Currently unpin_extent_range happens in the transaction commit context, so we are protected from ->last_byte_to_unpin changing while we're unpinning, because any new transactions would have to wait for us to complete before modifying ->last_byte_to_unpin. However in the future we may want to change how this works, for instance with async unpinning or other such TODO items. To prepare for that future explicitly protect ->last_byte_to_unpin with the commit_root_sem so we are sure it won't change while we're doing our work. Reviewed-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Josef Bacik <josef@toxicpanda.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>