If a blockdev module calls spdk_bdev_io_complete() within its
submit_request function, and the user's completion callback issues a new
I/O, it is possible to cause infinite recursion, consuming all available
stack space.
To avoid this, track whether a bdev_io is being processed by
submit_request, and if io_complete() is called in this case, defer the
completion via an event.
Change-Id: I6ccdb8ed4ee0d5738e6c9840d35431de52bd5fa2
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>