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_del_rcu - deletes entry from hash list without re-initialization
57 * @n: the element to delete from the hash list.
58 *
59 * Note: hlist_nulls_unhashed() on entry does not return true after this,
60 * the entry is in an undefined state. It is useful for RCU based
61 * lockfree traversal.
62 *
63 * In particular, it means that we can not poison the forward
64 * pointers that may still be used for walking the hash list.
65 *
66 * The caller must take whatever precautions are necessary
67 * (such as holding appropriate locks) to avoid racing
68 * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
69 * or hlist_nulls_del_rcu(), running on this same list.
70 * However, it is perfectly legal to run concurrently with
71 * the _rcu list-traversal primitives, such as
72 * hlist_nulls_for_each_entry().
73 */
74static inline void hlist_nulls_del_rcu(struct hlist_nulls_node *n)
75{
76 __hlist_nulls_del(n);
77 WRITE_ONCE(n->pprev, LIST_POISON2);
78}
79
80/**
81 * hlist_nulls_add_head_rcu
82 * @n: the element to add to the hash list.
83 * @h: the list to add to.
84 *
85 * Description:
86 * Adds the specified element to the specified hlist_nulls,
87 * while permitting racing traversals.
88 *
89 * The caller must take whatever precautions are necessary
90 * (such as holding appropriate locks) to avoid racing
91 * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
92 * or hlist_nulls_del_rcu(), running on this same list.
93 * However, it is perfectly legal to run concurrently with
94 * the _rcu list-traversal primitives, such as
95 * hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
96 * problems on Alpha CPUs. Regardless of the type of CPU, the
97 * list-traversal primitive must be guarded by rcu_read_lock().
98 */
99static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n,
100 struct hlist_nulls_head *h)
101{
102 struct hlist_nulls_node *first = h->first;
103
104 WRITE_ONCE(n->next, first);
105 WRITE_ONCE(n->pprev, &h->first);
106 rcu_assign_pointer(hlist_nulls_first_rcu(h), n);
107 if (!is_a_nulls(ptr: first))
108 WRITE_ONCE(first->pprev, &n->next);
109}
110
111/**
112 * hlist_nulls_add_tail_rcu
113 * @n: the element to add to the hash list.
114 * @h: the list to add to.
115 *
116 * Description:
117 * Adds the specified element to the specified hlist_nulls,
118 * while permitting racing traversals.
119 *
120 * The caller must take whatever precautions are necessary
121 * (such as holding appropriate locks) to avoid racing
122 * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
123 * or hlist_nulls_del_rcu(), running on this same list.
124 * However, it is perfectly legal to run concurrently with
125 * the _rcu list-traversal primitives, such as
126 * hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
127 * problems on Alpha CPUs. Regardless of the type of CPU, the
128 * list-traversal primitive must be guarded by rcu_read_lock().
129 */
130static inline void hlist_nulls_add_tail_rcu(struct hlist_nulls_node *n,
131 struct hlist_nulls_head *h)
132{
133 struct hlist_nulls_node *i, *last = NULL;
134
135 /* Note: write side code, so rcu accessors are not needed. */
136 for (i = h->first; !is_a_nulls(ptr: i); i = i->next)
137 last = i;
138
139 if (last) {
140 WRITE_ONCE(n->next, last->next);
141 n->pprev = &last->next;
142 rcu_assign_pointer(hlist_nulls_next_rcu(last), n);
143 } else {
144 hlist_nulls_add_head_rcu(n, h);
145 }
146}
147
148/* after that hlist_nulls_del will work */
149static inline void hlist_nulls_add_fake(struct hlist_nulls_node *n)
150{
151 n->pprev = &n->next;
152 n->next = (struct hlist_nulls_node *)NULLS_MARKER(NULL);
153}
154
155/**
156 * hlist_nulls_for_each_entry_rcu - iterate over rcu list of given type
157 * @tpos: the type * to use as a loop cursor.
158 * @pos: the &struct hlist_nulls_node to use as a loop cursor.
159 * @head: the head of the list.
160 * @member: the name of the hlist_nulls_node within the struct.
161 *
162 * The barrier() is needed to make sure compiler doesn't cache first element [1],
163 * as this loop can be restarted [2]
164 * [1] Documentation/memory-barriers.txt around line 1533
165 * [2] Documentation/RCU/rculist_nulls.rst around line 146
166 */
167#define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member) \
168 for (({barrier();}), \
169 pos = rcu_dereference_raw(hlist_nulls_first_rcu(head)); \
170 (!is_a_nulls(pos)) && \
171 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; }); \
172 pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)))
173
174/**
175 * hlist_nulls_for_each_entry_safe -
176 * iterate over list of given type safe against removal of list entry
177 * @tpos: the type * to use as a loop cursor.
178 * @pos: the &struct hlist_nulls_node to use as a loop cursor.
179 * @head: the head of the list.
180 * @member: the name of the hlist_nulls_node within the struct.
181 */
182#define hlist_nulls_for_each_entry_safe(tpos, pos, head, member) \
183 for (({barrier();}), \
184 pos = rcu_dereference_raw(hlist_nulls_first_rcu(head)); \
185 (!is_a_nulls(pos)) && \
186 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); \
187 pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)); 1; });)
188#endif
189#endif
190