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 | */ |
33 | static 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 | */ |
74 | static 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 | */ |
99 | static 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 | */ |
130 | static 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 */ |
149 | static 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 | |