blob: ae5872b1df0c669fc8365ce1754d2a128651a890
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 | */ |
38 | bool 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 = ACCESS_ONCE(head->first); |
45 | } while (cmpxchg(&head->first, first, new_first) != first); |
46 | |
47 | return !first; |
48 | } |
49 | EXPORT_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 | */ |
65 | struct 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 | } |
82 | EXPORT_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 | */ |
91 | struct 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 | } |
104 | EXPORT_SYMBOL_GPL(llist_reverse_order); |
105 |