block: make queue flags non-atomic

We can save some atomic ops in the IO path, if we clearly define
the rules of how to modify the queue flags.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

drivers/block/loop.c

@@ -546,7 +546,7 @@ static void loop_unplug(struct request_queue *q)
 {
 	struct loop_device *lo = q->queuedata;
 
-	clear_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags);
+	queue_flag_clear_unlocked(QUEUE_FLAG_PLUGGED, q);
 	blk_run_address_space(lo->lo_backing_file->f_mapping);
 }
 

drivers/block/ub.c

@@ -2399,7 +2399,7 @@ static void ub_disconnect(struct usb_interface *intf)
 		del_gendisk(lun->disk);
 		/*
 		 * I wish I could do:
-		 *    set_bit(QUEUE_FLAG_DEAD, &q->queue_flags);
+		 *    queue_flag_set(QUEUE_FLAG_DEAD, q);
 		 * As it is, we rely on our internal poisoning and let
 		 * the upper levels to spin furiously failing all the I/O.
 		 */