scsi: libsas: Defer works of new phys during suspend

During the processing of event PORT_BYTES_DMAED, the driver queues work
DISCE_DISCOVER_DOMAIN and then flushes workqueue ha->disco_q. If a new
phyup event occurs during resuming the controller, the work
PORTE_BYTES_DMAED of new phy occurs before suspended phy's. The work
DISCE_DISCOVER_DOMAIN of new phy requires an active SAS controller (it
needs to resume SAS controller by function scsi_sysfs_add_sdev() and some
other functions such as function add_device_link()). However, the
activation of the SAS controller requires completion of work
PORTE_BYTES_DMAED of suspended phys while it is blocked by new phy's work
on ha->event_q. So there is a deadlock and it is released only after resume
timeout.

To solve the issue, defer works of new phys during suspend and queue those
defer works after SAS controller becomes active.

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

···
 	sas_free_event(ev);
 }
 
+/* defer works of new phys during suspend */
+static bool sas_defer_event(struct asd_sas_phy *phy, struct asd_sas_event *ev)
+{
+	struct sas_ha_struct *ha = phy->ha;
+	unsigned long flags;
+	bool deferred = false;
+
+	spin_lock_irqsave(&ha->lock, flags);
+	if (test_bit(SAS_HA_RESUMING, &ha->state) && !phy->suspended) {
+		struct sas_work *sw = &ev->work;
+
+		list_add_tail(&sw->drain_node, &ha->defer_q);
+		deferred = true;
+	}
+	spin_unlock_irqrestore(&ha->lock, flags);
+	return deferred;
+}
+
 int sas_notify_port_event(struct asd_sas_phy *phy, enum port_event event,
 			  gfp_t gfp_flags)
 {
···
 		return -ENOMEM;
 
 	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)
···
 		return -ENOMEM;
 
 	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)

drivers/scsi/libsas/sas_init.c

···
 		sas_drain_work(ha);
 	clear_bit(SAS_HA_RESUMING, &ha->state);
 
+	sas_queue_deferred_work(ha);
 	/* send event PORTE_BROADCAST_RCVD to identify some new inserted
 	 * disks for expander
 	 */