Comment 27 for bug 554718

Yes, the bdi event does appear as a kernel event as well.

One thing I noticed tonight is that, when things go wrong, /dev/sda also no longer exists. (/dev/sda1, /dev/sda2, and /dev/sda5 do still exist, though.) I'll attach a log of udevd in debug mode when this occurs. I couldn't see anything obviously out of the ordinary myself.