4 * Lock-less NULL terminated single linked list
6 * If there are multiple producers and multiple consumers, llist_add
7 * can be used in producers and llist_del_all can be used in
8 * consumers. They can work simultaneously without lock. But
9 * llist_del_first can not be used here. Because llist_del_first
10 * depends on list->first->next does not changed if list->first is not
11 * changed during its operation, but llist_del_first, llist_add,
12 * llist_add (or llist_del_all, llist_add, llist_add) sequence in
13 * another consumer may violate that.
15 * If there are multiple producers and one consumer, llist_add can be
16 * used in producers and llist_del_all or llist_del_first can be used
19 * This can be summarized as follow:
21 * | add | del_first | del_all
26 * Where "-" stands for no lock is needed, while "L" stands for lock
29 * The list entries deleted via llist_del_all can be traversed with
30 * traversing function such as llist_for_each etc. But the list
31 * entries can not be traversed safely before deleted from the list.
32 * The order of deleted entries is from the newest to the oldest added
33 * one. If you want to traverse from the oldest to the newest, you
34 * must reverse the order by yourself before traversing.
36 * The basic atomic operation of this list is cmpxchg on long. On
37 * architectures that don't have NMI-safe cmpxchg implementation, the
38 * list can NOT be used in NMI handlers. So code that uses the list in
39 * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
41 * Copyright 2010,2011 Intel Corp.
42 * Author: Huang Ying <ying.huang@intel.com>
44 * This program is free software; you can redistribute it and/or
45 * modify it under the terms of the GNU General Public License version
46 * 2 as published by the Free Software Foundation;
48 * This program is distributed in the hope that it will be useful,
49 * but WITHOUT ANY WARRANTY; without even the implied warranty of
50 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
51 * GNU General Public License for more details.
53 * You should have received a copy of the GNU General Public License
54 * along with this program; if not, write to the Free Software
55 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
58 #include <linux/kernel.h>
59 #include <asm/system.h>
60 #include <asm/processor.h>
63 struct llist_node
*first
;
67 struct llist_node
*next
;
70 #define LLIST_HEAD_INIT(name) { NULL }
71 #define LLIST_HEAD(name) struct llist_head name = LLIST_HEAD_INIT(name)
74 * init_llist_head - initialize lock-less list head
75 * @head: the head for your lock-less list
77 static inline void init_llist_head(struct llist_head
*list
)
83 * llist_entry - get the struct of this entry
84 * @ptr: the &struct llist_node pointer.
85 * @type: the type of the struct this is embedded in.
86 * @member: the name of the llist_node within the struct.
88 #define llist_entry(ptr, type, member) \
89 container_of(ptr, type, member)
92 * llist_for_each - iterate over some deleted entries of a lock-less list
93 * @pos: the &struct llist_node to use as a loop cursor
94 * @node: the first entry of deleted list entries
96 * In general, some entries of the lock-less list can be traversed
97 * safely only after being deleted from list, so start with an entry
98 * instead of list head.
100 * If being used on entries deleted from lock-less list directly, the
101 * traverse order is from the newest to the oldest added entry. If
102 * you want to traverse from the oldest to the newest, you must
103 * reverse the order by yourself before traversing.
105 #define llist_for_each(pos, node) \
106 for ((pos) = (node); pos; (pos) = (pos)->next)
109 * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
110 * @pos: the type * to use as a loop cursor.
111 * @node: the fist entry of deleted list entries.
112 * @member: the name of the llist_node with the struct.
114 * In general, some entries of the lock-less list can be traversed
115 * safely only after being removed from list, so start with an entry
116 * instead of list head.
118 * If being used on entries deleted from lock-less list directly, the
119 * traverse order is from the newest to the oldest added entry. If
120 * you want to traverse from the oldest to the newest, you must
121 * reverse the order by yourself before traversing.
123 #define llist_for_each_entry(pos, node, member) \
124 for ((pos) = llist_entry((node), typeof(*(pos)), member); \
125 &(pos)->member != NULL; \
126 (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
129 * llist_empty - tests whether a lock-less list is empty
130 * @head: the list to test
132 * Not guaranteed to be accurate or up to date. Just a quick way to
133 * test whether the list is empty without deleting something from the
136 static inline bool llist_empty(const struct llist_head
*head
)
138 return ACCESS_ONCE(head
->first
) == NULL
;
141 static inline struct llist_node
*llist_next(struct llist_node
*node
)
147 * llist_add - add a new entry
148 * @new: new entry to be added
149 * @head: the head for your lock-less list
151 * Returns true if the list was empty prior to adding this entry.
153 static inline bool llist_add(struct llist_node
*new, struct llist_head
*head
)
155 struct llist_node
*entry
, *old_entry
;
161 entry
= cmpxchg(&head
->first
, old_entry
, new);
162 if (entry
== old_entry
)
166 return old_entry
== NULL
;
170 * llist_del_all - delete all entries from lock-less list
171 * @head: the head of lock-less list to delete all entries
173 * If list is empty, return NULL, otherwise, delete all entries and
174 * return the pointer to the first entry. The order of entries
175 * deleted is from the newest to the oldest added one.
177 static inline struct llist_node
*llist_del_all(struct llist_head
*head
)
179 return xchg(&head
->first
, NULL
);
182 extern bool llist_add_batch(struct llist_node
*new_first
,
183 struct llist_node
*new_last
,
184 struct llist_head
*head
);
185 extern struct llist_node
*llist_del_first(struct llist_head
*head
);
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