1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_RCULIST_BL_H
3 #define _LINUX_RCULIST_BL_H
4
5 /*
6 * RCU-protected bl list version. See include/linux/list_bl.h.
7 */
8 #include <linux/list_bl.h>
9 #include <linux/rcupdate.h>
10
11 static inline void hlist_bl_set_first_rcu(struct hlist_bl_head *h,
12 struct hlist_bl_node *n)
13 {
14 LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);
15 LIST_BL_BUG_ON(((unsigned long)h->first & LIST_BL_LOCKMASK) !=
16 LIST_BL_LOCKMASK);
17 rcu_assign_pointer(h->first,
18 (struct hlist_bl_node *)((unsigned long)n | LIST_BL_LOCKMASK));
19 }
20
21 static inline struct hlist_bl_node *hlist_bl_first_rcu(struct hlist_bl_head *h)
22 {
23 return (struct hlist_bl_node *)
24 ((unsigned long)rcu_dereference_check(h->first, hlist_bl_is_locked(h)) & ~LIST_BL_LOCKMASK);
25 }
26
27 /**
28 * hlist_bl_del_init_rcu - deletes entry from hash list with re-initialization
29 * @n: the element to delete from the hash list.
30 *
31 * Note: hlist_bl_unhashed() on the node returns true after this. It is
32 * useful for RCU based read lockfree traversal if the writer side
33 * must know if the list entry is still hashed or already unhashed.
34 *
35 * In particular, it means that we can not poison the forward pointers
36 * that may still be used for walking the hash list and we can only
37 * zero the pprev pointer so list_unhashed() will return true after
38 * this.
39 *
40 * The caller must take whatever precautions are necessary (such as
41 * holding appropriate locks) to avoid racing with another
42 * list-mutation primitive, such as hlist_bl_add_head_rcu() or
43 * hlist_bl_del_rcu(), running on this same list. However, it is
44 * perfectly legal to run concurrently with the _rcu list-traversal
45 * primitives, such as hlist_bl_for_each_entry_rcu().
46 */
47 static inline void hlist_bl_del_init_rcu(struct hlist_bl_node *n)
48 {
49 if (!hlist_bl_unhashed(n)) {
50 __hlist_bl_del(n);
51 n->pprev = NULL;
52 }
53 }
54
55 /**
56 * hlist_bl_del_rcu - deletes entry from hash list without re-initialization
57 * @n: the element to delete from the hash list.
58 *
59 * Note: hlist_bl_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_bl_add_head_rcu()
69 * or hlist_bl_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_bl_for_each_entry().
73 */
74 static inline void hlist_bl_del_rcu(struct hlist_bl_node *n)
75 {
76 __hlist_bl_del(n);
77 n->pprev = LIST_POISON2;
78 }
79
80 /**
81 * hlist_bl_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_bl,
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_bl_add_head_rcu()
92 * or hlist_bl_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_bl_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_bl_add_head_rcu(struct hlist_bl_node *n,
100 struct hlist_bl_head *h)
101 {
102 struct hlist_bl_node *first;
103
104 /* don't need hlist_bl_first_rcu because we're under lock */
105 first = hlist_bl_first(h);
106
107 n->next = first;
108 if (first)
109 first->pprev = &n->next;
110 n->pprev = &h->first;
111
112 /* need _rcu because we can have concurrent lock free readers */
113 hlist_bl_set_first_rcu(h, n);
114 }
115 /**
116 * hlist_bl_for_each_entry_rcu - iterate over rcu list of given type
117 * @tpos: the type * to use as a loop cursor.
118 * @pos: the &struct hlist_bl_node to use as a loop cursor.
119 * @head: the head for your list.
120 * @member: the name of the hlist_bl_node within the struct.
121 *
122 */
123 #define hlist_bl_for_each_entry_rcu(tpos, pos, head, member) \
124 for (pos = hlist_bl_first_rcu(head); \
125 pos && \
126 ({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1; }); \
127 pos = rcu_dereference_raw(pos->next))
128
129 #endif