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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/kernel.h>
53 :
54 : struct llist_head {
55 : struct llist_node *first;
56 : };
57 :
58 : struct llist_node {
59 : struct llist_node *next;
60 : };
61 :
62 : #define LLIST_HEAD_INIT(name) { NULL }
63 : #define LLIST_HEAD(name) struct llist_head name = LLIST_HEAD_INIT(name)
64 :
65 : /**
66 : * init_llist_head - initialize lock-less list head
67 : * @head: the head for your lock-less list
68 : */
69 22 : static inline void init_llist_head(struct llist_head *list)
70 : {
71 22 : list->first = NULL;
72 8 : }
73 :
74 : /**
75 : * llist_entry - get the struct of this entry
76 : * @ptr: the &struct llist_node pointer.
77 : * @type: the type of the struct this is embedded in.
78 : * @member: the name of the llist_node within the struct.
79 : */
80 : #define llist_entry(ptr, type, member) \
81 : container_of(ptr, type, member)
82 :
83 : /**
84 : * member_address_is_nonnull - check whether the member address is not NULL
85 : * @ptr: the object pointer (struct type * that contains the llist_node)
86 : * @member: the name of the llist_node within the struct.
87 : *
88 : * This macro is conceptually the same as
89 : * &ptr->member != NULL
90 : * but it works around the fact that compilers can decide that taking a member
91 : * address is never a NULL pointer.
92 : *
93 : * Real objects that start at a high address and have a member at NULL are
94 : * unlikely to exist, but such pointers may be returned e.g. by the
95 : * container_of() macro.
96 : */
97 : #define member_address_is_nonnull(ptr, member) \
98 : ((uintptr_t)(ptr) + offsetof(typeof(*(ptr)), member) != 0)
99 :
100 : /**
101 : * llist_for_each - iterate over some deleted entries of a lock-less list
102 : * @pos: the &struct llist_node to use as a loop cursor
103 : * @node: the first entry of deleted list entries
104 : *
105 : * In general, some entries of the lock-less list can be traversed
106 : * safely only after being deleted from list, so start with an entry
107 : * instead of list head.
108 : *
109 : * If being used on entries deleted from lock-less list directly, the
110 : * traverse order is from the newest to the oldest added entry. If
111 : * you want to traverse from the oldest to the newest, you must
112 : * reverse the order by yourself before traversing.
113 : */
114 : #define llist_for_each(pos, node) \
115 : for ((pos) = (node); pos; (pos) = (pos)->next)
116 :
117 : /**
118 : * llist_for_each_safe - iterate over some deleted entries of a lock-less list
119 : * safe against removal of list entry
120 : * @pos: the &struct llist_node to use as a loop cursor
121 : * @n: another &struct llist_node to use as temporary storage
122 : * @node: the first entry of deleted list entries
123 : *
124 : * In general, some entries of the lock-less list can be traversed
125 : * safely only after being deleted from list, so start with an entry
126 : * instead of list head.
127 : *
128 : * If being used on entries deleted from lock-less list directly, the
129 : * traverse order is from the newest to the oldest added entry. If
130 : * you want to traverse from the oldest to the newest, you must
131 : * reverse the order by yourself before traversing.
132 : */
133 : #define llist_for_each_safe(pos, n, node) \
134 : for ((pos) = (node); (pos) && ((n) = (pos)->next, true); (pos) = (n))
135 :
136 : /**
137 : * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
138 : * @pos: the type * to use as a loop cursor.
139 : * @node: the fist entry of deleted list entries.
140 : * @member: the name of the llist_node with the struct.
141 : *
142 : * In general, some entries of the lock-less list can be traversed
143 : * safely only after being removed from list, so start with an entry
144 : * instead of list head.
145 : *
146 : * If being used on entries deleted from lock-less list directly, the
147 : * traverse order is from the newest to the oldest added entry. If
148 : * you want to traverse from the oldest to the newest, you must
149 : * reverse the order by yourself before traversing.
150 : */
151 : #define llist_for_each_entry(pos, node, member) \
152 : for ((pos) = llist_entry((node), typeof(*(pos)), member); \
153 : member_address_is_nonnull(pos, member); \
154 : (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
155 :
156 : /**
157 : * llist_for_each_entry_safe - iterate over some deleted entries of lock-less list of given type
158 : * safe against removal of list entry
159 : * @pos: the type * to use as a loop cursor.
160 : * @n: another type * to use as temporary storage
161 : * @node: the first entry of deleted list entries.
162 : * @member: the name of the llist_node with the struct.
163 : *
164 : * In general, some entries of the lock-less list can be traversed
165 : * safely only after being removed from list, so start with an entry
166 : * instead of list head.
167 : *
168 : * If being used on entries deleted from lock-less list directly, the
169 : * traverse order is from the newest to the oldest added entry. If
170 : * you want to traverse from the oldest to the newest, you must
171 : * reverse the order by yourself before traversing.
172 : */
173 : #define llist_for_each_entry_safe(pos, n, node, member) \
174 : for (pos = llist_entry((node), typeof(*pos), member); \
175 : member_address_is_nonnull(pos, member) && \
176 : (n = llist_entry(pos->member.next, typeof(*n), member), true); \
177 : pos = n)
178 :
179 : /**
180 : * llist_empty - tests whether a lock-less list is empty
181 : * @head: the list to test
182 : *
183 : * Not guaranteed to be accurate or up to date. Just a quick way to
184 : * test whether the list is empty without deleting something from the
185 : * list.
186 : */
187 74906 : static inline bool llist_empty(const struct llist_head *head)
188 : {
189 73446 : return READ_ONCE(head->first) == NULL;
190 : }
191 :
192 : static inline struct llist_node *llist_next(struct llist_node *node)
193 : {
194 : return node->next;
195 : }
196 :
197 : extern bool llist_add_batch(struct llist_node *new_first,
198 : struct llist_node *new_last,
199 : struct llist_head *head);
200 :
201 : static inline bool __llist_add_batch(struct llist_node *new_first,
202 : struct llist_node *new_last,
203 : struct llist_head *head)
204 : {
205 : new_last->next = head->first;
206 : head->first = new_first;
207 : return new_last->next == NULL;
208 : }
209 :
210 : /**
211 : * llist_add - add a new entry
212 : * @new: new entry to be added
213 : * @head: the head for your lock-less list
214 : *
215 : * Returns true if the list was empty prior to adding this entry.
216 : */
217 11334 : static inline bool llist_add(struct llist_node *new, struct llist_head *head)
218 : {
219 11334 : return llist_add_batch(new, new, head);
220 : }
221 :
222 : static inline bool __llist_add(struct llist_node *new, struct llist_head *head)
223 : {
224 : return __llist_add_batch(new, new, head);
225 : }
226 :
227 : /**
228 : * llist_del_all - delete all entries from lock-less list
229 : * @head: the head of lock-less list to delete all entries
230 : *
231 : * If list is empty, return NULL, otherwise, delete all entries and
232 : * return the pointer to the first entry. The order of entries
233 : * deleted is from the newest to the oldest added one.
234 : */
235 10721 : static inline struct llist_node *llist_del_all(struct llist_head *head)
236 : {
237 10721 : return xchg(&head->first, NULL);
238 : }
239 :
240 : static inline struct llist_node *__llist_del_all(struct llist_head *head)
241 : {
242 : struct llist_node *first = head->first;
243 :
244 : head->first = NULL;
245 : return first;
246 : }
247 :
248 : extern struct llist_node *llist_del_first(struct llist_head *head);
249 :
250 : struct llist_node *llist_reverse_order(struct llist_node *head);
251 :
252 : #endif /* LLIST_H */
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