LXR linux/lib/llist.c

   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 handlers.  So code that uses the list in
   7 * an NMI 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/export.h>
  27#include <linux/llist.h>
  28
  29
  30/**
  31 * llist_add_batch - add several linked entries in batch
  32 * @new_first:  first entry in batch to be added
  33 * @new_last:   last entry in batch to be added
  34 * @head:       the head for your lock-less list
  35 *
  36 * Return whether list is empty before adding.
  37 */
  38bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
  39                     struct llist_head *head)
  40{
  41        struct llist_node *first;
  42
  43        do {
  44                new_last->next = first = READ_ONCE(head->first);
  45        } while (cmpxchg(&head->first, first, new_first) != first);
  46
  47        return !first;
  48}
  49EXPORT_SYMBOL_GPL(llist_add_batch);
  50
  51/**
  52 * llist_del_first - delete the first entry of lock-less list
  53 * @head:       the head for your lock-less list
  54 *
  55 * If list is empty, return NULL, otherwise, return the first entry
  56 * deleted, this is the newest added one.
  57 *
  58 * Only one llist_del_first user can be used simultaneously with
  59 * multiple llist_add users without lock.  Because otherwise
  60 * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
  61 * llist_add) sequence in another user may change @head->first->next,
  62 * but keep @head->first.  If multiple consumers are needed, please
  63 * use llist_del_all or use lock between consumers.
  64 */
  65struct llist_node *llist_del_first(struct llist_head *head)
  66{
  67        struct llist_node *entry, *old_entry, *next;
  68
  69        entry = smp_load_acquire(&head->first);
  70        for (;;) {
  71                if (entry == NULL)
  72                        return NULL;
  73                old_entry = entry;
  74                next = READ_ONCE(entry->next);
  75                entry = cmpxchg(&head->first, old_entry, next);
  76                if (entry == old_entry)
  77                        break;
  78        }
  79
  80        return entry;
  81}
  82EXPORT_SYMBOL_GPL(llist_del_first);
  83
  84/**
  85 * llist_reverse_order - reverse order of a llist chain
  86 * @head:       first item of the list to be reversed
  87 *
  88 * Reverse the order of a chain of llist entries and return the
  89 * new first entry.
  90 */
  91struct llist_node *llist_reverse_order(struct llist_node *head)
  92{
  93        struct llist_node *new_head = NULL;
  94
  95        while (head) {
  96                struct llist_node *tmp = head;
  97                head = head->next;
  98                tmp->next = new_head;
  99                new_head = tmp;
 100        }
 101
 102        return new_head;
 103}
 104EXPORT_SYMBOL_GPL(llist_reverse_order);
 105