usb-creator-gtk fails to clean up after itself after failed installation

[Jeff Lane ]

Following this bug: https://bugs.launchpad.net/ubuntu/+source/usb-creator/+bug/1497445

I discovered that usb-creator-gtk fails to unmount the ISO image it was using when I hit the Quit button.

Sometimes it at least unmounts the sqashfs mount it creates on the usb stick, sometimes not.

after I discovered this after a couple failed attempts, and I manually unmounted the ISO images. I then attempted to create a usb drive again, and again, after it failed, I discovered that the ISO was still mounted:

/home/bladernr/Downloads/ubuntu-15.04-desktop-amd64.iso on /tmp/tmpwilfzjih type iso9660 (ro)

To recreate this, you have to get it to fail per bug 1497445 and use the Quit button in the error dialog box, then check with the mount command to see the ISO still mounted.

Interestingly, after I did a 15.04, I tried a Wily image and discovered that it not only left the Vivid ISO mounted when it failed, it also left both the wily image mounted as well as the squashfs from the wily attempt.

/home/bladernr/Downloads/ubuntu-15.04-desktop-amd64.iso on /tmp/tmpwilfzjih type iso9660 (ro)
/home/bladernr/Downloads/wily-desktop-amd64.iso on /tmp/tmp4mpvpci9 type iso9660 (ro)
/media/bladernr/0EA3-4910/casper/filesystem.squashfs on /tmp/tmpn7qmccps type squashfs (ro)

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: usb-creator-gtk 0.2.56.3ubuntu0.2
ProcVersionSignature: Ubuntu 3.13.0-62.101-generic 3.13.11-ckt24
Uname: Linux 3.13.0-62-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.14.1-0ubuntu3.11
Architecture: amd64
CurrentDesktop: Unity
Date: Fri Sep 18 16:33:44 2015
InstallationDate: Installed on 2012-03-15 (1282 days ago)
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha amd64 (20120307)
SourcePackage: usb-creator
UpgradeStatus: Upgraded to trusty on 2014-04-20 (516 days ago)

[Jeff Lane  (bladernr)]

Because of repeated failed attempts to create USB devices, eventually usb-creator-gtk will fail because of the lack of loop devices. If I forgot to unmount all the ISO and squashfs mounts after the failed attempts at USB creation (2 mounts per attempt), I run out of loop devices and the creator fails immediately because it's unable to create a new squashfs mount, or unable to mount any more ISOs.