Branch data     Line data    Source code

       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                 :            :  */
      26                 :    1995935 : bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
      27                 :            :                      struct llist_head *head)
      28                 :            : {
      29                 :    1995935 :         struct llist_node *first;
      30                 :            : 
      31                 :    1995935 :         do {
      32                 :    1995935 :                 new_last->next = first = READ_ONCE(head->first);
      33         [ -  + ]:    1995935 :         } while (cmpxchg(&head->first, first, new_first) != first);
      34                 :            : 
      35                 :    1995935 :         return !first;
      36                 :            : }
      37                 :            : EXPORT_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                 :            :  */
      53                 :          0 : struct llist_node *llist_del_first(struct llist_head *head)
      54                 :            : {
      55                 :          0 :         struct llist_node *entry, *old_entry, *next;
      56                 :            : 
      57                 :          0 :         entry = smp_load_acquire(&head->first);
      58                 :          0 :         for (;;) {
      59         [ #  # ]:          0 :                 if (entry == NULL)
      60                 :            :                         return NULL;
      61                 :          0 :                 old_entry = entry;
      62                 :          0 :                 next = READ_ONCE(entry->next);
      63                 :          0 :                 entry = cmpxchg(&head->first, old_entry, next);
      64         [ #  # ]:          0 :                 if (entry == old_entry)
      65                 :            :                         break;
      66                 :            :         }
      67                 :            : 
      68                 :            :         return entry;
      69                 :            : }
      70                 :            : EXPORT_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                 :            :  */
      79                 :          0 : struct llist_node *llist_reverse_order(struct llist_node *head)
      80                 :            : {
      81                 :          0 :         struct llist_node *new_head = NULL;
      82                 :            : 
      83         [ #  # ]:          0 :         while (head) {
      84                 :          0 :                 struct llist_node *tmp = head;
      85                 :          0 :                 head = head->next;
      86                 :          0 :                 tmp->next = new_head;
      87                 :          0 :                 new_head = tmp;
      88                 :            :         }
      89                 :            : 
      90                 :          0 :         return new_head;
      91                 :            : }
      92                 :            : EXPORT_SYMBOL_GPL(llist_reverse_order);