scsi: virtio-scsi: Correctly handle the case where all LUNs are unplugged

Commit 5ff84372 ("scsi: virtio_scsi: unplug LUNs when events missed")
missed a corner case in which all the LUNs are unplugged at the same time.

In this case INQUIRY returns DID_BAD_TARGET. Detect this and unplug the
LUN.

Link: https://lore.kernel.org/r/20200729194806.4933-2-mlevitsk@redhat.comAcked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/virtio_scsi.c

@@ -350,6 +350,14 @@ static void virtscsi_rescan_hotunplug(struct virtio_scsi *vscsi)
 		if (result == 0 && inq_result[0] >> 5) {
 			/* PQ indicates the LUN is not attached */
 			scsi_remove_device(sdev);
+		} else if (host_byte(result) == DID_BAD_TARGET) {
+			/*
+			 * If all LUNs of a virtio-scsi device are unplugged
+			 * it will respond with BAD TARGET on any INQUIRY
+			 * command.
+			 * Remove the device in this case as well.
+			 */
+			scsi_remove_device(sdev);
 		}
 	}