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 if (!hlist_nulls_unhashed(n)) { 36 __hlist_nulls_del(n); 37 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 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 struct hlist_nulls_node *first = h->first; 95 96 n->next = first; 97 n->pprev = &h->first; 98 rcu_assign_pointer(hlist_nulls_first_rcu(h), n); 99 if (!is_a_nulls(first)) 100 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 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 for (i = h->first; !is_a_nulls(i); i = i->next) 129 last = i; 130 131 if (last) { 132 n->next = last->next; 133 n->pprev = &last->next; 134 rcu_assign_pointer(hlist_next_rcu(last), n); 135 } else { 136 hlist_nulls_add_head_rcu(n, h); 137 } 138 } 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 175