RB_PREV
while ((crs = RB_PREV(revoked_serial_tree, rt, ers)) != NULL) {
#define rb_prev(node) RB_PREV(linux_root, NULL, (node))
tse1 = RB_PREV(undo_hist_entry_rb_tree,
tse2 = RB_PREV(undo_hist_entry_rb_tree,
tse1 = RB_PREV(undo_hist_entry_rb_tree,