Resize a btrfs partition inside a logical LVM volume

Well, that was embarrassing. BTRFS needs to be mounted to be able to resize the partition.

How do I resize a partition? (shrink/grow)

In order to demonstrate and test the back references, Btrfs devel team has added an online resizer, which can both grow and shrink the filesystem via the btrfs commands.

First, ensure that your filesystem is mounted.

So, it doesn't matter that I was using a LVM volume, as long as it was mounted.

BTRFS takes filesystem mount point as an argument, not a device path.

In other words, intead of this:

btrfs filesystem resize max /dev/vg/lvhome

You should use actual path where the said volume was mounted:

btrfs filesystem resize max /home