scsi: libsas: Keep host active while processing events

Processing events such as PORTE_BROADCAST_RCVD may cause dependency issues
for runtime power management support. Such a problem would be that
handling a PORTE_BROADCAST_RCVD event requires that the host is resumed to
send SMP commands. However, in resuming the host, the phyup events
generated from re-enabling the phys are processed in the same workqueue as
the original PORTE_BROADCAST_RCVD event. As such, the host will never
finish resuming (as it waits for the phyup event processing), and then the
PORTE_BROADCAST_RCVD event can't be processed as the SMP commands are
blocked, and so we have a deadlock. Solve this problem by ensuring that
libsas keeps the host active until completely finished phy or port events,
such as PORTE_BYTES_DMAED. As such, we don't have to worry about resuming
the host for processing individual SMP commands in this example.

Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: John Garry <[e-mail]>
Signed-off-by: Xiang Chen <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/libsas/sas_event.c

···
 	list_for_each_entry_safe(sw, _sw, &ha->defer_q, drain_node) {
 		list_del_init(&sw->drain_node);
 		ret = sas_queue_work(ha, sw);
-		if (ret != 1)
+		if (ret != 1) {
+			pm_runtime_put(ha->dev);
 			sas_free_event(to_asd_sas_event(&sw->work));
+		}
 	}
 	spin_unlock_irq(&ha->lock);
 }
···
 static void sas_port_event_worker(struct work_struct *work)
 {
 	struct asd_sas_event *ev = to_asd_sas_event(work);
+	struct asd_sas_phy *phy = ev->phy;
+	struct sas_ha_struct *ha = phy->ha;
 
 	sas_port_event_fns[ev->event](work);
+	pm_runtime_put(ha->dev);
 	sas_free_event(ev);
 }
 
 static void sas_phy_event_worker(struct work_struct *work)
 {
 	struct asd_sas_event *ev = to_asd_sas_event(work);
+	struct asd_sas_phy *phy = ev->phy;
+	struct sas_ha_struct *ha = phy->ha;
 
 	sas_phy_event_fns[ev->event](work);
+	pm_runtime_put(ha->dev);
 	sas_free_event(ev);
 }
 
···
 	if (!ev)
 		return -ENOMEM;
 
+	/* Call pm_runtime_put() with pairs in sas_port_event_worker() */
+	pm_runtime_get_noresume(ha->dev);
+
 	INIT_SAS_EVENT(ev, sas_port_event_worker, phy, event);
 
 	if (sas_defer_event(phy, ev))
 		return 0;
 
 	ret = sas_queue_event(event, &ev->work, ha);
-	if (ret != 1)
+	if (ret != 1) {
+		pm_runtime_put(ha->dev);
 		sas_free_event(ev);
+	}
 
 	return ret;
 }
···
 	if (!ev)
 		return -ENOMEM;
 
+	/* Call pm_runtime_put() with pairs in sas_phy_event_worker() */
+	pm_runtime_get_noresume(ha->dev);
+
 	INIT_SAS_EVENT(ev, sas_phy_event_worker, phy, event);
 
 	if (sas_defer_event(phy, ev))
 		return 0;
 
 	ret = sas_queue_event(event, &ev->work, ha);
-	if (ret != 1)
+	if (ret != 1) {
+		pm_runtime_put(ha->dev);
 		sas_free_event(ev);
+	}
 
 	return ret;
 }