[SCSI] zfcp: invalid usage after free of port resources

In certain error scenarios ports, rports are getting attached,
validated and removed from the systems environment. Depending on the
layer this occurs asynchronously. This patch fixes the few races
which existed and ensures all references and cross references are
cleared at the time they're invalid. In addition fc transports
actions are only scheduled when required.
Signed-off-by: Swen Schillig <swen@vnet.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

drivers/s390/scsi/zfcp_aux.c

@@ -672,12 +672,15 @@ err_out:
  */
 void zfcp_port_dequeue(struct zfcp_port *port)
 {
-	wait_event(port->remove_wq, atomic_read(&port->refcount) == 0);
 	write_lock_irq(&zfcp_data.config_lock);
 	list_del(&port->list);
 	write_unlock_irq(&zfcp_data.config_lock);
-	if (port->rport)
+	if (port->rport) {
 		port->rport->dd_data = NULL;
+		port->rport = NULL;
+	}
+	wait_event(port->remove_wq, atomic_read(&port->refcount) == 0);
+	cancel_work_sync(&port->rport_work); /* usually not necessary */
 	zfcp_adapter_put(port->adapter);
 	sysfs_remove_group(&port->sysfs_device.kobj, &zfcp_sysfs_port_attrs);
 	device_unregister(&port->sysfs_device);

drivers/s390/scsi/zfcp_scsi.c

@@ -582,7 +582,9 @@ void zfcp_scsi_schedule_rport_block(struct zfcp_port *port)
 	zfcp_port_get(port);
 	port->rport_task = RPORT_DEL;
 
-	if (!queue_work(zfcp_data.work_queue, &port->rport_work))
+	if (port->rport && queue_work(zfcp_data.work_queue, &port->rport_work))
+		return;
+
 	zfcp_port_put(port);
 }