Login into system doesn't work when using BTRFS on /(root) and /home.

[Dee'Kej]

Hi!

1) I've just installed Linux Mint Maya (64bit, Mate).
2) I have Intel SSD 320 and I decided to use BTRFS as I used it with Mint 11 before. During installation I've created 4 primary partitions:
1. - SWAP
2. - /boot (ext4)
3. - / (root, BTRFS)
4. - /home (BTRFS)

Installation was successful. Then I booted to newly installed Linux, entered my login and password and got this message:
"Your home directory is listed as '/home/*****' but it does not appear to exist. Do you want to log in with the /(root) as your home directory? It is unlikely anything will work unless you use a failsafe session."

So the problem is that even after successful installation you can't login properly.
3) What happened? I've figured it out:
I logged in as root and took a look to /etc/fstab. After some time of Googling I've realized the changed from Linux Mint 11 Katya.
In /etc/fstab there are new options for partitions that use BTRFS, these options are "subvol=*****".
But one thing for this to be working is missing: Kernel needs option "rootflags=subvol=@" for all of this to be working.

I've changed /etc/default/grub config with this option, so the kernel uses it all the time (GRUB_CMDLINE_LINUX="rootflags=subvol=@"), run update-grub and rebooted. Afterward everything is working well and I could log in with my username without problems. So apparently the problem is that the Installation script of Linux Mint 13 doesn't add proper option for kernel to boot with, when someone uses BTRFS.

4) In no error case I expect succesful installation and successful log in afterwards.
5) Reproducible always.

And as far as I remember I've noticed this behaviour when I was trying Linux Mint 12. If I'm right, I suggest that the patch for this workaround would be also backported to Linux Mint 12 or even Linux Mint 11 if needed.

Last idea: I'm not really sure if it's good idea to let user login as root, when something like this happens. Some users are not so advanced with Linux and I think in some way it might be a vulnerability in security.