<linux/list.h>: Introduce the list_for_each_reverse() method

The list_head counterpart of list_for_each_entry_reverse() was missing,
add it to complete the list handling APIs in <linux/list.h>.

[ This new API is also relied on by a WIP scheduler patch, so this
  variant is not a theoretical possibility only. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org

include/linux/list.h

@@ -686,6 +686,14 @@ static inline void list_splice_tail_init(struct list_head *list,
 #define list_for_each(pos, head) \
 	for (pos = (head)->next; !list_is_head(pos, (head)); pos = pos->next)
 
+/**
+ * list_for_each_reverse - iterate backwards over a list
+ * @pos:	the &struct list_head to use as a loop cursor.
+ * @head:	the head for your list.
+ */
+#define list_for_each_reverse(pos, head) \
+	for (pos = (head)->prev; pos != (head); pos = pos->prev)
+
 /**
  * list_for_each_rcu - Iterate over a list in an RCU-safe fashion
  * @pos:	the &struct list_head to use as a loop cursor.