Comment by trumpdong

On ext4 things will start failing with -ENOSPC but recovery is as simple as deleting files that are taking up space - which may or may not require a reboot into single-user mode depending on how badly the running system is borked - but the filesystem remains intact, you don't have to drop the journal, you don't have to run fsck or any other repair tool. You can just delete files and get the space back.