1/*
2 * Lock-less NULL terminated single linked list
3 *
4 * The basic atomic operation of this list is cmpxchg on long. On
5 * architectures that don't have NMI-safe cmpxchg implementation, the
6 * list can NOT be used in NMI handlers. So code that uses the list in
7 * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
8 *
9 * Copyright 2010,2011 Intel Corp.
10 * Author: Huang Ying <ying.huang@intel.com>
11 *
12 * This program is free software; you can redistribute it and/or
13 * modify it under the terms of the GNU General Public License version
14 * 2 as published by the Free Software Foundation;
15 *
16 * This program is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 * GNU General Public License for more details.
20 *
21 * You should have received a copy of the GNU General Public License
22 * along with this program; if not, write to the Free Software
23 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
24 */
25#include <linux/kernel.h>
26#include <linux/export.h>
27#include <linux/llist.h>
28
29
30/**
31 * llist_add_batch - add several linked entries in batch
32 * @new_first: first entry in batch to be added
33 * @new_last: last entry in batch to be added
34 * @head: the head for your lock-less list
35 *
36 * Return whether list is empty before adding.
37 */
38bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
39 struct llist_head *head)
40{
41 struct llist_node *first;
42
43 do {
44 new_last->next = first = READ_ONCE(head->first);
45 } while (cmpxchg(&head->first, first, new_first) != first);
46
47 return !first;
48}
49EXPORT_SYMBOL_GPL(llist_add_batch);
50
51/**
52 * llist_del_first - delete the first entry of lock-less list
53 * @head: the head for your lock-less list
54 *
55 * If list is empty, return NULL, otherwise, return the first entry
56 * deleted, this is the newest added one.
57 *
58 * Only one llist_del_first user can be used simultaneously with
59 * multiple llist_add users without lock. Because otherwise
60 * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
61 * llist_add) sequence in another user may change @head->first->next,
62 * but keep @head->first. If multiple consumers are needed, please
63 * use llist_del_all or use lock between consumers.
64 */
65struct llist_node *llist_del_first(struct llist_head *head)
66{
67 struct llist_node *entry, *old_entry, *next;
68
69 entry = smp_load_acquire(&head->first);
70 for (;;) {
71 if (entry == NULL)
72 return NULL;
73 old_entry = entry;
74 next = READ_ONCE(entry->next);
75 entry = cmpxchg(&head->first, old_entry, next);
76 if (entry == old_entry)
77 break;
78 }
79
80 return entry;
81}
82EXPORT_SYMBOL_GPL(llist_del_first);
83
84/**
85 * llist_reverse_order - reverse order of a llist chain
86 * @head: first item of the list to be reversed
87 *
88 * Reverse the order of a chain of llist entries and return the
89 * new first entry.
90 */
91struct llist_node *llist_reverse_order(struct llist_node *head)
92{
93 struct llist_node *new_head = NULL;
94
95 while (head) {
96 struct llist_node *tmp = head;
97 head = head->next;
98 tmp->next = new_head;
99 new_head = tmp;
100 }
101
102 return new_head;
103}
104EXPORT_SYMBOL_GPL(llist_reverse_order);
105