"zpool import" hangs forever on r209755

[Rich]

Hey world,
I had a system I filed a bug about, wherein the system hung all
"zfs/zpool [command] queries some time after booting, followed by the
machine itself becoming entirely unresponsive.

I've upgraded it to a newer kernel, with CTF+DDB+DTRACE configured in
it, and a proper rev number, and I nuked /boot/zfs/zpool.cache after I
found the machine was hanging forever after it loaded zfs.ko. Now, the
machine boots, but zpool status returns "no pools available" [good]
and zpool import hangs forever with no output [which is bad].

I presume I can ask dtrace/ddb/etc for useful information regarding
this, but is this expected? Did some crazy commit make it in that was
immediately reverted after I fetched source?

Thanks,
- Rich