1 #ifndef _LINUX_RCULIST_NULLS_H
2 #define _LINUX_RCULIST_NULLS_H
3
4 #ifdef __KERNEL__
5
6 /*
7 * RCU-protected list version
8 */
9 #include <linux/list_nulls.h>
10 #include <linux/rcupdate.h>
11
12 /**
13 * hlist_nulls_del_init_rcu - deletes entry from hash list with re-initialization
14 * @n: the element to delete from the hash list.
15 *
16 * Note: hlist_nulls_unhashed() on the node return true after this. It is
17 * useful for RCU based read lockfree traversal if the writer side
18 * must know if the list entry is still hashed or already unhashed.
19 *
20 * In particular, it means that we can not poison the forward pointers
21 * that may still be used for walking the hash list and we can only
22 * zero the pprev pointer so list_unhashed() will return true after
23 * this.
24 *
25 * The caller must take whatever precautions are necessary (such as
26 * holding appropriate locks) to avoid racing with another
27 * list-mutation primitive, such as hlist_nulls_add_head_rcu() or
28 * hlist_nulls_del_rcu(), running on this same list. However, it is
29 * perfectly legal to run concurrently with the _rcu list-traversal
30 * primitives, such as hlist_nulls_for_each_entry_rcu().
31 */
32 static inline void hlist_nulls_del_init_rcu(struct hlist_nulls_node *n)
33 {
34 if (!hlist_nulls_unhashed(n)) {
35 __hlist_nulls_del(n);
36 n->pprev = NULL;
37 }
38 }
39
40 /**
41 * hlist_nulls_del_rcu - deletes entry from hash list without re-initialization
42 * @n: the element to delete from the hash list.
43 *
44 * Note: hlist_nulls_unhashed() on entry does not return true after this,
45 * the entry is in an undefined state. It is useful for RCU based
46 * lockfree traversal.
47 *
48 * In particular, it means that we can not poison the forward
49 * pointers that may still be used for walking the hash list.
50 *
51 * The caller must take whatever precautions are necessary
52 * (such as holding appropriate locks) to avoid racing
53 * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
54 * or hlist_nulls_del_rcu(), running on this same list.
55 * However, it is perfectly legal to run concurrently with
56 * the _rcu list-traversal primitives, such as
57 * hlist_nulls_for_each_entry().
58 */
59 static inline void hlist_nulls_del_rcu(struct hlist_nulls_node *n)
60 {
61 __hlist_nulls_del(n);
62 n->pprev = LIST_POISON2;
63 }
64
65 /**
66 * hlist_nulls_add_head_rcu
67 * @n: the element to add to the hash list.
68 * @h: the list to add to.
69 *
70 * Description:
71 * Adds the specified element to the specified hlist_nulls,
72 * while permitting racing traversals.
73 *
74 * The caller must take whatever precautions are necessary
75 * (such as holding appropriate locks) to avoid racing
76 * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
77 * or hlist_nulls_del_rcu(), running on this same list.
78 * However, it is perfectly legal to run concurrently with
79 * the _rcu list-traversal primitives, such as
80 * hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
81 * problems on Alpha CPUs. Regardless of the type of CPU, the
82 * list-traversal primitive must be guarded by rcu_read_lock().
83 */
84 static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n,
85 struct hlist_nulls_head *h)
86 {
87 struct hlist_nulls_node *first = h->first;
88
89 n->next = first;
90 n->pprev = &h->first;
91 rcu_assign_pointer(h->first, n);
92 if (!is_a_nulls(first))
93 first->pprev = &n->next;
94 }
95 /**
96 * hlist_nulls_for_each_entry_rcu - iterate over rcu list of given type
97 * @tpos: the type * to use as a loop cursor.
98 * @pos: the &struct hlist_nulls_node to use as a loop cursor.
99 * @head: the head for your list.
100 * @member: the name of the hlist_nulls_node within the struct.
101 *
102 */
103 #define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member) \
104 for (pos = rcu_dereference((head)->first); \
105 (!is_a_nulls(pos)) && \
106 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; }); \
107 pos = rcu_dereference(pos->next))
108
109 #endif
110 #endif
111
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