installer: fix the "umount: XXX not mounted" error message during postinst

chromeos-install

 #!/bin/sh -u
 # Copyright (c) 2010 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.
 #
 # A script to install from removable media to hard disk.
 
 # Load functions and constants for chromeos-install.
 . "$(dirname "$0")/chromeos-common.sh" || exit 1
 . /usr/lib/shflags || exit 1
@@ skipping 434 matching lines @@
 echo "Copying ESP..."
 fast_dd 512 ${ESP_IMG_SECTORS} ${START_ESP} ${ESP_IMG_OFFSET} \
   if=${ESP_IMG} of=${DST} conv=notrunc
 
 # If postinst fails, we should still clear stateful.
 if [ "${FLAGS_preserve_stateful}" -eq "${FLAGS_FALSE}" ]; then
   echo "Clearing the stateful partition..."
   loop_offset_setup $DST $START_STATEFUL
   sudo mkfs.ext3 -F -b 4096 -L "H-STATE" ${LOOP_DEV} \
     $(($NUM_STATEFUL_SECTORS / 8))
+  # Need to synchronize before releasing loop device, otherwise the losetup -d
+  # may get device busy.
+  sync
   loop_offset_cleanup
 fi
 
 # TODO: support arm during postinst so that we get partition selection and
 #       verified boot.
 if [ "$ARCH" != "ARM" ]; then
   # We can't guarantee that the kernel will see the new partition table, so
   # we can't use it directly. We could force the kernel to reload it with an
   # ioctl, but then we might have the UI mounting and displaying any old
   # filesystems left over from the last install, and we don't want that either.
@@ skipping 56 matching lines @@
     --set bootcmd="mmc read 0 C0008000 0 1; autoscr C0008000"
 fi
 
 # Force data to disk before we declare done.
 sync
 
 echo "------------------------------------------------------------"
 echo ""
 echo "Installation to '$DST' complete."
 echo "Please shutdown, remove the USB device, cross your fingers, and reboot."