The NFSv4 implementation in the Linux kernel through 4.11.1 allows local users to cause a denial of service (resource consumption) by leveraging improper channel callback shutdown when unmounting an NFSv4 filesystem, aka a "module reference and kernel daemon" leak.
https://www.spinics.net/lists/linux-nfs/msg63334.html
https://github.com/torvalds/linux/commit/c70422f760c120480fee4de6c38804c72aa26bc1
https://bugzilla.redhat.com/show_bug.cgi?id=1451386