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       1                 :            : /* SPDX-License-Identifier: GPL-2.0-only */
       2                 :            : #ifndef LLIST_H
       3                 :            : #define LLIST_H
       4                 :            : /*
       5                 :            :  * Lock-less NULL terminated single linked list
       6                 :            :  *
       7                 :            :  * Cases where locking is not needed:
       8                 :            :  * If there are multiple producers and multiple consumers, llist_add can be
       9                 :            :  * used in producers and llist_del_all can be used in consumers simultaneously
      10                 :            :  * without locking. Also a single consumer can use llist_del_first while
      11                 :            :  * multiple producers simultaneously use llist_add, without any locking.
      12                 :            :  *
      13                 :            :  * Cases where locking is needed:
      14                 :            :  * If we have multiple consumers with llist_del_first used in one consumer, and
      15                 :            :  * llist_del_first or llist_del_all used in other consumers, then a lock is
      16                 :            :  * needed.  This is because llist_del_first depends on list->first->next not
      17                 :            :  * changing, but without lock protection, there's no way to be sure about that
      18                 :            :  * if a preemption happens in the middle of the delete operation and on being
      19                 :            :  * preempted back, the list->first is the same as before causing the cmpxchg in
      20                 :            :  * llist_del_first to succeed. For example, while a llist_del_first operation
      21                 :            :  * is in progress in one consumer, then a llist_del_first, llist_add,
      22                 :            :  * llist_add (or llist_del_all, llist_add, llist_add) sequence in another
      23                 :            :  * consumer may cause violations.
      24                 :            :  *
      25                 :            :  * This can be summarized as follows:
      26                 :            :  *
      27                 :            :  *           |   add    | del_first |  del_all
      28                 :            :  * add       |    -     |     -     |     -
      29                 :            :  * del_first |          |     L     |     L
      30                 :            :  * del_all   |          |           |     -
      31                 :            :  *
      32                 :            :  * Where, a particular row's operation can happen concurrently with a column's
      33                 :            :  * operation, with "-" being no lock needed, while "L" being lock is needed.
      34                 :            :  *
      35                 :            :  * The list entries deleted via llist_del_all can be traversed with
      36                 :            :  * traversing function such as llist_for_each etc.  But the list
      37                 :            :  * entries can not be traversed safely before deleted from the list.
      38                 :            :  * The order of deleted entries is from the newest to the oldest added
      39                 :            :  * one.  If you want to traverse from the oldest to the newest, you
      40                 :            :  * must reverse the order by yourself before traversing.
      41                 :            :  *
      42                 :            :  * The basic atomic operation of this list is cmpxchg on long.  On
      43                 :            :  * architectures that don't have NMI-safe cmpxchg implementation, the
      44                 :            :  * list can NOT be used in NMI handlers.  So code that uses the list in
      45                 :            :  * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
      46                 :            :  *
      47                 :            :  * Copyright 2010,2011 Intel Corp.
      48                 :            :  *   Author: Huang Ying <ying.huang@intel.com>
      49                 :            :  */
      50                 :            : 
      51                 :            : #include <linux/atomic.h>
      52                 :            : #include <linux/kernel.h>
      53                 :            : 
      54                 :            : struct llist_head {
      55                 :            :         struct llist_node *first;
      56                 :            : };
      57                 :            : 
      58                 :            : struct llist_node {
      59                 :            :         struct llist_node *next;
      60                 :            : };
      61                 :            : 
      62                 :            : #define LLIST_HEAD_INIT(name)   { NULL }
      63                 :            : #define LLIST_HEAD(name)        struct llist_head name = LLIST_HEAD_INIT(name)
      64                 :            : 
      65                 :            : /**
      66                 :            :  * init_llist_head - initialize lock-less list head
      67                 :            :  * @head:       the head for your lock-less list
      68                 :            :  */
      69                 :            : static inline void init_llist_head(struct llist_head *list)
      70                 :            : {
      71                 :          3 :         list->first = NULL;
      72                 :            : }
      73                 :            : 
      74                 :            : /**
      75                 :            :  * llist_entry - get the struct of this entry
      76                 :            :  * @ptr:        the &struct llist_node pointer.
      77                 :            :  * @type:       the type of the struct this is embedded in.
      78                 :            :  * @member:     the name of the llist_node within the struct.
      79                 :            :  */
      80                 :            : #define llist_entry(ptr, type, member)          \
      81                 :            :         container_of(ptr, type, member)
      82                 :            : 
      83                 :            : /**
      84                 :            :  * member_address_is_nonnull - check whether the member address is not NULL
      85                 :            :  * @ptr:        the object pointer (struct type * that contains the llist_node)
      86                 :            :  * @member:     the name of the llist_node within the struct.
      87                 :            :  *
      88                 :            :  * This macro is conceptually the same as
      89                 :            :  *      &ptr->member != NULL
      90                 :            :  * but it works around the fact that compilers can decide that taking a member
      91                 :            :  * address is never a NULL pointer.
      92                 :            :  *
      93                 :            :  * Real objects that start at a high address and have a member at NULL are
      94                 :            :  * unlikely to exist, but such pointers may be returned e.g. by the
      95                 :            :  * container_of() macro.
      96                 :            :  */
      97                 :            : #define member_address_is_nonnull(ptr, member)  \
      98                 :            :         ((uintptr_t)(ptr) + offsetof(typeof(*(ptr)), member) != 0)
      99                 :            : 
     100                 :            : /**
     101                 :            :  * llist_for_each - iterate over some deleted entries of a lock-less list
     102                 :            :  * @pos:        the &struct llist_node to use as a loop cursor
     103                 :            :  * @node:       the first entry of deleted list entries
     104                 :            :  *
     105                 :            :  * In general, some entries of the lock-less list can be traversed
     106                 :            :  * safely only after being deleted from list, so start with an entry
     107                 :            :  * instead of list head.
     108                 :            :  *
     109                 :            :  * If being used on entries deleted from lock-less list directly, the
     110                 :            :  * traverse order is from the newest to the oldest added entry.  If
     111                 :            :  * you want to traverse from the oldest to the newest, you must
     112                 :            :  * reverse the order by yourself before traversing.
     113                 :            :  */
     114                 :            : #define llist_for_each(pos, node)                       \
     115                 :            :         for ((pos) = (node); pos; (pos) = (pos)->next)
     116                 :            : 
     117                 :            : /**
     118                 :            :  * llist_for_each_safe - iterate over some deleted entries of a lock-less list
     119                 :            :  *                       safe against removal of list entry
     120                 :            :  * @pos:        the &struct llist_node to use as a loop cursor
     121                 :            :  * @n:          another &struct llist_node to use as temporary storage
     122                 :            :  * @node:       the first entry of deleted list entries
     123                 :            :  *
     124                 :            :  * In general, some entries of the lock-less list can be traversed
     125                 :            :  * safely only after being deleted from list, so start with an entry
     126                 :            :  * instead of list head.
     127                 :            :  *
     128                 :            :  * If being used on entries deleted from lock-less list directly, the
     129                 :            :  * traverse order is from the newest to the oldest added entry.  If
     130                 :            :  * you want to traverse from the oldest to the newest, you must
     131                 :            :  * reverse the order by yourself before traversing.
     132                 :            :  */
     133                 :            : #define llist_for_each_safe(pos, n, node)                       \
     134                 :            :         for ((pos) = (node); (pos) && ((n) = (pos)->next, true); (pos) = (n))
     135                 :            : 
     136                 :            : /**
     137                 :            :  * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
     138                 :            :  * @pos:        the type * to use as a loop cursor.
     139                 :            :  * @node:       the fist entry of deleted list entries.
     140                 :            :  * @member:     the name of the llist_node with the struct.
     141                 :            :  *
     142                 :            :  * In general, some entries of the lock-less list can be traversed
     143                 :            :  * safely only after being removed from list, so start with an entry
     144                 :            :  * instead of list head.
     145                 :            :  *
     146                 :            :  * If being used on entries deleted from lock-less list directly, the
     147                 :            :  * traverse order is from the newest to the oldest added entry.  If
     148                 :            :  * you want to traverse from the oldest to the newest, you must
     149                 :            :  * reverse the order by yourself before traversing.
     150                 :            :  */
     151                 :            : #define llist_for_each_entry(pos, node, member)                         \
     152                 :            :         for ((pos) = llist_entry((node), typeof(*(pos)), member);       \
     153                 :            :              member_address_is_nonnull(pos, member);                    \
     154                 :            :              (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
     155                 :            : 
     156                 :            : /**
     157                 :            :  * llist_for_each_entry_safe - iterate over some deleted entries of lock-less list of given type
     158                 :            :  *                             safe against removal of list entry
     159                 :            :  * @pos:        the type * to use as a loop cursor.
     160                 :            :  * @n:          another type * to use as temporary storage
     161                 :            :  * @node:       the first entry of deleted list entries.
     162                 :            :  * @member:     the name of the llist_node with the struct.
     163                 :            :  *
     164                 :            :  * In general, some entries of the lock-less list can be traversed
     165                 :            :  * safely only after being removed from list, so start with an entry
     166                 :            :  * instead of list head.
     167                 :            :  *
     168                 :            :  * If being used on entries deleted from lock-less list directly, the
     169                 :            :  * traverse order is from the newest to the oldest added entry.  If
     170                 :            :  * you want to traverse from the oldest to the newest, you must
     171                 :            :  * reverse the order by yourself before traversing.
     172                 :            :  */
     173                 :            : #define llist_for_each_entry_safe(pos, n, node, member)                        \
     174                 :            :         for (pos = llist_entry((node), typeof(*pos), member);                  \
     175                 :            :              member_address_is_nonnull(pos, member) &&                         \
     176                 :            :                 (n = llist_entry(pos->member.next, typeof(*n), member), true); \
     177                 :            :              pos = n)
     178                 :            : 
     179                 :            : /**
     180                 :            :  * llist_empty - tests whether a lock-less list is empty
     181                 :            :  * @head:       the list to test
     182                 :            :  *
     183                 :            :  * Not guaranteed to be accurate or up to date.  Just a quick way to
     184                 :            :  * test whether the list is empty without deleting something from the
     185                 :            :  * list.
     186                 :            :  */
     187                 :            : static inline bool llist_empty(const struct llist_head *head)
     188                 :            : {
     189                 :          3 :         return READ_ONCE(head->first) == NULL;
     190                 :            : }
     191                 :            : 
     192                 :            : static inline struct llist_node *llist_next(struct llist_node *node)
     193                 :            : {
     194                 :            :         return node->next;
     195                 :            : }
     196                 :            : 
     197                 :            : extern bool llist_add_batch(struct llist_node *new_first,
     198                 :            :                             struct llist_node *new_last,
     199                 :            :                             struct llist_head *head);
     200                 :            : /**
     201                 :            :  * llist_add - add a new entry
     202                 :            :  * @new:        new entry to be added
     203                 :            :  * @head:       the head for your lock-less list
     204                 :            :  *
     205                 :            :  * Returns true if the list was empty prior to adding this entry.
     206                 :            :  */
     207                 :            : static inline bool llist_add(struct llist_node *new, struct llist_head *head)
     208                 :            : {
     209                 :          3 :         return llist_add_batch(new, new, head);
     210                 :            : }
     211                 :            : 
     212                 :            : /**
     213                 :            :  * llist_del_all - delete all entries from lock-less list
     214                 :            :  * @head:       the head of lock-less list to delete all entries
     215                 :            :  *
     216                 :            :  * If list is empty, return NULL, otherwise, delete all entries and
     217                 :            :  * return the pointer to the first entry.  The order of entries
     218                 :            :  * deleted is from the newest to the oldest added one.
     219                 :            :  */
     220                 :            : static inline struct llist_node *llist_del_all(struct llist_head *head)
     221                 :            : {
     222                 :          3 :         return xchg(&head->first, NULL);
     223                 :            : }
     224                 :            : 
     225                 :            : extern struct llist_node *llist_del_first(struct llist_head *head);
     226                 :            : 
     227                 :            : struct llist_node *llist_reverse_order(struct llist_node *head);
     228                 :            : 
     229                 :            : #endif /* LLIST_H */