xref: /openbmc/linux/lib/llist.c (revision dba8b46992c55946d3b092934f581a343403118f)
1 /*
2  * Lock-less NULL terminated single linked list
3  *
4  * The basic atomic operation of this list is cmpxchg on long.  On
5  * architectures that don't have NMI-safe cmpxchg implementation, the
6  * list can NOT be used in NMI handler.  So code uses the list in NMI
7  * handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
8  *
9  * Copyright 2010,2011 Intel Corp.
10  *   Author: Huang Ying <ying.huang@intel.com>
11  *
12  * This program is free software; you can redistribute it and/or
13  * modify it under the terms of the GNU General Public License version
14  * 2 as published by the Free Software Foundation;
15  *
16  * This program is distributed in the hope that it will be useful,
17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
19  * GNU General Public License for more details.
20  *
21  * You should have received a copy of the GNU General Public License
22  * along with this program; if not, write to the Free Software
23  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
24  */
25 #include <linux/kernel.h>
26 #include <linux/module.h>
27 #include <linux/interrupt.h>
28 #include <linux/llist.h>
29 
30 #include <asm/system.h>
31 
32 /**
33  * llist_add - add a new entry
34  * @new:	new entry to be added
35  * @head:	the head for your lock-less list
36  */
37 void llist_add(struct llist_node *new, struct llist_head *head)
38 {
39 	struct llist_node *entry, *old_entry;
40 
41 #ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
42 	BUG_ON(in_nmi());
43 #endif
44 
45 	entry = head->first;
46 	do {
47 		old_entry = entry;
48 		new->next = entry;
49 		cpu_relax();
50 	} while ((entry = cmpxchg(&head->first, old_entry, new)) != old_entry);
51 }
52 EXPORT_SYMBOL_GPL(llist_add);
53 
54 /**
55  * llist_add_batch - add several linked entries in batch
56  * @new_first:	first entry in batch to be added
57  * @new_last:	last entry in batch to be added
58  * @head:	the head for your lock-less list
59  */
60 void llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
61 		     struct llist_head *head)
62 {
63 	struct llist_node *entry, *old_entry;
64 
65 #ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
66 	BUG_ON(in_nmi());
67 #endif
68 
69 	entry = head->first;
70 	do {
71 		old_entry = entry;
72 		new_last->next = entry;
73 		cpu_relax();
74 	} while ((entry = cmpxchg(&head->first, old_entry, new_first)) != old_entry);
75 }
76 EXPORT_SYMBOL_GPL(llist_add_batch);
77 
78 /**
79  * llist_del_first - delete the first entry of lock-less list
80  * @head:	the head for your lock-less list
81  *
82  * If list is empty, return NULL, otherwise, return the first entry
83  * deleted, this is the newest added one.
84  *
85  * Only one llist_del_first user can be used simultaneously with
86  * multiple llist_add users without lock.  Because otherwise
87  * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
88  * llist_add) sequence in another user may change @head->first->next,
89  * but keep @head->first.  If multiple consumers are needed, please
90  * use llist_del_all or use lock between consumers.
91  */
92 struct llist_node *llist_del_first(struct llist_head *head)
93 {
94 	struct llist_node *entry, *old_entry, *next;
95 
96 #ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
97 	BUG_ON(in_nmi());
98 #endif
99 
100 	entry = head->first;
101 	do {
102 		if (entry == NULL)
103 			return NULL;
104 		old_entry = entry;
105 		next = entry->next;
106 		cpu_relax();
107 	} while ((entry = cmpxchg(&head->first, old_entry, next)) != old_entry);
108 
109 	return entry;
110 }
111 EXPORT_SYMBOL_GPL(llist_del_first);
112 
113 /**
114  * llist_del_all - delete all entries from lock-less list
115  * @head:	the head of lock-less list to delete all entries
116  *
117  * If list is empty, return NULL, otherwise, delete all entries and
118  * return the pointer to the first entry.  The order of entries
119  * deleted is from the newest to the oldest added one.
120  */
121 struct llist_node *llist_del_all(struct llist_head *head)
122 {
123 #ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
124 	BUG_ON(in_nmi());
125 #endif
126 
127 	return xchg(&head->first, NULL);
128 }
129 EXPORT_SYMBOL_GPL(llist_del_all);
130