1 // SPDX-License-Identifier: GPL-2.0-or-later
3 * Fast Userspace Mutexes (which I call "Futexes!").
4 * (C) Rusty Russell, IBM 2002
6 * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
7 * (C) Copyright 2003 Red Hat Inc, All Rights Reserved
9 * Removed page pinning, fix privately mapped COW pages and other cleanups
10 * (C) Copyright 2003, 2004 Jamie Lokier
12 * Robust futex support started by Ingo Molnar
13 * (C) Copyright 2006 Red Hat Inc, All Rights Reserved
14 * Thanks to Thomas Gleixner for suggestions, analysis and fixes.
16 * PI-futex support started by Ingo Molnar and Thomas Gleixner
17 * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
18 * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
20 * PRIVATE futexes by Eric Dumazet
21 * Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
23 * Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
24 * Copyright (C) IBM Corporation, 2009
25 * Thanks to Thomas Gleixner for conceptual design and careful reviews.
27 * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
28 * enough at me, Linus for the original (flawed) idea, Matthew
29 * Kirkwood for proof-of-concept implementation.
31 * "The futexes are also cursed."
32 * "But they come in a choice of three flavours!"
34 #include <linux/compat.h>
35 #include <linux/jhash.h>
36 #include <linux/pagemap.h>
37 #include <linux/syscalls.h>
38 #include <linux/hugetlb.h>
39 #include <linux/freezer.h>
40 #include <linux/memblock.h>
41 #include <linux/fault-inject.h>
42 #include <linux/time_namespace.h>
44 #include <asm/futex.h>
46 #include "locking/rtmutex_common.h"
49 * READ this before attempting to hack on futexes!
51 * Basic futex operation and ordering guarantees
52 * =============================================
54 * The waiter reads the futex value in user space and calls
55 * futex_wait(). This function computes the hash bucket and acquires
56 * the hash bucket lock. After that it reads the futex user space value
57 * again and verifies that the data has not changed. If it has not changed
58 * it enqueues itself into the hash bucket, releases the hash bucket lock
61 * The waker side modifies the user space value of the futex and calls
62 * futex_wake(). This function computes the hash bucket and acquires the
63 * hash bucket lock. Then it looks for waiters on that futex in the hash
64 * bucket and wakes them.
66 * In futex wake up scenarios where no tasks are blocked on a futex, taking
67 * the hb spinlock can be avoided and simply return. In order for this
68 * optimization to work, ordering guarantees must exist so that the waiter
69 * being added to the list is acknowledged when the list is concurrently being
70 * checked by the waker, avoiding scenarios like the following:
74 * sys_futex(WAIT, futex, val);
75 * futex_wait(futex, val);
78 * sys_futex(WAKE, futex);
83 * lock(hash_bucket(futex));
85 * unlock(hash_bucket(futex));
88 * This would cause the waiter on CPU 0 to wait forever because it
89 * missed the transition of the user space value from val to newval
90 * and the waker did not find the waiter in the hash bucket queue.
92 * The correct serialization ensures that a waiter either observes
93 * the changed user space value before blocking or is woken by a
98 * sys_futex(WAIT, futex, val);
99 * futex_wait(futex, val);
102 * smp_mb(); (A) <-- paired with -.
104 * lock(hash_bucket(futex)); |
108 * | sys_futex(WAKE, futex);
109 * | futex_wake(futex);
111 * `--------> smp_mb(); (B)
114 * unlock(hash_bucket(futex));
115 * schedule(); if (waiters)
116 * lock(hash_bucket(futex));
117 * else wake_waiters(futex);
118 * waiters--; (b) unlock(hash_bucket(futex));
120 * Where (A) orders the waiters increment and the futex value read through
121 * atomic operations (see hb_waiters_inc) and where (B) orders the write
122 * to futex and the waiters read (see hb_waiters_pending()).
124 * This yields the following case (where X:=waiters, Y:=futex):
132 * Which guarantees that x==0 && y==0 is impossible; which translates back into
133 * the guarantee that we cannot both miss the futex variable change and the
136 * Note that a new waiter is accounted for in (a) even when it is possible that
137 * the wait call can return error, in which case we backtrack from it in (b).
138 * Refer to the comment in queue_lock().
140 * Similarly, in order to account for waiters being requeued on another
141 * address we always increment the waiters for the destination bucket before
142 * acquiring the lock. It then decrements them again after releasing it -
143 * the code that actually moves the futex(es) between hash buckets (requeue_futex)
144 * will do the additional required waiter count housekeeping. This is done for
145 * double_lock_hb() and double_unlock_hb(), respectively.
148 #ifdef CONFIG_HAVE_FUTEX_CMPXCHG
149 #define futex_cmpxchg_enabled 1
151 static int __read_mostly futex_cmpxchg_enabled;
155 * Futex flags used to encode options to functions and preserve them across
159 # define FLAGS_SHARED 0x01
162 * NOMMU does not have per process address space. Let the compiler optimize
165 # define FLAGS_SHARED 0x00
167 #define FLAGS_CLOCKRT 0x02
168 #define FLAGS_HAS_TIMEOUT 0x04
171 * Priority Inheritance state:
173 struct futex_pi_state {
175 * list of 'owned' pi_state instances - these have to be
176 * cleaned up in do_exit() if the task exits prematurely:
178 struct list_head list;
183 struct rt_mutex pi_mutex;
185 struct task_struct *owner;
189 } __randomize_layout;
192 * struct futex_q - The hashed futex queue entry, one per waiting task
193 * @list: priority-sorted list of tasks waiting on this futex
194 * @task: the task waiting on the futex
195 * @lock_ptr: the hash bucket lock
196 * @key: the key the futex is hashed on
197 * @pi_state: optional priority inheritance state
198 * @rt_waiter: rt_waiter storage for use with requeue_pi
199 * @requeue_pi_key: the requeue_pi target futex key
200 * @bitset: bitset for the optional bitmasked wakeup
202 * We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so
203 * we can wake only the relevant ones (hashed queues may be shared).
205 * A futex_q has a woken state, just like tasks have TASK_RUNNING.
206 * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
207 * The order of wakeup is always to make the first condition true, then
210 * PI futexes are typically woken before they are removed from the hash list via
211 * the rt_mutex code. See unqueue_me_pi().
214 struct plist_node list;
216 struct task_struct *task;
217 spinlock_t *lock_ptr;
219 struct futex_pi_state *pi_state;
220 struct rt_mutex_waiter *rt_waiter;
221 union futex_key *requeue_pi_key;
223 } __randomize_layout;
225 static const struct futex_q futex_q_init = {
226 /* list gets initialized in queue_me()*/
227 .key = FUTEX_KEY_INIT,
228 .bitset = FUTEX_BITSET_MATCH_ANY
232 * Hash buckets are shared by all the futex_keys that hash to the same
233 * location. Each key may have multiple futex_q structures, one for each task
234 * waiting on a futex.
236 struct futex_hash_bucket {
239 struct plist_head chain;
240 } ____cacheline_aligned_in_smp;
243 * The base of the bucket array and its size are always used together
244 * (after initialization only in hash_futex()), so ensure that they
245 * reside in the same cacheline.
248 struct futex_hash_bucket *queues;
249 unsigned long hashsize;
250 } __futex_data __read_mostly __aligned(2*sizeof(long));
251 #define futex_queues (__futex_data.queues)
252 #define futex_hashsize (__futex_data.hashsize)
256 * Fault injections for futexes.
258 #ifdef CONFIG_FAIL_FUTEX
261 struct fault_attr attr;
265 .attr = FAULT_ATTR_INITIALIZER,
266 .ignore_private = false,
269 static int __init setup_fail_futex(char *str)
271 return setup_fault_attr(&fail_futex.attr, str);
273 __setup("fail_futex=", setup_fail_futex);
275 static bool should_fail_futex(bool fshared)
277 if (fail_futex.ignore_private && !fshared)
280 return should_fail(&fail_futex.attr, 1);
283 #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
285 static int __init fail_futex_debugfs(void)
287 umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
290 dir = fault_create_debugfs_attr("fail_futex", NULL,
295 debugfs_create_bool("ignore-private", mode, dir,
296 &fail_futex.ignore_private);
300 late_initcall(fail_futex_debugfs);
302 #endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
305 static inline bool should_fail_futex(bool fshared)
309 #endif /* CONFIG_FAIL_FUTEX */
312 static void compat_exit_robust_list(struct task_struct *curr);
314 static inline void compat_exit_robust_list(struct task_struct *curr) { }
318 * Reflects a new waiter being added to the waitqueue.
320 static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
323 atomic_inc(&hb->waiters);
325 * Full barrier (A), see the ordering comment above.
327 smp_mb__after_atomic();
332 * Reflects a waiter being removed from the waitqueue by wakeup
335 static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
338 atomic_dec(&hb->waiters);
342 static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
346 * Full barrier (B), see the ordering comment above.
349 return atomic_read(&hb->waiters);
356 * hash_futex - Return the hash bucket in the global hash
357 * @key: Pointer to the futex key for which the hash is calculated
359 * We hash on the keys returned from get_futex_key (see below) and return the
360 * corresponding hash bucket in the global hash.
362 static struct futex_hash_bucket *hash_futex(union futex_key *key)
364 u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
367 return &futex_queues[hash & (futex_hashsize - 1)];
372 * match_futex - Check whether two futex keys are equal
373 * @key1: Pointer to key1
374 * @key2: Pointer to key2
376 * Return 1 if two futex_keys are equal, 0 otherwise.
378 static inline int match_futex(union futex_key *key1, union futex_key *key2)
381 && key1->both.word == key2->both.word
382 && key1->both.ptr == key2->both.ptr
383 && key1->both.offset == key2->both.offset);
392 * futex_setup_timer - set up the sleeping hrtimer.
393 * @time: ptr to the given timeout value
394 * @timeout: the hrtimer_sleeper structure to be set up
395 * @flags: futex flags
396 * @range_ns: optional range in ns
398 * Return: Initialized hrtimer_sleeper structure or NULL if no timeout
401 static inline struct hrtimer_sleeper *
402 futex_setup_timer(ktime_t *time, struct hrtimer_sleeper *timeout,
403 int flags, u64 range_ns)
408 hrtimer_init_sleeper_on_stack(timeout, (flags & FLAGS_CLOCKRT) ?
409 CLOCK_REALTIME : CLOCK_MONOTONIC,
412 * If range_ns is 0, calling hrtimer_set_expires_range_ns() is
413 * effectively the same as calling hrtimer_set_expires().
415 hrtimer_set_expires_range_ns(&timeout->timer, *time, range_ns);
421 * Generate a machine wide unique identifier for this inode.
423 * This relies on u64 not wrapping in the life-time of the machine; which with
424 * 1ns resolution means almost 585 years.
426 * This further relies on the fact that a well formed program will not unmap
427 * the file while it has a (shared) futex waiting on it. This mapping will have
428 * a file reference which pins the mount and inode.
430 * If for some reason an inode gets evicted and read back in again, it will get
431 * a new sequence number and will _NOT_ match, even though it is the exact same
434 * It is important that match_futex() will never have a false-positive, esp.
435 * for PI futexes that can mess up the state. The above argues that false-negatives
436 * are only possible for malformed programs.
438 static u64 get_inode_sequence_number(struct inode *inode)
440 static atomic64_t i_seq;
443 /* Does the inode already have a sequence number? */
444 old = atomic64_read(&inode->i_sequence);
449 u64 new = atomic64_add_return(1, &i_seq);
450 if (WARN_ON_ONCE(!new))
453 old = atomic64_cmpxchg_relaxed(&inode->i_sequence, 0, new);
461 * get_futex_key() - Get parameters which are the keys for a futex
462 * @uaddr: virtual address of the futex
463 * @fshared: false for a PROCESS_PRIVATE futex, true for PROCESS_SHARED
464 * @key: address where result is stored.
465 * @rw: mapping needs to be read/write (values: FUTEX_READ,
468 * Return: a negative error code or 0
470 * The key words are stored in @key on success.
472 * For shared mappings (when @fshared), the key is:
474 * ( inode->i_sequence, page->index, offset_within_page )
476 * [ also see get_inode_sequence_number() ]
478 * For private mappings (or when !@fshared), the key is:
480 * ( current->mm, address, 0 )
482 * This allows (cross process, where applicable) identification of the futex
483 * without keeping the page pinned for the duration of the FUTEX_WAIT.
485 * lock_page() might sleep, the caller should not hold a spinlock.
487 static int get_futex_key(u32 __user *uaddr, bool fshared, union futex_key *key,
488 enum futex_access rw)
490 unsigned long address = (unsigned long)uaddr;
491 struct mm_struct *mm = current->mm;
492 struct page *page, *tail;
493 struct address_space *mapping;
497 * The futex address must be "naturally" aligned.
499 key->both.offset = address % PAGE_SIZE;
500 if (unlikely((address % sizeof(u32)) != 0))
502 address -= key->both.offset;
504 if (unlikely(!access_ok(uaddr, sizeof(u32))))
507 if (unlikely(should_fail_futex(fshared)))
511 * PROCESS_PRIVATE futexes are fast.
512 * As the mm cannot disappear under us and the 'key' only needs
513 * virtual address, we dont even have to find the underlying vma.
514 * Note : We do have to check 'uaddr' is a valid user address,
515 * but access_ok() should be faster than find_vma()
518 key->private.mm = mm;
519 key->private.address = address;
524 /* Ignore any VERIFY_READ mapping (futex common case) */
525 if (unlikely(should_fail_futex(true)))
528 err = get_user_pages_fast(address, 1, FOLL_WRITE, &page);
530 * If write access is not required (eg. FUTEX_WAIT), try
531 * and get read-only access.
533 if (err == -EFAULT && rw == FUTEX_READ) {
534 err = get_user_pages_fast(address, 1, 0, &page);
543 * The treatment of mapping from this point on is critical. The page
544 * lock protects many things but in this context the page lock
545 * stabilizes mapping, prevents inode freeing in the shared
546 * file-backed region case and guards against movement to swap cache.
548 * Strictly speaking the page lock is not needed in all cases being
549 * considered here and page lock forces unnecessarily serialization
550 * From this point on, mapping will be re-verified if necessary and
551 * page lock will be acquired only if it is unavoidable
553 * Mapping checks require the head page for any compound page so the
554 * head page and mapping is looked up now. For anonymous pages, it
555 * does not matter if the page splits in the future as the key is
556 * based on the address. For filesystem-backed pages, the tail is
557 * required as the index of the page determines the key. For
558 * base pages, there is no tail page and tail == page.
561 page = compound_head(page);
562 mapping = READ_ONCE(page->mapping);
565 * If page->mapping is NULL, then it cannot be a PageAnon
566 * page; but it might be the ZERO_PAGE or in the gate area or
567 * in a special mapping (all cases which we are happy to fail);
568 * or it may have been a good file page when get_user_pages_fast
569 * found it, but truncated or holepunched or subjected to
570 * invalidate_complete_page2 before we got the page lock (also
571 * cases which we are happy to fail). And we hold a reference,
572 * so refcount care in invalidate_complete_page's remove_mapping
573 * prevents drop_caches from setting mapping to NULL beneath us.
575 * The case we do have to guard against is when memory pressure made
576 * shmem_writepage move it from filecache to swapcache beneath us:
577 * an unlikely race, but we do need to retry for page->mapping.
579 if (unlikely(!mapping)) {
583 * Page lock is required to identify which special case above
584 * applies. If this is really a shmem page then the page lock
585 * will prevent unexpected transitions.
588 shmem_swizzled = PageSwapCache(page) || page->mapping;
599 * Private mappings are handled in a simple way.
601 * If the futex key is stored on an anonymous page, then the associated
602 * object is the mm which is implicitly pinned by the calling process.
604 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
605 * it's a read-only handle, it's expected that futexes attach to
606 * the object not the particular process.
608 if (PageAnon(page)) {
610 * A RO anonymous page will never change and thus doesn't make
611 * sense for futex operations.
613 if (unlikely(should_fail_futex(true)) || ro) {
618 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
619 key->private.mm = mm;
620 key->private.address = address;
626 * The associated futex object in this case is the inode and
627 * the page->mapping must be traversed. Ordinarily this should
628 * be stabilised under page lock but it's not strictly
629 * necessary in this case as we just want to pin the inode, not
630 * update the radix tree or anything like that.
632 * The RCU read lock is taken as the inode is finally freed
633 * under RCU. If the mapping still matches expectations then the
634 * mapping->host can be safely accessed as being a valid inode.
638 if (READ_ONCE(page->mapping) != mapping) {
645 inode = READ_ONCE(mapping->host);
653 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
654 key->shared.i_seq = get_inode_sequence_number(inode);
655 key->shared.pgoff = basepage_index(tail);
665 * fault_in_user_writeable() - Fault in user address and verify RW access
666 * @uaddr: pointer to faulting user space address
668 * Slow path to fixup the fault we just took in the atomic write
671 * We have no generic implementation of a non-destructive write to the
672 * user address. We know that we faulted in the atomic pagefault
673 * disabled section so we can as well avoid the #PF overhead by
674 * calling get_user_pages() right away.
676 static int fault_in_user_writeable(u32 __user *uaddr)
678 struct mm_struct *mm = current->mm;
682 ret = fixup_user_fault(mm, (unsigned long)uaddr,
683 FAULT_FLAG_WRITE, NULL);
684 mmap_read_unlock(mm);
686 return ret < 0 ? ret : 0;
690 * futex_top_waiter() - Return the highest priority waiter on a futex
691 * @hb: the hash bucket the futex_q's reside in
692 * @key: the futex key (to distinguish it from other futex futex_q's)
694 * Must be called with the hb lock held.
696 static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
697 union futex_key *key)
699 struct futex_q *this;
701 plist_for_each_entry(this, &hb->chain, list) {
702 if (match_futex(&this->key, key))
708 static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
709 u32 uval, u32 newval)
714 ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
720 static int get_futex_value_locked(u32 *dest, u32 __user *from)
725 ret = __get_user(*dest, from);
728 return ret ? -EFAULT : 0;
735 static int refill_pi_state_cache(void)
737 struct futex_pi_state *pi_state;
739 if (likely(current->pi_state_cache))
742 pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
747 INIT_LIST_HEAD(&pi_state->list);
748 /* pi_mutex gets initialized later */
749 pi_state->owner = NULL;
750 refcount_set(&pi_state->refcount, 1);
751 pi_state->key = FUTEX_KEY_INIT;
753 current->pi_state_cache = pi_state;
758 static struct futex_pi_state *alloc_pi_state(void)
760 struct futex_pi_state *pi_state = current->pi_state_cache;
763 current->pi_state_cache = NULL;
768 static void get_pi_state(struct futex_pi_state *pi_state)
770 WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount));
774 * Drops a reference to the pi_state object and frees or caches it
775 * when the last reference is gone.
777 static void put_pi_state(struct futex_pi_state *pi_state)
782 if (!refcount_dec_and_test(&pi_state->refcount))
786 * If pi_state->owner is NULL, the owner is most probably dying
787 * and has cleaned up the pi_state already
789 if (pi_state->owner) {
790 struct task_struct *owner;
792 raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
793 owner = pi_state->owner;
795 raw_spin_lock(&owner->pi_lock);
796 list_del_init(&pi_state->list);
797 raw_spin_unlock(&owner->pi_lock);
799 rt_mutex_proxy_unlock(&pi_state->pi_mutex, owner);
800 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
803 if (current->pi_state_cache) {
807 * pi_state->list is already empty.
808 * clear pi_state->owner.
809 * refcount is at 0 - put it back to 1.
811 pi_state->owner = NULL;
812 refcount_set(&pi_state->refcount, 1);
813 current->pi_state_cache = pi_state;
817 #ifdef CONFIG_FUTEX_PI
820 * This task is holding PI mutexes at exit time => bad.
821 * Kernel cleans up PI-state, but userspace is likely hosed.
822 * (Robust-futex cleanup is separate and might save the day for userspace.)
824 static void exit_pi_state_list(struct task_struct *curr)
826 struct list_head *next, *head = &curr->pi_state_list;
827 struct futex_pi_state *pi_state;
828 struct futex_hash_bucket *hb;
829 union futex_key key = FUTEX_KEY_INIT;
831 if (!futex_cmpxchg_enabled)
834 * We are a ZOMBIE and nobody can enqueue itself on
835 * pi_state_list anymore, but we have to be careful
836 * versus waiters unqueueing themselves:
838 raw_spin_lock_irq(&curr->pi_lock);
839 while (!list_empty(head)) {
841 pi_state = list_entry(next, struct futex_pi_state, list);
843 hb = hash_futex(&key);
846 * We can race against put_pi_state() removing itself from the
847 * list (a waiter going away). put_pi_state() will first
848 * decrement the reference count and then modify the list, so
849 * its possible to see the list entry but fail this reference
852 * In that case; drop the locks to let put_pi_state() make
853 * progress and retry the loop.
855 if (!refcount_inc_not_zero(&pi_state->refcount)) {
856 raw_spin_unlock_irq(&curr->pi_lock);
858 raw_spin_lock_irq(&curr->pi_lock);
861 raw_spin_unlock_irq(&curr->pi_lock);
863 spin_lock(&hb->lock);
864 raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
865 raw_spin_lock(&curr->pi_lock);
867 * We dropped the pi-lock, so re-check whether this
868 * task still owns the PI-state:
870 if (head->next != next) {
871 /* retain curr->pi_lock for the loop invariant */
872 raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
873 spin_unlock(&hb->lock);
874 put_pi_state(pi_state);
878 WARN_ON(pi_state->owner != curr);
879 WARN_ON(list_empty(&pi_state->list));
880 list_del_init(&pi_state->list);
881 pi_state->owner = NULL;
883 raw_spin_unlock(&curr->pi_lock);
884 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
885 spin_unlock(&hb->lock);
887 rt_mutex_futex_unlock(&pi_state->pi_mutex);
888 put_pi_state(pi_state);
890 raw_spin_lock_irq(&curr->pi_lock);
892 raw_spin_unlock_irq(&curr->pi_lock);
895 static inline void exit_pi_state_list(struct task_struct *curr) { }
899 * We need to check the following states:
901 * Waiter | pi_state | pi->owner | uTID | uODIED | ?
903 * [1] NULL | --- | --- | 0 | 0/1 | Valid
904 * [2] NULL | --- | --- | >0 | 0/1 | Valid
906 * [3] Found | NULL | -- | Any | 0/1 | Invalid
908 * [4] Found | Found | NULL | 0 | 1 | Valid
909 * [5] Found | Found | NULL | >0 | 1 | Invalid
911 * [6] Found | Found | task | 0 | 1 | Valid
913 * [7] Found | Found | NULL | Any | 0 | Invalid
915 * [8] Found | Found | task | ==taskTID | 0/1 | Valid
916 * [9] Found | Found | task | 0 | 0 | Invalid
917 * [10] Found | Found | task | !=taskTID | 0/1 | Invalid
919 * [1] Indicates that the kernel can acquire the futex atomically. We
920 * came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
922 * [2] Valid, if TID does not belong to a kernel thread. If no matching
923 * thread is found then it indicates that the owner TID has died.
925 * [3] Invalid. The waiter is queued on a non PI futex
927 * [4] Valid state after exit_robust_list(), which sets the user space
928 * value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
930 * [5] The user space value got manipulated between exit_robust_list()
931 * and exit_pi_state_list()
933 * [6] Valid state after exit_pi_state_list() which sets the new owner in
934 * the pi_state but cannot access the user space value.
936 * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
938 * [8] Owner and user space value match
940 * [9] There is no transient state which sets the user space TID to 0
941 * except exit_robust_list(), but this is indicated by the
942 * FUTEX_OWNER_DIED bit. See [4]
944 * [10] There is no transient state which leaves owner and user space
948 * Serialization and lifetime rules:
952 * hb -> futex_q, relation
953 * futex_q -> pi_state, relation
955 * (cannot be raw because hb can contain arbitrary amount
958 * pi_mutex->wait_lock:
962 * (and pi_mutex 'obviously')
966 * p->pi_state_list -> pi_state->list, relation
968 * pi_state->refcount:
976 * pi_mutex->wait_lock
982 * Validate that the existing waiter has a pi_state and sanity check
983 * the pi_state against the user space value. If correct, attach to
986 static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
987 struct futex_pi_state *pi_state,
988 struct futex_pi_state **ps)
990 pid_t pid = uval & FUTEX_TID_MASK;
995 * Userspace might have messed up non-PI and PI futexes [3]
997 if (unlikely(!pi_state))
1001 * We get here with hb->lock held, and having found a
1002 * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
1003 * has dropped the hb->lock in between queue_me() and unqueue_me_pi(),
1004 * which in turn means that futex_lock_pi() still has a reference on
1007 * The waiter holding a reference on @pi_state also protects against
1008 * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
1009 * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
1010 * free pi_state before we can take a reference ourselves.
1012 WARN_ON(!refcount_read(&pi_state->refcount));
1015 * Now that we have a pi_state, we can acquire wait_lock
1016 * and do the state validation.
1018 raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
1021 * Since {uval, pi_state} is serialized by wait_lock, and our current
1022 * uval was read without holding it, it can have changed. Verify it
1023 * still is what we expect it to be, otherwise retry the entire
1026 if (get_futex_value_locked(&uval2, uaddr))
1033 * Handle the owner died case:
1035 if (uval & FUTEX_OWNER_DIED) {
1037 * exit_pi_state_list sets owner to NULL and wakes the
1038 * topmost waiter. The task which acquires the
1039 * pi_state->rt_mutex will fixup owner.
1041 if (!pi_state->owner) {
1043 * No pi state owner, but the user space TID
1044 * is not 0. Inconsistent state. [5]
1049 * Take a ref on the state and return success. [4]
1055 * If TID is 0, then either the dying owner has not
1056 * yet executed exit_pi_state_list() or some waiter
1057 * acquired the rtmutex in the pi state, but did not
1058 * yet fixup the TID in user space.
1060 * Take a ref on the state and return success. [6]
1066 * If the owner died bit is not set, then the pi_state
1067 * must have an owner. [7]
1069 if (!pi_state->owner)
1074 * Bail out if user space manipulated the futex value. If pi
1075 * state exists then the owner TID must be the same as the
1076 * user space TID. [9/10]
1078 if (pid != task_pid_vnr(pi_state->owner))
1082 get_pi_state(pi_state);
1083 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1100 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1105 * wait_for_owner_exiting - Block until the owner has exited
1106 * @ret: owner's current futex lock status
1107 * @exiting: Pointer to the exiting task
1109 * Caller must hold a refcount on @exiting.
1111 static void wait_for_owner_exiting(int ret, struct task_struct *exiting)
1113 if (ret != -EBUSY) {
1114 WARN_ON_ONCE(exiting);
1118 if (WARN_ON_ONCE(ret == -EBUSY && !exiting))
1121 mutex_lock(&exiting->futex_exit_mutex);
1123 * No point in doing state checking here. If the waiter got here
1124 * while the task was in exec()->exec_futex_release() then it can
1125 * have any FUTEX_STATE_* value when the waiter has acquired the
1126 * mutex. OK, if running, EXITING or DEAD if it reached exit()
1127 * already. Highly unlikely and not a problem. Just one more round
1128 * through the futex maze.
1130 mutex_unlock(&exiting->futex_exit_mutex);
1132 put_task_struct(exiting);
1135 static int handle_exit_race(u32 __user *uaddr, u32 uval,
1136 struct task_struct *tsk)
1141 * If the futex exit state is not yet FUTEX_STATE_DEAD, tell the
1142 * caller that the alleged owner is busy.
1144 if (tsk && tsk->futex_state != FUTEX_STATE_DEAD)
1148 * Reread the user space value to handle the following situation:
1152 * sys_exit() sys_futex()
1153 * do_exit() futex_lock_pi()
1154 * futex_lock_pi_atomic()
1155 * exit_signals(tsk) No waiters:
1156 * tsk->flags |= PF_EXITING; *uaddr == 0x00000PID
1157 * mm_release(tsk) Set waiter bit
1158 * exit_robust_list(tsk) { *uaddr = 0x80000PID;
1159 * Set owner died attach_to_pi_owner() {
1160 * *uaddr = 0xC0000000; tsk = get_task(PID);
1161 * } if (!tsk->flags & PF_EXITING) {
1163 * tsk->futex_state = } else {
1164 * FUTEX_STATE_DEAD; if (tsk->futex_state !=
1167 * return -ESRCH; <--- FAIL
1170 * Returning ESRCH unconditionally is wrong here because the
1171 * user space value has been changed by the exiting task.
1173 * The same logic applies to the case where the exiting task is
1176 if (get_futex_value_locked(&uval2, uaddr))
1179 /* If the user space value has changed, try again. */
1184 * The exiting task did not have a robust list, the robust list was
1185 * corrupted or the user space value in *uaddr is simply bogus.
1186 * Give up and tell user space.
1192 * Lookup the task for the TID provided from user space and attach to
1193 * it after doing proper sanity checks.
1195 static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key,
1196 struct futex_pi_state **ps,
1197 struct task_struct **exiting)
1199 pid_t pid = uval & FUTEX_TID_MASK;
1200 struct futex_pi_state *pi_state;
1201 struct task_struct *p;
1204 * We are the first waiter - try to look up the real owner and attach
1205 * the new pi_state to it, but bail out when TID = 0 [1]
1207 * The !pid check is paranoid. None of the call sites should end up
1208 * with pid == 0, but better safe than sorry. Let the caller retry
1212 p = find_get_task_by_vpid(pid);
1214 return handle_exit_race(uaddr, uval, NULL);
1216 if (unlikely(p->flags & PF_KTHREAD)) {
1222 * We need to look at the task state to figure out, whether the
1223 * task is exiting. To protect against the change of the task state
1224 * in futex_exit_release(), we do this protected by p->pi_lock:
1226 raw_spin_lock_irq(&p->pi_lock);
1227 if (unlikely(p->futex_state != FUTEX_STATE_OK)) {
1229 * The task is on the way out. When the futex state is
1230 * FUTEX_STATE_DEAD, we know that the task has finished
1233 int ret = handle_exit_race(uaddr, uval, p);
1235 raw_spin_unlock_irq(&p->pi_lock);
1237 * If the owner task is between FUTEX_STATE_EXITING and
1238 * FUTEX_STATE_DEAD then store the task pointer and keep
1239 * the reference on the task struct. The calling code will
1240 * drop all locks, wait for the task to reach
1241 * FUTEX_STATE_DEAD and then drop the refcount. This is
1242 * required to prevent a live lock when the current task
1243 * preempted the exiting task between the two states.
1253 * No existing pi state. First waiter. [2]
1255 * This creates pi_state, we have hb->lock held, this means nothing can
1256 * observe this state, wait_lock is irrelevant.
1258 pi_state = alloc_pi_state();
1261 * Initialize the pi_mutex in locked state and make @p
1264 rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
1266 /* Store the key for possible exit cleanups: */
1267 pi_state->key = *key;
1269 WARN_ON(!list_empty(&pi_state->list));
1270 list_add(&pi_state->list, &p->pi_state_list);
1272 * Assignment without holding pi_state->pi_mutex.wait_lock is safe
1273 * because there is no concurrency as the object is not published yet.
1275 pi_state->owner = p;
1276 raw_spin_unlock_irq(&p->pi_lock);
1285 static int lookup_pi_state(u32 __user *uaddr, u32 uval,
1286 struct futex_hash_bucket *hb,
1287 union futex_key *key, struct futex_pi_state **ps,
1288 struct task_struct **exiting)
1290 struct futex_q *top_waiter = futex_top_waiter(hb, key);
1293 * If there is a waiter on that futex, validate it and
1294 * attach to the pi_state when the validation succeeds.
1297 return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
1300 * We are the first waiter - try to look up the owner based on
1301 * @uval and attach to it.
1303 return attach_to_pi_owner(uaddr, uval, key, ps, exiting);
1306 static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
1311 if (unlikely(should_fail_futex(true)))
1314 err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
1318 /* If user space value changed, let the caller retry */
1319 return curval != uval ? -EAGAIN : 0;
1323 * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
1324 * @uaddr: the pi futex user address
1325 * @hb: the pi futex hash bucket
1326 * @key: the futex key associated with uaddr and hb
1327 * @ps: the pi_state pointer where we store the result of the
1329 * @task: the task to perform the atomic lock work for. This will
1330 * be "current" except in the case of requeue pi.
1331 * @exiting: Pointer to store the task pointer of the owner task
1332 * which is in the middle of exiting
1333 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1336 * - 0 - ready to wait;
1337 * - 1 - acquired the lock;
1340 * The hb->lock and futex_key refs shall be held by the caller.
1342 * @exiting is only set when the return value is -EBUSY. If so, this holds
1343 * a refcount on the exiting task on return and the caller needs to drop it
1344 * after waiting for the exit to complete.
1346 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
1347 union futex_key *key,
1348 struct futex_pi_state **ps,
1349 struct task_struct *task,
1350 struct task_struct **exiting,
1353 u32 uval, newval, vpid = task_pid_vnr(task);
1354 struct futex_q *top_waiter;
1358 * Read the user space value first so we can validate a few
1359 * things before proceeding further.
1361 if (get_futex_value_locked(&uval, uaddr))
1364 if (unlikely(should_fail_futex(true)))
1370 if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
1373 if ((unlikely(should_fail_futex(true))))
1377 * Lookup existing state first. If it exists, try to attach to
1380 top_waiter = futex_top_waiter(hb, key);
1382 return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
1385 * No waiter and user TID is 0. We are here because the
1386 * waiters or the owner died bit is set or called from
1387 * requeue_cmp_pi or for whatever reason something took the
1390 if (!(uval & FUTEX_TID_MASK)) {
1392 * We take over the futex. No other waiters and the user space
1393 * TID is 0. We preserve the owner died bit.
1395 newval = uval & FUTEX_OWNER_DIED;
1398 /* The futex requeue_pi code can enforce the waiters bit */
1400 newval |= FUTEX_WAITERS;
1402 ret = lock_pi_update_atomic(uaddr, uval, newval);
1403 /* If the take over worked, return 1 */
1404 return ret < 0 ? ret : 1;
1408 * First waiter. Set the waiters bit before attaching ourself to
1409 * the owner. If owner tries to unlock, it will be forced into
1410 * the kernel and blocked on hb->lock.
1412 newval = uval | FUTEX_WAITERS;
1413 ret = lock_pi_update_atomic(uaddr, uval, newval);
1417 * If the update of the user space value succeeded, we try to
1418 * attach to the owner. If that fails, no harm done, we only
1419 * set the FUTEX_WAITERS bit in the user space variable.
1421 return attach_to_pi_owner(uaddr, newval, key, ps, exiting);
1425 * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
1426 * @q: The futex_q to unqueue
1428 * The q->lock_ptr must not be NULL and must be held by the caller.
1430 static void __unqueue_futex(struct futex_q *q)
1432 struct futex_hash_bucket *hb;
1434 if (WARN_ON_SMP(!q->lock_ptr) || WARN_ON(plist_node_empty(&q->list)))
1436 lockdep_assert_held(q->lock_ptr);
1438 hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
1439 plist_del(&q->list, &hb->chain);
1444 * The hash bucket lock must be held when this is called.
1445 * Afterwards, the futex_q must not be accessed. Callers
1446 * must ensure to later call wake_up_q() for the actual
1449 static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
1451 struct task_struct *p = q->task;
1453 if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
1459 * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
1460 * is written, without taking any locks. This is possible in the event
1461 * of a spurious wakeup, for example. A memory barrier is required here
1462 * to prevent the following store to lock_ptr from getting ahead of the
1463 * plist_del in __unqueue_futex().
1465 smp_store_release(&q->lock_ptr, NULL);
1468 * Queue the task for later wakeup for after we've released
1471 wake_q_add_safe(wake_q, p);
1475 * Caller must hold a reference on @pi_state.
1477 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
1480 struct task_struct *new_owner;
1481 bool postunlock = false;
1482 DEFINE_WAKE_Q(wake_q);
1485 new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
1486 if (WARN_ON_ONCE(!new_owner)) {
1488 * As per the comment in futex_unlock_pi() this should not happen.
1490 * When this happens, give up our locks and try again, giving
1491 * the futex_lock_pi() instance time to complete, either by
1492 * waiting on the rtmutex or removing itself from the futex
1500 * We pass it to the next owner. The WAITERS bit is always kept
1501 * enabled while there is PI state around. We cleanup the owner
1502 * died bit, because we are the owner.
1504 newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
1506 if (unlikely(should_fail_futex(true))) {
1511 ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
1512 if (!ret && (curval != uval)) {
1514 * If a unconditional UNLOCK_PI operation (user space did not
1515 * try the TID->0 transition) raced with a waiter setting the
1516 * FUTEX_WAITERS flag between get_user() and locking the hash
1517 * bucket lock, retry the operation.
1519 if ((FUTEX_TID_MASK & curval) == uval)
1529 * This is a point of no return; once we modify the uval there is no
1530 * going back and subsequent operations must not fail.
1533 raw_spin_lock(&pi_state->owner->pi_lock);
1534 WARN_ON(list_empty(&pi_state->list));
1535 list_del_init(&pi_state->list);
1536 raw_spin_unlock(&pi_state->owner->pi_lock);
1538 raw_spin_lock(&new_owner->pi_lock);
1539 WARN_ON(!list_empty(&pi_state->list));
1540 list_add(&pi_state->list, &new_owner->pi_state_list);
1541 pi_state->owner = new_owner;
1542 raw_spin_unlock(&new_owner->pi_lock);
1544 postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
1547 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1550 rt_mutex_postunlock(&wake_q);
1556 * Express the locking dependencies for lockdep:
1559 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1562 spin_lock(&hb1->lock);
1564 spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
1565 } else { /* hb1 > hb2 */
1566 spin_lock(&hb2->lock);
1567 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
1572 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1574 spin_unlock(&hb1->lock);
1576 spin_unlock(&hb2->lock);
1580 * Wake up waiters matching bitset queued on this futex (uaddr).
1583 futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
1585 struct futex_hash_bucket *hb;
1586 struct futex_q *this, *next;
1587 union futex_key key = FUTEX_KEY_INIT;
1589 DEFINE_WAKE_Q(wake_q);
1594 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_READ);
1595 if (unlikely(ret != 0))
1598 hb = hash_futex(&key);
1600 /* Make sure we really have tasks to wakeup */
1601 if (!hb_waiters_pending(hb))
1604 spin_lock(&hb->lock);
1606 plist_for_each_entry_safe(this, next, &hb->chain, list) {
1607 if (match_futex (&this->key, &key)) {
1608 if (this->pi_state || this->rt_waiter) {
1613 /* Check if one of the bits is set in both bitsets */
1614 if (!(this->bitset & bitset))
1617 mark_wake_futex(&wake_q, this);
1618 if (++ret >= nr_wake)
1623 spin_unlock(&hb->lock);
1628 static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
1630 unsigned int op = (encoded_op & 0x70000000) >> 28;
1631 unsigned int cmp = (encoded_op & 0x0f000000) >> 24;
1632 int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11);
1633 int cmparg = sign_extend32(encoded_op & 0x00000fff, 11);
1636 if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
1637 if (oparg < 0 || oparg > 31) {
1638 char comm[sizeof(current->comm)];
1640 * kill this print and return -EINVAL when userspace
1643 pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n",
1644 get_task_comm(comm, current), oparg);
1650 pagefault_disable();
1651 ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
1657 case FUTEX_OP_CMP_EQ:
1658 return oldval == cmparg;
1659 case FUTEX_OP_CMP_NE:
1660 return oldval != cmparg;
1661 case FUTEX_OP_CMP_LT:
1662 return oldval < cmparg;
1663 case FUTEX_OP_CMP_GE:
1664 return oldval >= cmparg;
1665 case FUTEX_OP_CMP_LE:
1666 return oldval <= cmparg;
1667 case FUTEX_OP_CMP_GT:
1668 return oldval > cmparg;
1675 * Wake up all waiters hashed on the physical page that is mapped
1676 * to this virtual address:
1679 futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
1680 int nr_wake, int nr_wake2, int op)
1682 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1683 struct futex_hash_bucket *hb1, *hb2;
1684 struct futex_q *this, *next;
1686 DEFINE_WAKE_Q(wake_q);
1689 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
1690 if (unlikely(ret != 0))
1692 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
1693 if (unlikely(ret != 0))
1696 hb1 = hash_futex(&key1);
1697 hb2 = hash_futex(&key2);
1700 double_lock_hb(hb1, hb2);
1701 op_ret = futex_atomic_op_inuser(op, uaddr2);
1702 if (unlikely(op_ret < 0)) {
1703 double_unlock_hb(hb1, hb2);
1705 if (!IS_ENABLED(CONFIG_MMU) ||
1706 unlikely(op_ret != -EFAULT && op_ret != -EAGAIN)) {
1708 * we don't get EFAULT from MMU faults if we don't have
1709 * an MMU, but we might get them from range checking
1715 if (op_ret == -EFAULT) {
1716 ret = fault_in_user_writeable(uaddr2);
1721 if (!(flags & FLAGS_SHARED)) {
1730 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1731 if (match_futex (&this->key, &key1)) {
1732 if (this->pi_state || this->rt_waiter) {
1736 mark_wake_futex(&wake_q, this);
1737 if (++ret >= nr_wake)
1744 plist_for_each_entry_safe(this, next, &hb2->chain, list) {
1745 if (match_futex (&this->key, &key2)) {
1746 if (this->pi_state || this->rt_waiter) {
1750 mark_wake_futex(&wake_q, this);
1751 if (++op_ret >= nr_wake2)
1759 double_unlock_hb(hb1, hb2);
1765 * requeue_futex() - Requeue a futex_q from one hb to another
1766 * @q: the futex_q to requeue
1767 * @hb1: the source hash_bucket
1768 * @hb2: the target hash_bucket
1769 * @key2: the new key for the requeued futex_q
1772 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1773 struct futex_hash_bucket *hb2, union futex_key *key2)
1777 * If key1 and key2 hash to the same bucket, no need to
1780 if (likely(&hb1->chain != &hb2->chain)) {
1781 plist_del(&q->list, &hb1->chain);
1782 hb_waiters_dec(hb1);
1783 hb_waiters_inc(hb2);
1784 plist_add(&q->list, &hb2->chain);
1785 q->lock_ptr = &hb2->lock;
1791 * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1793 * @key: the key of the requeue target futex
1794 * @hb: the hash_bucket of the requeue target futex
1796 * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1797 * target futex if it is uncontended or via a lock steal. Set the futex_q key
1798 * to the requeue target futex so the waiter can detect the wakeup on the right
1799 * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1800 * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
1801 * to protect access to the pi_state to fixup the owner later. Must be called
1802 * with both q->lock_ptr and hb->lock held.
1805 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1806 struct futex_hash_bucket *hb)
1812 WARN_ON(!q->rt_waiter);
1813 q->rt_waiter = NULL;
1815 q->lock_ptr = &hb->lock;
1817 wake_up_state(q->task, TASK_NORMAL);
1821 * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1822 * @pifutex: the user address of the to futex
1823 * @hb1: the from futex hash bucket, must be locked by the caller
1824 * @hb2: the to futex hash bucket, must be locked by the caller
1825 * @key1: the from futex key
1826 * @key2: the to futex key
1827 * @ps: address to store the pi_state pointer
1828 * @exiting: Pointer to store the task pointer of the owner task
1829 * which is in the middle of exiting
1830 * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1832 * Try and get the lock on behalf of the top waiter if we can do it atomically.
1833 * Wake the top waiter if we succeed. If the caller specified set_waiters,
1834 * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1835 * hb1 and hb2 must be held by the caller.
1837 * @exiting is only set when the return value is -EBUSY. If so, this holds
1838 * a refcount on the exiting task on return and the caller needs to drop it
1839 * after waiting for the exit to complete.
1842 * - 0 - failed to acquire the lock atomically;
1843 * - >0 - acquired the lock, return value is vpid of the top_waiter
1847 futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1,
1848 struct futex_hash_bucket *hb2, union futex_key *key1,
1849 union futex_key *key2, struct futex_pi_state **ps,
1850 struct task_struct **exiting, int set_waiters)
1852 struct futex_q *top_waiter = NULL;
1856 if (get_futex_value_locked(&curval, pifutex))
1859 if (unlikely(should_fail_futex(true)))
1863 * Find the top_waiter and determine if there are additional waiters.
1864 * If the caller intends to requeue more than 1 waiter to pifutex,
1865 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1866 * as we have means to handle the possible fault. If not, don't set
1867 * the bit unecessarily as it will force the subsequent unlock to enter
1870 top_waiter = futex_top_waiter(hb1, key1);
1872 /* There are no waiters, nothing for us to do. */
1876 /* Ensure we requeue to the expected futex. */
1877 if (!match_futex(top_waiter->requeue_pi_key, key2))
1881 * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
1882 * the contended case or if set_waiters is 1. The pi_state is returned
1883 * in ps in contended cases.
1885 vpid = task_pid_vnr(top_waiter->task);
1886 ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1887 exiting, set_waiters);
1889 requeue_pi_wake_futex(top_waiter, key2, hb2);
1896 * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1897 * @uaddr1: source futex user address
1898 * @flags: futex flags (FLAGS_SHARED, etc.)
1899 * @uaddr2: target futex user address
1900 * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
1901 * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1902 * @cmpval: @uaddr1 expected value (or %NULL)
1903 * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1904 * pi futex (pi to pi requeue is not supported)
1906 * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1907 * uaddr2 atomically on behalf of the top waiter.
1910 * - >=0 - on success, the number of tasks requeued or woken;
1913 static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1914 u32 __user *uaddr2, int nr_wake, int nr_requeue,
1915 u32 *cmpval, int requeue_pi)
1917 union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1918 int task_count = 0, ret;
1919 struct futex_pi_state *pi_state = NULL;
1920 struct futex_hash_bucket *hb1, *hb2;
1921 struct futex_q *this, *next;
1922 DEFINE_WAKE_Q(wake_q);
1924 if (nr_wake < 0 || nr_requeue < 0)
1928 * When PI not supported: return -ENOSYS if requeue_pi is true,
1929 * consequently the compiler knows requeue_pi is always false past
1930 * this point which will optimize away all the conditional code
1933 if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi)
1938 * Requeue PI only works on two distinct uaddrs. This
1939 * check is only valid for private futexes. See below.
1941 if (uaddr1 == uaddr2)
1945 * requeue_pi requires a pi_state, try to allocate it now
1946 * without any locks in case it fails.
1948 if (refill_pi_state_cache())
1951 * requeue_pi must wake as many tasks as it can, up to nr_wake
1952 * + nr_requeue, since it acquires the rt_mutex prior to
1953 * returning to userspace, so as to not leave the rt_mutex with
1954 * waiters and no owner. However, second and third wake-ups
1955 * cannot be predicted as they involve race conditions with the
1956 * first wake and a fault while looking up the pi_state. Both
1957 * pthread_cond_signal() and pthread_cond_broadcast() should
1965 ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
1966 if (unlikely(ret != 0))
1968 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
1969 requeue_pi ? FUTEX_WRITE : FUTEX_READ);
1970 if (unlikely(ret != 0))
1974 * The check above which compares uaddrs is not sufficient for
1975 * shared futexes. We need to compare the keys:
1977 if (requeue_pi && match_futex(&key1, &key2))
1980 hb1 = hash_futex(&key1);
1981 hb2 = hash_futex(&key2);
1984 hb_waiters_inc(hb2);
1985 double_lock_hb(hb1, hb2);
1987 if (likely(cmpval != NULL)) {
1990 ret = get_futex_value_locked(&curval, uaddr1);
1992 if (unlikely(ret)) {
1993 double_unlock_hb(hb1, hb2);
1994 hb_waiters_dec(hb2);
1996 ret = get_user(curval, uaddr1);
2000 if (!(flags & FLAGS_SHARED))
2005 if (curval != *cmpval) {
2011 if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
2012 struct task_struct *exiting = NULL;
2015 * Attempt to acquire uaddr2 and wake the top waiter. If we
2016 * intend to requeue waiters, force setting the FUTEX_WAITERS
2017 * bit. We force this here where we are able to easily handle
2018 * faults rather in the requeue loop below.
2020 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
2022 &exiting, nr_requeue);
2025 * At this point the top_waiter has either taken uaddr2 or is
2026 * waiting on it. If the former, then the pi_state will not
2027 * exist yet, look it up one more time to ensure we have a
2028 * reference to it. If the lock was taken, ret contains the
2029 * vpid of the top waiter task.
2030 * If the lock was not taken, we have pi_state and an initial
2031 * refcount on it. In case of an error we have nothing.
2037 * If we acquired the lock, then the user space value
2038 * of uaddr2 should be vpid. It cannot be changed by
2039 * the top waiter as it is blocked on hb2 lock if it
2040 * tries to do so. If something fiddled with it behind
2041 * our back the pi state lookup might unearth it. So
2042 * we rather use the known value than rereading and
2043 * handing potential crap to lookup_pi_state.
2045 * If that call succeeds then we have pi_state and an
2046 * initial refcount on it.
2048 ret = lookup_pi_state(uaddr2, ret, hb2, &key2,
2049 &pi_state, &exiting);
2054 /* We hold a reference on the pi state. */
2057 /* If the above failed, then pi_state is NULL */
2059 double_unlock_hb(hb1, hb2);
2060 hb_waiters_dec(hb2);
2061 ret = fault_in_user_writeable(uaddr2);
2068 * Two reasons for this:
2069 * - EBUSY: Owner is exiting and we just wait for the
2071 * - EAGAIN: The user space value changed.
2073 double_unlock_hb(hb1, hb2);
2074 hb_waiters_dec(hb2);
2076 * Handle the case where the owner is in the middle of
2077 * exiting. Wait for the exit to complete otherwise
2078 * this task might loop forever, aka. live lock.
2080 wait_for_owner_exiting(ret, exiting);
2088 plist_for_each_entry_safe(this, next, &hb1->chain, list) {
2089 if (task_count - nr_wake >= nr_requeue)
2092 if (!match_futex(&this->key, &key1))
2096 * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
2097 * be paired with each other and no other futex ops.
2099 * We should never be requeueing a futex_q with a pi_state,
2100 * which is awaiting a futex_unlock_pi().
2102 if ((requeue_pi && !this->rt_waiter) ||
2103 (!requeue_pi && this->rt_waiter) ||
2110 * Wake nr_wake waiters. For requeue_pi, if we acquired the
2111 * lock, we already woke the top_waiter. If not, it will be
2112 * woken by futex_unlock_pi().
2114 if (++task_count <= nr_wake && !requeue_pi) {
2115 mark_wake_futex(&wake_q, this);
2119 /* Ensure we requeue to the expected futex for requeue_pi. */
2120 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
2126 * Requeue nr_requeue waiters and possibly one more in the case
2127 * of requeue_pi if we couldn't acquire the lock atomically.
2131 * Prepare the waiter to take the rt_mutex. Take a
2132 * refcount on the pi_state and store the pointer in
2133 * the futex_q object of the waiter.
2135 get_pi_state(pi_state);
2136 this->pi_state = pi_state;
2137 ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
2142 * We got the lock. We do neither drop the
2143 * refcount on pi_state nor clear
2144 * this->pi_state because the waiter needs the
2145 * pi_state for cleaning up the user space
2146 * value. It will drop the refcount after
2149 requeue_pi_wake_futex(this, &key2, hb2);
2153 * rt_mutex_start_proxy_lock() detected a
2154 * potential deadlock when we tried to queue
2155 * that waiter. Drop the pi_state reference
2156 * which we took above and remove the pointer
2157 * to the state from the waiters futex_q
2160 this->pi_state = NULL;
2161 put_pi_state(pi_state);
2163 * We stop queueing more waiters and let user
2164 * space deal with the mess.
2169 requeue_futex(this, hb1, hb2, &key2);
2173 * We took an extra initial reference to the pi_state either
2174 * in futex_proxy_trylock_atomic() or in lookup_pi_state(). We
2175 * need to drop it here again.
2177 put_pi_state(pi_state);
2180 double_unlock_hb(hb1, hb2);
2182 hb_waiters_dec(hb2);
2183 return ret ? ret : task_count;
2186 /* The key must be already stored in q->key. */
2187 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
2188 __acquires(&hb->lock)
2190 struct futex_hash_bucket *hb;
2192 hb = hash_futex(&q->key);
2195 * Increment the counter before taking the lock so that
2196 * a potential waker won't miss a to-be-slept task that is
2197 * waiting for the spinlock. This is safe as all queue_lock()
2198 * users end up calling queue_me(). Similarly, for housekeeping,
2199 * decrement the counter at queue_unlock() when some error has
2200 * occurred and we don't end up adding the task to the list.
2202 hb_waiters_inc(hb); /* implies smp_mb(); (A) */
2204 q->lock_ptr = &hb->lock;
2206 spin_lock(&hb->lock);
2211 queue_unlock(struct futex_hash_bucket *hb)
2212 __releases(&hb->lock)
2214 spin_unlock(&hb->lock);
2218 static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
2223 * The priority used to register this element is
2224 * - either the real thread-priority for the real-time threads
2225 * (i.e. threads with a priority lower than MAX_RT_PRIO)
2226 * - or MAX_RT_PRIO for non-RT threads.
2227 * Thus, all RT-threads are woken first in priority order, and
2228 * the others are woken last, in FIFO order.
2230 prio = min(current->normal_prio, MAX_RT_PRIO);
2232 plist_node_init(&q->list, prio);
2233 plist_add(&q->list, &hb->chain);
2238 * queue_me() - Enqueue the futex_q on the futex_hash_bucket
2239 * @q: The futex_q to enqueue
2240 * @hb: The destination hash bucket
2242 * The hb->lock must be held by the caller, and is released here. A call to
2243 * queue_me() is typically paired with exactly one call to unqueue_me(). The
2244 * exceptions involve the PI related operations, which may use unqueue_me_pi()
2245 * or nothing if the unqueue is done as part of the wake process and the unqueue
2246 * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
2249 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
2250 __releases(&hb->lock)
2253 spin_unlock(&hb->lock);
2257 * unqueue_me() - Remove the futex_q from its futex_hash_bucket
2258 * @q: The futex_q to unqueue
2260 * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
2261 * be paired with exactly one earlier call to queue_me().
2264 * - 1 - if the futex_q was still queued (and we removed unqueued it);
2265 * - 0 - if the futex_q was already removed by the waking thread
2267 static int unqueue_me(struct futex_q *q)
2269 spinlock_t *lock_ptr;
2272 /* In the common case we don't take the spinlock, which is nice. */
2275 * q->lock_ptr can change between this read and the following spin_lock.
2276 * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
2277 * optimizing lock_ptr out of the logic below.
2279 lock_ptr = READ_ONCE(q->lock_ptr);
2280 if (lock_ptr != NULL) {
2281 spin_lock(lock_ptr);
2283 * q->lock_ptr can change between reading it and
2284 * spin_lock(), causing us to take the wrong lock. This
2285 * corrects the race condition.
2287 * Reasoning goes like this: if we have the wrong lock,
2288 * q->lock_ptr must have changed (maybe several times)
2289 * between reading it and the spin_lock(). It can
2290 * change again after the spin_lock() but only if it was
2291 * already changed before the spin_lock(). It cannot,
2292 * however, change back to the original value. Therefore
2293 * we can detect whether we acquired the correct lock.
2295 if (unlikely(lock_ptr != q->lock_ptr)) {
2296 spin_unlock(lock_ptr);
2301 BUG_ON(q->pi_state);
2303 spin_unlock(lock_ptr);
2311 * PI futexes can not be requeued and must remove themself from the
2312 * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
2315 static void unqueue_me_pi(struct futex_q *q)
2316 __releases(q->lock_ptr)
2320 BUG_ON(!q->pi_state);
2321 put_pi_state(q->pi_state);
2324 spin_unlock(q->lock_ptr);
2327 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
2328 struct task_struct *argowner)
2330 struct futex_pi_state *pi_state = q->pi_state;
2331 u32 uval, curval, newval;
2332 struct task_struct *oldowner, *newowner;
2336 lockdep_assert_held(q->lock_ptr);
2338 raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
2340 oldowner = pi_state->owner;
2343 * We are here because either:
2345 * - we stole the lock and pi_state->owner needs updating to reflect
2346 * that (@argowner == current),
2350 * - someone stole our lock and we need to fix things to point to the
2351 * new owner (@argowner == NULL).
2353 * Either way, we have to replace the TID in the user space variable.
2354 * This must be atomic as we have to preserve the owner died bit here.
2356 * Note: We write the user space value _before_ changing the pi_state
2357 * because we can fault here. Imagine swapped out pages or a fork
2358 * that marked all the anonymous memory readonly for cow.
2360 * Modifying pi_state _before_ the user space value would leave the
2361 * pi_state in an inconsistent state when we fault here, because we
2362 * need to drop the locks to handle the fault. This might be observed
2363 * in the PID check in lookup_pi_state.
2367 if (oldowner != current) {
2369 * We raced against a concurrent self; things are
2370 * already fixed up. Nothing to do.
2376 if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) {
2377 /* We got the lock after all, nothing to fix. */
2383 * Since we just failed the trylock; there must be an owner.
2385 newowner = rt_mutex_owner(&pi_state->pi_mutex);
2388 WARN_ON_ONCE(argowner != current);
2389 if (oldowner == current) {
2391 * We raced against a concurrent self; things are
2392 * already fixed up. Nothing to do.
2397 newowner = argowner;
2400 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
2402 if (!pi_state->owner)
2403 newtid |= FUTEX_OWNER_DIED;
2405 err = get_futex_value_locked(&uval, uaddr);
2410 newval = (uval & FUTEX_OWNER_DIED) | newtid;
2412 err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
2422 * We fixed up user space. Now we need to fix the pi_state
2425 if (pi_state->owner != NULL) {
2426 raw_spin_lock(&pi_state->owner->pi_lock);
2427 WARN_ON(list_empty(&pi_state->list));
2428 list_del_init(&pi_state->list);
2429 raw_spin_unlock(&pi_state->owner->pi_lock);
2432 pi_state->owner = newowner;
2434 raw_spin_lock(&newowner->pi_lock);
2435 WARN_ON(!list_empty(&pi_state->list));
2436 list_add(&pi_state->list, &newowner->pi_state_list);
2437 raw_spin_unlock(&newowner->pi_lock);
2438 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
2443 * In order to reschedule or handle a page fault, we need to drop the
2444 * locks here. In the case of a fault, this gives the other task
2445 * (either the highest priority waiter itself or the task which stole
2446 * the rtmutex) the chance to try the fixup of the pi_state. So once we
2447 * are back from handling the fault we need to check the pi_state after
2448 * reacquiring the locks and before trying to do another fixup. When
2449 * the fixup has been done already we simply return.
2451 * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
2452 * drop hb->lock since the caller owns the hb -> futex_q relation.
2453 * Dropping the pi_mutex->wait_lock requires the state revalidate.
2456 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
2457 spin_unlock(q->lock_ptr);
2461 ret = fault_in_user_writeable(uaddr);
2475 spin_lock(q->lock_ptr);
2476 raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
2479 * Check if someone else fixed it for us:
2481 if (pi_state->owner != oldowner) {
2492 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
2496 static long futex_wait_restart(struct restart_block *restart);
2499 * fixup_owner() - Post lock pi_state and corner case management
2500 * @uaddr: user address of the futex
2501 * @q: futex_q (contains pi_state and access to the rt_mutex)
2502 * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
2504 * After attempting to lock an rt_mutex, this function is called to cleanup
2505 * the pi_state owner as well as handle race conditions that may allow us to
2506 * acquire the lock. Must be called with the hb lock held.
2509 * - 1 - success, lock taken;
2510 * - 0 - success, lock not taken;
2511 * - <0 - on error (-EFAULT)
2513 static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
2519 * Got the lock. We might not be the anticipated owner if we
2520 * did a lock-steal - fix up the PI-state in that case:
2522 * Speculative pi_state->owner read (we don't hold wait_lock);
2523 * since we own the lock pi_state->owner == current is the
2524 * stable state, anything else needs more attention.
2526 if (q->pi_state->owner != current)
2527 ret = fixup_pi_state_owner(uaddr, q, current);
2528 return ret ? ret : locked;
2532 * If we didn't get the lock; check if anybody stole it from us. In
2533 * that case, we need to fix up the uval to point to them instead of
2534 * us, otherwise bad things happen. [10]
2536 * Another speculative read; pi_state->owner == current is unstable
2537 * but needs our attention.
2539 if (q->pi_state->owner == current) {
2540 ret = fixup_pi_state_owner(uaddr, q, NULL);
2545 * Paranoia check. If we did not take the lock, then we should not be
2546 * the owner of the rt_mutex.
2548 if (rt_mutex_owner(&q->pi_state->pi_mutex) == current) {
2549 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
2550 "pi-state %p\n", ret,
2551 q->pi_state->pi_mutex.owner,
2552 q->pi_state->owner);
2559 * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
2560 * @hb: the futex hash bucket, must be locked by the caller
2561 * @q: the futex_q to queue up on
2562 * @timeout: the prepared hrtimer_sleeper, or null for no timeout
2564 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
2565 struct hrtimer_sleeper *timeout)
2568 * The task state is guaranteed to be set before another task can
2569 * wake it. set_current_state() is implemented using smp_store_mb() and
2570 * queue_me() calls spin_unlock() upon completion, both serializing
2571 * access to the hash list and forcing another memory barrier.
2573 set_current_state(TASK_INTERRUPTIBLE);
2578 hrtimer_sleeper_start_expires(timeout, HRTIMER_MODE_ABS);
2581 * If we have been removed from the hash list, then another task
2582 * has tried to wake us, and we can skip the call to schedule().
2584 if (likely(!plist_node_empty(&q->list))) {
2586 * If the timer has already expired, current will already be
2587 * flagged for rescheduling. Only call schedule if there
2588 * is no timeout, or if it has yet to expire.
2590 if (!timeout || timeout->task)
2591 freezable_schedule();
2593 __set_current_state(TASK_RUNNING);
2597 * futex_wait_setup() - Prepare to wait on a futex
2598 * @uaddr: the futex userspace address
2599 * @val: the expected value
2600 * @flags: futex flags (FLAGS_SHARED, etc.)
2601 * @q: the associated futex_q
2602 * @hb: storage for hash_bucket pointer to be returned to caller
2604 * Setup the futex_q and locate the hash_bucket. Get the futex value and
2605 * compare it with the expected value. Handle atomic faults internally.
2606 * Return with the hb lock held and a q.key reference on success, and unlocked
2607 * with no q.key reference on failure.
2610 * - 0 - uaddr contains val and hb has been locked;
2611 * - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
2613 static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
2614 struct futex_q *q, struct futex_hash_bucket **hb)
2620 * Access the page AFTER the hash-bucket is locked.
2621 * Order is important:
2623 * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
2624 * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
2626 * The basic logical guarantee of a futex is that it blocks ONLY
2627 * if cond(var) is known to be true at the time of blocking, for
2628 * any cond. If we locked the hash-bucket after testing *uaddr, that
2629 * would open a race condition where we could block indefinitely with
2630 * cond(var) false, which would violate the guarantee.
2632 * On the other hand, we insert q and release the hash-bucket only
2633 * after testing *uaddr. This guarantees that futex_wait() will NOT
2634 * absorb a wakeup if *uaddr does not match the desired values
2635 * while the syscall executes.
2638 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, FUTEX_READ);
2639 if (unlikely(ret != 0))
2643 *hb = queue_lock(q);
2645 ret = get_futex_value_locked(&uval, uaddr);
2650 ret = get_user(uval, uaddr);
2654 if (!(flags & FLAGS_SHARED))
2668 static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
2669 ktime_t *abs_time, u32 bitset)
2671 struct hrtimer_sleeper timeout, *to;
2672 struct restart_block *restart;
2673 struct futex_hash_bucket *hb;
2674 struct futex_q q = futex_q_init;
2681 to = futex_setup_timer(abs_time, &timeout, flags,
2682 current->timer_slack_ns);
2685 * Prepare to wait on uaddr. On success, holds hb lock and increments
2688 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2692 /* queue_me and wait for wakeup, timeout, or a signal. */
2693 futex_wait_queue_me(hb, &q, to);
2695 /* If we were woken (and unqueued), we succeeded, whatever. */
2697 /* unqueue_me() drops q.key ref */
2698 if (!unqueue_me(&q))
2701 if (to && !to->task)
2705 * We expect signal_pending(current), but we might be the
2706 * victim of a spurious wakeup as well.
2708 if (!signal_pending(current))
2715 restart = ¤t->restart_block;
2716 restart->fn = futex_wait_restart;
2717 restart->futex.uaddr = uaddr;
2718 restart->futex.val = val;
2719 restart->futex.time = *abs_time;
2720 restart->futex.bitset = bitset;
2721 restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
2723 ret = -ERESTART_RESTARTBLOCK;
2727 hrtimer_cancel(&to->timer);
2728 destroy_hrtimer_on_stack(&to->timer);
2734 static long futex_wait_restart(struct restart_block *restart)
2736 u32 __user *uaddr = restart->futex.uaddr;
2737 ktime_t t, *tp = NULL;
2739 if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
2740 t = restart->futex.time;
2743 restart->fn = do_no_restart_syscall;
2745 return (long)futex_wait(uaddr, restart->futex.flags,
2746 restart->futex.val, tp, restart->futex.bitset);
2751 * Userspace tried a 0 -> TID atomic transition of the futex value
2752 * and failed. The kernel side here does the whole locking operation:
2753 * if there are waiters then it will block as a consequence of relying
2754 * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
2755 * a 0 value of the futex too.).
2757 * Also serves as futex trylock_pi()'ing, and due semantics.
2759 static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
2760 ktime_t *time, int trylock)
2762 struct hrtimer_sleeper timeout, *to;
2763 struct futex_pi_state *pi_state = NULL;
2764 struct task_struct *exiting = NULL;
2765 struct rt_mutex_waiter rt_waiter;
2766 struct futex_hash_bucket *hb;
2767 struct futex_q q = futex_q_init;
2770 if (!IS_ENABLED(CONFIG_FUTEX_PI))
2773 if (refill_pi_state_cache())
2776 to = futex_setup_timer(time, &timeout, FLAGS_CLOCKRT, 0);
2779 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE);
2780 if (unlikely(ret != 0))
2784 hb = queue_lock(&q);
2786 ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current,
2788 if (unlikely(ret)) {
2790 * Atomic work succeeded and we got the lock,
2791 * or failed. Either way, we do _not_ block.
2795 /* We got the lock. */
2797 goto out_unlock_put_key;
2803 * Two reasons for this:
2804 * - EBUSY: Task is exiting and we just wait for the
2806 * - EAGAIN: The user space value changed.
2810 * Handle the case where the owner is in the middle of
2811 * exiting. Wait for the exit to complete otherwise
2812 * this task might loop forever, aka. live lock.
2814 wait_for_owner_exiting(ret, exiting);
2818 goto out_unlock_put_key;
2822 WARN_ON(!q.pi_state);
2825 * Only actually queue now that the atomic ops are done:
2830 ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
2831 /* Fixup the trylock return value: */
2832 ret = ret ? 0 : -EWOULDBLOCK;
2836 rt_mutex_init_waiter(&rt_waiter);
2839 * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
2840 * hold it while doing rt_mutex_start_proxy(), because then it will
2841 * include hb->lock in the blocking chain, even through we'll not in
2842 * fact hold it while blocking. This will lead it to report -EDEADLK
2843 * and BUG when futex_unlock_pi() interleaves with this.
2845 * Therefore acquire wait_lock while holding hb->lock, but drop the
2846 * latter before calling __rt_mutex_start_proxy_lock(). This
2847 * interleaves with futex_unlock_pi() -- which does a similar lock
2848 * handoff -- such that the latter can observe the futex_q::pi_state
2849 * before __rt_mutex_start_proxy_lock() is done.
2851 raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
2852 spin_unlock(q.lock_ptr);
2854 * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
2855 * such that futex_unlock_pi() is guaranteed to observe the waiter when
2856 * it sees the futex_q::pi_state.
2858 ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
2859 raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
2868 hrtimer_sleeper_start_expires(to, HRTIMER_MODE_ABS);
2870 ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
2873 spin_lock(q.lock_ptr);
2875 * If we failed to acquire the lock (deadlock/signal/timeout), we must
2876 * first acquire the hb->lock before removing the lock from the
2877 * rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait
2880 * In particular; it is important that futex_unlock_pi() can not
2881 * observe this inconsistency.
2883 if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
2888 * Fixup the pi_state owner and possibly acquire the lock if we
2891 res = fixup_owner(uaddr, &q, !ret);
2893 * If fixup_owner() returned an error, proprogate that. If it acquired
2894 * the lock, clear our -ETIMEDOUT or -EINTR.
2897 ret = (res < 0) ? res : 0;
2900 * If fixup_owner() faulted and was unable to handle the fault, unlock
2901 * it and return the fault to userspace.
2903 if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) {
2904 pi_state = q.pi_state;
2905 get_pi_state(pi_state);
2908 /* Unqueue and drop the lock */
2912 rt_mutex_futex_unlock(&pi_state->pi_mutex);
2913 put_pi_state(pi_state);
2923 hrtimer_cancel(&to->timer);
2924 destroy_hrtimer_on_stack(&to->timer);
2926 return ret != -EINTR ? ret : -ERESTARTNOINTR;
2931 ret = fault_in_user_writeable(uaddr);
2935 if (!(flags & FLAGS_SHARED))
2942 * Userspace attempted a TID -> 0 atomic transition, and failed.
2943 * This is the in-kernel slowpath: we look up the PI state (if any),
2944 * and do the rt-mutex unlock.
2946 static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
2948 u32 curval, uval, vpid = task_pid_vnr(current);
2949 union futex_key key = FUTEX_KEY_INIT;
2950 struct futex_hash_bucket *hb;
2951 struct futex_q *top_waiter;
2954 if (!IS_ENABLED(CONFIG_FUTEX_PI))
2958 if (get_user(uval, uaddr))
2961 * We release only a lock we actually own:
2963 if ((uval & FUTEX_TID_MASK) != vpid)
2966 ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_WRITE);
2970 hb = hash_futex(&key);
2971 spin_lock(&hb->lock);
2974 * Check waiters first. We do not trust user space values at
2975 * all and we at least want to know if user space fiddled
2976 * with the futex value instead of blindly unlocking.
2978 top_waiter = futex_top_waiter(hb, &key);
2980 struct futex_pi_state *pi_state = top_waiter->pi_state;
2987 * If current does not own the pi_state then the futex is
2988 * inconsistent and user space fiddled with the futex value.
2990 if (pi_state->owner != current)
2993 get_pi_state(pi_state);
2995 * By taking wait_lock while still holding hb->lock, we ensure
2996 * there is no point where we hold neither; and therefore
2997 * wake_futex_pi() must observe a state consistent with what we
3000 * In particular; this forces __rt_mutex_start_proxy() to
3001 * complete such that we're guaranteed to observe the
3002 * rt_waiter. Also see the WARN in wake_futex_pi().
3004 raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
3005 spin_unlock(&hb->lock);
3007 /* drops pi_state->pi_mutex.wait_lock */
3008 ret = wake_futex_pi(uaddr, uval, pi_state);
3010 put_pi_state(pi_state);
3013 * Success, we're done! No tricky corner cases.
3018 * The atomic access to the futex value generated a
3019 * pagefault, so retry the user-access and the wakeup:
3024 * A unconditional UNLOCK_PI op raced against a waiter
3025 * setting the FUTEX_WAITERS bit. Try again.
3030 * wake_futex_pi has detected invalid state. Tell user
3037 * We have no kernel internal state, i.e. no waiters in the
3038 * kernel. Waiters which are about to queue themselves are stuck
3039 * on hb->lock. So we can safely ignore them. We do neither
3040 * preserve the WAITERS bit not the OWNER_DIED one. We are the
3043 if ((ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))) {
3044 spin_unlock(&hb->lock);
3059 * If uval has changed, let user space handle it.
3061 ret = (curval == uval) ? 0 : -EAGAIN;
3064 spin_unlock(&hb->lock);
3074 ret = fault_in_user_writeable(uaddr);
3082 * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
3083 * @hb: the hash_bucket futex_q was original enqueued on
3084 * @q: the futex_q woken while waiting to be requeued
3085 * @key2: the futex_key of the requeue target futex
3086 * @timeout: the timeout associated with the wait (NULL if none)
3088 * Detect if the task was woken on the initial futex as opposed to the requeue
3089 * target futex. If so, determine if it was a timeout or a signal that caused
3090 * the wakeup and return the appropriate error code to the caller. Must be
3091 * called with the hb lock held.
3094 * - 0 = no early wakeup detected;
3095 * - <0 = -ETIMEDOUT or -ERESTARTNOINTR
3098 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
3099 struct futex_q *q, union futex_key *key2,
3100 struct hrtimer_sleeper *timeout)
3105 * With the hb lock held, we avoid races while we process the wakeup.
3106 * We only need to hold hb (and not hb2) to ensure atomicity as the
3107 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
3108 * It can't be requeued from uaddr2 to something else since we don't
3109 * support a PI aware source futex for requeue.
3111 if (!match_futex(&q->key, key2)) {
3112 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
3114 * We were woken prior to requeue by a timeout or a signal.
3115 * Unqueue the futex_q and determine which it was.
3117 plist_del(&q->list, &hb->chain);
3120 /* Handle spurious wakeups gracefully */
3122 if (timeout && !timeout->task)
3124 else if (signal_pending(current))
3125 ret = -ERESTARTNOINTR;
3131 * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
3132 * @uaddr: the futex we initially wait on (non-pi)
3133 * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
3134 * the same type, no requeueing from private to shared, etc.
3135 * @val: the expected value of uaddr
3136 * @abs_time: absolute timeout
3137 * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
3138 * @uaddr2: the pi futex we will take prior to returning to user-space
3140 * The caller will wait on uaddr and will be requeued by futex_requeue() to
3141 * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
3142 * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
3143 * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
3144 * without one, the pi logic would not know which task to boost/deboost, if
3145 * there was a need to.
3147 * We call schedule in futex_wait_queue_me() when we enqueue and return there
3148 * via the following--
3149 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
3150 * 2) wakeup on uaddr2 after a requeue
3154 * If 3, cleanup and return -ERESTARTNOINTR.
3156 * If 2, we may then block on trying to take the rt_mutex and return via:
3157 * 5) successful lock
3160 * 8) other lock acquisition failure
3162 * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
3164 * If 4 or 7, we cleanup and return with -ETIMEDOUT.
3170 static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
3171 u32 val, ktime_t *abs_time, u32 bitset,
3174 struct hrtimer_sleeper timeout, *to;
3175 struct futex_pi_state *pi_state = NULL;
3176 struct rt_mutex_waiter rt_waiter;
3177 struct futex_hash_bucket *hb;
3178 union futex_key key2 = FUTEX_KEY_INIT;
3179 struct futex_q q = futex_q_init;
3182 if (!IS_ENABLED(CONFIG_FUTEX_PI))
3185 if (uaddr == uaddr2)
3191 to = futex_setup_timer(abs_time, &timeout, flags,
3192 current->timer_slack_ns);
3195 * The waiter is allocated on our stack, manipulated by the requeue
3196 * code while we sleep on uaddr.
3198 rt_mutex_init_waiter(&rt_waiter);
3200 ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
3201 if (unlikely(ret != 0))
3205 q.rt_waiter = &rt_waiter;
3206 q.requeue_pi_key = &key2;
3209 * Prepare to wait on uaddr. On success, increments q.key (key1) ref
3212 ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
3217 * The check above which compares uaddrs is not sufficient for
3218 * shared futexes. We need to compare the keys:
3220 if (match_futex(&q.key, &key2)) {
3226 /* Queue the futex_q, drop the hb lock, wait for wakeup. */
3227 futex_wait_queue_me(hb, &q, to);
3229 spin_lock(&hb->lock);
3230 ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
3231 spin_unlock(&hb->lock);
3236 * In order for us to be here, we know our q.key == key2, and since
3237 * we took the hb->lock above, we also know that futex_requeue() has
3238 * completed and we no longer have to concern ourselves with a wakeup
3239 * race with the atomic proxy lock acquisition by the requeue code. The
3240 * futex_requeue dropped our key1 reference and incremented our key2
3244 /* Check if the requeue code acquired the second futex for us. */
3247 * Got the lock. We might not be the anticipated owner if we
3248 * did a lock-steal - fix up the PI-state in that case.
3250 if (q.pi_state && (q.pi_state->owner != current)) {
3251 spin_lock(q.lock_ptr);
3252 ret = fixup_pi_state_owner(uaddr2, &q, current);
3253 if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
3254 pi_state = q.pi_state;
3255 get_pi_state(pi_state);
3258 * Drop the reference to the pi state which
3259 * the requeue_pi() code acquired for us.
3261 put_pi_state(q.pi_state);
3262 spin_unlock(q.lock_ptr);
3265 struct rt_mutex *pi_mutex;
3268 * We have been woken up by futex_unlock_pi(), a timeout, or a
3269 * signal. futex_unlock_pi() will not destroy the lock_ptr nor
3272 WARN_ON(!q.pi_state);
3273 pi_mutex = &q.pi_state->pi_mutex;
3274 ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);
3276 spin_lock(q.lock_ptr);
3277 if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
3280 debug_rt_mutex_free_waiter(&rt_waiter);
3282 * Fixup the pi_state owner and possibly acquire the lock if we
3285 res = fixup_owner(uaddr2, &q, !ret);
3287 * If fixup_owner() returned an error, proprogate that. If it
3288 * acquired the lock, clear -ETIMEDOUT or -EINTR.
3291 ret = (res < 0) ? res : 0;
3294 * If fixup_pi_state_owner() faulted and was unable to handle
3295 * the fault, unlock the rt_mutex and return the fault to
3298 if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
3299 pi_state = q.pi_state;
3300 get_pi_state(pi_state);
3303 /* Unqueue and drop the lock. */
3308 rt_mutex_futex_unlock(&pi_state->pi_mutex);
3309 put_pi_state(pi_state);
3312 if (ret == -EINTR) {
3314 * We've already been requeued, but cannot restart by calling
3315 * futex_lock_pi() directly. We could restart this syscall, but
3316 * it would detect that the user space "val" changed and return
3317 * -EWOULDBLOCK. Save the overhead of the restart and return
3318 * -EWOULDBLOCK directly.
3325 hrtimer_cancel(&to->timer);
3326 destroy_hrtimer_on_stack(&to->timer);
3332 * Support for robust futexes: the kernel cleans up held futexes at
3335 * Implementation: user-space maintains a per-thread list of locks it
3336 * is holding. Upon do_exit(), the kernel carefully walks this list,
3337 * and marks all locks that are owned by this thread with the
3338 * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
3339 * always manipulated with the lock held, so the list is private and
3340 * per-thread. Userspace also maintains a per-thread 'list_op_pending'
3341 * field, to allow the kernel to clean up if the thread dies after
3342 * acquiring the lock, but just before it could have added itself to
3343 * the list. There can only be one such pending lock.
3347 * sys_set_robust_list() - Set the robust-futex list head of a task
3348 * @head: pointer to the list-head
3349 * @len: length of the list-head, as userspace expects
3351 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
3354 if (!futex_cmpxchg_enabled)
3357 * The kernel knows only one size for now:
3359 if (unlikely(len != sizeof(*head)))
3362 current->robust_list = head;
3368 * sys_get_robust_list() - Get the robust-futex list head of a task
3369 * @pid: pid of the process [zero for current task]
3370 * @head_ptr: pointer to a list-head pointer, the kernel fills it in
3371 * @len_ptr: pointer to a length field, the kernel fills in the header size
3373 SYSCALL_DEFINE3(get_robust_list, int, pid,
3374 struct robust_list_head __user * __user *, head_ptr,
3375 size_t __user *, len_ptr)
3377 struct robust_list_head __user *head;
3379 struct task_struct *p;
3381 if (!futex_cmpxchg_enabled)
3390 p = find_task_by_vpid(pid);
3396 if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
3399 head = p->robust_list;
3402 if (put_user(sizeof(*head), len_ptr))
3404 return put_user(head, head_ptr);
3412 /* Constants for the pending_op argument of handle_futex_death */
3413 #define HANDLE_DEATH_PENDING true
3414 #define HANDLE_DEATH_LIST false
3417 * Process a futex-list entry, check whether it's owned by the
3418 * dying task, and do notification if so:
3420 static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr,
3421 bool pi, bool pending_op)
3423 u32 uval, nval, mval;
3426 /* Futex address must be 32bit aligned */
3427 if ((((unsigned long)uaddr) % sizeof(*uaddr)) != 0)
3431 if (get_user(uval, uaddr))
3435 * Special case for regular (non PI) futexes. The unlock path in
3436 * user space has two race scenarios:
3438 * 1. The unlock path releases the user space futex value and
3439 * before it can execute the futex() syscall to wake up
3440 * waiters it is killed.
3442 * 2. A woken up waiter is killed before it can acquire the
3443 * futex in user space.
3445 * In both cases the TID validation below prevents a wakeup of
3446 * potential waiters which can cause these waiters to block
3449 * In both cases the following conditions are met:
3451 * 1) task->robust_list->list_op_pending != NULL
3452 * @pending_op == true
3453 * 2) User space futex value == 0
3454 * 3) Regular futex: @pi == false
3456 * If these conditions are met, it is safe to attempt waking up a
3457 * potential waiter without touching the user space futex value and
3458 * trying to set the OWNER_DIED bit. The user space futex value is
3459 * uncontended and the rest of the user space mutex state is
3460 * consistent, so a woken waiter will just take over the
3461 * uncontended futex. Setting the OWNER_DIED bit would create
3462 * inconsistent state and malfunction of the user space owner died
3465 if (pending_op && !pi && !uval) {
3466 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
3470 if ((uval & FUTEX_TID_MASK) != task_pid_vnr(curr))
3474 * Ok, this dying thread is truly holding a futex
3475 * of interest. Set the OWNER_DIED bit atomically
3476 * via cmpxchg, and if the value had FUTEX_WAITERS
3477 * set, wake up a waiter (if any). (We have to do a
3478 * futex_wake() even if OWNER_DIED is already set -
3479 * to handle the rare but possible case of recursive
3480 * thread-death.) The rest of the cleanup is done in
3483 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
3486 * We are not holding a lock here, but we want to have
3487 * the pagefault_disable/enable() protection because
3488 * we want to handle the fault gracefully. If the
3489 * access fails we try to fault in the futex with R/W
3490 * verification via get_user_pages. get_user() above
3491 * does not guarantee R/W access. If that fails we
3492 * give up and leave the futex locked.
3494 if ((err = cmpxchg_futex_value_locked(&nval, uaddr, uval, mval))) {
3497 if (fault_in_user_writeable(uaddr))
3515 * Wake robust non-PI futexes here. The wakeup of
3516 * PI futexes happens in exit_pi_state():
3518 if (!pi && (uval & FUTEX_WAITERS))
3519 futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
3525 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
3527 static inline int fetch_robust_entry(struct robust_list __user **entry,
3528 struct robust_list __user * __user *head,
3531 unsigned long uentry;
3533 if (get_user(uentry, (unsigned long __user *)head))
3536 *entry = (void __user *)(uentry & ~1UL);
3543 * Walk curr->robust_list (very carefully, it's a userspace list!)
3544 * and mark any locks found there dead, and notify any waiters.
3546 * We silently return on any sign of list-walking problem.
3548 static void exit_robust_list(struct task_struct *curr)
3550 struct robust_list_head __user *head = curr->robust_list;
3551 struct robust_list __user *entry, *next_entry, *pending;
3552 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
3553 unsigned int next_pi;
3554 unsigned long futex_offset;
3557 if (!futex_cmpxchg_enabled)
3561 * Fetch the list head (which was registered earlier, via
3562 * sys_set_robust_list()):
3564 if (fetch_robust_entry(&entry, &head->list.next, &pi))
3567 * Fetch the relative futex offset:
3569 if (get_user(futex_offset, &head->futex_offset))
3572 * Fetch any possibly pending lock-add first, and handle it
3575 if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
3578 next_entry = NULL; /* avoid warning with gcc */
3579 while (entry != &head->list) {
3581 * Fetch the next entry in the list before calling
3582 * handle_futex_death:
3584 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
3586 * A pending lock might already be on the list, so
3587 * don't process it twice:
3589 if (entry != pending) {
3590 if (handle_futex_death((void __user *)entry + futex_offset,
3591 curr, pi, HANDLE_DEATH_LIST))
3599 * Avoid excessively long or circular lists:
3608 handle_futex_death((void __user *)pending + futex_offset,
3609 curr, pip, HANDLE_DEATH_PENDING);
3613 static void futex_cleanup(struct task_struct *tsk)
3615 if (unlikely(tsk->robust_list)) {
3616 exit_robust_list(tsk);
3617 tsk->robust_list = NULL;
3620 #ifdef CONFIG_COMPAT
3621 if (unlikely(tsk->compat_robust_list)) {
3622 compat_exit_robust_list(tsk);
3623 tsk->compat_robust_list = NULL;
3627 if (unlikely(!list_empty(&tsk->pi_state_list)))
3628 exit_pi_state_list(tsk);
3632 * futex_exit_recursive - Set the tasks futex state to FUTEX_STATE_DEAD
3633 * @tsk: task to set the state on
3635 * Set the futex exit state of the task lockless. The futex waiter code
3636 * observes that state when a task is exiting and loops until the task has
3637 * actually finished the futex cleanup. The worst case for this is that the
3638 * waiter runs through the wait loop until the state becomes visible.
3640 * This is called from the recursive fault handling path in do_exit().
3642 * This is best effort. Either the futex exit code has run already or
3643 * not. If the OWNER_DIED bit has been set on the futex then the waiter can
3644 * take it over. If not, the problem is pushed back to user space. If the
3645 * futex exit code did not run yet, then an already queued waiter might
3646 * block forever, but there is nothing which can be done about that.
3648 void futex_exit_recursive(struct task_struct *tsk)
3650 /* If the state is FUTEX_STATE_EXITING then futex_exit_mutex is held */
3651 if (tsk->futex_state == FUTEX_STATE_EXITING)
3652 mutex_unlock(&tsk->futex_exit_mutex);
3653 tsk->futex_state = FUTEX_STATE_DEAD;
3656 static void futex_cleanup_begin(struct task_struct *tsk)
3659 * Prevent various race issues against a concurrent incoming waiter
3660 * including live locks by forcing the waiter to block on
3661 * tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in
3662 * attach_to_pi_owner().
3664 mutex_lock(&tsk->futex_exit_mutex);
3667 * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock.
3669 * This ensures that all subsequent checks of tsk->futex_state in
3670 * attach_to_pi_owner() must observe FUTEX_STATE_EXITING with
3671 * tsk->pi_lock held.
3673 * It guarantees also that a pi_state which was queued right before
3674 * the state change under tsk->pi_lock by a concurrent waiter must
3675 * be observed in exit_pi_state_list().
3677 raw_spin_lock_irq(&tsk->pi_lock);
3678 tsk->futex_state = FUTEX_STATE_EXITING;
3679 raw_spin_unlock_irq(&tsk->pi_lock);
3682 static void futex_cleanup_end(struct task_struct *tsk, int state)
3685 * Lockless store. The only side effect is that an observer might
3686 * take another loop until it becomes visible.
3688 tsk->futex_state = state;
3690 * Drop the exit protection. This unblocks waiters which observed
3691 * FUTEX_STATE_EXITING to reevaluate the state.
3693 mutex_unlock(&tsk->futex_exit_mutex);
3696 void futex_exec_release(struct task_struct *tsk)
3699 * The state handling is done for consistency, but in the case of
3700 * exec() there is no way to prevent futher damage as the PID stays
3701 * the same. But for the unlikely and arguably buggy case that a
3702 * futex is held on exec(), this provides at least as much state
3703 * consistency protection which is possible.
3705 futex_cleanup_begin(tsk);
3708 * Reset the state to FUTEX_STATE_OK. The task is alive and about
3709 * exec a new binary.
3711 futex_cleanup_end(tsk, FUTEX_STATE_OK);
3714 void futex_exit_release(struct task_struct *tsk)
3716 futex_cleanup_begin(tsk);
3718 futex_cleanup_end(tsk, FUTEX_STATE_DEAD);
3721 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
3722 u32 __user *uaddr2, u32 val2, u32 val3)
3724 int cmd = op & FUTEX_CMD_MASK;
3725 unsigned int flags = 0;
3727 if (!(op & FUTEX_PRIVATE_FLAG))
3728 flags |= FLAGS_SHARED;
3730 if (op & FUTEX_CLOCK_REALTIME) {
3731 flags |= FLAGS_CLOCKRT;
3732 if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \
3733 cmd != FUTEX_WAIT_REQUEUE_PI)
3739 case FUTEX_UNLOCK_PI:
3740 case FUTEX_TRYLOCK_PI:
3741 case FUTEX_WAIT_REQUEUE_PI:
3742 case FUTEX_CMP_REQUEUE_PI:
3743 if (!futex_cmpxchg_enabled)
3749 val3 = FUTEX_BITSET_MATCH_ANY;
3751 case FUTEX_WAIT_BITSET:
3752 return futex_wait(uaddr, flags, val, timeout, val3);
3754 val3 = FUTEX_BITSET_MATCH_ANY;
3756 case FUTEX_WAKE_BITSET:
3757 return futex_wake(uaddr, flags, val, val3);
3759 return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
3760 case FUTEX_CMP_REQUEUE:
3761 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
3763 return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
3765 return futex_lock_pi(uaddr, flags, timeout, 0);
3766 case FUTEX_UNLOCK_PI:
3767 return futex_unlock_pi(uaddr, flags);
3768 case FUTEX_TRYLOCK_PI:
3769 return futex_lock_pi(uaddr, flags, NULL, 1);
3770 case FUTEX_WAIT_REQUEUE_PI:
3771 val3 = FUTEX_BITSET_MATCH_ANY;
3772 return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
3774 case FUTEX_CMP_REQUEUE_PI:
3775 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
3781 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
3782 struct __kernel_timespec __user *, utime, u32 __user *, uaddr2,
3785 struct timespec64 ts;
3786 ktime_t t, *tp = NULL;
3788 int cmd = op & FUTEX_CMD_MASK;
3790 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
3791 cmd == FUTEX_WAIT_BITSET ||
3792 cmd == FUTEX_WAIT_REQUEUE_PI)) {
3793 if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
3795 if (get_timespec64(&ts, utime))
3797 if (!timespec64_valid(&ts))
3800 t = timespec64_to_ktime(ts);
3801 if (cmd == FUTEX_WAIT)
3802 t = ktime_add_safe(ktime_get(), t);
3803 else if (!(op & FUTEX_CLOCK_REALTIME))
3804 t = timens_ktime_to_host(CLOCK_MONOTONIC, t);
3808 * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
3809 * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
3811 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
3812 cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
3813 val2 = (u32) (unsigned long) utime;
3815 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
3818 #ifdef CONFIG_COMPAT
3820 * Fetch a robust-list pointer. Bit 0 signals PI futexes:
3823 compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry,
3824 compat_uptr_t __user *head, unsigned int *pi)
3826 if (get_user(*uentry, head))
3829 *entry = compat_ptr((*uentry) & ~1);
3830 *pi = (unsigned int)(*uentry) & 1;
3835 static void __user *futex_uaddr(struct robust_list __user *entry,
3836 compat_long_t futex_offset)
3838 compat_uptr_t base = ptr_to_compat(entry);
3839 void __user *uaddr = compat_ptr(base + futex_offset);
3845 * Walk curr->robust_list (very carefully, it's a userspace list!)
3846 * and mark any locks found there dead, and notify any waiters.
3848 * We silently return on any sign of list-walking problem.
3850 static void compat_exit_robust_list(struct task_struct *curr)
3852 struct compat_robust_list_head __user *head = curr->compat_robust_list;
3853 struct robust_list __user *entry, *next_entry, *pending;
3854 unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
3855 unsigned int next_pi;
3856 compat_uptr_t uentry, next_uentry, upending;
3857 compat_long_t futex_offset;
3860 if (!futex_cmpxchg_enabled)
3864 * Fetch the list head (which was registered earlier, via
3865 * sys_set_robust_list()):
3867 if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &pi))
3870 * Fetch the relative futex offset:
3872 if (get_user(futex_offset, &head->futex_offset))
3875 * Fetch any possibly pending lock-add first, and handle it
3878 if (compat_fetch_robust_entry(&upending, &pending,
3879 &head->list_op_pending, &pip))
3882 next_entry = NULL; /* avoid warning with gcc */
3883 while (entry != (struct robust_list __user *) &head->list) {
3885 * Fetch the next entry in the list before calling
3886 * handle_futex_death:
3888 rc = compat_fetch_robust_entry(&next_uentry, &next_entry,
3889 (compat_uptr_t __user *)&entry->next, &next_pi);
3891 * A pending lock might already be on the list, so
3892 * dont process it twice:
3894 if (entry != pending) {
3895 void __user *uaddr = futex_uaddr(entry, futex_offset);
3897 if (handle_futex_death(uaddr, curr, pi,
3903 uentry = next_uentry;
3907 * Avoid excessively long or circular lists:
3915 void __user *uaddr = futex_uaddr(pending, futex_offset);
3917 handle_futex_death(uaddr, curr, pip, HANDLE_DEATH_PENDING);
3921 COMPAT_SYSCALL_DEFINE2(set_robust_list,
3922 struct compat_robust_list_head __user *, head,
3925 if (!futex_cmpxchg_enabled)
3928 if (unlikely(len != sizeof(*head)))
3931 current->compat_robust_list = head;
3936 COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
3937 compat_uptr_t __user *, head_ptr,
3938 compat_size_t __user *, len_ptr)
3940 struct compat_robust_list_head __user *head;
3942 struct task_struct *p;
3944 if (!futex_cmpxchg_enabled)
3953 p = find_task_by_vpid(pid);
3959 if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
3962 head = p->compat_robust_list;
3965 if (put_user(sizeof(*head), len_ptr))
3967 return put_user(ptr_to_compat(head), head_ptr);
3974 #endif /* CONFIG_COMPAT */
3976 #ifdef CONFIG_COMPAT_32BIT_TIME
3977 SYSCALL_DEFINE6(futex_time32, u32 __user *, uaddr, int, op, u32, val,
3978 struct old_timespec32 __user *, utime, u32 __user *, uaddr2,
3981 struct timespec64 ts;
3982 ktime_t t, *tp = NULL;
3984 int cmd = op & FUTEX_CMD_MASK;
3986 if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
3987 cmd == FUTEX_WAIT_BITSET ||
3988 cmd == FUTEX_WAIT_REQUEUE_PI)) {
3989 if (get_old_timespec32(&ts, utime))
3991 if (!timespec64_valid(&ts))
3994 t = timespec64_to_ktime(ts);
3995 if (cmd == FUTEX_WAIT)
3996 t = ktime_add_safe(ktime_get(), t);
3997 else if (!(op & FUTEX_CLOCK_REALTIME))
3998 t = timens_ktime_to_host(CLOCK_MONOTONIC, t);
4001 if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
4002 cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
4003 val2 = (int) (unsigned long) utime;
4005 return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
4007 #endif /* CONFIG_COMPAT_32BIT_TIME */
4009 static void __init futex_detect_cmpxchg(void)
4011 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
4015 * This will fail and we want it. Some arch implementations do
4016 * runtime detection of the futex_atomic_cmpxchg_inatomic()
4017 * functionality. We want to know that before we call in any
4018 * of the complex code paths. Also we want to prevent
4019 * registration of robust lists in that case. NULL is
4020 * guaranteed to fault and we get -EFAULT on functional
4021 * implementation, the non-functional ones will return
4024 if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
4025 futex_cmpxchg_enabled = 1;
4029 static int __init futex_init(void)
4031 unsigned int futex_shift;
4034 #if CONFIG_BASE_SMALL
4035 futex_hashsize = 16;
4037 futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
4040 futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
4042 futex_hashsize < 256 ? HASH_SMALL : 0,
4044 futex_hashsize, futex_hashsize);
4045 futex_hashsize = 1UL << futex_shift;
4047 futex_detect_cmpxchg();
4049 for (i = 0; i < futex_hashsize; i++) {
4050 atomic_set(&futex_queues[i].waiters, 0);
4051 plist_head_init(&futex_queues[i].chain);
4052 spin_lock_init(&futex_queues[i].lock);
4057 core_initcall(futex_init);