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/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_RCULIST_NULLS_H
#define _LINUX_RCULIST_NULLS_H
#ifdef __KERNEL__
/*
* RCU-protected list version
*/
#include <linux/list_nulls.h>
#include <linux/rcupdate.h>
/**
* hlist_nulls_del_init_rcu - deletes entry from hash list with re-initialization
* @n: the element to delete from the hash list.
*
* Note: hlist_nulls_unhashed() on the node return true after this. It is
* useful for RCU based read lockfree traversal if the writer side
* must know if the list entry is still hashed or already unhashed.
*
* In particular, it means that we can not poison the forward pointers
* that may still be used for walking the hash list and we can only
* zero the pprev pointer so list_unhashed() will return true after
* this.
*
* The caller must take whatever precautions are necessary (such as
* holding appropriate locks) to avoid racing with another
* list-mutation primitive, such as hlist_nulls_add_head_rcu() or
* hlist_nulls_del_rcu(), running on this same list. However, it is
* perfectly legal to run concurrently with the _rcu list-traversal
* primitives, such as hlist_nulls_for_each_entry_rcu().
*/
static inline void hlist_nulls_del_init_rcu(struct hlist_nulls_node *n)
{
if (!hlist_nulls_unhashed(n)) {
__hlist_nulls_del(n);
WRITE_ONCE(n->pprev, NULL);
}
}
/**
* hlist_nulls_first_rcu - returns the first element of the hash list.
* @head: the head of the list.
*/
#define hlist_nulls_first_rcu(head) \
(*((struct hlist_nulls_node __rcu __force **)&(head)->first))
/**
* hlist_nulls_next_rcu - returns the element of the list after @node.
* @node: element of the list.
*/
#define hlist_nulls_next_rcu(node) \
(*((struct hlist_nulls_node __rcu __force **)&(node)->next))
/**
* hlist_nulls_del_rcu - deletes entry from hash list without re-initialization
* @n: the element to delete from the hash list.
*
* Note: hlist_nulls_unhashed() on entry does not return true after this,
* the entry is in an undefined state. It is useful for RCU based
* lockfree traversal.
*
* In particular, it means that we can not poison the forward
* pointers that may still be used for walking the hash list.
*
* The caller must take whatever precautions are necessary
* (such as holding appropriate locks) to avoid racing
* with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
* or hlist_nulls_del_rcu(), running on this same list.
* However, it is perfectly legal to run concurrently with
* the _rcu list-traversal primitives, such as
* hlist_nulls_for_each_entry().
*/
static inline void hlist_nulls_del_rcu(struct hlist_nulls_node *n)
{
__hlist_nulls_del(n);
WRITE_ONCE(n->pprev, LIST_POISON2);
}
/**
* hlist_nulls_add_head_rcu
* @n: the element to add to the hash list.
* @h: the list to add to.
*
* Description:
* Adds the specified element to the specified hlist_nulls,
* while permitting racing traversals.
*
* The caller must take whatever precautions are necessary
* (such as holding appropriate locks) to avoid racing
* with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
* or hlist_nulls_del_rcu(), running on this same list.
* However, it is perfectly legal to run concurrently with
* the _rcu list-traversal primitives, such as
* hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
* problems on Alpha CPUs. Regardless of the type of CPU, the
* list-traversal primitive must be guarded by rcu_read_lock().
*/
static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n,
struct hlist_nulls_head *h)
{
struct hlist_nulls_node *first = h->first;
n->next = first;
WRITE_ONCE(n->pprev, &h->first);
rcu_assign_pointer(hlist_nulls_first_rcu(h), n);
if (!is_a_nulls(first))
WRITE_ONCE(first->pprev, &n->next);
}
/**
* hlist_nulls_add_tail_rcu
* @n: the element to add to the hash list.
* @h: the list to add to.
*
* Description:
* Adds the specified element to the specified hlist_nulls,
* while permitting racing traversals.
*
* The caller must take whatever precautions are necessary
* (such as holding appropriate locks) to avoid racing
* with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
* or hlist_nulls_del_rcu(), running on this same list.
* However, it is perfectly legal to run concurrently with
* the _rcu list-traversal primitives, such as
* hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
* problems on Alpha CPUs. Regardless of the type of CPU, the
* list-traversal primitive must be guarded by rcu_read_lock().
*/
static inline void hlist_nulls_add_tail_rcu(struct hlist_nulls_node *n,
struct hlist_nulls_head *h)
{
struct hlist_nulls_node *i, *last = NULL;
/* Note: write side code, so rcu accessors are not needed. */
for (i = h->first; !is_a_nulls(i); i = i->next)
last = i;
if (last) {
n->next = last->next;
n->pprev = &last->next;
rcu_assign_pointer(hlist_next_rcu(last), n);
} else {
hlist_nulls_add_head_rcu(n, h);
}
}
/**
* hlist_nulls_for_each_entry_rcu - iterate over rcu list of given type
* @tpos: the type * to use as a loop cursor.
* @pos: the &struct hlist_nulls_node to use as a loop cursor.
* @head: the head of the list.
* @member: the name of the hlist_nulls_node within the struct.
*
* The barrier() is needed to make sure compiler doesn't cache first element [1],
* as this loop can be restarted [2]
* [1] Documentation/core-api/atomic_ops.rst around line 114
* [2] Documentation/RCU/rculist_nulls.txt around line 146
*/
#define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member) \
for (({barrier();}), \
pos = rcu_dereference_raw(hlist_nulls_first_rcu(head)); \
(!is_a_nulls(pos)) && \
({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; }); \
pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)))
/**
* hlist_nulls_for_each_entry_safe -
* iterate over list of given type safe against removal of list entry
* @tpos: the type * to use as a loop cursor.
* @pos: the &struct hlist_nulls_node to use as a loop cursor.
* @head: the head of the list.
* @member: the name of the hlist_nulls_node within the struct.
*/
#define hlist_nulls_for_each_entry_safe(tpos, pos, head, member) \
for (({barrier();}), \
pos = rcu_dereference_raw(hlist_nulls_first_rcu(head)); \
(!is_a_nulls(pos)) && \
({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); \
pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)); 1; });)
#endif
#endif
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