Hot-remove of a device with a mounted partition

[Keith Busch]

On Wed, 29 Apr 2015, Sunad Bhandary wrote:
> 1) When the device is removed , sometimes(around 4-5 out of 10 times) the
> removal process hangs. The device nodes are still present under /dev. It
> seems like call to del_gendisk  function is hung and not returning.

Looks like it's stuck entrying a frozen queue. I'm not sure why it ever
succeeds in your test. :)

Thanks for the catch. We'll have to figure out some way to coordinate
this with blk-mq so its safe in all scenarios.