Comment # 6 on bug 1186332 from Coly Li

> > commit a666e5c05e7c ("dm: fix deadlock when swapping to encrypted device")
> > 

Since there is no further information or clue for the deadlock, I assume there
is swap I/O hitting encrypted device. And btw, the idea of limiting swap I/O on
encrypted device looks interesting, it may also be helpful for Bug #1177529,
which causes deadlock for swap I/O on dm-thin device.

This patch breaks our KABI, let me do more KABI fix and testing before
submitting it to our tree.

Thanks.

Coly Li