Runtime filesystem consistency checking

lockdep is brilliant for developers as it warns you early of your bugs, just as this 'recon' would warn ext3 developers of their bugs.
But lockdep used to report lots of false positives - this has got a lot better over the years though.

I'm not sure I'd enable lockdep or recon in production though. There is a real cost, and it is not at all likely to help more than it hurts.