forked from Minki/linux
4f1d2a030d
Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in llist_add_batch and llist_del_first. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg. Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails, enabling further code simplifications. No functional change intended. Link: https://lkml.kernel.org/r/20220712144917.4497-1-ubizjak@gmail.com Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
89 lines
2.5 KiB
C
89 lines
2.5 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
|
|
/*
|
|
* Lock-less NULL terminated single linked list
|
|
*
|
|
* 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 <ying.huang@intel.com>
|
|
*/
|
|
#include <linux/kernel.h>
|
|
#include <linux/export.h>
|
|
#include <linux/llist.h>
|
|
|
|
|
|
/**
|
|
* llist_add_batch - add several linked entries in batch
|
|
* @new_first: first entry in batch to be added
|
|
* @new_last: last entry in batch to be added
|
|
* @head: the head for your lock-less list
|
|
*
|
|
* Return whether list is empty before adding.
|
|
*/
|
|
bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
|
|
struct llist_head *head)
|
|
{
|
|
struct llist_node *first;
|
|
|
|
do {
|
|
new_last->next = first = READ_ONCE(head->first);
|
|
} while (!try_cmpxchg(&head->first, &first, new_first));
|
|
|
|
return !first;
|
|
}
|
|
EXPORT_SYMBOL_GPL(llist_add_batch);
|
|
|
|
/**
|
|
* llist_del_first - delete the first entry of lock-less list
|
|
* @head: the head for your lock-less list
|
|
*
|
|
* If list is empty, return NULL, otherwise, return the first entry
|
|
* deleted, this is the newest added one.
|
|
*
|
|
* Only one llist_del_first user can be used simultaneously with
|
|
* multiple llist_add users without lock. Because otherwise
|
|
* llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
|
|
* llist_add) sequence in another user may change @head->first->next,
|
|
* but keep @head->first. If multiple consumers are needed, please
|
|
* use llist_del_all or use lock between consumers.
|
|
*/
|
|
struct llist_node *llist_del_first(struct llist_head *head)
|
|
{
|
|
struct llist_node *entry, *next;
|
|
|
|
entry = smp_load_acquire(&head->first);
|
|
do {
|
|
if (entry == NULL)
|
|
return NULL;
|
|
next = READ_ONCE(entry->next);
|
|
} while (!try_cmpxchg(&head->first, &entry, next));
|
|
|
|
return entry;
|
|
}
|
|
EXPORT_SYMBOL_GPL(llist_del_first);
|
|
|
|
/**
|
|
* llist_reverse_order - reverse order of a llist chain
|
|
* @head: first item of the list to be reversed
|
|
*
|
|
* Reverse the order of a chain of llist entries and return the
|
|
* new first entry.
|
|
*/
|
|
struct llist_node *llist_reverse_order(struct llist_node *head)
|
|
{
|
|
struct llist_node *new_head = NULL;
|
|
|
|
while (head) {
|
|
struct llist_node *tmp = head;
|
|
head = head->next;
|
|
tmp->next = new_head;
|
|
new_head = tmp;
|
|
}
|
|
|
|
return new_head;
|
|
}
|
|
EXPORT_SYMBOL_GPL(llist_reverse_order);
|