1 /* SPDX-License-Identifier: GPL-2.0-only */ 2 #ifndef LLIST_H 3 #define LLIST_H 4 /* 5 * Lock-less NULL terminated single linked list 6 * 7 * Cases where locking is not needed: 8 * If there are multiple producers and multiple consumers, llist_add can be 9 * used in producers and llist_del_all can be used in consumers simultaneously 10 * without locking. Also a single consumer can use llist_del_first while 11 * multiple producers simultaneously use llist_add, without any locking. 12 * 13 * Cases where locking is needed: 14 * If we have multiple consumers with llist_del_first used in one consumer, and 15 * llist_del_first or llist_del_all used in other consumers, then a lock is 16 * needed. This is because llist_del_first depends on list->first->next not 17 * changing, but without lock protection, there's no way to be sure about that 18 * if a preemption happens in the middle of the delete operation and on being 19 * preempted back, the list->first is the same as before causing the cmpxchg in 20 * llist_del_first to succeed. For example, while a llist_del_first operation 21 * is in progress in one consumer, then a llist_del_first, llist_add, 22 * llist_add (or llist_del_all, llist_add, llist_add) sequence in another 23 * consumer may cause violations. 24 * 25 * This can be summarized as follows: 26 * 27 * | add | del_first | del_all 28 * add | - | - | - 29 * del_first | | L | L 30 * del_all | | | - 31 * 32 * Where, a particular row's operation can happen concurrently with a column's 33 * operation, with "-" being no lock needed, while "L" being lock is needed. 34 * 35 * The list entries deleted via llist_del_all can be traversed with 36 * traversing function such as llist_for_each etc. But the list 37 * entries can not be traversed safely before deleted from the list. 38 * The order of deleted entries is from the newest to the oldest added 39 * one. If you want to traverse from the oldest to the newest, you 40 * must reverse the order by yourself before traversing. 41 * 42 * The basic atomic operation of this list is cmpxchg on long. On 43 * architectures that don't have NMI-safe cmpxchg implementation, the 44 * list can NOT be used in NMI handlers. So code that uses the list in 45 * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG. 46 * 47 * Copyright 2010,2011 Intel Corp. 48 * Author: Huang Ying <ying.huang@intel.com> 49 */ 50 51 #include <linux/atomic.h> 52 #include <linux/kernel.h> 53 54 struct llist_head { 55 struct llist_node *first; 56 }; 57 58 struct llist_node { 59 struct llist_node *next; 60 }; 61 62 #define LLIST_HEAD_INIT(name) { NULL } 63 #define LLIST_HEAD(name) struct llist_head name = LLIST_HEAD_INIT(name) 64 65 /** 66 * init_llist_head - initialize lock-less list head 67 * @head: the head for your lock-less list 68 */ 69 static inline void init_llist_head(struct llist_head *list) 70 { 71 list->first = NULL; 72 } 73 74 /** 75 * llist_entry - get the struct of this entry 76 * @ptr: the &struct llist_node pointer. 77 * @type: the type of the struct this is embedded in. 78 * @member: the name of the llist_node within the struct. 79 */ 80 #define llist_entry(ptr, type, member) \ 81 container_of(ptr, type, member) 82 83 /** 84 * member_address_is_nonnull - check whether the member address is not NULL 85 * @ptr: the object pointer (struct type * that contains the llist_node) 86 * @member: the name of the llist_node within the struct. 87 * 88 * This macro is conceptually the same as 89 * &ptr->member != NULL 90 * but it works around the fact that compilers can decide that taking a member 91 * address is never a NULL pointer. 92 * 93 * Real objects that start at a high address and have a member at NULL are 94 * unlikely to exist, but such pointers may be returned e.g. by the 95 * container_of() macro. 96 */ 97 #define member_address_is_nonnull(ptr, member) \ 98 ((uintptr_t)(ptr) + offsetof(typeof(*(ptr)), member) != 0) 99 100 /** 101 * llist_for_each - iterate over some deleted entries of a lock-less list 102 * @pos: the &struct llist_node to use as a loop cursor 103 * @node: the first entry of deleted list entries 104 * 105 * In general, some entries of the lock-less list can be traversed 106 * safely only after being deleted from list, so start with an entry 107 * instead of list head. 108 * 109 * If being used on entries deleted from lock-less list directly, the 110 * traverse order is from the newest to the oldest added entry. If 111 * you want to traverse from the oldest to the newest, you must 112 * reverse the order by yourself before traversing. 113 */ 114 #define llist_for_each(pos, node) \ 115 for ((pos) = (node); pos; (pos) = (pos)->next) 116 117 /** 118 * llist_for_each_safe - iterate over some deleted entries of a lock-less list 119 * safe against removal of list entry 120 * @pos: the &struct llist_node to use as a loop cursor 121 * @n: another &struct llist_node to use as temporary storage 122 * @node: the first entry of deleted list entries 123 * 124 * In general, some entries of the lock-less list can be traversed 125 * safely only after being deleted from list, so start with an entry 126 * instead of list head. 127 * 128 * If being used on entries deleted from lock-less list directly, the 129 * traverse order is from the newest to the oldest added entry. If 130 * you want to traverse from the oldest to the newest, you must 131 * reverse the order by yourself before traversing. 132 */ 133 #define llist_for_each_safe(pos, n, node) \ 134 for ((pos) = (node); (pos) && ((n) = (pos)->next, true); (pos) = (n)) 135 136 /** 137 * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type 138 * @pos: the type * to use as a loop cursor. 139 * @node: the fist entry of deleted list entries. 140 * @member: the name of the llist_node with the struct. 141 * 142 * In general, some entries of the lock-less list can be traversed 143 * safely only after being removed from list, so start with an entry 144 * instead of list head. 145 * 146 * If being used on entries deleted from lock-less list directly, the 147 * traverse order is from the newest to the oldest added entry. If 148 * you want to traverse from the oldest to the newest, you must 149 * reverse the order by yourself before traversing. 150 */ 151 #define llist_for_each_entry(pos, node, member) \ 152 for ((pos) = llist_entry((node), typeof(*(pos)), member); \ 153 member_address_is_nonnull(pos, member); \ 154 (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member)) 155 156 /** 157 * llist_for_each_entry_safe - iterate over some deleted entries of lock-less list of given type 158 * safe against removal of list entry 159 * @pos: the type * to use as a loop cursor. 160 * @n: another type * to use as temporary storage 161 * @node: the first entry of deleted list entries. 162 * @member: the name of the llist_node with the struct. 163 * 164 * In general, some entries of the lock-less list can be traversed 165 * safely only after being removed from list, so start with an entry 166 * instead of list head. 167 * 168 * If being used on entries deleted from lock-less list directly, the 169 * traverse order is from the newest to the oldest added entry. If 170 * you want to traverse from the oldest to the newest, you must 171 * reverse the order by yourself before traversing. 172 */ 173 #define llist_for_each_entry_safe(pos, n, node, member) \ 174 for (pos = llist_entry((node), typeof(*pos), member); \ 175 member_address_is_nonnull(pos, member) && \ 176 (n = llist_entry(pos->member.next, typeof(*n), member), true); \ 177 pos = n) 178 179 /** 180 * llist_empty - tests whether a lock-less list is empty 181 * @head: the list to test 182 * 183 * Not guaranteed to be accurate or up to date. Just a quick way to 184 * test whether the list is empty without deleting something from the 185 * list. 186 */ 187 static inline bool llist_empty(const struct llist_head *head) 188 { 189 return READ_ONCE(head->first) == NULL; 190 } 191 192 static inline struct llist_node *llist_next(struct llist_node *node) 193 { 194 return node->next; 195 } 196 197 extern bool llist_add_batch(struct llist_node *new_first, 198 struct llist_node *new_last, 199 struct llist_head *head); 200 /** 201 * llist_add - add a new entry 202 * @new: new entry to be added 203 * @head: the head for your lock-less list 204 * 205 * Returns true if the list was empty prior to adding this entry. 206 */ 207 static inline bool llist_add(struct llist_node *new, struct llist_head *head) 208 { 209 return llist_add_batch(new, new, head); 210 } 211 212 /** 213 * llist_del_all - delete all entries from lock-less list 214 * @head: the head of lock-less list to delete all entries 215 * 216 * If list is empty, return NULL, otherwise, delete all entries and 217 * return the pointer to the first entry. The order of entries 218 * deleted is from the newest to the oldest added one. 219 */ 220 static inline struct llist_node *llist_del_all(struct llist_head *head) 221 { 222 return xchg(&head->first, NULL); 223 } 224 225 extern struct llist_node *llist_del_first(struct llist_head *head); 226 227 struct llist_node *llist_reverse_order(struct llist_node *head); 228 229 #endif /* LLIST_H */ 230