On Thu, Dec 24, 2015@03:27:01PM +0100, Christoph Hellwig wrote:

Make sure we synchronize access to the namespaces list and grab a reference
to the namespace before doing I/O.  Make sure to reject the ioctl if multiple
namespaces are present as it's entirely unsafe, and warn when using it even
with a single namespace.

Signed-off-by: Christoph Hellwig <hch at lst.de>
Reviewed-by: Sagi Grimberg <sagig at mellanox.com>

Okay, I accept the argument for allowing these to "hidden" namespaces
is not sufficiently justified.

Acked-by: Keith Busch <keith.busch at intel.com>