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 int __read_mostly futex_cmpxchg_enabled;
163 * Futex flags used to encode options to functions and preserve them across
166 #define FLAGS_SHARED 0x01
167 #define FLAGS_CLOCKRT 0x02
168 #define FLAGS_HAS_TIMEOUT 0x04
171 * Priority Inheritance state:
173 struct futex_pi_state {
175 * list of 'owned' pi_state instances - these have to be
176 * cleaned up in do_exit() if the task exits prematurely:
178 struct list_head list;
183 struct rt_mutex pi_mutex;
185 struct task_struct *owner;
192 * struct futex_q - The hashed futex queue entry, one per waiting task
193 * @list: priority-sorted list of tasks waiting on this futex
194 * @task: the task waiting on the futex
195 * @lock_ptr: the hash bucket lock
196 * @key: the key the futex is hashed on
197 * @pi_state: optional priority inheritance state
198 * @rt_waiter: rt_waiter storage for use with requeue_pi
199 * @requeue_pi_key: the requeue_pi target futex key
200 * @bitset: bitset for the optional bitmasked wakeup
202 * We use this hashed waitqueue, instead of a normal wait_queue_t, so
203 * we can wake only the relevant ones (hashed queues may be shared).
205 * A futex_q has a woken state, just like tasks have TASK_RUNNING.
206 * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
207 * The order of wakeup is always to make the first condition true, then
210 * PI futexes are typically woken before they are removed from the hash list via
211 * the rt_mutex code. See unqueue_me_pi().
214 struct plist_node list;
216 struct task_struct *task;
217 spinlock_t *lock_ptr;
219 struct futex_pi_state *pi_state;
220 struct rt_mutex_waiter *rt_waiter;
221 union futex_key *requeue_pi_key;
225 static const struct futex_q futex_q_init = {
226 /* list gets initialized in queue_me()*/
227 .key = FUTEX_KEY_INIT,
228 .bitset = FUTEX_BITSET_MATCH_ANY
232 * Hash buckets are shared by all the futex_keys that hash to the same
233 * location. Each key may have multiple futex_q structures, one for each task
234 * waiting on a futex.
236 struct futex_hash_bucket {
239 struct plist_head chain;
240 } ____cacheline_aligned_in_smp;
242 static unsigned long __read_mostly futex_hashsize;
244 static struct futex_hash_bucket *futex_queues;
246 static inline void futex_get_mm(union futex_key *key)
248 atomic_inc(&key->private.mm->mm_count);
250 * Ensure futex_get_mm() implies a full barrier such that
251 * get_futex_key() implies a full barrier. This is relied upon
252 * as full barrier (B), see the ordering comment above.
254 smp_mb__after_atomic_inc();
258 * Reflects a new waiter being added to the waitqueue.
260 static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
263 atomic_inc(&hb->waiters);
265 * Full barrier (A), see the ordering comment above.
267 smp_mb__after_atomic_inc();
272 * Reflects a waiter being removed from the waitqueue by wakeup
275 static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
278 atomic_dec(&hb->waiters);
282 static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
285 return atomic_read(&hb->waiters);
292 * We hash on the keys returned from get_futex_key (see below).
294 static struct futex_hash_bucket *hash_futex(union futex_key *key)
296 u32 hash = jhash2((u32*)&key->both.word,
297 (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
299 return &futex_queues[hash & (futex_hashsize - 1)];
303 * Return 1 if two futex_keys are equal, 0 otherwise.
305 static inline int match_futex(union futex_key *key1, union futex_key *key2)
308 && key1->both.word == key2->both.word
309 && key1->both.ptr == key2->both.ptr
310 && key1->both.offset == key2->both.offset);
314 * Take a reference to the resource addressed by a key.
315 * Can be called while holding spinlocks.
318 static void get_futex_key_refs(union futex_key *key)
323 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
325 ihold(key->shared.inode); /* implies MB (B) */
327 case FUT_OFF_MMSHARED:
328 futex_get_mm(key); /* implies MB (B) */
334 * Drop a reference to the resource addressed by a key.
335 * The hash bucket spinlock must not be held.
337 static void drop_futex_key_refs(union futex_key *key)
339 if (!key->both.ptr) {
340 /* If we're here then we tried to put a key we failed to get */
345 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
347 iput(key->shared.inode);
349 case FUT_OFF_MMSHARED:
350 mmdrop(key->private.mm);
356 * get_futex_key() - Get parameters which are the keys for a futex
357 * @uaddr: virtual address of the futex
358 * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
359 * @key: address where result is stored.
360 * @rw: mapping needs to be read/write (values: VERIFY_READ,
363 * Return: a negative error code or 0
365 * The key words are stored in *key on success.
367 * For shared mappings, it's (page->index, file_inode(vma->vm_file),
368 * offset_within_page). For private mappings, it's (uaddr, current->mm).
369 * We can usually work out the index without swapping in the page.
371 * lock_page() might sleep, the caller should not hold a spinlock.
374 get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
376 unsigned long address = (unsigned long)uaddr;
377 struct mm_struct *mm = current->mm;
378 struct page *page, *page_head;
382 * The futex address must be "naturally" aligned.
384 key->both.offset = address % PAGE_SIZE;
385 if (unlikely((address % sizeof(u32)) != 0))
387 address -= key->both.offset;
389 if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
393 * PROCESS_PRIVATE futexes are fast.
394 * As the mm cannot disappear under us and the 'key' only needs
395 * virtual address, we dont even have to find the underlying vma.
396 * Note : We do have to check 'uaddr' is a valid user address,
397 * but access_ok() should be faster than find_vma()
400 key->private.mm = mm;
401 key->private.address = address;
402 get_futex_key_refs(key); /* implies MB (B) */
407 err = get_user_pages_fast(address, 1, 1, &page);
409 * If write access is not required (eg. FUTEX_WAIT), try
410 * and get read-only access.
412 if (err == -EFAULT && rw == VERIFY_READ) {
413 err = get_user_pages_fast(address, 1, 0, &page);
421 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
423 if (unlikely(PageTail(page))) {
425 /* serialize against __split_huge_page_splitting() */
427 if (likely(__get_user_pages_fast(address, 1, !ro, &page) == 1)) {
428 page_head = compound_head(page);
430 * page_head is valid pointer but we must pin
431 * it before taking the PG_lock and/or
432 * PG_compound_lock. The moment we re-enable
433 * irqs __split_huge_page_splitting() can
434 * return and the head page can be freed from
435 * under us. We can't take the PG_lock and/or
436 * PG_compound_lock on a page that could be
437 * freed from under us.
439 if (page != page_head) {
450 page_head = compound_head(page);
451 if (page != page_head) {
457 lock_page(page_head);
460 * If page_head->mapping is NULL, then it cannot be a PageAnon
461 * page; but it might be the ZERO_PAGE or in the gate area or
462 * in a special mapping (all cases which we are happy to fail);
463 * or it may have been a good file page when get_user_pages_fast
464 * found it, but truncated or holepunched or subjected to
465 * invalidate_complete_page2 before we got the page lock (also
466 * cases which we are happy to fail). And we hold a reference,
467 * so refcount care in invalidate_complete_page's remove_mapping
468 * prevents drop_caches from setting mapping to NULL beneath us.
470 * The case we do have to guard against is when memory pressure made
471 * shmem_writepage move it from filecache to swapcache beneath us:
472 * an unlikely race, but we do need to retry for page_head->mapping.
474 if (!page_head->mapping) {
475 int shmem_swizzled = PageSwapCache(page_head);
476 unlock_page(page_head);
484 * Private mappings are handled in a simple way.
486 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
487 * it's a read-only handle, it's expected that futexes attach to
488 * the object not the particular process.
490 if (PageAnon(page_head)) {
492 * A RO anonymous page will never change and thus doesn't make
493 * sense for futex operations.
500 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
501 key->private.mm = mm;
502 key->private.address = address;
504 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
505 key->shared.inode = page_head->mapping->host;
506 key->shared.pgoff = basepage_index(page);
509 get_futex_key_refs(key); /* implies MB (B) */
512 unlock_page(page_head);
517 static inline void put_futex_key(union futex_key *key)
519 drop_futex_key_refs(key);
523 * fault_in_user_writeable() - Fault in user address and verify RW access
524 * @uaddr: pointer to faulting user space address
526 * Slow path to fixup the fault we just took in the atomic write
529 * We have no generic implementation of a non-destructive write to the
530 * user address. We know that we faulted in the atomic pagefault
531 * disabled section so we can as well avoid the #PF overhead by
532 * calling get_user_pages() right away.
534 static int fault_in_user_writeable(u32 __user *uaddr)
536 struct mm_struct *mm = current->mm;
539 down_read(&mm->mmap_sem);
540 ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
542 up_read(&mm->mmap_sem);
544 return ret < 0 ? ret : 0;
548 * futex_top_waiter() - Return the highest priority waiter on a futex
549 * @hb: the hash bucket the futex_q's reside in
550 * @key: the futex key (to distinguish it from other futex futex_q's)
552 * Must be called with the hb lock held.
554 static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
555 union futex_key *key)
557 struct futex_q *this;
559 plist_for_each_entry(this, &hb->chain, list) {
560 if (match_futex(&this->key, key))
566 static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
567 u32 uval, u32 newval)
572 ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
578 static int get_futex_value_locked(u32 *dest, u32 __user *from)
583 ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
586 return ret ? -EFAULT : 0;
593 static int refill_pi_state_cache(void)
595 struct futex_pi_state *pi_state;
597 if (likely(current->pi_state_cache))
600 pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
605 INIT_LIST_HEAD(&pi_state->list);
606 /* pi_mutex gets initialized later */
607 pi_state->owner = NULL;
608 atomic_set(&pi_state->refcount, 1);
609 pi_state->key = FUTEX_KEY_INIT;
611 current->pi_state_cache = pi_state;
616 static struct futex_pi_state * alloc_pi_state(void)
618 struct futex_pi_state *pi_state = current->pi_state_cache;
621 current->pi_state_cache = NULL;
626 static void free_pi_state(struct futex_pi_state *pi_state)
628 if (!atomic_dec_and_test(&pi_state->refcount))
632 * If pi_state->owner is NULL, the owner is most probably dying
633 * and has cleaned up the pi_state already
635 if (pi_state->owner) {
636 raw_spin_lock_irq(&pi_state->owner->pi_lock);
637 list_del_init(&pi_state->list);
638 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
640 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
643 if (current->pi_state_cache)
647 * pi_state->list is already empty.
648 * clear pi_state->owner.
649 * refcount is at 0 - put it back to 1.
651 pi_state->owner = NULL;
652 atomic_set(&pi_state->refcount, 1);
653 current->pi_state_cache = pi_state;
658 * Look up the task based on what TID userspace gave us.
661 static struct task_struct * futex_find_get_task(pid_t pid)
663 struct task_struct *p;
666 p = find_task_by_vpid(pid);
676 * This task is holding PI mutexes at exit time => bad.
677 * Kernel cleans up PI-state, but userspace is likely hosed.
678 * (Robust-futex cleanup is separate and might save the day for userspace.)
680 void exit_pi_state_list(struct task_struct *curr)
682 struct list_head *next, *head = &curr->pi_state_list;
683 struct futex_pi_state *pi_state;
684 struct futex_hash_bucket *hb;
685 union futex_key key = FUTEX_KEY_INIT;
687 if (!futex_cmpxchg_enabled)
690 * We are a ZOMBIE and nobody can enqueue itself on
691 * pi_state_list anymore, but we have to be careful
692 * versus waiters unqueueing themselves:
694 raw_spin_lock_irq(&curr->pi_lock);
695 while (!list_empty(head)) {
698 pi_state = list_entry(next, struct futex_pi_state, list);
700 hb = hash_futex(&key);
701 raw_spin_unlock_irq(&curr->pi_lock);
703 spin_lock(&hb->lock);
705 raw_spin_lock_irq(&curr->pi_lock);
707 * We dropped the pi-lock, so re-check whether this
708 * task still owns the PI-state:
710 if (head->next != next) {
711 spin_unlock(&hb->lock);
715 WARN_ON(pi_state->owner != curr);
716 WARN_ON(list_empty(&pi_state->list));
717 list_del_init(&pi_state->list);
718 pi_state->owner = NULL;
719 raw_spin_unlock_irq(&curr->pi_lock);
721 rt_mutex_unlock(&pi_state->pi_mutex);
723 spin_unlock(&hb->lock);
725 raw_spin_lock_irq(&curr->pi_lock);
727 raw_spin_unlock_irq(&curr->pi_lock);
731 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
732 union futex_key *key, struct futex_pi_state **ps)
734 struct futex_pi_state *pi_state = NULL;
735 struct futex_q *this, *next;
736 struct task_struct *p;
737 pid_t pid = uval & FUTEX_TID_MASK;
739 plist_for_each_entry_safe(this, next, &hb->chain, list) {
740 if (match_futex(&this->key, key)) {
742 * Another waiter already exists - bump up
743 * the refcount and return its pi_state:
745 pi_state = this->pi_state;
747 * Userspace might have messed up non-PI and PI futexes
749 if (unlikely(!pi_state))
752 WARN_ON(!atomic_read(&pi_state->refcount));
755 * When pi_state->owner is NULL then the owner died
756 * and another waiter is on the fly. pi_state->owner
757 * is fixed up by the task which acquires
758 * pi_state->rt_mutex.
760 * We do not check for pid == 0 which can happen when
761 * the owner died and robust_list_exit() cleared the
764 if (pid && pi_state->owner) {
766 * Bail out if user space manipulated the
769 if (pid != task_pid_vnr(pi_state->owner))
773 atomic_inc(&pi_state->refcount);
781 * We are the first waiter - try to look up the real owner and attach
782 * the new pi_state to it, but bail out when TID = 0
786 p = futex_find_get_task(pid);
791 * We need to look at the task state flags to figure out,
792 * whether the task is exiting. To protect against the do_exit
793 * change of the task flags, we do this protected by
796 raw_spin_lock_irq(&p->pi_lock);
797 if (unlikely(p->flags & PF_EXITING)) {
799 * The task is on the way out. When PF_EXITPIDONE is
800 * set, we know that the task has finished the
803 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
805 raw_spin_unlock_irq(&p->pi_lock);
810 pi_state = alloc_pi_state();
813 * Initialize the pi_mutex in locked state and make 'p'
816 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
818 /* Store the key for possible exit cleanups: */
819 pi_state->key = *key;
821 WARN_ON(!list_empty(&pi_state->list));
822 list_add(&pi_state->list, &p->pi_state_list);
824 raw_spin_unlock_irq(&p->pi_lock);
834 * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
835 * @uaddr: the pi futex user address
836 * @hb: the pi futex hash bucket
837 * @key: the futex key associated with uaddr and hb
838 * @ps: the pi_state pointer where we store the result of the
840 * @task: the task to perform the atomic lock work for. This will
841 * be "current" except in the case of requeue pi.
842 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
846 * 1 - acquired the lock;
849 * The hb->lock and futex_key refs shall be held by the caller.
851 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
852 union futex_key *key,
853 struct futex_pi_state **ps,
854 struct task_struct *task, int set_waiters)
856 int lock_taken, ret, force_take = 0;
857 u32 uval, newval, curval, vpid = task_pid_vnr(task);
860 ret = lock_taken = 0;
863 * To avoid races, we attempt to take the lock here again
864 * (by doing a 0 -> TID atomic cmpxchg), while holding all
865 * the locks. It will most likely not succeed.
869 newval |= FUTEX_WAITERS;
871 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval)))
877 if ((unlikely((curval & FUTEX_TID_MASK) == vpid)))
881 * Surprise - we got the lock. Just return to userspace:
883 if (unlikely(!curval))
889 * Set the FUTEX_WAITERS flag, so the owner will know it has someone
890 * to wake at the next unlock.
892 newval = curval | FUTEX_WAITERS;
895 * Should we force take the futex? See below.
897 if (unlikely(force_take)) {
899 * Keep the OWNER_DIED and the WAITERS bit and set the
902 newval = (curval & ~FUTEX_TID_MASK) | vpid;
907 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
909 if (unlikely(curval != uval))
913 * We took the lock due to forced take over.
915 if (unlikely(lock_taken))
919 * We dont have the lock. Look up the PI state (or create it if
920 * we are the first waiter):
922 ret = lookup_pi_state(uval, hb, key, ps);
928 * We failed to find an owner for this
929 * futex. So we have no pi_state to block
930 * on. This can happen in two cases:
933 * 2) A stale FUTEX_WAITERS bit
935 * Re-read the futex value.
937 if (get_futex_value_locked(&curval, uaddr))
941 * If the owner died or we have a stale
942 * WAITERS bit the owner TID in the user space
945 if (!(curval & FUTEX_TID_MASK)) {
958 * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
959 * @q: The futex_q to unqueue
961 * The q->lock_ptr must not be NULL and must be held by the caller.
963 static void __unqueue_futex(struct futex_q *q)
965 struct futex_hash_bucket *hb;
967 if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
968 || WARN_ON(plist_node_empty(&q->list)))
971 hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
972 plist_del(&q->list, &hb->chain);
977 * The hash bucket lock must be held when this is called.
978 * Afterwards, the futex_q must not be accessed.
980 static void wake_futex(struct futex_q *q)
982 struct task_struct *p = q->task;
984 if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
988 * We set q->lock_ptr = NULL _before_ we wake up the task. If
989 * a non-futex wake up happens on another CPU then the task
990 * might exit and p would dereference a non-existing task
991 * struct. Prevent this by holding a reference on p across the
998 * The waiting task can free the futex_q as soon as
999 * q->lock_ptr = NULL is written, without taking any locks. A
1000 * memory barrier is required here to prevent the following
1001 * store to lock_ptr from getting ahead of the plist_del.
1006 wake_up_state(p, TASK_NORMAL);
1010 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
1012 struct task_struct *new_owner;
1013 struct futex_pi_state *pi_state = this->pi_state;
1014 u32 uninitialized_var(curval), newval;
1020 * If current does not own the pi_state then the futex is
1021 * inconsistent and user space fiddled with the futex value.
1023 if (pi_state->owner != current)
1026 raw_spin_lock(&pi_state->pi_mutex.wait_lock);
1027 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
1030 * It is possible that the next waiter (the one that brought
1031 * this owner to the kernel) timed out and is no longer
1032 * waiting on the lock.
1035 new_owner = this->task;
1038 * We pass it to the next owner. (The WAITERS bit is always
1039 * kept enabled while there is PI state around. We must also
1040 * preserve the owner died bit.)
1042 if (!(uval & FUTEX_OWNER_DIED)) {
1045 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
1047 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
1049 else if (curval != uval)
1052 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
1057 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1058 WARN_ON(list_empty(&pi_state->list));
1059 list_del_init(&pi_state->list);
1060 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1062 raw_spin_lock_irq(&new_owner->pi_lock);
1063 WARN_ON(!list_empty(&pi_state->list));
1064 list_add(&pi_state->list, &new_owner->pi_state_list);
1065 pi_state->owner = new_owner;
1066 raw_spin_unlock_irq(&new_owner->pi_lock);
1068 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
1069 rt_mutex_unlock(&pi_state->pi_mutex);
1074 static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
1076 u32 uninitialized_var(oldval);
1079 * There is no waiter, so we unlock the futex. The owner died
1080 * bit has not to be preserved here. We are the owner:
1082 if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0))
1091 * Express the locking dependencies for lockdep:
1094 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1097 spin_lock(&hb1->lock);
1099 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
1100 } else { /* hb1 > hb2 */
1101 spin_lock(&hb2->lock);
1102 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
1107 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1109 spin_unlock(&hb1->lock);
1111 spin_unlock(&hb2->lock);
1115 * Wake up waiters matching bitset queued on this futex (uaddr).
1118 futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
1120 struct futex_hash_bucket *hb;
1121 struct futex_q *this, *next;
1122 union futex_key key = FUTEX_KEY_INIT;
1128 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
1129 if (unlikely(ret != 0))
1132 hb = hash_futex(&key);
1134 /* Make sure we really have tasks to wakeup */
1135 if (!hb_waiters_pending(hb))
1138 spin_lock(&hb->lock);
1140 plist_for_each_entry_safe(this, next, &hb->chain, list) {
1141 if (match_futex (&this->key, &key)) {
1142 if (this->pi_state || this->rt_waiter) {
1147 /* Check if one of the bits is set in both bitsets */
1148 if (!(this->bitset & bitset))
1152 if (++ret >= nr_wake)
1157 spin_unlock(&hb->lock);
1159 put_futex_key(&key);
1165 * Wake up all waiters hashed on the physical page that is mapped
1166 * to this virtual address:
1169 futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
1170 int nr_wake, int nr_wake2, int op)
1172 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1173 struct futex_hash_bucket *hb1, *hb2;
1174 struct futex_q *this, *next;
1178 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1179 if (unlikely(ret != 0))
1181 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
1182 if (unlikely(ret != 0))
1185 hb1 = hash_futex(&key1);
1186 hb2 = hash_futex(&key2);
1189 double_lock_hb(hb1, hb2);
1190 op_ret = futex_atomic_op_inuser(op, uaddr2);
1191 if (unlikely(op_ret < 0)) {
1193 double_unlock_hb(hb1, hb2);
1197 * we don't get EFAULT from MMU faults if we don't have an MMU,
1198 * but we might get them from range checking
1204 if (unlikely(op_ret != -EFAULT)) {
1209 ret = fault_in_user_writeable(uaddr2);
1213 if (!(flags & FLAGS_SHARED))
1216 put_futex_key(&key2);
1217 put_futex_key(&key1);
1221 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1222 if (match_futex (&this->key, &key1)) {
1223 if (this->pi_state || this->rt_waiter) {
1228 if (++ret >= nr_wake)
1235 plist_for_each_entry_safe(this, next, &hb2->chain, list) {
1236 if (match_futex (&this->key, &key2)) {
1237 if (this->pi_state || this->rt_waiter) {
1242 if (++op_ret >= nr_wake2)
1250 double_unlock_hb(hb1, hb2);
1252 put_futex_key(&key2);
1254 put_futex_key(&key1);
1260 * requeue_futex() - Requeue a futex_q from one hb to another
1261 * @q: the futex_q to requeue
1262 * @hb1: the source hash_bucket
1263 * @hb2: the target hash_bucket
1264 * @key2: the new key for the requeued futex_q
1267 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1268 struct futex_hash_bucket *hb2, union futex_key *key2)
1272 * If key1 and key2 hash to the same bucket, no need to
1275 if (likely(&hb1->chain != &hb2->chain)) {
1276 plist_del(&q->list, &hb1->chain);
1277 hb_waiters_dec(hb1);
1278 plist_add(&q->list, &hb2->chain);
1279 hb_waiters_inc(hb2);
1280 q->lock_ptr = &hb2->lock;
1282 get_futex_key_refs(key2);
1287 * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1289 * @key: the key of the requeue target futex
1290 * @hb: the hash_bucket of the requeue target futex
1292 * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1293 * target futex if it is uncontended or via a lock steal. Set the futex_q key
1294 * to the requeue target futex so the waiter can detect the wakeup on the right
1295 * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1296 * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
1297 * to protect access to the pi_state to fixup the owner later. Must be called
1298 * with both q->lock_ptr and hb->lock held.
1301 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1302 struct futex_hash_bucket *hb)
1304 get_futex_key_refs(key);
1309 WARN_ON(!q->rt_waiter);
1310 q->rt_waiter = NULL;
1312 q->lock_ptr = &hb->lock;
1314 wake_up_state(q->task, TASK_NORMAL);
1318 * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1319 * @pifutex: the user address of the to futex
1320 * @hb1: the from futex hash bucket, must be locked by the caller
1321 * @hb2: the to futex hash bucket, must be locked by the caller
1322 * @key1: the from futex key
1323 * @key2: the to futex key
1324 * @ps: address to store the pi_state pointer
1325 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1327 * Try and get the lock on behalf of the top waiter if we can do it atomically.
1328 * Wake the top waiter if we succeed. If the caller specified set_waiters,
1329 * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1330 * hb1 and hb2 must be held by the caller.
1333 * 0 - failed to acquire the lock atomically;
1334 * 1 - acquired the lock;
1337 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1338 struct futex_hash_bucket *hb1,
1339 struct futex_hash_bucket *hb2,
1340 union futex_key *key1, union futex_key *key2,
1341 struct futex_pi_state **ps, int set_waiters)
1343 struct futex_q *top_waiter = NULL;
1347 if (get_futex_value_locked(&curval, pifutex))
1351 * Find the top_waiter and determine if there are additional waiters.
1352 * If the caller intends to requeue more than 1 waiter to pifutex,
1353 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1354 * as we have means to handle the possible fault. If not, don't set
1355 * the bit unecessarily as it will force the subsequent unlock to enter
1358 top_waiter = futex_top_waiter(hb1, key1);
1360 /* There are no waiters, nothing for us to do. */
1364 /* Ensure we requeue to the expected futex. */
1365 if (!match_futex(top_waiter->requeue_pi_key, key2))
1369 * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
1370 * the contended case or if set_waiters is 1. The pi_state is returned
1371 * in ps in contended cases.
1373 ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1376 requeue_pi_wake_futex(top_waiter, key2, hb2);
1382 * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1383 * @uaddr1: source futex user address
1384 * @flags: futex flags (FLAGS_SHARED, etc.)
1385 * @uaddr2: target futex user address
1386 * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
1387 * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1388 * @cmpval: @uaddr1 expected value (or %NULL)
1389 * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1390 * pi futex (pi to pi requeue is not supported)
1392 * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1393 * uaddr2 atomically on behalf of the top waiter.
1396 * >=0 - on success, the number of tasks requeued or woken;
1399 static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1400 u32 __user *uaddr2, int nr_wake, int nr_requeue,
1401 u32 *cmpval, int requeue_pi)
1403 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1404 int drop_count = 0, task_count = 0, ret;
1405 struct futex_pi_state *pi_state = NULL;
1406 struct futex_hash_bucket *hb1, *hb2;
1407 struct futex_q *this, *next;
1412 * requeue_pi requires a pi_state, try to allocate it now
1413 * without any locks in case it fails.
1415 if (refill_pi_state_cache())
1418 * requeue_pi must wake as many tasks as it can, up to nr_wake
1419 * + nr_requeue, since it acquires the rt_mutex prior to
1420 * returning to userspace, so as to not leave the rt_mutex with
1421 * waiters and no owner. However, second and third wake-ups
1422 * cannot be predicted as they involve race conditions with the
1423 * first wake and a fault while looking up the pi_state. Both
1424 * pthread_cond_signal() and pthread_cond_broadcast() should
1432 if (pi_state != NULL) {
1434 * We will have to lookup the pi_state again, so free this one
1435 * to keep the accounting correct.
1437 free_pi_state(pi_state);
1441 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1442 if (unlikely(ret != 0))
1444 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
1445 requeue_pi ? VERIFY_WRITE : VERIFY_READ);
1446 if (unlikely(ret != 0))
1449 hb1 = hash_futex(&key1);
1450 hb2 = hash_futex(&key2);
1453 hb_waiters_inc(hb2);
1454 double_lock_hb(hb1, hb2);
1456 if (likely(cmpval != NULL)) {
1459 ret = get_futex_value_locked(&curval, uaddr1);
1461 if (unlikely(ret)) {
1462 double_unlock_hb(hb1, hb2);
1463 hb_waiters_dec(hb2);
1465 ret = get_user(curval, uaddr1);
1469 if (!(flags & FLAGS_SHARED))
1472 put_futex_key(&key2);
1473 put_futex_key(&key1);
1476 if (curval != *cmpval) {
1482 if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1484 * Attempt to acquire uaddr2 and wake the top waiter. If we
1485 * intend to requeue waiters, force setting the FUTEX_WAITERS
1486 * bit. We force this here where we are able to easily handle
1487 * faults rather in the requeue loop below.
1489 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1490 &key2, &pi_state, nr_requeue);
1493 * At this point the top_waiter has either taken uaddr2 or is
1494 * waiting on it. If the former, then the pi_state will not
1495 * exist yet, look it up one more time to ensure we have a
1502 ret = get_futex_value_locked(&curval2, uaddr2);
1504 ret = lookup_pi_state(curval2, hb2, &key2,
1512 double_unlock_hb(hb1, hb2);
1513 hb_waiters_dec(hb2);
1514 put_futex_key(&key2);
1515 put_futex_key(&key1);
1516 ret = fault_in_user_writeable(uaddr2);
1521 /* The owner was exiting, try again. */
1522 double_unlock_hb(hb1, hb2);
1523 hb_waiters_dec(hb2);
1524 put_futex_key(&key2);
1525 put_futex_key(&key1);
1533 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1534 if (task_count - nr_wake >= nr_requeue)
1537 if (!match_futex(&this->key, &key1))
1541 * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1542 * be paired with each other and no other futex ops.
1544 * We should never be requeueing a futex_q with a pi_state,
1545 * which is awaiting a futex_unlock_pi().
1547 if ((requeue_pi && !this->rt_waiter) ||
1548 (!requeue_pi && this->rt_waiter) ||
1555 * Wake nr_wake waiters. For requeue_pi, if we acquired the
1556 * lock, we already woke the top_waiter. If not, it will be
1557 * woken by futex_unlock_pi().
1559 if (++task_count <= nr_wake && !requeue_pi) {
1564 /* Ensure we requeue to the expected futex for requeue_pi. */
1565 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1571 * Requeue nr_requeue waiters and possibly one more in the case
1572 * of requeue_pi if we couldn't acquire the lock atomically.
1575 /* Prepare the waiter to take the rt_mutex. */
1576 atomic_inc(&pi_state->refcount);
1577 this->pi_state = pi_state;
1578 ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1582 /* We got the lock. */
1583 requeue_pi_wake_futex(this, &key2, hb2);
1588 this->pi_state = NULL;
1589 free_pi_state(pi_state);
1593 requeue_futex(this, hb1, hb2, &key2);
1598 double_unlock_hb(hb1, hb2);
1599 hb_waiters_dec(hb2);
1602 * drop_futex_key_refs() must be called outside the spinlocks. During
1603 * the requeue we moved futex_q's from the hash bucket at key1 to the
1604 * one at key2 and updated their key pointer. We no longer need to
1605 * hold the references to key1.
1607 while (--drop_count >= 0)
1608 drop_futex_key_refs(&key1);
1611 put_futex_key(&key2);
1613 put_futex_key(&key1);
1615 if (pi_state != NULL)
1616 free_pi_state(pi_state);
1617 return ret ? ret : task_count;
1620 /* The key must be already stored in q->key. */
1621 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
1622 __acquires(&hb->lock)
1624 struct futex_hash_bucket *hb;
1626 hb = hash_futex(&q->key);
1629 * Increment the counter before taking the lock so that
1630 * a potential waker won't miss a to-be-slept task that is
1631 * waiting for the spinlock. This is safe as all queue_lock()
1632 * users end up calling queue_me(). Similarly, for housekeeping,
1633 * decrement the counter at queue_unlock() when some error has
1634 * occurred and we don't end up adding the task to the list.
1638 q->lock_ptr = &hb->lock;
1640 spin_lock(&hb->lock); /* implies MB (A) */
1645 queue_unlock(struct futex_hash_bucket *hb)
1646 __releases(&hb->lock)
1648 spin_unlock(&hb->lock);
1653 * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1654 * @q: The futex_q to enqueue
1655 * @hb: The destination hash bucket
1657 * The hb->lock must be held by the caller, and is released here. A call to
1658 * queue_me() is typically paired with exactly one call to unqueue_me(). The
1659 * exceptions involve the PI related operations, which may use unqueue_me_pi()
1660 * or nothing if the unqueue is done as part of the wake process and the unqueue
1661 * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1664 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1665 __releases(&hb->lock)
1670 * The priority used to register this element is
1671 * - either the real thread-priority for the real-time threads
1672 * (i.e. threads with a priority lower than MAX_RT_PRIO)
1673 * - or MAX_RT_PRIO for non-RT threads.
1674 * Thus, all RT-threads are woken first in priority order, and
1675 * the others are woken last, in FIFO order.
1677 prio = min(current->normal_prio, MAX_RT_PRIO);
1679 plist_node_init(&q->list, prio);
1680 plist_add(&q->list, &hb->chain);
1682 spin_unlock(&hb->lock);
1686 * unqueue_me() - Remove the futex_q from its futex_hash_bucket
1687 * @q: The futex_q to unqueue
1689 * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
1690 * be paired with exactly one earlier call to queue_me().
1693 * 1 - if the futex_q was still queued (and we removed unqueued it);
1694 * 0 - if the futex_q was already removed by the waking thread
1696 static int unqueue_me(struct futex_q *q)
1698 spinlock_t *lock_ptr;
1701 /* In the common case we don't take the spinlock, which is nice. */
1703 lock_ptr = q->lock_ptr;
1705 if (lock_ptr != NULL) {
1706 spin_lock(lock_ptr);
1708 * q->lock_ptr can change between reading it and
1709 * spin_lock(), causing us to take the wrong lock. This
1710 * corrects the race condition.
1712 * Reasoning goes like this: if we have the wrong lock,
1713 * q->lock_ptr must have changed (maybe several times)
1714 * between reading it and the spin_lock(). It can
1715 * change again after the spin_lock() but only if it was
1716 * already changed before the spin_lock(). It cannot,
1717 * however, change back to the original value. Therefore
1718 * we can detect whether we acquired the correct lock.
1720 if (unlikely(lock_ptr != q->lock_ptr)) {
1721 spin_unlock(lock_ptr);
1726 BUG_ON(q->pi_state);
1728 spin_unlock(lock_ptr);
1732 drop_futex_key_refs(&q->key);
1737 * PI futexes can not be requeued and must remove themself from the
1738 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1741 static void unqueue_me_pi(struct futex_q *q)
1742 __releases(q->lock_ptr)
1746 BUG_ON(!q->pi_state);
1747 free_pi_state(q->pi_state);
1750 spin_unlock(q->lock_ptr);
1754 * Fixup the pi_state owner with the new owner.
1756 * Must be called with hash bucket lock held and mm->sem held for non
1759 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1760 struct task_struct *newowner)
1762 u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
1763 struct futex_pi_state *pi_state = q->pi_state;
1764 struct task_struct *oldowner = pi_state->owner;
1765 u32 uval, uninitialized_var(curval), newval;
1769 if (!pi_state->owner)
1770 newtid |= FUTEX_OWNER_DIED;
1773 * We are here either because we stole the rtmutex from the
1774 * previous highest priority waiter or we are the highest priority
1775 * waiter but failed to get the rtmutex the first time.
1776 * We have to replace the newowner TID in the user space variable.
1777 * This must be atomic as we have to preserve the owner died bit here.
1779 * Note: We write the user space value _before_ changing the pi_state
1780 * because we can fault here. Imagine swapped out pages or a fork
1781 * that marked all the anonymous memory readonly for cow.
1783 * Modifying pi_state _before_ the user space value would
1784 * leave the pi_state in an inconsistent state when we fault
1785 * here, because we need to drop the hash bucket lock to
1786 * handle the fault. This might be observed in the PID check
1787 * in lookup_pi_state.
1790 if (get_futex_value_locked(&uval, uaddr))
1794 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1796 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
1804 * We fixed up user space. Now we need to fix the pi_state
1807 if (pi_state->owner != NULL) {
1808 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1809 WARN_ON(list_empty(&pi_state->list));
1810 list_del_init(&pi_state->list);
1811 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1814 pi_state->owner = newowner;
1816 raw_spin_lock_irq(&newowner->pi_lock);
1817 WARN_ON(!list_empty(&pi_state->list));
1818 list_add(&pi_state->list, &newowner->pi_state_list);
1819 raw_spin_unlock_irq(&newowner->pi_lock);
1823 * To handle the page fault we need to drop the hash bucket
1824 * lock here. That gives the other task (either the highest priority
1825 * waiter itself or the task which stole the rtmutex) the
1826 * chance to try the fixup of the pi_state. So once we are
1827 * back from handling the fault we need to check the pi_state
1828 * after reacquiring the hash bucket lock and before trying to
1829 * do another fixup. When the fixup has been done already we
1833 spin_unlock(q->lock_ptr);
1835 ret = fault_in_user_writeable(uaddr);
1837 spin_lock(q->lock_ptr);
1840 * Check if someone else fixed it for us:
1842 if (pi_state->owner != oldowner)
1851 static long futex_wait_restart(struct restart_block *restart);
1854 * fixup_owner() - Post lock pi_state and corner case management
1855 * @uaddr: user address of the futex
1856 * @q: futex_q (contains pi_state and access to the rt_mutex)
1857 * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
1859 * After attempting to lock an rt_mutex, this function is called to cleanup
1860 * the pi_state owner as well as handle race conditions that may allow us to
1861 * acquire the lock. Must be called with the hb lock held.
1864 * 1 - success, lock taken;
1865 * 0 - success, lock not taken;
1866 * <0 - on error (-EFAULT)
1868 static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
1870 struct task_struct *owner;
1875 * Got the lock. We might not be the anticipated owner if we
1876 * did a lock-steal - fix up the PI-state in that case:
1878 if (q->pi_state->owner != current)
1879 ret = fixup_pi_state_owner(uaddr, q, current);
1884 * Catch the rare case, where the lock was released when we were on the
1885 * way back before we locked the hash bucket.
1887 if (q->pi_state->owner == current) {
1889 * Try to get the rt_mutex now. This might fail as some other
1890 * task acquired the rt_mutex after we removed ourself from the
1891 * rt_mutex waiters list.
1893 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
1899 * pi_state is incorrect, some other task did a lock steal and
1900 * we returned due to timeout or signal without taking the
1901 * rt_mutex. Too late.
1903 raw_spin_lock(&q->pi_state->pi_mutex.wait_lock);
1904 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
1906 owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
1907 raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock);
1908 ret = fixup_pi_state_owner(uaddr, q, owner);
1913 * Paranoia check. If we did not take the lock, then we should not be
1914 * the owner of the rt_mutex.
1916 if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
1917 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
1918 "pi-state %p\n", ret,
1919 q->pi_state->pi_mutex.owner,
1920 q->pi_state->owner);
1923 return ret ? ret : locked;
1927 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
1928 * @hb: the futex hash bucket, must be locked by the caller
1929 * @q: the futex_q to queue up on
1930 * @timeout: the prepared hrtimer_sleeper, or null for no timeout
1932 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
1933 struct hrtimer_sleeper *timeout)
1936 * The task state is guaranteed to be set before another task can
1937 * wake it. set_current_state() is implemented using set_mb() and
1938 * queue_me() calls spin_unlock() upon completion, both serializing
1939 * access to the hash list and forcing another memory barrier.
1941 set_current_state(TASK_INTERRUPTIBLE);
1946 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1947 if (!hrtimer_active(&timeout->timer))
1948 timeout->task = NULL;
1952 * If we have been removed from the hash list, then another task
1953 * has tried to wake us, and we can skip the call to schedule().
1955 if (likely(!plist_node_empty(&q->list))) {
1957 * If the timer has already expired, current will already be
1958 * flagged for rescheduling. Only call schedule if there
1959 * is no timeout, or if it has yet to expire.
1961 if (!timeout || timeout->task)
1962 freezable_schedule();
1964 __set_current_state(TASK_RUNNING);
1968 * futex_wait_setup() - Prepare to wait on a futex
1969 * @uaddr: the futex userspace address
1970 * @val: the expected value
1971 * @flags: futex flags (FLAGS_SHARED, etc.)
1972 * @q: the associated futex_q
1973 * @hb: storage for hash_bucket pointer to be returned to caller
1975 * Setup the futex_q and locate the hash_bucket. Get the futex value and
1976 * compare it with the expected value. Handle atomic faults internally.
1977 * Return with the hb lock held and a q.key reference on success, and unlocked
1978 * with no q.key reference on failure.
1981 * 0 - uaddr contains val and hb has been locked;
1982 * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
1984 static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
1985 struct futex_q *q, struct futex_hash_bucket **hb)
1991 * Access the page AFTER the hash-bucket is locked.
1992 * Order is important:
1994 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1995 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
1997 * The basic logical guarantee of a futex is that it blocks ONLY
1998 * if cond(var) is known to be true at the time of blocking, for
1999 * any cond. If we locked the hash-bucket after testing *uaddr, that
2000 * would open a race condition where we could block indefinitely with
2001 * cond(var) false, which would violate the guarantee.
2003 * On the other hand, we insert q and release the hash-bucket only
2004 * after testing *uaddr. This guarantees that futex_wait() will NOT
2005 * absorb a wakeup if *uaddr does not match the desired values
2006 * while the syscall executes.
2009 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
2010 if (unlikely(ret != 0))
2014 *hb = queue_lock(q);
2016 ret = get_futex_value_locked(&uval, uaddr);
2021 ret = get_user(uval, uaddr);
2025 if (!(flags & FLAGS_SHARED))
2028 put_futex_key(&q->key);
2039 put_futex_key(&q->key);
2043 static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
2044 ktime_t *abs_time, u32 bitset)
2046 struct hrtimer_sleeper timeout, *to = NULL;
2047 struct restart_block *restart;
2048 struct futex_hash_bucket *hb;
2049 struct futex_q q = futex_q_init;
2059 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2060 CLOCK_REALTIME : CLOCK_MONOTONIC,
2062 hrtimer_init_sleeper(to, current);
2063 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2064 current->timer_slack_ns);
2069 * Prepare to wait on uaddr. On success, holds hb lock and increments
2072 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2076 /* queue_me and wait for wakeup, timeout, or a signal. */
2077 futex_wait_queue_me(hb, &q, to);
2079 /* If we were woken (and unqueued), we succeeded, whatever. */
2081 /* unqueue_me() drops q.key ref */
2082 if (!unqueue_me(&q))
2085 if (to && !to->task)
2089 * We expect signal_pending(current), but we might be the
2090 * victim of a spurious wakeup as well.
2092 if (!signal_pending(current))
2099 restart = ¤t_thread_info()->restart_block;
2100 restart->fn = futex_wait_restart;
2101 restart->futex.uaddr = uaddr;
2102 restart->futex.val = val;
2103 restart->futex.time = abs_time->tv64;
2104 restart->futex.bitset = bitset;
2105 restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
2107 ret = -ERESTART_RESTARTBLOCK;
2111 hrtimer_cancel(&to->timer);
2112 destroy_hrtimer_on_stack(&to->timer);
2118 static long futex_wait_restart(struct restart_block *restart)
2120 u32 __user *uaddr = restart->futex.uaddr;
2121 ktime_t t, *tp = NULL;
2123 if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
2124 t.tv64 = restart->futex.time;
2127 restart->fn = do_no_restart_syscall;
2129 return (long)futex_wait(uaddr, restart->futex.flags,
2130 restart->futex.val, tp, restart->futex.bitset);
2135 * Userspace tried a 0 -> TID atomic transition of the futex value
2136 * and failed. The kernel side here does the whole locking operation:
2137 * if there are waiters then it will block, it does PI, etc. (Due to
2138 * races the kernel might see a 0 value of the futex too.)
2140 static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect,
2141 ktime_t *time, int trylock)
2143 struct hrtimer_sleeper timeout, *to = NULL;
2144 struct futex_hash_bucket *hb;
2145 struct futex_q q = futex_q_init;
2148 if (refill_pi_state_cache())
2153 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
2155 hrtimer_init_sleeper(to, current);
2156 hrtimer_set_expires(&to->timer, *time);
2160 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
2161 if (unlikely(ret != 0))
2165 hb = queue_lock(&q);
2167 ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
2168 if (unlikely(ret)) {
2171 /* We got the lock. */
2173 goto out_unlock_put_key;
2178 * Task is exiting and we just wait for the
2182 put_futex_key(&q.key);
2186 goto out_unlock_put_key;
2191 * Only actually queue now that the atomic ops are done:
2195 WARN_ON(!q.pi_state);
2197 * Block on the PI mutex:
2200 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
2202 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
2203 /* Fixup the trylock return value: */
2204 ret = ret ? 0 : -EWOULDBLOCK;
2207 spin_lock(q.lock_ptr);
2209 * Fixup the pi_state owner and possibly acquire the lock if we
2212 res = fixup_owner(uaddr, &q, !ret);
2214 * If fixup_owner() returned an error, proprogate that. If it acquired
2215 * the lock, clear our -ETIMEDOUT or -EINTR.
2218 ret = (res < 0) ? res : 0;
2221 * If fixup_owner() faulted and was unable to handle the fault, unlock
2222 * it and return the fault to userspace.
2224 if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
2225 rt_mutex_unlock(&q.pi_state->pi_mutex);
2227 /* Unqueue and drop the lock */
2236 put_futex_key(&q.key);
2239 destroy_hrtimer_on_stack(&to->timer);
2240 return ret != -EINTR ? ret : -ERESTARTNOINTR;
2245 ret = fault_in_user_writeable(uaddr);
2249 if (!(flags & FLAGS_SHARED))
2252 put_futex_key(&q.key);
2257 * Userspace attempted a TID -> 0 atomic transition, and failed.
2258 * This is the in-kernel slowpath: we look up the PI state (if any),
2259 * and do the rt-mutex unlock.
2261 static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
2263 struct futex_hash_bucket *hb;
2264 struct futex_q *this, *next;
2265 union futex_key key = FUTEX_KEY_INIT;
2266 u32 uval, vpid = task_pid_vnr(current);
2270 if (get_user(uval, uaddr))
2273 * We release only a lock we actually own:
2275 if ((uval & FUTEX_TID_MASK) != vpid)
2278 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
2279 if (unlikely(ret != 0))
2282 hb = hash_futex(&key);
2283 spin_lock(&hb->lock);
2286 * To avoid races, try to do the TID -> 0 atomic transition
2287 * again. If it succeeds then we can return without waking
2290 if (!(uval & FUTEX_OWNER_DIED) &&
2291 cmpxchg_futex_value_locked(&uval, uaddr, vpid, 0))
2294 * Rare case: we managed to release the lock atomically,
2295 * no need to wake anyone else up:
2297 if (unlikely(uval == vpid))
2301 * Ok, other tasks may need to be woken up - check waiters
2302 * and do the wakeup if necessary:
2304 plist_for_each_entry_safe(this, next, &hb->chain, list) {
2305 if (!match_futex (&this->key, &key))
2307 ret = wake_futex_pi(uaddr, uval, this);
2309 * The atomic access to the futex value
2310 * generated a pagefault, so retry the
2311 * user-access and the wakeup:
2318 * No waiters - kernel unlocks the futex:
2320 if (!(uval & FUTEX_OWNER_DIED)) {
2321 ret = unlock_futex_pi(uaddr, uval);
2327 spin_unlock(&hb->lock);
2328 put_futex_key(&key);
2334 spin_unlock(&hb->lock);
2335 put_futex_key(&key);
2337 ret = fault_in_user_writeable(uaddr);
2345 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2346 * @hb: the hash_bucket futex_q was original enqueued on
2347 * @q: the futex_q woken while waiting to be requeued
2348 * @key2: the futex_key of the requeue target futex
2349 * @timeout: the timeout associated with the wait (NULL if none)
2351 * Detect if the task was woken on the initial futex as opposed to the requeue
2352 * target futex. If so, determine if it was a timeout or a signal that caused
2353 * the wakeup and return the appropriate error code to the caller. Must be
2354 * called with the hb lock held.
2357 * 0 = no early wakeup detected;
2358 * <0 = -ETIMEDOUT or -ERESTARTNOINTR
2361 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2362 struct futex_q *q, union futex_key *key2,
2363 struct hrtimer_sleeper *timeout)
2368 * With the hb lock held, we avoid races while we process the wakeup.
2369 * We only need to hold hb (and not hb2) to ensure atomicity as the
2370 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2371 * It can't be requeued from uaddr2 to something else since we don't
2372 * support a PI aware source futex for requeue.
2374 if (!match_futex(&q->key, key2)) {
2375 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2377 * We were woken prior to requeue by a timeout or a signal.
2378 * Unqueue the futex_q and determine which it was.
2380 plist_del(&q->list, &hb->chain);
2383 /* Handle spurious wakeups gracefully */
2385 if (timeout && !timeout->task)
2387 else if (signal_pending(current))
2388 ret = -ERESTARTNOINTR;
2394 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2395 * @uaddr: the futex we initially wait on (non-pi)
2396 * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
2397 * the same type, no requeueing from private to shared, etc.
2398 * @val: the expected value of uaddr
2399 * @abs_time: absolute timeout
2400 * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
2401 * @uaddr2: the pi futex we will take prior to returning to user-space
2403 * The caller will wait on uaddr and will be requeued by futex_requeue() to
2404 * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
2405 * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
2406 * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
2407 * without one, the pi logic would not know which task to boost/deboost, if
2408 * there was a need to.
2410 * We call schedule in futex_wait_queue_me() when we enqueue and return there
2411 * via the following--
2412 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2413 * 2) wakeup on uaddr2 after a requeue
2417 * If 3, cleanup and return -ERESTARTNOINTR.
2419 * If 2, we may then block on trying to take the rt_mutex and return via:
2420 * 5) successful lock
2423 * 8) other lock acquisition failure
2425 * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2427 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2433 static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
2434 u32 val, ktime_t *abs_time, u32 bitset,
2437 struct hrtimer_sleeper timeout, *to = NULL;
2438 struct rt_mutex_waiter rt_waiter;
2439 struct rt_mutex *pi_mutex = NULL;
2440 struct futex_hash_bucket *hb;
2441 union futex_key key2 = FUTEX_KEY_INIT;
2442 struct futex_q q = futex_q_init;
2445 if (uaddr == uaddr2)
2453 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2454 CLOCK_REALTIME : CLOCK_MONOTONIC,
2456 hrtimer_init_sleeper(to, current);
2457 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2458 current->timer_slack_ns);
2462 * The waiter is allocated on our stack, manipulated by the requeue
2463 * code while we sleep on uaddr.
2465 debug_rt_mutex_init_waiter(&rt_waiter);
2466 RB_CLEAR_NODE(&rt_waiter.pi_tree_entry);
2467 RB_CLEAR_NODE(&rt_waiter.tree_entry);
2468 rt_waiter.task = NULL;
2470 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
2471 if (unlikely(ret != 0))
2475 q.rt_waiter = &rt_waiter;
2476 q.requeue_pi_key = &key2;
2479 * Prepare to wait on uaddr. On success, increments q.key (key1) ref
2482 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2486 /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2487 futex_wait_queue_me(hb, &q, to);
2489 spin_lock(&hb->lock);
2490 ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2491 spin_unlock(&hb->lock);
2496 * In order for us to be here, we know our q.key == key2, and since
2497 * we took the hb->lock above, we also know that futex_requeue() has
2498 * completed and we no longer have to concern ourselves with a wakeup
2499 * race with the atomic proxy lock acquisition by the requeue code. The
2500 * futex_requeue dropped our key1 reference and incremented our key2
2504 /* Check if the requeue code acquired the second futex for us. */
2507 * Got the lock. We might not be the anticipated owner if we
2508 * did a lock-steal - fix up the PI-state in that case.
2510 if (q.pi_state && (q.pi_state->owner != current)) {
2511 spin_lock(q.lock_ptr);
2512 ret = fixup_pi_state_owner(uaddr2, &q, current);
2513 spin_unlock(q.lock_ptr);
2517 * We have been woken up by futex_unlock_pi(), a timeout, or a
2518 * signal. futex_unlock_pi() will not destroy the lock_ptr nor
2521 WARN_ON(!q.pi_state);
2522 pi_mutex = &q.pi_state->pi_mutex;
2523 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
2524 debug_rt_mutex_free_waiter(&rt_waiter);
2526 spin_lock(q.lock_ptr);
2528 * Fixup the pi_state owner and possibly acquire the lock if we
2531 res = fixup_owner(uaddr2, &q, !ret);
2533 * If fixup_owner() returned an error, proprogate that. If it
2534 * acquired the lock, clear -ETIMEDOUT or -EINTR.
2537 ret = (res < 0) ? res : 0;
2539 /* Unqueue and drop the lock. */
2544 * If fixup_pi_state_owner() faulted and was unable to handle the
2545 * fault, unlock the rt_mutex and return the fault to userspace.
2547 if (ret == -EFAULT) {
2548 if (pi_mutex && rt_mutex_owner(pi_mutex) == current)
2549 rt_mutex_unlock(pi_mutex);
2550 } else if (ret == -EINTR) {
2552 * We've already been requeued, but cannot restart by calling
2553 * futex_lock_pi() directly. We could restart this syscall, but
2554 * it would detect that the user space "val" changed and return
2555 * -EWOULDBLOCK. Save the overhead of the restart and return
2556 * -EWOULDBLOCK directly.
2562 put_futex_key(&q.key);
2564 put_futex_key(&key2);
2568 hrtimer_cancel(&to->timer);
2569 destroy_hrtimer_on_stack(&to->timer);
2575 * Support for robust futexes: the kernel cleans up held futexes at
2578 * Implementation: user-space maintains a per-thread list of locks it
2579 * is holding. Upon do_exit(), the kernel carefully walks this list,
2580 * and marks all locks that are owned by this thread with the
2581 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2582 * always manipulated with the lock held, so the list is private and
2583 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2584 * field, to allow the kernel to clean up if the thread dies after
2585 * acquiring the lock, but just before it could have added itself to
2586 * the list. There can only be one such pending lock.
2590 * sys_set_robust_list() - Set the robust-futex list head of a task
2591 * @head: pointer to the list-head
2592 * @len: length of the list-head, as userspace expects
2594 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2597 if (!futex_cmpxchg_enabled)
2600 * The kernel knows only one size for now:
2602 if (unlikely(len != sizeof(*head)))
2605 current->robust_list = head;
2611 * sys_get_robust_list() - Get the robust-futex list head of a task
2612 * @pid: pid of the process [zero for current task]
2613 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
2614 * @len_ptr: pointer to a length field, the kernel fills in the header size
2616 SYSCALL_DEFINE3(get_robust_list, int, pid,
2617 struct robust_list_head __user * __user *, head_ptr,
2618 size_t __user *, len_ptr)
2620 struct robust_list_head __user *head;
2622 struct task_struct *p;
2624 if (!futex_cmpxchg_enabled)
2633 p = find_task_by_vpid(pid);
2639 if (!ptrace_may_access(p, PTRACE_MODE_READ))
2642 head = p->robust_list;
2645 if (put_user(sizeof(*head), len_ptr))
2647 return put_user(head, head_ptr);
2656 * Process a futex-list entry, check whether it's owned by the
2657 * dying task, and do notification if so:
2659 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
2661 u32 uval, uninitialized_var(nval), mval;
2664 if (get_user(uval, uaddr))
2667 if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
2669 * Ok, this dying thread is truly holding a futex
2670 * of interest. Set the OWNER_DIED bit atomically
2671 * via cmpxchg, and if the value had FUTEX_WAITERS
2672 * set, wake up a waiter (if any). (We have to do a
2673 * futex_wake() even if OWNER_DIED is already set -
2674 * to handle the rare but possible case of recursive
2675 * thread-death.) The rest of the cleanup is done in
2678 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
2680 * We are not holding a lock here, but we want to have
2681 * the pagefault_disable/enable() protection because
2682 * we want to handle the fault gracefully. If the
2683 * access fails we try to fault in the futex with R/W
2684 * verification via get_user_pages. get_user() above
2685 * does not guarantee R/W access. If that fails we
2686 * give up and leave the futex locked.
2688 if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
2689 if (fault_in_user_writeable(uaddr))
2697 * Wake robust non-PI futexes here. The wakeup of
2698 * PI futexes happens in exit_pi_state():
2700 if (!pi && (uval & FUTEX_WAITERS))
2701 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
2707 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
2709 static inline int fetch_robust_entry(struct robust_list __user **entry,
2710 struct robust_list __user * __user *head,
2713 unsigned long uentry;
2715 if (get_user(uentry, (unsigned long __user *)head))
2718 *entry = (void __user *)(uentry & ~1UL);
2725 * Walk curr->robust_list (very carefully, it's a userspace list!)
2726 * and mark any locks found there dead, and notify any waiters.
2728 * We silently return on any sign of list-walking problem.
2730 void exit_robust_list(struct task_struct *curr)
2732 struct robust_list_head __user *head = curr->robust_list;
2733 struct robust_list __user *entry, *next_entry, *pending;
2734 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
2735 unsigned int uninitialized_var(next_pi);
2736 unsigned long futex_offset;
2739 if (!futex_cmpxchg_enabled)
2743 * Fetch the list head (which was registered earlier, via
2744 * sys_set_robust_list()):
2746 if (fetch_robust_entry(&entry, &head->list.next, &pi))
2749 * Fetch the relative futex offset:
2751 if (get_user(futex_offset, &head->futex_offset))
2754 * Fetch any possibly pending lock-add first, and handle it
2757 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
2760 next_entry = NULL; /* avoid warning with gcc */
2761 while (entry != &head->list) {
2763 * Fetch the next entry in the list before calling
2764 * handle_futex_death:
2766 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
2768 * A pending lock might already be on the list, so
2769 * don't process it twice:
2771 if (entry != pending)
2772 if (handle_futex_death((void __user *)entry + futex_offset,
2780 * Avoid excessively long or circular lists:
2789 handle_futex_death((void __user *)pending + futex_offset,
2793 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
2794 u32 __user *uaddr2, u32 val2, u32 val3)
2796 int cmd = op & FUTEX_CMD_MASK;
2797 unsigned int flags = 0;
2799 if (!(op & FUTEX_PRIVATE_FLAG))
2800 flags |= FLAGS_SHARED;
2802 if (op & FUTEX_CLOCK_REALTIME) {
2803 flags |= FLAGS_CLOCKRT;
2804 if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
2810 case FUTEX_UNLOCK_PI:
2811 case FUTEX_TRYLOCK_PI:
2812 case FUTEX_WAIT_REQUEUE_PI:
2813 case FUTEX_CMP_REQUEUE_PI:
2814 if (!futex_cmpxchg_enabled)
2820 val3 = FUTEX_BITSET_MATCH_ANY;
2821 case FUTEX_WAIT_BITSET:
2822 return futex_wait(uaddr, flags, val, timeout, val3);
2824 val3 = FUTEX_BITSET_MATCH_ANY;
2825 case FUTEX_WAKE_BITSET:
2826 return futex_wake(uaddr, flags, val, val3);
2828 return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
2829 case FUTEX_CMP_REQUEUE:
2830 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
2832 return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
2834 return futex_lock_pi(uaddr, flags, val, timeout, 0);
2835 case FUTEX_UNLOCK_PI:
2836 return futex_unlock_pi(uaddr, flags);
2837 case FUTEX_TRYLOCK_PI:
2838 return futex_lock_pi(uaddr, flags, 0, timeout, 1);
2839 case FUTEX_WAIT_REQUEUE_PI:
2840 val3 = FUTEX_BITSET_MATCH_ANY;
2841 return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
2843 case FUTEX_CMP_REQUEUE_PI:
2844 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
2850 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
2851 struct timespec __user *, utime, u32 __user *, uaddr2,
2855 ktime_t t, *tp = NULL;
2857 int cmd = op & FUTEX_CMD_MASK;
2859 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
2860 cmd == FUTEX_WAIT_BITSET ||
2861 cmd == FUTEX_WAIT_REQUEUE_PI)) {
2862 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
2864 if (!timespec_valid(&ts))
2867 t = timespec_to_ktime(ts);
2868 if (cmd == FUTEX_WAIT)
2869 t = ktime_add_safe(ktime_get(), t);
2873 * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
2874 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
2876 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
2877 cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
2878 val2 = (u32) (unsigned long) utime;
2880 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
2883 static int __init futex_init(void)
2886 unsigned int futex_shift;
2889 #if CONFIG_BASE_SMALL
2890 futex_hashsize = 16;
2892 futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
2895 futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
2897 futex_hashsize < 256 ? HASH_SMALL : 0,
2899 futex_hashsize, futex_hashsize);
2900 futex_hashsize = 1UL << futex_shift;
2902 * This will fail and we want it. Some arch implementations do
2903 * runtime detection of the futex_atomic_cmpxchg_inatomic()
2904 * functionality. We want to know that before we call in any
2905 * of the complex code paths. Also we want to prevent
2906 * registration of robust lists in that case. NULL is
2907 * guaranteed to fault and we get -EFAULT on functional
2908 * implementation, the non-functional ones will return
2911 if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
2912 futex_cmpxchg_enabled = 1;
2914 for (i = 0; i < futex_hashsize; i++) {
2915 atomic_set(&futex_queues[i].waiters, 0);
2916 plist_head_init(&futex_queues[i].chain);
2917 spin_lock_init(&futex_queues[i].lock);
2922 __initcall(futex_init);