[PATCH 3/9] lock-less NULL terminated single list implementation

Huang Ying
2010-10-20T01:36:54Z

Cmpxchg is used to implement adding new entry to list, deleting first
entry of the list and some other operations.

Because this is a single list, so the tail can not be accessed in O(1).

This can be used in NMI handler.

Signed-off-by: Huang Ying <ying.huang@intel.com>
---
include/linux/llist.h | 64 +++++++++++++++++++++++++++++++++++++++++
lib/Kconfig | 3 +
lib/Makefile | 2 +
lib/llist.c | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 147 insertions(+)
create mode 100644 include/linux/llist.h
create mode 100644 lib/llist.c

--- /dev/null
+++ b/include/linux/llist.h
@@ -0,0 +1,64 @@
+#ifndef LLIST_H
+#define LLIST_H
+
+/* lock-less NULL terminated single linked list */
+struct llist_head {
+ struct llist_head *next;
+};
+
+#define LLIST_HEAD_INIT(name) { NULL }
+
+#define LLIST_HEAD(name) \
+ struct llist_head name = LLIST_HEAD_INIT(name)
+
+/**
+ * init_llist_head - initialize lock-less list head
+ * @head: the head for your lock-less list
+ */
+static inline void init_llist_head(struct llist_head *list)
+{
+ list->next = NULL;
+}
+
+/**
+ * llist_entry - get the struct of this entry
+ * @ptr: the &struct llist_head pointer.
+ * @type: the type of the struct this is embedded in.
+ * @member: the name of the llist_head within the struct.
+ */
+#define llist_entry(ptr, type, member) \
+ container_of(ptr, type, member)
+
+/**
+ * llist_for_each - iterate over a lock-less list
+ * @pos: the &struct llist_head to use as a loop cursor
+ * @head: the head for your lock-less list
+ */
+#define llist_for_each(pos, head) \
+ for (pos = (head)->next; pos; pos = pos->next)
+
+/**
+ * llist_for_each_entry - iterate over lock-less list of given type
+ * @pos: the type * to use as a loop cursor.
+ * @head: the head for your lock-less list.
+ * @member: the name of the llist_head with the struct.
+ */
+#define llist_for_each_entry(pos, head, member) \
+ for (pos = llist_entry((head)->next, typeof(*pos), member); \
+ &pos->member != NULL; \
+ pos = llist_entry(pos->member.next, typeof(*pos), member))
+
+/**
+ * llist_empty - tests whether a lock-less list is empty
+ * @head: the list to test
+ */
+static inline int llist_empty(const struct llist_head *head)
+{
+ return head->next == NULL;
+}
+
+void llist_add(struct llist_head *new, struct llist_head *head);
+struct llist_head *llist_del_first(struct llist_head *head);
+void llist_move_all(struct llist_head *list, struct llist_head *head);
+
+#endif /* LLIST_H */
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -210,4 +210,7 @@ config GENERIC_ATOMIC64
config LRU_CACHE
tristate

+config LLIST
+ bool
+
endmenu
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -106,6 +106,8 @@ obj-$(CONFIG_GENERIC_ATOMIC64) += atomic

obj-$(CONFIG_ATOMIC64_SELFTEST) += atomic64_test.o

+obj-$(CONFIG_LLIST) += llist.o
+
hostprogs-y := gen_crc32table
clean-files := crc32table.h

--- /dev/null
+++ b/lib/llist.c
@@ -0,0 +1,78 @@
+/*
+ * Simple lock-less NULL terminated single list implementation
+ *
+ * Copyright 2010 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/module.h>
+#include <linux/llist.h>
+#include <linux/errno.h>
+
+#include <asm/system.h>
+
+/**
+ * llist_add - add a new entry
+ * @new: new entry to be added
+ * @head: the head for your lock-less list
+ */
+void llist_add(struct llist_head *new, struct llist_head *head)
+{
+ struct llist_head *entry;
+
+ do {
+ entry = head->next;
+ new->next = entry;
+ } while (cmpxchg(&head->next, entry, new) != entry);
+}
+EXPORT_SYMBOL_GPL(llist_add);
+
+/**
+ * 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
+ */
+struct llist_head *llist_del_first(struct llist_head *head)
+{
+ struct llist_head *entry;
+
+ do {
+ entry = head->next;
+ if (entry == NULL)
+ return NULL;
+ } while (cmpxchg(&head->next, entry, entry->next) != entry);
+
+ return entry;
+}
+EXPORT_SYMBOL_GPL(llist_del_first);
+
+/**
+ * llist_move_all - delete all entries from one list and add them to another list
+ * @list: the head of lock-less list to delete all entries
+ * @head: the head of lock-less list to add the entries
+ *
+ * Remove all entries from @list lock-lessly, then add the entries to
+ * lock-less list @head.
+ */
+void llist_move_all(struct llist_head *list, struct llist_head *head)
+{
+ struct llist_head *entry;
+
+ entry = xchg(&list->next, NULL);
+ head->next = entry;
+}
+EXPORT_SYMBOL_GPL(llist_move_all);