firewire: fw-sbp2: fix another small generation access bug

queuecommand() looked at the remote and local node IDs before it read
the bus generation.  The corresponding race with sbp2_reconnect updating
these data was probably impossible to happen though because the current
code blocks the SCSI layer during reconnection.  However, better safe
than sorry, especially if someone later improves the code to not block
the SCSI layer.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

drivers/firewire/fw-sbp2.c

@@ -1423,7 +1423,7 @@ static int sbp2_scsi_queuecommand(struct scsi_cmnd *cmd, scsi_done_fn_t done)
 	struct fw_device *device = fw_device(lu->tgt->unit->device.parent);
 	struct sbp2_command_orb *orb;
 	unsigned int max_payload;
-	int retval = SCSI_MLQUEUE_HOST_BUSY;
+	int generation, retval = SCSI_MLQUEUE_HOST_BUSY;
 
 	/*
 	 * Bidirectional commands are not yet implemented, and unknown
@@ -1467,6 +1467,9 @@ static int sbp2_scsi_queuecommand(struct scsi_cmnd *cmd, scsi_done_fn_t done)
 	if (cmd->sc_data_direction == DMA_FROM_DEVICE)
 		orb->request.misc |= cpu_to_be32(COMMAND_ORB_DIRECTION);
 
+	generation = device->generation;
+	smp_rmb();    /* sbp2_map_scatterlist looks at tgt->address_high */
+
 	if (scsi_sg_count(cmd) && sbp2_map_scatterlist(orb, device, lu) < 0)
 		goto out;
 
@@ -1479,7 +1482,7 @@ static int sbp2_scsi_queuecommand(struct scsi_cmnd *cmd, scsi_done_fn_t done)
 	if (dma_mapping_error(device->card->device, orb->base.request_bus))
 		goto out;
 
-	sbp2_send_orb(&orb->base, lu, lu->tgt->node_id, lu->generation,
+	sbp2_send_orb(&orb->base, lu, lu->tgt->node_id, generation,
 		      lu->command_block_agent_address + SBP2_ORB_POINTER);
 	retval = 0;
  out: