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 handler.  So code uses the list in NMI
   7  * 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 - add a new entry
  34  * @new:        new entry to be added
  35  * @head:       the head for your lock-less list
  36  */
  37 void llist_add(struct llist_node *new, struct llist_head *head)
  38 {
  39         struct llist_node *entry, *old_entry;
  40
  41 #ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
  42         BUG_ON(in_nmi());
  43 #endif
  44
  45         entry = head->first;
  46         do {
  47                 old_entry = entry;
  48                 new->next = entry;
  49                 cpu_relax();
  50         } while ((entry = cmpxchg(&head->first, old_entry, new)) != old_entry);
  51 }
  52 EXPORT_SYMBOL_GPL(llist_add);
  53
  54 /**
  55  * llist_add_batch - add several linked entries in batch
  56  * @new_first:  first entry in batch to be added
  57  * @new_last:   last entry in batch to be added
  58  * @head:       the head for your lock-less list
  59  */
  60 void llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
  61                      struct llist_head *head)
  62 {
  63         struct llist_node *entry, *old_entry;
  64
  65 #ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
  66         BUG_ON(in_nmi());
  67 #endif
  68
  69         entry = head->first;
  70         do {
  71                 old_entry = entry;
  72                 new_last->next = entry;
  73                 cpu_relax();
  74         } while ((entry = cmpxchg(&head->first, old_entry, new_first)) != old_entry);
  75 }
  76 EXPORT_SYMBOL_GPL(llist_add_batch);
  77
  78 /**
  79  * llist_del_first - delete the first entry of lock-less list
  80  * @head:       the head for your lock-less list
  81  *
  82  * If list is empty, return NULL, otherwise, return the first entry
  83  * deleted, this is the newest added one.
  84  *
  85  * Only one llist_del_first user can be used simultaneously with
  86  * multiple llist_add users without lock.  Because otherwise
  87  * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
  88  * llist_add) sequence in another user may change @head->first->next,
  89  * but keep @head->first.  If multiple consumers are needed, please
  90  * use llist_del_all or use lock between consumers.
  91  */
  92 struct llist_node *llist_del_first(struct llist_head *head)
  93 {
  94         struct llist_node *entry, *old_entry, *next;
  95
  96 #ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
  97         BUG_ON(in_nmi());
  98 #endif
  99
 100         entry = head->first;
 101         do {
 102                 if (entry == NULL)
 103                         return NULL;
 104                 old_entry = entry;
 105                 next = entry->next;
 106                 cpu_relax();
 107         } while ((entry = cmpxchg(&head->first, old_entry, next)) != old_entry);
 108
 109         return entry;
 110 }
 111 EXPORT_SYMBOL_GPL(llist_del_first);
 112
 113 /**
 114  * llist_del_all - delete all entries from lock-less list
 115  * @head:       the head of lock-less list to delete all entries
 116  *
 117  * If list is empty, return NULL, otherwise, delete all entries and
 118  * return the pointer to the first entry.  The order of entries
 119  * deleted is from the newest to the oldest added one.
 120  */
 121 struct llist_node *llist_del_all(struct llist_head *head)
 122 {
 123 #ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
 124         BUG_ON(in_nmi());
 125 #endif
 126
 127         return xchg(&head->first, NULL);
 128 }
 129 EXPORT_SYMBOL_GPL(llist_del_all);