[NETNS]: Cleanup list walking in setup_net and cleanup_net

I proposed introducing a list_for_each_entry_continue_reverse macro
to be used in setup_net() when unrolling the failed ->init callback.

Here is the macro and some more cleanup in the setup_net() itself
to remove one variable from the stack :) The same thing is for the
cleanup_net() - the existing list_for_each_entry_reverse() is used.

Minor, but the code looks nicer.
Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/list.h

@@ -524,6 +524,20 @@ static inline void list_splice_init_rcu(struct list_head *list,
 	     prefetch(pos->member.next), &pos->member != (head);	\
 	     pos = list_entry(pos->member.next, typeof(*pos), member))
 
+/**
+ * list_for_each_entry_continue_reverse - iterate backwards from the given point
+ * @pos:	the type * to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the list_struct within the struct.
+ *
+ * Start to iterate over list of given type backwards, continuing after
+ * the current position.
+ */
+#define list_for_each_entry_continue_reverse(pos, head, member)		\
+	for (pos = list_entry(pos->member.prev, typeof(*pos), member);	\
+	     prefetch(pos->member.prev), &pos->member != (head);	\
+	     pos = list_entry(pos->member.prev, typeof(*pos), member))
+
 /**
  * list_for_each_entry_from - iterate over list of given type from the current point
  * @pos:	the type * to use as a loop cursor.

net/core/net_namespace.c

@@ -56,7 +56,6 @@ static void net_free(struct net *net)
 static void cleanup_net(struct work_struct *work)
 {
 	struct pernet_operations *ops;
-	struct list_head *ptr;
 	struct net *net;
 
 	net = container_of(work, struct net, work);
@@ -69,8 +68,7 @@ static void cleanup_net(struct work_struct *work)
 	net_unlock();
 
 	/* Run all of the network namespace exit methods */
-	list_for_each_prev(ptr, &pernet_list) {
-		ops = list_entry(ptr, struct pernet_operations, list);
+	list_for_each_entry_reverse(ops, &pernet_list, list) {
 		if (ops->exit)
 			ops->exit(net);
 	}
@@ -102,7 +100,6 @@ static int setup_net(struct net *net)
 {
 	/* Must be called with net_mutex held */
 	struct pernet_operations *ops;
-	struct list_head *ptr;
 	int error;
 
 	memset(net, 0, sizeof(struct net));
@@ -110,8 +107,7 @@ static int setup_net(struct net *net)
 	atomic_set(&net->use_count, 0);
 
 	error = 0;
-	list_for_each(ptr, &pernet_list) {
-		ops = list_entry(ptr, struct pernet_operations, list);
+	list_for_each_entry(ops, &pernet_list, list) {
 		if (ops->init) {
 			error = ops->init(net);
 			if (error < 0)
@@ -120,12 +116,12 @@ static int setup_net(struct net *net)
 	}
 out:
 	return error;
+
 out_undo:
 	/* Walk through the list backwards calling the exit functions
 	 * for the pernet modules whose init functions did not fail.
 	 */
-	for (ptr = ptr->prev; ptr != &pernet_list; ptr = ptr->prev) {
-		ops = list_entry(ptr, struct pernet_operations, list);
+	list_for_each_entry_continue_reverse(ops, &pernet_list, list) {
 		if (ops->exit)
 			ops->exit(net);
 	}