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1 : /* SPDX-License-Identifier: GPL-2.0-only */
2 : #ifndef LLIST_H
3 : #define LLIST_H
4 : /*
5 : * Lock-less NULL terminated single linked list
6 : *
7 : * Cases where locking is not needed:
8 : * If there are multiple producers and multiple consumers, llist_add can be
9 : * used in producers and llist_del_all can be used in consumers simultaneously
10 : * without locking. Also a single consumer can use llist_del_first while
11 : * multiple producers simultaneously use llist_add, without any locking.
12 : *
13 : * Cases where locking is needed:
14 : * If we have multiple consumers with llist_del_first used in one consumer, and
15 : * llist_del_first or llist_del_all used in other consumers, then a lock is
16 : * needed. This is because llist_del_first depends on list->first->next not
17 : * changing, but without lock protection, there's no way to be sure about that
18 : * if a preemption happens in the middle of the delete operation and on being
19 : * preempted back, the list->first is the same as before causing the cmpxchg in
20 : * llist_del_first to succeed. For example, while a llist_del_first operation
21 : * is in progress in one consumer, then a llist_del_first, llist_add,
22 : * llist_add (or llist_del_all, llist_add, llist_add) sequence in another
23 : * consumer may cause violations.
24 : *
25 : * This can be summarized as follows:
26 : *
27 : * | add | del_first | del_all
28 : * add | - | - | -
29 : * del_first | | L | L
30 : * del_all | | | -
31 : *
32 : * Where, a particular row's operation can happen concurrently with a column's
33 : * operation, with "-" being no lock needed, while "L" being lock is needed.
34 : *
35 : * The list entries deleted via llist_del_all can be traversed with
36 : * traversing function such as llist_for_each etc. But the list
37 : * entries can not be traversed safely before deleted from the list.
38 : * The order of deleted entries is from the newest to the oldest added
39 : * one. If you want to traverse from the oldest to the newest, you
40 : * must reverse the order by yourself before traversing.
41 : *
42 : * The basic atomic operation of this list is cmpxchg on long. On
43 : * architectures that don't have NMI-safe cmpxchg implementation, the
44 : * list can NOT be used in NMI handlers. So code that uses the list in
45 : * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
46 : *
47 : * Copyright 2010,2011 Intel Corp.
48 : * Author: Huang Ying <ying.huang@intel.com>
49 : */
50 :
51 : #include <linux/atomic.h>
52 : #include <linux/container_of.h>
53 : #include <linux/stddef.h>
54 : #include <linux/types.h>
55 :
56 : struct llist_head {
57 : struct llist_node *first;
58 : };
59 :
60 : struct llist_node {
61 : struct llist_node *next;
62 : };
63 :
64 : #define LLIST_HEAD_INIT(name) { NULL }
65 : #define LLIST_HEAD(name) struct llist_head name = LLIST_HEAD_INIT(name)
66 :
67 : /**
68 : * init_llist_head - initialize lock-less list head
69 : * @head: the head for your lock-less list
70 : */
71 : static inline void init_llist_head(struct llist_head *list)
72 : {
73 35 : list->first = NULL;
74 : }
75 :
76 : /**
77 : * llist_entry - get the struct of this entry
78 : * @ptr: the &struct llist_node pointer.
79 : * @type: the type of the struct this is embedded in.
80 : * @member: the name of the llist_node within the struct.
81 : */
82 : #define llist_entry(ptr, type, member) \
83 : container_of(ptr, type, member)
84 :
85 : /**
86 : * member_address_is_nonnull - check whether the member address is not NULL
87 : * @ptr: the object pointer (struct type * that contains the llist_node)
88 : * @member: the name of the llist_node within the struct.
89 : *
90 : * This macro is conceptually the same as
91 : * &ptr->member != NULL
92 : * but it works around the fact that compilers can decide that taking a member
93 : * address is never a NULL pointer.
94 : *
95 : * Real objects that start at a high address and have a member at NULL are
96 : * unlikely to exist, but such pointers may be returned e.g. by the
97 : * container_of() macro.
98 : */
99 : #define member_address_is_nonnull(ptr, member) \
100 : ((uintptr_t)(ptr) + offsetof(typeof(*(ptr)), member) != 0)
101 :
102 : /**
103 : * llist_for_each - iterate over some deleted entries of a lock-less list
104 : * @pos: the &struct llist_node to use as a loop cursor
105 : * @node: the first entry of deleted list entries
106 : *
107 : * In general, some entries of the lock-less list can be traversed
108 : * safely only after being deleted from list, so start with an entry
109 : * instead of list head.
110 : *
111 : * If being used on entries deleted from lock-less list directly, the
112 : * traverse order is from the newest to the oldest added entry. If
113 : * you want to traverse from the oldest to the newest, you must
114 : * reverse the order by yourself before traversing.
115 : */
116 : #define llist_for_each(pos, node) \
117 : for ((pos) = (node); pos; (pos) = (pos)->next)
118 :
119 : /**
120 : * llist_for_each_safe - iterate over some deleted entries of a lock-less list
121 : * safe against removal of list entry
122 : * @pos: the &struct llist_node to use as a loop cursor
123 : * @n: another &struct llist_node to use as temporary storage
124 : * @node: the first entry of deleted list entries
125 : *
126 : * In general, some entries of the lock-less list can be traversed
127 : * safely only after being deleted from list, so start with an entry
128 : * instead of list head.
129 : *
130 : * If being used on entries deleted from lock-less list directly, the
131 : * traverse order is from the newest to the oldest added entry. If
132 : * you want to traverse from the oldest to the newest, you must
133 : * reverse the order by yourself before traversing.
134 : */
135 : #define llist_for_each_safe(pos, n, node) \
136 : for ((pos) = (node); (pos) && ((n) = (pos)->next, true); (pos) = (n))
137 :
138 : /**
139 : * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
140 : * @pos: the type * to use as a loop cursor.
141 : * @node: the fist entry of deleted list entries.
142 : * @member: the name of the llist_node with the struct.
143 : *
144 : * In general, some entries of the lock-less list can be traversed
145 : * safely only after being removed from list, so start with an entry
146 : * instead of list head.
147 : *
148 : * If being used on entries deleted from lock-less list directly, the
149 : * traverse order is from the newest to the oldest added entry. If
150 : * you want to traverse from the oldest to the newest, you must
151 : * reverse the order by yourself before traversing.
152 : */
153 : #define llist_for_each_entry(pos, node, member) \
154 : for ((pos) = llist_entry((node), typeof(*(pos)), member); \
155 : member_address_is_nonnull(pos, member); \
156 : (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
157 :
158 : /**
159 : * llist_for_each_entry_safe - iterate over some deleted entries of lock-less list of given type
160 : * safe against removal of list entry
161 : * @pos: the type * to use as a loop cursor.
162 : * @n: another type * to use as temporary storage
163 : * @node: the first entry of deleted list entries.
164 : * @member: the name of the llist_node with the struct.
165 : *
166 : * In general, some entries of the lock-less list can be traversed
167 : * safely only after being removed from list, so start with an entry
168 : * instead of list head.
169 : *
170 : * If being used on entries deleted from lock-less list directly, the
171 : * traverse order is from the newest to the oldest added entry. If
172 : * you want to traverse from the oldest to the newest, you must
173 : * reverse the order by yourself before traversing.
174 : */
175 : #define llist_for_each_entry_safe(pos, n, node, member) \
176 : for (pos = llist_entry((node), typeof(*pos), member); \
177 : member_address_is_nonnull(pos, member) && \
178 : (n = llist_entry(pos->member.next, typeof(*n), member), true); \
179 : pos = n)
180 :
181 : /**
182 : * llist_empty - tests whether a lock-less list is empty
183 : * @head: the list to test
184 : *
185 : * Not guaranteed to be accurate or up to date. Just a quick way to
186 : * test whether the list is empty without deleting something from the
187 : * list.
188 : */
189 : static inline bool llist_empty(const struct llist_head *head)
190 : {
191 5446 : return READ_ONCE(head->first) == NULL;
192 : }
193 :
194 : static inline struct llist_node *llist_next(struct llist_node *node)
195 : {
196 : return node->next;
197 : }
198 :
199 : extern bool llist_add_batch(struct llist_node *new_first,
200 : struct llist_node *new_last,
201 : struct llist_head *head);
202 :
203 : static inline bool __llist_add_batch(struct llist_node *new_first,
204 : struct llist_node *new_last,
205 : struct llist_head *head)
206 : {
207 : new_last->next = head->first;
208 : head->first = new_first;
209 : return new_last->next == NULL;
210 : }
211 :
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 : */
219 : static inline bool llist_add(struct llist_node *new, struct llist_head *head)
220 : {
221 0 : return llist_add_batch(new, new, head);
222 : }
223 :
224 : static inline bool __llist_add(struct llist_node *new, struct llist_head *head)
225 : {
226 : return __llist_add_batch(new, new, head);
227 : }
228 :
229 : /**
230 : * llist_del_all - delete all entries from lock-less list
231 : * @head: the head of lock-less list to delete all entries
232 : *
233 : * If list is empty, return NULL, otherwise, delete all entries and
234 : * return the pointer to the first entry. The order of entries
235 : * deleted is from the newest to the oldest added one.
236 : */
237 : static inline struct llist_node *llist_del_all(struct llist_head *head)
238 : {
239 0 : return xchg(&head->first, NULL);
240 : }
241 :
242 : static inline struct llist_node *__llist_del_all(struct llist_head *head)
243 : {
244 : struct llist_node *first = head->first;
245 :
246 : head->first = NULL;
247 : return first;
248 : }
249 :
250 : extern struct llist_node *llist_del_first(struct llist_head *head);
251 :
252 : struct llist_node *llist_reverse_order(struct llist_node *head);
253 :
254 : #endif /* LLIST_H */
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