Code: static void lockd_down_net(struct svc_serv *serv, struct net *net)
{
	struct lockd_net *ln = net_generic(net, lockd_net_id);

 	if (ln->nlmsvc_users) {
 		if (--ln->nlmsvc_users == 0) {
 			nlm_shutdown_hosts_net(net);
			cancel_delayed_work_sync(&ln->grace_period_end);
			locks_end_grace(&ln->lockd_manager);
 			svc_shutdown_net(serv, net);
 			dprintk("lockd_down_net: per-net data destroyed; net=%p\n", net);
 		}
	} else {
		printk(KERN_ERR "lockd_down_net: no users! task=%p, net=%p\n",
				nlmsvc_task, net);
		BUG();
	}
}

Vulnerability Type: DoS 
CWE ID: CWE-404
Summary: 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.
Commit Message: Merge tag 'nfsd-4.12' of git://linux-nfs.org/~bfields/linux

Pull nfsd updates from Bruce Fields:
 "Another RDMA update from Chuck Lever, and a bunch of miscellaneous
  bugfixes"

* tag 'nfsd-4.12' of git://linux-nfs.org/~bfields/linux: (26 commits)
  nfsd: Fix up the "supattr_exclcreat" attributes
  nfsd: encoders mustn't use unitialized values in error cases
  nfsd: fix undefined behavior in nfsd4_layout_verify
  lockd: fix lockd shutdown race
  NFSv4: Fix callback server shutdown
  SUNRPC: Refactor svc_set_num_threads()
  NFSv4.x/callback: Create the callback service through svc_create_pooled
  lockd: remove redundant check on block
  svcrdma: Clean out old XDR encoders
  svcrdma: Remove the req_map cache
  svcrdma: Remove unused RDMA Write completion handler
  svcrdma: Reduce size of sge array in struct svc_rdma_op_ctxt
  svcrdma: Clean up RPC-over-RDMA backchannel reply processing
  svcrdma: Report Write/Reply chunk overruns
  svcrdma: Clean up RDMA_ERROR path
  svcrdma: Use rdma_rw API in RPC reply path
  svcrdma: Introduce local rdma_rw API helpers
  svcrdma: Clean up svc_rdma_get_inv_rkey()
  svcrdma: Add helper to save pages under I/O
  svcrdma: Eliminate RPCRDMA_SQ_DEPTH_MULT
  ...