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 */ hlist_nulls_del_init_rcu(struct hlist_nulls_node * n)33 static inline void hlist_nulls_del_init_rcu(struct hlist_nulls_node *n) 34 { 35 if (!hlist_nulls_unhashed(n)) { 36 __hlist_nulls_del(n); 37 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 */ hlist_nulls_del_rcu(struct hlist_nulls_node * n)74 static inline void hlist_nulls_del_rcu(struct hlist_nulls_node *n) 75 { 76 __hlist_nulls_del(n); 77 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 */ hlist_nulls_add_head_rcu(struct hlist_nulls_node * n,struct hlist_nulls_head * h)99 static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n, 100 struct hlist_nulls_head *h) 101 { 102 struct hlist_nulls_node *first = h->first; 103 104 WRITE_ONCE(n->next, first); 105 WRITE_ONCE(n->pprev, &h->first); 106 rcu_assign_pointer(hlist_nulls_first_rcu(h), n); 107 if (!is_a_nulls(first)) 108 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 */ hlist_nulls_add_tail_rcu(struct hlist_nulls_node * n,struct hlist_nulls_head * h)130 static inline void hlist_nulls_add_tail_rcu(struct hlist_nulls_node *n, 131 struct hlist_nulls_head *h) 132 { 133 struct hlist_nulls_node *i, *last = NULL; 134 135 /* Note: write side code, so rcu accessors are not needed. */ 136 for (i = h->first; !is_a_nulls(i); i = i->next) 137 last = i; 138 139 if (last) { 140 WRITE_ONCE(n->next, last->next); 141 n->pprev = &last->next; 142 rcu_assign_pointer(hlist_nulls_next_rcu(last), n); 143 } else { 144 hlist_nulls_add_head_rcu(n, h); 145 } 146 } 147 148 /* after that hlist_nulls_del will work */ hlist_nulls_add_fake(struct hlist_nulls_node * n)149 static inline void hlist_nulls_add_fake(struct hlist_nulls_node *n) 150 { 151 n->pprev = &n->next; 152 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/memory-barriers.txt around line 1533 165 * [2] Documentation/RCU/rculist_nulls.rst 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 190