firewire: fw-sbp2: don't add scsi_device twice

When a reconnect failed but re-login succeeded, __scsi_add_device was
called again.

In those cases, __scsi_add_device succeeded and returned the pointer to
the existing scsi_device.  fw-sbp2 then continued orderly, except that
it missed to call sbp2_cancel_orbs.  SCSI core would call fw-sbp2's
eh_abort_handler eventually if there had been an outstanding command.

This patch avoids the needless lookups and temporary allocations in SCSI
core and I/O stall and timeout until eh_abort_handler hits.

Also, __scsi_add_device tolerating calls for devices which already exist
is undocumented behavior on which we shouldn't rely.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Jarod Wilson <jwilson@redhat.com>

drivers/firewire/fw-sbp2.c

@@ -741,6 +741,12 @@ static void sbp2_login(struct work_struct *work)
 	PREPARE_DELAYED_WORK(&lu->work, sbp2_reconnect);
 	sbp2_agent_reset(lu);
 
+	/* This was a re-login. */
+	if (lu->sdev) {
+		sbp2_cancel_orbs(lu);
+		goto out;
+	}
+
 	if (lu->tgt->workarounds & SBP2_WORKAROUND_DELAY_INQUIRY)
 		ssleep(SBP2_INQUIRY_DELAY);