[SCSI] zfcp: fix deadlock caused by shared work queue tasks

Each adapter reopen trigger automatically a scan_port task which
is waiting for the ERP to be finished before further processing.
Since the initial device setup enqueues adapter, port and LUN which
are individual ERP actions, this process would start after
everything is done. Unfortunately the port_reopen requires another
scheduled work to be finished which is queued after the automatic
scan_port -> deadlock !

This fix creates an own work queue for ERP based nameserver requests.

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@HansenPartnership.com>

drivers/s390/scsi/zfcp_aux.c

@@ -168,6 +168,8 @@ static int __init zfcp_module_init(void)
 	if (!zfcp_data.gid_pn_cache)
 		goto out_gid_cache;
 
+	zfcp_data.work_queue = create_singlethread_workqueue("zfcp_wq");
+
 	INIT_LIST_HEAD(&zfcp_data.adapter_list_head);
 	sema_init(&zfcp_data.config_sema, 1);
 	rwlock_init(&zfcp_data.config_lock);

drivers/s390/scsi/zfcp_def.h

@@ -602,6 +602,7 @@ struct zfcp_data {
 	struct kmem_cache	*fsf_req_qtcb_cache;
 	struct kmem_cache	*sr_buffer_cache;
 	struct kmem_cache	*gid_pn_cache;
+	struct workqueue_struct	*work_queue;
 };
 
 /* struct used by memory pools for fsf_requests */

drivers/s390/scsi/zfcp_erp.c

@@ -869,7 +869,7 @@ static int zfcp_erp_port_strategy_open_common(struct zfcp_erp_action *act)
 		if (fc_host_port_type(adapter->scsi_host) == FC_PORTTYPE_PTP)
 			return zfcp_erp_open_ptp_port(act);
 		if (!(p_status & ZFCP_STATUS_PORT_DID_DID)) {
-			schedule_work(&port->gid_pn_work);
+			queue_work(zfcp_data.work_queue, &port->gid_pn_work);
 			return ZFCP_ERP_CONTINUES;
 		}
 	case ZFCP_ERP_STEP_NAMESERVER_LOOKUP:
@@ -1209,7 +1209,7 @@ static void zfcp_erp_schedule_work(struct zfcp_unit *unit)
 	atomic_set_mask(ZFCP_STATUS_UNIT_SCSI_WORK_PENDING, &unit->status);
 	INIT_WORK(&p->work, zfcp_erp_scsi_scan);
 	p->unit = unit;
-	schedule_work(&p->work);
+	queue_work(zfcp_data.work_queue, &p->work);
 }
 
 static void zfcp_erp_rport_register(struct zfcp_port *port)

drivers/s390/scsi/zfcp_fsf.c

@@ -329,7 +329,7 @@ static void zfcp_fsf_status_read_handler(struct zfcp_fsf_req *req)
 	zfcp_fsf_req_free(req);
 
 	atomic_inc(&adapter->stat_miss);
-	schedule_work(&adapter->stat_work);
+	queue_work(zfcp_data.work_queue, &adapter->stat_work);
 }
 
 static void zfcp_fsf_fsfstatus_qual_eval(struct zfcp_fsf_req *req)