1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_LIST_BL_H
3 #define _LINUX_LIST_BL_H
4
5 #include <linux/list.h>
6 #include <linux/bit_spinlock.h>
7
8 /*
9 * Special version of lists, where head of the list has a lock in the lowest
10 * bit. This is useful for scalable hash tables without increasing memory
11 * footprint overhead.
12 *
13 * For modification operations, the 0 bit of hlist_bl_head->first
14 * pointer must be set.
15 *
16 * With some small modifications, this can easily be adapted to store several
17 * arbitrary bits (not just a single lock bit), if the need arises to store
18 * some fast and compact auxiliary data.
19 */
20
21 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
22 #define LIST_BL_LOCKMASK 1UL
23 #else
24 #define LIST_BL_LOCKMASK 0UL
25 #endif
26
27 #ifdef CONFIG_DEBUG_LIST
28 #define LIST_BL_BUG_ON(x) BUG_ON(x)
29 #else
30 #define LIST_BL_BUG_ON(x)
31 #endif
32
33
34 struct hlist_bl_head {
35 struct hlist_bl_node *first;
36 };
37
38 struct hlist_bl_node {
39 struct hlist_bl_node *next, **pprev;
40 };
41 #define INIT_HLIST_BL_HEAD(ptr) \
42 ((ptr)->first = NULL)
43
44 static inline void INIT_HLIST_BL_NODE(struct hlist_bl_node *h)
45 {
46 h->next = NULL;
47 h->pprev = NULL;
48 }
49
50 #define hlist_bl_entry(ptr, type, member) container_of(ptr,type,member)
51
52 static inline bool hlist_bl_unhashed(const struct hlist_bl_node *h)
53 {
54 return !h->pprev;
55 }
56
57 static inline struct hlist_bl_node *hlist_bl_first(struct hlist_bl_head *h)
58 {
59 return (struct hlist_bl_node *)
60 ((unsigned long)h->first & ~LIST_BL_LOCKMASK);
61 }
62
63 static inline void hlist_bl_set_first(struct hlist_bl_head *h,
64 struct hlist_bl_node *n)
65 {
66 LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);
67 LIST_BL_BUG_ON(((unsigned long)h->first & LIST_BL_LOCKMASK) !=
68 LIST_BL_LOCKMASK);
69 h->first = (struct hlist_bl_node *)((unsigned long)n | LIST_BL_LOCKMASK);
70 }
71
72 static inline bool hlist_bl_empty(const struct hlist_bl_head *h)
73 {
74 return !((unsigned long)READ_ONCE(h->first) & ~LIST_BL_LOCKMASK);
75 }
76
77 static inline void hlist_bl_add_head(struct hlist_bl_node *n,
78 struct hlist_bl_head *h)
79 {
80 struct hlist_bl_node *first = hlist_bl_first(h);
81
82 n->next = first;
83 if (first)
84 first->pprev = &n->next;
85 n->pprev = &h->first;
86 hlist_bl_set_first(h, n);
87 }
88
89 static inline void hlist_bl_add_before(struct hlist_bl_node *n,
90 struct hlist_bl_node *next)
91 {
92 struct hlist_bl_node **pprev = next->pprev;
93
94 n->pprev = pprev;
95 n->next = next;
96 next->pprev = &n->next;
97
98 /* pprev may be `first`, so be careful not to lose the lock bit */
99 WRITE_ONCE(*pprev,
100 (struct hlist_bl_node *)
101 ((uintptr_t)n | ((uintptr_t)*pprev & LIST_BL_LOCKMASK)));
102 }
103
104 static inline void hlist_bl_add_behind(struct hlist_bl_node *n,
105 struct hlist_bl_node *prev)
106 {
107 n->next = prev->next;
108 n->pprev = &prev->next;
109 prev->next = n;
110
111 if (n->next)
112 n->next->pprev = &n->next;
113 }
114
115 static inline void __hlist_bl_del(struct hlist_bl_node *n)
116 {
117 struct hlist_bl_node *next = n->next;
118 struct hlist_bl_node **pprev = n->pprev;
119
120 LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);
121
122 /* pprev may be `first`, so be careful not to lose the lock bit */
123 WRITE_ONCE(*pprev,
124 (struct hlist_bl_node *)
125 ((unsigned long)next |
126 ((unsigned long)*pprev & LIST_BL_LOCKMASK)));
127 if (next)
128 next->pprev = pprev;
129 }
130
131 static inline void hlist_bl_del(struct hlist_bl_node *n)
132 {
133 __hlist_bl_del(n);
134 n->next = LIST_POISON1;
135 n->pprev = LIST_POISON2;
136 }
137
138 static inline void hlist_bl_del_init(struct hlist_bl_node *n)
139 {
140 if (!hlist_bl_unhashed(n)) {
141 __hlist_bl_del(n);
142 INIT_HLIST_BL_NODE(n);
143 }
144 }
145
146 static inline void hlist_bl_lock(struct hlist_bl_head *b)
147 {
148 bit_spin_lock(0, (unsigned long *)b);
149 }
150
151 static inline void hlist_bl_unlock(struct hlist_bl_head *b)
152 {
153 __bit_spin_unlock(0, (unsigned long *)b);
154 }
155
156 static inline bool hlist_bl_is_locked(struct hlist_bl_head *b)
157 {
158 return bit_spin_is_locked(0, (unsigned long *)b);
159 }
160
161 /**
162 * hlist_bl_for_each_entry - iterate over list of given type
163 * @tpos: the type * to use as a loop cursor.
164 * @pos: the &struct hlist_node to use as a loop cursor.
165 * @head: the head for your list.
166 * @member: the name of the hlist_node within the struct.
167 *
168 */
169 #define hlist_bl_for_each_entry(tpos, pos, head, member) \
170 for (pos = hlist_bl_first(head); \
171 pos && \
172 ({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1;}); \
173 pos = pos->next)
174
175 /**
176 * hlist_bl_for_each_entry_safe - 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_node to use as a loop cursor.
179 * @n: another &struct hlist_node to use as temporary storage
180 * @head: the head for your list.
181 * @member: the name of the hlist_node within the struct.
182 */
183 #define hlist_bl_for_each_entry_safe(tpos, pos, n, head, member) \
184 for (pos = hlist_bl_first(head); \
185 pos && ({ n = pos->next; 1; }) && \
186 ({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1;}); \
187 pos = n)
188
189 #endif
190
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