loop: fold loop_switch() into callers

The comments here are really outdated, and blk-mq made flushing much
simpler, so just fold the two cases into the callers.
Reviewed-by: NMing Lei <ming.lei@redhat.com>
Reviewed-by: NHannes Reinecke <hare@suse.com>
Signed-off-by: NOmar Sandoval <osandov@fb.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

drivers/block/loop.c

@@ -546,72 +546,12 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq)
 	}
 }
 
-struct switch_request {
-	struct file *file;
-	struct completion wait;
-};
-
 static inline void loop_update_dio(struct loop_device *lo)
 {
 	__loop_update_dio(lo, io_is_direct(lo->lo_backing_file) |
 			lo->use_dio);
 }
 
-/*
- * Do the actual switch; called from the BIO completion routine
- */
-static void do_loop_switch(struct loop_device *lo, struct switch_request *p)
-{
-	struct file *file = p->file;
-	struct file *old_file = lo->lo_backing_file;
-	struct address_space *mapping;
-
-	/* if no new file, only flush of queued bios requested */
-	if (!file)
-		return;
-
-	mapping = file->f_mapping;
-	mapping_set_gfp_mask(old_file->f_mapping, lo->old_gfp_mask);
-	lo->lo_backing_file = file;
-	lo->old_gfp_mask = mapping_gfp_mask(mapping);
-	mapping_set_gfp_mask(mapping, lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS));
-	loop_update_dio(lo);
-}
-
-/*
- * loop_switch performs the hard work of switching a backing store.
- * First it needs to flush existing IO, it does this by sending a magic
- * BIO down the pipe. The completion of this BIO does the actual switch.
- */
-static int loop_switch(struct loop_device *lo, struct file *file)
-{
-	struct switch_request w;
-
-	w.file = file;
-
-	/* freeze queue and wait for completion of scheduled requests */
-	blk_mq_freeze_queue(lo->lo_queue);
-
-	/* do the switch action */
-	do_loop_switch(lo, &w);
-
-	/* unfreeze */
-	blk_mq_unfreeze_queue(lo->lo_queue);
-
-	return 0;
-}
-
-/*
- * Helper to flush the IOs in loop, but keeping loop thread running
- */
-static int loop_flush(struct loop_device *lo)
-{
-	/* loop not yet configured, no running thread, nothing to flush */
-	if (lo->lo_state != Lo_bound)
-		return 0;
-	return loop_switch(lo, NULL);
-}
-
 static void loop_reread_partitions(struct loop_device *lo,
 				   struct block_device *bdev)
 {
@@ -676,9 +616,14 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
 		goto out_putf;
 
 	/* and ... switch */
-	error = loop_switch(lo, file);
-	if (error)
-		goto out_putf;
+	blk_mq_freeze_queue(lo->lo_queue);
+	mapping_set_gfp_mask(old_file->f_mapping, lo->old_gfp_mask);
+	lo->lo_backing_file = file;
+	lo->old_gfp_mask = mapping_gfp_mask(file->f_mapping);
+	mapping_set_gfp_mask(file->f_mapping,
+			     lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS));
+	loop_update_dio(lo);
+	blk_mq_unfreeze_queue(lo->lo_queue);
 
 	fput(old_file);
 	if (lo->lo_flags & LO_FLAGS_PARTSCAN)
@@ -1601,12 +1546,13 @@ static void lo_release(struct gendisk *disk, fmode_t mode)
 		err = loop_clr_fd(lo);
 		if (!err)
 			return;
-	} else {
+	} else if (lo->lo_state == Lo_bound) {
 		/*
 		 * Otherwise keep thread (if running) and config,
 		 * but flush possible ongoing bios in thread.
 		 */
-		loop_flush(lo);
+		blk_mq_freeze_queue(lo->lo_queue);
+		blk_mq_unfreeze_queue(lo->lo_queue);
 	}
 
 	mutex_unlock(&lo->lo_ctl_mutex);