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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 : : static inline void hlist_nulls_del_init_rcu(struct hlist_nulls_node *n)
34 : : {
35 [ # # # # ]: 0 : if (!hlist_nulls_unhashed(n)) {
36 : : __hlist_nulls_del(n);
37 : : WRITE_ONCE(n->pprev, NULL);
38 : : }
39 : : }
40 : :
41 : : #define hlist_nulls_first_rcu(head) \
42 : : (*((struct hlist_nulls_node __rcu __force **)&(head)->first))
43 : :
44 : : #define hlist_nulls_next_rcu(node) \
45 : : (*((struct hlist_nulls_node __rcu __force **)&(node)->next))
46 : :
47 : : /**
48 : : * hlist_nulls_del_rcu - deletes entry from hash list without re-initialization
49 : : * @n: the element to delete from the hash list.
50 : : *
51 : : * Note: hlist_nulls_unhashed() on entry does not return true after this,
52 : : * the entry is in an undefined state. It is useful for RCU based
53 : : * lockfree traversal.
54 : : *
55 : : * In particular, it means that we can not poison the forward
56 : : * pointers that may still be used for walking the hash list.
57 : : *
58 : : * The caller must take whatever precautions are necessary
59 : : * (such as holding appropriate locks) to avoid racing
60 : : * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
61 : : * or hlist_nulls_del_rcu(), running on this same list.
62 : : * However, it is perfectly legal to run concurrently with
63 : : * the _rcu list-traversal primitives, such as
64 : : * hlist_nulls_for_each_entry().
65 : : */
66 : : static inline void hlist_nulls_del_rcu(struct hlist_nulls_node *n)
67 : : {
68 : : __hlist_nulls_del(n);
69 : : WRITE_ONCE(n->pprev, LIST_POISON2);
70 : : }
71 : :
72 : : /**
73 : : * hlist_nulls_add_head_rcu
74 : : * @n: the element to add to the hash list.
75 : : * @h: the list to add to.
76 : : *
77 : : * Description:
78 : : * Adds the specified element to the specified hlist_nulls,
79 : : * while permitting racing traversals.
80 : : *
81 : : * The caller must take whatever precautions are necessary
82 : : * (such as holding appropriate locks) to avoid racing
83 : : * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
84 : : * or hlist_nulls_del_rcu(), running on this same list.
85 : : * However, it is perfectly legal to run concurrently with
86 : : * the _rcu list-traversal primitives, such as
87 : : * hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
88 : : * problems on Alpha CPUs. Regardless of the type of CPU, the
89 : : * list-traversal primitive must be guarded by rcu_read_lock().
90 : : */
91 : : static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n,
92 : : struct hlist_nulls_head *h)
93 : : {
94 : 0 : struct hlist_nulls_node *first = h->first;
95 : :
96 : 0 : n->next = first;
97 : 0 : WRITE_ONCE(n->pprev, &h->first);
98 : 0 : rcu_assign_pointer(hlist_nulls_first_rcu(h), n);
99 [ # # # # : 0 : if (!is_a_nulls(first))
# # # # ]
100 : 0 : WRITE_ONCE(first->pprev, &n->next);
101 : : }
102 : :
103 : : /**
104 : : * hlist_nulls_add_tail_rcu
105 : : * @n: the element to add to the hash list.
106 : : * @h: the list to add to.
107 : : *
108 : : * Description:
109 : : * Adds the specified element to the specified hlist_nulls,
110 : : * while permitting racing traversals.
111 : : *
112 : : * The caller must take whatever precautions are necessary
113 : : * (such as holding appropriate locks) to avoid racing
114 : : * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
115 : : * or hlist_nulls_del_rcu(), running on this same list.
116 : : * However, it is perfectly legal to run concurrently with
117 : : * the _rcu list-traversal primitives, such as
118 : : * hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
119 : : * problems on Alpha CPUs. Regardless of the type of CPU, the
120 : : * list-traversal primitive must be guarded by rcu_read_lock().
121 : : */
122 : 0 : static inline void hlist_nulls_add_tail_rcu(struct hlist_nulls_node *n,
123 : : struct hlist_nulls_head *h)
124 : : {
125 : : struct hlist_nulls_node *i, *last = NULL;
126 : :
127 : : /* Note: write side code, so rcu accessors are not needed. */
128 [ # # ]: 0 : for (i = h->first; !is_a_nulls(i); i = i->next)
129 : : last = i;
130 : :
131 [ # # ]: 0 : if (last) {
132 : 0 : n->next = last->next;
133 : 0 : n->pprev = &last->next;
134 : 0 : rcu_assign_pointer(hlist_next_rcu(last), n);
135 : : } else {
136 : : hlist_nulls_add_head_rcu(n, h);
137 : : }
138 : 0 : }
139 : :
140 : : /**
141 : : * hlist_nulls_for_each_entry_rcu - iterate over rcu list of given type
142 : : * @tpos: the type * to use as a loop cursor.
143 : : * @pos: the &struct hlist_nulls_node to use as a loop cursor.
144 : : * @head: the head for your list.
145 : : * @member: the name of the hlist_nulls_node within the struct.
146 : : *
147 : : * The barrier() is needed to make sure compiler doesn't cache first element [1],
148 : : * as this loop can be restarted [2]
149 : : * [1] Documentation/core-api/atomic_ops.rst around line 114
150 : : * [2] Documentation/RCU/rculist_nulls.txt around line 146
151 : : */
152 : : #define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member) \
153 : : for (({barrier();}), \
154 : : pos = rcu_dereference_raw(hlist_nulls_first_rcu(head)); \
155 : : (!is_a_nulls(pos)) && \
156 : : ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; }); \
157 : : pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)))
158 : :
159 : : /**
160 : : * hlist_nulls_for_each_entry_safe -
161 : : * iterate over list of given type safe against removal of list entry
162 : : * @tpos: the type * to use as a loop cursor.
163 : : * @pos: the &struct hlist_nulls_node to use as a loop cursor.
164 : : * @head: the head for your list.
165 : : * @member: the name of the hlist_nulls_node within the struct.
166 : : */
167 : : #define hlist_nulls_for_each_entry_safe(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); \
172 : : pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)); 1; });)
173 : : #endif
174 : : #endif
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