I'm not sure if this is a bug, but since it's very unusual (at least from what I've seen), I'm reporting it. Top shows this line: 8 root 18446744073709551615 -20 0 0 0 SW< 0.0 0.0 0:00 0 mdrecoveryd i.e. mdrecoveryd has a priority of 18446744073709551615
Must be running fast. :^) Can you try this with procps-3.20 from rawhide.
Fixed! Top shows: 8 root -1 -20 0 0 0 S 0.0 0.0 0:00.00 mdrecoveryd Closing as rawhide. Tell me if you don't want me to do this.