scsi: iscsi: Optimize work queue flush use

There is no need for one session to flush the entire iscsi_eh_timer_workq
when removing/unblocking a session. During removal we need to make sure our
works are not running anymore. And iscsi_unblock_session only needs to make
sure its work is done. The unblock work function will flush/cancel the
works it has conflicts with.

Link: https://lore.kernel.org/r/1593632868-6808-3-git-send-email-michael.christie@oracle.comSigned-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_transport_iscsi.c

@@ -1978,10 +1978,11 @@ void iscsi_unblock_session(struct iscsi_cls_session *session)
 {
 	queue_work(iscsi_eh_timer_workq, &session->unblock_work);
 	/*
-	 * make sure all the events have completed before tell the driver
-	 * it is safe
+	 * Blocking the session can be done from any context so we only
+	 * queue the block work. Make sure the unblock work has completed
+	 * because it flushes/cancels the other works and updates the state.
 	 */
-	flush_workqueue(iscsi_eh_timer_workq);
+	flush_work(&session->unblock_work);
 }
 EXPORT_SYMBOL_GPL(iscsi_unblock_session);
 
@@ -2205,11 +2206,9 @@ void iscsi_remove_session(struct iscsi_cls_session *session)
 	list_del(&session->sess_list);
 	spin_unlock_irqrestore(&sesslock, flags);
 
-	/* make sure there are no blocks/unblocks queued */
-	flush_workqueue(iscsi_eh_timer_workq);
-	/* make sure the timedout callout is not running */
-	if (!cancel_delayed_work(&session->recovery_work))
-		flush_workqueue(iscsi_eh_timer_workq);
+	flush_work(&session->block_work);
+	flush_work(&session->unblock_work);
+	cancel_delayed_work_sync(&session->recovery_work);
 	/*
 	 * If we are blocked let commands flow again. The lld or iscsi
 	 * layer should set up the queuecommand to fail commands.