1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Lock-less NULL terminated single linked list
4 *
5 * The basic atomic operation of this list is cmpxchg on long. On
6 * architectures that don't have NMI-safe cmpxchg implementation, the
7 * list can NOT be used in NMI handlers. So code that uses the list in
8 * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
9 *
10 * Copyright 2010,2011 Intel Corp.
11 * Author: Huang Ying <ying.huang@intel.com>
12 */
13 #include <linux/kernel.h>
14 #include <linux/export.h>
15 #include <linux/llist.h>
16
17
18 /**
19 * llist_add_batch - add several linked entries in batch
20 * @new_first: first entry in batch to be added
21 * @new_last: last entry in batch to be added
22 * @head: the head for your lock-less list
23 *
24 * Return whether list is empty before adding.
25 */
26 bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
27 struct llist_head *head)
28 {
29 struct llist_node *first;
30
31 do {
32 new_last->next = first = READ_ONCE(head->first);
33 } while (cmpxchg(&head->first, first, new_first) != first);
34
35 return !first;
36 }
37 EXPORT_SYMBOL_GPL(llist_add_batch);
38
39 /**
40 * llist_del_first - delete the first entry of lock-less list
41 * @head: the head for your lock-less list
42 *
43 * If list is empty, return NULL, otherwise, return the first entry
44 * deleted, this is the newest added one.
45 *
46 * Only one llist_del_first user can be used simultaneously with
47 * multiple llist_add users without lock. Because otherwise
48 * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
49 * llist_add) sequence in another user may change @head->first->next,
50 * but keep @head->first. If multiple consumers are needed, please
51 * use llist_del_all or use lock between consumers.
52 */
53 struct llist_node *llist_del_first(struct llist_head *head)
54 {
55 struct llist_node *entry, *old_entry, *next;
56
57 entry = smp_load_acquire(&head->first);
58 for (;;) {
59 if (entry == NULL)
60 return NULL;
61 old_entry = entry;
62 next = READ_ONCE(entry->next);
63 entry = cmpxchg(&head->first, old_entry, next);
64 if (entry == old_entry)
65 break;
66 }
67
68 return entry;
69 }
70 EXPORT_SYMBOL_GPL(llist_del_first);
71
72 /**
73 * llist_reverse_order - reverse order of a llist chain
74 * @head: first item of the list to be reversed
75 *
76 * Reverse the order of a chain of llist entries and return the
77 * new first entry.
78 */
79 struct llist_node *llist_reverse_order(struct llist_node *head)
80 {
81 struct llist_node *new_head = NULL;
82
83 while (head) {
84 struct llist_node *tmp = head;
85 head = head->next;
86 tmp->next = new_head;
87 new_head = tmp;
88 }
89
90 return new_head;
91 }
92 EXPORT_SYMBOL_GPL(llist_reverse_order);