1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Lock-less NULL terminated single linked list
4 *
5 * The basic atomic operation of this list is cmpxchg on long.  On
6 * architectures that don't have NMI-safe cmpxchg implementation, the
7 * list can NOT be used in NMI handlers.  So code that uses the list in
8 * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
9 *
10 * Copyright 2010,2011 Intel Corp.
11 *   Author: Huang Ying <ying.huang@intel.com>
12 */
13#include <linux/kernel.h>
14#include <linux/export.h>
15#include <linux/llist.h>
16
17
18/**
19 * llist_add_batch - add several linked entries in batch
20 * @new_first:	first entry in batch to be added
21 * @new_last:	last entry in batch to be added
22 * @head:	the head for your lock-less list
23 *
24 * Return whether list is empty before adding.
25 */
26bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
27		     struct llist_head *head)
28{
29	struct llist_node *first = READ_ONCE(head->first);
30
31	do {
32		new_last->next = first;
33	} while (!try_cmpxchg(&head->first, &first, new_first));
34
35	return !first;
36}
37EXPORT_SYMBOL_GPL(llist_add_batch);
38
39/**
40 * llist_del_first - delete the first entry of lock-less list
41 * @head:	the head for your lock-less list
42 *
43 * If list is empty, return NULL, otherwise, return the first entry
44 * deleted, this is the newest added one.
45 *
46 * Only one llist_del_first user can be used simultaneously with
47 * multiple llist_add users without lock.  Because otherwise
48 * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
49 * llist_add) sequence in another user may change @head->first->next,
50 * but keep @head->first.  If multiple consumers are needed, please
51 * use llist_del_all or use lock between consumers.
52 */
53struct llist_node *llist_del_first(struct llist_head *head)
54{
55	struct llist_node *entry, *next;
56
57	entry = smp_load_acquire(&head->first);
58	do {
59		if (entry == NULL)
60			return NULL;
61		next = READ_ONCE(entry->next);
62	} while (!try_cmpxchg(&head->first, &entry, next));
63
64	return entry;
65}
66EXPORT_SYMBOL_GPL(llist_del_first);
67
68/**
69 * llist_del_first_this - delete given entry of lock-less list if it is first
70 * @head:	the head for your lock-less list
71 * @this:	a list entry.
72 *
73 * If head of the list is given entry, delete and return %true else
74 * return %false.
75 *
76 * Multiple callers can safely call this concurrently with multiple
77 * llist_add() callers, providing all the callers offer a different @this.
78 */
79bool llist_del_first_this(struct llist_head *head,
80			  struct llist_node *this)
81{
82	struct llist_node *entry, *next;
83
84	/* acquire ensures orderig wrt try_cmpxchg() is llist_del_first() */
85	entry = smp_load_acquire(&head->first);
86	do {
87		if (entry != this)
88			return false;
89		next = READ_ONCE(entry->next);
90	} while (!try_cmpxchg(&head->first, &entry, next));
91
92	return true;
93}
94EXPORT_SYMBOL_GPL(llist_del_first_this);
95
96/**
97 * llist_reverse_order - reverse order of a llist chain
98 * @head:	first item of the list to be reversed
99 *
100 * Reverse the order of a chain of llist entries and return the
101 * new first entry.
102 */
103struct llist_node *llist_reverse_order(struct llist_node *head)
104{
105	struct llist_node *new_head = NULL;
106
107	while (head) {
108		struct llist_node *tmp = head;
109		head = head->next;
110		tmp->next = new_head;
111		new_head = tmp;
112	}
113
114	return new_head;
115}
116EXPORT_SYMBOL_GPL(llist_reverse_order);
117