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llist_del_first_this() deletes a specific entry from an llist, providing it is at the head of the list. Multiple threads can call this concurrently providing they each offer a different entry. This can be uses for a set of worker threads which are on the llist when they are idle. The head can always be woken, and when it is woken it can remove itself, and possibly wake the next if there is an excess of work to do. Signed-off-by: NeilBrown <neilb@suse.de> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
116 lines
3.3 KiB
C
116 lines
3.3 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_del_first_this - delete given entry of lock-less list if it is first
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* @head: the head for your lock-less list
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* @this: a list entry.
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*
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* If head of the list is given entry, delete and return %true else
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* return %false.
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*
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* Multiple callers can safely call this concurrently with multiple
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* llist_add() callers, providing all the callers offer a different @this.
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*/
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bool llist_del_first_this(struct llist_head *head,
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struct llist_node *this)
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{
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struct llist_node *entry, *next;
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/* acquire ensures orderig wrt try_cmpxchg() is llist_del_first() */
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entry = smp_load_acquire(&head->first);
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do {
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if (entry != this)
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return false;
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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 true;
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}
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EXPORT_SYMBOL_GPL(llist_del_first_this);
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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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