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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 : : */
33 : 0 : static inline void hlist_nulls_del_init_rcu(struct hlist_nulls_node *n)
34 : : {
35 [ # # # # ]: 0 : if (!hlist_nulls_unhashed(n)) {
36 [ # # # # ]: 0 : __hlist_nulls_del(n);
37 : 0 : 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 : 0 : static inline void hlist_nulls_del_rcu(struct hlist_nulls_node *n)
75 : : {
76 [ # # # # : 0 : __hlist_nulls_del(n);
# # # # ]
77 [ # # ]: 0 : 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 : 6 : static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n,
100 : : struct hlist_nulls_head *h)
101 : : {
102 : 6 : struct hlist_nulls_node *first = h->first;
103 : :
104 : 6 : n->next = first;
105 : 6 : WRITE_ONCE(n->pprev, &h->first);
106 [ - - + + : 6 : rcu_assign_pointer(hlist_nulls_first_rcu(h), n);
- - - - ]
107 [ - - + + : 6 : if (!is_a_nulls(first))
- - - - ]
108 : 3 : 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 : 0 : static inline void hlist_nulls_add_tail_rcu(struct hlist_nulls_node *n,
131 : : struct hlist_nulls_head *h)
132 : : {
133 : 0 : struct hlist_nulls_node *i, *last = NULL;
134 : :
135 : : /* Note: write side code, so rcu accessors are not needed. */
136 [ # # ]: 0 : for (i = h->first; !is_a_nulls(i); i = i->next)
137 : 0 : last = i;
138 : :
139 [ # # ]: 0 : if (last) {
140 : 0 : n->next = last->next;
141 : 0 : n->pprev = &last->next;
142 : 0 : rcu_assign_pointer(hlist_next_rcu(last), n);
143 : : } else {
144 : 0 : hlist_nulls_add_head_rcu(n, h);
145 : : }
146 : : }
147 : :
148 : : /* after that hlist_nulls_del will work */
149 : 0 : static inline void hlist_nulls_add_fake(struct hlist_nulls_node *n)
150 : : {
151 : 0 : n->pprev = &n->next;
152 : 0 : 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/core-api/atomic_ops.rst around line 114
165 : : * [2] Documentation/RCU/rculist_nulls.txt 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
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