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,
735 struct task_struct *task)
737 struct futex_pi_state *pi_state = NULL;
738 struct futex_q *this, *next;
739 struct task_struct *p;
740 pid_t pid = uval & FUTEX_TID_MASK;
742 plist_for_each_entry_safe(this, next, &hb->chain, list) {
743 if (match_futex(&this->key, key)) {
745 * Another waiter already exists - bump up
746 * the refcount and return its pi_state:
748 pi_state = this->pi_state;
750 * Userspace might have messed up non-PI and PI futexes
752 if (unlikely(!pi_state))
755 WARN_ON(!atomic_read(&pi_state->refcount));
758 * When pi_state->owner is NULL then the owner died
759 * and another waiter is on the fly. pi_state->owner
760 * is fixed up by the task which acquires
761 * pi_state->rt_mutex.
763 * We do not check for pid == 0 which can happen when
764 * the owner died and robust_list_exit() cleared the
767 if (pid && pi_state->owner) {
769 * Bail out if user space manipulated the
772 if (pid != task_pid_vnr(pi_state->owner))
777 * Protect against a corrupted uval. If uval
778 * is 0x80000000 then pid is 0 and the waiter
779 * bit is set. So the deadlock check in the
780 * calling code has failed and we did not fall
781 * into the check above due to !pid.
783 if (task && pi_state->owner == task)
786 atomic_inc(&pi_state->refcount);
794 * We are the first waiter - try to look up the real owner and attach
795 * the new pi_state to it, but bail out when TID = 0
799 p = futex_find_get_task(pid);
809 * We need to look at the task state flags to figure out,
810 * whether the task is exiting. To protect against the do_exit
811 * change of the task flags, we do this protected by
814 raw_spin_lock_irq(&p->pi_lock);
815 if (unlikely(p->flags & PF_EXITING)) {
817 * The task is on the way out. When PF_EXITPIDONE is
818 * set, we know that the task has finished the
821 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
823 raw_spin_unlock_irq(&p->pi_lock);
828 pi_state = alloc_pi_state();
831 * Initialize the pi_mutex in locked state and make 'p'
834 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
836 /* Store the key for possible exit cleanups: */
837 pi_state->key = *key;
839 WARN_ON(!list_empty(&pi_state->list));
840 list_add(&pi_state->list, &p->pi_state_list);
842 raw_spin_unlock_irq(&p->pi_lock);
852 * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
853 * @uaddr: the pi futex user address
854 * @hb: the pi futex hash bucket
855 * @key: the futex key associated with uaddr and hb
856 * @ps: the pi_state pointer where we store the result of the
858 * @task: the task to perform the atomic lock work for. This will
859 * be "current" except in the case of requeue pi.
860 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
864 * 1 - acquired the lock;
867 * The hb->lock and futex_key refs shall be held by the caller.
869 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
870 union futex_key *key,
871 struct futex_pi_state **ps,
872 struct task_struct *task, int set_waiters)
874 int lock_taken, ret, force_take = 0;
875 u32 uval, newval, curval, vpid = task_pid_vnr(task);
878 ret = lock_taken = 0;
881 * To avoid races, we attempt to take the lock here again
882 * (by doing a 0 -> TID atomic cmpxchg), while holding all
883 * the locks. It will most likely not succeed.
887 newval |= FUTEX_WAITERS;
889 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval)))
895 if ((unlikely((curval & FUTEX_TID_MASK) == vpid)))
899 * Surprise - we got the lock, but we do not trust user space at all.
901 if (unlikely(!curval)) {
903 * We verify whether there is kernel state for this
904 * futex. If not, we can safely assume, that the 0 ->
905 * TID transition is correct. If state exists, we do
906 * not bother to fixup the user space state as it was
909 return futex_top_waiter(hb, key) ? -EINVAL : 1;
915 * Set the FUTEX_WAITERS flag, so the owner will know it has someone
916 * to wake at the next unlock.
918 newval = curval | FUTEX_WAITERS;
921 * Should we force take the futex? See below.
923 if (unlikely(force_take)) {
925 * Keep the OWNER_DIED and the WAITERS bit and set the
928 newval = (curval & ~FUTEX_TID_MASK) | vpid;
933 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
935 if (unlikely(curval != uval))
939 * We took the lock due to forced take over.
941 if (unlikely(lock_taken))
945 * We dont have the lock. Look up the PI state (or create it if
946 * we are the first waiter):
948 ret = lookup_pi_state(uval, hb, key, ps, task);
954 * We failed to find an owner for this
955 * futex. So we have no pi_state to block
956 * on. This can happen in two cases:
959 * 2) A stale FUTEX_WAITERS bit
961 * Re-read the futex value.
963 if (get_futex_value_locked(&curval, uaddr))
967 * If the owner died or we have a stale
968 * WAITERS bit the owner TID in the user space
971 if (!(curval & FUTEX_TID_MASK)) {
984 * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
985 * @q: The futex_q to unqueue
987 * The q->lock_ptr must not be NULL and must be held by the caller.
989 static void __unqueue_futex(struct futex_q *q)
991 struct futex_hash_bucket *hb;
993 if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
994 || WARN_ON(plist_node_empty(&q->list)))
997 hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
998 plist_del(&q->list, &hb->chain);
1003 * The hash bucket lock must be held when this is called.
1004 * Afterwards, the futex_q must not be accessed.
1006 static void wake_futex(struct futex_q *q)
1008 struct task_struct *p = q->task;
1010 if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
1014 * We set q->lock_ptr = NULL _before_ we wake up the task. If
1015 * a non-futex wake up happens on another CPU then the task
1016 * might exit and p would dereference a non-existing task
1017 * struct. Prevent this by holding a reference on p across the
1024 * The waiting task can free the futex_q as soon as
1025 * q->lock_ptr = NULL is written, without taking any locks. A
1026 * memory barrier is required here to prevent the following
1027 * store to lock_ptr from getting ahead of the plist_del.
1032 wake_up_state(p, TASK_NORMAL);
1036 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
1038 struct task_struct *new_owner;
1039 struct futex_pi_state *pi_state = this->pi_state;
1040 u32 uninitialized_var(curval), newval;
1046 * If current does not own the pi_state then the futex is
1047 * inconsistent and user space fiddled with the futex value.
1049 if (pi_state->owner != current)
1052 raw_spin_lock(&pi_state->pi_mutex.wait_lock);
1053 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
1056 * It is possible that the next waiter (the one that brought
1057 * this owner to the kernel) timed out and is no longer
1058 * waiting on the lock.
1061 new_owner = this->task;
1064 * We pass it to the next owner. (The WAITERS bit is always
1065 * kept enabled while there is PI state around. We must also
1066 * preserve the owner died bit.)
1068 if (!(uval & FUTEX_OWNER_DIED)) {
1071 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
1073 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
1075 else if (curval != uval)
1078 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
1083 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1084 WARN_ON(list_empty(&pi_state->list));
1085 list_del_init(&pi_state->list);
1086 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1088 raw_spin_lock_irq(&new_owner->pi_lock);
1089 WARN_ON(!list_empty(&pi_state->list));
1090 list_add(&pi_state->list, &new_owner->pi_state_list);
1091 pi_state->owner = new_owner;
1092 raw_spin_unlock_irq(&new_owner->pi_lock);
1094 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
1095 rt_mutex_unlock(&pi_state->pi_mutex);
1100 static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
1102 u32 uninitialized_var(oldval);
1105 * There is no waiter, so we unlock the futex. The owner died
1106 * bit has not to be preserved here. We are the owner:
1108 if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0))
1117 * Express the locking dependencies for lockdep:
1120 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1123 spin_lock(&hb1->lock);
1125 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
1126 } else { /* hb1 > hb2 */
1127 spin_lock(&hb2->lock);
1128 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
1133 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1135 spin_unlock(&hb1->lock);
1137 spin_unlock(&hb2->lock);
1141 * Wake up waiters matching bitset queued on this futex (uaddr).
1144 futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
1146 struct futex_hash_bucket *hb;
1147 struct futex_q *this, *next;
1148 union futex_key key = FUTEX_KEY_INIT;
1154 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
1155 if (unlikely(ret != 0))
1158 hb = hash_futex(&key);
1160 /* Make sure we really have tasks to wakeup */
1161 if (!hb_waiters_pending(hb))
1164 spin_lock(&hb->lock);
1166 plist_for_each_entry_safe(this, next, &hb->chain, list) {
1167 if (match_futex (&this->key, &key)) {
1168 if (this->pi_state || this->rt_waiter) {
1173 /* Check if one of the bits is set in both bitsets */
1174 if (!(this->bitset & bitset))
1178 if (++ret >= nr_wake)
1183 spin_unlock(&hb->lock);
1185 put_futex_key(&key);
1191 * Wake up all waiters hashed on the physical page that is mapped
1192 * to this virtual address:
1195 futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
1196 int nr_wake, int nr_wake2, int op)
1198 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1199 struct futex_hash_bucket *hb1, *hb2;
1200 struct futex_q *this, *next;
1204 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1205 if (unlikely(ret != 0))
1207 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
1208 if (unlikely(ret != 0))
1211 hb1 = hash_futex(&key1);
1212 hb2 = hash_futex(&key2);
1215 double_lock_hb(hb1, hb2);
1216 op_ret = futex_atomic_op_inuser(op, uaddr2);
1217 if (unlikely(op_ret < 0)) {
1219 double_unlock_hb(hb1, hb2);
1223 * we don't get EFAULT from MMU faults if we don't have an MMU,
1224 * but we might get them from range checking
1230 if (unlikely(op_ret != -EFAULT)) {
1235 ret = fault_in_user_writeable(uaddr2);
1239 if (!(flags & FLAGS_SHARED))
1242 put_futex_key(&key2);
1243 put_futex_key(&key1);
1247 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1248 if (match_futex (&this->key, &key1)) {
1249 if (this->pi_state || this->rt_waiter) {
1254 if (++ret >= nr_wake)
1261 plist_for_each_entry_safe(this, next, &hb2->chain, list) {
1262 if (match_futex (&this->key, &key2)) {
1263 if (this->pi_state || this->rt_waiter) {
1268 if (++op_ret >= nr_wake2)
1276 double_unlock_hb(hb1, hb2);
1278 put_futex_key(&key2);
1280 put_futex_key(&key1);
1286 * requeue_futex() - Requeue a futex_q from one hb to another
1287 * @q: the futex_q to requeue
1288 * @hb1: the source hash_bucket
1289 * @hb2: the target hash_bucket
1290 * @key2: the new key for the requeued futex_q
1293 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1294 struct futex_hash_bucket *hb2, union futex_key *key2)
1298 * If key1 and key2 hash to the same bucket, no need to
1301 if (likely(&hb1->chain != &hb2->chain)) {
1302 plist_del(&q->list, &hb1->chain);
1303 hb_waiters_dec(hb1);
1304 plist_add(&q->list, &hb2->chain);
1305 hb_waiters_inc(hb2);
1306 q->lock_ptr = &hb2->lock;
1308 get_futex_key_refs(key2);
1313 * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1315 * @key: the key of the requeue target futex
1316 * @hb: the hash_bucket of the requeue target futex
1318 * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1319 * target futex if it is uncontended or via a lock steal. Set the futex_q key
1320 * to the requeue target futex so the waiter can detect the wakeup on the right
1321 * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1322 * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
1323 * to protect access to the pi_state to fixup the owner later. Must be called
1324 * with both q->lock_ptr and hb->lock held.
1327 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1328 struct futex_hash_bucket *hb)
1330 get_futex_key_refs(key);
1335 WARN_ON(!q->rt_waiter);
1336 q->rt_waiter = NULL;
1338 q->lock_ptr = &hb->lock;
1340 wake_up_state(q->task, TASK_NORMAL);
1344 * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1345 * @pifutex: the user address of the to futex
1346 * @hb1: the from futex hash bucket, must be locked by the caller
1347 * @hb2: the to futex hash bucket, must be locked by the caller
1348 * @key1: the from futex key
1349 * @key2: the to futex key
1350 * @ps: address to store the pi_state pointer
1351 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1353 * Try and get the lock on behalf of the top waiter if we can do it atomically.
1354 * Wake the top waiter if we succeed. If the caller specified set_waiters,
1355 * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1356 * hb1 and hb2 must be held by the caller.
1359 * 0 - failed to acquire the lock atomically;
1360 * >0 - acquired the lock, return value is vpid of the top_waiter
1363 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1364 struct futex_hash_bucket *hb1,
1365 struct futex_hash_bucket *hb2,
1366 union futex_key *key1, union futex_key *key2,
1367 struct futex_pi_state **ps, int set_waiters)
1369 struct futex_q *top_waiter = NULL;
1373 if (get_futex_value_locked(&curval, pifutex))
1377 * Find the top_waiter and determine if there are additional waiters.
1378 * If the caller intends to requeue more than 1 waiter to pifutex,
1379 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1380 * as we have means to handle the possible fault. If not, don't set
1381 * the bit unecessarily as it will force the subsequent unlock to enter
1384 top_waiter = futex_top_waiter(hb1, key1);
1386 /* There are no waiters, nothing for us to do. */
1390 /* Ensure we requeue to the expected futex. */
1391 if (!match_futex(top_waiter->requeue_pi_key, key2))
1395 * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
1396 * the contended case or if set_waiters is 1. The pi_state is returned
1397 * in ps in contended cases.
1399 vpid = task_pid_vnr(top_waiter->task);
1400 ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1403 requeue_pi_wake_futex(top_waiter, key2, hb2);
1410 * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1411 * @uaddr1: source futex user address
1412 * @flags: futex flags (FLAGS_SHARED, etc.)
1413 * @uaddr2: target futex user address
1414 * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
1415 * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1416 * @cmpval: @uaddr1 expected value (or %NULL)
1417 * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1418 * pi futex (pi to pi requeue is not supported)
1420 * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1421 * uaddr2 atomically on behalf of the top waiter.
1424 * >=0 - on success, the number of tasks requeued or woken;
1427 static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1428 u32 __user *uaddr2, int nr_wake, int nr_requeue,
1429 u32 *cmpval, int requeue_pi)
1431 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1432 int drop_count = 0, task_count = 0, ret;
1433 struct futex_pi_state *pi_state = NULL;
1434 struct futex_hash_bucket *hb1, *hb2;
1435 struct futex_q *this, *next;
1439 * Requeue PI only works on two distinct uaddrs. This
1440 * check is only valid for private futexes. See below.
1442 if (uaddr1 == uaddr2)
1446 * requeue_pi requires a pi_state, try to allocate it now
1447 * without any locks in case it fails.
1449 if (refill_pi_state_cache())
1452 * requeue_pi must wake as many tasks as it can, up to nr_wake
1453 * + nr_requeue, since it acquires the rt_mutex prior to
1454 * returning to userspace, so as to not leave the rt_mutex with
1455 * waiters and no owner. However, second and third wake-ups
1456 * cannot be predicted as they involve race conditions with the
1457 * first wake and a fault while looking up the pi_state. Both
1458 * pthread_cond_signal() and pthread_cond_broadcast() should
1466 if (pi_state != NULL) {
1468 * We will have to lookup the pi_state again, so free this one
1469 * to keep the accounting correct.
1471 free_pi_state(pi_state);
1475 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1476 if (unlikely(ret != 0))
1478 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
1479 requeue_pi ? VERIFY_WRITE : VERIFY_READ);
1480 if (unlikely(ret != 0))
1484 * The check above which compares uaddrs is not sufficient for
1485 * shared futexes. We need to compare the keys:
1487 if (requeue_pi && match_futex(&key1, &key2)) {
1492 hb1 = hash_futex(&key1);
1493 hb2 = hash_futex(&key2);
1496 hb_waiters_inc(hb2);
1497 double_lock_hb(hb1, hb2);
1499 if (likely(cmpval != NULL)) {
1502 ret = get_futex_value_locked(&curval, uaddr1);
1504 if (unlikely(ret)) {
1505 double_unlock_hb(hb1, hb2);
1506 hb_waiters_dec(hb2);
1508 ret = get_user(curval, uaddr1);
1512 if (!(flags & FLAGS_SHARED))
1515 put_futex_key(&key2);
1516 put_futex_key(&key1);
1519 if (curval != *cmpval) {
1525 if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1527 * Attempt to acquire uaddr2 and wake the top waiter. If we
1528 * intend to requeue waiters, force setting the FUTEX_WAITERS
1529 * bit. We force this here where we are able to easily handle
1530 * faults rather in the requeue loop below.
1532 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1533 &key2, &pi_state, nr_requeue);
1536 * At this point the top_waiter has either taken uaddr2 or is
1537 * waiting on it. If the former, then the pi_state will not
1538 * exist yet, look it up one more time to ensure we have a
1539 * reference to it. If the lock was taken, ret contains the
1540 * vpid of the top waiter task.
1547 * If we acquired the lock, then the user
1548 * space value of uaddr2 should be vpid. It
1549 * cannot be changed by the top waiter as it
1550 * is blocked on hb2 lock if it tries to do
1551 * so. If something fiddled with it behind our
1552 * back the pi state lookup might unearth
1553 * it. So we rather use the known value than
1554 * rereading and handing potential crap to
1557 ret = lookup_pi_state(ret, hb2, &key2, &pi_state, NULL);
1564 double_unlock_hb(hb1, hb2);
1565 hb_waiters_dec(hb2);
1566 put_futex_key(&key2);
1567 put_futex_key(&key1);
1568 ret = fault_in_user_writeable(uaddr2);
1573 /* The owner was exiting, try again. */
1574 double_unlock_hb(hb1, hb2);
1575 hb_waiters_dec(hb2);
1576 put_futex_key(&key2);
1577 put_futex_key(&key1);
1585 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1586 if (task_count - nr_wake >= nr_requeue)
1589 if (!match_futex(&this->key, &key1))
1593 * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1594 * be paired with each other and no other futex ops.
1596 * We should never be requeueing a futex_q with a pi_state,
1597 * which is awaiting a futex_unlock_pi().
1599 if ((requeue_pi && !this->rt_waiter) ||
1600 (!requeue_pi && this->rt_waiter) ||
1607 * Wake nr_wake waiters. For requeue_pi, if we acquired the
1608 * lock, we already woke the top_waiter. If not, it will be
1609 * woken by futex_unlock_pi().
1611 if (++task_count <= nr_wake && !requeue_pi) {
1616 /* Ensure we requeue to the expected futex for requeue_pi. */
1617 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1623 * Requeue nr_requeue waiters and possibly one more in the case
1624 * of requeue_pi if we couldn't acquire the lock atomically.
1627 /* Prepare the waiter to take the rt_mutex. */
1628 atomic_inc(&pi_state->refcount);
1629 this->pi_state = pi_state;
1630 ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1634 /* We got the lock. */
1635 requeue_pi_wake_futex(this, &key2, hb2);
1640 this->pi_state = NULL;
1641 free_pi_state(pi_state);
1645 requeue_futex(this, hb1, hb2, &key2);
1650 double_unlock_hb(hb1, hb2);
1651 hb_waiters_dec(hb2);
1654 * drop_futex_key_refs() must be called outside the spinlocks. During
1655 * the requeue we moved futex_q's from the hash bucket at key1 to the
1656 * one at key2 and updated their key pointer. We no longer need to
1657 * hold the references to key1.
1659 while (--drop_count >= 0)
1660 drop_futex_key_refs(&key1);
1663 put_futex_key(&key2);
1665 put_futex_key(&key1);
1667 if (pi_state != NULL)
1668 free_pi_state(pi_state);
1669 return ret ? ret : task_count;
1672 /* The key must be already stored in q->key. */
1673 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
1674 __acquires(&hb->lock)
1676 struct futex_hash_bucket *hb;
1678 hb = hash_futex(&q->key);
1681 * Increment the counter before taking the lock so that
1682 * a potential waker won't miss a to-be-slept task that is
1683 * waiting for the spinlock. This is safe as all queue_lock()
1684 * users end up calling queue_me(). Similarly, for housekeeping,
1685 * decrement the counter at queue_unlock() when some error has
1686 * occurred and we don't end up adding the task to the list.
1690 q->lock_ptr = &hb->lock;
1692 spin_lock(&hb->lock); /* implies MB (A) */
1697 queue_unlock(struct futex_hash_bucket *hb)
1698 __releases(&hb->lock)
1700 spin_unlock(&hb->lock);
1705 * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1706 * @q: The futex_q to enqueue
1707 * @hb: The destination hash bucket
1709 * The hb->lock must be held by the caller, and is released here. A call to
1710 * queue_me() is typically paired with exactly one call to unqueue_me(). The
1711 * exceptions involve the PI related operations, which may use unqueue_me_pi()
1712 * or nothing if the unqueue is done as part of the wake process and the unqueue
1713 * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1716 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1717 __releases(&hb->lock)
1722 * The priority used to register this element is
1723 * - either the real thread-priority for the real-time threads
1724 * (i.e. threads with a priority lower than MAX_RT_PRIO)
1725 * - or MAX_RT_PRIO for non-RT threads.
1726 * Thus, all RT-threads are woken first in priority order, and
1727 * the others are woken last, in FIFO order.
1729 prio = min(current->normal_prio, MAX_RT_PRIO);
1731 plist_node_init(&q->list, prio);
1732 plist_add(&q->list, &hb->chain);
1734 spin_unlock(&hb->lock);
1738 * unqueue_me() - Remove the futex_q from its futex_hash_bucket
1739 * @q: The futex_q to unqueue
1741 * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
1742 * be paired with exactly one earlier call to queue_me().
1745 * 1 - if the futex_q was still queued (and we removed unqueued it);
1746 * 0 - if the futex_q was already removed by the waking thread
1748 static int unqueue_me(struct futex_q *q)
1750 spinlock_t *lock_ptr;
1753 /* In the common case we don't take the spinlock, which is nice. */
1755 lock_ptr = q->lock_ptr;
1757 if (lock_ptr != NULL) {
1758 spin_lock(lock_ptr);
1760 * q->lock_ptr can change between reading it and
1761 * spin_lock(), causing us to take the wrong lock. This
1762 * corrects the race condition.
1764 * Reasoning goes like this: if we have the wrong lock,
1765 * q->lock_ptr must have changed (maybe several times)
1766 * between reading it and the spin_lock(). It can
1767 * change again after the spin_lock() but only if it was
1768 * already changed before the spin_lock(). It cannot,
1769 * however, change back to the original value. Therefore
1770 * we can detect whether we acquired the correct lock.
1772 if (unlikely(lock_ptr != q->lock_ptr)) {
1773 spin_unlock(lock_ptr);
1778 BUG_ON(q->pi_state);
1780 spin_unlock(lock_ptr);
1784 drop_futex_key_refs(&q->key);
1789 * PI futexes can not be requeued and must remove themself from the
1790 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1793 static void unqueue_me_pi(struct futex_q *q)
1794 __releases(q->lock_ptr)
1798 BUG_ON(!q->pi_state);
1799 free_pi_state(q->pi_state);
1802 spin_unlock(q->lock_ptr);
1806 * Fixup the pi_state owner with the new owner.
1808 * Must be called with hash bucket lock held and mm->sem held for non
1811 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1812 struct task_struct *newowner)
1814 u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
1815 struct futex_pi_state *pi_state = q->pi_state;
1816 struct task_struct *oldowner = pi_state->owner;
1817 u32 uval, uninitialized_var(curval), newval;
1821 if (!pi_state->owner)
1822 newtid |= FUTEX_OWNER_DIED;
1825 * We are here either because we stole the rtmutex from the
1826 * previous highest priority waiter or we are the highest priority
1827 * waiter but failed to get the rtmutex the first time.
1828 * We have to replace the newowner TID in the user space variable.
1829 * This must be atomic as we have to preserve the owner died bit here.
1831 * Note: We write the user space value _before_ changing the pi_state
1832 * because we can fault here. Imagine swapped out pages or a fork
1833 * that marked all the anonymous memory readonly for cow.
1835 * Modifying pi_state _before_ the user space value would
1836 * leave the pi_state in an inconsistent state when we fault
1837 * here, because we need to drop the hash bucket lock to
1838 * handle the fault. This might be observed in the PID check
1839 * in lookup_pi_state.
1842 if (get_futex_value_locked(&uval, uaddr))
1846 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1848 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
1856 * We fixed up user space. Now we need to fix the pi_state
1859 if (pi_state->owner != NULL) {
1860 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1861 WARN_ON(list_empty(&pi_state->list));
1862 list_del_init(&pi_state->list);
1863 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1866 pi_state->owner = newowner;
1868 raw_spin_lock_irq(&newowner->pi_lock);
1869 WARN_ON(!list_empty(&pi_state->list));
1870 list_add(&pi_state->list, &newowner->pi_state_list);
1871 raw_spin_unlock_irq(&newowner->pi_lock);
1875 * To handle the page fault we need to drop the hash bucket
1876 * lock here. That gives the other task (either the highest priority
1877 * waiter itself or the task which stole the rtmutex) the
1878 * chance to try the fixup of the pi_state. So once we are
1879 * back from handling the fault we need to check the pi_state
1880 * after reacquiring the hash bucket lock and before trying to
1881 * do another fixup. When the fixup has been done already we
1885 spin_unlock(q->lock_ptr);
1887 ret = fault_in_user_writeable(uaddr);
1889 spin_lock(q->lock_ptr);
1892 * Check if someone else fixed it for us:
1894 if (pi_state->owner != oldowner)
1903 static long futex_wait_restart(struct restart_block *restart);
1906 * fixup_owner() - Post lock pi_state and corner case management
1907 * @uaddr: user address of the futex
1908 * @q: futex_q (contains pi_state and access to the rt_mutex)
1909 * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
1911 * After attempting to lock an rt_mutex, this function is called to cleanup
1912 * the pi_state owner as well as handle race conditions that may allow us to
1913 * acquire the lock. Must be called with the hb lock held.
1916 * 1 - success, lock taken;
1917 * 0 - success, lock not taken;
1918 * <0 - on error (-EFAULT)
1920 static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
1922 struct task_struct *owner;
1927 * Got the lock. We might not be the anticipated owner if we
1928 * did a lock-steal - fix up the PI-state in that case:
1930 if (q->pi_state->owner != current)
1931 ret = fixup_pi_state_owner(uaddr, q, current);
1936 * Catch the rare case, where the lock was released when we were on the
1937 * way back before we locked the hash bucket.
1939 if (q->pi_state->owner == current) {
1941 * Try to get the rt_mutex now. This might fail as some other
1942 * task acquired the rt_mutex after we removed ourself from the
1943 * rt_mutex waiters list.
1945 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
1951 * pi_state is incorrect, some other task did a lock steal and
1952 * we returned due to timeout or signal without taking the
1953 * rt_mutex. Too late.
1955 raw_spin_lock(&q->pi_state->pi_mutex.wait_lock);
1956 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
1958 owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
1959 raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock);
1960 ret = fixup_pi_state_owner(uaddr, q, owner);
1965 * Paranoia check. If we did not take the lock, then we should not be
1966 * the owner of the rt_mutex.
1968 if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
1969 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
1970 "pi-state %p\n", ret,
1971 q->pi_state->pi_mutex.owner,
1972 q->pi_state->owner);
1975 return ret ? ret : locked;
1979 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
1980 * @hb: the futex hash bucket, must be locked by the caller
1981 * @q: the futex_q to queue up on
1982 * @timeout: the prepared hrtimer_sleeper, or null for no timeout
1984 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
1985 struct hrtimer_sleeper *timeout)
1988 * The task state is guaranteed to be set before another task can
1989 * wake it. set_current_state() is implemented using set_mb() and
1990 * queue_me() calls spin_unlock() upon completion, both serializing
1991 * access to the hash list and forcing another memory barrier.
1993 set_current_state(TASK_INTERRUPTIBLE);
1998 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1999 if (!hrtimer_active(&timeout->timer))
2000 timeout->task = NULL;
2004 * If we have been removed from the hash list, then another task
2005 * has tried to wake us, and we can skip the call to schedule().
2007 if (likely(!plist_node_empty(&q->list))) {
2009 * If the timer has already expired, current will already be
2010 * flagged for rescheduling. Only call schedule if there
2011 * is no timeout, or if it has yet to expire.
2013 if (!timeout || timeout->task)
2014 freezable_schedule();
2016 __set_current_state(TASK_RUNNING);
2020 * futex_wait_setup() - Prepare to wait on a futex
2021 * @uaddr: the futex userspace address
2022 * @val: the expected value
2023 * @flags: futex flags (FLAGS_SHARED, etc.)
2024 * @q: the associated futex_q
2025 * @hb: storage for hash_bucket pointer to be returned to caller
2027 * Setup the futex_q and locate the hash_bucket. Get the futex value and
2028 * compare it with the expected value. Handle atomic faults internally.
2029 * Return with the hb lock held and a q.key reference on success, and unlocked
2030 * with no q.key reference on failure.
2033 * 0 - uaddr contains val and hb has been locked;
2034 * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
2036 static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
2037 struct futex_q *q, struct futex_hash_bucket **hb)
2043 * Access the page AFTER the hash-bucket is locked.
2044 * Order is important:
2046 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
2047 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
2049 * The basic logical guarantee of a futex is that it blocks ONLY
2050 * if cond(var) is known to be true at the time of blocking, for
2051 * any cond. If we locked the hash-bucket after testing *uaddr, that
2052 * would open a race condition where we could block indefinitely with
2053 * cond(var) false, which would violate the guarantee.
2055 * On the other hand, we insert q and release the hash-bucket only
2056 * after testing *uaddr. This guarantees that futex_wait() will NOT
2057 * absorb a wakeup if *uaddr does not match the desired values
2058 * while the syscall executes.
2061 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
2062 if (unlikely(ret != 0))
2066 *hb = queue_lock(q);
2068 ret = get_futex_value_locked(&uval, uaddr);
2073 ret = get_user(uval, uaddr);
2077 if (!(flags & FLAGS_SHARED))
2080 put_futex_key(&q->key);
2091 put_futex_key(&q->key);
2095 static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
2096 ktime_t *abs_time, u32 bitset)
2098 struct hrtimer_sleeper timeout, *to = NULL;
2099 struct restart_block *restart;
2100 struct futex_hash_bucket *hb;
2101 struct futex_q q = futex_q_init;
2111 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2112 CLOCK_REALTIME : CLOCK_MONOTONIC,
2114 hrtimer_init_sleeper(to, current);
2115 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2116 current->timer_slack_ns);
2121 * Prepare to wait on uaddr. On success, holds hb lock and increments
2124 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2128 /* queue_me and wait for wakeup, timeout, or a signal. */
2129 futex_wait_queue_me(hb, &q, to);
2131 /* If we were woken (and unqueued), we succeeded, whatever. */
2133 /* unqueue_me() drops q.key ref */
2134 if (!unqueue_me(&q))
2137 if (to && !to->task)
2141 * We expect signal_pending(current), but we might be the
2142 * victim of a spurious wakeup as well.
2144 if (!signal_pending(current))
2151 restart = ¤t_thread_info()->restart_block;
2152 restart->fn = futex_wait_restart;
2153 restart->futex.uaddr = uaddr;
2154 restart->futex.val = val;
2155 restart->futex.time = abs_time->tv64;
2156 restart->futex.bitset = bitset;
2157 restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
2159 ret = -ERESTART_RESTARTBLOCK;
2163 hrtimer_cancel(&to->timer);
2164 destroy_hrtimer_on_stack(&to->timer);
2170 static long futex_wait_restart(struct restart_block *restart)
2172 u32 __user *uaddr = restart->futex.uaddr;
2173 ktime_t t, *tp = NULL;
2175 if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
2176 t.tv64 = restart->futex.time;
2179 restart->fn = do_no_restart_syscall;
2181 return (long)futex_wait(uaddr, restart->futex.flags,
2182 restart->futex.val, tp, restart->futex.bitset);
2187 * Userspace tried a 0 -> TID atomic transition of the futex value
2188 * and failed. The kernel side here does the whole locking operation:
2189 * if there are waiters then it will block, it does PI, etc. (Due to
2190 * races the kernel might see a 0 value of the futex too.)
2192 static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect,
2193 ktime_t *time, int trylock)
2195 struct hrtimer_sleeper timeout, *to = NULL;
2196 struct futex_hash_bucket *hb;
2197 struct futex_q q = futex_q_init;
2200 if (refill_pi_state_cache())
2205 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
2207 hrtimer_init_sleeper(to, current);
2208 hrtimer_set_expires(&to->timer, *time);
2212 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
2213 if (unlikely(ret != 0))
2217 hb = queue_lock(&q);
2219 ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
2220 if (unlikely(ret)) {
2223 /* We got the lock. */
2225 goto out_unlock_put_key;
2230 * Task is exiting and we just wait for the
2234 put_futex_key(&q.key);
2238 goto out_unlock_put_key;
2243 * Only actually queue now that the atomic ops are done:
2247 WARN_ON(!q.pi_state);
2249 * Block on the PI mutex:
2252 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
2254 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
2255 /* Fixup the trylock return value: */
2256 ret = ret ? 0 : -EWOULDBLOCK;
2259 spin_lock(q.lock_ptr);
2261 * Fixup the pi_state owner and possibly acquire the lock if we
2264 res = fixup_owner(uaddr, &q, !ret);
2266 * If fixup_owner() returned an error, proprogate that. If it acquired
2267 * the lock, clear our -ETIMEDOUT or -EINTR.
2270 ret = (res < 0) ? res : 0;
2273 * If fixup_owner() faulted and was unable to handle the fault, unlock
2274 * it and return the fault to userspace.
2276 if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
2277 rt_mutex_unlock(&q.pi_state->pi_mutex);
2279 /* Unqueue and drop the lock */
2288 put_futex_key(&q.key);
2291 destroy_hrtimer_on_stack(&to->timer);
2292 return ret != -EINTR ? ret : -ERESTARTNOINTR;
2297 ret = fault_in_user_writeable(uaddr);
2301 if (!(flags & FLAGS_SHARED))
2304 put_futex_key(&q.key);
2309 * Userspace attempted a TID -> 0 atomic transition, and failed.
2310 * This is the in-kernel slowpath: we look up the PI state (if any),
2311 * and do the rt-mutex unlock.
2313 static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
2315 struct futex_hash_bucket *hb;
2316 struct futex_q *this, *next;
2317 union futex_key key = FUTEX_KEY_INIT;
2318 u32 uval, vpid = task_pid_vnr(current);
2322 if (get_user(uval, uaddr))
2325 * We release only a lock we actually own:
2327 if ((uval & FUTEX_TID_MASK) != vpid)
2330 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
2331 if (unlikely(ret != 0))
2334 hb = hash_futex(&key);
2335 spin_lock(&hb->lock);
2338 * To avoid races, try to do the TID -> 0 atomic transition
2339 * again. If it succeeds then we can return without waking
2342 if (!(uval & FUTEX_OWNER_DIED) &&
2343 cmpxchg_futex_value_locked(&uval, uaddr, vpid, 0))
2346 * Rare case: we managed to release the lock atomically,
2347 * no need to wake anyone else up:
2349 if (unlikely(uval == vpid))
2353 * Ok, other tasks may need to be woken up - check waiters
2354 * and do the wakeup if necessary:
2356 plist_for_each_entry_safe(this, next, &hb->chain, list) {
2357 if (!match_futex (&this->key, &key))
2359 ret = wake_futex_pi(uaddr, uval, this);
2361 * The atomic access to the futex value
2362 * generated a pagefault, so retry the
2363 * user-access and the wakeup:
2370 * No waiters - kernel unlocks the futex:
2372 if (!(uval & FUTEX_OWNER_DIED)) {
2373 ret = unlock_futex_pi(uaddr, uval);
2379 spin_unlock(&hb->lock);
2380 put_futex_key(&key);
2386 spin_unlock(&hb->lock);
2387 put_futex_key(&key);
2389 ret = fault_in_user_writeable(uaddr);
2397 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2398 * @hb: the hash_bucket futex_q was original enqueued on
2399 * @q: the futex_q woken while waiting to be requeued
2400 * @key2: the futex_key of the requeue target futex
2401 * @timeout: the timeout associated with the wait (NULL if none)
2403 * Detect if the task was woken on the initial futex as opposed to the requeue
2404 * target futex. If so, determine if it was a timeout or a signal that caused
2405 * the wakeup and return the appropriate error code to the caller. Must be
2406 * called with the hb lock held.
2409 * 0 = no early wakeup detected;
2410 * <0 = -ETIMEDOUT or -ERESTARTNOINTR
2413 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2414 struct futex_q *q, union futex_key *key2,
2415 struct hrtimer_sleeper *timeout)
2420 * With the hb lock held, we avoid races while we process the wakeup.
2421 * We only need to hold hb (and not hb2) to ensure atomicity as the
2422 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2423 * It can't be requeued from uaddr2 to something else since we don't
2424 * support a PI aware source futex for requeue.
2426 if (!match_futex(&q->key, key2)) {
2427 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2429 * We were woken prior to requeue by a timeout or a signal.
2430 * Unqueue the futex_q and determine which it was.
2432 plist_del(&q->list, &hb->chain);
2435 /* Handle spurious wakeups gracefully */
2437 if (timeout && !timeout->task)
2439 else if (signal_pending(current))
2440 ret = -ERESTARTNOINTR;
2446 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2447 * @uaddr: the futex we initially wait on (non-pi)
2448 * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
2449 * the same type, no requeueing from private to shared, etc.
2450 * @val: the expected value of uaddr
2451 * @abs_time: absolute timeout
2452 * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
2453 * @uaddr2: the pi futex we will take prior to returning to user-space
2455 * The caller will wait on uaddr and will be requeued by futex_requeue() to
2456 * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
2457 * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
2458 * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
2459 * without one, the pi logic would not know which task to boost/deboost, if
2460 * there was a need to.
2462 * We call schedule in futex_wait_queue_me() when we enqueue and return there
2463 * via the following--
2464 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2465 * 2) wakeup on uaddr2 after a requeue
2469 * If 3, cleanup and return -ERESTARTNOINTR.
2471 * If 2, we may then block on trying to take the rt_mutex and return via:
2472 * 5) successful lock
2475 * 8) other lock acquisition failure
2477 * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2479 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2485 static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
2486 u32 val, ktime_t *abs_time, u32 bitset,
2489 struct hrtimer_sleeper timeout, *to = NULL;
2490 struct rt_mutex_waiter rt_waiter;
2491 struct rt_mutex *pi_mutex = NULL;
2492 struct futex_hash_bucket *hb;
2493 union futex_key key2 = FUTEX_KEY_INIT;
2494 struct futex_q q = futex_q_init;
2497 if (uaddr == uaddr2)
2505 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2506 CLOCK_REALTIME : CLOCK_MONOTONIC,
2508 hrtimer_init_sleeper(to, current);
2509 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2510 current->timer_slack_ns);
2514 * The waiter is allocated on our stack, manipulated by the requeue
2515 * code while we sleep on uaddr.
2517 debug_rt_mutex_init_waiter(&rt_waiter);
2518 RB_CLEAR_NODE(&rt_waiter.pi_tree_entry);
2519 RB_CLEAR_NODE(&rt_waiter.tree_entry);
2520 rt_waiter.task = NULL;
2522 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
2523 if (unlikely(ret != 0))
2527 q.rt_waiter = &rt_waiter;
2528 q.requeue_pi_key = &key2;
2531 * Prepare to wait on uaddr. On success, increments q.key (key1) ref
2534 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2539 * The check above which compares uaddrs is not sufficient for
2540 * shared futexes. We need to compare the keys:
2542 if (match_futex(&q.key, &key2)) {
2547 /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2548 futex_wait_queue_me(hb, &q, to);
2550 spin_lock(&hb->lock);
2551 ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2552 spin_unlock(&hb->lock);
2557 * In order for us to be here, we know our q.key == key2, and since
2558 * we took the hb->lock above, we also know that futex_requeue() has
2559 * completed and we no longer have to concern ourselves with a wakeup
2560 * race with the atomic proxy lock acquisition by the requeue code. The
2561 * futex_requeue dropped our key1 reference and incremented our key2
2565 /* Check if the requeue code acquired the second futex for us. */
2568 * Got the lock. We might not be the anticipated owner if we
2569 * did a lock-steal - fix up the PI-state in that case.
2571 if (q.pi_state && (q.pi_state->owner != current)) {
2572 spin_lock(q.lock_ptr);
2573 ret = fixup_pi_state_owner(uaddr2, &q, current);
2574 spin_unlock(q.lock_ptr);
2578 * We have been woken up by futex_unlock_pi(), a timeout, or a
2579 * signal. futex_unlock_pi() will not destroy the lock_ptr nor
2582 WARN_ON(!q.pi_state);
2583 pi_mutex = &q.pi_state->pi_mutex;
2584 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
2585 debug_rt_mutex_free_waiter(&rt_waiter);
2587 spin_lock(q.lock_ptr);
2589 * Fixup the pi_state owner and possibly acquire the lock if we
2592 res = fixup_owner(uaddr2, &q, !ret);
2594 * If fixup_owner() returned an error, proprogate that. If it
2595 * acquired the lock, clear -ETIMEDOUT or -EINTR.
2598 ret = (res < 0) ? res : 0;
2600 /* Unqueue and drop the lock. */
2605 * If fixup_pi_state_owner() faulted and was unable to handle the
2606 * fault, unlock the rt_mutex and return the fault to userspace.
2608 if (ret == -EFAULT) {
2609 if (pi_mutex && rt_mutex_owner(pi_mutex) == current)
2610 rt_mutex_unlock(pi_mutex);
2611 } else if (ret == -EINTR) {
2613 * We've already been requeued, but cannot restart by calling
2614 * futex_lock_pi() directly. We could restart this syscall, but
2615 * it would detect that the user space "val" changed and return
2616 * -EWOULDBLOCK. Save the overhead of the restart and return
2617 * -EWOULDBLOCK directly.
2623 put_futex_key(&q.key);
2625 put_futex_key(&key2);
2629 hrtimer_cancel(&to->timer);
2630 destroy_hrtimer_on_stack(&to->timer);
2636 * Support for robust futexes: the kernel cleans up held futexes at
2639 * Implementation: user-space maintains a per-thread list of locks it
2640 * is holding. Upon do_exit(), the kernel carefully walks this list,
2641 * and marks all locks that are owned by this thread with the
2642 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2643 * always manipulated with the lock held, so the list is private and
2644 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2645 * field, to allow the kernel to clean up if the thread dies after
2646 * acquiring the lock, but just before it could have added itself to
2647 * the list. There can only be one such pending lock.
2651 * sys_set_robust_list() - Set the robust-futex list head of a task
2652 * @head: pointer to the list-head
2653 * @len: length of the list-head, as userspace expects
2655 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2658 if (!futex_cmpxchg_enabled)
2661 * The kernel knows only one size for now:
2663 if (unlikely(len != sizeof(*head)))
2666 current->robust_list = head;
2672 * sys_get_robust_list() - Get the robust-futex list head of a task
2673 * @pid: pid of the process [zero for current task]
2674 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
2675 * @len_ptr: pointer to a length field, the kernel fills in the header size
2677 SYSCALL_DEFINE3(get_robust_list, int, pid,
2678 struct robust_list_head __user * __user *, head_ptr,
2679 size_t __user *, len_ptr)
2681 struct robust_list_head __user *head;
2683 struct task_struct *p;
2685 if (!futex_cmpxchg_enabled)
2694 p = find_task_by_vpid(pid);
2700 if (!ptrace_may_access(p, PTRACE_MODE_READ))
2703 head = p->robust_list;
2706 if (put_user(sizeof(*head), len_ptr))
2708 return put_user(head, head_ptr);
2717 * Process a futex-list entry, check whether it's owned by the
2718 * dying task, and do notification if so:
2720 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
2722 u32 uval, uninitialized_var(nval), mval;
2725 if (get_user(uval, uaddr))
2728 if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
2730 * Ok, this dying thread is truly holding a futex
2731 * of interest. Set the OWNER_DIED bit atomically
2732 * via cmpxchg, and if the value had FUTEX_WAITERS
2733 * set, wake up a waiter (if any). (We have to do a
2734 * futex_wake() even if OWNER_DIED is already set -
2735 * to handle the rare but possible case of recursive
2736 * thread-death.) The rest of the cleanup is done in
2739 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
2741 * We are not holding a lock here, but we want to have
2742 * the pagefault_disable/enable() protection because
2743 * we want to handle the fault gracefully. If the
2744 * access fails we try to fault in the futex with R/W
2745 * verification via get_user_pages. get_user() above
2746 * does not guarantee R/W access. If that fails we
2747 * give up and leave the futex locked.
2749 if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
2750 if (fault_in_user_writeable(uaddr))
2758 * Wake robust non-PI futexes here. The wakeup of
2759 * PI futexes happens in exit_pi_state():
2761 if (!pi && (uval & FUTEX_WAITERS))
2762 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
2768 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
2770 static inline int fetch_robust_entry(struct robust_list __user **entry,
2771 struct robust_list __user * __user *head,
2774 unsigned long uentry;
2776 if (get_user(uentry, (unsigned long __user *)head))
2779 *entry = (void __user *)(uentry & ~1UL);
2786 * Walk curr->robust_list (very carefully, it's a userspace list!)
2787 * and mark any locks found there dead, and notify any waiters.
2789 * We silently return on any sign of list-walking problem.
2791 void exit_robust_list(struct task_struct *curr)
2793 struct robust_list_head __user *head = curr->robust_list;
2794 struct robust_list __user *entry, *next_entry, *pending;
2795 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
2796 unsigned int uninitialized_var(next_pi);
2797 unsigned long futex_offset;
2800 if (!futex_cmpxchg_enabled)
2804 * Fetch the list head (which was registered earlier, via
2805 * sys_set_robust_list()):
2807 if (fetch_robust_entry(&entry, &head->list.next, &pi))
2810 * Fetch the relative futex offset:
2812 if (get_user(futex_offset, &head->futex_offset))
2815 * Fetch any possibly pending lock-add first, and handle it
2818 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
2821 next_entry = NULL; /* avoid warning with gcc */
2822 while (entry != &head->list) {
2824 * Fetch the next entry in the list before calling
2825 * handle_futex_death:
2827 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
2829 * A pending lock might already be on the list, so
2830 * don't process it twice:
2832 if (entry != pending)
2833 if (handle_futex_death((void __user *)entry + futex_offset,
2841 * Avoid excessively long or circular lists:
2850 handle_futex_death((void __user *)pending + futex_offset,
2854 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
2855 u32 __user *uaddr2, u32 val2, u32 val3)
2857 int cmd = op & FUTEX_CMD_MASK;
2858 unsigned int flags = 0;
2860 if (!(op & FUTEX_PRIVATE_FLAG))
2861 flags |= FLAGS_SHARED;
2863 if (op & FUTEX_CLOCK_REALTIME) {
2864 flags |= FLAGS_CLOCKRT;
2865 if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
2871 case FUTEX_UNLOCK_PI:
2872 case FUTEX_TRYLOCK_PI:
2873 case FUTEX_WAIT_REQUEUE_PI:
2874 case FUTEX_CMP_REQUEUE_PI:
2875 if (!futex_cmpxchg_enabled)
2881 val3 = FUTEX_BITSET_MATCH_ANY;
2882 case FUTEX_WAIT_BITSET:
2883 return futex_wait(uaddr, flags, val, timeout, val3);
2885 val3 = FUTEX_BITSET_MATCH_ANY;
2886 case FUTEX_WAKE_BITSET:
2887 return futex_wake(uaddr, flags, val, val3);
2889 return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
2890 case FUTEX_CMP_REQUEUE:
2891 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
2893 return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
2895 return futex_lock_pi(uaddr, flags, val, timeout, 0);
2896 case FUTEX_UNLOCK_PI:
2897 return futex_unlock_pi(uaddr, flags);
2898 case FUTEX_TRYLOCK_PI:
2899 return futex_lock_pi(uaddr, flags, 0, timeout, 1);
2900 case FUTEX_WAIT_REQUEUE_PI:
2901 val3 = FUTEX_BITSET_MATCH_ANY;
2902 return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
2904 case FUTEX_CMP_REQUEUE_PI:
2905 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
2911 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
2912 struct timespec __user *, utime, u32 __user *, uaddr2,
2916 ktime_t t, *tp = NULL;
2918 int cmd = op & FUTEX_CMD_MASK;
2920 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
2921 cmd == FUTEX_WAIT_BITSET ||
2922 cmd == FUTEX_WAIT_REQUEUE_PI)) {
2923 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
2925 if (!timespec_valid(&ts))
2928 t = timespec_to_ktime(ts);
2929 if (cmd == FUTEX_WAIT)
2930 t = ktime_add_safe(ktime_get(), t);
2934 * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
2935 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
2937 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
2938 cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
2939 val2 = (u32) (unsigned long) utime;
2941 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
2944 static void __init futex_detect_cmpxchg(void)
2946 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
2950 * This will fail and we want it. Some arch implementations do
2951 * runtime detection of the futex_atomic_cmpxchg_inatomic()
2952 * functionality. We want to know that before we call in any
2953 * of the complex code paths. Also we want to prevent
2954 * registration of robust lists in that case. NULL is
2955 * guaranteed to fault and we get -EFAULT on functional
2956 * implementation, the non-functional ones will return
2959 if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
2960 futex_cmpxchg_enabled = 1;
2964 static int __init futex_init(void)
2966 unsigned int futex_shift;
2969 #if CONFIG_BASE_SMALL
2970 futex_hashsize = 16;
2972 futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
2975 futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
2977 futex_hashsize < 256 ? HASH_SMALL : 0,
2979 futex_hashsize, futex_hashsize);
2980 futex_hashsize = 1UL << futex_shift;
2982 futex_detect_cmpxchg();
2984 for (i = 0; i < futex_hashsize; i++) {
2985 atomic_set(&futex_queues[i].waiters, 0);
2986 plist_head_init(&futex_queues[i].chain);
2987 spin_lock_init(&futex_queues[i].lock);
2992 __initcall(futex_init);