bcache oops with 3.12-rc3

Hello,
I have this reproducible crash soon after booting:
http://i.imgur.com/ynDFOI2.jpg

Partial transcript:
bch_insert_data
closure_queue
request_write
cached_dev_make_request

bcache is stacked on top of LVM.

I've confirmed it with this vanilla kernel:
http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.12-rc3-saucy/