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/* SPDX-License-Identifier: GPL-2.0-only */
#ifndef LLIST_H
#define LLIST_H
/*
* Lock-less NULL terminated single linked list
*
* Cases where locking is not needed:
* If there are multiple producers and multiple consumers, llist_add can be
* used in producers and llist_del_all can be used in consumers simultaneously
* without locking. Also a single consumer can use llist_del_first while
* multiple producers simultaneously use llist_add, without any locking.
*
* Cases where locking is needed:
* If we have multiple consumers with llist_del_first used in one consumer, and
* llist_del_first or llist_del_all used in other consumers, then a lock is
* needed. This is because llist_del_first depends on list->first->next not
* changing, but without lock protection, there's no way to be sure about that
* if a preemption happens in the middle of the delete operation and on being
* preempted back, the list->first is the same as before causing the cmpxchg in
* llist_del_first to succeed. For example, while a llist_del_first operation
* is in progress in one consumer, then a llist_del_first, llist_add,
* llist_add (or llist_del_all, llist_add, llist_add) sequence in another
* consumer may cause violations.
*
* This can be summarized as follows:
*
* | add | del_first | del_all
* add | - | - | -
* del_first | | L | L
* del_all | | | -
*
* Where, a particular row's operation can happen concurrently with a column's
* operation, with "-" being no lock needed, while "L" being lock is needed.
*
* The list entries deleted via llist_del_all can be traversed with
* traversing function such as llist_for_each etc. But the list
* entries can not be traversed safely before deleted from the list.
* The order of deleted entries is from the newest to the oldest added
* one. If you want to traverse from the oldest to the newest, you
* must reverse the order by yourself before traversing.
*
* The basic atomic operation of this list is cmpxchg on long. On
* architectures that don't have NMI-safe cmpxchg implementation, the
* list can NOT be used in NMI handlers. So code that uses the list in
* an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
*
* Copyright 2010,2011 Intel Corp.
* Author: Huang Ying <[email protected]>
*/
#include <linux/atomic.h>
#include <linux/kernel.h>
struct llist_head {
struct llist_node *first;
};
struct llist_node {
struct llist_node *next;
};
#define LLIST_HEAD_INIT(name) { NULL }
#define LLIST_HEAD(name) struct llist_head name = LLIST_HEAD_INIT(name)
/**
* init_llist_head - initialize lock-less list head
* @head: the head for your lock-less list
*/
static inline void init_llist_head(struct llist_head *list)
{
list->first = NULL;
}
/**
* llist_entry - get the struct of this entry
* @ptr: the &struct llist_node pointer.
* @type: the type of the struct this is embedded in.
* @member: the name of the llist_node within the struct.
*/
#define llist_entry(ptr, type, member) \
container_of(ptr, type, member)
/**
* member_address_is_nonnull - check whether the member address is not NULL
* @ptr: the object pointer (struct type * that contains the llist_node)
* @member: the name of the llist_node within the struct.
*
* This macro is conceptually the same as
* &ptr->member != NULL
* but it works around the fact that compilers can decide that taking a member
* address is never a NULL pointer.
*
* Real objects that start at a high address and have a member at NULL are
* unlikely to exist, but such pointers may be returned e.g. by the
* container_of() macro.
*/
#define member_address_is_nonnull(ptr, member) \
((uintptr_t)(ptr) + offsetof(typeof(*(ptr)), member) != 0)
/**
* llist_for_each - iterate over some deleted entries of a lock-less list
* @pos: the &struct llist_node to use as a loop cursor
* @node: the first entry of deleted list entries
*
* In general, some entries of the lock-less list can be traversed
* safely only after being deleted from list, so start with an entry
* instead of list head.
*
* If being used on entries deleted from lock-less list directly, the
* traverse order is from the newest to the oldest added entry. If
* you want to traverse from the oldest to the newest, you must
* reverse the order by yourself before traversing.
*/
#define llist_for_each(pos, node) \
for ((pos) = (node); pos; (pos) = (pos)->next)
/**
* llist_for_each_safe - iterate over some deleted entries of a lock-less list
* safe against removal of list entry
* @pos: the &struct llist_node to use as a loop cursor
* @n: another &struct llist_node to use as temporary storage
* @node: the first entry of deleted list entries
*
* In general, some entries of the lock-less list can be traversed
* safely only after being deleted from list, so start with an entry
* instead of list head.
*
* If being used on entries deleted from lock-less list directly, the
* traverse order is from the newest to the oldest added entry. If
* you want to traverse from the oldest to the newest, you must
* reverse the order by yourself before traversing.
*/
#define llist_for_each_safe(pos, n, node) \
for ((pos) = (node); (pos) && ((n) = (pos)->next, true); (pos) = (n))
/**
* llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
* @pos: the type * to use as a loop cursor.
* @node: the fist entry of deleted list entries.
* @member: the name of the llist_node with the struct.
*
* In general, some entries of the lock-less list can be traversed
* safely only after being removed from list, so start with an entry
* instead of list head.
*
* If being used on entries deleted from lock-less list directly, the
* traverse order is from the newest to the oldest added entry. If
* you want to traverse from the oldest to the newest, you must
* reverse the order by yourself before traversing.
*/
#define llist_for_each_entry(pos, node, member) \
for ((pos) = llist_entry((node), typeof(*(pos)), member); \
member_address_is_nonnull(pos, member); \
(pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
/**
* llist_for_each_entry_safe - iterate over some deleted entries of lock-less list of given type
* safe against removal of list entry
* @pos: the type * to use as a loop cursor.
* @n: another type * to use as temporary storage
* @node: the first entry of deleted list entries.
* @member: the name of the llist_node with the struct.
*
* In general, some entries of the lock-less list can be traversed
* safely only after being removed from list, so start with an entry
* instead of list head.
*
* If being used on entries deleted from lock-less list directly, the
* traverse order is from the newest to the oldest added entry. If
* you want to traverse from the oldest to the newest, you must
* reverse the order by yourself before traversing.
*/
#define llist_for_each_entry_safe(pos, n, node, member) \
for (pos = llist_entry((node), typeof(*pos), member); \
member_address_is_nonnull(pos, member) && \
(n = llist_entry(pos->member.next, typeof(*n), member), true); \
pos = n)
/**
* llist_empty - tests whether a lock-less list is empty
* @head: the list to test
*
* Not guaranteed to be accurate or up to date. Just a quick way to
* test whether the list is empty without deleting something from the
* list.
*/
static inline bool llist_empty(const struct llist_head *head)
{
return READ_ONCE(head->first) == NULL;
}
static inline struct llist_node *llist_next(struct llist_node *node)
{
return node->next;
}
extern bool llist_add_batch(struct llist_node *new_first,
struct llist_node *new_last,
struct llist_head *head);
static inline bool __llist_add_batch(struct llist_node *new_first,
struct llist_node *new_last,
struct llist_head *head)
{
new_last->next = head->first;
head->first = new_first;
return new_last->next == NULL;
}
/**
* llist_add - add a new entry
* @new: new entry to be added
* @head: the head for your lock-less list
*
* Returns true if the list was empty prior to adding this entry.
*/
static inline bool llist_add(struct llist_node *new, struct llist_head *head)
{
return llist_add_batch(new, new, head);
}
static inline bool __llist_add(struct llist_node *new, struct llist_head *head)
{
return __llist_add_batch(new, new, head);
}
/**
* llist_del_all - delete all entries from lock-less list
* @head: the head of lock-less list to delete all entries
*
* If list is empty, return NULL, otherwise, delete all entries and
* return the pointer to the first entry. The order of entries
* deleted is from the newest to the oldest added one.
*/
static inline struct llist_node *llist_del_all(struct llist_head *head)
{
return xchg(&head->first, NULL);
}
static inline struct llist_node *__llist_del_all(struct llist_head *head)
{
struct llist_node *first = head->first;
head->first = NULL;
return first;
}
extern struct llist_node *llist_del_first(struct llist_head *head);
struct llist_node *llist_reverse_order(struct llist_node *head);
#endif /* LLIST_H */
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