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 * READ this before attempting to hack on futexes!
75 * Basic futex operation and ordering guarantees
76 * =============================================
78 * The waiter reads the futex value in user space and calls
79 * futex_wait(). This function computes the hash bucket and acquires
80 * the hash bucket lock. After that it reads the futex user space value
81 * again and verifies that the data has not changed. If it has not changed
82 * it enqueues itself into the hash bucket, releases the hash bucket lock
85 * The waker side modifies the user space value of the futex and calls
86 * futex_wake(). This function computes the hash bucket and acquires the
87 * hash bucket lock. Then it looks for waiters on that futex in the hash
88 * bucket and wakes them.
90 * In futex wake up scenarios where no tasks are blocked on a futex, taking
91 * the hb spinlock can be avoided and simply return. In order for this
92 * optimization to work, ordering guarantees must exist so that the waiter
93 * being added to the list is acknowledged when the list is concurrently being
94 * checked by the waker, avoiding scenarios like the following:
98 * sys_futex(WAIT, futex, val);
99 * futex_wait(futex, val);
102 * sys_futex(WAKE, futex);
107 * lock(hash_bucket(futex));
109 * unlock(hash_bucket(futex));
112 * This would cause the waiter on CPU 0 to wait forever because it
113 * missed the transition of the user space value from val to newval
114 * and the waker did not find the waiter in the hash bucket queue.
116 * The correct serialization ensures that a waiter either observes
117 * the changed user space value before blocking or is woken by a
122 * sys_futex(WAIT, futex, val);
123 * futex_wait(futex, val);
126 * mb(); (A) <-- paired with -.
128 * lock(hash_bucket(futex)); |
132 * | sys_futex(WAKE, futex);
133 * | futex_wake(futex);
135 * `-------> mb(); (B)
138 * unlock(hash_bucket(futex));
139 * schedule(); if (waiters)
140 * lock(hash_bucket(futex));
141 * else wake_waiters(futex);
142 * waiters--; (b) unlock(hash_bucket(futex));
144 * Where (A) orders the waiters increment and the futex value read through
145 * atomic operations (see hb_waiters_inc) and where (B) orders the write
146 * to futex and the waiters read -- this is done by the barriers in
147 * get_futex_key_refs(), through either ihold or atomic_inc, depending on the
150 * This yields the following case (where X:=waiters, Y:=futex):
158 * Which guarantees that x==0 && y==0 is impossible; which translates back into
159 * the guarantee that we cannot both miss the futex variable change and the
162 * Note that a new waiter is accounted for in (a) even when it is possible that
163 * the wait call can return error, in which case we backtrack from it in (b).
164 * Refer to the comment in queue_lock().
166 * Similarly, in order to account for waiters being requeued on another
167 * address we always increment the waiters for the destination bucket before
168 * acquiring the lock. It then decrements them again after releasing it -
169 * the code that actually moves the futex(es) between hash buckets (requeue_futex)
170 * will do the additional required waiter count housekeeping. This is done for
171 * double_lock_hb() and double_unlock_hb(), respectively.
174 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
175 int __read_mostly futex_cmpxchg_enabled;
179 * Futex flags used to encode options to functions and preserve them across
182 #define FLAGS_SHARED 0x01
183 #define FLAGS_CLOCKRT 0x02
184 #define FLAGS_HAS_TIMEOUT 0x04
187 * Priority Inheritance state:
189 struct futex_pi_state {
191 * list of 'owned' pi_state instances - these have to be
192 * cleaned up in do_exit() if the task exits prematurely:
194 struct list_head list;
199 struct rt_mutex pi_mutex;
201 struct task_struct *owner;
208 * struct futex_q - The hashed futex queue entry, one per waiting task
209 * @list: priority-sorted list of tasks waiting on this futex
210 * @task: the task waiting on the futex
211 * @lock_ptr: the hash bucket lock
212 * @key: the key the futex is hashed on
213 * @pi_state: optional priority inheritance state
214 * @rt_waiter: rt_waiter storage for use with requeue_pi
215 * @requeue_pi_key: the requeue_pi target futex key
216 * @bitset: bitset for the optional bitmasked wakeup
218 * We use this hashed waitqueue, instead of a normal wait_queue_t, so
219 * we can wake only the relevant ones (hashed queues may be shared).
221 * A futex_q has a woken state, just like tasks have TASK_RUNNING.
222 * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
223 * The order of wakeup is always to make the first condition true, then
226 * PI futexes are typically woken before they are removed from the hash list via
227 * the rt_mutex code. See unqueue_me_pi().
230 struct plist_node list;
232 struct task_struct *task;
233 spinlock_t *lock_ptr;
235 struct futex_pi_state *pi_state;
236 struct rt_mutex_waiter *rt_waiter;
237 union futex_key *requeue_pi_key;
241 static const struct futex_q futex_q_init = {
242 /* list gets initialized in queue_me()*/
243 .key = FUTEX_KEY_INIT,
244 .bitset = FUTEX_BITSET_MATCH_ANY
248 * Hash buckets are shared by all the futex_keys that hash to the same
249 * location. Each key may have multiple futex_q structures, one for each task
250 * waiting on a futex.
252 struct futex_hash_bucket {
255 struct plist_head chain;
256 } ____cacheline_aligned_in_smp;
258 static unsigned long __read_mostly futex_hashsize;
260 static struct futex_hash_bucket *futex_queues;
262 static inline void futex_get_mm(union futex_key *key)
264 atomic_inc(&key->private.mm->mm_count);
266 * Ensure futex_get_mm() implies a full barrier such that
267 * get_futex_key() implies a full barrier. This is relied upon
268 * as full barrier (B), see the ordering comment above.
270 smp_mb__after_atomic();
274 * Reflects a new waiter being added to the waitqueue.
276 static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
279 atomic_inc(&hb->waiters);
281 * Full barrier (A), see the ordering comment above.
283 smp_mb__after_atomic();
288 * Reflects a waiter being removed from the waitqueue by wakeup
291 static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
294 atomic_dec(&hb->waiters);
298 static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
301 return atomic_read(&hb->waiters);
308 * We hash on the keys returned from get_futex_key (see below).
310 static struct futex_hash_bucket *hash_futex(union futex_key *key)
312 u32 hash = jhash2((u32*)&key->both.word,
313 (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
315 return &futex_queues[hash & (futex_hashsize - 1)];
319 * Return 1 if two futex_keys are equal, 0 otherwise.
321 static inline int match_futex(union futex_key *key1, union futex_key *key2)
324 && key1->both.word == key2->both.word
325 && key1->both.ptr == key2->both.ptr
326 && key1->both.offset == key2->both.offset);
330 * Take a reference to the resource addressed by a key.
331 * Can be called while holding spinlocks.
334 static void get_futex_key_refs(union futex_key *key)
339 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
341 ihold(key->shared.inode); /* implies MB (B) */
343 case FUT_OFF_MMSHARED:
344 futex_get_mm(key); /* implies MB (B) */
350 * Drop a reference to the resource addressed by a key.
351 * The hash bucket spinlock must not be held.
353 static void drop_futex_key_refs(union futex_key *key)
355 if (!key->both.ptr) {
356 /* If we're here then we tried to put a key we failed to get */
361 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
363 iput(key->shared.inode);
365 case FUT_OFF_MMSHARED:
366 mmdrop(key->private.mm);
372 * get_futex_key() - Get parameters which are the keys for a futex
373 * @uaddr: virtual address of the futex
374 * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
375 * @key: address where result is stored.
376 * @rw: mapping needs to be read/write (values: VERIFY_READ,
379 * Return: a negative error code or 0
381 * The key words are stored in *key on success.
383 * For shared mappings, it's (page->index, file_inode(vma->vm_file),
384 * offset_within_page). For private mappings, it's (uaddr, current->mm).
385 * We can usually work out the index without swapping in the page.
387 * lock_page() might sleep, the caller should not hold a spinlock.
390 get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
392 unsigned long address = (unsigned long)uaddr;
393 struct mm_struct *mm = current->mm;
394 struct page *page, *page_head;
398 * The futex address must be "naturally" aligned.
400 key->both.offset = address % PAGE_SIZE;
401 if (unlikely((address % sizeof(u32)) != 0))
403 address -= key->both.offset;
405 if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
409 * PROCESS_PRIVATE futexes are fast.
410 * As the mm cannot disappear under us and the 'key' only needs
411 * virtual address, we dont even have to find the underlying vma.
412 * Note : We do have to check 'uaddr' is a valid user address,
413 * but access_ok() should be faster than find_vma()
416 key->private.mm = mm;
417 key->private.address = address;
418 get_futex_key_refs(key); /* implies MB (B) */
423 err = get_user_pages_fast(address, 1, 1, &page);
425 * If write access is not required (eg. FUTEX_WAIT), try
426 * and get read-only access.
428 if (err == -EFAULT && rw == VERIFY_READ) {
429 err = get_user_pages_fast(address, 1, 0, &page);
437 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
439 if (unlikely(PageTail(page))) {
441 /* serialize against __split_huge_page_splitting() */
443 if (likely(__get_user_pages_fast(address, 1, !ro, &page) == 1)) {
444 page_head = compound_head(page);
446 * page_head is valid pointer but we must pin
447 * it before taking the PG_lock and/or
448 * PG_compound_lock. The moment we re-enable
449 * irqs __split_huge_page_splitting() can
450 * return and the head page can be freed from
451 * under us. We can't take the PG_lock and/or
452 * PG_compound_lock on a page that could be
453 * freed from under us.
455 if (page != page_head) {
466 page_head = compound_head(page);
467 if (page != page_head) {
473 lock_page(page_head);
476 * If page_head->mapping is NULL, then it cannot be a PageAnon
477 * page; but it might be the ZERO_PAGE or in the gate area or
478 * in a special mapping (all cases which we are happy to fail);
479 * or it may have been a good file page when get_user_pages_fast
480 * found it, but truncated or holepunched or subjected to
481 * invalidate_complete_page2 before we got the page lock (also
482 * cases which we are happy to fail). And we hold a reference,
483 * so refcount care in invalidate_complete_page's remove_mapping
484 * prevents drop_caches from setting mapping to NULL beneath us.
486 * The case we do have to guard against is when memory pressure made
487 * shmem_writepage move it from filecache to swapcache beneath us:
488 * an unlikely race, but we do need to retry for page_head->mapping.
490 if (!page_head->mapping) {
491 int shmem_swizzled = PageSwapCache(page_head);
492 unlock_page(page_head);
500 * Private mappings are handled in a simple way.
502 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
503 * it's a read-only handle, it's expected that futexes attach to
504 * the object not the particular process.
506 if (PageAnon(page_head)) {
508 * A RO anonymous page will never change and thus doesn't make
509 * sense for futex operations.
516 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
517 key->private.mm = mm;
518 key->private.address = address;
520 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
521 key->shared.inode = page_head->mapping->host;
522 key->shared.pgoff = basepage_index(page);
525 get_futex_key_refs(key); /* implies MB (B) */
528 unlock_page(page_head);
533 static inline void put_futex_key(union futex_key *key)
535 drop_futex_key_refs(key);
539 * fault_in_user_writeable() - Fault in user address and verify RW access
540 * @uaddr: pointer to faulting user space address
542 * Slow path to fixup the fault we just took in the atomic write
545 * We have no generic implementation of a non-destructive write to the
546 * user address. We know that we faulted in the atomic pagefault
547 * disabled section so we can as well avoid the #PF overhead by
548 * calling get_user_pages() right away.
550 static int fault_in_user_writeable(u32 __user *uaddr)
552 struct mm_struct *mm = current->mm;
555 down_read(&mm->mmap_sem);
556 ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
558 up_read(&mm->mmap_sem);
560 return ret < 0 ? ret : 0;
564 * futex_top_waiter() - Return the highest priority waiter on a futex
565 * @hb: the hash bucket the futex_q's reside in
566 * @key: the futex key (to distinguish it from other futex futex_q's)
568 * Must be called with the hb lock held.
570 static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
571 union futex_key *key)
573 struct futex_q *this;
575 plist_for_each_entry(this, &hb->chain, list) {
576 if (match_futex(&this->key, key))
582 static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
583 u32 uval, u32 newval)
588 ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
594 static int get_futex_value_locked(u32 *dest, u32 __user *from)
599 ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
602 return ret ? -EFAULT : 0;
609 static int refill_pi_state_cache(void)
611 struct futex_pi_state *pi_state;
613 if (likely(current->pi_state_cache))
616 pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
621 INIT_LIST_HEAD(&pi_state->list);
622 /* pi_mutex gets initialized later */
623 pi_state->owner = NULL;
624 atomic_set(&pi_state->refcount, 1);
625 pi_state->key = FUTEX_KEY_INIT;
627 current->pi_state_cache = pi_state;
632 static struct futex_pi_state * alloc_pi_state(void)
634 struct futex_pi_state *pi_state = current->pi_state_cache;
637 current->pi_state_cache = NULL;
642 static void free_pi_state(struct futex_pi_state *pi_state)
644 if (!atomic_dec_and_test(&pi_state->refcount))
648 * If pi_state->owner is NULL, the owner is most probably dying
649 * and has cleaned up the pi_state already
651 if (pi_state->owner) {
652 raw_spin_lock_irq(&pi_state->owner->pi_lock);
653 list_del_init(&pi_state->list);
654 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
656 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
659 if (current->pi_state_cache)
663 * pi_state->list is already empty.
664 * clear pi_state->owner.
665 * refcount is at 0 - put it back to 1.
667 pi_state->owner = NULL;
668 atomic_set(&pi_state->refcount, 1);
669 current->pi_state_cache = pi_state;
674 * Look up the task based on what TID userspace gave us.
677 static struct task_struct * futex_find_get_task(pid_t pid)
679 struct task_struct *p;
682 p = find_task_by_vpid(pid);
692 * This task is holding PI mutexes at exit time => bad.
693 * Kernel cleans up PI-state, but userspace is likely hosed.
694 * (Robust-futex cleanup is separate and might save the day for userspace.)
696 void exit_pi_state_list(struct task_struct *curr)
698 struct list_head *next, *head = &curr->pi_state_list;
699 struct futex_pi_state *pi_state;
700 struct futex_hash_bucket *hb;
701 union futex_key key = FUTEX_KEY_INIT;
703 if (!futex_cmpxchg_enabled)
706 * We are a ZOMBIE and nobody can enqueue itself on
707 * pi_state_list anymore, but we have to be careful
708 * versus waiters unqueueing themselves:
710 raw_spin_lock_irq(&curr->pi_lock);
711 while (!list_empty(head)) {
714 pi_state = list_entry(next, struct futex_pi_state, list);
716 hb = hash_futex(&key);
717 raw_spin_unlock_irq(&curr->pi_lock);
719 spin_lock(&hb->lock);
721 raw_spin_lock_irq(&curr->pi_lock);
723 * We dropped the pi-lock, so re-check whether this
724 * task still owns the PI-state:
726 if (head->next != next) {
727 spin_unlock(&hb->lock);
731 WARN_ON(pi_state->owner != curr);
732 WARN_ON(list_empty(&pi_state->list));
733 list_del_init(&pi_state->list);
734 pi_state->owner = NULL;
735 raw_spin_unlock_irq(&curr->pi_lock);
737 rt_mutex_unlock(&pi_state->pi_mutex);
739 spin_unlock(&hb->lock);
741 raw_spin_lock_irq(&curr->pi_lock);
743 raw_spin_unlock_irq(&curr->pi_lock);
747 * We need to check the following states:
749 * Waiter | pi_state | pi->owner | uTID | uODIED | ?
751 * [1] NULL | --- | --- | 0 | 0/1 | Valid
752 * [2] NULL | --- | --- | >0 | 0/1 | Valid
754 * [3] Found | NULL | -- | Any | 0/1 | Invalid
756 * [4] Found | Found | NULL | 0 | 1 | Valid
757 * [5] Found | Found | NULL | >0 | 1 | Invalid
759 * [6] Found | Found | task | 0 | 1 | Valid
761 * [7] Found | Found | NULL | Any | 0 | Invalid
763 * [8] Found | Found | task | ==taskTID | 0/1 | Valid
764 * [9] Found | Found | task | 0 | 0 | Invalid
765 * [10] Found | Found | task | !=taskTID | 0/1 | Invalid
767 * [1] Indicates that the kernel can acquire the futex atomically. We
768 * came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
770 * [2] Valid, if TID does not belong to a kernel thread. If no matching
771 * thread is found then it indicates that the owner TID has died.
773 * [3] Invalid. The waiter is queued on a non PI futex
775 * [4] Valid state after exit_robust_list(), which sets the user space
776 * value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
778 * [5] The user space value got manipulated between exit_robust_list()
779 * and exit_pi_state_list()
781 * [6] Valid state after exit_pi_state_list() which sets the new owner in
782 * the pi_state but cannot access the user space value.
784 * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
786 * [8] Owner and user space value match
788 * [9] There is no transient state which sets the user space TID to 0
789 * except exit_robust_list(), but this is indicated by the
790 * FUTEX_OWNER_DIED bit. See [4]
792 * [10] There is no transient state which leaves owner and user space
796 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
797 union futex_key *key, struct futex_pi_state **ps)
799 struct futex_pi_state *pi_state = NULL;
800 struct futex_q *this, *next;
801 struct task_struct *p;
802 pid_t pid = uval & FUTEX_TID_MASK;
804 plist_for_each_entry_safe(this, next, &hb->chain, list) {
805 if (match_futex(&this->key, key)) {
807 * Sanity check the waiter before increasing
808 * the refcount and attaching to it.
810 pi_state = this->pi_state;
812 * Userspace might have messed up non-PI and
815 if (unlikely(!pi_state))
818 WARN_ON(!atomic_read(&pi_state->refcount));
821 * Handle the owner died case:
823 if (uval & FUTEX_OWNER_DIED) {
825 * exit_pi_state_list sets owner to NULL and
826 * wakes the topmost waiter. The task which
827 * acquires the pi_state->rt_mutex will fixup
830 if (!pi_state->owner) {
832 * No pi state owner, but the user
833 * space TID is not 0. Inconsistent
839 * Take a ref on the state and
846 * If TID is 0, then either the dying owner
847 * has not yet executed exit_pi_state_list()
848 * or some waiter acquired the rtmutex in the
849 * pi state, but did not yet fixup the TID in
852 * Take a ref on the state and return. [6]
858 * If the owner died bit is not set,
859 * then the pi_state must have an
862 if (!pi_state->owner)
867 * Bail out if user space manipulated the
868 * futex value. If pi state exists then the
869 * owner TID must be the same as the user
872 if (pid != task_pid_vnr(pi_state->owner))
876 atomic_inc(&pi_state->refcount);
883 * We are the first waiter - try to look up the real owner and attach
884 * the new pi_state to it, but bail out when TID = 0 [1]
888 p = futex_find_get_task(pid);
898 * We need to look at the task state flags to figure out,
899 * whether the task is exiting. To protect against the do_exit
900 * change of the task flags, we do this protected by
903 raw_spin_lock_irq(&p->pi_lock);
904 if (unlikely(p->flags & PF_EXITING)) {
906 * The task is on the way out. When PF_EXITPIDONE is
907 * set, we know that the task has finished the
910 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
912 raw_spin_unlock_irq(&p->pi_lock);
918 * No existing pi state. First waiter. [2]
920 pi_state = alloc_pi_state();
923 * Initialize the pi_mutex in locked state and make 'p'
926 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
928 /* Store the key for possible exit cleanups: */
929 pi_state->key = *key;
931 WARN_ON(!list_empty(&pi_state->list));
932 list_add(&pi_state->list, &p->pi_state_list);
934 raw_spin_unlock_irq(&p->pi_lock);
944 * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
945 * @uaddr: the pi futex user address
946 * @hb: the pi futex hash bucket
947 * @key: the futex key associated with uaddr and hb
948 * @ps: the pi_state pointer where we store the result of the
950 * @task: the task to perform the atomic lock work for. This will
951 * be "current" except in the case of requeue pi.
952 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
956 * 1 - acquired the lock;
959 * The hb->lock and futex_key refs shall be held by the caller.
961 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
962 union futex_key *key,
963 struct futex_pi_state **ps,
964 struct task_struct *task, int set_waiters)
966 int lock_taken, ret, force_take = 0;
967 u32 uval, newval, curval, vpid = task_pid_vnr(task);
970 ret = lock_taken = 0;
973 * To avoid races, we attempt to take the lock here again
974 * (by doing a 0 -> TID atomic cmpxchg), while holding all
975 * the locks. It will most likely not succeed.
979 newval |= FUTEX_WAITERS;
981 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval)))
987 if ((unlikely((curval & FUTEX_TID_MASK) == vpid)))
991 * Surprise - we got the lock, but we do not trust user space at all.
993 if (unlikely(!curval)) {
995 * We verify whether there is kernel state for this
996 * futex. If not, we can safely assume, that the 0 ->
997 * TID transition is correct. If state exists, we do
998 * not bother to fixup the user space state as it was
1001 return futex_top_waiter(hb, key) ? -EINVAL : 1;
1007 * Set the FUTEX_WAITERS flag, so the owner will know it has someone
1008 * to wake at the next unlock.
1010 newval = curval | FUTEX_WAITERS;
1013 * Should we force take the futex? See below.
1015 if (unlikely(force_take)) {
1017 * Keep the OWNER_DIED and the WAITERS bit and set the
1020 newval = (curval & ~FUTEX_TID_MASK) | vpid;
1025 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
1027 if (unlikely(curval != uval))
1031 * We took the lock due to forced take over.
1033 if (unlikely(lock_taken))
1037 * We dont have the lock. Look up the PI state (or create it if
1038 * we are the first waiter):
1040 ret = lookup_pi_state(uval, hb, key, ps);
1042 if (unlikely(ret)) {
1046 * We failed to find an owner for this
1047 * futex. So we have no pi_state to block
1048 * on. This can happen in two cases:
1051 * 2) A stale FUTEX_WAITERS bit
1053 * Re-read the futex value.
1055 if (get_futex_value_locked(&curval, uaddr))
1059 * If the owner died or we have a stale
1060 * WAITERS bit the owner TID in the user space
1063 if (!(curval & FUTEX_TID_MASK)) {
1076 * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
1077 * @q: The futex_q to unqueue
1079 * The q->lock_ptr must not be NULL and must be held by the caller.
1081 static void __unqueue_futex(struct futex_q *q)
1083 struct futex_hash_bucket *hb;
1085 if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
1086 || WARN_ON(plist_node_empty(&q->list)))
1089 hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
1090 plist_del(&q->list, &hb->chain);
1095 * The hash bucket lock must be held when this is called.
1096 * Afterwards, the futex_q must not be accessed.
1098 static void wake_futex(struct futex_q *q)
1100 struct task_struct *p = q->task;
1102 if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
1106 * We set q->lock_ptr = NULL _before_ we wake up the task. If
1107 * a non-futex wake up happens on another CPU then the task
1108 * might exit and p would dereference a non-existing task
1109 * struct. Prevent this by holding a reference on p across the
1116 * The waiting task can free the futex_q as soon as
1117 * q->lock_ptr = NULL is written, without taking any locks. A
1118 * memory barrier is required here to prevent the following
1119 * store to lock_ptr from getting ahead of the plist_del.
1124 wake_up_state(p, TASK_NORMAL);
1128 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
1130 struct task_struct *new_owner;
1131 struct futex_pi_state *pi_state = this->pi_state;
1132 u32 uninitialized_var(curval), newval;
1139 * If current does not own the pi_state then the futex is
1140 * inconsistent and user space fiddled with the futex value.
1142 if (pi_state->owner != current)
1145 raw_spin_lock(&pi_state->pi_mutex.wait_lock);
1146 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
1149 * It is possible that the next waiter (the one that brought
1150 * this owner to the kernel) timed out and is no longer
1151 * waiting on the lock.
1154 new_owner = this->task;
1157 * We pass it to the next owner. The WAITERS bit is always
1158 * kept enabled while there is PI state around. We cleanup the
1159 * owner died bit, because we are the owner.
1161 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
1163 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
1165 else if (curval != uval)
1168 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
1172 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1173 WARN_ON(list_empty(&pi_state->list));
1174 list_del_init(&pi_state->list);
1175 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1177 raw_spin_lock_irq(&new_owner->pi_lock);
1178 WARN_ON(!list_empty(&pi_state->list));
1179 list_add(&pi_state->list, &new_owner->pi_state_list);
1180 pi_state->owner = new_owner;
1181 raw_spin_unlock_irq(&new_owner->pi_lock);
1183 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
1184 rt_mutex_unlock(&pi_state->pi_mutex);
1189 static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
1191 u32 uninitialized_var(oldval);
1194 * There is no waiter, so we unlock the futex. The owner died
1195 * bit has not to be preserved here. We are the owner:
1197 if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0))
1206 * Express the locking dependencies for lockdep:
1209 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1212 spin_lock(&hb1->lock);
1214 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
1215 } else { /* hb1 > hb2 */
1216 spin_lock(&hb2->lock);
1217 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
1222 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1224 spin_unlock(&hb1->lock);
1226 spin_unlock(&hb2->lock);
1230 * Wake up waiters matching bitset queued on this futex (uaddr).
1233 futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
1235 struct futex_hash_bucket *hb;
1236 struct futex_q *this, *next;
1237 union futex_key key = FUTEX_KEY_INIT;
1243 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
1244 if (unlikely(ret != 0))
1247 hb = hash_futex(&key);
1249 /* Make sure we really have tasks to wakeup */
1250 if (!hb_waiters_pending(hb))
1253 spin_lock(&hb->lock);
1255 plist_for_each_entry_safe(this, next, &hb->chain, list) {
1256 if (match_futex (&this->key, &key)) {
1257 if (this->pi_state || this->rt_waiter) {
1262 /* Check if one of the bits is set in both bitsets */
1263 if (!(this->bitset & bitset))
1267 if (++ret >= nr_wake)
1272 spin_unlock(&hb->lock);
1274 put_futex_key(&key);
1280 * Wake up all waiters hashed on the physical page that is mapped
1281 * to this virtual address:
1284 futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
1285 int nr_wake, int nr_wake2, int op)
1287 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1288 struct futex_hash_bucket *hb1, *hb2;
1289 struct futex_q *this, *next;
1293 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1294 if (unlikely(ret != 0))
1296 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
1297 if (unlikely(ret != 0))
1300 hb1 = hash_futex(&key1);
1301 hb2 = hash_futex(&key2);
1304 double_lock_hb(hb1, hb2);
1305 op_ret = futex_atomic_op_inuser(op, uaddr2);
1306 if (unlikely(op_ret < 0)) {
1308 double_unlock_hb(hb1, hb2);
1312 * we don't get EFAULT from MMU faults if we don't have an MMU,
1313 * but we might get them from range checking
1319 if (unlikely(op_ret != -EFAULT)) {
1324 ret = fault_in_user_writeable(uaddr2);
1328 if (!(flags & FLAGS_SHARED))
1331 put_futex_key(&key2);
1332 put_futex_key(&key1);
1336 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1337 if (match_futex (&this->key, &key1)) {
1338 if (this->pi_state || this->rt_waiter) {
1343 if (++ret >= nr_wake)
1350 plist_for_each_entry_safe(this, next, &hb2->chain, list) {
1351 if (match_futex (&this->key, &key2)) {
1352 if (this->pi_state || this->rt_waiter) {
1357 if (++op_ret >= nr_wake2)
1365 double_unlock_hb(hb1, hb2);
1367 put_futex_key(&key2);
1369 put_futex_key(&key1);
1375 * requeue_futex() - Requeue a futex_q from one hb to another
1376 * @q: the futex_q to requeue
1377 * @hb1: the source hash_bucket
1378 * @hb2: the target hash_bucket
1379 * @key2: the new key for the requeued futex_q
1382 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1383 struct futex_hash_bucket *hb2, union futex_key *key2)
1387 * If key1 and key2 hash to the same bucket, no need to
1390 if (likely(&hb1->chain != &hb2->chain)) {
1391 plist_del(&q->list, &hb1->chain);
1392 hb_waiters_dec(hb1);
1393 plist_add(&q->list, &hb2->chain);
1394 hb_waiters_inc(hb2);
1395 q->lock_ptr = &hb2->lock;
1397 get_futex_key_refs(key2);
1402 * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1404 * @key: the key of the requeue target futex
1405 * @hb: the hash_bucket of the requeue target futex
1407 * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1408 * target futex if it is uncontended or via a lock steal. Set the futex_q key
1409 * to the requeue target futex so the waiter can detect the wakeup on the right
1410 * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1411 * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
1412 * to protect access to the pi_state to fixup the owner later. Must be called
1413 * with both q->lock_ptr and hb->lock held.
1416 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1417 struct futex_hash_bucket *hb)
1419 get_futex_key_refs(key);
1424 WARN_ON(!q->rt_waiter);
1425 q->rt_waiter = NULL;
1427 q->lock_ptr = &hb->lock;
1429 wake_up_state(q->task, TASK_NORMAL);
1433 * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1434 * @pifutex: the user address of the to futex
1435 * @hb1: the from futex hash bucket, must be locked by the caller
1436 * @hb2: the to futex hash bucket, must be locked by the caller
1437 * @key1: the from futex key
1438 * @key2: the to futex key
1439 * @ps: address to store the pi_state pointer
1440 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1442 * Try and get the lock on behalf of the top waiter if we can do it atomically.
1443 * Wake the top waiter if we succeed. If the caller specified set_waiters,
1444 * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1445 * hb1 and hb2 must be held by the caller.
1448 * 0 - failed to acquire the lock atomically;
1449 * >0 - acquired the lock, return value is vpid of the top_waiter
1452 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1453 struct futex_hash_bucket *hb1,
1454 struct futex_hash_bucket *hb2,
1455 union futex_key *key1, union futex_key *key2,
1456 struct futex_pi_state **ps, int set_waiters)
1458 struct futex_q *top_waiter = NULL;
1462 if (get_futex_value_locked(&curval, pifutex))
1466 * Find the top_waiter and determine if there are additional waiters.
1467 * If the caller intends to requeue more than 1 waiter to pifutex,
1468 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1469 * as we have means to handle the possible fault. If not, don't set
1470 * the bit unecessarily as it will force the subsequent unlock to enter
1473 top_waiter = futex_top_waiter(hb1, key1);
1475 /* There are no waiters, nothing for us to do. */
1479 /* Ensure we requeue to the expected futex. */
1480 if (!match_futex(top_waiter->requeue_pi_key, key2))
1484 * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
1485 * the contended case or if set_waiters is 1. The pi_state is returned
1486 * in ps in contended cases.
1488 vpid = task_pid_vnr(top_waiter->task);
1489 ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1492 requeue_pi_wake_futex(top_waiter, key2, hb2);
1499 * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1500 * @uaddr1: source futex user address
1501 * @flags: futex flags (FLAGS_SHARED, etc.)
1502 * @uaddr2: target futex user address
1503 * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
1504 * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1505 * @cmpval: @uaddr1 expected value (or %NULL)
1506 * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1507 * pi futex (pi to pi requeue is not supported)
1509 * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1510 * uaddr2 atomically on behalf of the top waiter.
1513 * >=0 - on success, the number of tasks requeued or woken;
1516 static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1517 u32 __user *uaddr2, int nr_wake, int nr_requeue,
1518 u32 *cmpval, int requeue_pi)
1520 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1521 int drop_count = 0, task_count = 0, ret;
1522 struct futex_pi_state *pi_state = NULL;
1523 struct futex_hash_bucket *hb1, *hb2;
1524 struct futex_q *this, *next;
1528 * Requeue PI only works on two distinct uaddrs. This
1529 * check is only valid for private futexes. See below.
1531 if (uaddr1 == uaddr2)
1535 * requeue_pi requires a pi_state, try to allocate it now
1536 * without any locks in case it fails.
1538 if (refill_pi_state_cache())
1541 * requeue_pi must wake as many tasks as it can, up to nr_wake
1542 * + nr_requeue, since it acquires the rt_mutex prior to
1543 * returning to userspace, so as to not leave the rt_mutex with
1544 * waiters and no owner. However, second and third wake-ups
1545 * cannot be predicted as they involve race conditions with the
1546 * first wake and a fault while looking up the pi_state. Both
1547 * pthread_cond_signal() and pthread_cond_broadcast() should
1555 if (pi_state != NULL) {
1557 * We will have to lookup the pi_state again, so free this one
1558 * to keep the accounting correct.
1560 free_pi_state(pi_state);
1564 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1565 if (unlikely(ret != 0))
1567 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
1568 requeue_pi ? VERIFY_WRITE : VERIFY_READ);
1569 if (unlikely(ret != 0))
1573 * The check above which compares uaddrs is not sufficient for
1574 * shared futexes. We need to compare the keys:
1576 if (requeue_pi && match_futex(&key1, &key2)) {
1581 hb1 = hash_futex(&key1);
1582 hb2 = hash_futex(&key2);
1585 hb_waiters_inc(hb2);
1586 double_lock_hb(hb1, hb2);
1588 if (likely(cmpval != NULL)) {
1591 ret = get_futex_value_locked(&curval, uaddr1);
1593 if (unlikely(ret)) {
1594 double_unlock_hb(hb1, hb2);
1595 hb_waiters_dec(hb2);
1597 ret = get_user(curval, uaddr1);
1601 if (!(flags & FLAGS_SHARED))
1604 put_futex_key(&key2);
1605 put_futex_key(&key1);
1608 if (curval != *cmpval) {
1614 if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1616 * Attempt to acquire uaddr2 and wake the top waiter. If we
1617 * intend to requeue waiters, force setting the FUTEX_WAITERS
1618 * bit. We force this here where we are able to easily handle
1619 * faults rather in the requeue loop below.
1621 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1622 &key2, &pi_state, nr_requeue);
1625 * At this point the top_waiter has either taken uaddr2 or is
1626 * waiting on it. If the former, then the pi_state will not
1627 * exist yet, look it up one more time to ensure we have a
1628 * reference to it. If the lock was taken, ret contains the
1629 * vpid of the top waiter task.
1636 * If we acquired the lock, then the user
1637 * space value of uaddr2 should be vpid. It
1638 * cannot be changed by the top waiter as it
1639 * is blocked on hb2 lock if it tries to do
1640 * so. If something fiddled with it behind our
1641 * back the pi state lookup might unearth
1642 * it. So we rather use the known value than
1643 * rereading and handing potential crap to
1646 ret = lookup_pi_state(ret, hb2, &key2, &pi_state);
1653 double_unlock_hb(hb1, hb2);
1654 hb_waiters_dec(hb2);
1655 put_futex_key(&key2);
1656 put_futex_key(&key1);
1657 ret = fault_in_user_writeable(uaddr2);
1662 /* The owner was exiting, try again. */
1663 double_unlock_hb(hb1, hb2);
1664 hb_waiters_dec(hb2);
1665 put_futex_key(&key2);
1666 put_futex_key(&key1);
1674 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1675 if (task_count - nr_wake >= nr_requeue)
1678 if (!match_futex(&this->key, &key1))
1682 * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1683 * be paired with each other and no other futex ops.
1685 * We should never be requeueing a futex_q with a pi_state,
1686 * which is awaiting a futex_unlock_pi().
1688 if ((requeue_pi && !this->rt_waiter) ||
1689 (!requeue_pi && this->rt_waiter) ||
1696 * Wake nr_wake waiters. For requeue_pi, if we acquired the
1697 * lock, we already woke the top_waiter. If not, it will be
1698 * woken by futex_unlock_pi().
1700 if (++task_count <= nr_wake && !requeue_pi) {
1705 /* Ensure we requeue to the expected futex for requeue_pi. */
1706 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1712 * Requeue nr_requeue waiters and possibly one more in the case
1713 * of requeue_pi if we couldn't acquire the lock atomically.
1716 /* Prepare the waiter to take the rt_mutex. */
1717 atomic_inc(&pi_state->refcount);
1718 this->pi_state = pi_state;
1719 ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1723 /* We got the lock. */
1724 requeue_pi_wake_futex(this, &key2, hb2);
1729 this->pi_state = NULL;
1730 free_pi_state(pi_state);
1734 requeue_futex(this, hb1, hb2, &key2);
1739 double_unlock_hb(hb1, hb2);
1740 hb_waiters_dec(hb2);
1743 * drop_futex_key_refs() must be called outside the spinlocks. During
1744 * the requeue we moved futex_q's from the hash bucket at key1 to the
1745 * one at key2 and updated their key pointer. We no longer need to
1746 * hold the references to key1.
1748 while (--drop_count >= 0)
1749 drop_futex_key_refs(&key1);
1752 put_futex_key(&key2);
1754 put_futex_key(&key1);
1756 if (pi_state != NULL)
1757 free_pi_state(pi_state);
1758 return ret ? ret : task_count;
1761 /* The key must be already stored in q->key. */
1762 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
1763 __acquires(&hb->lock)
1765 struct futex_hash_bucket *hb;
1767 hb = hash_futex(&q->key);
1770 * Increment the counter before taking the lock so that
1771 * a potential waker won't miss a to-be-slept task that is
1772 * waiting for the spinlock. This is safe as all queue_lock()
1773 * users end up calling queue_me(). Similarly, for housekeeping,
1774 * decrement the counter at queue_unlock() when some error has
1775 * occurred and we don't end up adding the task to the list.
1779 q->lock_ptr = &hb->lock;
1781 spin_lock(&hb->lock); /* implies MB (A) */
1786 queue_unlock(struct futex_hash_bucket *hb)
1787 __releases(&hb->lock)
1789 spin_unlock(&hb->lock);
1794 * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1795 * @q: The futex_q to enqueue
1796 * @hb: The destination hash bucket
1798 * The hb->lock must be held by the caller, and is released here. A call to
1799 * queue_me() is typically paired with exactly one call to unqueue_me(). The
1800 * exceptions involve the PI related operations, which may use unqueue_me_pi()
1801 * or nothing if the unqueue is done as part of the wake process and the unqueue
1802 * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1805 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1806 __releases(&hb->lock)
1811 * The priority used to register this element is
1812 * - either the real thread-priority for the real-time threads
1813 * (i.e. threads with a priority lower than MAX_RT_PRIO)
1814 * - or MAX_RT_PRIO for non-RT threads.
1815 * Thus, all RT-threads are woken first in priority order, and
1816 * the others are woken last, in FIFO order.
1818 prio = min(current->normal_prio, MAX_RT_PRIO);
1820 plist_node_init(&q->list, prio);
1821 plist_add(&q->list, &hb->chain);
1823 spin_unlock(&hb->lock);
1827 * unqueue_me() - Remove the futex_q from its futex_hash_bucket
1828 * @q: The futex_q to unqueue
1830 * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
1831 * be paired with exactly one earlier call to queue_me().
1834 * 1 - if the futex_q was still queued (and we removed unqueued it);
1835 * 0 - if the futex_q was already removed by the waking thread
1837 static int unqueue_me(struct futex_q *q)
1839 spinlock_t *lock_ptr;
1842 /* In the common case we don't take the spinlock, which is nice. */
1844 lock_ptr = q->lock_ptr;
1846 if (lock_ptr != NULL) {
1847 spin_lock(lock_ptr);
1849 * q->lock_ptr can change between reading it and
1850 * spin_lock(), causing us to take the wrong lock. This
1851 * corrects the race condition.
1853 * Reasoning goes like this: if we have the wrong lock,
1854 * q->lock_ptr must have changed (maybe several times)
1855 * between reading it and the spin_lock(). It can
1856 * change again after the spin_lock() but only if it was
1857 * already changed before the spin_lock(). It cannot,
1858 * however, change back to the original value. Therefore
1859 * we can detect whether we acquired the correct lock.
1861 if (unlikely(lock_ptr != q->lock_ptr)) {
1862 spin_unlock(lock_ptr);
1867 BUG_ON(q->pi_state);
1869 spin_unlock(lock_ptr);
1873 drop_futex_key_refs(&q->key);
1878 * PI futexes can not be requeued and must remove themself from the
1879 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1882 static void unqueue_me_pi(struct futex_q *q)
1883 __releases(q->lock_ptr)
1887 BUG_ON(!q->pi_state);
1888 free_pi_state(q->pi_state);
1891 spin_unlock(q->lock_ptr);
1895 * Fixup the pi_state owner with the new owner.
1897 * Must be called with hash bucket lock held and mm->sem held for non
1900 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
1901 struct task_struct *newowner)
1903 u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
1904 struct futex_pi_state *pi_state = q->pi_state;
1905 struct task_struct *oldowner = pi_state->owner;
1906 u32 uval, uninitialized_var(curval), newval;
1910 if (!pi_state->owner)
1911 newtid |= FUTEX_OWNER_DIED;
1914 * We are here either because we stole the rtmutex from the
1915 * previous highest priority waiter or we are the highest priority
1916 * waiter but failed to get the rtmutex the first time.
1917 * We have to replace the newowner TID in the user space variable.
1918 * This must be atomic as we have to preserve the owner died bit here.
1920 * Note: We write the user space value _before_ changing the pi_state
1921 * because we can fault here. Imagine swapped out pages or a fork
1922 * that marked all the anonymous memory readonly for cow.
1924 * Modifying pi_state _before_ the user space value would
1925 * leave the pi_state in an inconsistent state when we fault
1926 * here, because we need to drop the hash bucket lock to
1927 * handle the fault. This might be observed in the PID check
1928 * in lookup_pi_state.
1931 if (get_futex_value_locked(&uval, uaddr))
1935 newval = (uval & FUTEX_OWNER_DIED) | newtid;
1937 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
1945 * We fixed up user space. Now we need to fix the pi_state
1948 if (pi_state->owner != NULL) {
1949 raw_spin_lock_irq(&pi_state->owner->pi_lock);
1950 WARN_ON(list_empty(&pi_state->list));
1951 list_del_init(&pi_state->list);
1952 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
1955 pi_state->owner = newowner;
1957 raw_spin_lock_irq(&newowner->pi_lock);
1958 WARN_ON(!list_empty(&pi_state->list));
1959 list_add(&pi_state->list, &newowner->pi_state_list);
1960 raw_spin_unlock_irq(&newowner->pi_lock);
1964 * To handle the page fault we need to drop the hash bucket
1965 * lock here. That gives the other task (either the highest priority
1966 * waiter itself or the task which stole the rtmutex) the
1967 * chance to try the fixup of the pi_state. So once we are
1968 * back from handling the fault we need to check the pi_state
1969 * after reacquiring the hash bucket lock and before trying to
1970 * do another fixup. When the fixup has been done already we
1974 spin_unlock(q->lock_ptr);
1976 ret = fault_in_user_writeable(uaddr);
1978 spin_lock(q->lock_ptr);
1981 * Check if someone else fixed it for us:
1983 if (pi_state->owner != oldowner)
1992 static long futex_wait_restart(struct restart_block *restart);
1995 * fixup_owner() - Post lock pi_state and corner case management
1996 * @uaddr: user address of the futex
1997 * @q: futex_q (contains pi_state and access to the rt_mutex)
1998 * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
2000 * After attempting to lock an rt_mutex, this function is called to cleanup
2001 * the pi_state owner as well as handle race conditions that may allow us to
2002 * acquire the lock. Must be called with the hb lock held.
2005 * 1 - success, lock taken;
2006 * 0 - success, lock not taken;
2007 * <0 - on error (-EFAULT)
2009 static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
2011 struct task_struct *owner;
2016 * Got the lock. We might not be the anticipated owner if we
2017 * did a lock-steal - fix up the PI-state in that case:
2019 if (q->pi_state->owner != current)
2020 ret = fixup_pi_state_owner(uaddr, q, current);
2025 * Catch the rare case, where the lock was released when we were on the
2026 * way back before we locked the hash bucket.
2028 if (q->pi_state->owner == current) {
2030 * Try to get the rt_mutex now. This might fail as some other
2031 * task acquired the rt_mutex after we removed ourself from the
2032 * rt_mutex waiters list.
2034 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
2040 * pi_state is incorrect, some other task did a lock steal and
2041 * we returned due to timeout or signal without taking the
2042 * rt_mutex. Too late.
2044 raw_spin_lock(&q->pi_state->pi_mutex.wait_lock);
2045 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
2047 owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
2048 raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock);
2049 ret = fixup_pi_state_owner(uaddr, q, owner);
2054 * Paranoia check. If we did not take the lock, then we should not be
2055 * the owner of the rt_mutex.
2057 if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
2058 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
2059 "pi-state %p\n", ret,
2060 q->pi_state->pi_mutex.owner,
2061 q->pi_state->owner);
2064 return ret ? ret : locked;
2068 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
2069 * @hb: the futex hash bucket, must be locked by the caller
2070 * @q: the futex_q to queue up on
2071 * @timeout: the prepared hrtimer_sleeper, or null for no timeout
2073 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
2074 struct hrtimer_sleeper *timeout)
2077 * The task state is guaranteed to be set before another task can
2078 * wake it. set_current_state() is implemented using set_mb() and
2079 * queue_me() calls spin_unlock() upon completion, both serializing
2080 * access to the hash list and forcing another memory barrier.
2082 set_current_state(TASK_INTERRUPTIBLE);
2087 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
2088 if (!hrtimer_active(&timeout->timer))
2089 timeout->task = NULL;
2093 * If we have been removed from the hash list, then another task
2094 * has tried to wake us, and we can skip the call to schedule().
2096 if (likely(!plist_node_empty(&q->list))) {
2098 * If the timer has already expired, current will already be
2099 * flagged for rescheduling. Only call schedule if there
2100 * is no timeout, or if it has yet to expire.
2102 if (!timeout || timeout->task)
2103 freezable_schedule();
2105 __set_current_state(TASK_RUNNING);
2109 * futex_wait_setup() - Prepare to wait on a futex
2110 * @uaddr: the futex userspace address
2111 * @val: the expected value
2112 * @flags: futex flags (FLAGS_SHARED, etc.)
2113 * @q: the associated futex_q
2114 * @hb: storage for hash_bucket pointer to be returned to caller
2116 * Setup the futex_q and locate the hash_bucket. Get the futex value and
2117 * compare it with the expected value. Handle atomic faults internally.
2118 * Return with the hb lock held and a q.key reference on success, and unlocked
2119 * with no q.key reference on failure.
2122 * 0 - uaddr contains val and hb has been locked;
2123 * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
2125 static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
2126 struct futex_q *q, struct futex_hash_bucket **hb)
2132 * Access the page AFTER the hash-bucket is locked.
2133 * Order is important:
2135 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
2136 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
2138 * The basic logical guarantee of a futex is that it blocks ONLY
2139 * if cond(var) is known to be true at the time of blocking, for
2140 * any cond. If we locked the hash-bucket after testing *uaddr, that
2141 * would open a race condition where we could block indefinitely with
2142 * cond(var) false, which would violate the guarantee.
2144 * On the other hand, we insert q and release the hash-bucket only
2145 * after testing *uaddr. This guarantees that futex_wait() will NOT
2146 * absorb a wakeup if *uaddr does not match the desired values
2147 * while the syscall executes.
2150 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
2151 if (unlikely(ret != 0))
2155 *hb = queue_lock(q);
2157 ret = get_futex_value_locked(&uval, uaddr);
2162 ret = get_user(uval, uaddr);
2166 if (!(flags & FLAGS_SHARED))
2169 put_futex_key(&q->key);
2180 put_futex_key(&q->key);
2184 static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
2185 ktime_t *abs_time, u32 bitset)
2187 struct hrtimer_sleeper timeout, *to = NULL;
2188 struct restart_block *restart;
2189 struct futex_hash_bucket *hb;
2190 struct futex_q q = futex_q_init;
2200 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2201 CLOCK_REALTIME : CLOCK_MONOTONIC,
2203 hrtimer_init_sleeper(to, current);
2204 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2205 current->timer_slack_ns);
2210 * Prepare to wait on uaddr. On success, holds hb lock and increments
2213 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2217 /* queue_me and wait for wakeup, timeout, or a signal. */
2218 futex_wait_queue_me(hb, &q, to);
2220 /* If we were woken (and unqueued), we succeeded, whatever. */
2222 /* unqueue_me() drops q.key ref */
2223 if (!unqueue_me(&q))
2226 if (to && !to->task)
2230 * We expect signal_pending(current), but we might be the
2231 * victim of a spurious wakeup as well.
2233 if (!signal_pending(current))
2240 restart = ¤t_thread_info()->restart_block;
2241 restart->fn = futex_wait_restart;
2242 restart->futex.uaddr = uaddr;
2243 restart->futex.val = val;
2244 restart->futex.time = abs_time->tv64;
2245 restart->futex.bitset = bitset;
2246 restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
2248 ret = -ERESTART_RESTARTBLOCK;
2252 hrtimer_cancel(&to->timer);
2253 destroy_hrtimer_on_stack(&to->timer);
2259 static long futex_wait_restart(struct restart_block *restart)
2261 u32 __user *uaddr = restart->futex.uaddr;
2262 ktime_t t, *tp = NULL;
2264 if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
2265 t.tv64 = restart->futex.time;
2268 restart->fn = do_no_restart_syscall;
2270 return (long)futex_wait(uaddr, restart->futex.flags,
2271 restart->futex.val, tp, restart->futex.bitset);
2276 * Userspace tried a 0 -> TID atomic transition of the futex value
2277 * and failed. The kernel side here does the whole locking operation:
2278 * if there are waiters then it will block, it does PI, etc. (Due to
2279 * races the kernel might see a 0 value of the futex too.)
2281 static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect,
2282 ktime_t *time, int trylock)
2284 struct hrtimer_sleeper timeout, *to = NULL;
2285 struct futex_hash_bucket *hb;
2286 struct futex_q q = futex_q_init;
2289 if (refill_pi_state_cache())
2294 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
2296 hrtimer_init_sleeper(to, current);
2297 hrtimer_set_expires(&to->timer, *time);
2301 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
2302 if (unlikely(ret != 0))
2306 hb = queue_lock(&q);
2308 ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
2309 if (unlikely(ret)) {
2312 /* We got the lock. */
2314 goto out_unlock_put_key;
2319 * Task is exiting and we just wait for the
2323 put_futex_key(&q.key);
2327 goto out_unlock_put_key;
2332 * Only actually queue now that the atomic ops are done:
2336 WARN_ON(!q.pi_state);
2338 * Block on the PI mutex:
2341 ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
2343 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
2344 /* Fixup the trylock return value: */
2345 ret = ret ? 0 : -EWOULDBLOCK;
2348 spin_lock(q.lock_ptr);
2350 * Fixup the pi_state owner and possibly acquire the lock if we
2353 res = fixup_owner(uaddr, &q, !ret);
2355 * If fixup_owner() returned an error, proprogate that. If it acquired
2356 * the lock, clear our -ETIMEDOUT or -EINTR.
2359 ret = (res < 0) ? res : 0;
2362 * If fixup_owner() faulted and was unable to handle the fault, unlock
2363 * it and return the fault to userspace.
2365 if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
2366 rt_mutex_unlock(&q.pi_state->pi_mutex);
2368 /* Unqueue and drop the lock */
2377 put_futex_key(&q.key);
2380 destroy_hrtimer_on_stack(&to->timer);
2381 return ret != -EINTR ? ret : -ERESTARTNOINTR;
2386 ret = fault_in_user_writeable(uaddr);
2390 if (!(flags & FLAGS_SHARED))
2393 put_futex_key(&q.key);
2398 * Userspace attempted a TID -> 0 atomic transition, and failed.
2399 * This is the in-kernel slowpath: we look up the PI state (if any),
2400 * and do the rt-mutex unlock.
2402 static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
2404 struct futex_hash_bucket *hb;
2405 struct futex_q *this, *next;
2406 union futex_key key = FUTEX_KEY_INIT;
2407 u32 uval, vpid = task_pid_vnr(current);
2411 if (get_user(uval, uaddr))
2414 * We release only a lock we actually own:
2416 if ((uval & FUTEX_TID_MASK) != vpid)
2419 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
2420 if (unlikely(ret != 0))
2423 hb = hash_futex(&key);
2424 spin_lock(&hb->lock);
2427 * To avoid races, try to do the TID -> 0 atomic transition
2428 * again. If it succeeds then we can return without waking
2429 * anyone else up. We only try this if neither the waiters nor
2430 * the owner died bit are set.
2432 if (!(uval & ~FUTEX_TID_MASK) &&
2433 cmpxchg_futex_value_locked(&uval, uaddr, vpid, 0))
2436 * Rare case: we managed to release the lock atomically,
2437 * no need to wake anyone else up:
2439 if (unlikely(uval == vpid))
2443 * Ok, other tasks may need to be woken up - check waiters
2444 * and do the wakeup if necessary:
2446 plist_for_each_entry_safe(this, next, &hb->chain, list) {
2447 if (!match_futex (&this->key, &key))
2449 ret = wake_futex_pi(uaddr, uval, this);
2451 * The atomic access to the futex value
2452 * generated a pagefault, so retry the
2453 * user-access and the wakeup:
2460 * No waiters - kernel unlocks the futex:
2462 ret = unlock_futex_pi(uaddr, uval);
2467 spin_unlock(&hb->lock);
2468 put_futex_key(&key);
2474 spin_unlock(&hb->lock);
2475 put_futex_key(&key);
2477 ret = fault_in_user_writeable(uaddr);
2485 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2486 * @hb: the hash_bucket futex_q was original enqueued on
2487 * @q: the futex_q woken while waiting to be requeued
2488 * @key2: the futex_key of the requeue target futex
2489 * @timeout: the timeout associated with the wait (NULL if none)
2491 * Detect if the task was woken on the initial futex as opposed to the requeue
2492 * target futex. If so, determine if it was a timeout or a signal that caused
2493 * the wakeup and return the appropriate error code to the caller. Must be
2494 * called with the hb lock held.
2497 * 0 = no early wakeup detected;
2498 * <0 = -ETIMEDOUT or -ERESTARTNOINTR
2501 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2502 struct futex_q *q, union futex_key *key2,
2503 struct hrtimer_sleeper *timeout)
2508 * With the hb lock held, we avoid races while we process the wakeup.
2509 * We only need to hold hb (and not hb2) to ensure atomicity as the
2510 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2511 * It can't be requeued from uaddr2 to something else since we don't
2512 * support a PI aware source futex for requeue.
2514 if (!match_futex(&q->key, key2)) {
2515 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2517 * We were woken prior to requeue by a timeout or a signal.
2518 * Unqueue the futex_q and determine which it was.
2520 plist_del(&q->list, &hb->chain);
2523 /* Handle spurious wakeups gracefully */
2525 if (timeout && !timeout->task)
2527 else if (signal_pending(current))
2528 ret = -ERESTARTNOINTR;
2534 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2535 * @uaddr: the futex we initially wait on (non-pi)
2536 * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
2537 * the same type, no requeueing from private to shared, etc.
2538 * @val: the expected value of uaddr
2539 * @abs_time: absolute timeout
2540 * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
2541 * @uaddr2: the pi futex we will take prior to returning to user-space
2543 * The caller will wait on uaddr and will be requeued by futex_requeue() to
2544 * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
2545 * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
2546 * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
2547 * without one, the pi logic would not know which task to boost/deboost, if
2548 * there was a need to.
2550 * We call schedule in futex_wait_queue_me() when we enqueue and return there
2551 * via the following--
2552 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2553 * 2) wakeup on uaddr2 after a requeue
2557 * If 3, cleanup and return -ERESTARTNOINTR.
2559 * If 2, we may then block on trying to take the rt_mutex and return via:
2560 * 5) successful lock
2563 * 8) other lock acquisition failure
2565 * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2567 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2573 static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
2574 u32 val, ktime_t *abs_time, u32 bitset,
2577 struct hrtimer_sleeper timeout, *to = NULL;
2578 struct rt_mutex_waiter rt_waiter;
2579 struct rt_mutex *pi_mutex = NULL;
2580 struct futex_hash_bucket *hb;
2581 union futex_key key2 = FUTEX_KEY_INIT;
2582 struct futex_q q = futex_q_init;
2585 if (uaddr == uaddr2)
2593 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2594 CLOCK_REALTIME : CLOCK_MONOTONIC,
2596 hrtimer_init_sleeper(to, current);
2597 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2598 current->timer_slack_ns);
2602 * The waiter is allocated on our stack, manipulated by the requeue
2603 * code while we sleep on uaddr.
2605 debug_rt_mutex_init_waiter(&rt_waiter);
2606 RB_CLEAR_NODE(&rt_waiter.pi_tree_entry);
2607 RB_CLEAR_NODE(&rt_waiter.tree_entry);
2608 rt_waiter.task = NULL;
2610 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
2611 if (unlikely(ret != 0))
2615 q.rt_waiter = &rt_waiter;
2616 q.requeue_pi_key = &key2;
2619 * Prepare to wait on uaddr. On success, increments q.key (key1) ref
2622 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2627 * The check above which compares uaddrs is not sufficient for
2628 * shared futexes. We need to compare the keys:
2630 if (match_futex(&q.key, &key2)) {
2635 /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2636 futex_wait_queue_me(hb, &q, to);
2638 spin_lock(&hb->lock);
2639 ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2640 spin_unlock(&hb->lock);
2645 * In order for us to be here, we know our q.key == key2, and since
2646 * we took the hb->lock above, we also know that futex_requeue() has
2647 * completed and we no longer have to concern ourselves with a wakeup
2648 * race with the atomic proxy lock acquisition by the requeue code. The
2649 * futex_requeue dropped our key1 reference and incremented our key2
2653 /* Check if the requeue code acquired the second futex for us. */
2656 * Got the lock. We might not be the anticipated owner if we
2657 * did a lock-steal - fix up the PI-state in that case.
2659 if (q.pi_state && (q.pi_state->owner != current)) {
2660 spin_lock(q.lock_ptr);
2661 ret = fixup_pi_state_owner(uaddr2, &q, current);
2662 spin_unlock(q.lock_ptr);
2666 * We have been woken up by futex_unlock_pi(), a timeout, or a
2667 * signal. futex_unlock_pi() will not destroy the lock_ptr nor
2670 WARN_ON(!q.pi_state);
2671 pi_mutex = &q.pi_state->pi_mutex;
2672 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
2673 debug_rt_mutex_free_waiter(&rt_waiter);
2675 spin_lock(q.lock_ptr);
2677 * Fixup the pi_state owner and possibly acquire the lock if we
2680 res = fixup_owner(uaddr2, &q, !ret);
2682 * If fixup_owner() returned an error, proprogate that. If it
2683 * acquired the lock, clear -ETIMEDOUT or -EINTR.
2686 ret = (res < 0) ? res : 0;
2688 /* Unqueue and drop the lock. */
2693 * If fixup_pi_state_owner() faulted and was unable to handle the
2694 * fault, unlock the rt_mutex and return the fault to userspace.
2696 if (ret == -EFAULT) {
2697 if (pi_mutex && rt_mutex_owner(pi_mutex) == current)
2698 rt_mutex_unlock(pi_mutex);
2699 } else if (ret == -EINTR) {
2701 * We've already been requeued, but cannot restart by calling
2702 * futex_lock_pi() directly. We could restart this syscall, but
2703 * it would detect that the user space "val" changed and return
2704 * -EWOULDBLOCK. Save the overhead of the restart and return
2705 * -EWOULDBLOCK directly.
2711 put_futex_key(&q.key);
2713 put_futex_key(&key2);
2717 hrtimer_cancel(&to->timer);
2718 destroy_hrtimer_on_stack(&to->timer);
2724 * Support for robust futexes: the kernel cleans up held futexes at
2727 * Implementation: user-space maintains a per-thread list of locks it
2728 * is holding. Upon do_exit(), the kernel carefully walks this list,
2729 * and marks all locks that are owned by this thread with the
2730 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2731 * always manipulated with the lock held, so the list is private and
2732 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2733 * field, to allow the kernel to clean up if the thread dies after
2734 * acquiring the lock, but just before it could have added itself to
2735 * the list. There can only be one such pending lock.
2739 * sys_set_robust_list() - Set the robust-futex list head of a task
2740 * @head: pointer to the list-head
2741 * @len: length of the list-head, as userspace expects
2743 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2746 if (!futex_cmpxchg_enabled)
2749 * The kernel knows only one size for now:
2751 if (unlikely(len != sizeof(*head)))
2754 current->robust_list = head;
2760 * sys_get_robust_list() - Get the robust-futex list head of a task
2761 * @pid: pid of the process [zero for current task]
2762 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
2763 * @len_ptr: pointer to a length field, the kernel fills in the header size
2765 SYSCALL_DEFINE3(get_robust_list, int, pid,
2766 struct robust_list_head __user * __user *, head_ptr,
2767 size_t __user *, len_ptr)
2769 struct robust_list_head __user *head;
2771 struct task_struct *p;
2773 if (!futex_cmpxchg_enabled)
2782 p = find_task_by_vpid(pid);
2788 if (!ptrace_may_access(p, PTRACE_MODE_READ))
2791 head = p->robust_list;
2794 if (put_user(sizeof(*head), len_ptr))
2796 return put_user(head, head_ptr);
2805 * Process a futex-list entry, check whether it's owned by the
2806 * dying task, and do notification if so:
2808 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
2810 u32 uval, uninitialized_var(nval), mval;
2813 if (get_user(uval, uaddr))
2816 if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
2818 * Ok, this dying thread is truly holding a futex
2819 * of interest. Set the OWNER_DIED bit atomically
2820 * via cmpxchg, and if the value had FUTEX_WAITERS
2821 * set, wake up a waiter (if any). (We have to do a
2822 * futex_wake() even if OWNER_DIED is already set -
2823 * to handle the rare but possible case of recursive
2824 * thread-death.) The rest of the cleanup is done in
2827 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
2829 * We are not holding a lock here, but we want to have
2830 * the pagefault_disable/enable() protection because
2831 * we want to handle the fault gracefully. If the
2832 * access fails we try to fault in the futex with R/W
2833 * verification via get_user_pages. get_user() above
2834 * does not guarantee R/W access. If that fails we
2835 * give up and leave the futex locked.
2837 if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
2838 if (fault_in_user_writeable(uaddr))
2846 * Wake robust non-PI futexes here. The wakeup of
2847 * PI futexes happens in exit_pi_state():
2849 if (!pi && (uval & FUTEX_WAITERS))
2850 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
2856 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
2858 static inline int fetch_robust_entry(struct robust_list __user **entry,
2859 struct robust_list __user * __user *head,
2862 unsigned long uentry;
2864 if (get_user(uentry, (unsigned long __user *)head))
2867 *entry = (void __user *)(uentry & ~1UL);
2874 * Walk curr->robust_list (very carefully, it's a userspace list!)
2875 * and mark any locks found there dead, and notify any waiters.
2877 * We silently return on any sign of list-walking problem.
2879 void exit_robust_list(struct task_struct *curr)
2881 struct robust_list_head __user *head = curr->robust_list;
2882 struct robust_list __user *entry, *next_entry, *pending;
2883 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
2884 unsigned int uninitialized_var(next_pi);
2885 unsigned long futex_offset;
2888 if (!futex_cmpxchg_enabled)
2892 * Fetch the list head (which was registered earlier, via
2893 * sys_set_robust_list()):
2895 if (fetch_robust_entry(&entry, &head->list.next, &pi))
2898 * Fetch the relative futex offset:
2900 if (get_user(futex_offset, &head->futex_offset))
2903 * Fetch any possibly pending lock-add first, and handle it
2906 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
2909 next_entry = NULL; /* avoid warning with gcc */
2910 while (entry != &head->list) {
2912 * Fetch the next entry in the list before calling
2913 * handle_futex_death:
2915 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
2917 * A pending lock might already be on the list, so
2918 * don't process it twice:
2920 if (entry != pending)
2921 if (handle_futex_death((void __user *)entry + futex_offset,
2929 * Avoid excessively long or circular lists:
2938 handle_futex_death((void __user *)pending + futex_offset,
2942 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
2943 u32 __user *uaddr2, u32 val2, u32 val3)
2945 int cmd = op & FUTEX_CMD_MASK;
2946 unsigned int flags = 0;
2948 if (!(op & FUTEX_PRIVATE_FLAG))
2949 flags |= FLAGS_SHARED;
2951 if (op & FUTEX_CLOCK_REALTIME) {
2952 flags |= FLAGS_CLOCKRT;
2953 if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
2959 case FUTEX_UNLOCK_PI:
2960 case FUTEX_TRYLOCK_PI:
2961 case FUTEX_WAIT_REQUEUE_PI:
2962 case FUTEX_CMP_REQUEUE_PI:
2963 if (!futex_cmpxchg_enabled)
2969 val3 = FUTEX_BITSET_MATCH_ANY;
2970 case FUTEX_WAIT_BITSET:
2971 return futex_wait(uaddr, flags, val, timeout, val3);
2973 val3 = FUTEX_BITSET_MATCH_ANY;
2974 case FUTEX_WAKE_BITSET:
2975 return futex_wake(uaddr, flags, val, val3);
2977 return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
2978 case FUTEX_CMP_REQUEUE:
2979 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
2981 return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
2983 return futex_lock_pi(uaddr, flags, val, timeout, 0);
2984 case FUTEX_UNLOCK_PI:
2985 return futex_unlock_pi(uaddr, flags);
2986 case FUTEX_TRYLOCK_PI:
2987 return futex_lock_pi(uaddr, flags, 0, timeout, 1);
2988 case FUTEX_WAIT_REQUEUE_PI:
2989 val3 = FUTEX_BITSET_MATCH_ANY;
2990 return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
2992 case FUTEX_CMP_REQUEUE_PI:
2993 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
2999 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
3000 struct timespec __user *, utime, u32 __user *, uaddr2,
3004 ktime_t t, *tp = NULL;
3006 int cmd = op & FUTEX_CMD_MASK;
3008 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
3009 cmd == FUTEX_WAIT_BITSET ||
3010 cmd == FUTEX_WAIT_REQUEUE_PI)) {
3011 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
3013 if (!timespec_valid(&ts))
3016 t = timespec_to_ktime(ts);
3017 if (cmd == FUTEX_WAIT)
3018 t = ktime_add_safe(ktime_get(), t);
3022 * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
3023 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
3025 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
3026 cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
3027 val2 = (u32) (unsigned long) utime;
3029 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
3032 static void __init futex_detect_cmpxchg(void)
3034 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
3038 * This will fail and we want it. Some arch implementations do
3039 * runtime detection of the futex_atomic_cmpxchg_inatomic()
3040 * functionality. We want to know that before we call in any
3041 * of the complex code paths. Also we want to prevent
3042 * registration of robust lists in that case. NULL is
3043 * guaranteed to fault and we get -EFAULT on functional
3044 * implementation, the non-functional ones will return
3047 if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
3048 futex_cmpxchg_enabled = 1;
3052 static int __init futex_init(void)
3054 unsigned int futex_shift;
3057 #if CONFIG_BASE_SMALL
3058 futex_hashsize = 16;
3060 futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
3063 futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
3065 futex_hashsize < 256 ? HASH_SMALL : 0,
3067 futex_hashsize, futex_hashsize);
3068 futex_hashsize = 1UL << futex_shift;
3070 futex_detect_cmpxchg();
3072 for (i = 0; i < futex_hashsize; i++) {
3073 atomic_set(&futex_queues[i].waiters, 0);
3074 plist_head_init(&futex_queues[i].chain);
3075 spin_lock_init(&futex_queues[i].lock);
3080 __initcall(futex_init);