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/export.h>
59 #include <linux/magic.h>
60 #include <linux/pid.h>
61 #include <linux/nsproxy.h>
62 #include <linux/ptrace.h>
63 #include <linux/sched/rt.h>
64 #include <linux/hugetlb.h>
65 #include <linux/freezer.h>
66 #include <linux/bootmem.h>
68 #include <asm/futex.h>
70 #include "locking/rtmutex_common.h"
73 * Basic futex operation and ordering guarantees:
75 * The waiter reads the futex value in user space and calls
76 * futex_wait(). This function computes the hash bucket and acquires
77 * the hash bucket lock. After that it reads the futex user space value
78 * again and verifies that the data has not changed. If it has not changed
79 * it enqueues itself into the hash bucket, releases the hash bucket lock
82 * The waker side modifies the user space value of the futex and calls
83 * futex_wake(). This function computes the hash bucket and acquires the
84 * hash bucket lock. Then it looks for waiters on that futex in the hash
85 * bucket and wakes them.
87 * In futex wake up scenarios where no tasks are blocked on a futex, taking
88 * the hb spinlock can be avoided and simply return. In order for this
89 * optimization to work, ordering guarantees must exist so that the waiter
90 * being added to the list is acknowledged when the list is concurrently being
91 * checked by the waker, avoiding scenarios like the following:
95 * sys_futex(WAIT, futex, val);
96 * futex_wait(futex, val);
99 * sys_futex(WAKE, futex);
104 * lock(hash_bucket(futex));
106 * unlock(hash_bucket(futex));
109 * This would cause the waiter on CPU 0 to wait forever because it
110 * missed the transition of the user space value from val to newval
111 * and the waker did not find the waiter in the hash bucket queue.
113 * The correct serialization ensures that a waiter either observes
114 * the changed user space value before blocking or is woken by a
119 * sys_futex(WAIT, futex, val);
120 * futex_wait(futex, val);
123 * mb(); (A) <-- paired with -.
125 * lock(hash_bucket(futex)); |
129 * | sys_futex(WAKE, futex);
130 * | futex_wake(futex);
132 * `-------> mb(); (B)
135 * unlock(hash_bucket(futex));
136 * schedule(); if (waiters)
137 * lock(hash_bucket(futex));
138 * wake_waiters(futex);
139 * unlock(hash_bucket(futex));
141 * Where (A) orders the waiters increment and the futex value read -- this
142 * is guaranteed by the head counter in the hb spinlock; and where (B)
143 * orders the write to futex and the waiters read -- this is done by the
144 * barriers in get_futex_key_refs(), through either ihold or atomic_inc,
145 * depending on the futex type.
147 * This yields the following case (where X:=waiters, Y:=futex):
155 * Which guarantees that x==0 && y==0 is impossible; which translates back into
156 * the guarantee that we cannot both miss the futex variable change and the
160 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
161 int __read_mostly futex_cmpxchg_enabled;
165 * Futex flags used to encode options to functions and preserve them across
168 #define FLAGS_SHARED 0x01
169 #define FLAGS_CLOCKRT 0x02
170 #define FLAGS_HAS_TIMEOUT 0x04
173 * Priority Inheritance state:
175 struct futex_pi_state {
177 * list of 'owned' pi_state instances - these have to be
178 * cleaned up in do_exit() if the task exits prematurely:
180 struct list_head list;
185 struct rt_mutex pi_mutex;
187 struct task_struct *owner;
194 * struct futex_q - The hashed futex queue entry, one per waiting task
195 * @list: priority-sorted list of tasks waiting on this futex
196 * @task: the task waiting on the futex
197 * @lock_ptr: the hash bucket lock
198 * @key: the key the futex is hashed on
199 * @pi_state: optional priority inheritance state
200 * @rt_waiter: rt_waiter storage for use with requeue_pi
201 * @requeue_pi_key: the requeue_pi target futex key
202 * @bitset: bitset for the optional bitmasked wakeup
204 * We use this hashed waitqueue, instead of a normal wait_queue_t, so
205 * we can wake only the relevant ones (hashed queues may be shared).
207 * A futex_q has a woken state, just like tasks have TASK_RUNNING.
208 * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
209 * The order of wakeup is always to make the first condition true, then
212 * PI futexes are typically woken before they are removed from the hash list via
213 * the rt_mutex code. See unqueue_me_pi().
216 struct plist_node list;
218 struct task_struct *task;
219 spinlock_t *lock_ptr;
221 struct futex_pi_state *pi_state;
222 struct rt_mutex_waiter *rt_waiter;
223 union futex_key *requeue_pi_key;
227 static const struct futex_q futex_q_init = {
228 /* list gets initialized in queue_me()*/
229 .key = FUTEX_KEY_INIT,
230 .bitset = FUTEX_BITSET_MATCH_ANY
234 * Hash buckets are shared by all the futex_keys that hash to the same
235 * location. Each key may have multiple futex_q structures, one for each task
236 * waiting on a futex.
238 struct futex_hash_bucket {
241 struct plist_head chain;
242 } ____cacheline_aligned_in_smp;
244 static unsigned long __read_mostly futex_hashsize;
246 static struct futex_hash_bucket *futex_queues;
248 static inline void futex_get_mm(union futex_key *key)
250 atomic_inc(&key->private.mm->mm_count);
252 * Ensure futex_get_mm() implies a full barrier such that
253 * get_futex_key() implies a full barrier. This is relied upon
254 * as full barrier (B), see the ordering comment above.
256 smp_mb__after_atomic_inc();
260 * Reflects a new waiter being added to the waitqueue.
262 static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
265 atomic_inc(&hb->waiters);
267 * Full barrier (A), see the ordering comment above.
269 smp_mb__after_atomic_inc();
274 * Reflects a waiter being removed from the waitqueue by wakeup
277 static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
280 atomic_dec(&hb->waiters);
284 static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
287 return atomic_read(&hb->waiters);
294 * We hash on the keys returned from get_futex_key (see below).
296 static struct futex_hash_bucket *hash_futex(union futex_key *key)
298 u32 hash = jhash2((u32*)&key->both.word,
299 (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
301 return &futex_queues[hash & (futex_hashsize - 1)];
305 * Return 1 if two futex_keys are equal, 0 otherwise.
307 static inline int match_futex(union futex_key *key1, union futex_key *key2)
310 && key1->both.word == key2->both.word
311 && key1->both.ptr == key2->both.ptr
312 && key1->both.offset == key2->both.offset);
316 * Take a reference to the resource addressed by a key.
317 * Can be called while holding spinlocks.
320 static void get_futex_key_refs(union futex_key *key)
325 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
327 ihold(key->shared.inode); /* implies MB (B) */
329 case FUT_OFF_MMSHARED:
330 futex_get_mm(key); /* implies MB (B) */
336 * Drop a reference to the resource addressed by a key.
337 * The hash bucket spinlock must not be held.
339 static void drop_futex_key_refs(union futex_key *key)
341 if (!key->both.ptr) {
342 /* If we're here then we tried to put a key we failed to get */
347 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
349 iput(key->shared.inode);
351 case FUT_OFF_MMSHARED:
352 mmdrop(key->private.mm);
358 * get_futex_key() - Get parameters which are the keys for a futex
359 * @uaddr: virtual address of the futex
360 * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
361 * @key: address where result is stored.
362 * @rw: mapping needs to be read/write (values: VERIFY_READ,
365 * Return: a negative error code or 0
367 * The key words are stored in *key on success.
369 * For shared mappings, it's (page->index, file_inode(vma->vm_file),
370 * offset_within_page). For private mappings, it's (uaddr, current->mm).
371 * We can usually work out the index without swapping in the page.
373 * lock_page() might sleep, the caller should not hold a spinlock.
376 get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
378 unsigned long address = (unsigned long)uaddr;
379 struct mm_struct *mm = current->mm;
380 struct page *page, *page_head;
384 * The futex address must be "naturally" aligned.
386 key->both.offset = address % PAGE_SIZE;
387 if (unlikely((address % sizeof(u32)) != 0))
389 address -= key->both.offset;
391 if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
395 * PROCESS_PRIVATE futexes are fast.
396 * As the mm cannot disappear under us and the 'key' only needs
397 * virtual address, we dont even have to find the underlying vma.
398 * Note : We do have to check 'uaddr' is a valid user address,
399 * but access_ok() should be faster than find_vma()
402 key->private.mm = mm;
403 key->private.address = address;
404 get_futex_key_refs(key); /* implies MB (B) */
409 err = get_user_pages_fast(address, 1, 1, &page);
411 * If write access is not required (eg. FUTEX_WAIT), try
412 * and get read-only access.
414 if (err == -EFAULT && rw == VERIFY_READ) {
415 err = get_user_pages_fast(address, 1, 0, &page);
423 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
425 if (unlikely(PageTail(page))) {
427 /* serialize against __split_huge_page_splitting() */
429 if (likely(__get_user_pages_fast(address, 1, !ro, &page) == 1)) {
430 page_head = compound_head(page);
432 * page_head is valid pointer but we must pin
433 * it before taking the PG_lock and/or
434 * PG_compound_lock. The moment we re-enable
435 * irqs __split_huge_page_splitting() can
436 * return and the head page can be freed from
437 * under us. We can't take the PG_lock and/or
438 * PG_compound_lock on a page that could be
439 * freed from under us.
441 if (page != page_head) {
452 page_head = compound_head(page);
453 if (page != page_head) {
459 lock_page(page_head);
462 * If page_head->mapping is NULL, then it cannot be a PageAnon
463 * page; but it might be the ZERO_PAGE or in the gate area or
464 * in a special mapping (all cases which we are happy to fail);
465 * or it may have been a good file page when get_user_pages_fast
466 * found it, but truncated or holepunched or subjected to
467 * invalidate_complete_page2 before we got the page lock (also
468 * cases which we are happy to fail). And we hold a reference,
469 * so refcount care in invalidate_complete_page's remove_mapping
470 * prevents drop_caches from setting mapping to NULL beneath us.
472 * The case we do have to guard against is when memory pressure made
473 * shmem_writepage move it from filecache to swapcache beneath us:
474 * an unlikely race, but we do need to retry for page_head->mapping.
476 if (!page_head->mapping) {
477 int shmem_swizzled = PageSwapCache(page_head);
478 unlock_page(page_head);
486 * Private mappings are handled in a simple way.
488 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
489 * it's a read-only handle, it's expected that futexes attach to
490 * the object not the particular process.
492 if (PageAnon(page_head)) {
494 * A RO anonymous page will never change and thus doesn't make
495 * sense for futex operations.
502 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
503 key->private.mm = mm;
504 key->private.address = address;
506 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
507 key->shared.inode = page_head->mapping->host;
508 key->shared.pgoff = basepage_index(page);
511 get_futex_key_refs(key); /* implies MB (B) */
514 unlock_page(page_head);
519 static inline void put_futex_key(union futex_key *key)
521 drop_futex_key_refs(key);
525 * fault_in_user_writeable() - Fault in user address and verify RW access
526 * @uaddr: pointer to faulting user space address
528 * Slow path to fixup the fault we just took in the atomic write
531 * We have no generic implementation of a non-destructive write to the
532 * user address. We know that we faulted in the atomic pagefault
533 * disabled section so we can as well avoid the #PF overhead by
534 * calling get_user_pages() right away.
536 static int fault_in_user_writeable(u32 __user *uaddr)
538 struct mm_struct *mm = current->mm;
541 down_read(&mm->mmap_sem);
542 ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
544 up_read(&mm->mmap_sem);
546 return ret < 0 ? ret : 0;
550 * futex_top_waiter() - Return the highest priority waiter on a futex
551 * @hb: the hash bucket the futex_q's reside in
552 * @key: the futex key (to distinguish it from other futex futex_q's)
554 * Must be called with the hb lock held.
556 static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
557 union futex_key *key)
559 struct futex_q *this;
561 plist_for_each_entry(this, &hb->chain, list) {
562 if (match_futex(&this->key, key))
568 static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
569 u32 uval, u32 newval)
574 ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
580 static int get_futex_value_locked(u32 *dest, u32 __user *from)
585 ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
588 return ret ? -EFAULT : 0;
595 static int refill_pi_state_cache(void)
597 struct futex_pi_state *pi_state;
599 if (likely(current->pi_state_cache))
602 pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
607 INIT_LIST_HEAD(&pi_state->list);
608 /* pi_mutex gets initialized later */
609 pi_state->owner = NULL;
610 atomic_set(&pi_state->refcount, 1);
611 pi_state->key = FUTEX_KEY_INIT;
613 current->pi_state_cache = pi_state;
618 static struct futex_pi_state * alloc_pi_state(void)
620 struct futex_pi_state *pi_state = current->pi_state_cache;
623 current->pi_state_cache = NULL;
628 static void free_pi_state(struct futex_pi_state *pi_state)
630 if (!atomic_dec_and_test(&pi_state->refcount))
634 * If pi_state->owner is NULL, the owner is most probably dying
635 * and has cleaned up the pi_state already
637 if (pi_state->owner) {
638 raw_spin_lock_irq(&pi_state->owner->pi_lock);
639 list_del_init(&pi_state->list);
640 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
642 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
645 if (current->pi_state_cache)
649 * pi_state->list is already empty.
650 * clear pi_state->owner.
651 * refcount is at 0 - put it back to 1.
653 pi_state->owner = NULL;
654 atomic_set(&pi_state->refcount, 1);
655 current->pi_state_cache = pi_state;
660 * Look up the task based on what TID userspace gave us.
663 static struct task_struct * futex_find_get_task(pid_t pid)
665 struct task_struct *p;
668 p = find_task_by_vpid(pid);
678 * This task is holding PI mutexes at exit time => bad.
679 * Kernel cleans up PI-state, but userspace is likely hosed.
680 * (Robust-futex cleanup is separate and might save the day for userspace.)
682 void exit_pi_state_list(struct task_struct *curr)
684 struct list_head *next, *head = &curr->pi_state_list;
685 struct futex_pi_state *pi_state;
686 struct futex_hash_bucket *hb;
687 union futex_key key = FUTEX_KEY_INIT;
689 if (!futex_cmpxchg_enabled)
692 * We are a ZOMBIE and nobody can enqueue itself on
693 * pi_state_list anymore, but we have to be careful
694 * versus waiters unqueueing themselves:
696 raw_spin_lock_irq(&curr->pi_lock);
697 while (!list_empty(head)) {
700 pi_state = list_entry(next, struct futex_pi_state, list);
702 hb = hash_futex(&key);
703 raw_spin_unlock_irq(&curr->pi_lock);
705 spin_lock(&hb->lock);
707 raw_spin_lock_irq(&curr->pi_lock);
709 * We dropped the pi-lock, so re-check whether this
710 * task still owns the PI-state:
712 if (head->next != next) {
713 spin_unlock(&hb->lock);
717 WARN_ON(pi_state->owner != curr);
718 WARN_ON(list_empty(&pi_state->list));
719 list_del_init(&pi_state->list);
720 pi_state->owner = NULL;
721 raw_spin_unlock_irq(&curr->pi_lock);
723 rt_mutex_unlock(&pi_state->pi_mutex);
725 spin_unlock(&hb->lock);
727 raw_spin_lock_irq(&curr->pi_lock);
729 raw_spin_unlock_irq(&curr->pi_lock);
733 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
734 union futex_key *key, struct futex_pi_state **ps)
736 struct futex_pi_state *pi_state = NULL;
737 struct futex_q *this, *next;
738 struct task_struct *p;
739 pid_t pid = uval & FUTEX_TID_MASK;
741 plist_for_each_entry_safe(this, next, &hb->chain, list) {
742 if (match_futex(&this->key, key)) {
744 * Another waiter already exists - bump up
745 * the refcount and return its pi_state:
747 pi_state = this->pi_state;
749 * Userspace might have messed up non-PI and PI futexes
751 if (unlikely(!pi_state))
754 WARN_ON(!atomic_read(&pi_state->refcount));
757 * When pi_state->owner is NULL then the owner died
758 * and another waiter is on the fly. pi_state->owner
759 * is fixed up by the task which acquires
760 * pi_state->rt_mutex.
762 * We do not check for pid == 0 which can happen when
763 * the owner died and robust_list_exit() cleared the
766 if (pid && pi_state->owner) {
768 * Bail out if user space manipulated the
771 if (pid != task_pid_vnr(pi_state->owner))
775 atomic_inc(&pi_state->refcount);
783 * We are the first waiter - try to look up the real owner and attach
784 * the new pi_state to it, but bail out when TID = 0
788 p = futex_find_get_task(pid);
793 * We need to look at the task state flags to figure out,
794 * whether the task is exiting. To protect against the do_exit
795 * change of the task flags, we do this protected by
798 raw_spin_lock_irq(&p->pi_lock);
799 if (unlikely(p->flags & PF_EXITING)) {
801 * The task is on the way out. When PF_EXITPIDONE is
802 * set, we know that the task has finished the
805 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
807 raw_spin_unlock_irq(&p->pi_lock);
812 pi_state = alloc_pi_state();
815 * Initialize the pi_mutex in locked state and make 'p'
818 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
820 /* Store the key for possible exit cleanups: */
821 pi_state->key = *key;
823 WARN_ON(!list_empty(&pi_state->list));
824 list_add(&pi_state->list, &p->pi_state_list);
826 raw_spin_unlock_irq(&p->pi_lock);
836 * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
837 * @uaddr: the pi futex user address
838 * @hb: the pi futex hash bucket
839 * @key: the futex key associated with uaddr and hb
840 * @ps: the pi_state pointer where we store the result of the
842 * @task: the task to perform the atomic lock work for. This will
843 * be "current" except in the case of requeue pi.
844 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
848 * 1 - acquired the lock;
851 * The hb->lock and futex_key refs shall be held by the caller.
853 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
854 union futex_key *key,
855 struct futex_pi_state **ps,
856 struct task_struct *task, int set_waiters)
858 int lock_taken, ret, force_take = 0;
859 u32 uval, newval, curval, vpid = task_pid_vnr(task);
862 ret = lock_taken = 0;
865 * To avoid races, we attempt to take the lock here again
866 * (by doing a 0 -> TID atomic cmpxchg), while holding all
867 * the locks. It will most likely not succeed.
871 newval |= FUTEX_WAITERS;
873 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval)))
879 if ((unlikely((curval & FUTEX_TID_MASK) == vpid)))
883 * Surprise - we got the lock. Just return to userspace:
885 if (unlikely(!curval))
891 * Set the FUTEX_WAITERS flag, so the owner will know it has someone
892 * to wake at the next unlock.
894 newval = curval | FUTEX_WAITERS;
897 * Should we force take the futex? See below.
899 if (unlikely(force_take)) {
901 * Keep the OWNER_DIED and the WAITERS bit and set the
904 newval = (curval & ~FUTEX_TID_MASK) | vpid;
909 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
911 if (unlikely(curval != uval))
915 * We took the lock due to forced take over.
917 if (unlikely(lock_taken))
921 * We dont have the lock. Look up the PI state (or create it if
922 * we are the first waiter):
924 ret = lookup_pi_state(uval, hb, key, ps);
930 * We failed to find an owner for this
931 * futex. So we have no pi_state to block
932 * on. This can happen in two cases:
935 * 2) A stale FUTEX_WAITERS bit
937 * Re-read the futex value.
939 if (get_futex_value_locked(&curval, uaddr))
943 * If the owner died or we have a stale
944 * WAITERS bit the owner TID in the user space
947 if (!(curval & FUTEX_TID_MASK)) {
960 * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
961 * @q: The futex_q to unqueue
963 * The q->lock_ptr must not be NULL and must be held by the caller.
965 static void __unqueue_futex(struct futex_q *q)
967 struct futex_hash_bucket *hb;
969 if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
970 || WARN_ON(plist_node_empty(&q->list)))
973 hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
974 plist_del(&q->list, &hb->chain);
979 * The hash bucket lock must be held when this is called.
980 * Afterwards, the futex_q must not be accessed.
982 static void wake_futex(struct futex_q *q)
984 struct task_struct *p = q->task;
986 if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
990 * We set q->lock_ptr = NULL _before_ we wake up the task. If
991 * a non-futex wake up happens on another CPU then the task
992 * might exit and p would dereference a non-existing task
993 * struct. Prevent this by holding a reference on p across the
1000 * The waiting task can free the futex_q as soon as
1001 * q->lock_ptr = NULL is written, without taking any locks. A
1002 * memory barrier is required here to prevent the following
1003 * store to lock_ptr from getting ahead of the plist_del.
1008 wake_up_state(p, TASK_NORMAL);
1012 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
1014 struct task_struct *new_owner;
1015 struct futex_pi_state *pi_state = this->pi_state;
1016 u32 uninitialized_var(curval), newval;
1022 * If current does not own the pi_state then the futex is
1023 * inconsistent and user space fiddled with the futex value.
1025 if (pi_state->owner != current)
1028 raw_spin_lock(&pi_state->pi_mutex.wait_lock);
1029 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
1032 * It is possible that the next waiter (the one that brought
1033 * this owner to the kernel) timed out and is no longer
1034 * waiting on the lock.
1037 new_owner = this->task;
1040 * We pass it to the next owner. (The WAITERS bit is always
1041 * kept enabled while there is PI state around. We must also
1042 * preserve the owner died bit.)
1044 if (!(uval & FUTEX_OWNER_DIED)) {
1047 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
1049 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
1051 else if (curval != uval)
1054 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
1059 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1060 WARN_ON(list_empty(&pi_state->list));
1061 list_del_init(&pi_state->list);
1062 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1064 raw_spin_lock_irq(&new_owner->pi_lock);
1065 WARN_ON(!list_empty(&pi_state->list));
1066 list_add(&pi_state->list, &new_owner->pi_state_list);
1067 pi_state->owner = new_owner;
1068 raw_spin_unlock_irq(&new_owner->pi_lock);
1070 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
1071 rt_mutex_unlock(&pi_state->pi_mutex);
1076 static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
1078 u32 uninitialized_var(oldval);
1081 * There is no waiter, so we unlock the futex. The owner died
1082 * bit has not to be preserved here. We are the owner:
1084 if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0))
1093 * Express the locking dependencies for lockdep:
1096 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1099 spin_lock(&hb1->lock);
1101 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
1102 } else { /* hb1 > hb2 */
1103 spin_lock(&hb2->lock);
1104 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
1109 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1111 spin_unlock(&hb1->lock);
1113 spin_unlock(&hb2->lock);
1117 * Wake up waiters matching bitset queued on this futex (uaddr).
1120 futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
1122 struct futex_hash_bucket *hb;
1123 struct futex_q *this, *next;
1124 union futex_key key = FUTEX_KEY_INIT;
1130 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
1131 if (unlikely(ret != 0))
1134 hb = hash_futex(&key);
1136 /* Make sure we really have tasks to wakeup */
1137 if (!hb_waiters_pending(hb))
1140 spin_lock(&hb->lock);
1142 plist_for_each_entry_safe(this, next, &hb->chain, list) {
1143 if (match_futex (&this->key, &key)) {
1144 if (this->pi_state || this->rt_waiter) {
1149 /* Check if one of the bits is set in both bitsets */
1150 if (!(this->bitset & bitset))
1154 if (++ret >= nr_wake)
1159 spin_unlock(&hb->lock);
1161 put_futex_key(&key);
1167 * Wake up all waiters hashed on the physical page that is mapped
1168 * to this virtual address:
1171 futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
1172 int nr_wake, int nr_wake2, int op)
1174 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1175 struct futex_hash_bucket *hb1, *hb2;
1176 struct futex_q *this, *next;
1180 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1181 if (unlikely(ret != 0))
1183 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
1184 if (unlikely(ret != 0))
1187 hb1 = hash_futex(&key1);
1188 hb2 = hash_futex(&key2);
1191 double_lock_hb(hb1, hb2);
1192 op_ret = futex_atomic_op_inuser(op, uaddr2);
1193 if (unlikely(op_ret < 0)) {
1195 double_unlock_hb(hb1, hb2);
1199 * we don't get EFAULT from MMU faults if we don't have an MMU,
1200 * but we might get them from range checking
1206 if (unlikely(op_ret != -EFAULT)) {
1211 ret = fault_in_user_writeable(uaddr2);
1215 if (!(flags & FLAGS_SHARED))
1218 put_futex_key(&key2);
1219 put_futex_key(&key1);
1223 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1224 if (match_futex (&this->key, &key1)) {
1225 if (this->pi_state || this->rt_waiter) {
1230 if (++ret >= nr_wake)
1237 plist_for_each_entry_safe(this, next, &hb2->chain, list) {
1238 if (match_futex (&this->key, &key2)) {
1239 if (this->pi_state || this->rt_waiter) {
1244 if (++op_ret >= nr_wake2)
1252 double_unlock_hb(hb1, hb2);
1254 put_futex_key(&key2);
1256 put_futex_key(&key1);
1262 * requeue_futex() - Requeue a futex_q from one hb to another
1263 * @q: the futex_q to requeue
1264 * @hb1: the source hash_bucket
1265 * @hb2: the target hash_bucket
1266 * @key2: the new key for the requeued futex_q
1269 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1270 struct futex_hash_bucket *hb2, union futex_key *key2)
1274 * If key1 and key2 hash to the same bucket, no need to
1277 if (likely(&hb1->chain != &hb2->chain)) {
1278 plist_del(&q->list, &hb1->chain);
1279 hb_waiters_dec(hb1);
1280 plist_add(&q->list, &hb2->chain);
1281 hb_waiters_inc(hb2);
1282 q->lock_ptr = &hb2->lock;
1284 get_futex_key_refs(key2);
1289 * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1291 * @key: the key of the requeue target futex
1292 * @hb: the hash_bucket of the requeue target futex
1294 * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1295 * target futex if it is uncontended or via a lock steal. Set the futex_q key
1296 * to the requeue target futex so the waiter can detect the wakeup on the right
1297 * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1298 * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
1299 * to protect access to the pi_state to fixup the owner later. Must be called
1300 * with both q->lock_ptr and hb->lock held.
1303 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1304 struct futex_hash_bucket *hb)
1306 get_futex_key_refs(key);
1311 WARN_ON(!q->rt_waiter);
1312 q->rt_waiter = NULL;
1314 q->lock_ptr = &hb->lock;
1316 wake_up_state(q->task, TASK_NORMAL);
1320 * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1321 * @pifutex: the user address of the to futex
1322 * @hb1: the from futex hash bucket, must be locked by the caller
1323 * @hb2: the to futex hash bucket, must be locked by the caller
1324 * @key1: the from futex key
1325 * @key2: the to futex key
1326 * @ps: address to store the pi_state pointer
1327 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1329 * Try and get the lock on behalf of the top waiter if we can do it atomically.
1330 * Wake the top waiter if we succeed. If the caller specified set_waiters,
1331 * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1332 * hb1 and hb2 must be held by the caller.
1335 * 0 - failed to acquire the lock atomically;
1336 * 1 - acquired the lock;
1339 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1340 struct futex_hash_bucket *hb1,
1341 struct futex_hash_bucket *hb2,
1342 union futex_key *key1, union futex_key *key2,
1343 struct futex_pi_state **ps, int set_waiters)
1345 struct futex_q *top_waiter = NULL;
1349 if (get_futex_value_locked(&curval, pifutex))
1353 * Find the top_waiter and determine if there are additional waiters.
1354 * If the caller intends to requeue more than 1 waiter to pifutex,
1355 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1356 * as we have means to handle the possible fault. If not, don't set
1357 * the bit unecessarily as it will force the subsequent unlock to enter
1360 top_waiter = futex_top_waiter(hb1, key1);
1362 /* There are no waiters, nothing for us to do. */
1366 /* Ensure we requeue to the expected futex. */
1367 if (!match_futex(top_waiter->requeue_pi_key, key2))
1371 * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
1372 * the contended case or if set_waiters is 1. The pi_state is returned
1373 * in ps in contended cases.
1375 ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1378 requeue_pi_wake_futex(top_waiter, key2, hb2);
1384 * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1385 * @uaddr1: source futex user address
1386 * @flags: futex flags (FLAGS_SHARED, etc.)
1387 * @uaddr2: target futex user address
1388 * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
1389 * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1390 * @cmpval: @uaddr1 expected value (or %NULL)
1391 * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1392 * pi futex (pi to pi requeue is not supported)
1394 * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1395 * uaddr2 atomically on behalf of the top waiter.
1398 * >=0 - on success, the number of tasks requeued or woken;
1401 static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1402 u32 __user *uaddr2, int nr_wake, int nr_requeue,
1403 u32 *cmpval, int requeue_pi)
1405 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1406 int drop_count = 0, task_count = 0, ret;
1407 struct futex_pi_state *pi_state = NULL;
1408 struct futex_hash_bucket *hb1, *hb2;
1409 struct futex_q *this, *next;
1414 * requeue_pi requires a pi_state, try to allocate it now
1415 * without any locks in case it fails.
1417 if (refill_pi_state_cache())
1420 * requeue_pi must wake as many tasks as it can, up to nr_wake
1421 * + nr_requeue, since it acquires the rt_mutex prior to
1422 * returning to userspace, so as to not leave the rt_mutex with
1423 * waiters and no owner. However, second and third wake-ups
1424 * cannot be predicted as they involve race conditions with the
1425 * first wake and a fault while looking up the pi_state. Both
1426 * pthread_cond_signal() and pthread_cond_broadcast() should
1434 if (pi_state != NULL) {
1436 * We will have to lookup the pi_state again, so free this one
1437 * to keep the accounting correct.
1439 free_pi_state(pi_state);
1443 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1444 if (unlikely(ret != 0))
1446 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
1447 requeue_pi ? VERIFY_WRITE : VERIFY_READ);
1448 if (unlikely(ret != 0))
1451 hb1 = hash_futex(&key1);
1452 hb2 = hash_futex(&key2);
1455 hb_waiters_inc(hb2);
1456 double_lock_hb(hb1, hb2);
1458 if (likely(cmpval != NULL)) {
1461 ret = get_futex_value_locked(&curval, uaddr1);
1463 if (unlikely(ret)) {
1464 double_unlock_hb(hb1, hb2);
1465 hb_waiters_dec(hb2);
1467 ret = get_user(curval, uaddr1);
1471 if (!(flags & FLAGS_SHARED))
1474 put_futex_key(&key2);
1475 put_futex_key(&key1);
1478 if (curval != *cmpval) {
1484 if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1486 * Attempt to acquire uaddr2 and wake the top waiter. If we
1487 * intend to requeue waiters, force setting the FUTEX_WAITERS
1488 * bit. We force this here where we are able to easily handle
1489 * faults rather in the requeue loop below.
1491 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1492 &key2, &pi_state, nr_requeue);
1495 * At this point the top_waiter has either taken uaddr2 or is
1496 * waiting on it. If the former, then the pi_state will not
1497 * exist yet, look it up one more time to ensure we have a
1504 ret = get_futex_value_locked(&curval2, uaddr2);
1506 ret = lookup_pi_state(curval2, hb2, &key2,
1514 double_unlock_hb(hb1, hb2);
1515 hb_waiters_dec(hb2);
1516 put_futex_key(&key2);
1517 put_futex_key(&key1);
1518 ret = fault_in_user_writeable(uaddr2);
1523 /* The owner was exiting, try again. */
1524 double_unlock_hb(hb1, hb2);
1525 hb_waiters_dec(hb2);
1526 put_futex_key(&key2);
1527 put_futex_key(&key1);
1535 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1536 if (task_count - nr_wake >= nr_requeue)
1539 if (!match_futex(&this->key, &key1))
1543 * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1544 * be paired with each other and no other futex ops.
1546 * We should never be requeueing a futex_q with a pi_state,
1547 * which is awaiting a futex_unlock_pi().
1549 if ((requeue_pi && !this->rt_waiter) ||
1550 (!requeue_pi && this->rt_waiter) ||
1557 * Wake nr_wake waiters. For requeue_pi, if we acquired the
1558 * lock, we already woke the top_waiter. If not, it will be
1559 * woken by futex_unlock_pi().
1561 if (++task_count <= nr_wake && !requeue_pi) {
1566 /* Ensure we requeue to the expected futex for requeue_pi. */
1567 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1573 * Requeue nr_requeue waiters and possibly one more in the case
1574 * of requeue_pi if we couldn't acquire the lock atomically.
1577 /* Prepare the waiter to take the rt_mutex. */
1578 atomic_inc(&pi_state->refcount);
1579 this->pi_state = pi_state;
1580 ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1584 /* We got the lock. */
1585 requeue_pi_wake_futex(this, &key2, hb2);
1590 this->pi_state = NULL;
1591 free_pi_state(pi_state);
1595 requeue_futex(this, hb1, hb2, &key2);
1600 double_unlock_hb(hb1, hb2);
1601 hb_waiters_dec(hb2);
1604 * drop_futex_key_refs() must be called outside the spinlocks. During
1605 * the requeue we moved futex_q's from the hash bucket at key1 to the
1606 * one at key2 and updated their key pointer. We no longer need to
1607 * hold the references to key1.
1609 while (--drop_count >= 0)
1610 drop_futex_key_refs(&key1);
1613 put_futex_key(&key2);
1615 put_futex_key(&key1);
1617 if (pi_state != NULL)
1618 free_pi_state(pi_state);
1619 return ret ? ret : task_count;
1622 /* The key must be already stored in q->key. */
1623 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
1624 __acquires(&hb->lock)
1626 struct futex_hash_bucket *hb;
1628 hb = hash_futex(&q->key);
1631 * Increment the counter before taking the lock so that
1632 * a potential waker won't miss a to-be-slept task that is
1633 * waiting for the spinlock. This is safe as all queue_lock()
1634 * users end up calling queue_me(). Similarly, for housekeeping,
1635 * decrement the counter at queue_unlock() when some error has
1636 * occurred and we don't end up adding the task to the list.
1640 q->lock_ptr = &hb->lock;
1642 spin_lock(&hb->lock); /* implies MB (A) */
1647 queue_unlock(struct futex_hash_bucket *hb)
1648 __releases(&hb->lock)
1650 spin_unlock(&hb->lock);
1655 * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1656 * @q: The futex_q to enqueue
1657 * @hb: The destination hash bucket
1659 * The hb->lock must be held by the caller, and is released here. A call to
1660 * queue_me() is typically paired with exactly one call to unqueue_me(). The
1661 * exceptions involve the PI related operations, which may use unqueue_me_pi()
1662 * or nothing if the unqueue is done as part of the wake process and the unqueue
1663 * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1666 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1667 __releases(&hb->lock)
1672 * The priority used to register this element is
1673 * - either the real thread-priority for the real-time threads
1674 * (i.e. threads with a priority lower than MAX_RT_PRIO)
1675 * - or MAX_RT_PRIO for non-RT threads.
1676 * Thus, all RT-threads are woken first in priority order, and
1677 * the others are woken last, in FIFO order.
1679 prio = min(current->normal_prio, MAX_RT_PRIO);
1681 plist_node_init(&q->list, prio);
1682 plist_add(&q->list, &hb->chain);
1684 spin_unlock(&hb->lock);
1688 * unqueue_me() - Remove the futex_q from its futex_hash_bucket
1689 * @q: The futex_q to unqueue
1691 * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
1692 * be paired with exactly one earlier call to queue_me().
1695 * 1 - if the futex_q was still queued (and we removed unqueued it);
1696 * 0 - if the futex_q was already removed by the waking thread
1698 static int unqueue_me(struct futex_q *q)
1700 spinlock_t *lock_ptr;
1703 /* In the common case we don't take the spinlock, which is nice. */
1705 lock_ptr = q->lock_ptr;
1707 if (lock_ptr != NULL) {
1708 spin_lock(lock_ptr);
1710 * q->lock_ptr can change between reading it and
1711 * spin_lock(), causing us to take the wrong lock. This
1712 * corrects the race condition.
1714 * Reasoning goes like this: if we have the wrong lock,
1715 * q->lock_ptr must have changed (maybe several times)
1716 * between reading it and the spin_lock(). It can
1717 * change again after the spin_lock() but only if it was
1718 * already changed before the spin_lock(). It cannot,
1719 * however, change back to the original value. Therefore
1720 * we can detect whether we acquired the correct lock.
1722 if (unlikely(lock_ptr != q->lock_ptr)) {
1723 spin_unlock(lock_ptr);
1728 BUG_ON(q->pi_state);
1730 spin_unlock(lock_ptr);
1734 drop_futex_key_refs(&q->key);
1739 * PI futexes can not be requeued and must remove themself from the
1740 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1743 static void unqueue_me_pi(struct futex_q *q)
1744 __releases(q->lock_ptr)
1748 BUG_ON(!q->pi_state);
1749 free_pi_state(q->pi_state);
1752 spin_unlock(q->lock_ptr);
1756 * Fixup the pi_state owner with the new owner.
1758 * Must be called with hash bucket lock held and mm->sem held for non
1761 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1762 struct task_struct *newowner)
1764 u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
1765 struct futex_pi_state *pi_state = q->pi_state;
1766 struct task_struct *oldowner = pi_state->owner;
1767 u32 uval, uninitialized_var(curval), newval;
1771 if (!pi_state->owner)
1772 newtid |= FUTEX_OWNER_DIED;
1775 * We are here either because we stole the rtmutex from the
1776 * previous highest priority waiter or we are the highest priority
1777 * waiter but failed to get the rtmutex the first time.
1778 * We have to replace the newowner TID in the user space variable.
1779 * This must be atomic as we have to preserve the owner died bit here.
1781 * Note: We write the user space value _before_ changing the pi_state
1782 * because we can fault here. Imagine swapped out pages or a fork
1783 * that marked all the anonymous memory readonly for cow.
1785 * Modifying pi_state _before_ the user space value would
1786 * leave the pi_state in an inconsistent state when we fault
1787 * here, because we need to drop the hash bucket lock to
1788 * handle the fault. This might be observed in the PID check
1789 * in lookup_pi_state.
1792 if (get_futex_value_locked(&uval, uaddr))
1796 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1798 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
1806 * We fixed up user space. Now we need to fix the pi_state
1809 if (pi_state->owner != NULL) {
1810 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1811 WARN_ON(list_empty(&pi_state->list));
1812 list_del_init(&pi_state->list);
1813 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1816 pi_state->owner = newowner;
1818 raw_spin_lock_irq(&newowner->pi_lock);
1819 WARN_ON(!list_empty(&pi_state->list));
1820 list_add(&pi_state->list, &newowner->pi_state_list);
1821 raw_spin_unlock_irq(&newowner->pi_lock);
1825 * To handle the page fault we need to drop the hash bucket
1826 * lock here. That gives the other task (either the highest priority
1827 * waiter itself or the task which stole the rtmutex) the
1828 * chance to try the fixup of the pi_state. So once we are
1829 * back from handling the fault we need to check the pi_state
1830 * after reacquiring the hash bucket lock and before trying to
1831 * do another fixup. When the fixup has been done already we
1835 spin_unlock(q->lock_ptr);
1837 ret = fault_in_user_writeable(uaddr);
1839 spin_lock(q->lock_ptr);
1842 * Check if someone else fixed it for us:
1844 if (pi_state->owner != oldowner)
1853 static long futex_wait_restart(struct restart_block *restart);
1856 * fixup_owner() - Post lock pi_state and corner case management
1857 * @uaddr: user address of the futex
1858 * @q: futex_q (contains pi_state and access to the rt_mutex)
1859 * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
1861 * After attempting to lock an rt_mutex, this function is called to cleanup
1862 * the pi_state owner as well as handle race conditions that may allow us to
1863 * acquire the lock. Must be called with the hb lock held.
1866 * 1 - success, lock taken;
1867 * 0 - success, lock not taken;
1868 * <0 - on error (-EFAULT)
1870 static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
1872 struct task_struct *owner;
1877 * Got the lock. We might not be the anticipated owner if we
1878 * did a lock-steal - fix up the PI-state in that case:
1880 if (q->pi_state->owner != current)
1881 ret = fixup_pi_state_owner(uaddr, q, current);
1886 * Catch the rare case, where the lock was released when we were on the
1887 * way back before we locked the hash bucket.
1889 if (q->pi_state->owner == current) {
1891 * Try to get the rt_mutex now. This might fail as some other
1892 * task acquired the rt_mutex after we removed ourself from the
1893 * rt_mutex waiters list.
1895 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
1901 * pi_state is incorrect, some other task did a lock steal and
1902 * we returned due to timeout or signal without taking the
1903 * rt_mutex. Too late.
1905 raw_spin_lock(&q->pi_state->pi_mutex.wait_lock);
1906 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
1908 owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
1909 raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock);
1910 ret = fixup_pi_state_owner(uaddr, q, owner);
1915 * Paranoia check. If we did not take the lock, then we should not be
1916 * the owner of the rt_mutex.
1918 if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
1919 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
1920 "pi-state %p\n", ret,
1921 q->pi_state->pi_mutex.owner,
1922 q->pi_state->owner);
1925 return ret ? ret : locked;
1929 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
1930 * @hb: the futex hash bucket, must be locked by the caller
1931 * @q: the futex_q to queue up on
1932 * @timeout: the prepared hrtimer_sleeper, or null for no timeout
1934 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
1935 struct hrtimer_sleeper *timeout)
1938 * The task state is guaranteed to be set before another task can
1939 * wake it. set_current_state() is implemented using set_mb() and
1940 * queue_me() calls spin_unlock() upon completion, both serializing
1941 * access to the hash list and forcing another memory barrier.
1943 set_current_state(TASK_INTERRUPTIBLE);
1948 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1949 if (!hrtimer_active(&timeout->timer))
1950 timeout->task = NULL;
1954 * If we have been removed from the hash list, then another task
1955 * has tried to wake us, and we can skip the call to schedule().
1957 if (likely(!plist_node_empty(&q->list))) {
1959 * If the timer has already expired, current will already be
1960 * flagged for rescheduling. Only call schedule if there
1961 * is no timeout, or if it has yet to expire.
1963 if (!timeout || timeout->task)
1964 freezable_schedule();
1966 __set_current_state(TASK_RUNNING);
1970 * futex_wait_setup() - Prepare to wait on a futex
1971 * @uaddr: the futex userspace address
1972 * @val: the expected value
1973 * @flags: futex flags (FLAGS_SHARED, etc.)
1974 * @q: the associated futex_q
1975 * @hb: storage for hash_bucket pointer to be returned to caller
1977 * Setup the futex_q and locate the hash_bucket. Get the futex value and
1978 * compare it with the expected value. Handle atomic faults internally.
1979 * Return with the hb lock held and a q.key reference on success, and unlocked
1980 * with no q.key reference on failure.
1983 * 0 - uaddr contains val and hb has been locked;
1984 * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
1986 static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
1987 struct futex_q *q, struct futex_hash_bucket **hb)
1993 * Access the page AFTER the hash-bucket is locked.
1994 * Order is important:
1996 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1997 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
1999 * The basic logical guarantee of a futex is that it blocks ONLY
2000 * if cond(var) is known to be true at the time of blocking, for
2001 * any cond. If we locked the hash-bucket after testing *uaddr, that
2002 * would open a race condition where we could block indefinitely with
2003 * cond(var) false, which would violate the guarantee.
2005 * On the other hand, we insert q and release the hash-bucket only
2006 * after testing *uaddr. This guarantees that futex_wait() will NOT
2007 * absorb a wakeup if *uaddr does not match the desired values
2008 * while the syscall executes.
2011 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
2012 if (unlikely(ret != 0))
2016 *hb = queue_lock(q);
2018 ret = get_futex_value_locked(&uval, uaddr);
2023 ret = get_user(uval, uaddr);
2027 if (!(flags & FLAGS_SHARED))
2030 put_futex_key(&q->key);
2041 put_futex_key(&q->key);
2045 static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
2046 ktime_t *abs_time, u32 bitset)
2048 struct hrtimer_sleeper timeout, *to = NULL;
2049 struct restart_block *restart;
2050 struct futex_hash_bucket *hb;
2051 struct futex_q q = futex_q_init;
2061 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2062 CLOCK_REALTIME : CLOCK_MONOTONIC,
2064 hrtimer_init_sleeper(to, current);
2065 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2066 current->timer_slack_ns);
2071 * Prepare to wait on uaddr. On success, holds hb lock and increments
2074 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2078 /* queue_me and wait for wakeup, timeout, or a signal. */
2079 futex_wait_queue_me(hb, &q, to);
2081 /* If we were woken (and unqueued), we succeeded, whatever. */
2083 /* unqueue_me() drops q.key ref */
2084 if (!unqueue_me(&q))
2087 if (to && !to->task)
2091 * We expect signal_pending(current), but we might be the
2092 * victim of a spurious wakeup as well.
2094 if (!signal_pending(current))
2101 restart = ¤t_thread_info()->restart_block;
2102 restart->fn = futex_wait_restart;
2103 restart->futex.uaddr = uaddr;
2104 restart->futex.val = val;
2105 restart->futex.time = abs_time->tv64;
2106 restart->futex.bitset = bitset;
2107 restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
2109 ret = -ERESTART_RESTARTBLOCK;
2113 hrtimer_cancel(&to->timer);
2114 destroy_hrtimer_on_stack(&to->timer);
2120 static long futex_wait_restart(struct restart_block *restart)
2122 u32 __user *uaddr = restart->futex.uaddr;
2123 ktime_t t, *tp = NULL;
2125 if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
2126 t.tv64 = restart->futex.time;
2129 restart->fn = do_no_restart_syscall;
2131 return (long)futex_wait(uaddr, restart->futex.flags,
2132 restart->futex.val, tp, restart->futex.bitset);
2137 * Userspace tried a 0 -> TID atomic transition of the futex value
2138 * and failed. The kernel side here does the whole locking operation:
2139 * if there are waiters then it will block, it does PI, etc. (Due to
2140 * races the kernel might see a 0 value of the futex too.)
2142 static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect,
2143 ktime_t *time, int trylock)
2145 struct hrtimer_sleeper timeout, *to = NULL;
2146 struct futex_hash_bucket *hb;
2147 struct futex_q q = futex_q_init;
2150 if (refill_pi_state_cache())
2155 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
2157 hrtimer_init_sleeper(to, current);
2158 hrtimer_set_expires(&to->timer, *time);
2162 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
2163 if (unlikely(ret != 0))
2167 hb = queue_lock(&q);
2169 ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
2170 if (unlikely(ret)) {
2173 /* We got the lock. */
2175 goto out_unlock_put_key;
2180 * Task is exiting and we just wait for the
2184 put_futex_key(&q.key);
2188 goto out_unlock_put_key;
2193 * Only actually queue now that the atomic ops are done:
2197 WARN_ON(!q.pi_state);
2199 * Block on the PI mutex:
2202 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
2204 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
2205 /* Fixup the trylock return value: */
2206 ret = ret ? 0 : -EWOULDBLOCK;
2209 spin_lock(q.lock_ptr);
2211 * Fixup the pi_state owner and possibly acquire the lock if we
2214 res = fixup_owner(uaddr, &q, !ret);
2216 * If fixup_owner() returned an error, proprogate that. If it acquired
2217 * the lock, clear our -ETIMEDOUT or -EINTR.
2220 ret = (res < 0) ? res : 0;
2223 * If fixup_owner() faulted and was unable to handle the fault, unlock
2224 * it and return the fault to userspace.
2226 if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
2227 rt_mutex_unlock(&q.pi_state->pi_mutex);
2229 /* Unqueue and drop the lock */
2238 put_futex_key(&q.key);
2241 destroy_hrtimer_on_stack(&to->timer);
2242 return ret != -EINTR ? ret : -ERESTARTNOINTR;
2247 ret = fault_in_user_writeable(uaddr);
2251 if (!(flags & FLAGS_SHARED))
2254 put_futex_key(&q.key);
2259 * Userspace attempted a TID -> 0 atomic transition, and failed.
2260 * This is the in-kernel slowpath: we look up the PI state (if any),
2261 * and do the rt-mutex unlock.
2263 static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
2265 struct futex_hash_bucket *hb;
2266 struct futex_q *this, *next;
2267 union futex_key key = FUTEX_KEY_INIT;
2268 u32 uval, vpid = task_pid_vnr(current);
2272 if (get_user(uval, uaddr))
2275 * We release only a lock we actually own:
2277 if ((uval & FUTEX_TID_MASK) != vpid)
2280 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
2281 if (unlikely(ret != 0))
2284 hb = hash_futex(&key);
2285 spin_lock(&hb->lock);
2288 * To avoid races, try to do the TID -> 0 atomic transition
2289 * again. If it succeeds then we can return without waking
2292 if (!(uval & FUTEX_OWNER_DIED) &&
2293 cmpxchg_futex_value_locked(&uval, uaddr, vpid, 0))
2296 * Rare case: we managed to release the lock atomically,
2297 * no need to wake anyone else up:
2299 if (unlikely(uval == vpid))
2303 * Ok, other tasks may need to be woken up - check waiters
2304 * and do the wakeup if necessary:
2306 plist_for_each_entry_safe(this, next, &hb->chain, list) {
2307 if (!match_futex (&this->key, &key))
2309 ret = wake_futex_pi(uaddr, uval, this);
2311 * The atomic access to the futex value
2312 * generated a pagefault, so retry the
2313 * user-access and the wakeup:
2320 * No waiters - kernel unlocks the futex:
2322 if (!(uval & FUTEX_OWNER_DIED)) {
2323 ret = unlock_futex_pi(uaddr, uval);
2329 spin_unlock(&hb->lock);
2330 put_futex_key(&key);
2336 spin_unlock(&hb->lock);
2337 put_futex_key(&key);
2339 ret = fault_in_user_writeable(uaddr);
2347 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2348 * @hb: the hash_bucket futex_q was original enqueued on
2349 * @q: the futex_q woken while waiting to be requeued
2350 * @key2: the futex_key of the requeue target futex
2351 * @timeout: the timeout associated with the wait (NULL if none)
2353 * Detect if the task was woken on the initial futex as opposed to the requeue
2354 * target futex. If so, determine if it was a timeout or a signal that caused
2355 * the wakeup and return the appropriate error code to the caller. Must be
2356 * called with the hb lock held.
2359 * 0 = no early wakeup detected;
2360 * <0 = -ETIMEDOUT or -ERESTARTNOINTR
2363 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2364 struct futex_q *q, union futex_key *key2,
2365 struct hrtimer_sleeper *timeout)
2370 * With the hb lock held, we avoid races while we process the wakeup.
2371 * We only need to hold hb (and not hb2) to ensure atomicity as the
2372 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2373 * It can't be requeued from uaddr2 to something else since we don't
2374 * support a PI aware source futex for requeue.
2376 if (!match_futex(&q->key, key2)) {
2377 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2379 * We were woken prior to requeue by a timeout or a signal.
2380 * Unqueue the futex_q and determine which it was.
2382 plist_del(&q->list, &hb->chain);
2385 /* Handle spurious wakeups gracefully */
2387 if (timeout && !timeout->task)
2389 else if (signal_pending(current))
2390 ret = -ERESTARTNOINTR;
2396 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2397 * @uaddr: the futex we initially wait on (non-pi)
2398 * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
2399 * the same type, no requeueing from private to shared, etc.
2400 * @val: the expected value of uaddr
2401 * @abs_time: absolute timeout
2402 * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
2403 * @uaddr2: the pi futex we will take prior to returning to user-space
2405 * The caller will wait on uaddr and will be requeued by futex_requeue() to
2406 * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
2407 * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
2408 * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
2409 * without one, the pi logic would not know which task to boost/deboost, if
2410 * there was a need to.
2412 * We call schedule in futex_wait_queue_me() when we enqueue and return there
2413 * via the following--
2414 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2415 * 2) wakeup on uaddr2 after a requeue
2419 * If 3, cleanup and return -ERESTARTNOINTR.
2421 * If 2, we may then block on trying to take the rt_mutex and return via:
2422 * 5) successful lock
2425 * 8) other lock acquisition failure
2427 * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2429 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2435 static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
2436 u32 val, ktime_t *abs_time, u32 bitset,
2439 struct hrtimer_sleeper timeout, *to = NULL;
2440 struct rt_mutex_waiter rt_waiter;
2441 struct rt_mutex *pi_mutex = NULL;
2442 struct futex_hash_bucket *hb;
2443 union futex_key key2 = FUTEX_KEY_INIT;
2444 struct futex_q q = futex_q_init;
2447 if (uaddr == uaddr2)
2455 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2456 CLOCK_REALTIME : CLOCK_MONOTONIC,
2458 hrtimer_init_sleeper(to, current);
2459 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2460 current->timer_slack_ns);
2464 * The waiter is allocated on our stack, manipulated by the requeue
2465 * code while we sleep on uaddr.
2467 debug_rt_mutex_init_waiter(&rt_waiter);
2468 RB_CLEAR_NODE(&rt_waiter.pi_tree_entry);
2469 RB_CLEAR_NODE(&rt_waiter.tree_entry);
2470 rt_waiter.task = NULL;
2472 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
2473 if (unlikely(ret != 0))
2477 q.rt_waiter = &rt_waiter;
2478 q.requeue_pi_key = &key2;
2481 * Prepare to wait on uaddr. On success, increments q.key (key1) ref
2484 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2488 /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2489 futex_wait_queue_me(hb, &q, to);
2491 spin_lock(&hb->lock);
2492 ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2493 spin_unlock(&hb->lock);
2498 * In order for us to be here, we know our q.key == key2, and since
2499 * we took the hb->lock above, we also know that futex_requeue() has
2500 * completed and we no longer have to concern ourselves with a wakeup
2501 * race with the atomic proxy lock acquisition by the requeue code. The
2502 * futex_requeue dropped our key1 reference and incremented our key2
2506 /* Check if the requeue code acquired the second futex for us. */
2509 * Got the lock. We might not be the anticipated owner if we
2510 * did a lock-steal - fix up the PI-state in that case.
2512 if (q.pi_state && (q.pi_state->owner != current)) {
2513 spin_lock(q.lock_ptr);
2514 ret = fixup_pi_state_owner(uaddr2, &q, current);
2515 spin_unlock(q.lock_ptr);
2519 * We have been woken up by futex_unlock_pi(), a timeout, or a
2520 * signal. futex_unlock_pi() will not destroy the lock_ptr nor
2523 WARN_ON(!q.pi_state);
2524 pi_mutex = &q.pi_state->pi_mutex;
2525 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
2526 debug_rt_mutex_free_waiter(&rt_waiter);
2528 spin_lock(q.lock_ptr);
2530 * Fixup the pi_state owner and possibly acquire the lock if we
2533 res = fixup_owner(uaddr2, &q, !ret);
2535 * If fixup_owner() returned an error, proprogate that. If it
2536 * acquired the lock, clear -ETIMEDOUT or -EINTR.
2539 ret = (res < 0) ? res : 0;
2541 /* Unqueue and drop the lock. */
2546 * If fixup_pi_state_owner() faulted and was unable to handle the
2547 * fault, unlock the rt_mutex and return the fault to userspace.
2549 if (ret == -EFAULT) {
2550 if (pi_mutex && rt_mutex_owner(pi_mutex) == current)
2551 rt_mutex_unlock(pi_mutex);
2552 } else if (ret == -EINTR) {
2554 * We've already been requeued, but cannot restart by calling
2555 * futex_lock_pi() directly. We could restart this syscall, but
2556 * it would detect that the user space "val" changed and return
2557 * -EWOULDBLOCK. Save the overhead of the restart and return
2558 * -EWOULDBLOCK directly.
2564 put_futex_key(&q.key);
2566 put_futex_key(&key2);
2570 hrtimer_cancel(&to->timer);
2571 destroy_hrtimer_on_stack(&to->timer);
2577 * Support for robust futexes: the kernel cleans up held futexes at
2580 * Implementation: user-space maintains a per-thread list of locks it
2581 * is holding. Upon do_exit(), the kernel carefully walks this list,
2582 * and marks all locks that are owned by this thread with the
2583 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2584 * always manipulated with the lock held, so the list is private and
2585 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2586 * field, to allow the kernel to clean up if the thread dies after
2587 * acquiring the lock, but just before it could have added itself to
2588 * the list. There can only be one such pending lock.
2592 * sys_set_robust_list() - Set the robust-futex list head of a task
2593 * @head: pointer to the list-head
2594 * @len: length of the list-head, as userspace expects
2596 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2599 if (!futex_cmpxchg_enabled)
2602 * The kernel knows only one size for now:
2604 if (unlikely(len != sizeof(*head)))
2607 current->robust_list = head;
2613 * sys_get_robust_list() - Get the robust-futex list head of a task
2614 * @pid: pid of the process [zero for current task]
2615 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
2616 * @len_ptr: pointer to a length field, the kernel fills in the header size
2618 SYSCALL_DEFINE3(get_robust_list, int, pid,
2619 struct robust_list_head __user * __user *, head_ptr,
2620 size_t __user *, len_ptr)
2622 struct robust_list_head __user *head;
2624 struct task_struct *p;
2626 if (!futex_cmpxchg_enabled)
2635 p = find_task_by_vpid(pid);
2641 if (!ptrace_may_access(p, PTRACE_MODE_READ))
2644 head = p->robust_list;
2647 if (put_user(sizeof(*head), len_ptr))
2649 return put_user(head, head_ptr);
2658 * Process a futex-list entry, check whether it's owned by the
2659 * dying task, and do notification if so:
2661 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
2663 u32 uval, uninitialized_var(nval), mval;
2666 if (get_user(uval, uaddr))
2669 if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
2671 * Ok, this dying thread is truly holding a futex
2672 * of interest. Set the OWNER_DIED bit atomically
2673 * via cmpxchg, and if the value had FUTEX_WAITERS
2674 * set, wake up a waiter (if any). (We have to do a
2675 * futex_wake() even if OWNER_DIED is already set -
2676 * to handle the rare but possible case of recursive
2677 * thread-death.) The rest of the cleanup is done in
2680 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
2682 * We are not holding a lock here, but we want to have
2683 * the pagefault_disable/enable() protection because
2684 * we want to handle the fault gracefully. If the
2685 * access fails we try to fault in the futex with R/W
2686 * verification via get_user_pages. get_user() above
2687 * does not guarantee R/W access. If that fails we
2688 * give up and leave the futex locked.
2690 if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
2691 if (fault_in_user_writeable(uaddr))
2699 * Wake robust non-PI futexes here. The wakeup of
2700 * PI futexes happens in exit_pi_state():
2702 if (!pi && (uval & FUTEX_WAITERS))
2703 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
2709 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
2711 static inline int fetch_robust_entry(struct robust_list __user **entry,
2712 struct robust_list __user * __user *head,
2715 unsigned long uentry;
2717 if (get_user(uentry, (unsigned long __user *)head))
2720 *entry = (void __user *)(uentry & ~1UL);
2727 * Walk curr->robust_list (very carefully, it's a userspace list!)
2728 * and mark any locks found there dead, and notify any waiters.
2730 * We silently return on any sign of list-walking problem.
2732 void exit_robust_list(struct task_struct *curr)
2734 struct robust_list_head __user *head = curr->robust_list;
2735 struct robust_list __user *entry, *next_entry, *pending;
2736 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
2737 unsigned int uninitialized_var(next_pi);
2738 unsigned long futex_offset;
2741 if (!futex_cmpxchg_enabled)
2745 * Fetch the list head (which was registered earlier, via
2746 * sys_set_robust_list()):
2748 if (fetch_robust_entry(&entry, &head->list.next, &pi))
2751 * Fetch the relative futex offset:
2753 if (get_user(futex_offset, &head->futex_offset))
2756 * Fetch any possibly pending lock-add first, and handle it
2759 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
2762 next_entry = NULL; /* avoid warning with gcc */
2763 while (entry != &head->list) {
2765 * Fetch the next entry in the list before calling
2766 * handle_futex_death:
2768 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
2770 * A pending lock might already be on the list, so
2771 * don't process it twice:
2773 if (entry != pending)
2774 if (handle_futex_death((void __user *)entry + futex_offset,
2782 * Avoid excessively long or circular lists:
2791 handle_futex_death((void __user *)pending + futex_offset,
2795 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
2796 u32 __user *uaddr2, u32 val2, u32 val3)
2798 int cmd = op & FUTEX_CMD_MASK;
2799 unsigned int flags = 0;
2801 if (!(op & FUTEX_PRIVATE_FLAG))
2802 flags |= FLAGS_SHARED;
2804 if (op & FUTEX_CLOCK_REALTIME) {
2805 flags |= FLAGS_CLOCKRT;
2806 if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
2812 case FUTEX_UNLOCK_PI:
2813 case FUTEX_TRYLOCK_PI:
2814 case FUTEX_WAIT_REQUEUE_PI:
2815 case FUTEX_CMP_REQUEUE_PI:
2816 if (!futex_cmpxchg_enabled)
2822 val3 = FUTEX_BITSET_MATCH_ANY;
2823 case FUTEX_WAIT_BITSET:
2824 return futex_wait(uaddr, flags, val, timeout, val3);
2826 val3 = FUTEX_BITSET_MATCH_ANY;
2827 case FUTEX_WAKE_BITSET:
2828 return futex_wake(uaddr, flags, val, val3);
2830 return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
2831 case FUTEX_CMP_REQUEUE:
2832 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
2834 return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
2836 return futex_lock_pi(uaddr, flags, val, timeout, 0);
2837 case FUTEX_UNLOCK_PI:
2838 return futex_unlock_pi(uaddr, flags);
2839 case FUTEX_TRYLOCK_PI:
2840 return futex_lock_pi(uaddr, flags, 0, timeout, 1);
2841 case FUTEX_WAIT_REQUEUE_PI:
2842 val3 = FUTEX_BITSET_MATCH_ANY;
2843 return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
2845 case FUTEX_CMP_REQUEUE_PI:
2846 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
2852 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
2853 struct timespec __user *, utime, u32 __user *, uaddr2,
2857 ktime_t t, *tp = NULL;
2859 int cmd = op & FUTEX_CMD_MASK;
2861 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
2862 cmd == FUTEX_WAIT_BITSET ||
2863 cmd == FUTEX_WAIT_REQUEUE_PI)) {
2864 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
2866 if (!timespec_valid(&ts))
2869 t = timespec_to_ktime(ts);
2870 if (cmd == FUTEX_WAIT)
2871 t = ktime_add_safe(ktime_get(), t);
2875 * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
2876 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
2878 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
2879 cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
2880 val2 = (u32) (unsigned long) utime;
2882 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
2885 static void __init futex_detect_cmpxchg(void)
2887 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
2891 * This will fail and we want it. Some arch implementations do
2892 * runtime detection of the futex_atomic_cmpxchg_inatomic()
2893 * functionality. We want to know that before we call in any
2894 * of the complex code paths. Also we want to prevent
2895 * registration of robust lists in that case. NULL is
2896 * guaranteed to fault and we get -EFAULT on functional
2897 * implementation, the non-functional ones will return
2900 if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
2901 futex_cmpxchg_enabled = 1;
2905 static int __init futex_init(void)
2907 unsigned int futex_shift;
2910 #if CONFIG_BASE_SMALL
2911 futex_hashsize = 16;
2913 futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
2916 futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
2918 futex_hashsize < 256 ? HASH_SMALL : 0,
2920 futex_hashsize, futex_hashsize);
2921 futex_hashsize = 1UL << futex_shift;
2923 futex_detect_cmpxchg();
2925 for (i = 0; i < futex_hashsize; i++) {
2926 atomic_set(&futex_queues[i].waiters, 0);
2927 plist_head_init(&futex_queues[i].chain);
2928 spin_lock_init(&futex_queues[i].lock);
2933 __initcall(futex_init);