Index: sbin/umount/umount.8
===================================================================
--- sbin/umount/umount.8
+++ sbin/umount/umount.8
@@ -28,7 +28,7 @@
 .\"     @(#)umount.8	8.2 (Berkeley) 5/8/95
 .\" $FreeBSD: head/sbin/umount/umount.8 314436 2017-02-28 23:42:47Z imp $
 .\"
-.Dd September 10, 2016
+.Dd July 25, 2017
 .Dt UMOUNT 8
 .Os
 .Sh NAME
@@ -36,7 +36,7 @@
 .Nd unmount file systems
 .Sh SYNOPSIS
 .Nm
-.Op Fl fnv
+.Op Fl fNnv
 .Ar special ... | node ... | fsid ...
 .Nm
 .Fl a | A
@@ -81,6 +81,17 @@
 For NFS, a forced dismount can take up to 1 minute or more to
 complete against an unresponsive server and may throw away
 data not yet written to the server for this case.
+If a process, such as
+.Xr df 1
+or
+.Nm
+without the
+.Fl f
+flag is hung on an
+.Tn NFS
+mount point, use the
+.Fl N
+flag instead.
 Also, doing a forced dismount of an NFSv3 mount when
 .Xr rpc.lockd 8
 is running is unsafe and can result in a crash.
@@ -94,6 +105,20 @@
 option, will only unmount
 .Tn NFS
 file systems.
+.It Fl N
+Do a forced dismount of an
+.Tn NFS
+mount point without checking the mount path.
+This option can only be used with the path to the mount point
+.Ar node
+and the path must be specified exactly as it was at mount time.
+This option is useful when a process is hung waiting for an unresponsive
+.Tn NFS
+server while holding a vnode lock on the mounted-on vnode, such that
+.Nm
+with the
+.Fl f
+flag can't complete.
 .It Fl n
 Unless the
 .Fl f
Index: sbin/umount/umount.c
===================================================================
--- sbin/umount/umount.c
+++ sbin/umount/umount.c
@@ -86,13 +86,13 @@
 int
 main(int argc, char *argv[])
 {
-	int all, errs, ch, mntsize, error;
+	int all, errs, ch, mntsize, error, nfsforce, ret;
 	char **typelist = NULL;
 	struct statfs *mntbuf, *sfs;
 	struct addrinfo hints;
 
-	all = errs = 0;
-	while ((ch = getopt(argc, argv, "AaF:fh:nt:v")) != -1)
+	nfsforce = all = errs = 0;
+	while ((ch = getopt(argc, argv, "AaF:fh:Nnt:v")) != -1)
 		switch (ch) {
 		case 'A':
 			all = 2;
@@ -110,6 +110,9 @@
 			all = 2;
 			nfshost = optarg;
 			break;
+		case 'N':
+			nfsforce = 1;
+			break;
 		case 'n':
 			fflag |= MNT_NONBUSY;
 			break;
@@ -138,6 +141,9 @@
 	if ((argc == 0 && !all) || (argc != 0 && all))
 		usage();
 
+	if (argc == 0 && nfsforce != 0)
+		usage();
+
 	/* -h implies "-t nfs" if no -t flag. */
 	if ((nfshost != NULL) && (typelist == NULL))
 		typelist = makevfslist("nfs");
@@ -175,7 +181,20 @@
 		break;
 	case 0:
 		for (errs = 0; *argv != NULL; ++argv)
-			if (checkname(*argv, typelist) != 0)
+			if (nfsforce != 0) {
+				/*
+				 * First do the nfssvc() syscall to shut down
+				 * the mount point and then do the forced
+				 * dismount.
+				 */
+				ret = nfssvc(NFSSVC_FORCEDISM, *argv);
+				if (ret >= 0)
+					ret = unmount(*argv, MNT_FORCE);
+				if (ret < 0) {
+					warn("%s", *argv);
+					errs = 1;
+				}
+			} else if (checkname(*argv, typelist) != 0)
 				errs = 1;
 		break;
 	}
@@ -635,7 +654,7 @@
 {
 
 	(void)fprintf(stderr, "%s\n%s\n",
-	    "usage: umount [-fnv] special ... | node ... | fsid ...",
+	    "usage: umount [-fNnv] special ... | node ... | fsid ...",
 	    "       umount -a | -A [-F fstab] [-fnv] [-h host] [-t type]");
 	exit(1);
 }
Index: sys/fs/nfsclient/nfs_clport.c
===================================================================
--- sys/fs/nfsclient/nfs_clport.c
+++ sys/fs/nfsclient/nfs_clport.c
@@ -1311,6 +1311,7 @@
 	cap_rights_t rights;
 	char *buf;
 	int error;
+	struct mount *mp;
 
 	if (uap->flag & NFSSVC_CBADDSOCK) {
 		error = copyin(uap->argp, (caddr_t)&nfscbdarg, sizeof(nfscbdarg));
@@ -1365,6 +1366,44 @@
 			    dumpmntopts.ndmnt_blen);
 			free(buf, M_TEMP);
 		}
+	} else if (uap->flag & NFSSVC_FORCEDISM) {
+		buf = malloc(MNAMELEN + 1, M_TEMP, M_WAITOK);
+		error = copyinstr(uap->argp, buf, MNAMELEN + 1, NULL);
+		if (error == 0) {
+			mtx_lock(&mountlist_mtx);
+			TAILQ_FOREACH(mp, &mountlist, mnt_list) {
+				if (strcmp(mp->mnt_stat.f_mntonname, buf) ==
+				    0 && strcmp(mp->mnt_stat.f_fstypename,
+				    "nfs") == 0 && mp->mnt_data != NULL) {
+					vfs_ref(mp);
+					break;
+				}
+			}
+			mtx_unlock(&mountlist_mtx);
+
+			if (mp != NULL) {
+				/*
+				 * First, set MNTK_UNMOUNTF so that no new
+				 * RPCs will fail.
+				 * Then, call newnfs_nmcancelreqs() to cause
+				 * any RPCs in progress on the mount point to
+				 * fail.
+				 * This will cause any process waiting for an
+				 * RPC to complete while holding a vnode lock
+				 * on the mounted-on vnode (such as "df" or
+				 * a non-forced "umount") to fail.
+				 * This will unlock the mounted-on vnode so
+				 * a forced dismount can succeed.
+				 */
+				MNT_ILOCK(mp);
+				mp->mnt_kern_flag |= MNTK_UNMOUNTF;
+				MNT_IUNLOCK(mp);
+				newnfs_nmcancelreqs(VFSTONFS(mp));
+				vfs_rel(mp);
+			} else
+				error = EINVAL;
+		}
+		free(buf, M_TEMP);
 	} else {
 		error = EINVAL;
 	}
Index: sys/nfs/nfs_nfssvc.c
===================================================================
--- sys/nfs/nfs_nfssvc.c
+++ sys/nfs/nfs_nfssvc.c
@@ -92,7 +92,7 @@
 	    nfsd_call_nfsserver != NULL)
 		error = (*nfsd_call_nfsserver)(td, uap);
 	else if ((uap->flag & (NFSSVC_CBADDSOCK | NFSSVC_NFSCBD |
-	    NFSSVC_DUMPMNTOPTS)) && nfsd_call_nfscl != NULL)
+	    NFSSVC_DUMPMNTOPTS | NFSSVC_FORCEDISM)) && nfsd_call_nfscl != NULL)
 		error = (*nfsd_call_nfscl)(td, uap);
 	else if ((uap->flag & (NFSSVC_IDNAME | NFSSVC_GETSTATS |
 	    NFSSVC_GSSDADDPORT | NFSSVC_GSSDADDFIRST | NFSSVC_GSSDDELETEALL |
Index: sys/nfs/nfssvc.h
===================================================================
--- sys/nfs/nfssvc.h
+++ sys/nfs/nfssvc.h
@@ -70,6 +70,7 @@
 #define	NFSSVC_RESUMENFSD	0x08000000
 #define	NFSSVC_DUMPMNTOPTS	0x10000000
 #define	NFSSVC_NEWSTRUCT	0x20000000
+#define	NFSSVC_FORCEDISM	0x40000000
 
 /* Argument structure for NFSSVC_DUMPMNTOPTS. */
 struct nfscl_dumpmntopts {