LXR linux/lib/llist.c

   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;
  30
  31        do {
  32                new_last->next = first = READ_ONCE(head->first);
  33        } while (cmpxchg(&head->first, first, new_first) != 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, *old_entry, *next;
  56
  57        entry = smp_load_acquire(&head->first);
  58        for (;;) {
  59                if (entry == NULL)
  60                        return NULL;
  61                old_entry = entry;
  62                next = READ_ONCE(entry->next);
  63                entry = cmpxchg(&head->first, old_entry, next);
  64                if (entry == old_entry)
  65                        break;
  66        }
  67
  68        return entry;
  69}
  70EXPORT_SYMBOL_GPL(llist_del_first);
  71
  72/**
  73 * llist_reverse_order - reverse order of a llist chain
  74 * @head:       first item of the list to be reversed
  75 *
  76 * Reverse the order of a chain of llist entries and return the
  77 * new first entry.
  78 */
  79struct llist_node *llist_reverse_order(struct llist_node *head)
  80{
  81        struct llist_node *new_head = NULL;
  82
  83        while (head) {
  84                struct llist_node *tmp = head;
  85                head = head->next;
  86                tmp->next = new_head;
  87                new_head = tmp;
  88        }
  89
  90        return new_head;
  91}
  92EXPORT_SYMBOL_GPL(llist_reverse_order);
  93