, of the rt_mutex.
1660 if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
1661 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
1662 "pi-state %p\n", ret,
1663 q->pi_state->pi_mutex.owner,
1664 q->pi_state->owner);
1667 return ret ? ret : locked;
1671 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
1672 * @hb: the futex hash bucket, must be locked by the caller
1673 * @q: the futex_q to queue up on
1674 * @timeout: the prepared hrtimer_sleeper, or null for no timeout
1676 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
1677 struct hrtimer_sleeper *timeout)
1680 * The task state is guaranteed to be set before another task can
1681 * wake it. set_current_state() is implemented using set_mb() and
1682 * queue_me() calls spin_unlock() upon completion, both serializing
1683 * access to the hash list and forcing another memory barrier.
1685 set_current_state(TASK_INTERRUPTIBLE);
1690 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1691 if (!hrtimer_active(&timeout->timer))
1692 timeout->task = NULL;
1696 * If we have been removed from the hash list, then another task
1697 * has tried to wake us, and we can skip the call to schedule().
1699 if (likely(!plist_node_empty(&q->list))) {
1701 * If the timer has already expired, current will already be
1702 * flagged for rescheduling. Only call schedule if there
1703 * is no timeout, or if it has yet to expire.
1705 if (!timeout || timeout->task)
1708 __set_current_state(TASK_RUNNING);
1712 * futex_wait_setup() - Prepare to wait on a futex
1713 * @uaddr: the futex userspace address
1714 * @val: the expected value
1715 * @fshared: whether the futex is shared (1) or not (0)
1716 * @q: the associated futex_q
1717 * @hb: storage for hash_bucket pointer to be returned to caller
1719 * Setup the futex_q and locate the hash_bucket. Get the futex value and
1720 * compare it with the expected value. Handle atomic faults internally.
1721 * Return with the hb lock held and a q.key reference on success, and unlocked
1722 * with no q.key reference on failure.
1725 * 0 - uaddr contains val and hb has been locked
1726 * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlcoked
1728 static int futex_wait_setup(u32 __user *uaddr, u32 val, int fshared,
1729 struct futex_q *q, struct futex_hash_bucket **hb)
1735 * Access the page AFTER the hash-bucket is locked.
1736 * Order is important:
1738 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1739 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
1741 * The basic logical guarantee of a futex is that it blocks ONLY
1742 * if cond(var) is known to be true at the time of blocking, for
1743 * any cond. If we queued after testing *uaddr, that would open
1744 * a race condition where we could block indefinitely with
1745 * cond(var) false, which would violate the guarantee.
1747 * A consequence is that futex_wait() can return zero and absorb
1748 * a wakeup when *uaddr != val on entry to the syscall. This is
1752 q->key = FUTEX_KEY_INIT;
1753 ret = get_futex_key(uaddr, fshared, &q->key);
1754 if (unlikely(ret != 0))
1758 *hb = queue_lock(q);
1760 ret = get_futex_value_locked(&uval, uaddr);
1763 queue_unlock(q, *hb);
1765 ret = get_user(uval, uaddr);
1772 put_futex_key(fshared, &q->key);
1777 queue_unlock(q, *hb);
1783 put_futex_key(fshared, &q->key);
1787 static int futex_wait(u32 __user *uaddr, int fshared,
1788 u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
1790 struct hrtimer_sleeper timeout, *to = NULL;
1791 struct restart_block *restart;
1792 struct futex_hash_bucket *hb;
1802 q.requeue_pi_key = NULL;
1807 hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
1808 CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1809 hrtimer_init_sleeper(to, current);
1810 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
1811 current->timer_slack_ns);
1815 /* Prepare to wait on uaddr. */
1816 ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
1820 /* queue_me and wait for wakeup, timeout, or a signal. */
1821 futex_wait_queue_me(hb, &q, to);
1823 /* If we were woken (and unqueued), we succeeded, whatever. */
1825 if (!unqueue_me(&q))
1828 if (to && !to->task)
1832 * We expect signal_pending(current), but we might be the
1833 * victim of a spurious wakeup as well.
1835 if (!signal_pending(current)) {
1836 put_futex_key(fshared, &q.key);
1844 restart = ¤t_thread_info()->restart_block;
1845 restart->fn = futex_wait_restart;
1846 restart->futex.uaddr = (u32 *)uaddr;
1847 restart->futex.val = val;
1848 restart->futex.time = abs_time->tv64;
1849 restart->futex.bitset = bitset;
1850 restart->futex.flags = FLAGS_HAS_TIMEOUT;
1853 restart->futex.flags |= FLAGS_SHARED;
1855 restart->futex.flags |= FLAGS_CLOCKRT;
1857 ret = -ERESTART_RESTARTBLOCK;
1860 put_futex_key(fshared, &q.key);
1863 hrtimer_cancel(&to->timer);
1864 destroy_hrtimer_on_stack(&to->timer);
1870 static long futex_wait_restart(struct restart_block *restart)
1872 u32 __user *uaddr = (u32 __user *)restart->futex.uaddr;
1874 ktime_t t, *tp = NULL;
1876 if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
1877 t.tv64 = restart->futex.time;
1880 restart->fn = do_no_restart_syscall;
1881 if (restart->futex.flags & FLAGS_SHARED)
1883 return (long)futex_wait(uaddr, fshared, restart->futex.val, tp,
1884 restart->futex.bitset,
1885 restart->futex.flags & FLAGS_CLOCKRT);
1890 * Userspace tried a 0 -> TID atomic transition of the futex value
1891 * and failed. The kernel side here does the whole locking operation:
1892 * if there are waiters then it will block, it does PI, etc. (Due to
1893 * races the kernel might see a 0 value of the futex too.)
1895 static int futex_lock_pi(u32 __user *uaddr, int fshared,
1896 int detect, ktime_t *time, int trylock)
1898 struct hrtimer_sleeper timeout, *to = NULL;
1899 struct futex_hash_bucket *hb;
1903 if (refill_pi_state_cache())
1908 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
1910 hrtimer_init_sleeper(to, current);
1911 hrtimer_set_expires(&to->timer, *time);
1916 q.requeue_pi_key = NULL;
1918 q.key = FUTEX_KEY_INIT;
1919 ret = get_futex_key(uaddr, fshared, &q.key);
1920 if (unlikely(ret != 0))
1924 hb = queue_lock(&q);
1926 ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
1927 if (unlikely(ret)) {
1930 /* We got the lock. */
1932 goto out_unlock_put_key;
1937 * Task is exiting and we just wait for the
1940 queue_unlock(&q, hb);
1941 put_futex_key(fshared, &q.key);
1945 goto out_unlock_put_key;
1950 * Only actually queue now that the atomic ops are done:
1954 WARN_ON(!q.pi_state);
1956 * Block on the PI mutex:
1959 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
1961 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
1962 /* Fixup the trylock return value: */
1963 ret = ret ? 0 : -EWOULDBLOCK;
1966 spin_lock(q.lock_ptr);
1968 * Fixup the pi_state owner and possibly acquire the lock if we
1971 res = fixup_owner(uaddr, fshared, &q, !ret);
1973 * If fixup_owner() returned an error, proprogate that. If it acquired
1974 * the lock, clear our -ETIMEDOUT or -EINTR.
1977 ret = (res < 0) ? res : 0;
1980 * If fixup_owner() faulted and was unable to handle the fault, unlock
1981 * it and return the fault to userspace.
1983 if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
1984 rt_mutex_unlock(&q.pi_state->pi_mutex);
1986 /* Unqueue and drop the lock */
1992 queue_unlock(&q, hb);
1995 put_futex_key(fshared, &q.key);
1998 destroy_hrtimer_on_stack(&to->timer);
1999 return ret != -EINTR ? ret : -ERESTARTNOINTR;
2002 queue_unlock(&q, hb);
2004 ret = fault_in_user_writeable(uaddr);
2011 put_futex_key(fshared, &q.key);
2016 * Userspace attempted a TID -> 0 atomic transition, and failed.
2017 * This is the in-kernel slowpath: we look up the PI state (if any),
2018 * and do the rt-mutex unlock.
2020 static int futex_unlock_pi(u32 __user *uaddr, int fshared)
2022 struct futex_hash_bucket *hb;
2023 struct futex_q *this, *next;
2025 struct plist_head *head;
2026 union futex_key key = FUTEX_KEY_INIT;
2030 if (get_user(uval, uaddr))
2033 * We release only a lock we actually own:
2035 if ((uval & FUTEX_TID_MASK) != task_pid_vnr(current))
2038 ret = get_futex_key(uaddr, fshared, &key);
2039 if (unlikely(ret != 0))
2042 hb = hash_futex(&key);
2043 spin_lock(&hb->lock);
2046 * To avoid races, try to do the TID -> 0 atomic transition
2047 * again. If it succeeds then we can return without waking
2050 if (!(uval & FUTEX_OWNER_DIED))
2051 uval = cmpxchg_futex_value_locked(uaddr, task_pid_vnr(current), 0);
2054 if (unlikely(uval == -EFAULT))
2057 * Rare case: we managed to release the lock atomically,
2058 * no need to wake anyone else up:
2060 if (unlikely(uval == task_pid_vnr(current)))
2064 * Ok, other tasks may need to be woken up - check waiters
2065 * and do the wakeup if necessary:
2069 plist_for_each_entry_safe(this, next, head, list) {
2070 if (!match_futex (&this->key, &key))
2072 ret = wake_futex_pi(uaddr, uval, this);
2074 * The atomic access to the futex value
2075 * generated a pagefault, so retry the
2076 * user-access and the wakeup:
2083 * No waiters - kernel unlocks the futex:
2085 if (!(uval & FUTEX_OWNER_DIED)) {
2086 ret = unlock_futex_pi(uaddr, uval);
2092 spin_unlock(&hb->lock);
2093 put_futex_key(fshared, &key);
2099 spin_unlock(&hb->lock);
2100 put_futex_key(fshared, &key);
2102 ret = fault_in_user_writeable(uaddr);
2110 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2111 * @hb: the hash_bucket futex_q was original enqueued on
2112 * @q: the futex_q woken while waiting to be requeued
2113 * @key2: the futex_key of the requeue target futex
2114 * @timeout: the timeout associated with the wait (NULL if none)
2116 * Detect if the task was woken on the initial futex as opposed to the requeue
2117 * target futex. If so, determine if it was a timeout or a signal that caused
2118 * the wakeup and return the appropriate error code to the caller. Must be
2119 * called with the hb lock held.
2122 * 0 - no early wakeup detected
2123 * <0 - -ETIMEDOUT or -ERESTARTNOINTR
2126 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2127 struct futex_q *q, union futex_key *key2,
2128 struct hrtimer_sleeper *timeout)
2133 * With the hb lock held, we avoid races while we process the wakeup.
2134 * We only need to hold hb (and not hb2) to ensure atomicity as the
2135 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2136 * It can't be requeued from uaddr2 to something else since we don't
2137 * support a PI aware source futex for requeue.
2139 if (!match_futex(&q->key, key2)) {
2140 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2142 * We were woken prior to requeue by a timeout or a signal.
2143 * Unqueue the futex_q and determine which it was.
2145 plist_del(&q->list, &q->list.plist);
2147 /* Handle spurious wakeups gracefully */
2149 if (timeout && !timeout->task)
2151 else if (signal_pending(current))
2152 ret = -ERESTARTNOINTR;
2158 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2159 * @uaddr: the futex we initially wait on (non-pi)
2160 * @fshared: whether the futexes are shared (1) or not (0). They must be
2161 * the same type, no requeueing from private to shared, etc.
2162 * @val: the expected value of uaddr
2163 * @abs_time: absolute timeout
2164 * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
2165 * @clockrt: whether to use CLOCK_REALTIME (1) or CLOCK_MONOTONIC (0)
2166 * @uaddr2: the pi futex we will take prior to returning to user-space
2168 * The caller will wait on uaddr and will be requeued by futex_requeue() to
2169 * uaddr2 which must be PI aware. Normal wakeup will wake on uaddr2 and
2170 * complete the acquisition of the rt_mutex prior to returning to userspace.
2171 * This ensures the rt_mutex maintains an owner when it has waiters; without
2172 * one, the pi logic wouldn't know which task to boost/deboost, if there was a
2175 * We call schedule in futex_wait_queue_me() when we enqueue and return there
2176 * via the following:
2177 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2178 * 2) wakeup on uaddr2 after a requeue
2182 * If 3, cleanup and return -ERESTARTNOINTR.
2184 * If 2, we may then block on trying to take the rt_mutex and return via:
2185 * 5) successful lock
2188 * 8) other lock acquisition failure
2190 * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2192 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2198 static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
2199 u32 val, ktime_t *abs_time, u32 bitset,
2200 int clockrt, u32 __user *uaddr2)
2202 struct hrtimer_sleeper timeout, *to = NULL;
2203 struct rt_mutex_waiter rt_waiter;
2204 struct rt_mutex *pi_mutex = NULL;
2205 struct futex_hash_bucket *hb;
2206 union futex_key key2;
2215 hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
2216 CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
2217 hrtimer_init_sleeper(to, current);
2218 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2219 current->timer_slack_ns);
2223 * The waiter is allocated on our stack, manipulated by the requeue
2224 * code while we sleep on uaddr.
2226 debug_rt_mutex_init_waiter(&rt_waiter);
2227 rt_waiter.task = NULL;
2229 key2 = FUTEX_KEY_INIT;
2230 ret = get_futex_key(uaddr2, fshared, &key2);
2231 if (unlikely(ret != 0))
2236 q.rt_waiter = &rt_waiter;
2237 q.requeue_pi_key = &key2;
2239 /* Prepare to wait on uaddr. */
2240 ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
2244 /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2245 futex_wait_queue_me(hb, &q, to);
2247 spin_lock(&hb->lock);
2248 ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2249 spin_unlock(&hb->lock);
2254 * In order for us to be here, we know our q.key == key2, and since
2255 * we took the hb->lock above, we also know that futex_requeue() has
2256 * completed and we no longer have to concern ourselves with a wakeup
2257 * race with the atomic proxy lock acquition by the requeue code.
2260 /* Check if the requeue code acquired the second futex for us. */
2263 * Got the lock. We might not be the anticipated owner if we
2264 * did a lock-steal - fix up the PI-state in that case.
2266 if (q.pi_state && (q.pi_state->owner != current)) {
2267 spin_lock(q.lock_ptr);
2268 ret = fixup_pi_state_owner(uaddr2, &q, current,
2270 spin_unlock(q.lock_ptr);
2274 * We have been woken up by futex_unlock_pi(), a timeout, or a
2275 * signal. futex_unlock_pi() will not destroy the lock_ptr nor
2278 WARN_ON(!&q.pi_state);
2279 pi_mutex = &q.pi_state->pi_mutex;
2280 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
2281 debug_rt_mutex_free_waiter(&rt_waiter);
2283 spin_lock(q.lock_ptr);
2285 * Fixup the pi_state owner and possibly acquire the lock if we
2288 res = fixup_owner(uaddr2, fshared, &q, !ret);
2290 * If fixup_owner() returned an error, proprogate that. If it
2291 * acquired the lock, clear -ETIMEDOUT or -EINTR.
2294 ret = (res < 0) ? res : 0;
2296 /* Unqueue and drop the lock. */
2301 * If fixup_pi_state_owner() faulted and was unable to handle the
2302 * fault, unlock the rt_mutex and return the fault to userspace.
2304 if (ret == -EFAULT) {
2305 if (rt_mutex_owner(pi_mutex) == current)
2306 rt_mutex_unlock(pi_mutex);
2307 } else if (ret == -EINTR) {
2309 * We've already been requeued, but cannot restart by calling
2310 * futex_lock_pi() directly. We could restart this syscall, but
2311 * it would detect that the user space "val" changed and return
2312 * -EWOULDBLOCK. Save the overhead of the restart and return
2313 * -EWOULDBLOCK directly.
2319 put_futex_key(fshared, &q.key);
2321 put_futex_key(fshared, &key2);
2325 hrtimer_cancel(&to->timer);
2326 destroy_hrtimer_on_stack(&to->timer);
2332 * Support for robust futexes: the kernel cleans up held futexes at
2335 * Implementation: user-space maintains a per-thread list of locks it
2336 * is holding. Upon do_exit(), the kernel carefully walks this list,
2337 * and marks all locks that are owned by this thread with the
2338 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2339 * always manipulated with the lock held, so the list is private and
2340 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2341 * field, to allow the kernel to clean up if the thread dies after
2342 * acquiring the lock, but just before it could have added itself to
2343 * the list. There can only be one such pending lock.
2347 * sys_set_robust_list() - Set the robust-futex list head of a task
2348 * @head: pointer to the list-head
2349 * @len: length of the list-head, as userspace expects
2351 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2354 if (!futex_cmpxchg_enabled)
2357 * The kernel knows only one size for now:
2359 if (unlikely(len != sizeof(*head)))
2362 current->robust_list = head;
2368 * sys_get_robust_list() - Get the robust-futex list head of a task
2369 * @pid: pid of the process [zero for current task]
2370 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
2371 * @len_ptr: pointer to a length field, the kernel fills in the header size
2373 SYSCALL_DEFINE3(get_robust_list, int, pid,
2374 struct robust_list_head __user * __user *, head_ptr,
2375 size_t __user *, len_ptr)
2377 struct robust_list_head __user *head;
2379 const struct cred *cred = current_cred(), *pcred;
2381 if (!futex_cmpxchg_enabled)
2385 head = current->robust_list;
2387 struct task_struct *p;
2391 p = find_task_by_vpid(pid);
2395 pcred = __task_cred(p);
2396 if (cred->euid != pcred->euid &&
2397 cred->euid != pcred->uid &&
2398 !capable(CAP_SYS_PTRACE))
2400 head = p->robust_list;
2404 if (put_user(sizeof(*head), len_ptr))
2406 return put_user(head, head_ptr);
2415 * Process a futex-list entry, check whether it's owned by the
2416 * dying task, and do notification if so:
2418 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
2420 u32 uval, nval, mval;
2423 if (get_user(uval, uaddr))
2426 if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
2428 * Ok, this dying thread is truly holding a futex
2429 * of interest. Set the OWNER_DIED bit atomically
2430 * via cmpxchg, and if the value had FUTEX_WAITERS
2431 * set, wake up a waiter (if any). (We have to do a
2432 * futex_wake() even if OWNER_DIED is already set -
2433 * to handle the rare but possible case of recursive
2434 * thread-death.) The rest of the cleanup is done in
2437 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
2438 nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
2440 if (nval == -EFAULT)
2447 * Wake robust non-PI futexes here. The wakeup of
2448 * PI futexes happens in exit_pi_state():
2450 if (!pi && (uval & FUTEX_WAITERS))
2451 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
2457 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
2459 static inline int fetch_robust_entry(struct robust_list __user **entry,
2460 struct robust_list __user * __user *head,
2463 unsigned long uentry;
2465 if (get_user(uentry, (unsigned long __user *)head))
2468 *entry = (void __user *)(uentry & ~1UL);
2475 * Walk curr->robust_list (very carefully, it's a userspace list!)
2476 * and mark any locks found there dead, and notify any waiters.
2478 * We silently return on any sign of list-walking problem.
2480 void exit_robust_list(struct task_struct *curr)
2482 struct robust_list_head __user *head = curr->robust_list;
2483 struct robust_list __user *entry, *next_entry, *pending;
2484 unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
2485 unsigned long futex_offset;
2488 if (!futex_cmpxchg_enabled)
2492 * Fetch the list head (which was registered earlier, via
2493 * sys_set_robust_list()):
2495 if (fetch_robust_entry(&entry, &head->list.next, &pi))
2498 * Fetch the relative futex offset:
2500 if (get_user(futex_offset, &head->futex_offset))
2503 * Fetch any possibly pending lock-add first, and handle it
2506 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
2509 next_entry = NULL; /* avoid warning with gcc */
2510 while (entry != &head->list) {
2512 * Fetch the next entry in the list before calling
2513 * handle_futex_death:
2515 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
2517 * A pending lock might already be on the list, so
2518 * don't process it twice:
2520 if (entry != pending)
2521 if (handle_futex_death((void __user *)entry + futex_offset,
2529 * Avoid excessively long or circular lists:
2538 handle_futex_death((void __user *)pending + futex_offset,
2542 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
2543 u32 __user *uaddr2, u32 val2, u32 val3)
2545 int clockrt, ret = -ENOSYS;
2546 int cmd = op & FUTEX_CMD_MASK;
2549 if (!(op & FUTEX_PRIVATE_FLAG))
2552 clockrt = op & FUTEX_CLOCK_REALTIME;
2553 if (clockrt && cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
2558 val3 = FUTEX_BITSET_MATCH_ANY;
2559 case FUTEX_WAIT_BITSET:
2560 ret = futex_wait(uaddr, fshared, val, timeout, val3, clockrt);
2563 val3 = FUTEX_BITSET_MATCH_ANY;
2564 case FUTEX_WAKE_BITSET:
2565 ret = futex_wake(uaddr, fshared, val, val3);
2568 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL, 0);
2570 case FUTEX_CMP_REQUEUE:
2571 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
2575 ret = futex_wake_op(uaddr, fshared, uaddr2, val, val2, val3);
2578 if (futex_cmpxchg_enabled)
2579 ret = futex_lock_pi(uaddr, fshared, val, timeout, 0);
2581 case FUTEX_UNLOCK_PI:
2582 if (futex_cmpxchg_enabled)
2583 ret = futex_unlock_pi(uaddr, fshared);
2585 case FUTEX_TRYLOCK_PI:
2586 if (futex_cmpxchg_enabled)
2587 ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1);
2589 case FUTEX_WAIT_REQUEUE_PI:
2590 val3 = FUTEX_BITSET_MATCH_ANY;
2591 ret = futex_wait_requeue_pi(uaddr, fshared, val, timeout, val3,
2594 case FUTEX_CMP_REQUEUE_PI:
2595 ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
2605 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
2606 struct timespec __user *, utime, u32 __user *, uaddr2,
2610 ktime_t t, *tp = NULL;
2612 int cmd = op & FUTEX_CMD_MASK;
2614 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
2615 cmd == FUTEX_WAIT_BITSET ||
2616 cmd == FUTEX_WAIT_REQUEUE_PI)) {
2617 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
2619 if (!timespec_valid(&ts))
2622 t = timespec_to_ktime(ts);
2623 if (cmd == FUTEX_WAIT)
2624 t = ktime_add_safe(ktime_get(), t);
2628 * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
2629 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
2631 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
2632 cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
2633 val2 = (u32) (unsigned long) utime;
2635 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
2638 static int __init futex_init(void)
2644 * This will fail and we want it. Some arch implementations do
2645 * runtime detection of the futex_atomic_cmpxchg_inatomic()
2646 * functionality. We want to know that before we call in any
2647 * of the complex code paths. Also we want to prevent
2648 * registration of robust lists in that case. NULL is
2649 * guaranteed to fault and we get -EFAULT on functional
2650 * implementation, the non functional ones will return
2653 curval = cmpxchg_futex_value_locked(NULL, 0, 0);
2654 if (curval == -EFAULT)
2655 futex_cmpxchg_enabled = 1;
2657 for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
2658 plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock);
2659 spin_lock_init(&futex_queues[i].lock);
2664 __initcall(futex_init);