// 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_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_del_first_this - delete given entry of lock-less list if it is first * @head:	the head for your lock-less list * @this:	a list entry. * * If head of the list is given entry, delete and return %true else * return %false. * * Multiple callers can safely call this concurrently with multiple * llist_add() callers, providing all the callers offer a different @this. */bool llist_del_first_this(struct llist_head *head,			  struct llist_node *this){	struct llist_node *entry, *next; 	/* acquire ensures orderig wrt try_cmpxchg() is llist_del_first() */	entry = smp_load_acquire(&head->first);	do {		if (entry != this)			return false;		next = READ_ONCE(entry->next);	} while (!try_cmpxchg(&head->first, &entry, next)); 	return true;}EXPORT_SYMBOL_GPL(llist_del_first_this); /** * 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);