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 */ 33static 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 */ 66static 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 */ 91static 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_for_each_entry_rcu - iterate over rcu list of given type 105 * @tpos: the type * to use as a loop cursor. 106 * @pos: the &struct hlist_nulls_node to use as a loop cursor. 107 * @head: the head for your list. 108 * @member: the name of the hlist_nulls_node within the struct. 109 * 110 * The barrier() is needed to make sure compiler doesn't cache first element [1], 111 * as this loop can be restarted [2] 112 * [1] Documentation/core-api/atomic_ops.rst around line 114 113 * [2] Documentation/RCU/rculist_nulls.txt around line 146 114 */ 115#define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member) \ 116 for (({barrier();}), \ 117 pos = rcu_dereference_raw(hlist_nulls_first_rcu(head)); \ 118 (!is_a_nulls(pos)) && \ 119 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; }); \ 120 pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos))) 121 122/** 123 * hlist_nulls_for_each_entry_safe - 124 * iterate over list of given type safe against removal of list entry 125 * @tpos: the type * to use as a loop cursor. 126 * @pos: the &struct hlist_nulls_node to use as a loop cursor. 127 * @head: the head for your list. 128 * @member: the name of the hlist_nulls_node within the struct. 129 */ 130#define hlist_nulls_for_each_entry_safe(tpos, pos, head, member) \ 131 for (({barrier();}), \ 132 pos = rcu_dereference_raw(hlist_nulls_first_rcu(head)); \ 133 (!is_a_nulls(pos)) && \ 134 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); \ 135 pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)); 1; });) 136#endif 137#endif 138