Subject: umount: avoid calling readlink on mountpoints.
References: bnc#794529

We normally want to canonicalize a path given to umount
in case it contains symlinks.  This ensure the right entry
is removed from  /etc/mtab.
However if the mountpoint is for a non-responsive NFS server,
that readlink could hang (*will* have if mounted with -o noac).

In the normal case where no symlinks are used we don't need the
readlink() and we can easily detect this by checking if the
mount table contains the given name.
If it does, use the name as-is.
If it doesn't, then call canonicalize()

---
 mount/umount.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

Index: util-linux-2.19.1/mount/umount.c
===================================================================
--- util-linux-2.19.1.orig/mount-deprecated/umount.c
+++ util-linux-2.19.1/mount-deprecated/umount.c
@@ -588,12 +588,22 @@ umount_file (char *arg) {
 		return 0;
 	}
 
+	/* If the name given is listed in the mount table, don't
+	 * bother  with canonicalize() - it can block an a non-responsive
+	 * NFS server.
+	 */
+	file = arg;
+	mc = getmntdirbackward(arg, NULL);
+	if (!mc && !nocanonicalize)
 	file = canonicalize(arg); /* mtab paths are canonicalized */
+	else
+		file = strdup(arg);
 
 try_loopdev:
 	if (verbose > 1)
 		printf(_("Trying to unmount %s\n"), file);
 
+	if (!mc)
 	mc = getmntdirbackward(file, NULL);
 	if (!mc) {
 		mc = getmntdevbackward(file, NULL);