BLIST_SINGLELUN

[Christoph Hellwig <hch@infradead.org>]

Does anyone still have a device listed in the blacklist with
BLIST_SINGLELUN?

>From reading the source code I'm not sure the code actually works as
expected currently, or did for a long time.

While scsi_target_queue_ready makes sure to only queue commands to the
right lun as long as starget_sdev_user is set, scsi_single_lun_run
clears starget_sdev_user as soon as the any command completes on a
target marked with the flag, allowing the following situation:

 - cmd 1 lun 0		submitted
 - cmd 2 lun 0		submitted
 - cmd 1 lun 0		completed
 - cmd 9 lun 1		submitted

and thus having commands for two luns in flight at the same time
if we hit the narrow enough race of entering the scsi_request_fn
for lun 1 before scsi_single_lun_run does so for lun 0.