1#ifndef LLIST_H
2#define LLIST_H
3/*
4 * Lock-less NULL terminated single linked list
5 *
6 * Cases where locking is not needed:
7 * If there are multiple producers and multiple consumers, llist_add can be
8 * used in producers and llist_del_all can be used in consumers simultaneously
9 * without locking. Also a single consumer can use llist_del_first while
10 * multiple producers simultaneously use llist_add, without any locking.
11 *
12 * Cases where locking is needed:
13 * If we have multiple consumers with llist_del_first used in one consumer, and
14 * llist_del_first or llist_del_all used in other consumers, then a lock is
15 * needed. This is because llist_del_first depends on list->first->next not
16 * changing, but without lock protection, there's no way to be sure about that
17 * if a preemption happens in the middle of the delete operation and on being
18 * preempted back, the list->first is the same as before causing the cmpxchg in
19 * llist_del_first to succeed. For example, while a llist_del_first operation
20 * is in progress in one consumer, then a llist_del_first, llist_add,
21 * llist_add (or llist_del_all, llist_add, llist_add) sequence in another
22 * consumer may cause violations.
23 *
24 * This can be summarized as follows:
25 *
26 * | add | del_first | del_all
27 * add | - | - | -
28 * del_first | | L | L
29 * del_all | | | -
30 *
31 * Where, a particular row's operation can happen concurrently with a column's
32 * operation, with "-" being no lock needed, while "L" being lock is needed.
33 *
34 * The list entries deleted via llist_del_all can be traversed with
35 * traversing function such as llist_for_each etc. But the list
36 * entries can not be traversed safely before deleted from the list.
37 * The order of deleted entries is from the newest to the oldest added
38 * one. If you want to traverse from the oldest to the newest, you
39 * must reverse the order by yourself before traversing.
40 *
41 * The basic atomic operation of this list is cmpxchg on long. On
42 * architectures that don't have NMI-safe cmpxchg implementation, the
43 * list can NOT be used in NMI handlers. So code that uses the list in
44 * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
45 *
46 * Copyright 2010,2011 Intel Corp.
47 * Author: Huang Ying <ying.huang@intel.com>
48 *
49 * This program is free software; you can redistribute it and/or
50 * modify it under the terms of the GNU General Public License version
51 * 2 as published by the Free Software Foundation;
52 *
53 * This program is distributed in the hope that it will be useful,
54 * but WITHOUT ANY WARRANTY; without even the implied warranty of
55 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
56 * GNU General Public License for more details.
57 *
58 * You should have received a copy of the GNU General Public License
59 * along with this program; if not, write to the Free Software
60 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
61 */
62
63#include <linux/atomic.h>
64#include <linux/kernel.h>
65
66struct llist_head {
67 struct llist_node *first;
68};
69
70struct llist_node {
71 struct llist_node *next;
72};
73
74#define LLIST_HEAD_INIT(name) { NULL }
75#define LLIST_HEAD(name) struct llist_head name = LLIST_HEAD_INIT(name)
76
77/**
78 * init_llist_head - initialize lock-less list head
79 * @head: the head for your lock-less list
80 */
81static inline void init_llist_head(struct llist_head *list)
82{
83 list->first = NULL;
84}
85
86/**
87 * llist_entry - get the struct of this entry
88 * @ptr: the &struct llist_node pointer.
89 * @type: the type of the struct this is embedded in.
90 * @member: the name of the llist_node within the struct.
91 */
92#define llist_entry(ptr, type, member) \
93 container_of(ptr, type, member)
94
95/**
96 * member_address_is_nonnull - check whether the member address is not NULL
97 * @ptr: the object pointer (struct type * that contains the llist_node)
98 * @member: the name of the llist_node within the struct.
99 *
100 * This macro is conceptually the same as
101 * &ptr->member != NULL
102 * but it works around the fact that compilers can decide that taking a member
103 * address is never a NULL pointer.
104 *
105 * Real objects that start at a high address and have a member at NULL are
106 * unlikely to exist, but such pointers may be returned e.g. by the
107 * container_of() macro.
108 */
109#define member_address_is_nonnull(ptr, member) \
110 ((uintptr_t)(ptr) + offsetof(typeof(*(ptr)), member) != 0)
111
112/**
113 * llist_for_each - iterate over some deleted entries of a lock-less list
114 * @pos: the &struct llist_node to use as a loop cursor
115 * @node: the first entry of deleted list entries
116 *
117 * In general, some entries of the lock-less list can be traversed
118 * safely only after being deleted from list, so start with an entry
119 * instead of list head.
120 *
121 * If being used on entries deleted from lock-less list directly, the
122 * traverse order is from the newest to the oldest added entry. If
123 * you want to traverse from the oldest to the newest, you must
124 * reverse the order by yourself before traversing.
125 */
126#define llist_for_each(pos, node) \
127 for ((pos) = (node); pos; (pos) = (pos)->next)
128
129/**
130 * llist_for_each_safe - iterate over some deleted entries of a lock-less list
131 * safe against removal of list entry
132 * @pos: the &struct llist_node to use as a loop cursor
133 * @n: another &struct llist_node to use as temporary storage
134 * @node: the first entry of deleted list entries
135 *
136 * In general, some entries of the lock-less list can be traversed
137 * safely only after being deleted from list, so start with an entry
138 * instead of list head.
139 *
140 * If being used on entries deleted from lock-less list directly, the
141 * traverse order is from the newest to the oldest added entry. If
142 * you want to traverse from the oldest to the newest, you must
143 * reverse the order by yourself before traversing.
144 */
145#define llist_for_each_safe(pos, n, node) \
146 for ((pos) = (node); (pos) && ((n) = (pos)->next, true); (pos) = (n))
147
148/**
149 * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
150 * @pos: the type * to use as a loop cursor.
151 * @node: the fist entry of deleted list entries.
152 * @member: the name of the llist_node with the struct.
153 *
154 * In general, some entries of the lock-less list can be traversed
155 * safely only after being removed from list, so start with an entry
156 * instead of list head.
157 *
158 * If being used on entries deleted from lock-less list directly, the
159 * traverse order is from the newest to the oldest added entry. If
160 * you want to traverse from the oldest to the newest, you must
161 * reverse the order by yourself before traversing.
162 */
163#define llist_for_each_entry(pos, node, member) \
164 for ((pos) = llist_entry((node), typeof(*(pos)), member); \
165 member_address_is_nonnull(pos, member); \
166 (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
167
168/**
169 * llist_for_each_entry_safe - iterate over some deleted entries of lock-less list of given type
170 * safe against removal of list entry
171 * @pos: the type * to use as a loop cursor.
172 * @n: another type * to use as temporary storage
173 * @node: the first entry of deleted list entries.
174 * @member: the name of the llist_node with the struct.
175 *
176 * In general, some entries of the lock-less list can be traversed
177 * safely only after being removed from list, so start with an entry
178 * instead of list head.
179 *
180 * If being used on entries deleted from lock-less list directly, the
181 * traverse order is from the newest to the oldest added entry. If
182 * you want to traverse from the oldest to the newest, you must
183 * reverse the order by yourself before traversing.
184 */
185#define llist_for_each_entry_safe(pos, n, node, member) \
186 for (pos = llist_entry((node), typeof(*pos), member); \
187 member_address_is_nonnull(pos, member) && \
188 (n = llist_entry(pos->member.next, typeof(*n), member), true); \
189 pos = n)
190
191/**
192 * llist_empty - tests whether a lock-less list is empty
193 * @head: the list to test
194 *
195 * Not guaranteed to be accurate or up to date. Just a quick way to
196 * test whether the list is empty without deleting something from the
197 * list.
198 */
199static inline bool llist_empty(const struct llist_head *head)
200{
201 return READ_ONCE(head->first) == NULL;
202}
203
204static inline struct llist_node *llist_next(struct llist_node *node)
205{
206 return node->next;
207}
208
209extern bool llist_add_batch(struct llist_node *new_first,
210 struct llist_node *new_last,
211 struct llist_head *head);
212/**
213 * llist_add - add a new entry
214 * @new: new entry to be added
215 * @head: the head for your lock-less list
216 *
217 * Returns true if the list was empty prior to adding this entry.
218 */
219static inline bool llist_add(struct llist_node *new, struct llist_head *head)
220{
221 return llist_add_batch(new, new, head);
222}
223
224/**
225 * llist_del_all - delete all entries from lock-less list
226 * @head: the head of lock-less list to delete all entries
227 *
228 * If list is empty, return NULL, otherwise, delete all entries and
229 * return the pointer to the first entry. The order of entries
230 * deleted is from the newest to the oldest added one.
231 */
232static inline struct llist_node *llist_del_all(struct llist_head *head)
233{
234 return xchg(&head->first, NULL);
235}
236
237extern struct llist_node *llist_del_first(struct llist_head *head);
238
239struct llist_node *llist_reverse_order(struct llist_node *head);
240
241#endif /* LLIST_H */
242