Issue with subdivision surface I made a circle and then made a boolean cut into it with another circle. But when I apply the sub. surface, the outer circle is fine but the inner section changes into a weird quadrilateral. I want the cut to be in a shape of a circle. How do I solve this?
Remove the sub surface modifier
Delete the center edge on both sides
Select the big and small edge and press F to fill the edge. With the f2 addon just press F until it fill all the edge. Repeat on both sides
Then add the sub surface modifier 
If you need smooth inner side add crease.