scsi: target: tcmu: Userspace must not complete queued commands

scsi: target: tcmu: Userspace must not complete queued commands

When tcmu queues a new command - no matter whether in command ring or in
qfull_queue - a cmd_id from IDR udev->commands is assigned to the command.

If userspace sends a wrong command completion containing the cmd_id of a
command on the qfull_queue, tcmu_handle_completions() finds the command in
the IDR and calls tcmu_handle_completion() for it. This might do some nasty
things because commands in qfull_queue do not have a valid dbi list.

To fix this bug, we no longer add queued commands to the idr.  Instead the
cmd_id is assign when a command is written to the command ring.

Due to this change I had to adapt the source code at several places where
up to now an idr_for_each had been done.

[mkp: fix checkpatch warnings]

Link: https://lore.kernel.org/r/20200518164833.12775-1-bstroesser@ts.fujitsu.com
Acked-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Bodo Stroesser <bstroesser@ts.fujitsu.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>