void clear_commit_marks(struct commit *commit, unsigned int mark)
 {
-       struct commit_list *parents;
+       while (commit) {
+               struct commit_list *parents;
 
-       commit->object.flags &= ~mark;
-       parents = commit->parents;
-       while (parents) {
-               struct commit *parent = parents->item;
+               if (!(mark & commit->object.flags))
+                       return;
 
-               /* Have we already cleared this? */
-               if (mark & parent->object.flags)
-                       clear_commit_marks(parent, mark);
-               parents = parents->next;
+               commit->object.flags &= ~mark;
+
+               parents = commit->parents;
+               if (!parents)
+                       return;
+
+               while ((parents = parents->next))
+                       clear_commit_marks(parents->item, mark);
+
+               commit = commit->parents->item;
        }
 }