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>
67 #include <linux/fault-inject.h>
69 #include <asm/futex.h>
71 #include "locking/rtmutex_common.h"
74 * READ this before attempting to hack on futexes!
76 * Basic futex operation and ordering guarantees
77 * =============================================
79 * The waiter reads the futex value in user space and calls
80 * futex_wait(). This function computes the hash bucket and acquires
81 * the hash bucket lock. After that it reads the futex user space value
82 * again and verifies that the data has not changed. If it has not changed
83 * it enqueues itself into the hash bucket, releases the hash bucket lock
86 * The waker side modifies the user space value of the futex and calls
87 * futex_wake(). This function computes the hash bucket and acquires the
88 * hash bucket lock. Then it looks for waiters on that futex in the hash
89 * bucket and wakes them.
91 * In futex wake up scenarios where no tasks are blocked on a futex, taking
92 * the hb spinlock can be avoided and simply return. In order for this
93 * optimization to work, ordering guarantees must exist so that the waiter
94 * being added to the list is acknowledged when the list is concurrently being
95 * checked by the waker, avoiding scenarios like the following:
99 * sys_futex(WAIT, futex, val);
100 * futex_wait(futex, val);
103 * sys_futex(WAKE, futex);
108 * lock(hash_bucket(futex));
110 * unlock(hash_bucket(futex));
113 * This would cause the waiter on CPU 0 to wait forever because it
114 * missed the transition of the user space value from val to newval
115 * and the waker did not find the waiter in the hash bucket queue.
117 * The correct serialization ensures that a waiter either observes
118 * the changed user space value before blocking or is woken by a
123 * sys_futex(WAIT, futex, val);
124 * futex_wait(futex, val);
127 * mb(); (A) <-- paired with -.
129 * lock(hash_bucket(futex)); |
133 * | sys_futex(WAKE, futex);
134 * | futex_wake(futex);
136 * `-------> mb(); (B)
139 * unlock(hash_bucket(futex));
140 * schedule(); if (waiters)
141 * lock(hash_bucket(futex));
142 * else wake_waiters(futex);
143 * waiters--; (b) unlock(hash_bucket(futex));
145 * Where (A) orders the waiters increment and the futex value read through
146 * atomic operations (see hb_waiters_inc) and where (B) orders the write
147 * to futex and the waiters read -- this is done by the barriers for both
148 * shared and private futexes in get_futex_key_refs().
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;
259 * The base of the bucket array and its size are always used together
260 * (after initialization only in hash_futex()), so ensure that they
261 * reside in the same cacheline.
264 struct futex_hash_bucket *queues;
265 unsigned long hashsize;
266 } __futex_data __read_mostly __aligned(2*sizeof(long));
267 #define futex_queues (__futex_data.queues)
268 #define futex_hashsize (__futex_data.hashsize)
272 * Fault injections for futexes.
274 #ifdef CONFIG_FAIL_FUTEX
277 struct fault_attr attr;
281 .attr = FAULT_ATTR_INITIALIZER,
282 .ignore_private = false,
285 static int __init setup_fail_futex(char *str)
287 return setup_fault_attr(&fail_futex.attr, str);
289 __setup("fail_futex=", setup_fail_futex);
291 static bool should_fail_futex(bool fshared)
293 if (fail_futex.ignore_private && !fshared)
296 return should_fail(&fail_futex.attr, 1);
299 #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
301 static int __init fail_futex_debugfs(void)
303 umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
306 dir = fault_create_debugfs_attr("fail_futex", NULL,
311 if (!debugfs_create_bool("ignore-private", mode, dir,
312 &fail_futex.ignore_private)) {
313 debugfs_remove_recursive(dir);
320 late_initcall(fail_futex_debugfs);
322 #endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
325 static inline bool should_fail_futex(bool fshared)
329 #endif /* CONFIG_FAIL_FUTEX */
331 static inline void futex_get_mm(union futex_key *key)
333 atomic_inc(&key->private.mm->mm_count);
335 * Ensure futex_get_mm() implies a full barrier such that
336 * get_futex_key() implies a full barrier. This is relied upon
337 * as full barrier (B), see the ordering comment above.
339 smp_mb__after_atomic();
343 * Reflects a new waiter being added to the waitqueue.
345 static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
348 atomic_inc(&hb->waiters);
350 * Full barrier (A), see the ordering comment above.
352 smp_mb__after_atomic();
357 * Reflects a waiter being removed from the waitqueue by wakeup
360 static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
363 atomic_dec(&hb->waiters);
367 static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
370 return atomic_read(&hb->waiters);
377 * We hash on the keys returned from get_futex_key (see below).
379 static struct futex_hash_bucket *hash_futex(union futex_key *key)
381 u32 hash = jhash2((u32*)&key->both.word,
382 (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
384 return &futex_queues[hash & (futex_hashsize - 1)];
388 * Return 1 if two futex_keys are equal, 0 otherwise.
390 static inline int match_futex(union futex_key *key1, union futex_key *key2)
393 && key1->both.word == key2->both.word
394 && key1->both.ptr == key2->both.ptr
395 && key1->both.offset == key2->both.offset);
399 * Take a reference to the resource addressed by a key.
400 * Can be called while holding spinlocks.
403 static void get_futex_key_refs(union futex_key *key)
408 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
410 ihold(key->shared.inode); /* implies MB (B) */
412 case FUT_OFF_MMSHARED:
413 futex_get_mm(key); /* implies MB (B) */
417 * Private futexes do not hold reference on an inode or
418 * mm, therefore the only purpose of calling get_futex_key_refs
419 * is because we need the barrier for the lockless waiter check.
421 smp_mb(); /* explicit MB (B) */
426 * Drop a reference to the resource addressed by a key.
427 * The hash bucket spinlock must not be held. This is
428 * a no-op for private futexes, see comment in the get
431 static void drop_futex_key_refs(union futex_key *key)
433 if (!key->both.ptr) {
434 /* If we're here then we tried to put a key we failed to get */
439 switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
441 iput(key->shared.inode);
443 case FUT_OFF_MMSHARED:
444 mmdrop(key->private.mm);
450 * get_futex_key() - Get parameters which are the keys for a futex
451 * @uaddr: virtual address of the futex
452 * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
453 * @key: address where result is stored.
454 * @rw: mapping needs to be read/write (values: VERIFY_READ,
457 * Return: a negative error code or 0
459 * The key words are stored in *key on success.
461 * For shared mappings, it's (page->index, file_inode(vma->vm_file),
462 * offset_within_page). For private mappings, it's (uaddr, current->mm).
463 * We can usually work out the index without swapping in the page.
465 * lock_page() might sleep, the caller should not hold a spinlock.
468 get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
470 unsigned long address = (unsigned long)uaddr;
471 struct mm_struct *mm = current->mm;
472 struct page *page, *page_head;
476 * The futex address must be "naturally" aligned.
478 key->both.offset = address % PAGE_SIZE;
479 if (unlikely((address % sizeof(u32)) != 0))
481 address -= key->both.offset;
483 if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
486 if (unlikely(should_fail_futex(fshared)))
490 * PROCESS_PRIVATE futexes are fast.
491 * As the mm cannot disappear under us and the 'key' only needs
492 * virtual address, we dont even have to find the underlying vma.
493 * Note : We do have to check 'uaddr' is a valid user address,
494 * but access_ok() should be faster than find_vma()
497 key->private.mm = mm;
498 key->private.address = address;
499 get_futex_key_refs(key); /* implies MB (B) */
504 /* Ignore any VERIFY_READ mapping (futex common case) */
505 if (unlikely(should_fail_futex(fshared)))
508 err = get_user_pages_fast(address, 1, 1, &page);
510 * If write access is not required (eg. FUTEX_WAIT), try
511 * and get read-only access.
513 if (err == -EFAULT && rw == VERIFY_READ) {
514 err = get_user_pages_fast(address, 1, 0, &page);
522 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
524 if (unlikely(PageTail(page))) {
526 /* serialize against __split_huge_page_splitting() */
528 if (likely(__get_user_pages_fast(address, 1, !ro, &page) == 1)) {
529 page_head = compound_head(page);
531 * page_head is valid pointer but we must pin
532 * it before taking the PG_lock and/or
533 * PG_compound_lock. The moment we re-enable
534 * irqs __split_huge_page_splitting() can
535 * return and the head page can be freed from
536 * under us. We can't take the PG_lock and/or
537 * PG_compound_lock on a page that could be
538 * freed from under us.
540 if (page != page_head) {
551 page_head = compound_head(page);
552 if (page != page_head) {
558 lock_page(page_head);
561 * If page_head->mapping is NULL, then it cannot be a PageAnon
562 * page; but it might be the ZERO_PAGE or in the gate area or
563 * in a special mapping (all cases which we are happy to fail);
564 * or it may have been a good file page when get_user_pages_fast
565 * found it, but truncated or holepunched or subjected to
566 * invalidate_complete_page2 before we got the page lock (also
567 * cases which we are happy to fail). And we hold a reference,
568 * so refcount care in invalidate_complete_page's remove_mapping
569 * prevents drop_caches from setting mapping to NULL beneath us.
571 * The case we do have to guard against is when memory pressure made
572 * shmem_writepage move it from filecache to swapcache beneath us:
573 * an unlikely race, but we do need to retry for page_head->mapping.
575 if (!page_head->mapping) {
576 int shmem_swizzled = PageSwapCache(page_head);
577 unlock_page(page_head);
585 * Private mappings are handled in a simple way.
587 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
588 * it's a read-only handle, it's expected that futexes attach to
589 * the object not the particular process.
591 if (PageAnon(page_head)) {
593 * A RO anonymous page will never change and thus doesn't make
594 * sense for futex operations.
596 if (unlikely(should_fail_futex(fshared)) || ro) {
601 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
602 key->private.mm = mm;
603 key->private.address = address;
605 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
606 key->shared.inode = page_head->mapping->host;
607 key->shared.pgoff = basepage_index(page);
610 get_futex_key_refs(key); /* implies MB (B) */
613 unlock_page(page_head);
618 static inline void put_futex_key(union futex_key *key)
620 drop_futex_key_refs(key);
624 * fault_in_user_writeable() - Fault in user address and verify RW access
625 * @uaddr: pointer to faulting user space address
627 * Slow path to fixup the fault we just took in the atomic write
630 * We have no generic implementation of a non-destructive write to the
631 * user address. We know that we faulted in the atomic pagefault
632 * disabled section so we can as well avoid the #PF overhead by
633 * calling get_user_pages() right away.
635 static int fault_in_user_writeable(u32 __user *uaddr)
637 struct mm_struct *mm = current->mm;
640 down_read(&mm->mmap_sem);
641 ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
643 up_read(&mm->mmap_sem);
645 return ret < 0 ? ret : 0;
649 * futex_top_waiter() - Return the highest priority waiter on a futex
650 * @hb: the hash bucket the futex_q's reside in
651 * @key: the futex key (to distinguish it from other futex futex_q's)
653 * Must be called with the hb lock held.
655 static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
656 union futex_key *key)
658 struct futex_q *this;
660 plist_for_each_entry(this, &hb->chain, list) {
661 if (match_futex(&this->key, key))
667 static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
668 u32 uval, u32 newval)
673 ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
679 static int get_futex_value_locked(u32 *dest, u32 __user *from)
684 ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
687 return ret ? -EFAULT : 0;
694 static int refill_pi_state_cache(void)
696 struct futex_pi_state *pi_state;
698 if (likely(current->pi_state_cache))
701 pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
706 INIT_LIST_HEAD(&pi_state->list);
707 /* pi_mutex gets initialized later */
708 pi_state->owner = NULL;
709 atomic_set(&pi_state->refcount, 1);
710 pi_state->key = FUTEX_KEY_INIT;
712 current->pi_state_cache = pi_state;
717 static struct futex_pi_state * alloc_pi_state(void)
719 struct futex_pi_state *pi_state = current->pi_state_cache;
722 current->pi_state_cache = NULL;
728 * Must be called with the hb lock held.
730 static void free_pi_state(struct futex_pi_state *pi_state)
735 if (!atomic_dec_and_test(&pi_state->refcount))
739 * If pi_state->owner is NULL, the owner is most probably dying
740 * and has cleaned up the pi_state already
742 if (pi_state->owner) {
743 raw_spin_lock_irq(&pi_state->owner->pi_lock);
744 list_del_init(&pi_state->list);
745 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
747 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
750 if (current->pi_state_cache)
754 * pi_state->list is already empty.
755 * clear pi_state->owner.
756 * refcount is at 0 - put it back to 1.
758 pi_state->owner = NULL;
759 atomic_set(&pi_state->refcount, 1);
760 current->pi_state_cache = pi_state;
765 * Look up the task based on what TID userspace gave us.
768 static struct task_struct * futex_find_get_task(pid_t pid)
770 struct task_struct *p;
773 p = find_task_by_vpid(pid);
783 * This task is holding PI mutexes at exit time => bad.
784 * Kernel cleans up PI-state, but userspace is likely hosed.
785 * (Robust-futex cleanup is separate and might save the day for userspace.)
787 void exit_pi_state_list(struct task_struct *curr)
789 struct list_head *next, *head = &curr->pi_state_list;
790 struct futex_pi_state *pi_state;
791 struct futex_hash_bucket *hb;
792 union futex_key key = FUTEX_KEY_INIT;
794 if (!futex_cmpxchg_enabled)
797 * We are a ZOMBIE and nobody can enqueue itself on
798 * pi_state_list anymore, but we have to be careful
799 * versus waiters unqueueing themselves:
801 raw_spin_lock_irq(&curr->pi_lock);
802 while (!list_empty(head)) {
805 pi_state = list_entry(next, struct futex_pi_state, list);
807 hb = hash_futex(&key);
808 raw_spin_unlock_irq(&curr->pi_lock);
810 spin_lock(&hb->lock);
812 raw_spin_lock_irq(&curr->pi_lock);
814 * We dropped the pi-lock, so re-check whether this
815 * task still owns the PI-state:
817 if (head->next != next) {
818 raw_spin_unlock_irq(&curr->pi_lock);
819 spin_unlock(&hb->lock);
820 raw_spin_lock_irq(&curr->pi_lock);
824 WARN_ON(pi_state->owner != curr);
825 WARN_ON(list_empty(&pi_state->list));
826 list_del_init(&pi_state->list);
827 pi_state->owner = NULL;
828 raw_spin_unlock_irq(&curr->pi_lock);
830 rt_mutex_unlock(&pi_state->pi_mutex);
832 spin_unlock(&hb->lock);
834 raw_spin_lock_irq(&curr->pi_lock);
836 raw_spin_unlock_irq(&curr->pi_lock);
840 * We need to check the following states:
842 * Waiter | pi_state | pi->owner | uTID | uODIED | ?
844 * [1] NULL | --- | --- | 0 | 0/1 | Valid
845 * [2] NULL | --- | --- | >0 | 0/1 | Valid
847 * [3] Found | NULL | -- | Any | 0/1 | Invalid
849 * [4] Found | Found | NULL | 0 | 1 | Valid
850 * [5] Found | Found | NULL | >0 | 1 | Invalid
852 * [6] Found | Found | task | 0 | 1 | Valid
854 * [7] Found | Found | NULL | Any | 0 | Invalid
856 * [8] Found | Found | task | ==taskTID | 0/1 | Valid
857 * [9] Found | Found | task | 0 | 0 | Invalid
858 * [10] Found | Found | task | !=taskTID | 0/1 | Invalid
860 * [1] Indicates that the kernel can acquire the futex atomically. We
861 * came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
863 * [2] Valid, if TID does not belong to a kernel thread. If no matching
864 * thread is found then it indicates that the owner TID has died.
866 * [3] Invalid. The waiter is queued on a non PI futex
868 * [4] Valid state after exit_robust_list(), which sets the user space
869 * value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
871 * [5] The user space value got manipulated between exit_robust_list()
872 * and exit_pi_state_list()
874 * [6] Valid state after exit_pi_state_list() which sets the new owner in
875 * the pi_state but cannot access the user space value.
877 * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
879 * [8] Owner and user space value match
881 * [9] There is no transient state which sets the user space TID to 0
882 * except exit_robust_list(), but this is indicated by the
883 * FUTEX_OWNER_DIED bit. See [4]
885 * [10] There is no transient state which leaves owner and user space
890 * Validate that the existing waiter has a pi_state and sanity check
891 * the pi_state against the user space value. If correct, attach to
894 static int attach_to_pi_state(u32 uval, struct futex_pi_state *pi_state,
895 struct futex_pi_state **ps)
897 pid_t pid = uval & FUTEX_TID_MASK;
900 * Userspace might have messed up non-PI and PI futexes [3]
902 if (unlikely(!pi_state))
905 WARN_ON(!atomic_read(&pi_state->refcount));
908 * Handle the owner died case:
910 if (uval & FUTEX_OWNER_DIED) {
912 * exit_pi_state_list sets owner to NULL and wakes the
913 * topmost waiter. The task which acquires the
914 * pi_state->rt_mutex will fixup owner.
916 if (!pi_state->owner) {
918 * No pi state owner, but the user space TID
919 * is not 0. Inconsistent state. [5]
924 * Take a ref on the state and return success. [4]
930 * If TID is 0, then either the dying owner has not
931 * yet executed exit_pi_state_list() or some waiter
932 * acquired the rtmutex in the pi state, but did not
933 * yet fixup the TID in user space.
935 * Take a ref on the state and return success. [6]
941 * If the owner died bit is not set, then the pi_state
942 * must have an owner. [7]
944 if (!pi_state->owner)
949 * Bail out if user space manipulated the futex value. If pi
950 * state exists then the owner TID must be the same as the
951 * user space TID. [9/10]
953 if (pid != task_pid_vnr(pi_state->owner))
956 atomic_inc(&pi_state->refcount);
962 * Lookup the task for the TID provided from user space and attach to
963 * it after doing proper sanity checks.
965 static int attach_to_pi_owner(u32 uval, union futex_key *key,
966 struct futex_pi_state **ps)
968 pid_t pid = uval & FUTEX_TID_MASK;
969 struct futex_pi_state *pi_state;
970 struct task_struct *p;
973 * We are the first waiter - try to look up the real owner and attach
974 * the new pi_state to it, but bail out when TID = 0 [1]
978 p = futex_find_get_task(pid);
982 if (unlikely(p->flags & PF_KTHREAD)) {
988 * We need to look at the task state flags to figure out,
989 * whether the task is exiting. To protect against the do_exit
990 * change of the task flags, we do this protected by
993 raw_spin_lock_irq(&p->pi_lock);
994 if (unlikely(p->flags & PF_EXITING)) {
996 * The task is on the way out. When PF_EXITPIDONE is
997 * set, we know that the task has finished the
1000 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
1002 raw_spin_unlock_irq(&p->pi_lock);
1008 * No existing pi state. First waiter. [2]
1010 pi_state = alloc_pi_state();
1013 * Initialize the pi_mutex in locked state and make @p
1016 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
1018 /* Store the key for possible exit cleanups: */
1019 pi_state->key = *key;
1021 WARN_ON(!list_empty(&pi_state->list));
1022 list_add(&pi_state->list, &p->pi_state_list);
1023 pi_state->owner = p;
1024 raw_spin_unlock_irq(&p->pi_lock);
1033 static int lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
1034 union futex_key *key, struct futex_pi_state **ps)
1036 struct futex_q *match = futex_top_waiter(hb, key);
1039 * If there is a waiter on that futex, validate it and
1040 * attach to the pi_state when the validation succeeds.
1043 return attach_to_pi_state(uval, match->pi_state, ps);
1046 * We are the first waiter - try to look up the owner based on
1047 * @uval and attach to it.
1049 return attach_to_pi_owner(uval, key, ps);
1052 static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
1054 u32 uninitialized_var(curval);
1056 if (unlikely(should_fail_futex(true)))
1059 if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
1062 /*If user space value changed, let the caller retry */
1063 return curval != uval ? -EAGAIN : 0;
1067 * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
1068 * @uaddr: the pi futex user address
1069 * @hb: the pi futex hash bucket
1070 * @key: the futex key associated with uaddr and hb
1071 * @ps: the pi_state pointer where we store the result of the
1073 * @task: the task to perform the atomic lock work for. This will
1074 * be "current" except in the case of requeue pi.
1075 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1078 * 0 - ready to wait;
1079 * 1 - acquired the lock;
1082 * The hb->lock and futex_key refs shall be held by the caller.
1084 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
1085 union futex_key *key,
1086 struct futex_pi_state **ps,
1087 struct task_struct *task, int set_waiters)
1089 u32 uval, newval, vpid = task_pid_vnr(task);
1090 struct futex_q *match;
1094 * Read the user space value first so we can validate a few
1095 * things before proceeding further.
1097 if (get_futex_value_locked(&uval, uaddr))
1100 if (unlikely(should_fail_futex(true)))
1106 if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
1109 if ((unlikely(should_fail_futex(true))))
1113 * Lookup existing state first. If it exists, try to attach to
1116 match = futex_top_waiter(hb, key);
1118 return attach_to_pi_state(uval, match->pi_state, ps);
1121 * No waiter and user TID is 0. We are here because the
1122 * waiters or the owner died bit is set or called from
1123 * requeue_cmp_pi or for whatever reason something took the
1126 if (!(uval & FUTEX_TID_MASK)) {
1128 * We take over the futex. No other waiters and the user space
1129 * TID is 0. We preserve the owner died bit.
1131 newval = uval & FUTEX_OWNER_DIED;
1134 /* The futex requeue_pi code can enforce the waiters bit */
1136 newval |= FUTEX_WAITERS;
1138 ret = lock_pi_update_atomic(uaddr, uval, newval);
1139 /* If the take over worked, return 1 */
1140 return ret < 0 ? ret : 1;
1144 * First waiter. Set the waiters bit before attaching ourself to
1145 * the owner. If owner tries to unlock, it will be forced into
1146 * the kernel and blocked on hb->lock.
1148 newval = uval | FUTEX_WAITERS;
1149 ret = lock_pi_update_atomic(uaddr, uval, newval);
1153 * If the update of the user space value succeeded, we try to
1154 * attach to the owner. If that fails, no harm done, we only
1155 * set the FUTEX_WAITERS bit in the user space variable.
1157 return attach_to_pi_owner(uval, key, ps);
1161 * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
1162 * @q: The futex_q to unqueue
1164 * The q->lock_ptr must not be NULL and must be held by the caller.
1166 static void __unqueue_futex(struct futex_q *q)
1168 struct futex_hash_bucket *hb;
1170 if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
1171 || WARN_ON(plist_node_empty(&q->list)))
1174 hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
1175 plist_del(&q->list, &hb->chain);
1180 * The hash bucket lock must be held when this is called.
1181 * Afterwards, the futex_q must not be accessed. Callers
1182 * must ensure to later call wake_up_q() for the actual
1185 static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
1187 struct task_struct *p = q->task;
1189 if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
1193 * Queue the task for later wakeup for after we've released
1194 * the hb->lock. wake_q_add() grabs reference to p.
1196 wake_q_add(wake_q, p);
1199 * The waiting task can free the futex_q as soon as
1200 * q->lock_ptr = NULL is written, without taking any locks. A
1201 * memory barrier is required here to prevent the following
1202 * store to lock_ptr from getting ahead of the plist_del.
1208 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this,
1209 struct futex_hash_bucket *hb)
1211 struct task_struct *new_owner;
1212 struct futex_pi_state *pi_state = this->pi_state;
1213 u32 uninitialized_var(curval), newval;
1215 WAKE_Q(wake_sleeper_q);
1223 * If current does not own the pi_state then the futex is
1224 * inconsistent and user space fiddled with the futex value.
1226 if (pi_state->owner != current)
1229 raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
1230 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
1233 * It is possible that the next waiter (the one that brought
1234 * this owner to the kernel) timed out and is no longer
1235 * waiting on the lock.
1238 new_owner = this->task;
1241 * We pass it to the next owner. The WAITERS bit is always
1242 * kept enabled while there is PI state around. We cleanup the
1243 * owner died bit, because we are the owner.
1245 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
1247 if (unlikely(should_fail_futex(true)))
1250 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
1252 else if (curval != uval)
1255 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1259 raw_spin_lock(&pi_state->owner->pi_lock);
1260 WARN_ON(list_empty(&pi_state->list));
1261 list_del_init(&pi_state->list);
1262 raw_spin_unlock(&pi_state->owner->pi_lock);
1264 raw_spin_lock(&new_owner->pi_lock);
1265 WARN_ON(!list_empty(&pi_state->list));
1266 list_add(&pi_state->list, &new_owner->pi_state_list);
1267 pi_state->owner = new_owner;
1268 raw_spin_unlock(&new_owner->pi_lock);
1270 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1272 deboost = rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q,
1276 * First unlock HB so the waiter does not spin on it once he got woken
1277 * up. Second wake up the waiter before the priority is adjusted. If we
1278 * deboost first (and lose our higher priority), then the task might get
1279 * scheduled away before the wake up can take place.
1281 spin_unlock(&hb->lock);
1283 wake_up_q_sleeper(&wake_sleeper_q);
1285 rt_mutex_adjust_prio(current);
1291 * Express the locking dependencies for lockdep:
1294 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1297 spin_lock(&hb1->lock);
1299 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
1300 } else { /* hb1 > hb2 */
1301 spin_lock(&hb2->lock);
1302 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
1307 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1309 spin_unlock(&hb1->lock);
1311 spin_unlock(&hb2->lock);
1315 * Wake up waiters matching bitset queued on this futex (uaddr).
1318 futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
1320 struct futex_hash_bucket *hb;
1321 struct futex_q *this, *next;
1322 union futex_key key = FUTEX_KEY_INIT;
1329 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
1330 if (unlikely(ret != 0))
1333 hb = hash_futex(&key);
1335 /* Make sure we really have tasks to wakeup */
1336 if (!hb_waiters_pending(hb))
1339 spin_lock(&hb->lock);
1341 plist_for_each_entry_safe(this, next, &hb->chain, list) {
1342 if (match_futex (&this->key, &key)) {
1343 if (this->pi_state || this->rt_waiter) {
1348 /* Check if one of the bits is set in both bitsets */
1349 if (!(this->bitset & bitset))
1352 mark_wake_futex(&wake_q, this);
1353 if (++ret >= nr_wake)
1358 spin_unlock(&hb->lock);
1361 put_futex_key(&key);
1367 * Wake up all waiters hashed on the physical page that is mapped
1368 * to this virtual address:
1371 futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
1372 int nr_wake, int nr_wake2, int op)
1374 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1375 struct futex_hash_bucket *hb1, *hb2;
1376 struct futex_q *this, *next;
1381 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1382 if (unlikely(ret != 0))
1384 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
1385 if (unlikely(ret != 0))
1388 hb1 = hash_futex(&key1);
1389 hb2 = hash_futex(&key2);
1392 double_lock_hb(hb1, hb2);
1393 op_ret = futex_atomic_op_inuser(op, uaddr2);
1394 if (unlikely(op_ret < 0)) {
1396 double_unlock_hb(hb1, hb2);
1400 * we don't get EFAULT from MMU faults if we don't have an MMU,
1401 * but we might get them from range checking
1407 if (unlikely(op_ret != -EFAULT)) {
1412 ret = fault_in_user_writeable(uaddr2);
1416 if (!(flags & FLAGS_SHARED))
1419 put_futex_key(&key2);
1420 put_futex_key(&key1);
1424 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1425 if (match_futex (&this->key, &key1)) {
1426 if (this->pi_state || this->rt_waiter) {
1430 mark_wake_futex(&wake_q, this);
1431 if (++ret >= nr_wake)
1438 plist_for_each_entry_safe(this, next, &hb2->chain, list) {
1439 if (match_futex (&this->key, &key2)) {
1440 if (this->pi_state || this->rt_waiter) {
1444 mark_wake_futex(&wake_q, this);
1445 if (++op_ret >= nr_wake2)
1453 double_unlock_hb(hb1, hb2);
1456 put_futex_key(&key2);
1458 put_futex_key(&key1);
1464 * requeue_futex() - Requeue a futex_q from one hb to another
1465 * @q: the futex_q to requeue
1466 * @hb1: the source hash_bucket
1467 * @hb2: the target hash_bucket
1468 * @key2: the new key for the requeued futex_q
1471 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1472 struct futex_hash_bucket *hb2, union futex_key *key2)
1476 * If key1 and key2 hash to the same bucket, no need to
1479 if (likely(&hb1->chain != &hb2->chain)) {
1480 plist_del(&q->list, &hb1->chain);
1481 hb_waiters_dec(hb1);
1482 plist_add(&q->list, &hb2->chain);
1483 hb_waiters_inc(hb2);
1484 q->lock_ptr = &hb2->lock;
1486 get_futex_key_refs(key2);
1491 * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1493 * @key: the key of the requeue target futex
1494 * @hb: the hash_bucket of the requeue target futex
1496 * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1497 * target futex if it is uncontended or via a lock steal. Set the futex_q key
1498 * to the requeue target futex so the waiter can detect the wakeup on the right
1499 * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1500 * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
1501 * to protect access to the pi_state to fixup the owner later. Must be called
1502 * with both q->lock_ptr and hb->lock held.
1505 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1506 struct futex_hash_bucket *hb)
1508 get_futex_key_refs(key);
1513 WARN_ON(!q->rt_waiter);
1514 q->rt_waiter = NULL;
1516 q->lock_ptr = &hb->lock;
1518 wake_up_state(q->task, TASK_NORMAL);
1522 * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1523 * @pifutex: the user address of the to futex
1524 * @hb1: the from futex hash bucket, must be locked by the caller
1525 * @hb2: the to futex hash bucket, must be locked by the caller
1526 * @key1: the from futex key
1527 * @key2: the to futex key
1528 * @ps: address to store the pi_state pointer
1529 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1531 * Try and get the lock on behalf of the top waiter if we can do it atomically.
1532 * Wake the top waiter if we succeed. If the caller specified set_waiters,
1533 * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1534 * hb1 and hb2 must be held by the caller.
1537 * 0 - failed to acquire the lock atomically;
1538 * >0 - acquired the lock, return value is vpid of the top_waiter
1541 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1542 struct futex_hash_bucket *hb1,
1543 struct futex_hash_bucket *hb2,
1544 union futex_key *key1, union futex_key *key2,
1545 struct futex_pi_state **ps, int set_waiters)
1547 struct futex_q *top_waiter = NULL;
1551 if (get_futex_value_locked(&curval, pifutex))
1554 if (unlikely(should_fail_futex(true)))
1558 * Find the top_waiter and determine if there are additional waiters.
1559 * If the caller intends to requeue more than 1 waiter to pifutex,
1560 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1561 * as we have means to handle the possible fault. If not, don't set
1562 * the bit unecessarily as it will force the subsequent unlock to enter
1565 top_waiter = futex_top_waiter(hb1, key1);
1567 /* There are no waiters, nothing for us to do. */
1571 /* Ensure we requeue to the expected futex. */
1572 if (!match_futex(top_waiter->requeue_pi_key, key2))
1576 * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
1577 * the contended case or if set_waiters is 1. The pi_state is returned
1578 * in ps in contended cases.
1580 vpid = task_pid_vnr(top_waiter->task);
1581 ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1584 requeue_pi_wake_futex(top_waiter, key2, hb2);
1591 * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1592 * @uaddr1: source futex user address
1593 * @flags: futex flags (FLAGS_SHARED, etc.)
1594 * @uaddr2: target futex user address
1595 * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
1596 * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1597 * @cmpval: @uaddr1 expected value (or %NULL)
1598 * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1599 * pi futex (pi to pi requeue is not supported)
1601 * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1602 * uaddr2 atomically on behalf of the top waiter.
1605 * >=0 - on success, the number of tasks requeued or woken;
1608 static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1609 u32 __user *uaddr2, int nr_wake, int nr_requeue,
1610 u32 *cmpval, int requeue_pi)
1612 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1613 int drop_count = 0, task_count = 0, ret;
1614 struct futex_pi_state *pi_state = NULL;
1615 struct futex_hash_bucket *hb1, *hb2;
1616 struct futex_q *this, *next;
1621 * Requeue PI only works on two distinct uaddrs. This
1622 * check is only valid for private futexes. See below.
1624 if (uaddr1 == uaddr2)
1628 * requeue_pi requires a pi_state, try to allocate it now
1629 * without any locks in case it fails.
1631 if (refill_pi_state_cache())
1634 * requeue_pi must wake as many tasks as it can, up to nr_wake
1635 * + nr_requeue, since it acquires the rt_mutex prior to
1636 * returning to userspace, so as to not leave the rt_mutex with
1637 * waiters and no owner. However, second and third wake-ups
1638 * cannot be predicted as they involve race conditions with the
1639 * first wake and a fault while looking up the pi_state. Both
1640 * pthread_cond_signal() and pthread_cond_broadcast() should
1648 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1649 if (unlikely(ret != 0))
1651 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
1652 requeue_pi ? VERIFY_WRITE : VERIFY_READ);
1653 if (unlikely(ret != 0))
1657 * The check above which compares uaddrs is not sufficient for
1658 * shared futexes. We need to compare the keys:
1660 if (requeue_pi && match_futex(&key1, &key2)) {
1665 hb1 = hash_futex(&key1);
1666 hb2 = hash_futex(&key2);
1669 hb_waiters_inc(hb2);
1670 double_lock_hb(hb1, hb2);
1672 if (likely(cmpval != NULL)) {
1675 ret = get_futex_value_locked(&curval, uaddr1);
1677 if (unlikely(ret)) {
1678 double_unlock_hb(hb1, hb2);
1679 hb_waiters_dec(hb2);
1681 ret = get_user(curval, uaddr1);
1685 if (!(flags & FLAGS_SHARED))
1688 put_futex_key(&key2);
1689 put_futex_key(&key1);
1692 if (curval != *cmpval) {
1698 if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1700 * Attempt to acquire uaddr2 and wake the top waiter. If we
1701 * intend to requeue waiters, force setting the FUTEX_WAITERS
1702 * bit. We force this here where we are able to easily handle
1703 * faults rather in the requeue loop below.
1705 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1706 &key2, &pi_state, nr_requeue);
1709 * At this point the top_waiter has either taken uaddr2 or is
1710 * waiting on it. If the former, then the pi_state will not
1711 * exist yet, look it up one more time to ensure we have a
1712 * reference to it. If the lock was taken, ret contains the
1713 * vpid of the top waiter task.
1720 * If we acquired the lock, then the user
1721 * space value of uaddr2 should be vpid. It
1722 * cannot be changed by the top waiter as it
1723 * is blocked on hb2 lock if it tries to do
1724 * so. If something fiddled with it behind our
1725 * back the pi state lookup might unearth
1726 * it. So we rather use the known value than
1727 * rereading and handing potential crap to
1730 ret = lookup_pi_state(ret, hb2, &key2, &pi_state);
1737 free_pi_state(pi_state);
1739 double_unlock_hb(hb1, hb2);
1740 hb_waiters_dec(hb2);
1741 put_futex_key(&key2);
1742 put_futex_key(&key1);
1743 ret = fault_in_user_writeable(uaddr2);
1749 * Two reasons for this:
1750 * - Owner is exiting and we just wait for the
1752 * - The user space value changed.
1754 free_pi_state(pi_state);
1756 double_unlock_hb(hb1, hb2);
1757 hb_waiters_dec(hb2);
1758 put_futex_key(&key2);
1759 put_futex_key(&key1);
1767 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1768 if (task_count - nr_wake >= nr_requeue)
1771 if (!match_futex(&this->key, &key1))
1775 * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1776 * be paired with each other and no other futex ops.
1778 * We should never be requeueing a futex_q with a pi_state,
1779 * which is awaiting a futex_unlock_pi().
1781 if ((requeue_pi && !this->rt_waiter) ||
1782 (!requeue_pi && this->rt_waiter) ||
1789 * Wake nr_wake waiters. For requeue_pi, if we acquired the
1790 * lock, we already woke the top_waiter. If not, it will be
1791 * woken by futex_unlock_pi().
1793 if (++task_count <= nr_wake && !requeue_pi) {
1794 mark_wake_futex(&wake_q, this);
1798 /* Ensure we requeue to the expected futex for requeue_pi. */
1799 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1805 * Requeue nr_requeue waiters and possibly one more in the case
1806 * of requeue_pi if we couldn't acquire the lock atomically.
1809 /* Prepare the waiter to take the rt_mutex. */
1810 atomic_inc(&pi_state->refcount);
1811 this->pi_state = pi_state;
1812 ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1816 /* We got the lock. */
1817 requeue_pi_wake_futex(this, &key2, hb2);
1820 } else if (ret == -EAGAIN) {
1822 * Waiter was woken by timeout or
1823 * signal and has set pi_blocked_on to
1824 * PI_WAKEUP_INPROGRESS before we
1825 * tried to enqueue it on the rtmutex.
1827 this->pi_state = NULL;
1828 free_pi_state(pi_state);
1832 this->pi_state = NULL;
1833 free_pi_state(pi_state);
1837 requeue_futex(this, hb1, hb2, &key2);
1842 free_pi_state(pi_state);
1843 double_unlock_hb(hb1, hb2);
1845 hb_waiters_dec(hb2);
1848 * drop_futex_key_refs() must be called outside the spinlocks. During
1849 * the requeue we moved futex_q's from the hash bucket at key1 to the
1850 * one at key2 and updated their key pointer. We no longer need to
1851 * hold the references to key1.
1853 while (--drop_count >= 0)
1854 drop_futex_key_refs(&key1);
1857 put_futex_key(&key2);
1859 put_futex_key(&key1);
1861 return ret ? ret : task_count;
1864 /* The key must be already stored in q->key. */
1865 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
1866 __acquires(&hb->lock)
1868 struct futex_hash_bucket *hb;
1870 hb = hash_futex(&q->key);
1873 * Increment the counter before taking the lock so that
1874 * a potential waker won't miss a to-be-slept task that is
1875 * waiting for the spinlock. This is safe as all queue_lock()
1876 * users end up calling queue_me(). Similarly, for housekeeping,
1877 * decrement the counter at queue_unlock() when some error has
1878 * occurred and we don't end up adding the task to the list.
1882 q->lock_ptr = &hb->lock;
1884 spin_lock(&hb->lock); /* implies MB (A) */
1889 queue_unlock(struct futex_hash_bucket *hb)
1890 __releases(&hb->lock)
1892 spin_unlock(&hb->lock);
1897 * queue_me() - Enqueue the futex_q on the futex_hash_bucket
1898 * @q: The futex_q to enqueue
1899 * @hb: The destination hash bucket
1901 * The hb->lock must be held by the caller, and is released here. A call to
1902 * queue_me() is typically paired with exactly one call to unqueue_me(). The
1903 * exceptions involve the PI related operations, which may use unqueue_me_pi()
1904 * or nothing if the unqueue is done as part of the wake process and the unqueue
1905 * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1908 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
1909 __releases(&hb->lock)
1914 * The priority used to register this element is
1915 * - either the real thread-priority for the real-time threads
1916 * (i.e. threads with a priority lower than MAX_RT_PRIO)
1917 * - or MAX_RT_PRIO for non-RT threads.
1918 * Thus, all RT-threads are woken first in priority order, and
1919 * the others are woken last, in FIFO order.
1921 prio = min(current->normal_prio, MAX_RT_PRIO);
1923 plist_node_init(&q->list, prio);
1924 plist_add(&q->list, &hb->chain);
1926 spin_unlock(&hb->lock);
1930 * unqueue_me() - Remove the futex_q from its futex_hash_bucket
1931 * @q: The futex_q to unqueue
1933 * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
1934 * be paired with exactly one earlier call to queue_me().
1937 * 1 - if the futex_q was still queued (and we removed unqueued it);
1938 * 0 - if the futex_q was already removed by the waking thread
1940 static int unqueue_me(struct futex_q *q)
1942 spinlock_t *lock_ptr;
1945 /* In the common case we don't take the spinlock, which is nice. */
1947 lock_ptr = q->lock_ptr;
1949 if (lock_ptr != NULL) {
1950 spin_lock(lock_ptr);
1952 * q->lock_ptr can change between reading it and
1953 * spin_lock(), causing us to take the wrong lock. This
1954 * corrects the race condition.
1956 * Reasoning goes like this: if we have the wrong lock,
1957 * q->lock_ptr must have changed (maybe several times)
1958 * between reading it and the spin_lock(). It can
1959 * change again after the spin_lock() but only if it was
1960 * already changed before the spin_lock(). It cannot,
1961 * however, change back to the original value. Therefore
1962 * we can detect whether we acquired the correct lock.
1964 if (unlikely(lock_ptr != q->lock_ptr)) {
1965 spin_unlock(lock_ptr);
1970 BUG_ON(q->pi_state);
1972 spin_unlock(lock_ptr);
1976 drop_futex_key_refs(&q->key);
1981 * PI futexes can not be requeued and must remove themself from the
1982 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1985 static void unqueue_me_pi(struct futex_q *q)
1986 __releases(q->lock_ptr)
1990 BUG_ON(!q->pi_state);
1991 free_pi_state(q->pi_state);
1994 spin_unlock(q->lock_ptr);
1998 * Fixup the pi_state owner with the new owner.
2000 * Must be called with hash bucket lock held and mm->sem held for non
2003 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
2004 struct task_struct *newowner)
2006 u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
2007 struct futex_pi_state *pi_state = q->pi_state;
2008 struct task_struct *oldowner = pi_state->owner;
2009 u32 uval, uninitialized_var(curval), newval;
2013 if (!pi_state->owner)
2014 newtid |= FUTEX_OWNER_DIED;
2017 * We are here either because we stole the rtmutex from the
2018 * previous highest priority waiter or we are the highest priority
2019 * waiter but failed to get the rtmutex the first time.
2020 * We have to replace the newowner TID in the user space variable.
2021 * This must be atomic as we have to preserve the owner died bit here.
2023 * Note: We write the user space value _before_ changing the pi_state
2024 * because we can fault here. Imagine swapped out pages or a fork
2025 * that marked all the anonymous memory readonly for cow.
2027 * Modifying pi_state _before_ the user space value would
2028 * leave the pi_state in an inconsistent state when we fault
2029 * here, because we need to drop the hash bucket lock to
2030 * handle the fault. This might be observed in the PID check
2031 * in lookup_pi_state.
2034 if (get_futex_value_locked(&uval, uaddr))
2038 newval = (uval & FUTEX_OWNER_DIED) | newtid;
2040 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
2048 * We fixed up user space. Now we need to fix the pi_state
2051 if (pi_state->owner != NULL) {
2052 raw_spin_lock_irq(&pi_state->owner->pi_lock);
2053 WARN_ON(list_empty(&pi_state->list));
2054 list_del_init(&pi_state->list);
2055 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
2058 pi_state->owner = newowner;
2060 raw_spin_lock_irq(&newowner->pi_lock);
2061 WARN_ON(!list_empty(&pi_state->list));
2062 list_add(&pi_state->list, &newowner->pi_state_list);
2063 raw_spin_unlock_irq(&newowner->pi_lock);
2067 * To handle the page fault we need to drop the hash bucket
2068 * lock here. That gives the other task (either the highest priority
2069 * waiter itself or the task which stole the rtmutex) the
2070 * chance to try the fixup of the pi_state. So once we are
2071 * back from handling the fault we need to check the pi_state
2072 * after reacquiring the hash bucket lock and before trying to
2073 * do another fixup. When the fixup has been done already we
2077 spin_unlock(q->lock_ptr);
2079 ret = fault_in_user_writeable(uaddr);
2081 spin_lock(q->lock_ptr);
2084 * Check if someone else fixed it for us:
2086 if (pi_state->owner != oldowner)
2095 static long futex_wait_restart(struct restart_block *restart);
2098 * fixup_owner() - Post lock pi_state and corner case management
2099 * @uaddr: user address of the futex
2100 * @q: futex_q (contains pi_state and access to the rt_mutex)
2101 * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
2103 * After attempting to lock an rt_mutex, this function is called to cleanup
2104 * the pi_state owner as well as handle race conditions that may allow us to
2105 * acquire the lock. Must be called with the hb lock held.
2108 * 1 - success, lock taken;
2109 * 0 - success, lock not taken;
2110 * <0 - on error (-EFAULT)
2112 static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
2114 struct task_struct *owner;
2119 * Got the lock. We might not be the anticipated owner if we
2120 * did a lock-steal - fix up the PI-state in that case:
2122 if (q->pi_state->owner != current)
2123 ret = fixup_pi_state_owner(uaddr, q, current);
2128 * Catch the rare case, where the lock was released when we were on the
2129 * way back before we locked the hash bucket.
2131 if (q->pi_state->owner == current) {
2133 * Try to get the rt_mutex now. This might fail as some other
2134 * task acquired the rt_mutex after we removed ourself from the
2135 * rt_mutex waiters list.
2137 if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
2143 * pi_state is incorrect, some other task did a lock steal and
2144 * we returned due to timeout or signal without taking the
2145 * rt_mutex. Too late.
2147 raw_spin_lock_irq(&q->pi_state->pi_mutex.wait_lock);
2148 owner = rt_mutex_owner(&q->pi_state->pi_mutex);
2150 owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
2151 raw_spin_unlock_irq(&q->pi_state->pi_mutex.wait_lock);
2152 ret = fixup_pi_state_owner(uaddr, q, owner);
2157 * Paranoia check. If we did not take the lock, then we should not be
2158 * the owner of the rt_mutex.
2160 if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
2161 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
2162 "pi-state %p\n", ret,
2163 q->pi_state->pi_mutex.owner,
2164 q->pi_state->owner);
2167 return ret ? ret : locked;
2171 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
2172 * @hb: the futex hash bucket, must be locked by the caller
2173 * @q: the futex_q to queue up on
2174 * @timeout: the prepared hrtimer_sleeper, or null for no timeout
2176 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
2177 struct hrtimer_sleeper *timeout)
2180 * The task state is guaranteed to be set before another task can
2181 * wake it. set_current_state() is implemented using smp_store_mb() and
2182 * queue_me() calls spin_unlock() upon completion, both serializing
2183 * access to the hash list and forcing another memory barrier.
2185 set_current_state(TASK_INTERRUPTIBLE);
2190 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
2193 * If we have been removed from the hash list, then another task
2194 * has tried to wake us, and we can skip the call to schedule().
2196 if (likely(!plist_node_empty(&q->list))) {
2198 * If the timer has already expired, current will already be
2199 * flagged for rescheduling. Only call schedule if there
2200 * is no timeout, or if it has yet to expire.
2202 if (!timeout || timeout->task)
2203 freezable_schedule();
2205 __set_current_state(TASK_RUNNING);
2209 * futex_wait_setup() - Prepare to wait on a futex
2210 * @uaddr: the futex userspace address
2211 * @val: the expected value
2212 * @flags: futex flags (FLAGS_SHARED, etc.)
2213 * @q: the associated futex_q
2214 * @hb: storage for hash_bucket pointer to be returned to caller
2216 * Setup the futex_q and locate the hash_bucket. Get the futex value and
2217 * compare it with the expected value. Handle atomic faults internally.
2218 * Return with the hb lock held and a q.key reference on success, and unlocked
2219 * with no q.key reference on failure.
2222 * 0 - uaddr contains val and hb has been locked;
2223 * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
2225 static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
2226 struct futex_q *q, struct futex_hash_bucket **hb)
2232 * Access the page AFTER the hash-bucket is locked.
2233 * Order is important:
2235 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
2236 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
2238 * The basic logical guarantee of a futex is that it blocks ONLY
2239 * if cond(var) is known to be true at the time of blocking, for
2240 * any cond. If we locked the hash-bucket after testing *uaddr, that
2241 * would open a race condition where we could block indefinitely with
2242 * cond(var) false, which would violate the guarantee.
2244 * On the other hand, we insert q and release the hash-bucket only
2245 * after testing *uaddr. This guarantees that futex_wait() will NOT
2246 * absorb a wakeup if *uaddr does not match the desired values
2247 * while the syscall executes.
2250 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
2251 if (unlikely(ret != 0))
2255 *hb = queue_lock(q);
2257 ret = get_futex_value_locked(&uval, uaddr);
2262 ret = get_user(uval, uaddr);
2266 if (!(flags & FLAGS_SHARED))
2269 put_futex_key(&q->key);
2280 put_futex_key(&q->key);
2284 static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
2285 ktime_t *abs_time, u32 bitset)
2287 struct hrtimer_sleeper timeout, *to = NULL;
2288 struct restart_block *restart;
2289 struct futex_hash_bucket *hb;
2290 struct futex_q q = futex_q_init;
2300 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2301 CLOCK_REALTIME : CLOCK_MONOTONIC,
2303 hrtimer_init_sleeper(to, current);
2304 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2305 current->timer_slack_ns);
2310 * Prepare to wait on uaddr. On success, holds hb lock and increments
2313 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2317 /* queue_me and wait for wakeup, timeout, or a signal. */
2318 futex_wait_queue_me(hb, &q, to);
2320 /* If we were woken (and unqueued), we succeeded, whatever. */
2322 /* unqueue_me() drops q.key ref */
2323 if (!unqueue_me(&q))
2326 if (to && !to->task)
2330 * We expect signal_pending(current), but we might be the
2331 * victim of a spurious wakeup as well.
2333 if (!signal_pending(current))
2340 restart = ¤t->restart_block;
2341 restart->fn = futex_wait_restart;
2342 restart->futex.uaddr = uaddr;
2343 restart->futex.val = val;
2344 restart->futex.time = abs_time->tv64;
2345 restart->futex.bitset = bitset;
2346 restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
2348 ret = -ERESTART_RESTARTBLOCK;
2352 hrtimer_cancel(&to->timer);
2353 destroy_hrtimer_on_stack(&to->timer);
2359 static long futex_wait_restart(struct restart_block *restart)
2361 u32 __user *uaddr = restart->futex.uaddr;
2362 ktime_t t, *tp = NULL;
2364 if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
2365 t.tv64 = restart->futex.time;
2368 restart->fn = do_no_restart_syscall;
2370 return (long)futex_wait(uaddr, restart->futex.flags,
2371 restart->futex.val, tp, restart->futex.bitset);
2376 * Userspace tried a 0 -> TID atomic transition of the futex value
2377 * and failed. The kernel side here does the whole locking operation:
2378 * if there are waiters then it will block as a consequence of relying
2379 * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
2380 * a 0 value of the futex too.).
2382 * Also serves as futex trylock_pi()'ing, and due semantics.
2384 static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
2385 ktime_t *time, int trylock)
2387 struct hrtimer_sleeper timeout, *to = NULL;
2388 struct futex_hash_bucket *hb;
2389 struct futex_q q = futex_q_init;
2392 if (refill_pi_state_cache())
2397 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
2399 hrtimer_init_sleeper(to, current);
2400 hrtimer_set_expires(&to->timer, *time);
2404 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
2405 if (unlikely(ret != 0))
2409 hb = queue_lock(&q);
2411 ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
2412 if (unlikely(ret)) {
2414 * Atomic work succeeded and we got the lock,
2415 * or failed. Either way, we do _not_ block.
2419 /* We got the lock. */
2421 goto out_unlock_put_key;
2426 * Two reasons for this:
2427 * - Task is exiting and we just wait for the
2429 * - The user space value changed.
2432 put_futex_key(&q.key);
2436 goto out_unlock_put_key;
2441 * Only actually queue now that the atomic ops are done:
2445 WARN_ON(!q.pi_state);
2447 * Block on the PI mutex:
2450 ret = rt_mutex_timed_futex_lock(&q.pi_state->pi_mutex, to);
2452 ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
2453 /* Fixup the trylock return value: */
2454 ret = ret ? 0 : -EWOULDBLOCK;
2457 spin_lock(q.lock_ptr);
2459 * Fixup the pi_state owner and possibly acquire the lock if we
2462 res = fixup_owner(uaddr, &q, !ret);
2464 * If fixup_owner() returned an error, proprogate that. If it acquired
2465 * the lock, clear our -ETIMEDOUT or -EINTR.
2468 ret = (res < 0) ? res : 0;
2471 * If fixup_owner() faulted and was unable to handle the fault, unlock
2472 * it and return the fault to userspace.
2474 if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
2475 rt_mutex_unlock(&q.pi_state->pi_mutex);
2477 /* Unqueue and drop the lock */
2486 put_futex_key(&q.key);
2489 destroy_hrtimer_on_stack(&to->timer);
2490 return ret != -EINTR ? ret : -ERESTARTNOINTR;
2495 ret = fault_in_user_writeable(uaddr);
2499 if (!(flags & FLAGS_SHARED))
2502 put_futex_key(&q.key);
2507 * Userspace attempted a TID -> 0 atomic transition, and failed.
2508 * This is the in-kernel slowpath: we look up the PI state (if any),
2509 * and do the rt-mutex unlock.
2511 static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
2513 u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current);
2514 union futex_key key = FUTEX_KEY_INIT;
2515 struct futex_hash_bucket *hb;
2516 struct futex_q *match;
2520 if (get_user(uval, uaddr))
2523 * We release only a lock we actually own:
2525 if ((uval & FUTEX_TID_MASK) != vpid)
2528 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
2532 hb = hash_futex(&key);
2533 spin_lock(&hb->lock);
2536 * Check waiters first. We do not trust user space values at
2537 * all and we at least want to know if user space fiddled
2538 * with the futex value instead of blindly unlocking.
2540 match = futex_top_waiter(hb, &key);
2542 ret = wake_futex_pi(uaddr, uval, match, hb);
2544 * In case of success wake_futex_pi dropped the hash
2550 * The atomic access to the futex value generated a
2551 * pagefault, so retry the user-access and the wakeup:
2556 * wake_futex_pi has detected invalid state. Tell user
2563 * We have no kernel internal state, i.e. no waiters in the
2564 * kernel. Waiters which are about to queue themselves are stuck
2565 * on hb->lock. So we can safely ignore them. We do neither
2566 * preserve the WAITERS bit not the OWNER_DIED one. We are the
2569 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))
2573 * If uval has changed, let user space handle it.
2575 ret = (curval == uval) ? 0 : -EAGAIN;
2578 spin_unlock(&hb->lock);
2580 put_futex_key(&key);
2584 spin_unlock(&hb->lock);
2585 put_futex_key(&key);
2587 ret = fault_in_user_writeable(uaddr);
2595 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2596 * @hb: the hash_bucket futex_q was original enqueued on
2597 * @q: the futex_q woken while waiting to be requeued
2598 * @key2: the futex_key of the requeue target futex
2599 * @timeout: the timeout associated with the wait (NULL if none)
2601 * Detect if the task was woken on the initial futex as opposed to the requeue
2602 * target futex. If so, determine if it was a timeout or a signal that caused
2603 * the wakeup and return the appropriate error code to the caller. Must be
2604 * called with the hb lock held.
2607 * 0 = no early wakeup detected;
2608 * <0 = -ETIMEDOUT or -ERESTARTNOINTR
2611 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2612 struct futex_q *q, union futex_key *key2,
2613 struct hrtimer_sleeper *timeout)
2618 * With the hb lock held, we avoid races while we process the wakeup.
2619 * We only need to hold hb (and not hb2) to ensure atomicity as the
2620 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2621 * It can't be requeued from uaddr2 to something else since we don't
2622 * support a PI aware source futex for requeue.
2624 if (!match_futex(&q->key, key2)) {
2625 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2627 * We were woken prior to requeue by a timeout or a signal.
2628 * Unqueue the futex_q and determine which it was.
2630 plist_del(&q->list, &hb->chain);
2633 /* Handle spurious wakeups gracefully */
2635 if (timeout && !timeout->task)
2637 else if (signal_pending(current))
2638 ret = -ERESTARTNOINTR;
2644 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2645 * @uaddr: the futex we initially wait on (non-pi)
2646 * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
2647 * the same type, no requeueing from private to shared, etc.
2648 * @val: the expected value of uaddr
2649 * @abs_time: absolute timeout
2650 * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
2651 * @uaddr2: the pi futex we will take prior to returning to user-space
2653 * The caller will wait on uaddr and will be requeued by futex_requeue() to
2654 * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
2655 * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
2656 * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
2657 * without one, the pi logic would not know which task to boost/deboost, if
2658 * there was a need to.
2660 * We call schedule in futex_wait_queue_me() when we enqueue and return there
2661 * via the following--
2662 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2663 * 2) wakeup on uaddr2 after a requeue
2667 * If 3, cleanup and return -ERESTARTNOINTR.
2669 * If 2, we may then block on trying to take the rt_mutex and return via:
2670 * 5) successful lock
2673 * 8) other lock acquisition failure
2675 * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2677 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
2683 static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
2684 u32 val, ktime_t *abs_time, u32 bitset,
2687 struct hrtimer_sleeper timeout, *to = NULL;
2688 struct rt_mutex_waiter rt_waiter;
2689 struct rt_mutex *pi_mutex = NULL;
2690 struct futex_hash_bucket *hb, *hb2;
2691 union futex_key key2 = FUTEX_KEY_INIT;
2692 struct futex_q q = futex_q_init;
2695 if (uaddr == uaddr2)
2703 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2704 CLOCK_REALTIME : CLOCK_MONOTONIC,
2706 hrtimer_init_sleeper(to, current);
2707 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2708 current->timer_slack_ns);
2712 * The waiter is allocated on our stack, manipulated by the requeue
2713 * code while we sleep on uaddr.
2715 rt_mutex_init_waiter(&rt_waiter, false);
2717 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
2718 if (unlikely(ret != 0))
2722 q.rt_waiter = &rt_waiter;
2723 q.requeue_pi_key = &key2;
2726 * Prepare to wait on uaddr. On success, increments q.key (key1) ref
2729 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2734 * The check above which compares uaddrs is not sufficient for
2735 * shared futexes. We need to compare the keys:
2737 if (match_futex(&q.key, &key2)) {
2743 /* Queue the futex_q, drop the hb lock, wait for wakeup. */
2744 futex_wait_queue_me(hb, &q, to);
2747 * On RT we must avoid races with requeue and trying to block
2748 * on two mutexes (hb->lock and uaddr2's rtmutex) by
2749 * serializing access to pi_blocked_on with pi_lock.
2751 raw_spin_lock_irq(¤t->pi_lock);
2752 if (current->pi_blocked_on) {
2754 * We have been requeued or are in the process of
2757 raw_spin_unlock_irq(¤t->pi_lock);
2760 * Setting pi_blocked_on to PI_WAKEUP_INPROGRESS
2761 * prevents a concurrent requeue from moving us to the
2762 * uaddr2 rtmutex. After that we can safely acquire
2763 * (and possibly block on) hb->lock.
2765 current->pi_blocked_on = PI_WAKEUP_INPROGRESS;
2766 raw_spin_unlock_irq(¤t->pi_lock);
2768 spin_lock(&hb->lock);
2771 * Clean up pi_blocked_on. We might leak it otherwise
2772 * when we succeeded with the hb->lock in the fast
2775 raw_spin_lock_irq(¤t->pi_lock);
2776 current->pi_blocked_on = NULL;
2777 raw_spin_unlock_irq(¤t->pi_lock);
2779 ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2780 spin_unlock(&hb->lock);
2786 * In order to be here, we have either been requeued, are in
2787 * the process of being requeued, or requeue successfully
2788 * acquired uaddr2 on our behalf. If pi_blocked_on was
2789 * non-null above, we may be racing with a requeue. Do not
2790 * rely on q->lock_ptr to be hb2->lock until after blocking on
2791 * hb->lock or hb2->lock. The futex_requeue dropped our key1
2792 * reference and incremented our key2 reference count.
2794 hb2 = hash_futex(&key2);
2796 /* Check if the requeue code acquired the second futex for us. */
2799 * Got the lock. We might not be the anticipated owner if we
2800 * did a lock-steal - fix up the PI-state in that case.
2802 if (q.pi_state && (q.pi_state->owner != current)) {
2803 spin_lock(&hb2->lock);
2804 BUG_ON(&hb2->lock != q.lock_ptr);
2805 ret = fixup_pi_state_owner(uaddr2, &q, current);
2807 * Drop the reference to the pi state which
2808 * the requeue_pi() code acquired for us.
2810 free_pi_state(q.pi_state);
2811 spin_unlock(&hb2->lock);
2815 * We have been woken up by futex_unlock_pi(), a timeout, or a
2816 * signal. futex_unlock_pi() will not destroy the lock_ptr nor
2819 WARN_ON(!q.pi_state);
2820 pi_mutex = &q.pi_state->pi_mutex;
2821 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter);
2822 debug_rt_mutex_free_waiter(&rt_waiter);
2824 spin_lock(&hb2->lock);
2825 BUG_ON(&hb2->lock != q.lock_ptr);
2827 * Fixup the pi_state owner and possibly acquire the lock if we
2830 res = fixup_owner(uaddr2, &q, !ret);
2832 * If fixup_owner() returned an error, proprogate that. If it
2833 * acquired the lock, clear -ETIMEDOUT or -EINTR.
2836 ret = (res < 0) ? res : 0;
2838 /* Unqueue and drop the lock. */
2843 * If fixup_pi_state_owner() faulted and was unable to handle the
2844 * fault, unlock the rt_mutex and return the fault to userspace.
2846 if (ret == -EFAULT) {
2847 if (pi_mutex && rt_mutex_owner(pi_mutex) == current)
2848 rt_mutex_unlock(pi_mutex);
2849 } else if (ret == -EINTR) {
2851 * We've already been requeued, but cannot restart by calling
2852 * futex_lock_pi() directly. We could restart this syscall, but
2853 * it would detect that the user space "val" changed and return
2854 * -EWOULDBLOCK. Save the overhead of the restart and return
2855 * -EWOULDBLOCK directly.
2861 put_futex_key(&q.key);
2863 put_futex_key(&key2);
2867 hrtimer_cancel(&to->timer);
2868 destroy_hrtimer_on_stack(&to->timer);
2874 * Support for robust futexes: the kernel cleans up held futexes at
2877 * Implementation: user-space maintains a per-thread list of locks it
2878 * is holding. Upon do_exit(), the kernel carefully walks this list,
2879 * and marks all locks that are owned by this thread with the
2880 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2881 * always manipulated with the lock held, so the list is private and
2882 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
2883 * field, to allow the kernel to clean up if the thread dies after
2884 * acquiring the lock, but just before it could have added itself to
2885 * the list. There can only be one such pending lock.
2889 * sys_set_robust_list() - Set the robust-futex list head of a task
2890 * @head: pointer to the list-head
2891 * @len: length of the list-head, as userspace expects
2893 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2896 if (!futex_cmpxchg_enabled)
2899 * The kernel knows only one size for now:
2901 if (unlikely(len != sizeof(*head)))
2904 current->robust_list = head;
2910 * sys_get_robust_list() - Get the robust-futex list head of a task
2911 * @pid: pid of the process [zero for current task]
2912 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
2913 * @len_ptr: pointer to a length field, the kernel fills in the header size
2915 SYSCALL_DEFINE3(get_robust_list, int, pid,
2916 struct robust_list_head __user * __user *, head_ptr,
2917 size_t __user *, len_ptr)
2919 struct robust_list_head __user *head;
2921 struct task_struct *p;
2923 if (!futex_cmpxchg_enabled)
2932 p = find_task_by_vpid(pid);
2938 if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
2941 head = p->robust_list;
2944 if (put_user(sizeof(*head), len_ptr))
2946 return put_user(head, head_ptr);
2955 * Process a futex-list entry, check whether it's owned by the
2956 * dying task, and do notification if so:
2958 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
2960 u32 uval, uninitialized_var(nval), mval;
2963 if (get_user(uval, uaddr))
2966 if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
2968 * Ok, this dying thread is truly holding a futex
2969 * of interest. Set the OWNER_DIED bit atomically
2970 * via cmpxchg, and if the value had FUTEX_WAITERS
2971 * set, wake up a waiter (if any). (We have to do a
2972 * futex_wake() even if OWNER_DIED is already set -
2973 * to handle the rare but possible case of recursive
2974 * thread-death.) The rest of the cleanup is done in
2977 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
2979 * We are not holding a lock here, but we want to have
2980 * the pagefault_disable/enable() protection because
2981 * we want to handle the fault gracefully. If the
2982 * access fails we try to fault in the futex with R/W
2983 * verification via get_user_pages. get_user() above
2984 * does not guarantee R/W access. If that fails we
2985 * give up and leave the futex locked.
2987 if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
2988 if (fault_in_user_writeable(uaddr))
2996 * Wake robust non-PI futexes here. The wakeup of
2997 * PI futexes happens in exit_pi_state():
2999 if (!pi && (uval & FUTEX_WAITERS))
3000 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
3006 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
3008 static inline int fetch_robust_entry(struct robust_list __user **entry,
3009 struct robust_list __user * __user *head,
3012 unsigned long uentry;
3014 if (get_user(uentry, (unsigned long __user *)head))
3017 *entry = (void __user *)(uentry & ~1UL);
3024 * Walk curr->robust_list (very carefully, it's a userspace list!)
3025 * and mark any locks found there dead, and notify any waiters.
3027 * We silently return on any sign of list-walking problem.
3029 void exit_robust_list(struct task_struct *curr)
3031 struct robust_list_head __user *head = curr->robust_list;
3032 struct robust_list __user *entry, *next_entry, *pending;
3033 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
3034 unsigned int uninitialized_var(next_pi);
3035 unsigned long futex_offset;
3038 if (!futex_cmpxchg_enabled)
3042 * Fetch the list head (which was registered earlier, via
3043 * sys_set_robust_list()):
3045 if (fetch_robust_entry(&entry, &head->list.next, &pi))
3048 * Fetch the relative futex offset:
3050 if (get_user(futex_offset, &head->futex_offset))
3053 * Fetch any possibly pending lock-add first, and handle it
3056 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
3059 next_entry = NULL; /* avoid warning with gcc */
3060 while (entry != &head->list) {
3062 * Fetch the next entry in the list before calling
3063 * handle_futex_death:
3065 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
3067 * A pending lock might already be on the list, so
3068 * don't process it twice:
3070 if (entry != pending)
3071 if (handle_futex_death((void __user *)entry + futex_offset,
3079 * Avoid excessively long or circular lists:
3088 handle_futex_death((void __user *)pending + futex_offset,
3092 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
3093 u32 __user *uaddr2, u32 val2, u32 val3)
3095 int cmd = op & FUTEX_CMD_MASK;
3096 unsigned int flags = 0;
3098 if (!(op & FUTEX_PRIVATE_FLAG))
3099 flags |= FLAGS_SHARED;
3101 if (op & FUTEX_CLOCK_REALTIME) {
3102 flags |= FLAGS_CLOCKRT;
3103 if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
3109 case FUTEX_UNLOCK_PI:
3110 case FUTEX_TRYLOCK_PI:
3111 case FUTEX_WAIT_REQUEUE_PI:
3112 case FUTEX_CMP_REQUEUE_PI:
3113 if (!futex_cmpxchg_enabled)
3119 val3 = FUTEX_BITSET_MATCH_ANY;
3120 case FUTEX_WAIT_BITSET:
3121 return futex_wait(uaddr, flags, val, timeout, val3);
3123 val3 = FUTEX_BITSET_MATCH_ANY;
3124 case FUTEX_WAKE_BITSET:
3125 return futex_wake(uaddr, flags, val, val3);
3127 return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
3128 case FUTEX_CMP_REQUEUE:
3129 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
3131 return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
3133 return futex_lock_pi(uaddr, flags, timeout, 0);
3134 case FUTEX_UNLOCK_PI:
3135 return futex_unlock_pi(uaddr, flags);
3136 case FUTEX_TRYLOCK_PI:
3137 return futex_lock_pi(uaddr, flags, NULL, 1);
3138 case FUTEX_WAIT_REQUEUE_PI:
3139 val3 = FUTEX_BITSET_MATCH_ANY;
3140 return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
3142 case FUTEX_CMP_REQUEUE_PI:
3143 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
3149 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
3150 struct timespec __user *, utime, u32 __user *, uaddr2,
3154 ktime_t t, *tp = NULL;
3156 int cmd = op & FUTEX_CMD_MASK;
3158 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
3159 cmd == FUTEX_WAIT_BITSET ||
3160 cmd == FUTEX_WAIT_REQUEUE_PI)) {
3161 if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
3163 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
3165 if (!timespec_valid(&ts))
3168 t = timespec_to_ktime(ts);
3169 if (cmd == FUTEX_WAIT)
3170 t = ktime_add_safe(ktime_get(), t);
3174 * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
3175 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
3177 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
3178 cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
3179 val2 = (u32) (unsigned long) utime;
3181 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
3184 static void __init futex_detect_cmpxchg(void)
3186 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
3190 * This will fail and we want it. Some arch implementations do
3191 * runtime detection of the futex_atomic_cmpxchg_inatomic()
3192 * functionality. We want to know that before we call in any
3193 * of the complex code paths. Also we want to prevent
3194 * registration of robust lists in that case. NULL is
3195 * guaranteed to fault and we get -EFAULT on functional
3196 * implementation, the non-functional ones will return
3199 if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
3200 futex_cmpxchg_enabled = 1;
3204 static int __init futex_init(void)
3206 unsigned int futex_shift;
3209 #if CONFIG_BASE_SMALL
3210 futex_hashsize = 16;
3212 futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
3215 futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
3217 futex_hashsize < 256 ? HASH_SMALL : 0,
3219 futex_hashsize, futex_hashsize);
3220 futex_hashsize = 1UL << futex_shift;
3222 futex_detect_cmpxchg();
3224 for (i = 0; i < futex_hashsize; i++) {
3225 atomic_set(&futex_queues[i].waiters, 0);
3226 plist_head_init(&futex_queues[i].chain);
3227 spin_lock_init(&futex_queues[i].lock);
3232 __initcall(futex_init);