Comment # 2 on bug 1149980 from Stefan Hundhammer

From that y2log it appears that it's the Btrfs subvolumes that cause all those
confusing errors in the log.

All entries in /proc/mounts (reformatted and minus the mount option to avoid
Bugzilla mangling it completely):

tmpfs       /                           tmpfs
tmpfs       /                           tmpfs
proc        /proc                       proc
sysfs       /sys                        sysfs
/dev/loop0  /parts/mp_0000              squashfs
/dev/loop1  /parts/mp_0001              squashfs
devtmpfs    /dev                        devtmpfs
devpts      /dev/pts                    devpts
rpc_pipefs  /var/lib/nfs/rpc_pipefs     rpc_pipefs
/dev/loop2  /mounts/mp_0000             squashfs
/dev/loop3  /mounts/mp_0001             squashfs
/dev/loop5  /mounts/mp_0003             squashfs
/dev/loop6  /mounts/mp_0004             squashfs
/dev/sda2   /mnt                        btrfs
/dev/sda2   /mnt/.snapshots             btrfs
/dev/sda2   /mnt/boot/grub2/i386-pc     btrfs
/dev/sda2   /mnt/boot/grub2/x86_64-efi  btrfs
/dev/sda2   /mnt/home                   btrfs
/dev/sda2   /mnt/opt                    btrfs
/dev/sda2   /mnt/root                   btrfs
/dev/sda2   /mnt/srv                    btrfs
/dev/sda2   /mnt/tmp                    btrfs
/dev/sda2   /mnt/usr/local              btrfs
/dev/sda2   /mnt/var                    btrfs
devtmpfs    /mnt/dev                    devtmpfs
proc        /mnt/proc                   proc
sysfs       /mnt/sys                    sysfs
tmpfs       /mnt/run                    tmpfs


But we only need mounts to /mnt, so let's grep for that:

/dev/sda2   /mnt                        btrfs
/dev/sda2   /mnt/.snapshots             btrfs
/dev/sda2   /mnt/boot/grub2/i386-pc     btrfs
/dev/sda2   /mnt/boot/grub2/x86_64-efi  btrfs
/dev/sda2   /mnt/home                   btrfs
/dev/sda2   /mnt/opt                    btrfs
/dev/sda2   /mnt/root                   btrfs
/dev/sda2   /mnt/srv                    btrfs
/dev/sda2   /mnt/tmp                    btrfs
/dev/sda2   /mnt/usr/local              btrfs
/dev/sda2   /mnt/var                    btrfs
devtmpfs    /mnt/dev                    devtmpfs
proc        /mnt/proc                   proc
sysfs       /mnt/sys                    sysfs
tmpfs       /mnt/run                    tmpfs


Notice that all the snapshots on the root filesystem are also there. But
unmounting them separately is what fails with that "filesystem busy" error, so
that's what we need to avoid.