If you actually mount it as ext4 and enable the new features, yes. However, if y...

JoshTriplett on July 23, 2015 | parent | context | favorite | on: rm -r fs/ext3

If you actually mount it as ext4 and enable the new features, yes. However, if you mount ext2 or ext3 using the ext2/3 implementation in the ext4 driver, that doesn't break backward compatibility with ext2/3.