mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-24 21:24:00 +08:00
fb4214db50
1. This is mostly theoretical, but llist_add*() need ACCESS_ONCE(). Otherwise it is not guaranteed that the first cmpxchg() uses the same value for old_entry and new_last->next. 2. These helpers cache the result of cmpxchg() and read the initial value of head->first before the main loop. I do not think this makes sense. In the likely case cmpxchg() succeeds, otherwise it doesn't hurt to reload head->first. I think it would be better to simplify the code and simply read ->first before cmpxchg(). Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Andrey Vagin <avagin@openvz.org> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: David Howells <dhowells@redhat.com> Cc: Huang Ying <ying.huang@intel.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
84 lines
2.7 KiB
C
84 lines
2.7 KiB
C
/*
|
|
* 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>
|
|
*
|
|
* This program is free software; you can redistribute it and/or
|
|
* modify it under the terms of the GNU General Public License version
|
|
* 2 as published by the Free Software Foundation;
|
|
*
|
|
* This program is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
* GNU General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU General Public License
|
|
* along with this program; if not, write to the Free Software
|
|
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
|
|
*/
|
|
#include <linux/kernel.h>
|
|
#include <linux/export.h>
|
|
#include <linux/interrupt.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 = ACCESS_ONCE(head->first);
|
|
} while (cmpxchg(&head->first, first, new_first) != 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, *old_entry, *next;
|
|
|
|
entry = head->first;
|
|
for (;;) {
|
|
if (entry == NULL)
|
|
return NULL;
|
|
old_entry = entry;
|
|
next = entry->next;
|
|
entry = cmpxchg(&head->first, old_entry, next);
|
|
if (entry == old_entry)
|
|
break;
|
|
}
|
|
|
|
return entry;
|
|
}
|
|
EXPORT_SYMBOL_GPL(llist_del_first);
|