scsi: zfcp: fix request object use-after-free in send path causing wrong traces

When tracing instances where we open and close WKA ports, we also pass the
request-ID of the respective FSF command.

But after successfully sending the FSF command we must not use the
request-object anymore, as this might result in an use-after-free (see
"zfcp: fix request object use-after-free in send path causing seqno
errors" ).

To fix this add a new variable that caches the request-ID before sending
the request. This won't change during the hand-off to the FCP channel,
and so it's safe to trace this cached request-ID later, instead of using
the request object.

Signed-off-by: Benjamin Block <[e-mail]>
Fixes: d27a7cb91960 ("zfcp: trace on request for open and close of WKA port")
Cc: <[e-mail]> #2.6.38+
Reviewed-by: Steffen Maier <[e-mail]>
Reviewed-by: Jens Remus <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/s390/scsi/zfcp_fsf.c

···
 {
 	struct zfcp_qdio *qdio = wka_port->adapter->qdio;
 	struct zfcp_fsf_req *req;
+	unsigned long req_id = 0;
 	int retval = -EIO;
 
 	spin_lock_irq(&qdio->req_q_lock);
···
 	hton24(req->qtcb->bottom.support.d_id, wka_port->d_id);
 	req->data = wka_port;
 
+	req_id = req->req_id;
+
 	zfcp_fsf_start_timer(req, ZFCP_FSF_REQUEST_TIMEOUT);
 	retval = zfcp_fsf_req_send(req);
 	if (retval)
···
 out:
 	spin_unlock_irq(&qdio->req_q_lock);
 	if (!retval)
-		zfcp_dbf_rec_run_wka("fsowp_1", wka_port, req->req_id);
+		zfcp_dbf_rec_run_wka("fsowp_1", wka_port, req_id);
 	return retval;
 }
 
···
 {
 	struct zfcp_qdio *qdio = wka_port->adapter->qdio;
 	struct zfcp_fsf_req *req;
+	unsigned long req_id = 0;
 	int retval = -EIO;
 
 	spin_lock_irq(&qdio->req_q_lock);
···
 	req->data = wka_port;
 	req->qtcb->header.port_handle = wka_port->handle;
 
+	req_id = req->req_id;
+
 	zfcp_fsf_start_timer(req, ZFCP_FSF_REQUEST_TIMEOUT);
 	retval = zfcp_fsf_req_send(req);
 	if (retval)
···
 out:
 	spin_unlock_irq(&qdio->req_q_lock);
 	if (!retval)
-		zfcp_dbf_rec_run_wka("fscwp_1", wka_port, req->req_id);
+		zfcp_dbf_rec_run_wka("fscwp_1", wka_port, req_id);
 	return retval;
 }