scsi: iscsi: Speed up session unblocking and removal

When the iSCSI class was added upstream, blocking a queue was fast because
it just set some flag bits and didn't handle I/O that was in the process of
being sent to the driver. That's no longer the case so blocking a queue is
expensive and we can end up with a backlog of blocks by the time we have
relogged in and are trying to start the queues.

For the session unblock case, this has try to cancel the block and recovery
work in case they are still queued so we can avoid unneeded queue
manipulations. For removal, we also now try to cancel all the recovery
related works since a couple lines down we will set the session and device
state so running those functions are not necessary.

Link: https://lore.kernel.org/r/20220226230435.38733-3-michael.christie@oracle.comReviewed-by: Lee Duncan <lduncan@suse.com>
Reviewed-by: Chris Leech <cleech@redhat.com>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_transport_iscsi.c

@@ -1944,7 +1944,8 @@ static void __iscsi_unblock_session(struct work_struct *work)
  */
 void iscsi_unblock_session(struct iscsi_cls_session *session)
 {
-	flush_work(&session->block_work);
+	if (!cancel_work_sync(&session->block_work))
+		cancel_delayed_work_sync(&session->recovery_work);
 
 	queue_work(iscsi_eh_timer_workq, &session->unblock_work);
 	/*
@@ -2177,9 +2178,9 @@ void iscsi_remove_session(struct iscsi_cls_session *session)
 		list_del(&session->sess_list);
 	spin_unlock_irqrestore(&sesslock, flags);
 
-	flush_work(&session->block_work);
-	flush_work(&session->unblock_work);
-	cancel_delayed_work_sync(&session->recovery_work);
+	if (!cancel_work_sync(&session->block_work))
+		cancel_delayed_work_sync(&session->recovery_work);
+	cancel_work_sync(&session->unblock_work);
 	/*
 	 * If we are blocked let commands flow again. The lld or iscsi
 	 * layer should set up the queuecommand to fail commands.