scsi: iscsi: ql4xxx: Use per-session workqueue for unbinding

We currently allocate a workqueue per host and only use it for removing the
target. For the session per host case we could be using this workqueue to
be able to do recoveries (block, unblock, timeout handling) in parallel. To
also allow offload drivers to do their session recoveries in parallel, this
drops the per host workqueue and replaces it with a per session one.

Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Lee Duncan <[e-mail]>
Reviewed-by: Chris Leech <[e-mail]>
Signed-off-by: Mike Christie <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/qla4xxx/ql4_os.c

···
 		ql4_printk(KERN_INFO, ha, "scsi%ld: %s: ddb[%d]"
 			   " start scan\n", ha->host_no, __func__,
 			   ddb_entry->fw_ddb_index);
-		scsi_queue_work(ha->host, &ddb_entry->sess->scan_work);
+		queue_work(ddb_entry->sess->workq, &ddb_entry->sess->scan_work);
 	}
 	return QLA_SUCCESS;
 }

drivers/scsi/scsi_transport_iscsi.c

···
 
 int iscsi_add_session(struct iscsi_cls_session *session, unsigned int target_id)
 {
+	struct Scsi_Host *shost = iscsi_session_to_shost(session);
 	unsigned long flags;
 	int id = 0;
 	int err;
 
 	session->sid = atomic_add_return(1, &iscsi_session_nr);
+
+	session->workq = alloc_workqueue("iscsi_ctrl_%d:%d",
+			WQ_SYSFS | WQ_MEM_RECLAIM | WQ_UNBOUND, 0,
+			shost->host_no, session->sid);
+	if (!session->workq)
+		return -ENOMEM;
 
 	if (target_id == ISCSI_MAX_TARGET) {
 		id = ida_simple_get(&iscsi_sess_ida, 0, 0, GFP_KERNEL);
···
 		if (id < 0) {
 			iscsi_cls_session_printk(KERN_ERR, session,
 					"Failure in Target ID Allocation\n");
-			return id;
+			err = id;
+			goto destroy_wq;
 		}
 		session->target_id = (unsigned int)id;
 		session->ida_used = true;
···
 release_ida:
 	if (session->ida_used)
 		ida_simple_remove(&iscsi_sess_ida, session->target_id);
-
+destroy_wq:
+	destroy_workqueue(session->workq);
 	return err;
 }
 EXPORT_SYMBOL_GPL(iscsi_add_session);
···
 					 "for session. Error %d.\n", err);
 
 	transport_unregister_device(&session->dev);
+
+	destroy_workqueue(session->workq);
 
 	ISCSI_DBG_TRANS_SESSION(session, "Completing session removal\n");
 	device_del(&session->dev);
···
 	case ISCSI_UEVENT_UNBIND_SESSION:
 		session = iscsi_session_lookup(ev->u.d_session.sid);
 		if (session)
-			scsi_queue_work(iscsi_session_to_shost(session),
-					&session->unbind_work);
+			queue_work(session->workq, &session->unbind_work);
 		else
 			err = -EINVAL;
 		break;
···
 	INIT_LIST_HEAD(&priv->list);
 	priv->iscsi_transport = tt;
 	priv->t.user_scan = iscsi_user_scan;
-	priv->t.create_work_queue = 1;
 
 	priv->dev.class = &iscsi_transport_class;
 	dev_set_name(&priv->dev, "%s", tt->name);

include/scsi/scsi_transport_iscsi.h

···
 	bool recovery_tmo_sysfs_override;
 	struct delayed_work recovery_work;
 
+	struct workqueue_struct *workq;
+
 	unsigned int target_id;
 	bool ida_used;