dm mpath: only flush workqueue when needed

The workqueues are shared by many multipath devices, only flush whole
workqueue when necessary.  Otherwise, we just flush works as needed.
Signed-off-by: wuzhouhui <wuzhouhui14@mails.ucas.ac.cn>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-mpath.c

@@ -1211,6 +1211,7 @@ static void flush_multipath_work(struct multipath *m)
 		set_bit(MPATHF_PG_INIT_DISABLED, &m->flags);
 		smp_mb__after_atomic();
 
+		if (atomic_read(&m->pg_init_in_progress))
 			flush_workqueue(kmpath_handlerd);
 		multipath_wait_for_pg_init_completion(m);
 
@@ -1218,7 +1219,8 @@ static void flush_multipath_work(struct multipath *m)
 		smp_mb__after_atomic();
 	}
 
-	flush_workqueue(kmultipathd);
+	if (m->queue_mode == DM_TYPE_BIO_BASED)
+		flush_work(&m->process_queued_bios);
 	flush_work(&m->trigger_event);
 }