// SPDX-License-Identifier: GPL-2.0-only
/*
* Lock-less NULL terminated single linked list
*
* The basic atomic operation of this list is cmpxchg on long. On
* architectures that don't have NMI-safe cmpxchg implementation, the
* list can NOT be used in NMI handlers. So code that uses the list in
* an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
*
* Copyright 2010,2011 Intel Corp.
* Author: Huang Ying <ying.huang@intel.com>
*/
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/llist.h>
/**
* llist_add_batch - add several linked entries in batch
* @new_first: first entry in batch to be added
* @new_last: last entry in batch to be added
* @head: the head for your lock-less list
*
* Return whether list is empty before adding.
*/
bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
struct llist_head *head)
{
struct llist_node *first = READ_ONCE(head->first);
do {
new_last->next = first;
} while (!try_cmpxchg(&head->first, &first, new_first));
return !first;
}
EXPORT_SYMBOL_GPL(llist_add_batch);
/**
* llist_del_first - delete the first entry of lock-less list
* @head: the head for your lock-less list
*
* If list is empty, return NULL, otherwise, return the first entry
* deleted, this is the newest added one.
*
* Only one llist_del_first user can be used simultaneously with
* multiple llist_add users without lock. Because otherwise
* llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
* llist_add) sequence in another user may change @head->first->next,
* but keep @head->first. If multiple consumers are needed, please
* use llist_del_all or use lock between consumers.
*/
struct llist_node *llist_del_first(struct llist_head *head)
{
struct llist_node *entry, *next;
entry = smp_load_acquire(&head->first);
do {
if (entry == NULL)
return NULL;
next = READ_ONCE(entry->next);
} while (!try_cmpxchg(&head->first, &entry, next));
return entry;
}
EXPORT_SYMBOL_GPL(llist_del_first);
/**
* llist_del_first_this - delete given entry of lock-less list if it is first
* @head: the head for your lock-less list
* @this: a list entry.
*
* If head of the list is given entry, delete and return %true else
* return %false.
*
* Multiple callers can safely call this concurrently with multiple
* llist_add() callers, providing all the callers offer a different @this.
*/
bool llist_del_first_this(struct llist_head *head,
struct llist_node *this)
{
struct llist_node *entry, *next;
/* acquire ensures orderig wrt try_cmpxchg() is llist_del_first() */
entry = smp_load_acquire(&head->first);
do {
if (entry != this)
return false;
next = READ_ONCE(entry->next);
} while (!try_cmpxchg(&head->first, &entry, next));
return true;
}
EXPORT_SYMBOL_GPL(llist_del_first_this);
/**
* llist_reverse_order - reverse order of a llist chain
* @head: first item of the list to be reversed
*
* Reverse the order of a chain of llist entries and return the
* new first entry.
*/
struct llist_node *llist_reverse_order(struct llist_node *head)
{
struct llist_node *new_head = NULL;
while (head) {
struct llist_node *tmp = head;
head = head->next;
tmp->next = new_head;
new_head = tmp;
}
return new_head;
}
EXPORT_SYMBOL_GPL(llist_reverse_order);
