libdrm 2.4.60 is too buggy when used with Nouveau.
Please add into Debian the version 2.4.61 as soon as possible (or you may revert to 2.4.59). The bug is very serious.
See https://bugs.freedesktop.org/show_bug.cgi?id=89842 for the source of my claim.
-- Victor Porton - http://portonvictor.org