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1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_RCULIST_NULLS_H
3#define _LINUX_RCULIST_NULLS_H
4
5#ifdef __KERNEL__
6
7/*
8 * RCU-protected list version
9 */
10#include <linux/list_nulls.h>
11#include <linux/rcupdate.h>
12
13/**
14 * hlist_nulls_del_init_rcu - deletes entry from hash list with re-initialization
15 * @n: the element to delete from the hash list.
16 *
17 * Note: hlist_nulls_unhashed() on the node return true after this. It is
18 * useful for RCU based read lockfree traversal if the writer side
19 * must know if the list entry is still hashed or already unhashed.
20 *
21 * In particular, it means that we can not poison the forward pointers
22 * that may still be used for walking the hash list and we can only
23 * zero the pprev pointer so list_unhashed() will return true after
24 * this.
25 *
26 * The caller must take whatever precautions are necessary (such as
27 * holding appropriate locks) to avoid racing with another
28 * list-mutation primitive, such as hlist_nulls_add_head_rcu() or
29 * hlist_nulls_del_rcu(), running on this same list. However, it is
30 * perfectly legal to run concurrently with the _rcu list-traversal
31 * primitives, such as hlist_nulls_for_each_entry_rcu().
32 */
33static inline void hlist_nulls_del_init_rcu(struct hlist_nulls_node *n)
34{
35 if (!hlist_nulls_unhashed(h: n)) {
36 __hlist_nulls_del(n);
37 WRITE_ONCE(n->pprev, NULL);
38 }
39}
40
41/**
42 * hlist_nulls_first_rcu - returns the first element of the hash list.
43 * @head: the head of the list.
44 */
45#define hlist_nulls_first_rcu(head) \
46 (*((struct hlist_nulls_node __rcu __force **)&(head)->first))
47
48/**
49 * hlist_nulls_next_rcu - returns the element of the list after @node.
50 * @node: element of the list.
51 */
52#define hlist_nulls_next_rcu(node) \
53 (*((struct hlist_nulls_node __rcu __force **)&(node)->next))
54
55/**
56 * hlist_nulls_pprev_rcu - returns the dereferenced pprev of @node.
57 * @node: element of the list.
58 */
59#define hlist_nulls_pprev_rcu(node) \
60 (*((struct hlist_nulls_node __rcu __force **)(node)->pprev))
61
62/**
63 * hlist_nulls_del_rcu - deletes entry from hash list without re-initialization
64 * @n: the element to delete from the hash list.
65 *
66 * Note: hlist_nulls_unhashed() on entry does not return true after this,
67 * the entry is in an undefined state. It is useful for RCU based
68 * lockfree traversal.
69 *
70 * In particular, it means that we can not poison the forward
71 * pointers that may still be used for walking the hash list.
72 *
73 * The caller must take whatever precautions are necessary
74 * (such as holding appropriate locks) to avoid racing
75 * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
76 * or hlist_nulls_del_rcu(), running on this same list.
77 * However, it is perfectly legal to run concurrently with
78 * the _rcu list-traversal primitives, such as
79 * hlist_nulls_for_each_entry().
80 */
81static inline void hlist_nulls_del_rcu(struct hlist_nulls_node *n)
82{
83 __hlist_nulls_del(n);
84 WRITE_ONCE(n->pprev, LIST_POISON2);
85}
86
87/**
88 * hlist_nulls_add_head_rcu
89 * @n: the element to add to the hash list.
90 * @h: the list to add to.
91 *
92 * Description:
93 * Adds the specified element to the specified hlist_nulls,
94 * while permitting racing traversals.
95 *
96 * The caller must take whatever precautions are necessary
97 * (such as holding appropriate locks) to avoid racing
98 * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
99 * or hlist_nulls_del_rcu(), running on this same list.
100 * However, it is perfectly legal to run concurrently with
101 * the _rcu list-traversal primitives, such as
102 * hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
103 * problems on Alpha CPUs. Regardless of the type of CPU, the
104 * list-traversal primitive must be guarded by rcu_read_lock().
105 */
106static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n,
107 struct hlist_nulls_head *h)
108{
109 struct hlist_nulls_node *first = h->first;
110
111 WRITE_ONCE(n->next, first);
112 WRITE_ONCE(n->pprev, &h->first);
113 rcu_assign_pointer(hlist_nulls_first_rcu(h), n);
114 if (!is_a_nulls(ptr: first))
115 WRITE_ONCE(first->pprev, &n->next);
116}
117
118/**
119 * hlist_nulls_add_tail_rcu
120 * @n: the element to add to the hash list.
121 * @h: the list to add to.
122 *
123 * Description:
124 * Adds the specified element to the specified hlist_nulls,
125 * while permitting racing traversals.
126 *
127 * The caller must take whatever precautions are necessary
128 * (such as holding appropriate locks) to avoid racing
129 * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
130 * or hlist_nulls_del_rcu(), running on this same list.
131 * However, it is perfectly legal to run concurrently with
132 * the _rcu list-traversal primitives, such as
133 * hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
134 * problems on Alpha CPUs. Regardless of the type of CPU, the
135 * list-traversal primitive must be guarded by rcu_read_lock().
136 */
137static inline void hlist_nulls_add_tail_rcu(struct hlist_nulls_node *n,
138 struct hlist_nulls_head *h)
139{
140 struct hlist_nulls_node *i, *last = NULL;
141
142 /* Note: write side code, so rcu accessors are not needed. */
143 for (i = h->first; !is_a_nulls(ptr: i); i = i->next)
144 last = i;
145
146 if (last) {
147 WRITE_ONCE(n->next, last->next);
148 WRITE_ONCE(n->pprev, &last->next);
149 rcu_assign_pointer(hlist_nulls_next_rcu(last), n);
150 } else {
151 hlist_nulls_add_head_rcu(n, h);
152 }
153}
154
155/* after that hlist_nulls_del will work */
156static inline void hlist_nulls_add_fake(struct hlist_nulls_node *n)
157{
158 WRITE_ONCE(n->pprev, &n->next);
159 WRITE_ONCE(n->next, (struct hlist_nulls_node *)NULLS_MARKER(NULL));
160}
161
162/**
163 * hlist_nulls_replace_rcu - replace an old entry by a new one
164 * @old: the element to be replaced
165 * @new: the new element to insert
166 *
167 * Description:
168 * Replace the old entry with the new one in a RCU-protected hlist_nulls, while
169 * permitting racing traversals.
170 *
171 * The caller must take whatever precautions are necessary (such as holding
172 * appropriate locks) to avoid racing with another list-mutation primitive, such
173 * as hlist_nulls_add_head_rcu() or hlist_nulls_del_rcu(), running on this same
174 * list. However, it is perfectly legal to run concurrently with the _rcu
175 * list-traversal primitives, such as hlist_nulls_for_each_entry_rcu().
176 */
177static inline void hlist_nulls_replace_rcu(struct hlist_nulls_node *old,
178 struct hlist_nulls_node *new)
179{
180 struct hlist_nulls_node *next = old->next;
181
182 WRITE_ONCE(new->next, next);
183 WRITE_ONCE(new->pprev, old->pprev);
184 rcu_assign_pointer(hlist_nulls_pprev_rcu(new), new);
185 if (!is_a_nulls(ptr: next))
186 WRITE_ONCE(next->pprev, &new->next);
187}
188
189/**
190 * hlist_nulls_replace_init_rcu - replace an old entry by a new one and
191 * initialize the old
192 * @old: the element to be replaced
193 * @new: the new element to insert
194 *
195 * Description:
196 * Replace the old entry with the new one in a RCU-protected hlist_nulls, while
197 * permitting racing traversals, and reinitialize the old entry.
198 *
199 * Note: @old must be hashed.
200 *
201 * The caller must take whatever precautions are necessary (such as holding
202 * appropriate locks) to avoid racing with another list-mutation primitive, such
203 * as hlist_nulls_add_head_rcu() or hlist_nulls_del_rcu(), running on this same
204 * list. However, it is perfectly legal to run concurrently with the _rcu
205 * list-traversal primitives, such as hlist_nulls_for_each_entry_rcu().
206 */
207static inline void hlist_nulls_replace_init_rcu(struct hlist_nulls_node *old,
208 struct hlist_nulls_node *new)
209{
210 hlist_nulls_replace_rcu(old, new);
211 WRITE_ONCE(old->pprev, NULL);
212}
213
214/**
215 * hlist_nulls_for_each_entry_rcu - iterate over rcu list of given type
216 * @tpos: the type * to use as a loop cursor.
217 * @pos: the &struct hlist_nulls_node to use as a loop cursor.
218 * @head: the head of the list.
219 * @member: the name of the hlist_nulls_node within the struct.
220 *
221 * The barrier() is needed to make sure compiler doesn't cache first element [1],
222 * as this loop can be restarted [2]
223 * [1] Documentation/memory-barriers.txt around line 1533
224 * [2] Documentation/RCU/rculist_nulls.rst around line 146
225 */
226#define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member) \
227 for (({barrier();}), \
228 pos = rcu_dereference_raw(hlist_nulls_first_rcu(head)); \
229 (!is_a_nulls(pos)) && \
230 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; }); \
231 pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)))
232
233/**
234 * hlist_nulls_for_each_entry_safe -
235 * iterate over list of given type safe against removal of list entry
236 * @tpos: the type * to use as a loop cursor.
237 * @pos: the &struct hlist_nulls_node to use as a loop cursor.
238 * @head: the head of the list.
239 * @member: the name of the hlist_nulls_node within the struct.
240 */
241#define hlist_nulls_for_each_entry_safe(tpos, pos, head, member) \
242 for (({barrier();}), \
243 pos = rcu_dereference_raw(hlist_nulls_first_rcu(head)); \
244 (!is_a_nulls(pos)) && \
245 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); \
246 pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)); 1; });)
247#endif
248#endif
249

source code of linux/include/linux/rculist_nulls.h