scsi: core: Don't wait for quiesce in scsi_device_block()

scsi_device_block() is only called from scsi_target_block(), which calls it
repeatedly for every child device. For targets with many devices, waiting
for every queue to quiesce may cause a substantial delay (we measured more
than 100s delay for blocking a FC rport with 2048 LUNs).

Just call blk_mq_wait_quiesce_done() once from scsi_target_block() after
stopping all queues.

Signed-off-by: Martin Wilck <mwilck@suse.com>
Link: https://lore.kernel.org/r/20230614103616.31857-6-mwilck@suse.com
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_lib.c

@@ -2771,8 +2771,9 @@ EXPORT_SYMBOL_GPL(scsi_internal_device_block_nowait);
  * @sdev: device to block
  * @data: dummy argument, ignored
  *
- * Pause SCSI command processing on the specified device and wait until all
- * ongoing scsi_queue_rq() calls have finished. May sleep.
+ * Pause SCSI command processing on the specified device. Callers must wait
+ * until all ongoing scsi_queue_rq() calls have finished after this function
+ * returns.
  *
  * Note:
  * This routine transitions the device to the SDEV_BLOCK state (which must be
@@ -2786,17 +2787,15 @@ static void scsi_device_block(struct scsi_device *sdev, void *data)
 
 	mutex_lock(&sdev->state_mutex);
 	err = __scsi_internal_device_block_nowait(sdev);
-	if (err == 0) {
+	if (err == 0)
 		/*
 		 * scsi_stop_queue() must be called with the state_mutex
 		 * held. Otherwise a simultaneous scsi_start_queue() call
 		 * might unquiesce the queue before we quiesce it.
 		 */
 		scsi_stop_queue(sdev);
-		mutex_unlock(&sdev->state_mutex);
-		blk_mq_wait_quiesce_done(sdev->request_queue->tag_set);
-	} else
-		mutex_unlock(&sdev->state_mutex);
+
+	mutex_unlock(&sdev->state_mutex);
 
 	WARN_ONCE(err, "__scsi_internal_device_block_nowait(%s) failed: err = %d\n",
 		  dev_name(&sdev->sdev_gendev), err);
@@ -2894,11 +2893,15 @@ target_block(struct device *dev, void *data)
 void
 scsi_target_block(struct device *dev)
 {
+	struct Scsi_Host *shost = dev_to_shost(dev);
+
 	if (scsi_is_target_device(dev))
 		starget_for_each_device(to_scsi_target(dev), NULL,
 					scsi_device_block);
 	else
 		device_for_each_child(dev, NULL, target_block);
+
+	blk_mq_wait_quiesce_done(&shost->tag_set);
 }
 EXPORT_SYMBOL_GPL(scsi_target_block);