4 files changed, 260 insertions, 0 deletions

diff --git a/include/linux/llist.h b/include/linux/llist.h
new file mode 100644
index 000000000000..aa0c8b5b3cd0
--- /dev/null
+++ b/include/linux/llist.h
@@ -0,0 +1,126 @@
+#ifndef LLIST_H
+#define LLIST_H
+/*
+ * Lock-less NULL terminated single linked list
+ *
+ * If there are multiple producers and multiple consumers, llist_add
+ * can be used in producers and llist_del_all can be used in
+ * consumers.  They can work simultaneously without lock.  But
+ * llist_del_first can not be used here.  Because llist_del_first
+ * depends on list->first->next does not changed if list->first is not
+ * changed during its operation, but llist_del_first, llist_add,
+ * llist_add (or llist_del_all, llist_add, llist_add) sequence in
+ * another consumer may violate that.
+ *
+ * If there are multiple producers and one consumer, llist_add can be
+ * used in producers and llist_del_all or llist_del_first can be used
+ * in the consumer.
+ *
+ * This can be summarized as follow:
+ *
+ *           |   add    | del_first |  del_all
+ * add       |    -     |     -     |     -
+ * del_first |          |     L     |     L
+ * del_all   |          |           |     -
+ *
+ * Where "-" stands for no lock is needed, while "L" stands for lock
+ * is needed.
+ *
+ * The list entries deleted via llist_del_all can be traversed with
+ * traversing function such as llist_for_each etc.  But the list
+ * entries can not be traversed safely before deleted from the list.
+ * The order of deleted entries is from the newest to the oldest added
+ * one.  If you want to traverse from the oldest to the newest, you
+ * must reverse the order by yourself before traversing.
+ *
+ * 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 handler.  So code uses the list in NMI
+ * handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
+ */
+
+struct llist_head {
+        struct llist_node *first;
+};
+
+struct llist_node {
+        struct llist_node *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->first = NULL;
+}
+
+/**
+ * llist_entry - get the struct of this entry
+ * @ptr:        the &struct llist_node pointer.
+ * @type:       the type of the struct this is embedded in.
+ * @member:     the name of the llist_node within the struct.
+ */
+#define llist_entry(ptr, type, member)          \
+        container_of(ptr, type, member)
+
+/**
+ * llist_for_each - iterate over some deleted entries of a lock-less list
+ * @pos:        the &struct llist_node to use as a loop cursor
+ * @node:       the first entry of deleted list entries
+ *
+ * In general, some entries of the lock-less list can be traversed
+ * safely only after being deleted from list, so start with an entry
+ * instead of list head.
+ *
+ * If being used on entries deleted from lock-less list directly, the
+ * traverse order is from the newest to the oldest added entry.  If
+ * you want to traverse from the oldest to the newest, you must
+ * reverse the order by yourself before traversing.
+ */
+#define llist_for_each(pos, node)                       \
+        for ((pos) = (node); pos; (pos) = (pos)->next)
+
+/**
+ * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
+ * @pos:        the type * to use as a loop cursor.
+ * @node:       the fist entry of deleted list entries.
+ * @member:     the name of the llist_node with the struct.
+ *
+ * In general, some entries of the lock-less list can be traversed
+ * safely only after being removed from list, so start with an entry
+ * instead of list head.
+ *
+ * If being used on entries deleted from lock-less list directly, the
+ * traverse order is from the newest to the oldest added entry.  If
+ * you want to traverse from the oldest to the newest, you must
+ * reverse the order by yourself before traversing.
+ */
+#define llist_for_each_entry(pos, node, member)                         \
+        for ((pos) = llist_entry((node), 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
+ *
+ * Not guaranteed to be accurate or up to date.  Just a quick way to
+ * test whether the list is empty without deleting something from the
+ * list.
+ */
+static inline int llist_empty(const struct llist_head *head)
+{
+        return ACCESS_ONCE(head->first) == NULL;
+}
+
+void llist_add(struct llist_node *new, struct llist_head *head);
+void llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
+                     struct llist_head *head);
+struct llist_node *llist_del_first(struct llist_head *head);
+struct llist_node *llist_del_all(struct llist_head *head);
+#endif /* LLIST_H */
diff --git a/lib/Kconfig b/lib/Kconfig
index 830181cc7a83..25c19678a30f 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -262,4 +262,7 @@ config AVERAGE
 
           If unsure, say N.
 
+config LLIST
+        bool
+
 endmenu
diff --git a/lib/Makefile b/lib/Makefile
index 6b597fdb1898..d770b817202e 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -112,6 +112,8 @@ obj-$(CONFIG_AVERAGE) += average.o
 
 obj-$(CONFIG_CPU_RMAP) += cpu_rmap.o
 
+obj-$(CONFIG_LLIST) += llist.o
+
 hostprogs-y     := gen_crc32table
 clean-files     := crc32table.h
 
diff --git a/lib/llist.c b/lib/llist.c
new file mode 100644
index 000000000000..da445724fa1f
--- /dev/null
+++ b/lib/llist.c
@@ -0,0 +1,129 @@
+/*
+ * 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 handler.  So code uses the list in 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/module.h>
+#include <linux/interrupt.h>
+#include <linux/llist.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_node *new, struct llist_head *head)
+{
+        struct llist_node *entry, *old_entry;
+
+#ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
+        BUG_ON(in_nmi());
+#endif
+
+        entry = head->first;
+        do {
+                old_entry = entry;
+                new->next = entry;
+                cpu_relax();
+        } while ((entry = cmpxchg(&head->first, old_entry, new)) != old_entry);
+}
+EXPORT_SYMBOL_GPL(llist_add);
+
+/**
+ * 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
+ */
+void llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
+                     struct llist_head *head)
+{
+        struct llist_node *entry, *old_entry;
+
+#ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
+        BUG_ON(in_nmi());
+#endif
+
+        entry = head->first;
+        do {
+                old_entry = entry;
+                new_last->next = entry;
+                cpu_relax();
+        } while ((entry = cmpxchg(&head->first, old_entry, new_first)) != old_entry);
+}
+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;
+
+#ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
+        BUG_ON(in_nmi());
+#endif
+
+        entry = head->first;
+        do {
+                if (entry == NULL)
+                        return NULL;
+                old_entry = entry;
+                next = entry->next;
+                cpu_relax();
+        } while ((entry = cmpxchg(&head->first, old_entry, next)) != old_entry);
+
+        return entry;
+}
+EXPORT_SYMBOL_GPL(llist_del_first);
+
+/**
+ * llist_del_all - delete all entries from lock-less list
+ * @head:       the head of lock-less list to delete all entries
+ *
+ * If list is empty, return NULL, otherwise, delete all entries and
+ * return the pointer to the first entry.  The order of entries
+ * deleted is from the newest to the oldest added one.
+ */
+struct llist_node *llist_del_all(struct llist_head *head)
+{
+#ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
+        BUG_ON(in_nmi());
+#endif
+
+        return xchg(&head->first, NULL);
+}
+EXPORT_SYMBOL_GPL(llist_del_all);