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/module.h>
  27 #include <linux/interrupt.h>
  28 #include <linux/llist.h>
  29
  30 #include <asm/system.h>
  31
  32 /**
  33  * llist_add_batch - add several linked entries in batch
  34  * @new_first:  first entry in batch to be added
  35  * @new_last:   last entry in batch to be added
  36  * @head:       the head for your lock-less list
  37  *
  38  * Return whether list is empty before adding.
  39  */
  40 bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
  41                      struct llist_head *head)
  42 {
  43         struct llist_node *entry, *old_entry;
  44
  45         entry = head->first;
  46         for (;;) {
  47                 old_entry = entry;
  48                 new_last->next = entry;
  49                 entry = cmpxchg(&head->first, old_entry, new_first);
  50                 if (entry == old_entry)
  51                         break;
  52                 cpu_relax();
  53         }
  54
  55         return old_entry == NULL;
  56 }
  57 EXPORT_SYMBOL_GPL(llist_add_batch);
  58
  59 /**
  60  * llist_del_first - delete the first entry of lock-less list
  61  * @head:       the head for your lock-less list
  62  *
  63  * If list is empty, return NULL, otherwise, return the first entry
  64  * deleted, this is the newest added one.
  65  *
  66  * Only one llist_del_first user can be used simultaneously with
  67  * multiple llist_add users without lock.  Because otherwise
  68  * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
  69  * llist_add) sequence in another user may change @head->first->next,
  70  * but keep @head->first.  If multiple consumers are needed, please
  71  * use llist_del_all or use lock between consumers.
  72  */
  73 struct llist_node *llist_del_first(struct llist_head *head)
  74 {
  75         struct llist_node *entry, *old_entry, *next;
  76
  77         entry = head->first;
  78         for (;;) {
  79                 if (entry == NULL)
  80                         return NULL;
  81                 old_entry = entry;
  82                 next = entry->next;
  83                 entry = cmpxchg(&head->first, old_entry, next);
  84                 if (entry == old_entry)
  85                         break;
  86                 cpu_relax();
  87         }
  88
  89         return entry;
  90 }
  91 EXPORT_SYMBOL_GPL(llist_del_first);