The 42 limit comes from the aufs code itself. My guess is that it's because of stack depth: if you stack these kernel data structures too many levels deep, you

The 42 limit comes from the aufs code itself. My guess is that it's because of stack depth: if you stack these kernel data structures too many levels deep, you might trigger an overflow somewhere. The hardcoded limit is probably a pragmatic way to avoid that. Of course if you had infinite memory and those kernel data structures were designed to never overflow, then you would have a performance problem on your hands instead of a kernel panic :)