[PATCH v3 6/8] scsi: don't wait for quiesce in scsi_device_block()

[mwilck@suse.com]

From: Martin Wilck <mwilck@suse.com>

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>
---
 drivers/scsi/scsi_lib.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 657d10c57205..25ec6eb8df7f 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2772,8 +2772,8 @@ 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
@@ -2788,10 +2788,8 @@ static void scsi_device_block(struct scsi_device *sdev, void *data)
 	mutex_lock(&sdev->state_mutex);
 	err = __scsi_internal_device_block_nowait(sdev);
 	mutex_unlock(&sdev->state_mutex);
-	if (err == 0) {
+	if (err == 0)
 		scsi_stop_queue(sdev);
-		blk_mq_wait_quiesce_done(sdev->request_queue->tag_set);
-	}
 
 	WARN_ONCE(err, "__scsi_internal_device_block_nowait(%s) failed: err = %d\n",
 		  dev_name(&sdev->sdev_gendev), err);
@@ -2889,11 +2887,15 @@ 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);
 
-- 
2.40.1