Description: Module reference leak due to improper shut down of callback channel on umount
References:
 https://www.spinics.net/lists/linux-nfs/msg63334.html
 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c70422f760c120480fee4de6c38804c72aa26bc1
Notes:
 bwh> Upstream fix says this was introduced by commit bb6aeba736ba
 bwh> "NFSv4.x: Switch to using svc_set_num_threads() to manage the callback
 bwh> threads" in 4.9.
Bugs:
 https://bugzilla.redhat.com/show_bug.cgi?id=1451386
 https://bugs.debian.org/863550
upstream: released (4.12-rc1) [9e0d87680d689f1758185851c3da6eafb16e71e1, ed6473ddc704a2005b9900ca08e236ebb2d8540a]
4.9-upstream-stable: released (4.9.52) [d9f9b83539ab9b1ebb5cbdfa0a5a9994e20e6a0d, f609266b12d214437cf9d68245dc27f8d4f69836]
3.16-upstream-stable: N/A "Vulnerable code not present"
3.2-upstream-stable: N/A "Vulnerable code not present"
sid: released (4.9.30-1) [bugfix/all/sunrpc-refactor-svc_set_num_threads.patch, bugfix/all/nfsv4-fix-callback-server-shutdown.patch]
4.9-stretch-security: N/A "Fixed before branching point"
3.16-jessie-security: N/A "Vulnerable code not present"
3.2-wheezy-security: N/A "Vulnerable code not present"