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6a6d7602ca
try_cmpxchg implicitly assigns old head->first value to "first" when cmpxchg fails. There is no need to re-read the value in the loop. Link: https://lkml.kernel.org/r/20221017145226.4044-1-ubizjak@gmail.com Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
88 lines
2.5 KiB
C
88 lines
2.5 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Lock-less NULL terminated single linked list
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*
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* The basic atomic operation of this list is cmpxchg on long. On
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* architectures that don't have NMI-safe cmpxchg implementation, the
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* list can NOT be used in NMI handlers. So code that uses the list in
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* an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
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*
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* Copyright 2010,2011 Intel Corp.
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* Author: Huang Ying <ying.huang@intel.com>
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*/
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#include <linux/kernel.h>
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#include <linux/export.h>
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#include <linux/llist.h>
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/**
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* llist_add_batch - add several linked entries in batch
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* @new_first: first entry in batch to be added
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* @new_last: last entry in batch to be added
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* @head: the head for your lock-less list
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*
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* Return whether list is empty before adding.
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*/
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bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
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struct llist_head *head)
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{
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struct llist_node *first = READ_ONCE(head->first);
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do {
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new_last->next = first;
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} while (!try_cmpxchg(&head->first, &first, new_first));
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return !first;
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}
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EXPORT_SYMBOL_GPL(llist_add_batch);
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/**
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* llist_del_first - delete the first entry of lock-less list
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* @head: the head for your lock-less list
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*
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* If list is empty, return NULL, otherwise, return the first entry
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* deleted, this is the newest added one.
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*
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* Only one llist_del_first user can be used simultaneously with
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* multiple llist_add users without lock. Because otherwise
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* llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
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* llist_add) sequence in another user may change @head->first->next,
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* but keep @head->first. If multiple consumers are needed, please
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* use llist_del_all or use lock between consumers.
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*/
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struct llist_node *llist_del_first(struct llist_head *head)
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{
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struct llist_node *entry, *next;
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entry = smp_load_acquire(&head->first);
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do {
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if (entry == NULL)
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return NULL;
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next = READ_ONCE(entry->next);
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} while (!try_cmpxchg(&head->first, &entry, next));
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return entry;
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}
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EXPORT_SYMBOL_GPL(llist_del_first);
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/**
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* llist_reverse_order - reverse order of a llist chain
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* @head: first item of the list to be reversed
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*
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* Reverse the order of a chain of llist entries and return the
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* new first entry.
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*/
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struct llist_node *llist_reverse_order(struct llist_node *head)
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{
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struct llist_node *new_head = NULL;
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while (head) {
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struct llist_node *tmp = head;
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head = head->next;
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tmp->next = new_head;
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new_head = tmp;
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}
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return new_head;
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}
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EXPORT_SYMBOL_GPL(llist_reverse_order);
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