Try this:
btrfs check --repair /dev/sda1
https://btrfs.wiki.kernel.org/index.php/Btrfsck#btrfs_check_--repair
EDIT: I will add that it is good to release (unmount).
Try this:
btrfs check --repair /dev/sda1
https://btrfs.wiki.kernel.org/index.php/Btrfsck#btrfs_check_--repair
EDIT: I will add that it is good to release (unmount).