Commit 62f96cb0 introduced per-devices
queues and locks, which was fine as far as it went, but left in place a
global which controlled access to submitting requests to the host.  This
should have been made per-device as well, since it causes I/O hangs when
multiple block devices are in use.

This patch fixes that by replacing the global with an activity flag in the
device structure in order to tell whether the queue is currently being run.
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>