Add a safe_unmount function and use it in enter_chroot.

src/scripts/enter_chroot.sh

 #!/bin/bash
 
 # Copyright (c) 2009 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Script to enter the chroot environment
 
 # Load common constants.  This should be the first executable line.
 # The path to common.sh should be relative to your script's location.
@@ skipping 171 matching lines @@
     # Remove any dups from lock file while installing new one
     sort -n "$TMP_LOCKFILE" | uniq > "$LOCKFILE"
 
     if [ -s "$LOCKFILE" ]; then
       echo "At least one other pid is running in the chroot, so not"
       echo "tearing down env."
     else
       MOUNTED_PATH=$(readlink -f "$FLAGS_chroot")
       echo "Unmounting chroot environment."
       for i in $(mount | grep -F "on $MOUNTED_PATH/" | awk '{print $3}'); do
-        sudo umount "$i" || die "Failed to umount $i"
+        safe_umount "$i"
       done
     fi
   ) 200>>"$LOCKFILE" || die "teardown_env failed"
 }
 
 if [ $FLAGS_mount -eq $FLAGS_TRUE ]
 then
   setup_env
   echo "Make sure you run"
   echo "    $0 --unmount"
@@ skipping 42 matching lines @@
 
 # Run command or interactive shell.  Also include the non-chrooted path to
 # the source trunk for scripts that may need to print it (e.g.
 # build_image.sh).
 sudo chroot "$FLAGS_chroot" sudo -i -u $USER $CHROOT_PASSTHRU \
   EXTERNAL_TRUNK_PATH="${FLAGS_trunk}" LANG=C "$@"
 
 # Remove trap and explicitly unmount
 trap - EXIT
 teardown_env