scsi: core: Make sure sdev->queue_depth is <= max(shost->can_queue, 1024)

Limit SCSI device's queue depth to max(host->can_queue, 1024) in
scsi_change_queue_depth(). 1024 is big enough for saturating current fast
SCSI LUN(SSD or RAID volume on multiple SSDs). Also single hardware queue
depth is usually enough for saturating single LUN because per-core
performance is often considered in storage design.

This patch is needed for replacing sdev->device_busy with sbitmap which has
to be pre-allocated with reasonable max depth.

Link: https://lore.kernel.org/r/20210122023317.687987-13-ming.lei@redhat.com
Cc: Omar Sandoval <osandov@fb.com>
Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Sumanesh Samanta <sumanesh.samanta@broadcom.com>
Cc: Ewan D. Milne <emilne@redhat.com>
Tested-by: Sumanesh Samanta <sumanesh.samanta@broadcom.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi.c

@@ -214,6 +214,15 @@ void scsi_finish_command(struct scsi_cmnd *cmd)
 	scsi_io_completion(cmd, good_bytes);
 }
 
+
+/*
+ * 1024 is big enough for saturating the fast scsi LUN now
+ */
+static int scsi_device_max_queue_depth(struct scsi_device *sdev)
+{
+	return max_t(int, sdev->host->can_queue, 1024);
+}
+
 /**
  * scsi_change_queue_depth - change a device's queue depth
  * @sdev: SCSI Device in question
@@ -223,6 +232,8 @@ void scsi_finish_command(struct scsi_cmnd *cmd)
  */
 int scsi_change_queue_depth(struct scsi_device *sdev, int depth)
 {
+	depth = min_t(int, depth, scsi_device_max_queue_depth(sdev));
+
 	if (depth > 0) {
 		sdev->queue_depth = depth;
 		wmb();