[PATCH] sbp2: fix deadlocks and delays on device removal/rmmod

Fixes for deadlocks of the ieee1394 and scsi subsystems and long delays in
futile error recovery attempts when SBP-2 devices are removed or drivers are
unloaded.

 - Complete commands quickly with DID_NO_CONNECT if the 1394 node is gone or if
   the 1394 low-level driver was unloaded.
 - Skip unnecessary work in the eh_abort_handler and eh_device_reset_handler if
   the node or 1394 low-level driver is gone.
 - Let scsi's high-level shut down gracefully when sbp2 is being unloaded or
   detached from the 1394 unit. A call to scsi_remove_device is added for this
   purpose, which requires us to store a scsi_device pointer.
 - scsi_device pointer is obtained from slave_alloc hook and cleared by
   slave_destroy. This avoids usage of the pointer after the scsi device was
   deleted e.g. by the user via scsi_mod's sysfs interface.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Jody McIntyre <scjody@steamballoon.com>
Cc: Ben Collins <bcollins@debian.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>